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Sample records for algaas buffer layer

  1. Undoped Buffer Layer Development.

    DTIC Science & Technology

    1984-01-01

    boiled for several hours in aqua regia , followed by boiling for several more hours in deionized water before being dried in air and loaded into the...different from Report) 1S. SUPPLEMENTARY NOTES it. IKy WORDS (Canal... an reverse 4aaIo It eesarav d Ientify by block nuinbr) Epitaxial layer MBE

  2. Doped LZO buffer layers for laminated conductors

    DOEpatents

    Paranthaman, Mariappan Parans [Knoxville, TN; Schoop, Urs [Westborough, MA; Goyal, Amit [Knoxville, TN; Thieme, Cornelis Leo Hans [Westborough, MA; Verebelyi, Darren T [Oxford, MA; Rupich, Martin W [Framingham, MA

    2010-03-23

    A laminated conductor includes a metallic substrate having a surface, a biaxially textured buffer layer supported by the surface of the substrate, the biaxially textured buffer layer comprising LZO and a dopant for mitigating metal diffusion through the LZO, and a biaxially textured conductor layer supported by the biaxially textured buffer layer.

  3. Buffer layer for thin film structures

    SciTech Connect

    Foltyn, Stephen R.; Jia, Quanxi; Arendt, Paul N.; Wang, Haiyan

    2010-06-15

    A composite structure including a base substrate and a layer of a mixture of strontium titanate and strontium ruthenate is provided. A superconducting article can include a composite structure including an outermost layer of magnesium oxide, a buffer layer of strontium titanate or a mixture of strontium titanate and strontium ruthenate and a top-layer of a superconducting material such as YBCO upon the buffer layer.

  4. Buffer layer for thin film structures

    DOEpatents

    Foltyn, Stephen R.; Jia, Quanxi; Arendt, Paul N.; Wang, Haiyan

    2006-10-31

    A composite structure including a base substrate and a layer of a mixture of strontium titanate and strontium ruthenate is provided. A superconducting article can include a composite structure including an outermost layer of magnesium oxide, a buffer layer of strontium titanate or a mixture of strontium titanate and strontium ruthenate and a top-layer of a superconducting material such as YBCO upon the buffer layer.

  5. Buffer layers on biaxially textured metal substrates

    DOEpatents

    Shoup, Shara S.; Paranthamam, Mariappan; Beach, David B.; Kroeger, Donald M.; Goyal, Amit

    2001-01-01

    A method is disclosed for forming a biaxially textured buffer layer on a biaxially oriented metal substrate by using a sol-gel coating technique followed by pyrolyzing/annealing in a reducing atmosphere. This method is advantageous for providing substrates for depositing electronically active materials thereon.

  6. Lightwave coupler utilizing a tapered buffer layer.

    PubMed

    Kishioka, K

    1988-06-01

    We discuss the performance of a lightwave coupler utilizing a tapered buffer layer. The coupler with a ridge waveguide is fabricated on a glass substrate and high coupling efficiencies of 75% and 50% are measured for the operations of coupling from the waveguide to a light beam and from the laser beam into the waveguide, respectively. Further, experimental results of the rigid connection between the optical fiber and the waveguide are demonstrated. We also describe how the coupler differs from the conventional tapered guiding-layer coupler.

  7. Buffer layers and articles for electronic devices

    DOEpatents

    Paranthaman, Mariappan P.; Aytug, Tolga; Christen, David K.; Feenstra, Roeland; Goyal, Amit

    2004-07-20

    Materials for depositing buffer layers on biaxially textured and untextured metallic and metal oxide substrates for use in the manufacture of superconducting and other electronic articles comprise RMnO.sub.3, R.sub.1-x A.sub.x MnO.sub.3, and combinations thereof; wherein R includes an element selected from the group consisting of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y, and A includes an element selected from the group consisting of Be, Mg, Ca, Sr, Ba, and Ra.

  8. Buffer layer optimization for high efficiency CIGS solar cells

    NASA Astrophysics Data System (ADS)

    Severino, N.; Bednar, N.; Adamovic, N.

    2016-10-01

    This work presents a study concerning the numerical optimization of a buffer layer for high efficiency CIGS solar cells. The dependence of the solar cell properties on the buffer layer material, the layer thickness, the type and density of defects within the same layer were numerically investigated and analysed. Promising results were obtained with alternative Cd-free buffer layers (ZnSnO, InS and ZnS) in place of the standard CdS.

  9. Back contact buffer layer for thin-film solar cells

    DOEpatents

    Compaan, Alvin D.; Plotnikov, Victor V.

    2014-09-09

    A photovoltaic cell structure is disclosed that includes a buffer/passivation layer at a CdTe/Back contact interface. The buffer/passivation layer is formed from the same material that forms the n-type semiconductor active layer. In one embodiment, the buffer layer and the n-type semiconductor active layer are formed from cadmium sulfide (CdS). A method of forming a photovoltaic cell includes the step of forming the semiconductor active layers and the buffer/passivation layer within the same deposition chamber and using the same material source.

  10. Thin film photovoltaic devices with a minimally conductive buffer layer

    DOEpatents

    Barnes, Teresa M.; Burst, James

    2016-11-15

    A thin film photovoltaic device (100) with a tunable, minimally conductive buffer (128) layer is provided. The photovoltaic device (100) may include a back contact (150), a transparent front contact stack (120), and an absorber (140) positioned between the front contact stack (120) and the back contact (150). The front contact stack (120) may include a low resistivity transparent conductive oxide (TCO) layer (124) and a buffer layer (128) that is proximate to the absorber layer (140). The photovoltaic device (100) may also include a window layer (130) between the buffer layer (128) and the absorber (140). In some cases, the buffer layer (128) is minimally conductive, with its resistivity being tunable, and the buffer layer (128) may be formed as an alloy from a host oxide and a high-permittivity oxide. The high-permittivity oxide may further be chosen to have a bandgap greater than the host oxide.

  11. Buffer layers for REBCO films for use in superconducting devices

    DOEpatents

    Goyal, Amit; Wee, Sung-Hun

    2014-06-10

    A superconducting article includes a substrate having a biaxially textured surface. A biaxially textured buffer layer, which can be a cap layer, is supported by the substrate. The buffer layer includes a double perovskite of the formula A.sub.2B'B''O.sub.6, where A is rare earth or alkaline earth metal and B' and B'' are different transition metal cations. A biaxially textured superconductor layer is deposited so as to be supported by the buffer layer. A method of making a superconducting article is also disclosed.

  12. Buffer layers on metal alloy substrates for superconducting tapes

    DOEpatents

    Jia, Quanxi; Foltyn, Stephen R.; Arendt, Paul N.; Groves, James R.

    2004-10-05

    An article including a substrate, at least one intermediate layer upon the surface of the substrate, a layer of an oriented cubic oxide material having a rock-salt-like structure upon the at least one intermediate layer, and a layer of a SrRuO.sub.3 buffer material upon the oriented cubic oxide material layer is provided together with additional layers such as a HTS top-layer of YBCO directly upon the layer of a SrRuO.sub.3 buffer material layer. With a HTS top-layer of YBCO upon at least one layer of the SrRuO.sub.3 buffer material in such an article, J.sub.c 's of up to 1.3.times.10.sup.6 A/cm.sup.2 have been demonstrated with projected I.sub.c 's of over 200 Amperes across a sample 1 cm wide.

  13. Current isolating epitaxial buffer layers for high voltage photodiode array

    DOEpatents

    Morse, Jeffrey D.; Cooper, Gregory A.

    2002-01-01

    An array of photodiodes in series on a common semi-insulating substrate has a non-conductive buffer layer between the photodiodes and the semi-insulating substrate. The buffer layer reduces current injection leakage between the photodiodes of the array and allows optical energy to be converted to high voltage electrical energy.

  14. Mitigation of substrate defects in reticles using multilayer buffer layers

    DOEpatents

    Mirkarimi, Paul B.; Bajt, Sasa; Stearns, Daniel G.

    2001-01-01

    A multilayer film is used as a buffer layer to minimize the size of defects on a reticle substrate prior to deposition of a reflective coating on the substrate. The multilayer buffer layer deposited intermediate the reticle substrate and the reflective coating produces a smoothing of small particles and other defects on the reticle substrate. The reduction in defect size is controlled by surface relaxation during the buffer layer growth process and by the degree of intermixing and volume contraction of the materials at the multilayer interfaces. The buffer layers are deposited at near-normal incidence via a low particulate ion beam sputtering process. The growth surface of the buffer layer may also be heated by a secondary ion source to increase the degree of intermixing and improve the mitigation of defects.

  15. Methods for improved growth of group III nitride buffer layers

    DOEpatents

    Melnik, Yurity; Chen, Lu; Kojiri, Hidehiro

    2014-07-15

    Methods are disclosed for growing high crystal quality group III-nitride epitaxial layers with advanced multiple buffer layer techniques. In an embodiment, a method includes forming group III-nitride buffer layers that contain aluminum on suitable substrate in a processing chamber of a hydride vapor phase epitaxy processing system. A hydrogen halide or halogen gas is flowing into the growth zone during deposition of buffer layers to suppress homogeneous particle formation. Some combinations of low temperature buffers that contain aluminum (e.g., AlN, AlGaN) and high temperature buffers that contain aluminum (e.g., AlN, AlGaN) may be used to improve crystal quality and morphology of subsequently grown group III-nitride epitaxial layers. The buffer may be deposited on the substrate, or on the surface of another buffer. The additional buffer layers may be added as interlayers in group III-nitride layers (e.g., GaN, AlGaN, AlN).

  16. On buffer layers as non-reflecting computational boundaries

    NASA Technical Reports Server (NTRS)

    Hayder, M. Ehtesham; Turkel, Eli L.

    1996-01-01

    We examine an absorbing buffer layer technique for use as a non-reflecting boundary condition in the numerical simulation of flows. One such formulation was by Ta'asan and Nark for the linearized Euler equations. They modified the flow inside the buffer zone to artificially make it supersonic in the layer. We examine how this approach can be extended to the nonlinear Euler equations. We consider both a conservative and a non-conservative form modifying the governing equations in the buffer layer. We compare this with the case that the governing equations in the layer are the same as in the interior domain. We test the effectiveness of these buffer layers by a simulation of an excited axisymmetric jet based on a nonlinear compressible Navier-Stokes equations.

  17. Buffer layers for high-Tc thin films on sapphire

    NASA Technical Reports Server (NTRS)

    Wu, X. D.; Foltyn, S. R.; Muenchausen, R. E.; Cooke, D. W.; Pique, A.; Kalokitis, D.; Pendrick, V.; Belohoubek, E.

    1992-01-01

    Buffer layers of various oxides including CeO2 and yttrium-stabilized zirconia (YSZ) have been deposited on R-plane sapphire. The orientation and crystallinity of the layers were optimized to promote epitaxial growth of YBa2Cu3O(7-delta) (YBCO) thin films. An ion beam channeling minimum yield of about 3 percent was obtained in the CeO2 layer on sapphire, indicating excellent crystallinity of the buffer layer. Among the buffer materials used, CeO2 was found to be the best one for YBCO thin films on R-plane sapphire. High Tc and Jc were obtained in YBCO thin films on sapphire with buffer layers. Surface resistances of the YBCO films were about 4 mOmega at 77 K and 25 GHz.

  18. Enhanced adhesion for LIGA microfabrication by using a buffer layer

    DOEpatents

    Bajikar, Sateesh S.; De Carlo, Francesco; Song, Joshua J.

    2001-01-01

    The present invention is an improvement on the LIGA microfabrication process wherein a buffer layer is applied to the upper or working surface of a substrate prior to the placement of a resist onto the surface of the substrate. The buffer layer is made from an inert low-Z material (low atomic weight), a material that absorbs secondary X-rays emissions from the substrate that are generated from the substrate upon exposure to a primary X-rays source. Suitable materials for the buffer layer include polyamides and polyimide. The preferred polyimide is synthesized form pyromellitic anhydride and oxydianiline (PMDA-ODA).

  19. Enhanced adhesion for LIGA microfabrication by using a buffer layer

    DOEpatents

    Bajikar, Sateesh S.; De Carlo, Francesco; Song, Joshua J.

    2004-01-27

    The present invention is an improvement on the LIGA microfabrication process wherein a buffer layer is applied to the upper or working surface of a substrate prior to the placement of a resist onto the surface of the substrate. The buffer layer is made from an inert low-Z material (low atomic weight), a material that absorbs secondary X-rays emissions from the substrate that are generated from the substrate upon exposure to a primary X-rays source. Suitable materials for the buffer layer include polyamides and polyimide. The preferred polyimide is synthesized form pyromellitic anhydride and oxydianiline (PMDA-ODA).

  20. Rare earth zirconium oxide buffer layers on metal substrates

    DOEpatents

    Williams, Robert K.; Paranthaman, Mariappan; Chirayil, Thomas G.; Lee, Dominic F.; Goyal, Amit; Feenstra, Roeland

    2001-01-01

    A laminate article comprises a substrate and a biaxially textured (RE.sub.x A.sub.(1-x)).sub.2 O.sub.2-(x/2) buffer layer over the substrate, wherein 0buffer layer can be deposited using sol-gel or metal-organic decomposition. The laminate article can include a layer of YBCO over the (RE.sub.x A.sub.(1-x)).sub.2 O.sub.2-(x/2) buffer layer. A layer of CeO.sub.2 between the YBCO layer and the (RE.sub.x A.sub.(1-x)).sub.2 O.sub.2-(x/2) buffer layer can also be include. Further included can be a layer of YSZ between the CeO.sub.2 layer and the (RE.sub.x A.sub.(1-x)).sub.2 O.sub.2-(x/2) buffer layer. The substrate can be a biaxially textured metal, such as nickel. A method of forming the laminate article is also disclosed.

  1. Method of depositing buffer layers on biaxially textured metal substrates

    DOEpatents

    Beach, David B.; Morrell, Jonathan S.; Paranthaman, Mariappan; Chirayil, Thomas; Specht, Eliot D.; Goyal, Amit

    2002-08-27

    A laminate article comprises a substrate and a biaxially textured (RE.sup.1.sub.x RE.sup.2.sub.(1-x)).sub.2 O.sub.3 buffer layer over the substrate, wherein 0buffer layer can be deposited using sol-gel or metal-organic decomposition. The laminate article can include a layer of YBCO over the (RE.sup.1.sub.x RE.sup.2.sub.(1-x)).sub.2 O.sub.3 buffer layer. A layer of CeO.sub.2 between the YBCO layer and the (RE.sup.1.sub.x RE.sup.2.sub.(1-x)).sub.2 O.sub.3 buffer can also be include. Further included can be a layer of YSZ between the CeO.sub.2 layer and the (RE.sup.1.sub.x RE.sup.2.sub.(1-x)).sub.2 O.sub.3 buffer layer. The substrate can be a biaxially textured metal, such as nickel. A method of forming the laminate article is also disclosed.

  2. Buffer layers on metal alloy substrates for superconducting tapes

    DOEpatents

    Jia, Quanxi; Foltyn, Stephen R.; Arendt, Paul N.; Groves, James R.

    2004-06-29

    An article including a substrate, a layer of an inert oxide material upon the surface of the substrate, a layer of an amorphous oxide or oxynitride material upon the inert oxide material layer, a layer of an oriented cubic oxide material having a rock-salt-like structure upon the amorphous oxide material layer, and a layer of a SrRuO.sub.3 buffer material upon the oriented cubic oxide material layer is provided together with additional layers such as a HTS top-layer of YBCO directly upon the layer of a SrRuO.sub.3 buffer material layer. With a HTS top-layer of YBCO upon at least one layer of the SrRuO.sub.3 buffer material in such an article, J.sub.c 's of up to 1.3.times.10.sup.6 A/cm.sup.2 have been demonstrated with projected IC's of over 200 Amperes across a sample 1 cm wide.

  3. Conductive and robust nitride buffer layers on biaxially textured substrates

    DOEpatents

    Sankar, Sambasivan [Chicago, IL; Goyal, Amit [Knoxville, TN; Barnett, Scott A [Evanston, IL; Kim, Ilwon [Skokie, IL; Kroeger, Donald M [Knoxville, TN

    2009-03-31

    The present invention relates to epitaxial, electrically conducting and mechanically robust, cubic nitride buffer layers deposited epitaxially on biaxially textured substrates such as metals and alloys. The invention comprises of a biaxially textured substrate with epitaxial layers of nitrides. The invention also discloses a method to form such epitaxial layers using a high rate deposition method as well as without the use of forming gases. The invention further comprises epitaxial layers of oxides on the biaxially textured nitride layer. In some embodiments the article further comprises electromagnetic devices which may have superconducting properties.

  4. Conductive and robust nitride buffer layers on biaxially textured substrates

    DOEpatents

    Sankar, Sambasivan; Goyal, Amit; Barnett, Scott A.; Kim, Ilwon; Kroeger, Donald M.

    2004-08-31

    The present invention relates to epitaxial, electrically conducting and mechanically robust, cubic nitride buffer layers deposited epitaxially on biaxially textured substrates such as metal and alloys. The invention comprises of a biaxially textured substrate with epitaxial layers of nitrides. The invention also discloses a method to form such epitaxial layers using a high rate deposition method as well as without the use of forming gases. The invention further comprises epitaxial layers of oxides on the biaxially textured nitride layers. In some embodiments the article further comprises electromagnetic devices which may be super conducting properties.

  5. Substrate-induced magnetism in epitaxial graphene buffer layers.

    PubMed

    Ramasubramaniam, A; Medhekar, N V; Shenoy, V B

    2009-07-08

    Magnetism in graphene is of fundamental as well as technological interest, with potential applications in molecular magnets and spintronic devices. While defects and/or adsorbates in freestanding graphene nanoribbons and graphene sheets have been shown to cause itinerant magnetism, controlling the density and distribution of defects and adsorbates is in general difficult. We show from first principles calculations that graphene buffer layers on SiC(0001) can also show intrinsic magnetism. The formation of graphene-substrate chemical bonds disrupts the graphene pi-bonds and causes localization of graphene states near the Fermi level. Exchange interactions between these states lead to itinerant magnetism in the graphene buffer layer. We demonstrate the occurrence of magnetism in graphene buffer layers on both bulk-terminated as well as more realistic adatom-terminated SiC(0001) surfaces. Our calculations show that adatom density has a profound effect on the spin distribution in the graphene buffer layer, thereby providing a means of engineering magnetism in epitaxial graphene.

  6. Buffer layer engineering on graphene via various oxidation methods for atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Takahashi, Nobuaki; Nagashio, Kosuke

    2016-12-01

    The integration of a high-k oxide on graphene using atomic layer deposition requires an electrically reliable buffer layer. In this study, Y was selected as the buffer layer due to its highest oxidation ability among the rare-earth elements, and various oxidation methods (atmospheric, and high-pressure O2 and ozone annealing) were applied to the Y metal buffer layer. By optimizing the oxidation conditions of the top-gate insulator, we successfully improved the capacitance of the top gate Y2O3 insulator and demonstrated a large I on/I off ratio for bilayer graphene under an external electric field.

  7. Semiconducting chalcogenide buffer layer for oxide heteroepitaxy on Si(001)

    NASA Astrophysics Data System (ADS)

    Schmidt, D. A.; Ohta, Taisuke; Lu, C.-Y.; Bostwick, Aaron A.; Yu, Q.; Rotenberg, Eli; Ohuchi, F. S.; Olmstead, Marjorie A.

    2006-05-01

    We report controlled laminar growth of a crystalline transition metal oxide on Si(001) without SiOx or silicide formation by utilizing the chalcogenide semiconductor gallium sesquiselenide (Ga2Se3) as a nonreactive buffer layer. Initial nucleation of both pure and Co-doped anatase (TiO2) is along Ga2Se3 nanowire structures, coalescing to a flat, multidomain film within two molecular layers. Arsenic-terminated Si(001) [Si(001):As] is stable against pure O2, but oxidizes when both Ti and O2 are present. The Si -TiO2 valence band offset using either buffer layer is about 2.8eV, producing a staggered band alignment.

  8. Advanced titania buffer layer architectures prepared by chemical solution deposition

    NASA Astrophysics Data System (ADS)

    Kunert, J.; Bäcker, M.; Brunkahl, O.; Wesolowski, D.; Edney, C.; Clem, P.; Thomas, N.; Liersch, A.

    2011-08-01

    Chemical solution deposition (CSD) was used to grow high-quality (100) oriented films of SrTiO3 (STO) on CSD CaTiO3 (CTO), Ba0.1Ca0.9TiO3 (BCT) and STO seed and template layers. These template films bridge the lattice misfit between STO and the nickel-tungsten (NiW) substrate, assisting in dense growth of textured STO. Additional niobium (Nb) doping of the STO buffer layer reduces oxygen diffusion which is necessary to avoid undesired oxidation of the NiW. The investigated templates offer suitable alternatives to established standard buffer systems like La2Zr2O7 (LZO) and CeO2 for coated conductors.

  9. High Jc coated conductors with a simple buffer layer architecture

    NASA Astrophysics Data System (ADS)

    Gianni, L.; Baldini, A.; Bindi, M.; Gauzzi, A.; Rampino, S.; Zannella, S.

    2005-10-01

    We report on the in situ route for the continuous fabrication of YBCO coated conductors (CC) by thermal co-evaporation. CC architecture consists of YBCO film grown on biaxially textured Ni-alloys tapes buffered with a single layer of CeO2. The buffer layer deposition has been optimized by either e-beam or thermal evaporation using respectively ceria or metallic cerium. Best results have been obtained on CeO2 film, with a thickness less or equal than 100 nm, grown in a reducing atmosphere at 690 °C with a growth rate of 2.4 Å/s. The optimal samples exhibit a highly biaxial texture, as indicated by FWHM values in the range of 5-8° and 4-6° for respectively in- and out-of-plane orientations. The layers are characterized by an uniform and crack-free surface with an average roughness lower than 10 nm. SIMS analysis confirms the effectiveness of CeO2 buffer layer against Ni interdiffusion. This template allows to obtain YBCO films strong textured, with good superconductive properties. YBCO texture data are equivalent the CeO2 ones. Midpoint critical temperature, Tc, falls reproducibly in 87-88 K range, with transition widths ΔTc < 2-3 K. Critical current density, Jc, up to 2 MA/cm2 at 77 K in self-field, have been achieved in a meter long CC corresponding to Ic/width value of 130 A/cm-width. Uniformity and reproducibility of long CC properties are under optimization.

  10. Alloys containing antimony as metamorphic buffer layer for device applications

    NASA Astrophysics Data System (ADS)

    Rodriguez, Benny Perez

    This work explores the stress/strain relaxation kinetics in metamorphic buffer layers of GaAs1-xSbx/GaAs (001) grown by molecular beam epitaxy. The real-time stress/strain evolution was obtained using an in situ multi-beam optical sensor measurement, and combined with detailed analysis from x-ray diffraction, transmission electron microscopy, and atomic force microscopy. Several distinct stages of the strain relaxation were observed during growth of GaAs1-xSbx constant composition buffer layers, which are separated into three main regimes: pseudomorphic growth, fast strain relaxation and saturation. Constant composition layers of GaAs0.5Sb0.5/GaAs initially relax elastically followed by the rapid nucleation of both 60° and pure edge dislocations. The saturation regime is distinguished by coalescence of small islands that appears to trigger the formation of threading dislocations. The strain relaxation profile for GaAs0.5Sb0.5, GaAs0.61Sb0.39, and In0.2Ga0.8As films were modeled using Dodson and Tsao's model of effective stress, with a new representation for elastic interactions of misfit dislocations. The model results agree with the experimental data and show that repulsive interaction of misfit dislocations is responsible for the large residual stress. Using this model, estimated line dislocation densities are in good agreement with the values obtained experimentally. This could have potential application in the design of metamorphic buffer layers because our observations are made in real time on individual growth, without the need of external characterization to measure the dislocation density. In addition, this model offers new insights in estimating the dislocation glide energy for simulation purposes. Linearly graded GaAs1-xSbx films resulted in a decreased Sb incorporation, higher residual stress, and bifurcation in the tilt of the sample. Less aggressive grading resulted in more uniform incorporation and lower residual stress. Step graded films resulted in

  11. Photo-induced wettability of TiO{sub 2} film with Au buffer layer

    SciTech Connect

    Purkayastha, Debarun Dhar; Sangani, L. D. Varma; Krishna, M. Ghanashyam; Madhurima, V.

    2014-04-24

    The effect of thickness of Au buffer layer (15-25 nm) between TiO{sub 2} film and substrate on the wettability of TiO{sub 2} films is reported. TiO{sub 2} films grown on Au buffer layer have a higher contact angle of 96-;100° as compared to 47.6o for the film grown without buffer layer. The transition from hydrophobicity to hydrophilicity under UV irradiation occurs within 10 min. for the buffer layered films whereas it is almost 30 min. for the film grown without buffer layer. The enhanced photo induced hydrophilicity is shown to be surface energy driven.

  12. Buffer layers on rolled nickel or copper as superconductor substrates

    DOEpatents

    Paranthaman, Mariappan; Lee, Dominic F.; Kroeger, Donald M.; Goyal, Amit

    2000-01-01

    Buffer layer architectures are epitaxially deposited on biaxially-textured rolled substrates of nickel and/or copper and their alloys for high current conductors, and more particularly buffer layer architectures such as Y.sub.2 O.sub.3 /Ni, YSZ/Y.sub.2 O.sub.3 /Ni, Yb.sub.2 O.sub.3 /Ni, Yb.sub.2 O.sub.3 /Y.sub.2 O.sub.3 /Ni, Yb.sub.2 O.sub.3 /CeO.sub.2 /Ni, RE.sub.2 O.sub.3 /Ni (RE=Rare Earth), and Yb.sub.2 O.sub.3 /YSZ/CeO.sub.2 /Ni, Y.sub.2 O.sub.3 /Cu, YSZ/Y.sub.2 O.sub.3 /Cu, Yb.sub.2 O.sub.3 /Cu, Yb.sub.2 O.sub.3 /Y.sub.2 O.sub.3 /Cu, Yb.sub.2 O.sub.3 /CeO.sub.2 /Cu, RE.sub.2 O.sub.3 /Cu, and Yb.sub.2 O.sub.3 /YSZ/CeO.sub.2 /Cu. Deposition methods include physical vapor deposition techniques which include electron-beam evaporation, rf magnetron sputtering, pulsed laser deposition, thermal evaporation, and solution precursor approach, which includes chemical vapor deposition, combustion CVD, metal-organic decomposition, sol-gel processing, and plasma spray.

  13. Leakage effects in n-GaAs MESFET with n-GaAs buffer layer

    NASA Technical Reports Server (NTRS)

    Wang, Y. C.; Bahrami, M.

    1983-01-01

    Whereas improvement of the interface between the active layer and the buffer layer has been demonstrated, the leakage effects can be important if the buffer layer resistivity is not sufficiently high and/or the buffer layer thickness is not sufficiently small. It was found that two buffer leakage currents exist from the channel under the gate to the source and from drain to the channel in addition to the buffer leakage resistance between drain and source. It is shown that for a 1 micron gate-length n-GaAs MESFET, if the buffer layer resistivity is 12 OHM-CM and the buffer layer thickness h is 2 microns, the performance of the device degrades drastically. It is suggested that h should be below 2 microns.

  14. Doped Y.sub.2O.sub.3 buffer layers for laminated conductors

    DOEpatents

    Paranthaman, Mariappan Parans [Knoxville, TN; Schoop, Urs [Westborough, MA; Goyal, Amit [Knoxville, TN; Thieme, Cornelis Leo Hans [Westborough, MA; Verebelyi, Darren T [Oxford, MA; Rupich, Martin W [Framingham, MA

    2007-08-21

    A laminated conductor includes a metallic substrate having a surface, a biaxially textured buffer layer supported by the surface of the metallic substrate, the biaxially textured buffer layer comprising Y.sub.2O.sub.3 and a dopant for blocking cation diffusion through the Y.sub.2O.sub.3, and a biaxially textured conductor layer supported by the biaxially textured buffer layer.

  15. Superconducting composite with multilayer patterns and multiple buffer layers

    DOEpatents

    Wu, X.D.; Muenchausen, R.E.

    1993-10-12

    An article of manufacture is described including a substrate, a patterned interlayer of a material selected from the group consisting of magnesium oxide, barium-titanium oxide or barium-zirconium oxide, the patterned interlayer material overcoated with a secondary interlayer material of yttria-stabilized zirconia or magnesium-aluminum oxide, upon the surface of the substrate whereby an intermediate article with an exposed surface of both the overcoated patterned interlayer and the substrate is formed, a coating of a buffer layer selected from the group consisting of cerium oxide, yttrium oxide, curium oxide, dysprosium oxide, erbium oxide, europium oxide, iron oxide, gadolinium oxide, holmium oxide, indium oxide, lanthanum oxide, manganese oxide, lutetium oxide, neodymium oxide, praseodymium oxide, plutonium oxide, samarium oxide, terbium oxide, thallium oxide, thulium oxide, yttrium oxide and ytterbium oxide over the entire exposed surface of the intermediate article, and, a ceramic superconductor. 5 figures.

  16. Development of N/P AlGaAs free-standing top solar cells for tandem applications

    NASA Technical Reports Server (NTRS)

    Negley, Gerald H.; Dinetta, Louis C.; Cummings, John R.; Hannon, Margaret H.; Sims, Paul E.; Barnett, Allen M.

    1991-01-01

    The combination of a free standing AlGaAs top solar cell and an existing bottom solar cell is the highest performance, lowest risk approach to implementing the tandem cell concept. The solar cell consists of an AlGaAs substrate layer, an AlGaAs base layer, an AlGaAs emitter, and an ultra-thin AlGaAs window layer. The window layer is compositionally graded which minimizes reflection at the window layer/emitter interface and creates a built-in electric field to improve quantum response in the blue region of the spectrum. Liquid phase epitaxy (LPE) is the only viable method to produce this free standing top solar cell. Small (0.125 sq cm), transparent p/n AlGaAs top solar cells were demonstrated with optimum bandgap for combination with a silicon bottom solar cell. The efficiency of an AlGaAs/Si stack using the free standing AlGaAs device upon an existing silicon bottom solar cell is 24 pct. (1X, Air Mass Zero (AM0). The n/p AlGaAs top solar cell is being developed in order to facilitate the wiring configuration. The two terminal tandem stack will retain fit, form, and function of existing silicon solar cells. Progress in the development of large area (8 and 16 sq cm), free standing AlGaAs top solar cells is discussed.

  17. Reducing interface recombination for Cu(In,Ga)Se{sub 2} by atomic layer deposited buffer layers

    SciTech Connect

    Hultqvist, Adam; Bent, Stacey F.; Li, Jian V.; Kuciauskas, Darius; Dippo, Patricia; Contreras, Miguel A.; Levi, Dean H.

    2015-07-20

    Partial CuInGaSe{sub 2} (CIGS) solar cell stacks with different atomic layer deposited buffer layers and pretreatments were analyzed by photoluminescence (PL) and capacitance voltage (CV) measurements to investigate the buffer layer/CIGS interface. Atomic layer deposited ZnS, ZnO, and SnO{sub x} buffer layers were compared with chemical bath deposited CdS buffer layers. Band bending, charge density, and interface state density were extracted from the CV measurement using an analysis technique new to CIGS. The surface recombination velocity calculated from the density of interface traps for a ZnS/CIGS stack shows a remarkably low value of 810 cm/s, approaching the range of single crystalline II–VI systems. Both the PL spectra and its lifetime depend on the buffer layer; thus, these measurements are not only sensitive to the absorber but also to the absorber/buffer layer system. Pretreatment of the CIGS prior to the buffer layer deposition plays a significant role on the electrical properties for the same buffer layer/CIGS stack, further illuminating the importance of good interface formation. Finally, ZnS is found to be the best performing buffer layer in this study, especially if the CIGS surface is pretreated with potassium cyanide.

  18. Characterization of Cu buffer layers for growth of L10-FeNi thin films

    NASA Astrophysics Data System (ADS)

    Mizuguchi, M.; Sekiya, S.; Takanashi, K.

    2010-05-01

    A Cu(001) layer was fabricated on a Au(001) layer to investigate the use of Cu as a buffer layer for growing L10-FeNi thin films. The epitaxial growth of a Cu buffer layer was observed using reflection high-energy electron diffraction. The flatness of the layer improved drastically with an increase in the substrate temperature although the layer was an alloy (AuCu3). An FeNi thin film was epitaxially grown on the AuCu3 buffer layer by alternate monatomic layer deposition and the formation of an L10-FeNi ordered alloy was expected. The AuCu3 buffer layer is thus a promising candidate material for the growth of L10-FeNi thin films.

  19. Superconducting composite with multilayer patterns and multiple buffer layers

    DOEpatents

    Wu, Xin D.; Muenchausen, Ross E.

    1993-01-01

    An article of manufacture including a substrate, a patterned interlayer of a material selected from the group consisting of magnesium oxide, barium-titanium oxide or barium-zirconium oxide, the patterned interlayer material overcoated with a secondary interlayer material of yttria-stabilized zirconia or magnesium-aluminum oxide, upon the surface of the substrate whereby an intermediate article with an exposed surface of both the overcoated patterned interlayer and the substrate is formed, a coating of a buffer layer selected from the group consisting of cerium oxide, yttrium oxide, curium oxide, dysprosium oxide, erbium oxide, europium oxide, iron oxide, gadolinium oxide, holmium oxide, indium oxide, lanthanum oxide, manganese oxide, lutetium oxide, neodymium oxide, praseodymium oxide, plutonium oxide, samarium oxide, terbium oxide, thallium oxide, thulium oxide, yttrium oxide and ytterbium oxide over the entire exposed surface of the intermediate article, and, a ceramic superco n FIELD OF THE INVENTION The present invention relates to the field of superconducting articles having two distinct regions of superconductive material with differing in-plane orientations whereby the conductivity across the boundary between the two regions can be tailored. This invention is the result of a contract with the Department of Energy (Contract No. W-7405-ENG-36).

  20. Effect of Oxide Buffer Layer on the Thermochromic Properties of VO2 Thin Films

    NASA Astrophysics Data System (ADS)

    Koo, Hyun; Xu, Lu; Ko, Kyeong-Eun; Ahn, Seunghyun; Chang, Se-Hong; Park, Chan

    2013-12-01

    VO2 thin films were deposited on soda lime glass substrates with ZnO, TiO2, SnO2, and CeO2 thin films applied as buffer layers between the VO2 films and the substrates in order to investigate the effect of buffer layer on the formation and the thermochromic properties of VO2 film. Buffer layers with thicknesses over 50 nm were found to affect the formation of VO2 film, which was confirmed by XRD spectra. By using ZnO, TiO2, and SnO2 buffer layers, monoclinic VO2 (VO2(M)) film was successfully fabricated on soda lime glass at 370 °C. On the contrary, films of VO2(B), which is known to have no phase transition near room temperature, were formed rather than VO2(M) when the film was deposited on CeO2 buffer layer at the same film deposition temperature. The excellent thermochromic properties of the films deposited on ZnO, TiO2, and SnO2 buffer layers were confirmed from the temperature dependence of electrical resistivity from room temperature to 80 °C. Especially, due to the tendency of ZnO thin film to grow with a high degree of preferred orientation on soda lime glass at low temperature, the VO2 film deposited on ZnO buffer layer exhibits the best thermochromic properties compared to those on other buffer layer materials used in this study. These results suggest that deposition of VO2 films on soda lime glass at low temperature with excellent thermochromic properties can be achieved by considering the buffer layer material having structural similarity with VO2. Moreover, the degree of crystallization of buffer layer is also related with that of VO2 film, and thus ZnO can be one of the most effective buffer layer materials.

  1. Buffer layer investigations on MFIS capacitors consisting of ferroelectric poly[vinylidene fluoride trifluoroethylene

    NASA Astrophysics Data System (ADS)

    Henkel, K.; Seime, B.; Paloumpa, I.; Müller, K.; Schmeißer, D.

    2010-02-01

    In this paper we present capacitance-voltage (CV) measurements on metal-ferroelectric-insulator-semiconductor (MFIS) capacitors with poly[vinylidene fluoride trifluoroethylene] (P[VDF/TrFE] as ferroelectric layer and SiO2, Al2O3 and HfO2 as buffering insulator layer. In order to discuss our data in a quantitative manner we perform fits to the data based on a model proposed by Miller and McWorther. The improvement of the polarization values and subsequently its effect on the hysteresis of the CV curve by the successive shrinking of the buffer layer thickness and the following choice of a high-k buffer material is demonstrated. Our data underline that a saturated polarization of P[VDF/TrFE] cannot be controlled with a SiO2 buffer layer and the insertion of a high-k buffer layer is essential for further improvements of the characteristics of MFIS stacks.

  2. Method of deforming a biaxially textured buffer layer on a textured metallic substrate and articles therefrom

    DOEpatents

    Lee, Dominic F.; Kroeger, Donald M.; Goyal, Amit

    2000-01-01

    The present invention provides methods and biaxially textured articles having a deformed epitaxial layer formed therefrom for use with high temperature superconductors, photovoltaic, ferroelectric, or optical devices. A buffer layer is epitaxially deposited onto biaxially-textured substrates and then mechanically deformed. The deformation process minimizes or eliminates grooves, or other irregularities, formed on the buffer layer while maintaining the biaxial texture of the buffer layer. Advantageously, the biaxial texture of the buffer layer is not altered during subsequent heat treatments of the deformed buffer. The present invention provides mechanical densification procedures which can be incorporated into the processing of superconducting films through the powder deposit or precursor approaches without incurring unfavorable high-angle grain boundaries.

  3. Simulation study on single event burnout in linear doping buffer layer engineered power VDMOSFET

    NASA Astrophysics Data System (ADS)

    Yunpeng, Jia; Hongyuan, Su; Rui, Jin; Dongqing, Hu; Yu, Wu

    2016-02-01

    The addition of a buffer layer can improve the device's secondary breakdown voltage, thus, improving the single event burnout (SEB) threshold voltage. In this paper, an N type linear doping buffer layer is proposed. According to quasi-stationary avalanche simulation and heavy ion beam simulation, the results show that an optimized linear doping buffer layer is critical. As SEB is induced by heavy ions impacting, the electric field of an optimized linear doping buffer device is much lower than that with an optimized constant doping buffer layer at a given buffer layer thickness and the same biasing voltages. Secondary breakdown voltage and the parasitic bipolar turn-on current are much higher than those with the optimized constant doping buffer layer. So the linear buffer layer is more advantageous to improving the device's SEB performance. Project supported by the National Natural Science Foundation of China (No. 61176071), the Doctoral Fund of Ministry of Education of China (No. 20111103120016), and the Science and Technology Program of State Grid Corporation of China (No. SGRI-WD-71-13-006).

  4. Selective oxidation of buried AlGaAs for fabrication of vertical-cavity lasers

    SciTech Connect

    Choquette, K.D.; Geib, K.M.; Chui, H.C.; Hou, H.Q.; Hull, R.

    1996-06-01

    The authors discuss the selective conversion of buried layers of AlGaAs to a stable oxide and the implementation of this oxide into high performance vertical-cavity surface emitting lasers (VCSELs). The rate of lateral oxidation is shown to be linear with an Arrhenius temperature dependence. The measured activation energies vary with Al composition, providing a high degree of oxidation selectivity between AlGaAs alloys. Thus buried oxide layers can be selectively fabricated within the VCSEL through small compositional variations in the AlGaAs layers. The oxidation of AlGaAs alloys, as opposed to AlAs, is found to provide robust processing of reliable lasers. The insulating and low refractive index oxide provides enhanced electrical and optical confinement for ultralow threshold currents in oxide-apertured VCSELs.

  5. Method of depositing an electrically conductive oxide buffer layer on a textured substrate and articles formed therefrom

    DOEpatents

    Paranthaman, M. Parans; Aytug, Tolga; Christen, David K.

    2003-09-09

    An article with an improved buffer layer architecture includes a substrate having a textured metal surface, and an electrically conductive lanthanum metal oxide epitaxial buffer layer on the surface of the substrate. The article can also include an epitaxial superconducting layer deposited on the epitaxial buffer layer. An epitaxial capping layer can be placed between the epitaxial buffer layer and the superconducting layer. A method for preparing an epitaxial article includes providing a substrate with a metal surface and depositing on the metal surface a lanthanum metal oxide epitaxial buffer layer. The method can further include depositing a superconducting layer on the epitaxial buffer layer, and depositing an epitaxial capping layer between the epitaxial buffer layer and the superconducting layer.

  6. Method of depositing an electrically conductive oxide buffer layer on a textured substrate and articles formed therefrom

    DOEpatents

    Paranthaman, M. Parans; Aytug, Tolga; Christen, David K.

    2005-10-18

    An article with an improved buffer layer architecture includes a substrate having a textured metal surface, and an electrically conductive lanthanum metal oxide epitaxial buffer layer on the surface of the substrate. The article can also include an epitaxial superconducting layer deposited on the epitaxial buffer layer. An epitaxial capping layer can be placed between the epitaxial buffer layer and the superconducting layer. A method for preparing an epitaxial article includes providing a substrate with a metal surface and depositing on the metal surface a lanthanum metal oxide epitaxial buffer layer. The method can further include depositing a superconducting layer on the epitaxial buffer layer, and depositing an epitaxial capping layer between the epitaxial buffer layer and the superconducting layer.

  7. New Approach to Depositing Yttria-Stabilized Zirconia Buffer Layers for Coated Conductors (Postprint)

    DTIC Science & Technology

    2012-02-01

    distribution unlimited. See additional restrictions described on inside pages STINFO COPY © 2003 Materials Research Society AIR... additional layer in the buffer layer stack—a transient nickel layer deposited directly on the substrate. Regardless of the substrate and protective layers...Ridge Na- tional Laboratory ( ORNL ), Oak Ridge, TN, were precleaned in organic solvents (acetone, ethanol, chloro- form) using ultrasonic agitation

  8. Microstructures of YBa2Cu3Oy Layers Deposited on Conductive Layer-Buffered Metal Tapes

    NASA Astrophysics Data System (ADS)

    Ichinose, Ataru; Hashimoto, Masayuki; Horii, Shigeru; Doi, Toshiya

    REBa2Cu3Oy (REBCO; RE: rare-earth elements)-coated conductors (CCs) have high potential for use in superconducting devices. In particular, REBCO CCs are useful for superconducting devices working at relatively high temperatures near 77 K. The important issues in their applications are high performance, reliability and low cost. To date, sufficient performance for some applications has almost been achieved by considerable efforts. The establishment of the reliability of superconducting devices is under way at present. The issue of low cost must be resolved to realize the application of superconducting devices in the near future. Therefore, we have attempted several ways to reduce the cost of REBCO CCs. The coated conductors using a Nb-doped SrTiO3 buffer layer and Ni-plated Cu and stainless steel laminate metal tapes have recently been developed to eliminate the use of electric stabilization layers of Cu and Ag, which are expected to reduce the material cost. Good superconducting properties are obtained at 77 K. The critical current density (JC) at 77 K under a magnetic self-field is determined to be more than 2x106 A/cm2. The microstructures of the CCs are analyzed by transmission electron microscopy to obtain a much higher quality. By microscopic structure analysis, an overgrowth of the buffer layer is observed at a grain boundary of the metal substrate, which is one of the reasons for the high JC.

  9. MgO buffer layers on rolled nickel or copper as superconductor substrates

    DOEpatents

    Paranthaman, Mariappan; Goyal, Amit; Kroeger, Donald M.; List, III, Frederic A.

    2001-01-01

    Buffer layer architectures are epitaxially deposited on biaxially-textured rolled-Ni and/or Cu substrates for high current conductors, and more particularly buffer layer architectures such as MgO/Ag/Pt/Ni, MgO/Ag/Pd/Ni, MgO/Ag/Ni, MgO/Ag/Pd/Cu, MgO/Ag/Pt/Cu, and MgO/Ag/Cu. Techniques used to deposit these buffer layers include electron beam evaporation, thermal evaporation, rf magnetron sputtering, pulsed laser deposition, metal-organic chemical vapor deposition (MOCVD), combustion CVD, and spray pyrolysis.

  10. Method for making MgO buffer layers on rolled nickel or copper as superconductor substrates

    DOEpatents

    Paranthaman, Mariappan; Goyal, Amit; Kroeger, Donald M.; List, III, Frederic A.

    2002-01-01

    Buffer layer architectures are epitaxially deposited on biaxially-textured rolled-Ni and/or Cu substrates for high current conductors, and more particularly buffer layer architectures such as MgO/Ag/Pt/Ni, MgO/Ag/Pd/Ni, MgO/Ag/Ni, MgO/Ag/Pd/Cu, MgO/Ag/Pt/Cu, and MgO/Ag/Cu. Techniques used to deposit these buffer layers include electron beam evaporation, thermal evaporation, rf magnetron sputtering, pulsed laser deposition, metal-organic chemical vapor deposition (MOCVD), combustion CVD, and spray pyrolysis.

  11. Growth Optimization of YBa2NbO6 Buffer Layers (Postprint)

    DTIC Science & Technology

    2012-02-01

    single crystals, and IBAD MgO buffered Inconel substrates has been investigated. X-ray diffraction confirms the epitaxial growth of highly h00 oriented...YBNO thin films on single crystal substrates and IBAD MgO buffered Inconel substrates. The best average surface roughness of the YBNO films...diffraction, crystal, buffered, inconel , epitaxial, films, substrates, layers, growth, investigated, sufficient, preliminary, critical 16. SECURITY

  12. Efficient organic photovoltaic devices using a combination of exciton blocking layer and anodic buffer layer

    NASA Astrophysics Data System (ADS)

    Chan, M. Y.; Lee, C. S.; Lai, S. L.; Fung, M. K.; Wong, F. L.; Sun, H. Y.; Lau, K. M.; Lee, S. T.

    2006-11-01

    By using bathophenanthroline (BPhen) as an exciton blocking layer (EBL) at the organic/cathode contact of a standard copper phthalocyanine/C60 organic photovoltaic (OPV) device, power conversion efficiency was substantially increased from 0.86% to 2.64%. The BPhen-based devices showed a 45% increase in power conversion efficiency over that of an equivalent device with an EBL of bathocuproine. The performance improvement was analyzed in terms of the electron energy levels, optical transparencies and electron mobilities of the two EBLs. Based on these results, the roles of and requirements for an effective EBL were discussed. Combining the use of BPhen and a WO3 anodic buffer layer further increased the power conversion efficiency of the OPV device to 3.33%.

  13. GaAs buffer layer technique for vertical nanowire growth on Si substrate

    SciTech Connect

    Xu, Xiaoqing Parizi, Kokab B.; Huo, Yijie; Kang, Yangsen; Philip Wong, H.-S.; Li, Yang

    2014-02-24

    Gold catalyzed vapor-liquid-solid method is widely applied to III–V nanowire (NW) growth on Si substrate. However, the easy oxidation of Si, possible Si contamination in the NWs, high defect density in the NWs, and high sensitivity of the NW morphology to growth conditions largely limit its controllability. In this work, we developed a buffer layer technique by introducing a GaAs thin film with predefined polarity as a template. It is found that samples grown on these buffer layers all have high vertical NW yields in general, due to the single-orientation of the buffer layers. Low temperature buffer with smoother surface leads to highest yield of vertical NWs, while high temperature (HT) buffer with better crystallinity results in perfect NW quality. The defect-free property we observed here is very promising for optoelectronic device applications based on GaAs NW. Moreover, the buffer layers can eliminate Si contamination by preventing Si-Au alloy formation and by increasing the thickness of the Si diffusion barrier, thus providing more flexibility to vertical NW growth. The buffer layer technique we demonstrated here could be easily extended to other III-V on Si system for electronic and photonic applications.

  14. Critical CuI buffer layer surface density for organic molecular crystal orientation change

    SciTech Connect

    Ahn, Kwangseok; Kim, Jong Beom; Lee, Dong Ryeol; Kim, Hyo Jung; Lee, Hyun Hwi

    2015-01-21

    We have determined the critical surface density of the CuI buffer layer inserted to change the preferred orientation of copper phthalocyanine (CuPc) crystals grown on the buffer layer. X-ray reflectivity measurements were performed to obtain the density profiles of the buffer layers and out-of-plane and 2D grazing-incidence X-ray diffraction measurements were performed to determine the preferred orientations of the molecular crystals. Remarkably, it was found that the preferred orientation of the CuPc film is completely changed from edge-on (1 0 0) to face-on (1 1 −2) by a CuI buffer layer with a very low surface density, so low that a large proportion of the substrate surface is bare.

  15. Pulsed Laser Deposition of YBCO With Yttrium Oxide Buffer Layers (Postprint)

    DTIC Science & Technology

    2012-02-01

    AFRL-RZ-WP-TP-2012-0092 PULSED LASER DEPOSITION OF YBCO WITH YTTRIUM OXIDE BUFFER LAYERS (POSTPRINT) Paul N. Barnes, Timothy J. Haugan...Paper Postprint 01 January 2002 – 01 January 2004 4. TITLE AND SUBTITLE PULSED LASER DEPOSITION OF YBCO WITH YTTRIUM OXIDE BUFFER LAYERS (POSTPRINT...Textured metallic substrate based HTS coated conductors with the YBCO /CeO2/YSZ/CeO2/Ni architecture have already been shown to exhibit high current

  16. Organic Photovoltaic Cells with Improved Performance Using Bathophenanthroline as a Buffer Layer

    NASA Astrophysics Data System (ADS)

    Wang, Na-na; Yu, Jun-sheng; Lin, Hui; Jiang, Ya-dong

    2010-02-01

    The role of bathophenanthroline (Bphen) as a buffer layer inserted between fullerene (C60) and Ag cathode in organic photovoltaic (OPV) cell was discussed. By introducing Bphen as a buffer layer with thicknes from 0 to 2.5 nm, the power conversion efficiency of the OPV cell based on copper phthalocyanine (CuPc) and C60 was increased from 0.87% to 2.25% under AM 1.5 solar illumination at an intensity of 100 mW/cm2, which was higher than that of bathocuproine used as a buffer layer. The photocurrent-voltage characteristics showed that Bphen effectively improves electron transport through C60 layer into Ag electrode and leads to balance charge carrier transport capability. The influence of Bphen thickness on OPV cells was also investigated. Furthermore, the absorption spectrum shows that an additional Bphen layer enhances the light harvest capability of CuPc/C60.

  17. Matching characteristics of different buffer layers with VO2 thin films

    NASA Astrophysics Data System (ADS)

    Yang, Kai; Zhang, Dongping; Liu, Yi; Guan, Tianrui; Qin, Xiaonan; Zhong, Aihua; Cai, Xingmin; Fan, Ping; Lv, Weizhong

    2016-10-01

    VO2 thin films were fabricated by reactive DC magnetron sputtering on different buffer layers of MgF2, Al2O3 and TiO2, respectively. The crystallinity and orientation relationship, thickness of VO2 thin films, atoms vibrational modes, optical and electrical property, surface morphology of films were characterized by X-ray diffraction, Raman scattering microscopy, step profiler, spectrophotometer, four-probe technique, and scanning electron microscopy, respectively. XRD results investigated that the films have preferential crystalline planes VO2 (011). The crystallinity of VO2 films grown on TiO2 buffer layers are superior to VO2 directly deposited on soda-lime glass. The Raman bands of the VO2 films correspond to an Ag symmetry mode of VO2 (M). The sample prepared on 100nm TiO2 buffer layer appears nanorods structure, and exhibits remarkable solar energy modulation ability as high as 5.82% in full spectrum and 23% in near infrared spectrum. Cross-sectional SEM image of the thin films samples indicate that MgF2 buffer layer has clear interface with VO2 layer. But there are serious interdiffusion phenomenons between Al2O3, TiO2 buffer layer with VO2 layer.

  18. Photovoltaic devices comprising zinc stannate buffer layer and method for making

    DOEpatents

    Wu, Xuanzhi; Sheldon, Peter; Coutts, Timothy J.

    2001-01-01

    A photovoltaic device has a buffer layer zinc stannate Zn.sub.2 SnO.sub.4 disposed between the semiconductor junction structure and the transparent conducting oxide (TCO) layer to prevent formation of localized junctions with the TCO through a thin window semiconductor layer, to prevent shunting through etched grain boundaries of semiconductors, and to relieve stresses and improve adhesion between these layers.

  19. The roles of buffer layer thickness on the properties of the ZnO epitaxial films

    NASA Astrophysics Data System (ADS)

    Tang, Kun; Huang, Shimin; Gu, Shulin; Zhu, Shunming; Ye, Jiandong; Xu, Zhonghua; Zheng, Youdou

    2016-12-01

    In this article, the authors have investigated the optimization of the buffer thickness for obtaining high-quality ZnO epi-films on sapphire substrates. The growth mechanism of the buffers with different thickness has been clearly revealed, including the initial nucleation and vertical growth, the subsequent lateral growth with small grain coalescence, and the final vertical growth along the existing larger grains. Overall, the quality of the buffer improves with increasing thickness except the deformed surface morphology. However, by a full-scale evaluation of the properties for the epi-layers, the quality of the epi-film is briefly determined by the surface morphology of the buffer, rather than the structural, optical, or electrical properties of it. The best quality epi-layer has been grown on the buffer with a smooth surface and well-coalescent grains. Meanwhile, due to the huge lattice mismatch between sapphire and ZnO, dislocations are inevitably formed during the growth of buffers. More importantly, as the film grows thicker, the dislocations may attracting other smaller dislocations and defects to reduce the total line energy and thus result in the formation of V-shape defects, which are connected with the bottom of the threading dislocations in the buffers. The V-defects appear as deep and large hexagonal pits from top view and they may act as electron traps which would affect the free carrier concentration of the epi-layers.

  20. YSZ buffer layers and YBCO superconducting tapes with enhanced biaxial alignment and properties

    NASA Astrophysics Data System (ADS)

    Savvides, N.; Gnanarajan, S.

    2003-05-01

    Commercial applications of YBa 2Cu 3O 7 (YBCO) superconducting cables require viable and scalable manufacturing processes. We have investigated the evolution of the biaxial alignment of yttria-stabilized zirconia (YSZ) buffer layers with increasing film thickness (50-900 nm) and report on a method of fabricating highly aligned YBCO tapes using a thin epitaxial YSZ buffer layer as template. The method employs magnetron and ion beam assisted deposition (IBAD) techniques followed by epitaxial growth to produce the buffer architectures IBAD-YSZ and epi-YSZ/IBAD-YSZ onto optically polished hastelloy metal substrates. Subsequent in situ deposition of YBCO films is used to determine the biaxial alignment at the surface of the buffer architecture, and to show that 100-200 nm thick epi-YSZ layers suffice to yield YBCO tapes that have enhanced biaxial alignment (Δ φ=9-10°) and high critical current densities: J c(77 K)=(1-2)×10 6 A cm -2 and J c(5 K,1 T)=8×10 6 A cm -2. Atomic force microscopy of the surface microstructure of the YSZ buffer layers and YBCO films reveals some grain coarsening in the epi-YSZ layers compared to the IBAD-YSZ layers while the YBCO tapes show significant outgrowths (∼200 nm) and large grains (800-1200 nm) that are similar to high- Jc YBCO films grown on single crystal MgO(1 0 0) substrates.

  1. Dependence of Magnetic Properties of Co/Pt Multilayers on Deposition Temperature of Pt Buffer Layers

    NASA Astrophysics Data System (ADS)

    Shiomi, Shigeru; Nishimura, Tomotaka; Kobayashi, Tadashi; Masuda, Morio

    1993-04-01

    A 15-nm-thick Pt buffer layer was deposited on a glass slide at temperature Ts(Ptbuf) ranging from 30 to 300°C by e-gun evaporation. Following the cooling in vacuum to ambient temperature, Co and Pt layers have been alternately deposited on it. Very large perpendicular anisotropy and coercivity have been obtained at Ts(Ptbuf) higher than 200°C. The (111) preferred orientation of the Co/Pt multilayer as well as the Pt buffer layer became more pronounced with elevating Ts(Ptbuf), to which the enhancement of perpendicular anisotropy with elevating Ts(Ptbuf) might be ascribable.

  2. Perpendicular magnetization of CoFeB on top of an amorphous buffer layer

    NASA Astrophysics Data System (ADS)

    Kim, Dongseok; Jung, K. Y.; Joo, Sungjung; Jang, Youngjae; Hong, Jinki; Lee, B. C.; You, C. Y.; Cho, J. H.; Kim, M. Y.; Rhie, K.

    2015-01-01

    Perpendicular magnetic anisotropy was observed in sputtered FeZr/CoFeB/MgO multilayers. A thin paramagnetic amorphous FeZr layer was used as a buffer layer and perpendicular anisotropy was obtained by annealing the samples without an external magnetic field. The critical CoFeB thickness for perpendicular anisotropy was 1.8 nm; the anisotropy changes from out-of-plane to in-plane as the CoFeB thickness increases beyond this point. Perpendicular anisotropy was also enhanced when a Ta layer was capped on top of the MgO layer. The amorphous buffer provided better perpendicular anisotropy than previously reported Ta buffer, and it may be applied to perpendicular magnetization MRAM devices where good uniformity of tunnel junctions is required.

  3. Method of Making Self-Aligned GAAS/ALGAAS FET’s.

    DTIC Science & Technology

    having a predetermined crystalline structure is obtained having a heavily doped top GaAs layer, having a heavily doped AlGaAs layer under the top layer...recess is wider at the base of the recess than at the top of the recess because of the predetermined crystalline structure and the orientation-dependent

  4. Improving performance of inverted organic solar cells using ZTO nanoparticles as cathode buffer layer

    NASA Astrophysics Data System (ADS)

    Tsai, Meng-Yen; Cheng, Wen-Hui; Jeng, Jiann-Shing; Chen, Jen-Sue

    2016-06-01

    In this study, a low-temperature solution-processed zinc tin oxide (ZTO) films are successfully utilized as the cathode buffer layer in the inverted organic P3HT:PCBM bulk heterojunction solar cells. ZTO film cathode buffer layer with an appropriate Sn-doping concentration outperforms the zinc oxide (ZnO) film with an improved power conversion efficiency (1.96% (ZTO film) vs. 1.56% (ZnO film)). Furthermore, ZTO nanoparticles (NPs) are also synthesized via low-temperature solution route and the device with ZTO NPs buffer layer exhibits a significant improvement in device performance to reach a PCE of 2.60%. The crystallinity of the cathode buffer layer plays an influential factor in the performance. From impedance spectroscopy analysis, a correlation between short circuit current (Jsc), carrier life time (τavg) and, thus, PCE is observed. The interplay between composition and crystallinity of the cathode buffer layers is discussed to find their influences on the solar cell performance.

  5. The effect of the carbon nanotube buffer layer on the performance of a Li metal battery.

    PubMed

    Zhang, Ding; Zhou, Yi; Liu, Changhong; Fan, Shoushan

    2016-06-07

    Lithium (Li) metal is one of the most promising candidates as an anode for the next-generation energy storage systems because of its high specific capacity and lowest negative electrochemical potential. But the growth of Li dendrites limits the application of the Li metal battery. In this work, a type of modified Li metal battery with a carbon nanotube (CNT) buffer layer inserted between the separator and the Li metal electrode was reported. The electrochemical results show that the modified batteries have a much better rate capability and cycling performance than the conventional Li metal batteries. The mechanism study by electrochemical impedance spectroscopy reveals that the modified battery has a smaller charge transfer resistance and larger Li ion diffusion coefficient during the deposition process on the Li electrode than the conventional Li metal batteries. Symmetric battery tests show that the interfacial behavior of the Li metal electrode with the buffer layer is more stable than the naked Li metal electrode. The morphological characterization of the CNT buffer layer and Li metal lamina reveals that the CNT buffer layer has restrained the growth of Li dendrites. The CNT buffer layer has great potential to solve the safety problem of the Li metal battery.

  6. Amorphous carbon buffer layers for separating free gallium nitride films

    NASA Astrophysics Data System (ADS)

    Altakhov, A. S.; Gorbunov, R. I.; Kasharina, L. A.; Latyshev, F. E.; Tarala, V. A.; Shreter, Yu. G.

    2016-11-01

    The possibility of using amorphous diamond-like carbon (DLC) films for self-separation of gallium nitride (GaN) layers grown by hydride vapor-phase epitaxy has been analyzed. DLC films have been synthesized by plasma-enhanced chemical vapor deposition under low pressure on sapphire (Al2O3) substrates with a (0001) crystallographic orientation. The samples have been studied by the methods of Raman scattering and X-ray diffraction analysis. It is shown that thin DLC films affect only slightly the processes of nucleation and growth of gallium nitride films. Notably, the strength of the "GaN film-Al2O3" substrate interface decreases, which facilitates separation of the GaN layers.

  7. Defect Reduction in Epitaxial Growth Using Superlattice Buffer Layers

    DTIC Science & Technology

    1988-07-01

    Katsuyama, Y. J. Yang and S. M. Bedair, Electron Dev. Lett., vol. 8, p. 240, 1987. 0 -15 -" Journal of (ryOstal (io iih 77 (108(,) ,xQ 9i4 S9 North-I...layer facilitat the csea of Gaosu 3 (5% in H2) + 500 sccm of H , and ed cross-sectional thickness measurements. trimethylgallium (TMG) + 500 sccm of H

  8. Evaluation of methods for application of epitaxial layers of superconductor and buffer layers

    SciTech Connect

    1997-06-01

    The recent achievements in a number of laboratories of critical currents in excess of 1.0x10{sup 6} amp/cm{sup 2} at 77K in YBCO deposited over suitably textured buffer/substrate composites have stimulated interest in the potential applications of coated conductors at high temperatures and high magnetic fields. As of today, two different approaches for obtaining the textured substrates have been identified. These are: Los Alamos National Laboratory`s (LANL) ion-beam assisted deposition called IBAD, to obtain a highly textured yttria-stabilized zirconia (YSZ) buffer on nickel alloy strips, and Oak Ridge National Laboratory`s (ORNL) rolling assisted, bi-axial texturized substrate option called RABiTS. Similarly, based on the published literature, the available options to form High Temperature Superconductor (HTS) films on metallic, semi-metallic or ceramic substrates can be divided into: physical methods, and non-physical or chemical methods. Under these two major groups, the schemes being proposed consist of: - Sputtering - Electron-Beam Evaporation - Flash Evaporation - Molecular Beam Epitaxy - Laser Ablation - Electrophoresis - Chemical Vapor Deposition (Including Metal-Organic Chemical Vapor Deposition) - Sol-Gel - Metal-Organic Decomposition - Electrodeposition, and - Aerosol/Spray Pyrolysis. In general, a spool- to-spool or reel-to-reel type of continuous manufacturing scheme developed out of any of the above techniques, would consist of: - Preparation of Substrate Material - Preparation and Application of the Buffer Layer(s) - Preparation and Application of the HTS Material and Required Post-Annealing, and - Preparation and Application of the External Protective Layer. These operations would be affected by various process parameters which can be classified into: Chemistry and Material Related Parameters; and Engineering and Environmental Based Parameters. Thus, one can see that for successful development of the coated conductors manufacturing process, an

  9. Hafnium nitride buffer layers for growth of GaN on silicon

    DOEpatents

    Armitage, Robert D.; Weber, Eicke R.

    2005-08-16

    Gallium nitride is grown by plasma-assisted molecular-beam epitaxy on (111) and (001) silicon substrates using hafnium nitride buffer layers. Wurtzite GaN epitaxial layers are obtained on both the (111) and (001) HfN/Si surfaces, with crack-free thickness up to 1.2 {character pullout}m. However, growth on the (001) surface results in nearly stress-free films, suggesting that much thicker crack-free layers could be obtained.

  10. Buffer layer between a planar optical concentrator and a solar cell

    SciTech Connect

    Solano, Manuel E.; Barber, Greg D.; Lakhtakia, Akhlesh; Faryad, Muhammad; Monk, Peter B.; Mallouk, Thomas E.

    2015-09-15

    The effect of inserting a buffer layer between a periodically multilayered isotropic dielectric (PMLID) material acting as a planar optical concentrator and a photovoltaic solar cell was theoretically investigated. The substitution of the photovoltaic material by a cheaper dielectric material in a large area of the structure could reduce the fabrication costs without significantly reducing the efficiency of the solar cell. Both crystalline silicon (c-Si) and gallium arsenide (GaAs) were considered as the photovoltaic material. We found that the buffer layer can act as an antireflection coating at the interface of the PMLID and the photovoltaic materials, and the structure increases the spectrally averaged electron-hole pair density by 36% for c-Si and 38% for GaAs compared to the structure without buffer layer. Numerical evidence indicates that the optimal structure is robust with respect to small changes in the grating profile.

  11. Effect of buffer layer and external stress on magnetic properties of flexible FeGa films

    NASA Astrophysics Data System (ADS)

    Zhang, Xiaoshan; Zhan, Qingfeng; Dai, Guohong; Liu, Yiwei; Zuo, Zhenghu; Yang, Huali; Chen, Bin; Li, Run-Wei

    2013-05-01

    We systematically investigated the effect of a Ta buffer layer and external stress on the magnetic properties of magnetostrictive Fe81Ga19 films deposited on flexible polyethylene terephthalate (PET) substrates. The Ta buffer layers could effectively smoothen the rough surface of PET. As a result, the FeGa films grown on Ta buffer layers exhibit a weaker uniaxial magnetic anisotropy and lower coercivity, as compared to those films directly grown on PET substrates. By inward and outward bending the FeGa/Ta/PET samples, external in-plane compressive and tensile stresses were applied to the magnetic films. Due to the inverse magnetostrictive effect of FeGa, both the coercivity and squareness of hysteresis loops for FeGa/Ta films could be well tuned under various strains.

  12. Growth and micro structural studies on Yittria Stabilized Zirconia (YSZ) and Strontium Titanate (STO) buffer layers

    NASA Technical Reports Server (NTRS)

    Srinivas, S.; Pinto, R.; Pai, S. P.; Dsousa, D. P.; Apte, P. R.; Kumar, D.; Purandare, S. C.; Bhatnagar, A. K.

    1995-01-01

    Microstructure of Yittria Stabilized Zirconia (YSZ) and Strontium Titanate (STO) of radio frequency magnetron sputtered buffer layers was studied at various sputtering conditions on Si (100), Sapphire and LaAlO3 (100) substrates. The effect of substrate temperatures up to 800 C and sputtering gas pressures in the range of 50 mTorr. of growth conditions was studied. The buffer layers of YSZ and STO showed a strong tendency for columnar growth was observed above 15 mTorr sputtering gas pressure and at high substrate temperatures. Post annealing of these films in oxygen atmosphere reduced the oxygen deficiency and strain generated during growth of the films. Strong c-axis oriented superconducting YBa2Cu3O7-x (YBCO) thin films were obtained on these buffer layers using pulsed laser ablation technique. YBCO films deposited on multilayers of YSZ and STO were shown to have better superconducting properties.

  13. Accelerating the L10 ordering transition of FePt(001) nanograins using composite buffer layers

    NASA Astrophysics Data System (ADS)

    Li, Guoqing; Zheng, Yuanping; Hayashi, Kenichi; Takanashi, Koki

    2011-07-01

    This paper reports fabrication of 2-nm-thick L10 FePt films at a low substrate temperature of 400 °C using composite MgO and FeAl buffer layers on (001) MgO substrates. The FeAl buffer layer is crucial in promoting the ordered L10 growth of (001) FePt by allowing additional heat uptake. The MgO buffer layer prevents interlayer diffusion of FeAl into the FePt films and induces (001) texture growth. The deposited FePt films consist of isolated nanograins about 13 nm in size. These films have (001) texture and perpendicular magnetic anisotropy with a coercivity of up to 19 kOe. They have potential applications in perpendicular magnetic recording.

  14. Coercivity enhancement of Nd-Fe-B thin film magnets by Dy buffer and capping layers

    NASA Astrophysics Data System (ADS)

    You, C. Y.; Wang, J. W.; Lu, Z. X.

    2012-04-01

    The Dy layer was inserted into the structure of SiO2/Ti/Nd-Fe-B/Ti as the buffer or capping layer of the Nd-Fe-B layer. The insertions of Dy layers had no significant influence on the film texture with the easy axis mainly perpendicular to the film plane. The film without Dy layer gave the out-of-plane coercivity of 533 kA/m, maximum magnetic energy product (BH)max of 245 kJ/m3. With a Dy buffer layer, the out-of-plane coercivity and (BH)max were increased to 1074 kA/m, 291 kJ/m3 respectively. The film with Dy capping layer had a coercivity of 1035 kA/m and (BH)max of 286 kJ/m3. Microstructure observations showed that the Nd-rich phases were evolved into grain boundaries from triple junctions by a Dy buffer layer deposition, resulting in a well magnetic decoupling of Nd2Fe14B neighboring grains. Through capping a Dy layer, the environment of grain boundaries had been improved and some Dy diffused into Nd2Fe14B phases, which contributed to the enhancement of magnetic performance.

  15. The role of buffer layers and double windows layers in a solar cell CZTS performances

    NASA Astrophysics Data System (ADS)

    Mebarkia, C.; Dib, D.; Zerfaoui, H.; Belghit, R.

    2016-07-01

    In the overall context of the diversification of the use of natural resources, the use of renewable energy including solar photovoltaic has become increasingly indispensable. As such, the development of a new generation of photovoltaic cells based on CuZnSnS4 (CZTS) looks promising. Cu2ZnSnS4 (CZTS) is a new film absorber, with good physical properties (band gap energy 1.4-1.6 eV with a large absorption coefficient over 104 cm-1). Indeed, the performance of these cells exceeded 30% in recent years. In the present paper, our work based on modeling and numerical simulation, we used SCAPS to study the performance of solar cells based on Cu2ZnSnS4 (CZTS) and thus evaluate the electrical efficiency η for typical structures of n-ZnO:Al / i-ZnO / n-CdS / p-CZTS and n-ITO / n-ZnO:Al / n-CdS /p-CZTS. Furthermore, the influence of the change of CdS by ZnSeand In2S3buffer layer was treated in this paper.

  16. Indium Tin Oxide Electrode with an Ultrathin Al Buffer Layer for Flexible Organic Light Emitting Diode

    NASA Astrophysics Data System (ADS)

    Sim, Boyeon; Hwang, Hyeonseok; Ryu, Seungyoon; Baik, Hongkoo; Lee, Myeongkyu

    2010-06-01

    This paper reports that the mechanical and electrical stability of indium tin oxide (ITO) film deposited on flexible plastic substrate can be much enhanced with a thin Al buffer layer while maintaining a visible transmittance over 75%. The improved stability is attributed to the effective elastic mismatch between the film and the substrate reduced by a ductile interlayer. A polymer light emitting diode fabricated using an ITO/Al anode exhibited a luminance of 13,000 cd/m2 with a current efficiency of 16 cd/A. Bending-induced degradation of the device performance was also alleviated when a mechanical buffer layer was inserted.

  17. CdS/CdTe thin-film solar cell with a zinc stannate buffer layer

    NASA Astrophysics Data System (ADS)

    Wu, X.; Sheldon, P.; Mahathongdy, Y.; Ribelin, R.; Mason, A.; Moutinho, H. R.; Coutts, T. J.

    1999-03-01

    This paper describes an improved CdS/CdTe polycrystalline thin-film solar-cell device structure that integrates a zinc stannate (Zn2SnO4 or ZTO) buffer layer between the transparent conductive oxide (TCO) layer and the CdS window layer. Zinc stannate films have a high bandgap, high transmittance, low absorptance, and low surface roughness. In addition, these films are chemically stable and exhibit higher resistivities that are roughly matched to that of the CdS window layer in the device structure. Preliminary device results have demonstrated that by integrating a ZTO buffer layer in both SnO2-based and Cd2SnO4 (CTO)-based CdS/CdTe devices, performance and reproducibility can be significantly enhanced.

  18. Strain compensation in a semiconducting device structure using an intentionally mismatched uniform buffer layer

    NASA Astrophysics Data System (ADS)

    Kujofsa, Tedi; Ayers, John E.

    2016-12-01

    The extent of strain relaxation in semiconducting device heterostructures has important implications in the design of high electron mobility transistors, light-emitting diodes, and laser diodes, in which the residual strain affects the device characteristics. In this work, we develop the theoretical framework for understanding strain compensation in a semiconductor device layer using a uniform buffer layer which can be intentionally mismatched to the material above. Specifically, we determined the critical condition for complete strain compensation in the device layer by intentionally introducing a compositional mismatch at the device-buffer interface. We present minimum energy calculations and show that for a given device layer with fixed mismatch and layer thickness, the buffer layer may be designed with the appropriate combination of thickness and mismatch such that the device layer will have zero residual strain in equilibrium. Such a structure can be referred to as a completely strain-compensated design. In the more general case, there may be partial strain compensation, and we give a simple physics-based Gaussian-type function describing the residual strain in the device layer. We have applied this general framework to In x Ga1-x As/GaAs (001) heterostructures for the purpose of illustration, but the work is applicable to any diamond or zinc blende (001) heteroepitaxial material system.

  19. Exciton-blocking phosphonic acid-treated anode buffer layers for organic photovoltaics

    NASA Astrophysics Data System (ADS)

    Zimmerman, Jeramy D.; Song, Byeongseop; Griffith, Olga; Forrest, Stephen R.

    2013-12-01

    We demonstrate significant improvements in power conversion efficiency of bilayer organic photovoltaics by replacing the exciton-quenching MoO3 anode buffer layer with an exciton-blocking benzylphosphonic acid (BPA)-treated MoO3 or NiO layer. We show that the phosphonic acid treatment creates buffers that block up to 70% of excitons without sacrificing the hole extraction efficiency. Compared to untreated MoO3 anode buffers, BPA-treated NiO buffers exhibit a ˜ 25% increase in the near-infrared spectral response in diphenylanilo functionalized squaraine (DPSQ)/C60-based bilayer devices, increasing the power conversion efficiency under 1 sun AM1.5G simulated solar illumination from 4.8 ± 0.2% to 5.4 ± 0.3%. The efficiency can be further increased to 5.9 ± 0.3% by incorporating a highly conductive exciton blocking bathophenanthroline (BPhen):C60 cathode buffer. We find similar increases in efficiency in two other small-molecule photovoltaic systems, indicating the generality of the phosphonic acid-treated buffer approach to enhance exciton blocking.

  20. Methods of producing free-standing semiconductors using sacrificial buffer layers and recyclable substrates

    DOEpatents

    Ptak, Aaron Joseph; Lin, Yong; Norman, Andrew; Alberi, Kirstin

    2015-05-26

    A method of producing semiconductor materials and devices that incorporate the semiconductor materials are provided. In particular, a method is provided of producing a semiconductor material, such as a III-V semiconductor, on a spinel substrate using a sacrificial buffer layer, and devices such as photovoltaic cells that incorporate the semiconductor materials. The sacrificial buffer material and semiconductor materials may be deposited using lattice-matching epitaxy or coincident site lattice-matching epitaxy, resulting in a close degree of lattice matching between the substrate material and deposited material for a wide variety of material compositions. The sacrificial buffer layer may be dissolved using an epitaxial liftoff technique in order to separate the semiconductor device from the spinel substrate, and the spinel substrate may be reused in the subsequent fabrication of other semiconductor devices. The low-defect density semiconductor materials produced using this method result in the enhanced performance of the semiconductor devices that incorporate the semiconductor materials.

  1. Benzocyclobutene (BCB) Polymer as Amphibious Buffer Layer for Graphene Field-Effect Transistor.

    PubMed

    Wu, Yun; Zou, Jianjun; Huo, Shuai; Lu, Haiyan; Kong, Yuecan; Chen, Tangshen; Wu, Wei; Xu, Jingxia

    2015-08-01

    Owing to the scattering and trapping effects, the interfaces of dielectric/graphene or substrate/graphene can tailor the performance of field-effect transistor (FET). In this letter, the polymer of benzocyclobutene (BCB) was used as an amphibious buffer layer and located at between the layers of substrate and graphene and between the layers of dielectric and graphene. Interestingly, with the help of nonpolar and hydrophobic BCB buffer layer, the large-scale top-gated, chemical vapor deposited (CVD) graphene transistors was prepared on Si/SiO2 substrate, its cutoff frequency (fT) and the maximum cutoff frequency (fmax) of the graphene field-effect transistor (GFET) can be reached at 12 GHz and 11 GHz, respectively.

  2. Effect of buffer layer on thermochromic performances of VO2 films fabricated by magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Zhu, Benqin; Tao, Haizheng; Zhao, Xiujian

    2016-03-01

    As a well-developed industrial fabricating method, magnetron sputtering technique has its distinct advantages for the large-scale production. In order to investigate the effect of buffer layer on the formation and thermochromic performances of VO2 films, using RF magnetron sputtering method, we fabricated three kinds of buffer layers SiO2, TiO2 and SnO2 on soda lime float-glass. Then according to the reactive DC magnetron sputtering method, VO2 films were deposited. Due to the restriction of heat treatment temperature when using soda lime float-glass as substrates, dense rutile phase TiO2 cannot be formed, leading to the formation of vanadium oxide compounds containing Na ions. When using SnO2 as buffer layer, we found that relatively high pure VO2 can be deposited more easily. In addition, compared with the effect of SiO2 buffer layer, we observed an enhanced visible transparency, a decreased infrared emissivity, which should be mainly originated from the modified morphology and/or the hetero-structured VO2/SnO2 interface.

  3. Sol-gel deposition of buffer layers on biaxially textured metal substances

    DOEpatents

    Shoup, Shara S.; Paranthamam, Mariappan; Beach, David B.; Kroeger, Donald M.; Goyal, Amit

    2000-01-01

    A method is disclosed for forming a biaxially textured buffer layer on a biaxially oriented metal substrate by using a sol-gel coating technique followed by pyrolyzing/annealing in a reducing atmosphere. This method is advantageous for providing substrates for depositing electronically active materials thereon.

  4. Growth and micro structural studies on Yittria Stabilized Zirconia (YSZ) and Strontium Titanate (STO) buffer layers

    SciTech Connect

    Srinivas, S.; Bhatnagar, A.K.; Pinto, R.

    1994-12-31

    Microstructure of Yittria Stabilized Zirconia (YSZ) and Strontium Titanate (STO) of radio frequency magnetron sputtered buffer layers was studied at various sputtering conditions on Si<100>, Sapphire and LaAlO{sub 3} <100> substrates. The effect of substrate temperatures upto 800 C and sputtering gas pressures in the range of 50 mTorr. of growth conditions was studied. The buffer layers of YSZ and STO showed a strong tendency for columnar structure with variation growth conditions. The buffer layers of YSZ and STO showed orientation. The tendency for columnar growth was observed above 15 mTorr sputtering gas pressure and at high substrate temperatures. Post annealing of these films in oxygen atmosphere reduced the oxygen deficiency and strain generated during growth of the films. Strong c-axis oriented superconducting YBa{sub 2}Cu{sub 9}O{sub 7-x} (YBCO) thin films were obtained on these buffer layers using pulsed laser ablation technique. YBCO films deposited on multilayers of YSZ and STO were shown to have better superconducting properties.

  5. Sol-gel deposition of buffer layers on biaxially textured metal substances

    SciTech Connect

    Shoup, S.S.; Paranthamam, M.; Beach, D.B.; Kroeger, D.M.; Goyal, A.

    2000-06-20

    A method is disclosed for forming a biaxially textured buffer layer on a biaxially oriented metal substrate by using a sol-gel coating technique followed by pyrolyzing/annealing in a reducing atmosphere. This method is advantageous for providing substrates for depositing electronically active materials thereon.

  6. Characterization of Cu buffer layers for growth of L1{sub 0}-FeNi thin films

    SciTech Connect

    Mizuguchi, M.; Sekiya, S.; Takanashi, K.

    2010-05-15

    A Cu(001) layer was fabricated on a Au(001) layer to investigate the use of Cu as a buffer layer for growing L1{sub 0}-FeNi thin films. The epitaxial growth of a Cu buffer layer was observed using reflection high-energy electron diffraction. The flatness of the layer improved drastically with an increase in the substrate temperature although the layer was an alloy (AuCu{sub 3}). An FeNi thin film was epitaxially grown on the AuCu{sub 3} buffer layer by alternate monatomic layer deposition and the formation of an L1{sub 0}-FeNi ordered alloy was expected. The AuCu{sub 3} buffer layer is thus a promising candidate material for the growth of L1{sub 0}-FeNi thin films.

  7. Final Report: Rational Design of Wide Band Gap Buffer Layers for High-Efficiency Thin-Film Photovoltaics

    SciTech Connect

    Lordi, Vincenzo

    2016-09-30

    The main objective of this project is to enable rational design of wide band gap buffer layer materials for CIGS thin-film PV by building understanding of the correlation of atomic-scale defects in the buffer layer and at the buffer/absorber interface with device electrical properties. Optimized wide band gap buffers are needed to reduce efficiency loss from parasitic absorption in the buffer. The approach uses first-principles materials simulations coupled with nanoscale analytical electron microscopy as well as device electrical characterization. Materials and devices are produced by an industrial partner in a manufacturing line to maximize relevance, with the goal of enabling R&D of new buffer layer compositions or deposition processes to push device efficiencies above 21%. Cadmium sulfide (CdS) is the reference material for analysis, as the prototypical high-performing buffer material.

  8. Layer-based buffer aware rate adaptation design for SHVC video streaming

    NASA Astrophysics Data System (ADS)

    Gudumasu, Srinivas; Hamza, Ahmed; Asbun, Eduardo; He, Yong; Ye, Yan

    2016-09-01

    This paper proposes a layer based buffer aware rate adaptation design which is able to avoid abrupt video quality fluctuation, reduce re-buffering latency and improve bandwidth utilization when compared to a conventional simulcast based adaptive streaming system. The proposed adaptation design schedules DASH segment requests based on the estimated bandwidth, dependencies among video layers and layer buffer fullness. Scalable HEVC video coding is the latest state-of-art video coding technique that can alleviate various issues caused by simulcast based adaptive video streaming. With scalable coded video streams, the video is encoded once into a number of layers representing different qualities and/or resolutions: a base layer (BL) and one or more enhancement layers (EL), each incrementally enhancing the quality of the lower layers. Such layer based coding structure allows fine granularity rate adaptation for the video streaming applications. Two video streaming use cases are presented in this paper. The first use case is to stream HD SHVC video over a wireless network where available bandwidth varies, and the performance comparison between proposed layer-based streaming approach and conventional simulcast streaming approach is provided. The second use case is to stream 4K/UHD SHVC video over a hybrid access network that consists of a 5G millimeter wave high-speed wireless link and a conventional wired or WiFi network. The simulation results verify that the proposed layer based rate adaptation approach is able to utilize the bandwidth more efficiently. As a result, a more consistent viewing experience with higher quality video content and minimal video quality fluctuations can be presented to the user.

  9. Epitaxial growth of cadmium telluride films on silicon with a buffer silicon carbide layer

    NASA Astrophysics Data System (ADS)

    Antipov, V. V.; Kukushkin, S. A.; Osipov, A. V.

    2017-02-01

    An epitaxial 1-3-μm-thick cadmium telluride film has been grown on silicon with a buffer silicon carbide layer using the method of open thermal evaporation and condensation in vacuum for the first time. The optimum substrate temperature was 500°C at an evaporator temperature of 580°C, and the growth time was 4 s. In order to provide more qualitative growth of cadmium telluride, a high-quality 100-nm-thick buffer silicon carbide layer was previously synthesized on the silicon surface using the method of topochemical substitution of atoms. The ellipsometric, Raman, X-ray diffraction, and electron-diffraction analyses showed a high structural perfection of the CdTe layer in the absence of a polycrystalline phase.

  10. Epitaxial MOD-YSZ buffer layers on IBAD-YSZ substrates

    NASA Astrophysics Data System (ADS)

    Jarzina, H.; Sievers, S.; Jooss, Ch; Freyhardt, H. C.; Lobinger, P.; Roesky, H. W.

    2005-03-01

    There are a number of reports on the epitaxial growth of MOD buffer layers for coated conductors. However, the quality of superconducting films deposited on top of these layers is often poor. We demonstrate that Y Ba2Cu3O7 (YBCO) layers with a high critical current density of 20 MA cm-2 (8 K) can be deposited on MOD-YSZ (ZrO2:10 mol% Y2O3) which has been grown epitaxially on YSZ(001) single crystals. Furthermore, high jc YBCO films are obtained on a MOD-YSZ buffer deposited on an IBAD (ion-beam-assisted-deposition)-YSZ substrate. In this case, critical current densities of 11 MA cm-2 (8 K) are observed. Finally, multilayers of MOD-YSZ on IBAD-YSZ substrates are prepared, where the development of texture with increasing film thickness is discussed as well as its possible technological impact.

  11. Improvement of luminescence properties of GaN buffer layer for fast nitride scintillator structures

    NASA Astrophysics Data System (ADS)

    Hubáček, T.; Hospodková, A.; Oswald, J.; Kuldová, K.; Pangrác, J.

    2017-04-01

    We have optimized technology of GaN buffer layer growth with respect to the application in fast scintillation structures. The deep defect luminescence so called yellow band (YB) with decay time up to tens of microseconds is undesired for these applications and should be suppressed or at least the ratio of intensities of excitonic to YB maximum has to be considerably increased. The required photoluminescence properties were achieved by optimization of growth parameters of nucleation and coalescence layer on sapphire substrate. We have shown that decrease of NH3 flow, decrease of coalescence temperature, increase of nucleation time and nucleation pressure lead to improvement of the structure and luminescence properties of the buffer layer. Results indicate a significant increased ratio of excitonic/YB luminescence intensity.

  12. From front contact to back contact in cadmium telluride/cadmium sulfide solar cells: Buffer layer and interfacial layer

    NASA Astrophysics Data System (ADS)

    Roussillon, Yann

    Cadmium telluride (CdTe) polycrystalline thin film solar cells, with their near optimum direct band-gap of 1.4 eV matching almost perfectly the sun radiation spectrum, are a strong contender as a less expensive alternative, among photovoltaic materials, than the more commonly used silicon-based cells. Polycrystalline solar cells are usually deposited over large areas. Such devices often exhibit strong fluctuations (nonuniformities) in electronic properties, which originate from deposition and post-deposition processes, and are detrimental to the device performance. Therefore their effects need to be constrained. A new approach in this work was, when a CdS/CdTe solar cell is exposed to light and immersed in a proper electrolyte, fluctuations in surface potential can drive electrochemical reactions which result in a nonuniform interfacial layer that could balance the original nonuniformity. This approach improved the device efficiency for CdS/CdTe photovoltaic devices from 1--3% to 11--12%. Cadmium sulfide (CdS), used as a window layer and heterojunction partner to CdTe, is electrically inactive and absorb light energies above its band-gap of 2.4 eV. Therefore, to maximize the device efficiency, a thin US layer needs to be used. However, more defects, such as pinholes, are likely to be present in the film, leading to shunts. A resistive transparent layer, called buffer layer, is therefore deposited before CdS. A key observation was that the open-circuit voltage (Voc) for cells made using a buffer layer was high, around 800 mV, similar to cells without buffer layer after Cu doping. The standard p-n junction theory cannot explain this phenomena, therefore an alternative junction mechanism, similar to metal-insulator-semiconductor devices, was developed. Furthermore, alternative Cu-free back-contacts were used in conjunction with a buffer layer. The Voc of the devices was found to be dependent of the back contact used. This change occurs as the back-contact junction

  13. Development of buffer layers on 30 mm wide textured metal substrates for REBCO coated conductors

    NASA Astrophysics Data System (ADS)

    Yamaguchi, T.; Ota, H.; Ohki, K.; Konishi, M.; Ohmatsu, K.

    2010-11-01

    We have been studying REBa2Cu3Ox (RE: rare earth elements) coated conductors on clad-type substrates. We developed coated conductors on the 10 mm wide clad-type tape, and succeeded in obtaining the maximum critical current of 380 A/cm with the 2.0 μm thick GdBa2Cu3Ox superconducting film. At present, we are trying to widen the tape width from 10 mm to 30 mm in order to increase production throughput. We report our recent progress on scaling-up of the buffer layers and their properties. The buffer layers consisted of three layers; CeO2 as the seed layer, yttrium-stabilized zirconia (YSZ) as the diffusion barrier layer and CeO2 as the lattice matching layer. They were grown by the RF-sputtering method and the electron beam evaporation technique (EB). EB deposition has possibility of higher throughput compared with the RF-sputtering. The intensity ratio of (2 0 0) to (2 0 0) + (1 1 1) for the lattice matching layer showed as high as 98%. The uniform properties of 40 m long and 30 mm wide substrates were successfully produced by all sputtering method. Additionally, the tape travel speed of the seed layer can be increased from 7 m/h (RF-sputtering deposition) to 10 m/h (EB deposition) on short sample (0.3 m long).

  14. Solution-processed In2S3 buffer layer for chalcopyrite thin film solar cells

    NASA Astrophysics Data System (ADS)

    Wang, Lan; Lin, Xianzhong; Ennaoui, Ahmed; Wolf, Christian; Lux-Steiner, Martha Ch.; Klenk, Reiner

    2016-02-01

    We report a route to deposit In2S3 thin films from air-stable, low-cost molecular precursor inks for Cd-free buffer layers in chalcopyrite-based thin film solar cells. Different precursor compositions and processing conditions were studied to define a reproducible and robust process. By adjusting the ink properties, this method can be applied in different printing and coating techniques. Here we report on two techniques, namely spin-coating and inkjet printing. Active area efficiencies of 12.8% and 12.2% have been achieved for In2S3-buffered solar cells respectively, matching the performance of CdS-buffered cells prepared with the same batch of absorbers.

  15. Coincident site lattice-matched growth of semiconductors on substrates using compliant buffer layers

    DOEpatents

    Norman, Andrew

    2016-08-23

    A method of producing semiconductor materials and devices that incorporate the semiconductor materials are provided. In particular, a method is provided of producing a semiconductor material, such as a III-V semiconductor, on a silicon substrate using a compliant buffer layer, and devices such as photovoltaic cells that incorporate the semiconductor materials. The compliant buffer material and semiconductor materials may be deposited using coincident site lattice-matching epitaxy, resulting in a close degree of lattice matching between the substrate material and deposited material for a wide variety of material compositions. The coincident site lattice matching epitaxial process, as well as the use of a ductile buffer material, reduce the internal stresses and associated crystal defects within the deposited semiconductor materials fabricated using the disclosed method. As a result, the semiconductor devices provided herein possess enhanced performance characteristics due to a relatively low density of crystal defects.

  16. Pyroelectric and dielectric properties of ferroelectric films with interposed dielectric buffer layers

    NASA Astrophysics Data System (ADS)

    Espinal, Y.; Kesim, M. T.; Misirlioglu, I. B.; Trolier-McKinstry, S.; Mantese, J. V.; Alpay, S. P.

    2014-12-01

    The dielectric and pyroelectric properties of c-domain ferroelectric films with linear dielectric buffer layers were investigated theoretically. Computations were carried out for multilayers consisting of PbZr0.2Ti0.8O3 with Al2O3, SiO2, Si3N4, HfO2, and TiO2 buffers on metalized Si. It is shown that the dielectric and pyroelectric properties of such multilayers can be increased by the presence of the buffer compared to ferroelectric monolayers. Calculations for PbZr0.2Ti0.8O3 films with 1% Al2O3 interposed between electrodes on Si show that the dielectric and pyroelectric coefficients are 310 and 0.070 μC cm-2 °C-1, respectively. Both values are higher than the intrinsic response of PbZr0.2Ti0.8O3 monolayer on Si.

  17. Effects of buffer layers on the structural and electronic properties of InSb films

    SciTech Connect

    Weng, X.; Rudawski, N.G.; Wang, P.T.; Goldman, R.S.; Partin, D.L.; Heremans, J.

    2005-02-15

    We have investigated the effects of various buffer layers on the structural and electronic properties of n-doped InSb films. We find a significant decrease in room-temperature electron mobility of InSb films grown on low-misfit GaSb buffers, and a significant increase in room-temperature electron mobility of InSb films grown on high-misfit InAlSb or step-graded GaSb+InAlSb buffers, in comparison with those grown directly on GaAs. Plan-view transmission electron microscopy (TEM) indicates a significant increase in threading dislocation density for InSb films grown on the low-misfit buffers, and a significant decrease in threading dislocation density for InSb films grown on high-misfit or step-graded buffers, in comparison with those grown directly on GaAs. Cross-sectional TEM reveals the role of the film/buffer interfaces in the nucleation (filtering) of threading dislocations for the low-misfit (high-misfit and step-graded) buffers. A quantitative analysis of electron mobility and carrier-concentration dependence on threading dislocation density suggests that electron scattering from the lattice dilation associated with threading dislocations has a stronger effect on electron mobility than electron scattering from the depletion potential surrounding the dislocations. Furthermore, while lattice dilation is the predominant mobility-limiting factor in these n-doped InSb films, ionized impurity scattering associated with dopants also plays a role in limiting the electron mobility.

  18. Effects of buffer layers on the structural and electronic properties of InSb films

    NASA Astrophysics Data System (ADS)

    Weng, X.; Rudawski, N. G.; Wang, P. T.; Goldman, R. S.; Partin, D. L.; Heremans, J.

    2005-02-01

    We have investigated the effects of various buffer layers on the structural and electronic properties of n-doped InSb films. We find a significant decrease in room-temperature electron mobility of InSb films grown on low-misfit GaSb buffers, and a significant increase in room-temperature electron mobility of InSb films grown on high-misfit InAlSb or step-graded GaSb +InAlSb buffers, in comparison with those grown directly on GaAs. Plan-view transmission electron microscopy (TEM) indicates a significant increase in threading dislocation density for InSb films grown on the low-misfit buffers, and a significant decrease in threading dislocation density for InSb films grown on high-misfit or step-graded buffers, in comparison with those grown directly on GaAs. Cross-sectional TEM reveals the role of the film/buffer interfaces in the nucleation (filtering) of threading dislocations for the low-misfit (high-misfit and step-graded) buffers. A quantitative analysis of electron mobility and carrier-concentration dependence on threading dislocation density suggests that electron scattering from the lattice dilation associated with threading dislocations has a stronger effect on electron mobility than electron scattering from the depletion potential surrounding the dislocations. Furthermore, while lattice dilation is the predominant mobility-limiting factor in these n-doped InSb films, ionized impurity scattering associated with dopants also plays a role in limiting the electron mobility.

  19. Electron dynamics of the buffer layer and bilayer graphene on SiC

    SciTech Connect

    Shearer, Alex J.; Caplins, Benjamin W.; Suich, David E.; Harris, Charles B.; Johns, James E.; Hersam, Mark C.

    2014-06-09

    Angle- and time-resolved two-photon photoemission (TPPE) was used to investigate electronic states in the buffer layer of 4H-SiC(0001). An image potential state (IPS) series was observed on this strongly surface-bound buffer layer, and dispersion measurements indicated free-electron-like behavior for all states in this series. These results were compared with TPPE taken on bilayer graphene, which also show the existence of a free-electron-like IPS series. Lifetimes for the n = 2, and n = 3 states were obtained from time-resolved TPPE; slightly increased lifetimes were observed in the bilayer graphene sample for the n = 2 the n = 3 states. Despite the large band gap of graphene at the center of the Brillouin zone, the lifetime results demonstrate that the graphene layers do not behave as a simple tunneling barrier, suggesting that the buffer layer and graphene overlayers play a direct role in the decay of IPS electrons.

  20. Selective thermal terahertz emission from GaAs and AlGaAs

    SciTech Connect

    Požela, K. Širmulis, E.; Kašalynas, I.; Šilėnas, A.; Požela, J.; Jucienė, V.

    2014-09-01

    The selective thermally stimulated terahertz (THz) radiation emission from GaAs and AlGaAs alloys are experimentally observed at frequencies of coupled oscillations of free electron plasma and different branches of interface AlGaAs optical phonons. The effect of strong absorption of incident radiation with large oblique angle (26°) by heated GaAs and AlGaAs is revealed. The coherent THz radiation emission with the frequency of 7.6 THz from the heated high conductivity GaAs (n = 4 × 10{sup 18 }cm{sup −3}) layer is observed. The results are highly relevant to application in optoelectronic THz devices.

  1. Exploring Cd-Zn-O-S alloys for optimal buffer layers in thin-film photovoltaics

    NASA Astrophysics Data System (ADS)

    Varley, J.; He, X.; Mackie, N.; Rockett, A.; Lordi, V.

    2015-03-01

    The development of thin-film photovoltaics has largely focused on alternative absorber materials, while the choices for other layers in the solar cell stack have remained somewhat limited. In particular, cadmium sulfide (CdS) is widely used as the buffer layer in typical record devices utilizing absorbers like Cu(In,Ga)Se2 (CIGSe) or Cu2ZnSnS4 (CZTS) despite leading to a loss of solar photocurrent due to its band gap of 2.4 eV. While different buffers such as Zn(S,O,OH) are beginning to become competitive with CdS, the identification of additional wider-band gap alternatives with electrical properties comparable to or better than CdS is highly desirable. Here we use hybrid functional calculations to characterize CdxZn1-xOyS1-y candidate buffer layers in the quaternary phase space composed by Cd, Zn, O, and S. We focus on the band gaps and band offsets of the alloys to assess strategies for improving absorption losses from conventional CdS buffers while maintaining similar conduction band offsets known to facilitate good device performance. We also consider additional criteria such as lattice matching to identify regions in the composition space that may provide improved epitaxy to CIGSe and CZTS absorbers. Lastly, we incorporate our calculated alloy properties into simulations of typical CIGSe devices to identify the CdxZn1-xOyS1-y buffer compositions that lead to the best performance. This work performed under the auspices of the USDoE by LLNL under Contract DE-AC52-07NA27344 and funded by the DoE EERE through the SunShot BRIDGE program.

  2. Effect of magnetic structural processing on structure and texture of La2Zr2O7 buffer layers

    NASA Astrophysics Data System (ADS)

    Chibirova, F. Kh.; Kotina, G. V.; Bovina, E. A.; Tarasova, D. V.; Polisan, A. A.; Parkhomenko, Yu. N.

    2016-11-01

    Epitaxial CeO2 seed layer and La2Zr2O7 (LZO) buffer layers were deposited on biaxially-textured Ni-5 at.% W (NiW) tape substrate by liquid-phase polymer assisted nanoparticles deposition (PAND) method. LZO layers deposited by PAND have consistently shown tilting of the c-axis toward the direction of the sample’s surface normal. A new approach increasing the sharpening of the buffer texture by magnetic structural processing (MSP) of buffer layers was tested. The LZO layers, deposited on the seed and buffer layers after MSP, have dense and smooth surface structure, and more importantly, significantly improved out-of-plane texture, compared with the LZO layers that were deposited on a layer without MSP. Transmission electron microscopy study confirmed the c-axis tilting of CeO2 and LZO layers and revealed the absence of interfaces between LZO layers which have been grown on the layers after MSP. There are very small (2-4 nm) gated pores in the single-crystal structure of LZO layers that are not typical for structure of LZO layers obtained by liquid-phase methods. Thus the LZO buffer layers can serve as an effective metal-ion diffusion barrier.

  3. Ultrathin Polyaniline-based Buffer Layer for Highly Efficient Polymer Solar Cells with Wide Applicability

    NASA Astrophysics Data System (ADS)

    Zhao, Wenchao; Ye, Long; Zhang, Shaoqing; Fan, Bin; Sun, Mingliang; Hou, Jianhui

    2014-10-01

    Interfacial buffer layers often attribute the improved device performance in organic optoelectronic device. Herein, a water-soluble hydrochloric acid doped polyanilines (HAPAN) were utilized as p-type electrode buffer layer in highly efficient polymer solar cells (PSC) based on PBDTTT-EFT and several representative polymers. The PBDTTT-EFT-based conventional PSC featuring ultrathin HAPAN (1.3 nm) delivered high PCE approximately 9%, which is one of the highest values among conventional PSC devices. Moreover, ultrathin HAPAN also exhibited wide applicability in a variety of efficient photovoltaic polymers including PBDTTT-C-T, PTB7, PBDTBDD, PBTTDPP-T, PDPP3T and P3HT. The excellent performances were originated from the high transparency, small film roughness and suitable work function.

  4. Selective growth of Pb islands on graphene/SiC buffer layers

    SciTech Connect

    Liu, X. T.; Miao, Y. P.; Ma, D. Y.; Hu, T. W.; Ma, F. E-mail: kwxu@mail.xjtu.edu.cn; Chu, Paul K.; Xu, K. W. E-mail: kwxu@mail.xjtu.edu.cn

    2015-02-14

    Graphene is fabricated by thermal decomposition of silicon carbide (SiC) and Pb islands are deposited by Pb flux in molecular beam epitaxy chamber. It is found that graphene domains and SiC buffer layer coexist. Selective growth of Pb islands on SiC buffer layer rather than on graphene domains is observed. It can be ascribed to the higher adsorption energy of Pb atoms on the 6√(3) reconstruction of SiC. However, once Pb islands nucleate on graphene domains, they will grow very large owing to the lower diffusion barrier of Pb atoms on graphene. The results are consistent with first-principle calculations. Since Pb atoms on graphene are nearly free-standing, Pb islands grow in even-number mode.

  5. Plasmonic absorption enhancement in organic solar cells by nano disks in a buffer layer

    NASA Astrophysics Data System (ADS)

    Kim, Inho; Seok Jeong, Doo; Seong Lee, Taek; Seong Lee, Wook; Lee, Kyeong-Seok

    2012-05-01

    We demonstrate using finite-difference-time-domain calculations that embedding Ag nano disks (NDs) in the buffer layers of thin P3HT:PCBM organic solar cells can enhance optical absorption in the active layers at specific wavelength range. We show that the aspect ratio of the NDs is a key parameter for strong plasmonic absorption enhancement. Two different plasmonic absorption bands are observed stemming from optical refractive index differences among the layers surrounding the NDs in the solar cell devices. One absorption band by the surface plasmon mode localized at the interface of indium tin oxide/ND, which is undesirable for plasmonic absorption enhancement in the active layer, become negligible as the aspect ratio of the diameter-to-height increased. The other absorption band by the dipole-like surface plasmon mode, which plays a main role in enhancing the absorption in the active layer, is spectrally tunable by adjusting the aspect ratio of the NDs. The influences of diameter, height, and coverage of the NDs on optical absorption in the active layer are discussed. Embedding the optimal size NDs in the buffer layer leads to the enhanced total absorption in the 50 nm thick active layer by 16% relative to that without the NDs, and the optical absorption keeps enhanced with increasing the active layer thickness up to 90 nm. However, further increases in the active layer thickness are detrimental to absorption enhancement, which is considered to be caused by destructive interference between scattered light by the NDs and incident light.

  6. Effect of ZnO seed layer on the morphology and optical properties of ZnO nanorods grown on GaN buffer layers

    SciTech Connect

    Nandi, R. Mohan, S. Major, S. S.; Srinivasa, R. S.

    2014-04-24

    ZnO nanorods were grown by chemical bath deposition on sputtered, polycrystalline GaN buffer layers with and without ZnO seed layer. Scanning electron microscopy and X-ray diffraction show that the ZnO nanorods on GaN buffer layers are not vertically well aligned. Photoluminescence spectrum of ZnO nanorods grown on GaN buffer layer, however exhibits a much stronger near-band-edge emission and negligible defect emission, compared to the nanorods grown on ZnO buffer layer. These features are attributed to gallium incorporation at the ZnO-GaN interface. The introduction of a thin (25 nm) ZnO seed layer on GaN buffer layer significantly improves the morphology and vertical alignment of ZnO-NRs without sacrificing the high optical quality of ZnO nanorods on GaN buffer layer. The presence of a thick (200 nm) ZnO seed layer completely masks the effect of the underlying GaN buffer layer on the morphology and optical properties of nanorods.

  7. ZnS/Zn(O,OH)S-based buffer layer deposition for solar cells

    DOEpatents

    Bhattacharya, Raghu N.

    2009-11-03

    The invention provides CBD ZnS/Zn(O,OH)S and spray deposited ZnS/Zn(O,OH)S buffer layers prepared from a solution of zinc salt, thiourea and ammonium hydroxide dissolved in a non-aqueous/aqueous solvent mixture or in 100% non-aqueous solvent. Non-aqueous solvents useful in the invention include methanol, isopropanol and triethyl-amine. One-step deposition procedures are described for CIS, CIGS and other solar cell devices.

  8. Growth and characterization of CdS buffer layers by CBD and MOCVD

    SciTech Connect

    Morrone, A.A.; Huang, C.; Li, S.S.

    1999-03-01

    Thin film CdS has been widely used in thin-film photovoltaic devices. The most efficient Cu(In,&hthinsp;Ga)Se{sub 2} (CIGS) solar cells reported to date utilized a thin CdS buffer layer prepared by a reactive solution growth technique known as chemical bath deposition (CBD). Considerable effort has been directed to better understand the role and find a replacement for the CBD CdS process in CIGS-based solar cells. We reported a low temperature ({approximately}150&hthinsp;{degree}C) Metalorganic Chemical Vapor Deposition (MOCVD) CdS thin film buffer layer process for CIGS absorbers. Many prior studies have reported that CBD CdS contains a mixture of crystal structures. Recent investigations of CBD CdS thin films by ellipsometry suggested a multilayer structure. In this study we compare CdS thin films prepared by CBD and MOCVD and the effects of annealing. TED and XRD are used to characterize the crystal structure, the film microstructure is studied by HRTEM, and the optical properties are studied by Raman and spectrophotometry. All of these characterization techniques reveal superior crystalline film quality for CdS films grown by MOCVD compared to those grown by CBD. Dual Beam Optical Modulation (DBOM) studies showed that the MOCVD and CBD CdS buffer layer processes have nearly the same effect on CIGS absorbers when combined with a cadmium partial electrolyte aqueous dip. {copyright} {ital 1999 American Institute of Physics.}

  9. GaN on Silicon Substrate with AlN Buffer Layer for UV Photodiode

    NASA Astrophysics Data System (ADS)

    Chuah, L. S.; Thahab, S. M.; Hassan, Z.

    Nitrogen plasma-assisted molecular beam epitaxy (PAMBE) deposited GaN thin films on (111) n-type silicon substrate with different thickness AlN buffer layers are investigated and distinguished by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM) and Raman scattering. The thickness of AlN buffer layer ranged from 200 nm to 300 nm. Besides that, the electrical characteristics of the GaN thin film for ultraviolet detecting utilizations are studied by calculating the photo current/dark current ratio on a metal-semiconductor-metal (MSM) photodiode with and without the illumination of Hg-lamp source. The devices have been tested over room temperature (RT). The photocurrent analysis, together with the study of Schottky barrier height (SBH) development, ascertain that the principal mechanism of photo transport is thermionic emission. The photocurrent value is rigorously dependent on Schottky barrier height. The GaN/AlN(200 nm)/n-Si MSM photodiode produces the highest photo/dark current ratio for the lowest strain that consists of the GaN film grown on the AlN (200 nm) buffer layer.

  10. High performance polymer solar cells with as-prepared zirconium acetylacetonate film as cathode buffer layer

    PubMed Central

    Tan, Zhan'ao; Li, Shusheng; Wang, Fuzhi; Qian, Deping; Lin, Jun; Hou, Jianhui; Li, Yongfang

    2014-01-01

    Low-work-function active metals are commonly used as cathode in polymer solar cells (PSCs), but sensitivity of the active metals towards moisture and oxygen results in poor stability of the devices. Therefore, solution-proceessable and stable cathode buffer layer is of great importance for the application of PSCs. Here we demonstrate high performance PSCs by employing as-prepared zirconium acetylacetonate (a-ZrAcac) film spin-cast from its ethanol solution as cathode buffer layer. The PSCs based on a low bandgap polymer PBDTBDD as donor and PC60BM as acceptor with a-ZrAcac/Al cathode demonstrated an average power conversion efficiency (PCE) of 8.75% which is significantly improved than that of the devices with traditional Ca/Al cathode. The improved photovoltaic performance is benefitted from the decreased series resistance and enhanced light harvest of the PSCs with the a-ZrAcac/Al cathode. The results indicate that a-ZrAcac is a promising high performance cathode buffer layer for fabricating large area flexible PSCs. PMID:24732976

  11. Performance enhancement in inverted solar cells by interfacial modification of ZnO nanoparticle buffer layer.

    PubMed

    Ambade, Swapnil B; Ambade, Rohan B; Kim, Seojin; Park, Hanok; Yoo, Dong Jin; Leel, Soo-Hyoung

    2014-11-01

    Polymer solar cells (PSCs) have attracted increasing attention in recent years. The rapid progress and mounting interest suggest the feasibility of PSC commercialization. However, critical issues such as stability and the weak nature of their interfaces posses quite a challenge. In the context of improving stability, PSCs with inverted geometry consising of inorganic oxide layer acting as an n-buffer offer quite the panacea. Zinc oxide (ZnO) is one of the most preferred semiconducting wide band gap oxides as an efficient cathode layer that effectively extracts and transports photoelectrons from the acceptor to the conducting indium-doped tin oxide (ITO) due to its high conductivity and transparency. However, the existence of a back charge transfer from metal oxides to electron-donating conjugated polymer and poor contact with the bulk heterojunction (BHJ) active layer results in serious interfacial recombination and leads to relatively low photovoltaic performance. One approach to improving the performance and charge selectivity of these types of inverted devices consists of modifying the interface between the inorganic metal oxide (e.g., ZnO) and organic active layer using a sub-monolayer of interfacial materials (e.g., functional dyes). In this work, we demonstrate that the photovoltaic parameters of inverted solar cells comprising a thin overlayer of functional dyes over ZnO nanoparticle as an n-buffer layer are highly influenced by the anchoring groups they possess. While an inverted PSC containing an n-buffer of only ZnO exhibited an overall power conversion efficiency (PCE) of 2.87%, the devices with an interlayer of dyes containing functional cyano-carboxylic, cyano-cyano, and carboxylic groups exhibited PCE of 3.52%, 3.39%, and 3.21%, respectively, due to increased forward charge collection resulting from enhanced electronic coupling between the ZnO and BHJ active layers.

  12. Multi-filamentary REBCO tapes fabricated by scratching a buffer layer along the tape longitudinal direction

    NASA Astrophysics Data System (ADS)

    Kurihara, Chihaya; Fujita, Shinji; Nakamura, Naonori; Igarashi, Mitsunori; Iijima, Yasuhiro; Higashikawa, Kohei; Uetsuhara, Dai; Kiss, Takanobu; Iwakuma, Masataka

    2016-11-01

    A method for making multi-filamentary REBCO tapes by only scratching buffer layer was developed for coil application which requires accurate magnetic fields. By continuous Ic measurement, we found that our new multi-filamentary tape could provide almost equal Ic compared to conventional tapes. Then, using EBSD and RTR-SHPM methods, a divided structure of REBCO layer was surely confirmed. AC loss was also decreased. Furthermore, the result of delamination test of our new multi-filamentary tape showed enough mechanical property. As a result, we have succeeded in developing 100 m class multi-filamentary tape for superconducting coil.

  13. Improvement of the interfacial Dzyaloshinskii-Moriya interaction by introducing a Ta buffer layer

    SciTech Connect

    Kim, Nam-Hui; Jung, Jinyong; Cho, Jaehun; You, Chun-Yeol; Han, Dong-Soo; Kim, June-Seo Swagten, Henk J. M.

    2015-10-05

    We report systematic measurements of the interfacial Dzyaloshinskii-Moriya interaction (iDMI) by employing Brillouin light scattering in Pt/Co/AlO{sub x} and Ta/Pt/Co/AlO{sub x} structures. By introducing a tantalum buffer layer, the saturation magnetization and the interfacial perpendicular magnetic anisotropy are significantly improved due to the better interface between heavy metal and ferromagnetic layer. From the frequency shift between Stokes- and anti-Stokes spin-waves, we successively obtain considerably larger iDM energy densities (D{sub max} = 1.65 ± 0.13 mJ/m{sup 2} at t{sub Co} = 1.35 nm) upon adding the Ta buffer layer, despite the nominally identical interface materials. Moreover, the energy density shows an inverse proportionality with the Co layer thickness, which is the critical clue that the observed iDMI is indeed originating from the interface between the Pt and Co layers.

  14. Formation of a Buffer Layer for Graphene on C-Face SiC{0001}

    NASA Astrophysics Data System (ADS)

    He, Guowei; Srivastava, N.; Feenstra, R. M.

    2014-04-01

    Graphene films prepared by heating the SiC surface (the C-face of the {0001} surface) in a Si-rich environment have been studied using low-energy electron diffraction (LEED) and low-energy electron microscopy. Upon graphitization, an interface with symmetry is observed by in situ LEED. After oxidation, the interface displays symmetry. Electron reflectivity measurements indicate that these interface structures arise from a graphene-like "buffer layer" that forms between the graphene and the SiC, similar to that observed on Si-face SiC. From a dynamical LEED structure calculation for the oxidized C-face surface, it is found to consist of a graphene layer sitting on top of a silicate (Si2O3) layer, with the silicate layer having the well-known structure as previously studied on bare SiC surfaces. Based on this result, the structure of the interface prior to oxidation is discussed.

  15. Development of Solution Buffer Layers for RABiTS Based YBCO Coated Conductors

    SciTech Connect

    Paranthaman, Mariappan Parans; Qiu, Xiaofeng; List III, Frederick Alyious; Zhang, Yifei; Li, Xiaoping; Sathyamurthy, Srivatsan; Thieme, C. L. H.; Rupich, M. W.

    2011-01-01

    Abstract The main objective of this research is to find a suitable alternate solution based seed layer for the standard RABiTS three-layer architecture of physical vapor deposited CeO cap/YSZ barrier/Y O seed on Ni-5%W metal tape. In the present work, we have identified CeO buffer layer as a potential replacement for Y O seeds. Using a metal-organic deposition (MOD) process, we have grown smooth, crack-free, epitaxial thin films of CeO (pure and Zr, Cu and Gd-doped) directly on biaxially textured Ni-5W substrates in short lengths. Detailed XRD studies indicate that a single epitaxial CeO phase with slightly improved out-of-plane texture compared to the texture of the underlying Ni-W substrates can be achieved in pure, undoped CeO samples. We have also demonstrated the growth of YSZ barrier layers on pure CeO seeds using sputtering. Both sputtered CeO cap layers and MOD-YBCO films were grown epitaxially on these YSZ-buffered MOD-CeO /Ni-5W substrates. High critical currents per unit width, of 264 A/cm (critical current density, of 3.3 MA/cm ) at 77 K and 0.01 T was achieved for 0.8 m thick MOD-YBCO films grown on MOD-CeO seeds. These results indicate that CeO films can be grown directly on Ni-5W substrates and still support high performance YBCO coated conductors. This work holds promise for a route for producing low-cost buffer architecture for RABiTS based YBCO coated conductors.

  16. Dummy Fill Aware Buffer Insertion after Layer Assignment Based on an Effective Estimation Model

    NASA Astrophysics Data System (ADS)

    Jia, Yanming; Cai, Yici; Hong, Xianlong

    This paper studies the impact of dummy fill for chemical mechanical polishing (CMP)-induced capacitance variation on buffer insertion based on a virtual CMP fill estimation model. Compared with existing methods, our algorithm is more feasible by performing buffer insertion not in post-process but during early physical design. Our contributions are threefold. First, we introduce an improved fast dummy fill amount estimation algorithm based on [4], and use some speedup techniques (tile merging, fill factor and amount assigning) for early estimation. Second, based on some reasonable assumptions, we present an optimum virtual dummy fill method to estimate dummy position and the effect on the interconnect capacitance. Then the dummy fill estimation model was verified by our experiments. Third, we use this model in early buffer insertion after layer assignment considering the effects of dummy fill. Experimental results verified the necessity of early dummy fill estimation and the validity of our algorithm. Buffer insertion considering dummy fill during early physical design is necessary and our algorithm is promising.

  17. Study of optical waveguide sensor using metamaterial as buffer layer with non-linear cladding and substrate

    NASA Astrophysics Data System (ADS)

    Kumar, Santosh; Kumari, Anamika; Raghuwanshi, Sanjeev K.

    2015-05-01

    In this paper, dispersion equation of optical waveguide using metamaterial as buffer layer with non-linear cladding and substrate is pointed. The sensitivity of TE in metamaterial optical waveguide sensor is computed mathematically. The impacts of buffer layer with non-linear cladding and substrate on metamaterial optical waveguide sensor are also tried out. The effects of various parameters on sensitivity of sensor are obtained through MATLAB. It is expected that metamaterial as buffer layer with non-linear cladding and substrate profile has a huge application in leaky fibre sensor, gas sensor and chemical sensor for oil and under grounds mining industries.

  18. Theoretical Study of the Effect of an AlGaAs Double Heterostructure on Metal-Semiconductor-Metal Photodetector Performance

    NASA Technical Reports Server (NTRS)

    Salem, Ali F.; Smith, Arlynn W.; Brennan, Kevin F.

    1994-01-01

    The impulse and square-wave input response of different GaAs metal-semiconductor-metal photodetector (MSM) designs are theoretically examined using a two dimensional drift- diffusion numerical calculation with a thermionic-field emission boundary condition model for the heterojunctions. The rise time and the fall time of the output signal current are calculated for a simple GaAs, epitaxially grown, MSM device as well as for various double-heterostructure barrier devices. The double heterostructure devices consist of an AlGaAs layer sandwiched between the top GaAs active, absorption layer and the bottom GaAs substrate. The effect of the depth of the AlGaAs layer on the speed and responsivity of the MSM devices is examined. It is found that there is an optimal depth, at fixed applied bias, of the AlGaAs layer within the structure that provides maximum responsivity at minimal compromise in speed.

  19. Growth and photoluminescence characteristics of AlGaAs nanowires

    NASA Astrophysics Data System (ADS)

    Wu, Z. H.; Sun, M.; Mei, X. Y.; Ruda, H. E.

    2004-07-01

    Growth of high-quality single-crystal AlGaAs nanowires was demonstrated using the vapor-liquid-solid (VLS) mechanism with molecular-beam epitaxy (MBE). Highly ordered AlGaAs nanowire arrays and GaAs /AlGaAs multilayer nanowires were also prepared. Photoluminescence (PL) from homogeneous AlGaAs and GaAs /AlGaAs multilayer nanowires was measured. The Al composition of the AlGaAs nanowires was found to be significantly lower than that for planar MBE films grown under the same conditions, as determined from PL and energy-dispersive x-ray spectroscopy measurements. This is explained in terms of the different growth mechanisms for VLS and normal MBE. Such AlGaAs nanowires are expected to have a wide range of applications in electronic and photonic devices.

  20. Layer coupling and read disturbances in a buffered magnetic logic environment

    NASA Astrophysics Data System (ADS)

    Windbacher, Thomas; Makarov, Alexander; Sverdlov, Viktor; Selberherr, Siegfried

    2016-10-01

    There are two major obstacles impeding computing systems from further advancements: The power dissipation due to leakage and the energy spent for the information transfer between memory and processor(s). The first issue is commonly handled by shutting down unused circuit parts, however, when the dormant circuits are turned on again, their previous state must be recovered. This is commonly realized by retrieving the required information from the memory, which exacerbates the limited bandwidth between memory and processor(s). In order to circumvent these limitations, we have proposed a non-volatile buffered magnetic logic grid with instant-on capability. Non-volatile magnetic flip flops and spin-transfer torque majority gates are combined to a compact regular structure, which enables a small layout foot print as well as it guarantees the reduction of the information transfer due to a shared buffer. In the proposed structure the information is passed from one magnetic layer to another by first running a current through the magnetic layer to be read, which subsequently generates a magnetization orientation encoded spin-transfer torque, when the polarized electron spins enter the next layer. Since the current passing through the junction also exerts a spin-transfer torque on the read layer, its magnetization orientation could be destabilized which might cause a read disturbance. However, during our simulations it was also found out that the stray fields of neighboring layers have a non-negligible influence on the proposed copy operation. In this work we investigate these potential read disturbances in detail for a 2-bit shift register for varying stray field strength by changing the thickness of the interconnection layer. We found that for closer proximity the acting stray fields not only stabilize but also speed up the copy procedure, while for increasing interconnection layer thickness oscillating domain walls are formed and the copy operation becomes unreliable.

  1. Fibronectin layers by matrix-assisted pulsed laser evaporation from saline buffer-based cryogenic targets.

    PubMed

    Sima, F; Davidson, P; Pauthe, E; Sima, L E; Gallet, O; Mihailescu, I N; Anselme, K

    2011-10-01

    The deposition of fibronectin (FN) from saline buffer-based cryogenic targets by matrix-assisted pulsed laser evaporation (MAPLE) onto silicon substrates is reported. A uniform distribution of FN was revealed by Ponceau staining after control experiments on nitrocellulose paper. Well-organized particulates with heights from hundreds of nanometers up to more than 1 μm packed in homogeneous layers were evidenced by optical microscopy and profilometry on Si substrates. Atomic force microscopy images showed regions composed of buffer and FN aggregates forming a compact film. Comparison of infrared spectra of drop-cast and MAPLE-deposited FN confirmed the preservation of composition and showed no degradation of the protein. The protein deposition on Si was confirmed by antibody staining. Small aggregates and fluorescent fibrils were visualized by fluorescence microscopy. Superior attachment of human osteoprogenitor cells cultivated for 3 h proved the presence of stable and intact FN molecules after transfer.

  2. Buffer Layer Effects on Tandem InGaAs TPV Devices

    NASA Technical Reports Server (NTRS)

    Wilt, David M.; Wehrer, Rebecca J.; Maurer, William F.

    2004-01-01

    Single junction indium gallium arsenide (InGaAs) based TPV devices have demonstrated efficiencies in excess of 20% at radiator temperatures of 1058 C. Modeling suggests that efficiency improvements in single bandgap devices should continue although they will eventually plateau. One approach for extending efficiencies beyond the single bandgap limit is to follow the technique taken in the solar cell field, namely tandem TPV cells. Tandem photovoltaic devices are traditionally composed of cells of decreasing bandgap, connected electrically and optically in series. The incident light impinges upon the highest bandgap first. This device acts as a sieve, absorbing the high-energy photons, while allowing the remainder to pass through to the underlying cell(s), and so on. Tandem devices reduce the energy lost to overexcitation as well as reducing the current density (Jsc). Reduced Jsc results in lower resistive losses and enables the use of thinner and lower doped lateral current conducting layers as well as a higher pitch grid design. Fabricating TPV tandem devices utilizing InGaAs for all of the component cells in a two cell tandem necessitates the inclusion of a buffer layer in-between the high bandgap device (In0.53 Ga0.47As - 0.74eV) and the low bandgap device (In0.66Ga0.34As - 0.63eV) to accommodate the approximately 1% lattice strain generated due to the change in InGaAs composition. To incorporate only a single buffer layer structure, we have investigated the use of the indium phosphide (InP) substrate as a superstrate. Thus the high-bandgap, lattice- matched device is deposited first, followed by the buffer structure and the low-bandgap cell. The near perfect transparency of the high bandgap (1.35eV) iron-doped InP permits the device to be oriented such that the light enters through the substrate. In this paper we examine the impact of the buffer layer on the underlying lattice-matched InGaAs device. 0.74eV InGaAs devices were produced in a variety of

  3. SrO(001) on graphene: a universal buffer layer for integration of complex oxides

    NASA Astrophysics Data System (ADS)

    Ahmed, Adam; Wen, Hua; Pinchuk, Igor; Zhu, Tiancong; Kawakami, Roland

    2015-03-01

    We report the successful growth of high-quality crystalline SrO on highly-ordered pyrolytic graphite (HOPG) and single layer graphene by molecular beam epitaxy. The epitaxial SrO layers have (001) orientation as confirmed by x-ray diffraction (XRD), and atomic force microscopy measurements show rms surface roughness of optimal films to be 1.2 Å. Transport measurements of exfoliated graphene after SrO deposition show a strong dependence between the Dirac point and Sr oxidation. To show the utility of SrO as a buffer layer for complex oxide integration, we grew perovskite crystal SrTiO3 on SrO, and it was also confirmed to have (001) orientation from x-ray diffraction. This materials advancement opens the door to integration of many other complex oxides to explore novel correlated electron physics in graphene.

  4. ZnO buffer layer for metal films on silicon substrates

    DOEpatents

    Ihlefeld, Jon

    2014-09-16

    Dramatic improvements in metallization integrity and electroceramic thin film performance can be achieved by the use of the ZnO buffer layer to minimize interfacial energy between metallization and adhesion layers. In particular, the invention provides a substrate metallization method utilizing a ZnO adhesion layer that has a high work of adhesion, which in turn enables processing under thermal budgets typically reserved for more exotic ceramic, single-crystal, or metal foil substrates. Embodiments of the present invention can be used in a broad range of applications beyond ferroelectric capacitors, including microelectromechanical systems, micro-printed heaters and sensors, and electrochemical energy storage, where integrity of metallized silicon to high temperatures is necessary.

  5. Lattice-matched HfN buffer layers for epitaxy of GaN on Si

    SciTech Connect

    Armitage, Robert; Yang, Qing; Feick, Henning; Gebauer, Joerg; Weber, Eicke R.; Shinkai, Satoko; Sasaki, Katsutaka

    2002-05-08

    Gallium nitride is grown by plasma-assisted molecular-beam epitaxy on (111) and (001) silicon substrates using sputter-deposited hafnium nitride buffer layers. Wurtzite GaN epitaxial layers are obtained on both the (111) and (001) HfN/Si surfaces, with crack-free thickness up to 1.2 (mu)m. Initial results for GaN grown on the (111) surface show a photoluminescence peak width of 17 meV at 11 K, and an asymmetric x-ray rocking curve width of 20 arcmin. Wurtzite GaN on HfN/Si(001) shows reduced structural quality and peculiar low-temperature luminescence features. However, growth on the (001) surface results in nearly stress-free films, suggesting that much thicker crack-free layers could be obtained.

  6. Effect of buffer layers on performance of organic photovoltaic devices based on copper phthalocyanine-perylene dye heterojunction

    NASA Astrophysics Data System (ADS)

    Signerski, R.; Jarosz, G.

    2011-12-01

    The work presents the results of research on the systems formed from thin films of copper phthalocyanine (CuPc), N-N'-dimethylperylene-3,4,9,10-dicarboximide (MePTCDI), electrodes of ITO and Ag, and from buffer layers: MoO3 at ITO and BCP at Ag. We have observed the effect of each buffer layer on voltage dependence of dark current and photocurrent, and on open circuit voltage-light intensity relationship. The system with both buffer layers exhibited the highest values of open circuit voltage and fill factor. The buffer layers improve transport of charge carriers within near-electrode regions, reduce dissociation of excitons on electrodes and reveal processes of charge carrier generation and recombination within the CuPc/MePTCDI junction.

  7. Efficient quantum dot light-emitting diodes with solution-processable molybdenum oxide as the anode buffer layer

    NASA Astrophysics Data System (ADS)

    He, Shaojian; Li, Shusheng; Wang, Fuzhi; Wang, Andrew Y.; Lin, Jun; Tan, Zhan'ao

    2013-05-01

    Quantum dot light-emitting diodes (QD-LEDs) are characterized by pure and saturated emission colors with narrow bandwidth. Optimization of the device interface is an effective way to achieve stable and high-performance QD-LEDs. Here we utilized solution-processed molybdenum oxide (MoOx) as the anode buffer layer on ITO to build efficient QD-LEDs. Using MoOx as the anode buffer layer provides the QD-LED with good Ohmic contact and a small charge transfer resistance. The device luminance is nearly independent of the thickness of the MoOx anode buffer layer. The QD-LEDs with a MoOx anode buffer layer exhibit a maximum luminance and luminous efficiency of 5230 cd m-2 and 0.67 cd A-1 for the yellow emission at 580 nm, and 7842 cd m-2 and 1.49 cd A-1 for the red emission at 610 nm, respectively.

  8. Optimization of CdS Buffer Layer for High Efficiency CIGS Solar Cells.

    PubMed

    Kim, Donguk; Jang, Yong-Jun; Jung, Ho-Sung; Kim, Minha; Baek, Dohyun; Yi, Junsin; Lee, Jaehyeong; Choi, Youngkwan

    2016-05-01

    In present work, effects of the thickness on the structural and optical properties of chemically deposited CdS thin films were investigated. In addition, we fabricated Cu(In, Ga)Se2 solar cells with various thicknesses of CdS buffer layer and optimized the thickness for a high efficiency. When the CdS thin films were thicker, the crystallinity improved but the transmittance decreased. The short-circuit current density (J(sc)) and the fill factor are the major efficiency limiting factors for the CIGS solar cells. As the thickness of the CdS buffer layer, the open-circuit voltage (V(oc)) and the fill factor increased, whereas the J(sc) slightly decreased. The improvement of the fill factor and thus efficiency resulted from larger shunt resistance. For the solar cells without a high resistive intrinsic ZnO layer, the highest efficiency was acquired at the thickness of 89 nm. With further increasing the thickness, the J(sc) decreased significantly, resulting in poor efficiency.

  9. Design of optimal buffer layers for CuInGaSe2 thin-film solar cells(Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Lordi, Vincenzo; Varley, Joel B.; He, Xiaoqing; Rockett, Angus A.; Bailey, Jeff; Zapalac, Geordie H.; Mackie, Neil; Poplavskyy, Dmitry; Bayman, Atiye

    2016-09-01

    Optimizing the buffer layer in manufactured thin-film PV is essential to maximize device efficiency. Here, we describe a combined synthesis, characterization, and theory effort to design optimal buffers based on the (Cd,Zn)(O,S) alloy system for CIGS devices. Optimization of buffer composition and absorber/buffer interface properties in light of several competing requirements for maximum device efficiency were performed, along with process variations to control the film and interface quality. The most relevant buffer properties controlling performance include band gap, conduction band offset with absorber, dopability, interface quality, and film crystallinity. Control of an all-PVD deposition process enabled variation of buffer composition, crystallinity, doping, and quality of the absorber/buffer interface. Analytical electron microscopy was used to characterize the film composition and morphology, while hybrid density functional theory was used to predict optimal compositions and growth parameters based on computed material properties. Process variations were developed to produce layers with controlled crystallinity, varying from amorphous to fully epitaxial, depending primarily on oxygen content. Elemental intermixing between buffer and absorber, particularly involving Cd and Cu, also is controlled and significantly affects device performance. Secondary phase formation at the interface is observed for some conditions and may be detrimental depending on the morphology. Theoretical calculations suggest optimal composition ranges for the buffer based on a suite of computed properties and drive process optimizations connected with observed film properties. Prepared by LLNL under Contract DE-AC52-07NA27344.

  10. a Novel pt and Npt Mixed Igbt Having a New n-BUFFER Layer

    NASA Astrophysics Data System (ADS)

    Zhang, Fei; Luo, Shuhua; Zhang, Liang; Wang, Wei; Yu, Wen; Li, Chengfang; Sun, Xiaowei

    For the first time, a novel mixed insulated gate bipolar transistor (MIGBT) is proposed and verified by two-dimensional (2D) mixed device-circuit simulations. The structure of the proposed device is almost identical with that of the conventional IGBT, except for the buffer layer which is formed by employing the n+/n- structure, so that the trade-off relation between the conduction and switching losses is greatly improved and efficiently decoupled. Furthermore, the proposed device exhibits larger forward blocking voltage and positive temperature coefficient of the forward voltage drop, facilitating parallel integration.

  11. Heterointegration of III-V on silicon using a crystalline oxide buffer layer

    NASA Astrophysics Data System (ADS)

    Bhatnagar, K.; Rojas-Ramirez, J. S.; Contreras-Guerrero, R.; Caro, M.; Droopad, R.

    2015-09-01

    The integration of III-V compound semiconductors with Si can combine the cost advantage and maturity of Si technology with the superior performance of III-V materials. We have achieved the heteroepitaxial growth of III-V compound semiconductors on a crystalline SrTiO3 buffer layer grown on Si(0 0 1) substrates. A two-step growth process utilizing a high temperature nucleation layer of GaAs, followed by a low-temperature GaAs layer at a higher growth rate was employed to achieve highly crystalline thick GaAs layers on the SrTiO3/Si substrates with low surface roughness as seen by AFM. The effect of the GaAs nucleation layer on different surface terminations for the SrTiO3 layer was studied for both on axis and miscut wafers, which led to the conclusion that the Sr terminated surface on miscut substrates provides the best GaAs films. Using GaAs/STO/Si as virtual substrates, we have optimized the growth of high quality GaSb using the interfacial misfit (IMF) dislocation array technique. This work can lead to the possibility of realizing infrared detectors and next-generation high mobility III-V CMOS within the existing Si substrate infrastructure.

  12. Body centered cubic buffer layers for enhanced lateral grain growth of Co/Cu multilayers

    NASA Astrophysics Data System (ADS)

    Tsunoda, Masakiyo; Takahashi, Daisuke; Takahashi, Migaku

    2003-05-01

    The effect of buffer layers (BLs) on metallurgical microstructure and giant magnetoresistance of Co/Cu multilayers fabricated on them is discussed. The lateral grain size and the magnetoresistance (MR) ratio of multilayers are generally enlarged with changing the chemical composition of BLs toward a limiting concentration, within the range where the solid solution of body-centered-cubic (bcc) structure is formed. A guiding principle for material research for the BLs, which realize flat interfaces with large lateral grain size in the multilayers, is deduced from the correlation between the MR ratio of the multilayers and the surface energy of bcc BLs: the difference between the surface energy of BL (γS) and the interfacial energy (γSL) in Young-Dupré's equation (cos θ=(γS-γSL)/γL) should agree with the surface energy of Co layer (γL), which is deposited first on the BL.

  13. Multilayers Diamond-Like Carbon Film with Germanium Buffer Layers by Pulsed Laser Deposition

    NASA Astrophysics Data System (ADS)

    Cheng, Y.; Lu, Y. M.; Guo, Y. L.; Huang, G. J.; Wang, S. Y.; Tian, F. T.

    Multilayer diamond-like carbon film with germanium buffer layers, which was composed of several thick DLC layers and thin germanium island “layers” and named as Ge-DLC film, was prepared on the germanium substrate by ultraviolet laser. The Ge-DLC film had almost same surface roughness as the pure DLC film. Hardness of the Ge-DLC film was above 48.1GPa, which was almost the same as that of pure DLC film. Meanwhile, compared to the pure DLC film, the critical load of Ge-DLC film on the germanium substrate increased from 81.6mN to 143.8mN. Moreover, Ge-DLC film on germanium substrates had no change after fastness tests. The results showed that Ge-DLC film not only kept high hardness but also had higher critical load than that of pure DLC film. Therefore, it could be used as practical protective films.

  14. Uncovering the role of cathode buffer layer in organic solar cells

    PubMed Central

    Qi, Boyuan; Zhang, Zhi-Guo; Wang, Jizheng

    2015-01-01

    Organic solar cells (OSCs) as the third generation photovoltaic devices have drawn intense research, for their ability to be easily deposited by low-cost solution coating technologies. However the cathode in conventional OSCs, Ca, can be only deposited by thermal evaporation and is highly unstable in ambient. Therefore various solution processible cathode buffer layers (CBLs) are synthesized as substitute of Ca and show excellent effect in optimizing performance of OSCs. Yet, there is still no universal consensus on the mechanism that how CBL works, which is evidently a critical scientific issue that should be addressed. In this article detailed studies are targeted on the interfacial physics at the interface between active layer and cathode (with and without treatment of a polar CBL) by using ultraviolet photoelectron spectroscopy, capacitance-voltage measurement, and impedance spectroscopy. The experimental data demonstrate that CBL mainly takes effect in three ways: suppressing surface states at the surface of active layer, protecting the active layer from being damaged by thermally evaporated cathode, and changing the energy level alignment by forming dipole moments with active layer and/or cathode. Our findings here provide a comprehensive picture of interfacial physics in devices with and without CBL. PMID:25588623

  15. Growth and superconductivity of REBCO bulk processed by a seed/buffer layer/precursor construction

    NASA Astrophysics Data System (ADS)

    Y Li, T.; Cheng, L.; Yan, S. B.; Sun, L. J.; Yao, X.; Yoshida, Y.; Ikuta, H.

    2010-12-01

    The buffer layer has been used, for the first time, in the cold-seeding melt-growth (MG) process for REBCO superconductor bulks. In this modified method, a mini pellet was inserted between the seed and the bulk precursor. Notably, the chemical contamination, from the seed material (either REBCO films or SmBCO/NdBCO crystals), was mostly absorbed by the mini pellet. Thus a uniformly high Tc REBCO bulk was readily gained. Secondly, the higher limits of the maximum processing temperature (Tmax) were evidently raised, which is promisingly beneficial for broadening the growth window and overcoming the self-nucleation in the growth of large-sized bulk. In short, the success of this work is that it protects the bulk from seed-induced contamination, and breaks the limit of Tmax caused by the intrinsic properties of the seed material. By means of this simple seed/buffer layer/precursor construction, we successfully fabricated a large single grain of GdBCO bulk superconductor with a diameter of 56 mm.

  16. Buffer layers on metal surfaces having biaxial texture as superconductor substrates

    DOEpatents

    Paranthaman, Mariappan; Lee, Dominic F.; Kroeger, Donald M.; Goyal, Amit

    2000-01-01

    Buffer layer architectures are epitaxially deposited on biaxially-textured rolled substrates of nickel and/or copper and their alloys for high current conductors, and more particularly buffer layer architectures such as Y.sub.2 O.sub.3 /Ni, YSZ/Y.sub.2 O.sub.3 /Ni, RE.sub.2 O.sub.3 /Ni, (RE=Rare Earth), RE.sub.2 O.sub.3 /Y.sub.2 O.sub.3 /Ni, RE.sub.2 O.sub.3 /CeO.sub.2 /Ni, and RE.sub.2 O.sub.3 /YSZ/CeO.sub.2 /Ni, Y.sub.2 O.sub.3 /Cu, YSZ/Y.sub.2 O.sub.3 /Cu, RE.sub.2 O.sub.3 /Cu, RE.sub.2 O.sub.3 /Y.sub.2 O.sub.3 /Cu, RE.sub.2 O.sub.3 /CeO.sub.2 /Cu, and RE.sub.2 O.sub.3 /YSZ/CeO.sub.2 /Cu. Deposition methods include physical vapor deposition techniques which include electron-beam evaporation, rf magnetron sputtering, pulsed laser deposition, thermal evaporation, and solution precursor approaches, which include chemical vapor deposition, combustion CVD, metal-organic decomposition, sol-gel processing, and plasma spray.

  17. Fabrication of YSZ buffer layer by single source MOCVD technique for YBCO coated conductor

    NASA Astrophysics Data System (ADS)

    Jun, Byung-Hyuk; Sun, Jong-Won; Kim, Ho-Jin; Lee, Dong-Wook; Jung, Choong-Hwan; Park, Soon-Dong; Kim, Chan-Joong

    2003-10-01

    Yttria stabilized zirconia (YSZ) buffer layers were deposited by a metal organic chemical vapor deposition technique using a single liquid source for the application of YBa 2Cu 3O 7- δ (YBCO) coated conductor. Y:Zr mole ratio was 0.2:0.8, and tetrahydrofuran (THF) was used as a solvent. The (1 0 0) single crystal MgO substrate was used for searching the deposition conditions. Bi-axially oriented CeO 2 and NiO films were fabricated on {1 0 0} <0 0 1> textured Ni substrate by the same method and used as templates. At a constant working pressure of 10 Torr, the deposition temperatures (660-800 °C) and oxygen flow rates (100-500 sccm) were changed to find the optimum deposition condition. The best (1 0 0) oriented YSZ film on MgO was obtained at 740 °C and O 2 flow rate of 300 sccm. For a YSZ buffer layer with this deposition condition on a CeO 2/Ni template, full width half maximum values of the in-plane ( ϕ-scan) and out-of-plane ( ω-scan) alignments were 10.6° and 9.8°, respectively. The SEM image of YSZ film on CeO 2/Ni showed surface morphologies without microcracks. The film deposition rate was about 100 nm/min.

  18. Calcium manganate: A promising candidate as buffer layer for hybrid halide perovskite photovoltaic-thermoelectric systems

    SciTech Connect

    Zhao, Pengjun; Wang, Hongguang; Kong, Wenwen; Xu, Jinbao Wang, Lei; Ren, Wei; Bian, Liang; Chang, Aimin

    2014-11-21

    We have systematically studied the feasibility of CaMnO{sub 3} thin film, an n-type perovskite, to be utilized as the buffer layer for hybrid halide perovskite photovoltaic-thermoelectric device. Locations of the conduction band and the valence band, spontaneous polarization performance, and optical properties were investigated. Results indicate the energy band of CaMnO{sub 3} can match up well with that of CH{sub 3}NH{sub 3}PbI{sub 3} on separating electron-hole pairs. In addition, the consistent polarization angle helps enlarge the open circuit voltage of the composite system. Besides, CaMnO{sub 3} film shows large absorption coefficient and low extinction coefficient under visible irradiation, demonstrating high carrier concentration, which is beneficial to the current density. More importantly, benign thermoelectric properties enable CaMnO{sub 3} film to assimilate phonon vibration from CH{sub 3}NH3PbI{sub 3}. All the above features lead to a bright future of CaMnO{sub 3} film, which can be a promising candidate as a buffer layer for hybrid halide perovskite photovoltaic-thermoelectric systems.

  19. Preparation of electron buffer layer with crystalline ZnO nanoparticles in inverted organic photovoltaic cells

    NASA Astrophysics Data System (ADS)

    Lee, Donghwan; Kang, Taeho; Choi, Yoon-Young; Oh, Seong-Geun

    2017-06-01

    Zinc oxide (ZnO) nanoparticles synthesized through sol-gel method were used to fabricate the electron buffer layer in inverted organic photovoltaic cells (OPVs) after thermal treatment. To investigate the effect of thermal treatment on the formation of crystalline ZnO nanoparticles, the amorphous ZnO nanoparticles were treated via hydrothermal method. The crystalline phase of ZnO with well-ordered structure could be obtained when the amorphous phase of ZnO was processed under hydrothermal treatment at 170 °C. The crystalline structure of ZnO thin film in inverted organic solar cell could be obtained under relatively low annealing temperature by using thermally treated ZnO nanoparticles. The OPVs fabricated by using crystalline ZnO nanoparticles for electron buffer layer exhibited higher efficiency than the conventional ZnO nanoparticles. The best power conversion efficiency (PCE) was achieved for 7.16% through the ZnO film using the crystalline ZnO nanoparticles. The proposed method to prepared ZnO nanoparticles (NPs) could effectively reduce energy consumption during the fabrication of OPVs, which would greatly contribute to advantages such as lower manufacturing costs, higher productivity and application on flexible substrates.

  20. MIS and MFIS Devices: DyScO3 as a gate-oxide and buffer-layer

    NASA Astrophysics Data System (ADS)

    Melgarejo, R.; Karan, N. K.; Saavedra-Arias, J.; Pradhan, D. K.; Thomas, R.; Katiyar, R. S.

    2008-03-01

    Metal-Ferroelectric-Insulator-Semiconductor (MFIS) structure is of importance in nonvolatile memories, as insulating buffer layer that prevents interdiffusion between the ferroelectric (FE) and the Si substrate. However, insulating layer has some disadvantages viz. generation of depolarization field in FE film and increase of operation voltage. To overcome this, it is important to find a FE with low ɛr (compared to normal FE) and an insulating buffer layer with high ɛr (compared to ɛr = 3.9 of SiO2). High-k materials viz. LaAlO3, SiN, HfO2, HfAlO etc. have been studied as buffer layers in the MFIS structures and as gate-oxide in metal-insulator-silicon (MIS). Recently, a novel gate dielectric material, DyScO3 was considered and studies indicate that crystallization temperature significantly increased and the film on Si remained amorphous even at 1000 C annealing. Considering the requirements on crystallization temperature, ɛr, electrical stability for high-k buffer layers, DyScO3 seems to be very promising for future MFIS device applications. Therefore, the evaluations of MOCVD grown DyScO3 as gate-oxide for MIS and the buffer layers for Bi3.25La0.75Ti3O12 based MFIS structures are presented.

  1. Growth and characterization aluminum gallium nitride/gallium nitride heterostructures on silicon(111) wafers using various buffer layers

    NASA Astrophysics Data System (ADS)

    Venugopal, Rajesh

    Devices based on nitride wide bandgap semiconductors are suitable for several promising applications such as blue lasers, LEDs, HEMTs etc. Due to the absence of bulk nitride crystals, nitride films are grown on lattice mismatched substrates like Al2O3 and 6H-SiC. However from a cost and integration standpoint silicon would be the substrate of choice for the growth of these materials. Nitride heterostructure growth on large area Si(111) is hence attempted by Metal Organic Chemical Vapor Deposition (MOCVD) in an modified AIX 200/4 system. The large lattice and thermal mismatch prevents the direct deposition of GaN on Si and also causes GaN layers grown on Si to crack severely. It is hence necessary to use buffer layers to alleviate this lattice and thermal mismatch. Several buffer layer schemes are used for this purpose. The crystal quality of the AlGaN/GaN heterostructures grown under various conditions on these buffers are studied using several methods like Photoluminescence, X-ray diffraction, Electron Microscopy etc. The quality of heterostructures grown on these buffers is compared in order to identify the strengths and weaknesses of each buffer and to also map the effects of process parameters on nitride layers deposited on each buffer.

  2. Buffer influence on magnetic dead layer, critical current, and thermal stability in magnetic tunnel junctions with perpendicular magnetic anisotropy

    NASA Astrophysics Data System (ADS)

    Frankowski, Marek; Żywczak, Antoni; Czapkiewicz, Maciej; Zietek, Sławomir; Kanak, Jarosław; Banasik, Monika; Powroźnik, Wiesław; Skowroński, Witold; Checiński, Jakub; Wrona, Jerzy; Głowiński, Hubert; Dubowik, Janusz; Ansermet, Jean-Philippe; Stobiecki, Tomasz

    2015-06-01

    We present a detailed study of Ta/Ru-based buffers and their influence on features crucial from the point of view of applications of Magnetic Tunnel Junctions (MTJs) such as critical switching current and thermal stability. We study buffer/FeCoB/MgO/Ta/Ru and buffer/MgO/FeCoB/Ta/Ru layers, investigating the crystallographic texture, the roughness of the buffers, the magnetic domain pattern, the magnetic dead layer thickness, and the perpendicular magnetic anisotropy fields for each sample. Additionally, we examine the effect of the current induced magnetization switching for complete nanopillar MTJs with lateral dimensions of 270 × 180 nm. Buffer Ta 5/Ru 10/Ta 3 (thicknesses in nm), which has the thickest dead layer, exhibits a much larger thermal stability factor (63 compared to 32.5) while featuring a slightly lower critical current density value (1.25 MA/cm2 compared to 1.5 MA/cm2) than the buffer with the thinnest dead layer Ta 5/Ru 20/Ta 5. We can account for these results by considering the difference in damping which compensates for the difference in the switching barrier heights.

  3. Semi-insulating Sn-Zr-O: Tunable resistance buffer layers

    SciTech Connect

    Barnes, Teresa M.; Burst, James M.; Reese, Matthew O.; Perkins, Craig L.

    2015-03-02

    Highly resistive and transparent (HRT) buffer layers are critical components of solar cells and other opto-electronic devices. HRT layers are often undoped transparent conducting oxides. However, these oxides can be too conductive to form an optimal HRT. Here, we present a method to produce HRT layers with tunable electrical resistivity, despite the presence of high concentrations of unintentionally or intentionally added dopants in the film. This method relies on alloying wide-bandgap, high-k dielectric materials (e.g., ZrO{sub 2}) into the host oxide to tune the resistivity. We demonstrate Sn{sub x}Zr{sub 1−x}O{sub 2}:F films with tunable resistivities varying from 0.001 to 10 Ω cm, which are controlled by the Zr mole fraction in the films. Increasing Zr suppresses carriers by expanding the bandgap almost entirely by shifting the valence-band position, which allows the HRT layers to maintain good conduction-band alignment for a low-resistance front contact.

  4. Artificially MoO3 graded ITO anodes for acidic buffer layer free organic photovoltaics

    NASA Astrophysics Data System (ADS)

    Lee, Hye-Min; Kim, Seok-Soon; Kim, Han-Ki

    2016-02-01

    We report characteristics of MoO3 graded ITO anodes prepared by a RF/DC graded sputtering for acidic poly(3,4-ethylene dioxylene thiophene):poly(styrene sulfonic acid) (PEDOT:PSS)-free organic solar cells (OSCs). Graded sputtering of the MoO3 buffer layer on top of the ITO layer produced MoO3 graded ITO anodes with a sheet resistance of 12.67 Ω/square, a resistivity of 2.54 × 10-4 Ω cm, and an optical transmittance of 86.78%, all of which were comparable to a conventional ITO anode. In addition, the MoO3 graded ITO electrode showed a greater work function of 4.92 eV than that (4.6 eV) of an ITO anode, which is beneficial for hole extraction from an organic active layer. Due to the high work function of MoO3 graded ITO electrodes, the acidic PEDOT:PSS-free OSCs fabricated on the MoO3 graded ITO electrode exhibited a power conversion efficiency 3.60% greater than that of a PEDOT:PSS-free OSC on the conventional ITO anode. The successful operation of PEDOT:PSS-free OSCs indicates simpler fabrication steps for cost-effective OSCs and elimination of interfacial reactions caused by the acidic PEDOT:PSS layer for reliable OSCs.

  5. The role of Ag buffer layer in Fe islands growth on Ge (111) surfaces

    SciTech Connect

    Fu, Tsu-Yi Wu, Jia-Yuan; Jhou, Ming-Kuan; Hsu, Hung-Chan

    2015-05-07

    Sub-monolayer iron atoms were deposited at room temperature on Ge (111)-c(2 × 8) substrates with and without Ag buffer layers. The behavior of Fe islands growth was investigated by using scanning tunneling microscope (STM) after different annealing temperatures. STM images show that iron atoms will cause defects and holes on substrates at room temperature. As the annealing temperature rises, iron atoms pull out germanium to form various kinds of alloyed islands. However, the silver layer can protect the Ag/Ge(111)-(√3×√3) reconstruction from forming defects. The phase diagram shows that ring, dot, and triangular defects were only found on Ge (111)-c(2 × 8) substrates. The kinds of islands found in Fe/Ge system are similar to Fe/Ag/Ge system. It indicates that Ge atoms were pulled out to form islands at high annealing temperatures whether there was a Ag layer or not. But a few differences in big pyramidal or strip islands show that the silver layer affects the development of islands by changing the surface symmetry and diffusion coefficient. The structure characters of various islands are also discussed.

  6. Optimal Cu buffer layer thickness for growing epitaxial Co overlayers on Si(111)7 x 7

    SciTech Connect

    Ivanov, Yu. P.; Zotov, A. V.; Ilin, A. I.; Davydenko, A. V.

    2011-10-15

    Using scanning tunneling microscopy, reflection high energy diffraction and magnetic optical Kerr effect measurements, growth mode and the magnetic properties of epitaxial Co films on Si(111) with epitaxial Cu(111) buffer layers of various thicknesses have been studied. The strained 3.5-monolayer-thick Cu/Si(111) film has been found to be an optimal buffer, in which case an almost ideal layer-by-layer like growth of Co is observed up to six Co monolayers, due to a negligible lattice mismatch. The coercivity of Co films grown in this layer-by-layer like fashion has been determined to be about 10 Oe, testifying to the high quality of the formed Co film and Co/Cu interface. Changeover of the Co film growth mode from layer-by-layer like to multilayer has been found to result in the transition of the film magnetic properties from isotropic to markedly uniaxially anisotropic.

  7. Effects of Cd-free buffer layer for CuInSe{sub 2} thin-film solar cells

    SciTech Connect

    Nii, T.; Sugiyama, I.; Kase, T.; Sato, M.; Kaniyama, Y.; Kuriyagawa, S.; Kushiya, K.; Takeshita, H.

    1994-12-31

    ZnO buffer layer by a chemical-bath deposition (CBD) method is developed in this study to improve the interface quality between n-ZnO window layer and p-CuInSe{sub 2} (CIS) thin-film absorber in CIS thin-film solar cells as one of the approaches to the fabrication of Cd-free thin-film solar cells. The optimization of the fabrication conditions of CBD-ZnO leads to the efficiency of about 10%. These results indicate the CBD-ZnO buffer layer has rather high capability to fabricate high-efficiency CIS thin-film solar cells.

  8. Performance improvement of MEH-PPV:PCBM solar cells using bathocuproine and bathophenanthroline as the buffer layers

    NASA Astrophysics Data System (ADS)

    Liu Xiao, Dong; Zhao, Su-Ling; Xu, Zheng; Zhang, Fu-Jun; Zhang, Tian-Hui; Gong, Wei; Yan, Guang; Kong, Chao; Wang, Yong-Sheng; Xu, Xu-Rong

    2011-06-01

    In this work, bathocuproine (BCP) and bathophenanthroline (Bphen), commonly used in small-molecule organic solar cells (OSCs), are adopted as the buffer layers to improve the performance of the polymer solar cells (PSCs) based on poly(2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV): [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) bulk heterojunction. By inserting BCP or Bphen between the active layer and the top cathode, all the performance parameters are dramatically improved. The power conversion efficiency is increased by about 70% and 120% with 5-nm BCP and 12-nm Bphen layers, respectively, when compared with that of the devices without any buffer layer. The performance enhancement is attributed to BCP or Bphen (i) increasing the optical field, and hence the absorption in the active layer, (ii) effectively blocking the excitons generated in MEH-PPV from quenching at organic/aluminum (Al) interface due to the large band-gap of BCP or Bphen, which results in a significant reduction in series resistance (Rs), and (iii) preventing damage to the active layer during the metal deposition. Compared with the traditional device using LiF as the buffer layer, the BCP-based devices show a comparable efficiency, while the Bphen-based devices show a much larger efficiency. This is due to the higher electron mobility in Bphen than that in BCP, which facilitates the electron transport and extraction through the buffer layer to the cathode.

  9. Effect of organic buffer layer in the electrical properties of amorphous-indium gallium zinc oxide thin film transistor.

    PubMed

    Wang, Jian-Xun; Hyung, Gun Woo; Li, Zhao-Hui; Son, Sung-Yong; Kwon, Sang Jik; Kim, Young Kwan; Cho, Eou Sik

    2012-07-01

    In this research, we reported on the fabrication of top-contact amorphous-indium gallium zinc oxide (a-IGZO) thin-film transistors (TFTs) with an organic buffer layer between inorganic gate dielectric and active layer in order to improve the electrical properties of devices. By inserting an organic buffer layer, it was possible to make an affirmation of the improvements in the electrical characteristics of a-IGZO TFTs such as subthreshold slope (SS), on/off current ratio (I(ON/OFF)), off-state current, and saturation field-effect mobility (muFE). The a-IGZO TFTs with the cross-linked polyvinyl alcohol (c-PVA) buffer layer exhibited the pronounced improvements of the muFE (17.4 cm2/Vs), SS (0.9 V/decade), and I(ON/OFF) (8.9 x 10(6)).

  10. Dislocation annihilation in regrown GaN on nanoporous GaN template with optimization of buffer layer growth

    NASA Astrophysics Data System (ADS)

    Soh, C. B.; Hartono, H.; Chow, S. Y.; Chua, S. J.; Fitzgerald, E. A.

    2007-01-01

    Nanoporous GaN template has been fabricated by electrochemical etching to give hexagonal pits with nanoscale pores of size 20-50nm in the underlying grains. The effect of GaN buffer layer grown at various temperatures from 650to1015°C on these as-fabricated nanopores templates is investigated by transmission electron microscopy. The buffer layer grown at the optimized temperature of 850°C partially fill up the pores and voids with annihilation of threading dislocations, serving as an excellent template for high-quality GaN growth. This phenomenon is, however, not observed for the samples grown with other temperature buffer layers. Micro-Raman measurements show significant strain relaxation and improvement in the crystal quality of the overgrown GaN layer on nanoporous GaN template as compared to overgrown on conventional GaN template.

  11. New MBE buffer for micron- and quarter-micron-gateGaAs MESFETs

    NASA Technical Reports Server (NTRS)

    1988-01-01

    A new buffer layer has been developed that eliminates backgating in GaAs MESFETs and substantially reduces short-channel effects in GaAs MESFETs with 0.27-micron-long gates. The new buffer is grown by molecular beam epitaxy (MBE) at a substrate temperature of 200 C using Ga and As sub 4 beam fluxes. The buffer is crystalline, highly resistive, optically inactive, and can be overgrown with high quality GaAs. GaAs MESFETs with a gate length of 0.27 microns that incorporate the new buffer show improved dc and RF properties in comparison with a similar MESFET with a thin undoped GaAs buffer. To demonstrate the backgating performance improvement afforded by the new buffer, MESFETs were fabricated using a number of different buffer layers and structures. A schematic cross section of the MESFET structure used in this study is shown. The measured gate length, gate width, and source-drain spacing of this device are 2,98, and 5.5 microns, respectively. An ohmic contact, isolated from the MESFET by mesa etching, served as the sidegate. The MESFETs were fabricated in MBE n-GaAs layers grown on the new buffer and also in MBE n-GaAs layers grown on buffer layers of undoped GaAs, AlGaAs, and GaAs/AlGaAs superlattices. All the buffer layers were grown by MBE and are 2 microns thick. The active layer is doped to approximately 2 x 10 to the 17th/cu cm with silicon and is 0.3 microns thick.

  12. Inverted Organic Solar Cells with Improved Performance using Varied Cathode Buffer Layers

    NASA Astrophysics Data System (ADS)

    Guan, Zhi-qiang; Yu, Jun-sheng; Zang, Yue; Zeng, Xing-xin

    2012-10-01

    Organic solar cells with inverted planar heterojunction structure based on subphthalocyanine and C60 were fabricated using several kinds of materials as cathode buffer layer (CBL), including tris-8-hydroxy-quinolinato aluminum (Alq3), bathophenanthroline (Bphen), bathocuproine, 2,3,8,9,14,15-hexakis-dodecyl-sulfanyl-5,6,11,12,17,18-hexaazatrinaphthylene (HATNA), and an inorganic compound of Cs2CO3. The influence of the lowest unoccupied molecular orbital level and the electron mobility of organic CBL on the solar cells performance was compared. The results showed that Alq3, Bphen, and HATNA could significantly improve the device performance. The highest efficiency was obtained from device with annealed HATNA as CBL and increased for more than 7 times compared with device without CBL. Furthermore, the simulation results with space charge-limited current theory indicated that the Schottky barrier at the organic/electrode interface in inverted OSC structure was reduced for 27% by inserting HATNA CBL.

  13. Compact hematite buffer layer as a promoter of nanorod photoanode performances

    PubMed Central

    Milan, R.; Cattarin, S.; Comisso, N.; Baratto, C.; Kaunisto, K.; Tkachenko, N. V.; Concina, I.

    2016-01-01

    The effect of a thin α-Fe2O3 compact buffer layer (BL) on the photoelectrochemical performances of a bare α-Fe2O3 nanorods photoanode is investigated. The BL is prepared through a simple spray deposition onto a fluorine-doped tin oxide (FTO) conducting glass substrate before the growth of a α-Fe2O3 nanorods via a hydrothermal process. Insertion of the hematite BL between the FTO and the nanorods markedly enhances the generated photocurrent, by limiting undesired losses of photogenerated charges at the FTO||electrolyte interface. The proposed approach warrants a marked improvement of material performances, with no additional thermal treatment and no use/dispersion of rare or toxic species, in agreement with the principles of green chemistry. PMID:27733756

  14. Compact hematite buffer layer as a promoter of nanorod photoanode performances

    NASA Astrophysics Data System (ADS)

    Milan, R.; Cattarin, S.; Comisso, N.; Baratto, C.; Kaunisto, K.; Tkachenko, N. V.; Concina, I.

    2016-10-01

    The effect of a thin α-Fe2O3 compact buffer layer (BL) on the photoelectrochemical performances of a bare α-Fe2O3 nanorods photoanode is investigated. The BL is prepared through a simple spray deposition onto a fluorine-doped tin oxide (FTO) conducting glass substrate before the growth of a α-Fe2O3 nanorods via a hydrothermal process. Insertion of the hematite BL between the FTO and the nanorods markedly enhances the generated photocurrent, by limiting undesired losses of photogenerated charges at the FTO||electrolyte interface. The proposed approach warrants a marked improvement of material performances, with no additional thermal treatment and no use/dispersion of rare or toxic species, in agreement with the principles of green chemistry.

  15. Interlaced, Nanostructured Interface with Graphene Buffer Layer Reduces Thermal Boundary Resistance in Nano/Microelectronic Systems.

    PubMed

    Tao, Lei; Theruvakkattil Sreenivasan, Sreeprasad; Shahsavari, Rouzbeh

    2017-01-11

    Improving heat transfer in hybrid nano/microelectronic systems is a challenge, mainly due to the high thermal boundary resistance (TBR) across the interface. Herein, we focus on gallium nitride (GaN)/diamond interface-as a model system with various high power, high temperature, and optoelectronic applications-and perform extensive reverse nonequilibrium molecular dynamics simulations, decoding the interplay between the pillar length, size, shape, hierarchy, density, arrangement, system size, and the interfacial heat transfer mechanisms to substantially reduce TBR in GaN-on-diamond devices. We found that changing the conventional planar interface to nanoengineered, interlaced architecture with optimal geometry results in >80% reduction in TBR. Moreover, introduction of conformal graphene buffer layer further reduces the TBR by ∼33%. Our findings demonstrate that the enhanced generation of intermediate frequency phonons activates the dominant group velocities, resulting in reduced TBR. This work has important implications on experimental studies, opening up a new space for engineering hybrid nano/microelectronics.

  16. Effect of Reaction Temperature of CdS Buffer Layers by Chemical Bath Deposition Method.

    PubMed

    Kim, Hye Jin; Kim, Chae-Woong; Jung, Duk Young; Jeong, Chaehwan

    2016-05-01

    This study investigated CdS deposition on a Cu(In,Ga)Se2 (CIGS) film via chemical bath deposition (CBD) in order to obtain a high-quality optimized buffer layer. The thickness and reaction temperature (from 50 degrees C to 65 degrees C) were investigated, and we found that an increase in the reaction temperature during CBD, resulted in a thicker CdS layer. We obtained a thin film with a thickness of 50 nm at a reaction temperature of 60 degrees C, which also exhibited the highest photoelectric conversion efficiency for use in solar cells. Room temperature time-resolved photoluminescence (TR-PL) measurements were performed on the Cu(In,Ga)Se2 (CIGS) thin film and CdS/CIGS samples to determine the recombination process of the photo-generated minority carrier. The device performance was found to be dependent on the thickness of the CdS layer. As the thickness of the CdS increases, the fill factor and the series resistance increased to 61.66% and decreased to 8.35 Ω, respectively. The best condition was observed at a reaction temperature of 60 degrees C, and its conversion efficiency was 12.20%.

  17. R.F. Sputtering Deposition of Buffer Layers for Si/YBCO Integrated Microelectronics

    NASA Astrophysics Data System (ADS)

    Rombolà, G.; Ballarini, V.; Chiodoni, A.; Gozzelino, L.; Mezzetti, E.; Minetti, B.; Pirri, C. F.; Tresso, E.; Camerlingo, C.

    The aim of the present work is the optimization of the Si/buffer-layer/YBCO multilayer deposition process so as to grow superconducting films of quality suitable for device applications. The structural properties of the Si/CeO2 system, obtained by RF magnetron sputtering of CeO2 targets in Ar atmosphere, have been studied. More than 50 films have been deposited and some of them submitted to post-deposition annealing treatments both in N2 and O2 atmospheres. The presence of an unwanted amorphous SiO2 layer at the Si/CeO2 interface compromises the YBCO c-axis orientation, and therefore the sharpness of the R versus T transition. A newly designed deposition system has been realized: it has been specially conceived for obtaining bi- and tri-layers, adopting two targets in YSZ and CeO2, respectively. Results on YSZ/Si and CeO2/YSZ/Si systems obtained with the new machine are presented and discussed: (100) oriented YSZ films with nominal thickness of 40 nm have been obtained. The CeO2 film subsequently deposited has the desired (100) orientation. The YBCO film, in the final YBCO/YSZ/CeO2/Si configuration, is c-axis oriented.

  18. Direct electron injection into an oxide insulator using a cathode buffer layer

    PubMed Central

    Lee, Eungkyu; Lee, Jinwon; Kim, Ji-Hoon; Lim, Keon-Hee; Seok Byun, Jun; Ko, Jieun; Dong Kim, Young; Park, Yongsup; Kim, Youn Sang

    2015-01-01

    Injecting charge carriers into the mobile bands of an inorganic oxide insulator (for example, SiO2, HfO2) is a highly complicated task, or even impossible without external energy sources such as photons. This is because oxide insulators exhibit very low electron affinity and high ionization energy levels. Here we show that a ZnO layer acting as a cathode buffer layer permits direct electron injection into the conduction bands of various oxide insulators (for example, SiO2, Ta2O5, HfO2, Al2O3) from a metal cathode. Studies of current–voltage characteristics reveal that the current ohmically passes through the ZnO/oxide-insulator interface. Our findings suggests that the oxide insulators could be used for simply fabricated, transparent and highly stable electronic valves. With this strategy, we demonstrate an electrostatic discharging diode that uses 100-nm SiO2 as an active layer exhibiting an on/off ratio of ∼107, and protects the ZnO thin-film transistors from high electrical stresses. PMID:25864642

  19. Solution-dispersed CuO nanoparticles anode buffer layer: Effect of ultrasonic agitation duration on photovoltaic performance

    NASA Astrophysics Data System (ADS)

    Sabri, Nasehah Syamin; Yap, Chi Chin; Yahaya, Muhammad; Salleh, Muhamad Mat; Jumali, Mohammad Hafizuddin Haji

    2016-11-01

    The performance of inverted type hybrid organic solar cell based on poly(3-hexyltheopene):[6,6]-phenyl C61-butyric acid methyl ester (P3HT:PCBM) can be improved by adding an anode buffer layer of copper oxide (CuO). CuO that serves as an electron blocking layer which could effectively reduce the charge recombination at the photoactive layer (P3HT:PCBM)/silver (Ag) interfaces. At the same time, Cuo anode buffer layer could accelerate the holes collection from the photoactive layer to the top electrode. In this study we investigated the effects of ultrasonic agitation duration in preparation of solution-dispersed CuO anode buffer layer on the performance of the devices with a configuration of fluorine tin oxide (FTO)/zinc oxide (ZnO) nanorod arrays/P3HT:PCBM/ CuO/Ag. Different durations of ultrasonic agitation (0, 5, 15 and 25 min) were used for CuO nanoparticles solution dispersion to obtain the optimum particle size distribution of CuO. It was found that the smallest average particle size of CuO was obtained by applying the ultrasonic agitation for longest duration of 25 min. The highest power conversion efficiency of 1.22% was recorded from the device incorporating with CuO anode buffer layer with the smallest average particle size. It is believed that CuO anode buffer layer with the smallest average particle size had the least agglomerates, thus leading to better film formation and contact surface area.

  20. Effect of Alloy 625 Buffer Layer on Hardfacing of Modified 9Cr-1Mo Steel Using Nickel Base Hardfacing Alloy

    NASA Astrophysics Data System (ADS)

    Chakraborty, Gopa; Das, C. R.; Albert, S. K.; Bhaduri, A. K.; Murugesan, S.; Dasgupta, Arup

    2016-04-01

    Dashpot piston, made up of modified 9Cr-1Mo steel, is a part of diverse safety rod used for safe shutdown of a nuclear reactor. This component was hardfaced using nickel base AWS ER NiCr-B alloy and extensive cracking was experienced during direct deposition of this alloy on dashpot piston. Cracking reduced considerably and the component was successfully hardfaced by application of Inconel 625 as buffer layer prior to hardface deposition. Hence, a separate study was undertaken to investigate the role of buffer layer in reducing the cracking and on the microstructure of the hardfaced deposit. Results indicate that in the direct deposition of hardfacing alloy on modified 9Cr-1Mo steel, both heat-affected zone (HAZ) formed and the deposit layer are hard making the thickness of the hard layer formed equal to combined thickness of both HAZ and deposit. This hard layer is unable to absorb thermal stresses resulting in the cracking of the deposit. By providing a buffer layer of Alloy 625 followed by a post-weld heat treatment, HAZ formed in the modified 9Cr-1Mo steel is effectively tempered, and HAZ formed during the subsequent deposition of the hardfacing alloy over the Alloy 625 buffer layer is almost completely confined to Alloy 625, which does not harden. This reduces the cracking susceptibility of the deposit. Further, unlike in the case of direct deposition on modified 9Cr-1Mo steel, dilution of the deposit by Ni-base buffer layer does not alter the hardness of the deposit and desired hardness on the deposit surface could be achieved even with lower thickness of the deposit. This gives an option for reducing the recommended thickness of the deposit, which can also reduce the risk of cracking.

  1. Improved performance of polymer solar cells by using inorganic, organic, and doped cathode buffer layers

    NASA Astrophysics Data System (ADS)

    Taohong, Wang; Changbo, Chen; Kunping, Guo; Guo, Chen; Tao, Xu; Bin, Wei

    2016-03-01

    The interface between the active layer and the electrode is one of the most critical factors that could affect the device performance of polymer solar cells. In this work, based on the typical poly(3-hexylthiophene):[6,6]-phenyl C61-butyric acid methyl ester (P3HT:PCBM) polymer solar cell, we studied the effect of the cathode buffer layer (CBL) between the top metal electrode and the active layer on the device performance. Several inorganic and organic materials commonly used as the electron injection layer in an organic light-emitting diode (OLED) were employed as the CBL in the P3HT:PCBM polymer solar cells. Our results demonstrate that the inorganic and organic materials like Cs2CO3, bathophenanthroline (Bphen), and 8-hydroxyquinolatolithium (Liq) can be used as CBL to efficiently improve the device performance of the P3HT:PCBM polymer solar cells. The P3HT:PCBM devices employed various CBLs possess power conversion efficiencies (PCEs) of 3.0%-3.3%, which are ca. 50% improved compared to that of the device without CBL. Furthermore, by using the doped organic materials Bphen:Cs2CO3 and Bphen:Liq as the CBL, the PCE of the P3HT:PCBM device will be further improved to 3.5%, which is ca. 70% higher than that of the device without a CBL and ca. 10% increased compared with that of the devices with a neat inorganic or organic CBL. Project supported by the National Natural Science Foundation of China (Grant No. 61204014), the “Chenguang” Project (13CG42) supported by Shanghai Municipal Education Commission and Shanghai Education Development Foundation, China, and the Shanghai University Young Teacher Training Program of Shanghai Municipality, China.

  2. Contribution of the buffer layer to the Raman spectrum of epitaxial graphene on SiC(0001)

    NASA Astrophysics Data System (ADS)

    Fromm, F.; Oliveira, M. H., Jr.; Molina-Sánchez, A.; Hundhausen, M.; Lopes, J. M. J.; Riechert, H.; Wirtz, L.; Seyller, T.

    2013-04-01

    We report a Raman study of the so-called buffer layer with (6\\sqrt 3\\times 6\\sqrt 3)R30^{\\circ } periodicity which forms the intrinsic interface structure between epitaxial graphene and SiC(0001). We show that this interface structure leads to a non-vanishing signal in the Raman spectrum at frequencies in the range of the D- and G-band of graphene and discuss its shape and intensity. Ab initio phonon calculations reveal that these features can be attributed to the vibrational density of states of the buffer layer.

  3. Crystallinity of YBCO thin films on an MgO substrate using an amorphous buffer layer deposited at a low temperature

    NASA Astrophysics Data System (ADS)

    Nakamura, Y.; Kudo, S.; Mukaida, M.; Ohshima, S.

    2002-10-01

    We have investigated crystallinity of YBCO films on an MgO substrate using an amorphous buffer layer. The evaluated films are obtained as follows: an amorphous YBCO buffer layer is deposited on the MgO substrate at a low temperature (200 °C); and then, an amorphous buffer layer is crystallized by the thermal annealing at a high temperature from 910 to 1030 °C; finally, main YBCO film is grown on the crystalline YBCO buffer layer over the MgO substrate. A significant improvement in the crystalline quality of the YBCO films was achieved, when amorphous buffer layers of 100 nm in thickness were crystallized by annealing temperature 950 °C and then annealing is continued for 1 h in air atmosphere. We confirmed that YBCO films grown on a well-crystallized buffer layer had better crystallinity than ones on bare MgO substrate, which has substantially large lattice mismatch.

  4. Characteristics of GaN-based light emitting diodes with different thicknesses of buffer layer grown by HVPE and MOCVD

    NASA Astrophysics Data System (ADS)

    Tian, Pengfei; Edwards, Paul R.; Wallace, Michael J.; Martin, Robert W.; McKendry, Jonathan J. D.; Gu, Erdan; Dawson, Martin D.; Qiu, Zhi-Jun; Jia, Chuanyu; Chen, Zhizhong; Zhang, Guoyi; Zheng, Lirong; Liu, Ran

    2017-02-01

    GaN-based light emitting diodes (LEDs) have been fabricated on sapphire substrates with different thicknesses of GaN buffer layer grown by a combination of hydride vapor phase epitaxy and metalorganic chemical vapor deposition. We analyzed the LED efficiency and modulation characteristics with buffer thicknesses of 12 μm and 30 μm. With the buffer thickness increase, cathodoluminescence hyperspectral imaging shows that the dislocation density in the buffer layer decreases from  ∼1.3  ×  108 cm‑2 to  ∼1.0  ×  108 cm‑2, and Raman spectra suggest that the compressive stress in the quantum wells is partly relaxed, which leads to a large blue shift in the peak emission wavelength of the photoluminescence and electroluminescent spectra. The combined effects of the low dislocation density and stress relaxation lead to improvements in the efficiency of LEDs with the 30 μm GaN buffer, but the electrical-to-optical modulation bandwidth is higher for the LEDs with the 12 μm GaN buffer. A rate equation analysis suggests that defect-related nonradiative recombination can help increase the modulation bandwidth but reduce the LED efficiency at low currents, suggesting that a compromise should be made in the choice of defect density.

  5. Morphology and arrangement of InN nanocolumns deposited by radio-frequency sputtering: Effect of the buffer layer

    NASA Astrophysics Data System (ADS)

    Monteagudo-Lerma, L.; Valdueza-Felip, S.; Núñez-Cascajero, A.; Ruiz, A.; González-Herráez, M.; Monroy, E.; Naranjo, F. B.

    2016-01-01

    We present the structural and optical properties of (0001)-oriented nanocolumnar films of InN deposited on c-sapphire substrates by radio-frequency reactive sputtering. It is observed that the column density and dimensions are highly dependent on the growth parameters of the buffer layer. We investigate four buffer layers consisting of (i) 30 nm of low-growth-rate InN, (ii) 30 nm of AlN deposited on the unbiased substrate (us), (iii) 30 nm of AlN deposited on the reverse-biased substrate (bs), and (iv) a 60-nm-thick bilayer consisting of 30-nm-thick bs-AlN deposited on top of 30-nm-thick us-AlN. Differences in the layer nucleation process due to the buffer layer induce variations of the column density in the range of (2.5-16)×109 cm-2, and of the column diameter in the range of 87-176 nm. Best results in terms of mosaicity are obtained using the bs-AlN buffer layer, which leads to a full width at half-maximum of the InN(0002) rocking curve of 1.2°. A residual compressive strain is still present in the nanocolumns. All samples exhibit room temperature photoluminescence emission at ~1.6 eV, and an apparent optical band gap at ~1.7 eV estimated from linear optical transmittance measurements.

  6. Carbon doped GaN buffer layer using propane for high electron mobility transistor applications: Growth and device results

    SciTech Connect

    Li, X.; Nilsson, D.; Danielsson, Ö.; Pedersen, H.; Janzén, E.; Forsberg, U.; Bergsten, J.; Rorsman, N.

    2015-12-28

    The creation of a semi insulating (SI) buffer layer in AlGaN/GaN High Electron Mobility Transistor (HEMT) devices is crucial for preventing a current path beneath the two-dimensional electron gas (2DEG). In this investigation, we evaluate the use of a gaseous carbon gas precursor, propane, for creating a SI GaN buffer layer in a HEMT structure. The carbon doped profile, using propane gas, is a two stepped profile with a high carbon doping (1.5 × 10{sup 18 }cm{sup −3}) epitaxial layer closest to the substrate and a lower doped layer (3 × 10{sup 16 }cm{sup −3}) closest to the 2DEG channel. Secondary Ion Mass Spectrometry measurement shows a uniform incorporation versus depth, and no memory effect from carbon doping can be seen. The high carbon doping (1.5 × 10{sup 18 }cm{sup −3}) does not influence the surface morphology, and a roughness root-mean-square value of 0.43 nm is obtained from Atomic Force Microscopy. High resolution X-ray diffraction measurements show very sharp peaks and no structural degradation can be seen related to the heavy carbon doped layer. HEMTs are fabricated and show an extremely low drain induced barrier lowering value of 0.1 mV/V, demonstrating an excellent buffer isolation. The carbon doped GaN buffer layer using propane gas is compared to samples using carbon from the trimethylgallium molecule, showing equally low leakage currents, demonstrating the capability of growing highly resistive buffer layers using a gaseous carbon source.

  7. Carbon doped GaN buffer layer using propane for high electron mobility transistor applications: Growth and device results

    NASA Astrophysics Data System (ADS)

    Li, X.; Bergsten, J.; Nilsson, D.; Danielsson, Ö.; Pedersen, H.; Rorsman, N.; Janzén, E.; Forsberg, U.

    2015-12-01

    The creation of a semi insulating (SI) buffer layer in AlGaN/GaN High Electron Mobility Transistor (HEMT) devices is crucial for preventing a current path beneath the two-dimensional electron gas (2DEG). In this investigation, we evaluate the use of a gaseous carbon gas precursor, propane, for creating a SI GaN buffer layer in a HEMT structure. The carbon doped profile, using propane gas, is a two stepped profile with a high carbon doping (1.5 × 1018 cm-3) epitaxial layer closest to the substrate and a lower doped layer (3 × 1016 cm-3) closest to the 2DEG channel. Secondary Ion Mass Spectrometry measurement shows a uniform incorporation versus depth, and no memory effect from carbon doping can be seen. The high carbon doping (1.5 × 1018 cm-3) does not influence the surface morphology, and a roughness root-mean-square value of 0.43 nm is obtained from Atomic Force Microscopy. High resolution X-ray diffraction measurements show very sharp peaks and no structural degradation can be seen related to the heavy carbon doped layer. HEMTs are fabricated and show an extremely low drain induced barrier lowering value of 0.1 mV/V, demonstrating an excellent buffer isolation. The carbon doped GaN buffer layer using propane gas is compared to samples using carbon from the trimethylgallium molecule, showing equally low leakage currents, demonstrating the capability of growing highly resistive buffer layers using a gaseous carbon source.

  8. Epitaxial MgB2 thin films on ZrB2 buffer layers: structural characterization by synchrotron radiation

    NASA Astrophysics Data System (ADS)

    Ferrando, V.; Tarantini, C.; Bellingeri, E.; Manfrinetti, P.; Pallecchi, I.; Marré, D.; Plantevin, O.; Putti, M.; Felici, R.; Ferdeghini, C.

    2004-12-01

    Structural and superconducting properties of magnesium diboride thin films grown by pulsed laser deposition on zirconium diboride buffer layers were studied. We demonstrate that the ZrB2 layer is compatible with the MgB2 two step deposition process. Synchrotron radiation measurements, in particular anomalous diffraction measurements, allowed us to separate MgB2 peaks from ZrB2 ones and revealed that both layers have a single in plane orientation with a sharp interface between them. Moreover, the buffer layer avoids oxygen contamination from the sapphire substrate. The critical temperature of this film is near 37.6 K and the upper critical field measured at the Grenoble High Magnetic Field Laboratory up to 20.3 T is comparable with the highest ones reported in literature.

  9. Threading dislocations in GaAs epitaxial layers on various thickness Ge buffers on 300 mm Si substrates

    NASA Astrophysics Data System (ADS)

    Bogumilowicz, Y.; Hartmann, J. M.; Rochat, N.; Salaun, A.; Martin, M.; Bassani, F.; Baron, T.; David, S.; Bao, X.-Y.; Sanchez, E.

    2016-11-01

    We have grown GaAs epitaxial layers on Ge buffers, themselves on Si (001) substrates, using an Applied Materials 300 mm metal organic chemical vapor deposition tool. We varied the Ge buffer thickness between 0.36 and 1.38 μm and studied the properties of a 0.27 μm thick GaAs layer on top. We found that increasing the Ge buffer thickness yielded smoother GaAs films with an rms surface roughness as low as 0.5 nm obtained on a 5×5 μm2 area. The bow of the substrate increased following a linear law with the epitaxial stack thickness up to 240 μm for a 1.65 μm stack. We have also characterized the threading dislocations present in the GaAs layers using X-ray diffraction and cathodoluminescence. Increasing the Ge buffer thickness resulted in lower threading dislocation densities, enabling us to obtain anti-phase boundary - free GaAs films with a threading dislocation density as low as 3×107 cm-2. In addition, atomic force microscopy surface topology measurements showed the presence of pits in the GaAs layers whose density agreed well with other threading dislocation density assessments. It thus seems that threading dislocations can in certain cases induce some growth rate variations, making them visible in as-grown GaAs films. Using thicker Ge buffers results in smoother films with less threading dislocations, with the side effect of increasing the bow on the wafer. If bow is not an issue, this is a practical approach to improve the GaAs (on Ge buffer) on silicon quality.

  10. Efficient quantum dot light-emitting diodes with solution-processable molybdenum oxide as the anode buffer layer.

    PubMed

    He, Shaojian; Li, Shusheng; Wang, Fuzhi; Wang, Andrew Y; Lin, Jun; Tan, Zhan'ao

    2013-05-03

    Quantum dot light-emitting diodes (QD-LEDs) are characterized by pure and saturated emission colors with narrow bandwidth. Optimization of the device interface is an effective way to achieve stable and high-performance QD-LEDs. Here we utilized solution-processed molybdenum oxide (MoOx) as the anode buffer layer on ITO to build efficient QD-LEDs. Using MoOx as the anode buffer layer provides the QD-LED with good Ohmic contact and a small charge transfer resistance. The device luminance is nearly independent of the thickness of the MoOx anode buffer layer. The QD-LEDs with a MoOx anode buffer layer exhibit a maximum luminance and luminous efficiency of 5230 cd m(-2) and 0.67 cd A(-1) for the yellow emission at 580 nm, and 7842 cd m(-2) and 1.49 cd A(-1) for the red emission at 610 nm, respectively.

  11. Improved performance and stability of organic light-emitting devices with silicon oxy-nitride buffer layer

    NASA Astrophysics Data System (ADS)

    Poon, C. O.; Wong, F. L.; Tong, S. W.; Zhang, R. Q.; Lee, C. S.; Lee, S. T.

    2003-08-01

    The use of silicon oxy-nitride (SiOxNy) as an anode buffer layer in organic light-emitting devices (OLEDs) with a configuration of indium tin oxide (ITO)/SiOxNy/α-naphtylphenyliphenyl diamine (NPB)/8-hydroxyquinoline aluminum/Mg:Ag has been studied. With a SiOxNy buffer layer several angstroms thick, the device efficiency increased from 3.0 to 3.8 cd/A. The buffer layer also protected the ITO surface from contamination due to air exposure. Upon exposing the cleaned ITO substrate to air for one day before device fabrication, the device current efficiency and turn-on voltage degraded to 2.1 cd/A and 4.3 V, respectively, from 3 cd/A and 3.3 V for the device fabricated on an as-cleaned ITO surface. In contrast, devices prepared on air-exposed SiOxNy/ITO surface had almost the same current efficiency (3.85 cd/A) and turn on voltage (3.7 V) comparing to devices (3.8 cd/A and 3.7 V) fabricated on freshly prepared SiOxNy/ITO surface. The results suggested that SiOxNy is a promising anode buffer layer for OLEDs, for both efficiency and stability enhancements.

  12. Characterization of MFIS Structure with Dy-Doped ZrO2 Buffer Layer

    NASA Astrophysics Data System (ADS)

    Im, J. H.; Ah, G. Z.; Han, D. H.; Park, B. E.

    2011-12-01

    To evaluate the feasibility of DZO thin film as an insulating buffer layer for ferroelectric gate field effect transistors (Fe-FETs) with a metal-ferroelectric-insulator-semiconductor (MFIS) structure, we fabricated DZO/Si and BLT/DZO/Si structures by a sol-gel method. Equivalent oxide thickness (EOT) values of the DZO thin films were about 12.4nm, 11.9nm, 11.2nm and 11.1 nm for 650 °C, 700 °C 750 °C, and 800 °C,, respectively. Hysteresis was observed in all capacitance-voltage (C-V) curves of the DZO/Si structures, but hysteresis of the 750-°C-annealed film was negligible. The leakage current densities of the DZO thin films on Si showed the good characteristics regardless of the annealing temperature variations. The C-V characteristics of Au/300-nm-thick BLT/750-°C-annealed DZO/Si structure showed clockwise hysteresis loops, and the memory window width increased as the bias voltage increased. The maximum value of the memory window width was about 1.9 V at ±7 V.

  13. Cd-Zn-O-S alloys for optimal buffer layers in thin-film photovoltaics (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Varley, Joel B.; He, Xiaoqing; Mackie, Neil; Rockett, Angus A.; Lordi, Vincenzo

    2015-09-01

    Advances in thin-film photovoltaics have largely focused on modifying the absorber layer(s), while the choices for other layers in the solar cell stack have remained somewhat limited. In particular, cadmium sulfide (CdS) is widely used as the buffer layer in typical record devices utilizing absorbers like Cu(In,Ga)Se2 (CIGSe) or Cu2ZnSnS4 (CZTS) despite leading to a loss of solar photocurrent due to its band gap of 2.4 eV. While different buffers such as Zn(S,O,OH) are beginning to become competitive with CdS, the identification of additional wider-band gap alternatives with electrical properties comparable to or better than CdS is highly desirable. Here we use hybrid density functional calculations to characterize CdxZn1-xOyS1-y candidate buffer layers in the quaternary phase space composed by Cd, Zn, O, and S. We focus on the band gaps and band offsets of the alloys to assess strategies for improving absorption losses from conventional CdS buffers while maintaining similar conduction band offsets known to facilitate good device performance. We also consider additional criteria such as lattice matching to identify regions in the composition space that may provide improved epitaxy to CIGSe and CZTS absorbers. Lastly, we incorporate our calculated alloy properties into device model simulations of typical CIGSe devices to identify the CdxZn1-xOyS1-y buffer compositions that lead to the best performance. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 and funded by the Department of Energy office of Energy Efficiency and Renewable Energy (EERE) through the SunShot Bridging Research Interactions through collaborative Development Grants in Energy (BRIDGE) program.

  14. Improving the performance of perovskite solar cells with glycerol-doped PEDOT:PSS buffer layer

    NASA Astrophysics Data System (ADS)

    Jian-Feng, Li; Chuang, Zhao; Heng, Zhang; Jun-Feng, Tong; Peng, Zhang; Chun-Yan, Yang; Yang-Jun, Xia; Duo-Wang, Fan

    2016-02-01

    In this paper, we investigate the effects of glycerol doping on transmittance, conductivity and surface morphology of poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate)) (PEDOT:PSS) and its influence on the performance of perovskite solar cells. . The conductivity of PEDOT:PSS is improved obviously by doping glycerol. The maximum of the conductivity is 0.89 S/cm when the doping concentration reaches 6 wt%, which increases about 127 times compared with undoped. The perovskite solar cells are fabricated with a configuration of indium tin oxide (ITO)/PEDOT:PSS/CH3NH3PbI3/PC61BM/Al, where PEDOT:PSS and PC61BM are used as hole and electron transport layers, respectively. The results show an improvement of hole charge transport as well as an increase of short-circuit current density and a reduction of series resistance, owing to the higher conductivity of the doped PEDOT:PSS. Consequently, it improves the whole performance of perovskite solar cell. The power conversion efficiency (PCE) of the device is improved from 8.57% to 11.03% under AM 1.5 G (100 mW/cm2 illumination) after the buffer layer has been modified. Project supported by the National Natural Science Foundation of China (Grant Nos. 61264002, 61166002, 91333206, and 51463011), the Natural Science Foundation of Gansu Province, China (Grant No. 1308RJZA159), the New Century Excellent Talents in University of Ministry of Education of China (Grant No. NCET-13-0840), the Research Project of Graduate Teacher of Gansu Province, China (Grant No. 2014A-0042), and the Postdoctoral Science Foundation from Lanzhou Jiaotong University, China.

  15. Optimization of the Energy Level Alignment between the Photoactive Layer and the Cathode Contact Utilizing Solution-Processed Hafnium Acetylacetonate as Buffer Layer for Efficient Polymer Solar Cells.

    PubMed

    Yu, Lu; Li, Qiuxiang; Shi, Zhenzhen; Liu, Hao; Wang, Yaping; Wang, Fuzhi; Zhang, Bing; Dai, Songyuan; Lin, Jun; Tan, Zhan'ao

    2016-01-13

    The insertion of an appropriate interfacial buffer layer between the photoactive layer and the contact electrodes makes a great impact on the performance of polymer solar cells (PSCs). Ideal interfacial buffer layers could minimize the interfacial traps and the interfacial barriers caused by the incompatibility between the photoactive layer and the electrodes. In this work, we utilized solution-processed hafnium(IV) acetylacetonate (Hf(acac)4) as an effective cathode buffer layer (CBL) in PSCs to optimize the energy level alignment between the photoactive layer and the cathode contact, with the short-circuit current density (Jsc), open-circuit voltage (Voc), and fill factor (FF) all simultaneously improved with Hf(acac)4 CBL, leading to enhanced power conversion efficiencies (PCEs). Ultraviolet photoemission spectroscopy (UPS) and scanning Kelvin probe microscopy (SKPM) were performed to confirm that the interfacial dipoles were formed with the same orientation direction as the built-in potential between the photoactive layer and Hf(acac)4 CBL, benefiting the exciton separation and electron transport/extraction. In addition, the optical characteristics and surface morphology of the Hf(acac)4 CBL were also investigated.

  16. Zn (O,S) buffer layers by atomic layer deposition in Cu (In,Ga)Se2 based thin film solar cells: Band alignment and sulfur gradient

    NASA Astrophysics Data System (ADS)

    Platzer-Björkman, C.; Törndahl, T.; Abou-Ras, D.; Malmström, J.; Kessler, J.; Stolt, L.

    2006-08-01

    Thin film solar cells with the structure sodalimeglass /Mo/Cu(In,Ga)Se2/Zn(O,S)/ZnO/ZnO:Al are studied for varying thickness and sulfur content of the Zn (O,S) buffer layer. These Zn (O,S) layers were deposited by atomic layer deposition (ALD) at 120°C. Devices with no or small concentrations of sulfur in the buffer layer show low open-circuit voltages. This is explained by the cliff, or negative conduction-band offset (CBO), of -0.2eV measured by photoelectron spectroscopy (PES) and optical methods for the Cu (In,Ga)Se2 (CIGS)/ZnO interface. Devices with ZnS buffer layers exhibit very low photocurrent. This is expected from the large positive CBO (spike) of 1.2eV measured for the CIGS /ZnS interface. For devices with Zn (O,S) buffer layers, two different deposition recipes were found to yield devices with efficiencies equal to or above reference devices in which standard CdS buffer layers were used; ultrathin Zn (O,S) layers with S /Zn ratios of 0.8-0.9, and Zn (O,S) layers of around 30nm with average S /Zn ratios of 0.3. The sulfur concentration increases towards the CIGS interface as revealed by transmission electron microscopy and in vacuo PES measurements. The occurrence of this sulfur gradient in ALD-Zn (O,S) is explained by longer incubation time for ZnO growth compared to ZnS growth. For the Zn (O,S) film with high sulfur content, the CBO is large which causes blocking of the photocurrent unless the film is ultrathin. For the Zn (O,S) film with lower sulfur content, a CBO of 0.2eV is obtained which is close to ideal, according to simulations. Efficiencies of up to 16.4% are obtained for devices with this buffer layer.

  17. Simultaneous enhancement of photovoltage and charge transfer in Cu2O-based photocathode using buffer and protective layers

    NASA Astrophysics Data System (ADS)

    Li, Changli; Hisatomi, Takashi; Watanabe, Osamu; Nakabayashi, Mamiko; Shibata, Naoya; Domen, Kazunari; Delaunay, Jean-Jacques

    2016-07-01

    Coating n-type buffer and protective layers on Cu2O may be an effective means to improve the photoelectrochemical (PEC) water-splitting performance of Cu2O-based photocathodes. In this letter, the functions of the buffer layer and protective layer on Cu2O are examined. It is found that a Ga2O3 buffer layer can form a buried junction with Cu2O, which inhibits Cu2O self-reduction as well as increases the photovoltage through a small conduction band offset between the two semiconductors. The introduction of a TiO2 thin protective layer not only improves the stability of the photocathode but also enhances the electron transfer from the photocathode surface into the electrolyte, thus resulting in an increase in photocurrent at positive potentials. These results show that the selection of overlayers with appropriate conduction band positions provides an effective strategy for obtaining a high photovoltage and high photocurrent in PEC systems.

  18. Enhancing the blocking temperature of perpendicular-exchange biased Cr2O3 thin films using buffer layers

    NASA Astrophysics Data System (ADS)

    Shimomura, Naoki; Pati, Satya Prakash; Nozaki, Tomohiro; Shibata, Tatsuo; Sahashi, Masashi

    2017-02-01

    In this study, we investigated the effect of buffer layers on the blocking temperature (TB) of perpendicular exchange bias of thin Cr2O3/Co exchange coupled films with a Ru spacer and revealed a high TB of 260 K for 20-nm-thick Cr2O3 thin films. By comparing the TB values of the 20-nm-thick Cr2O3 films on Pt and α-Fe2O3 buffers, we investigated the lattice strain effect on the TB. We show that higher TB values can be obtained using an α-Fe2O3 buffer, which is likely because of the lattice strain-induced increase in Cr2O3 magnetocrystalline anisotropy.

  19. Electron channel mobility in silicon-doped Ga2O3 MOSFETs with a resistive buffer layer

    NASA Astrophysics Data System (ADS)

    Wong, Man Hoi; Sasaki, Kohei; Kuramata, Akito; Yamakoshi, Shigenobu; Higashiwaki, Masataka

    2016-12-01

    The electron mobility in depletion-mode lateral β-Ga2O3(010) metal-oxide-semiconductor field-effect transistors (MOSFETs) with an n-channel formed by Si-ion (Si+) implantation doping was extracted using low-field electrical measurements on FET structures. An undoped Ga2O3 buffer layer protected the channel against charge compensation by suppressing outdiffusion of deep Fe acceptors from the semi-insulating substrate. The molecular beam epitaxy growth temperature was identified as a key process parameter for eliminating parasitic conduction at the buffer/substrate growth interface. Devices with a resistive buffer showed room temperature channel mobilities of 90-100 cm2 V-1 s-1 at carrier concentrations of low- to mid-1017 cm-3, with small in-plane mobility anisotropy of 10-15% ascribable to anisotropic carrier scattering.

  20. Enhanced field emission from ZnO nanowire arrays utilizing MgO buffer between seed layer and silicon substrate

    NASA Astrophysics Data System (ADS)

    Chen, Si; Chen, Jiangtao; Liu, Jianlin; Qi, Jing; Wang, Yuhua

    2016-11-01

    Field emitters based on ZnO nanowires and other nanomaterials are promising high-brightness electron sources for field emission display, microscopy and other applications. The performance of a ZnO nanowire field emitter is linked to the quality, conductivity and alignment of the nanowires on a substrate, therefore requiring ways to improve these parameters. Here, ZnO nanowire arrays were grown on ZnO seed layer on silicon substrate with MgO buffer between the seed layer and Si. The turn-on field and enhancement factor of these nanowire arrays are 3.79 V/μm and 3754, respectively. These properties are improved greatly compared to those of ZnO nanowire arrays grown on ZnO seed layer without MgO buffer, which are 5.06 V/μm and 1697, respectively. The enhanced field emission properties can be attributed to better electron transport in seed layer, and better nanowire alignment because of MgO buffer.

  1. Aqueous Chemical Solution Deposition of Novel, Thick and Dense Lattice-Matched Single Buffer Layers Suitable for YBCO Coated Conductors: Preparation and Characterization

    PubMed Central

    Narayanan, Vyshnavi; Van Steenberge, Sigelinde; Lommens, Petra; Van Driessche, Isabel

    2012-01-01

    In this work we present the preparation and characterization of cerium doped lanthanum zirconate (LCZO) films and non-stoichiometric lanthanum zirconate (LZO) buffer layers on metallic Ni-5% W substrates using chemical solution deposition (CSD), starting from aqueous precursor solutions. La2Zr2O7 films doped with varying percentages of Ce at constant La concentration (La0.5CexZr1−xOy) were prepared as well as non-stoichiometric La0.5+xZr0.5−xOy buffer layers with different percentages of La and Zr ratios. The variation in the composition of these thin films enables the creation of novel buffer layers with tailored lattice parameters. This leads to different lattice mismatches with the YBa2Cu3O7−x (YBCO) superconducting layer on top and with the buffer layers or substrate underneath. This possibility of minimized lattice mismatch should allow the use of one single buffer layer instead of the current complicated buffer architectures such as Ni-(5% W)/LZO/LZO/CeO2. Here, single, crack-free LCZO and non-stoichiometric LZO layers with thicknesses of up to 140 nm could be obtained in one single CSD step. The crystallinity and microstructure of these layers were studied by XRD, and SEM and the effective buffer layer action was studied using XPS depth profiling.

  2. Probing temperature gradients within the GaN buffer layer of AlGaN/GaN high electron mobility transistors with Raman thermography

    SciTech Connect

    Hodges, C. Pomeroy, J.; Kuball, M.

    2014-02-14

    We demonstrate the ability of confocal Raman thermography using a spatial filter and azimuthal polarization to probe vertical temperature gradients within the GaN buffer layer of operating AlGaN/GaN high electron mobility transistors. Temperature gradients in the GaN layer are measured by using offset focal planes to minimize the contribution from different regions of the GaN buffer. The measured temperature gradient is in good agreement with a thermal simulation treating the GaN thermal conductivity as homogeneous throughout the layer and including a low thermal conductivity nucleation layer to model the heat flow between the buffer and substrate.

  3. Development of Buffer Layer Technologies for LWIR and VLWIR HgCdTe Integration on Si

    DTIC Science & Technology

    2007-11-02

    the-art HgCdTe films ) can only be achieved on a Si(211)B surface orientation. Since Si-based digital electronics utilizes the (100) orientation...for the large lattice mismatch (and crystallographic orientation change) are urgently needed to overcome these problems. Currently ZnTe/ CdTe ...technologies are based on i) the use of ultrathin, GeSi films as obedient buffers ii) wafer bonding of lattice-matched buffers. Summary of the most

  4. Investigations into alterntive substrate, absorber, and buffer layer processing for Cu(In,Ga)Se{sub 2}-based solar cells

    SciTech Connect

    Tuttle, J.R.; Berens, T.A.; Keane, J.

    1996-05-01

    High-performance Cu(In,Ga)Se{sub 2}(CIGS)-based solar cells are presently fabricated within a narrow range of processing options. In this contribution, alternative substrate, absorber, and buffer layer processing is considered. Cell performance varies considerably when alternative substrates are employed. These variations are narrowed with the addition of Na via a Na{sub 2}S compound. Sputtered and electrodeposited CIGS precursors and completed absorbers show promise as alternatives to evaporation. A recrystallization process is required to improve their quality. (In,Ga){sub y}Se buffer layers contribute to cell performance above 10. Further improvements in these alternatives will lead to combined cell performance greater than 10% in the near term.

  5. Chemical Bath Deposited Zinc Sulfide Buffer Layers for Copper Indium Gallium Sulfur-selenide Solar Cells and Device Analysis

    SciTech Connect

    Kundu, Sambhu N.; Olsen, Larry C.

    2005-01-03

    Cd free CIGSS thin film solar cell structures with a MgF2/TCO/CGD-ZnS/CIGSS/Mo/SLG structure have been fabricated using chemical bath deposited (CBD)-ZnS buffer layers and high quality CIGSS absorber layers supplied from Shell Solar Industries. The use of CBD-ZnS, which is a higher band gap materials than CdS, improved the quantum efficiency of fabricated cells at lower wavelengths, leading to an increase in short circuit current. The best cell to date yielded an active area (0.43 cm2) efficiency of 13.3%. This paper also presents a discussion of the issues relating to the use of the CBD-ZnS buffer materials for improving device performance.

  6. Advanced Architecture for Colloidal PbS Quantum Dot Solar Cells Exploiting a CdSe Quantum Dot Buffer Layer.

    PubMed

    Zhao, Tianshuo; Goodwin, Earl D; Guo, Jiacen; Wang, Han; Diroll, Benjamin T; Murray, Christopher B; Kagan, Cherie R

    2016-09-22

    Advanced architectures are required to further improve the performance of colloidal PbS heterojunction quantum dot solar cells. Here, we introduce a CdI2-treated CdSe quantum dot buffer layer at the junction between ZnO nanoparticles and PbS quantum dots in the solar cells. We exploit the surface- and size-tunable electronic properties of the CdSe quantum dots to optimize its carrier concentration and energy band alignment in the heterojunction. We combine optical, electrical, and analytical measurements to show that the CdSe quantum dot buffer layer suppresses interface recombination and contributes additional photogenerated carriers, increasing the open-circuit voltage and short-circuit current of PbS quantum dot solar cells, leading to a 25% increase in solar power conversion efficiency.

  7. Thermally robust perpendicular Co/Pd-based synthetic antiferromagnetic coupling enabled by a W capping or buffer layer.

    PubMed

    Lee, Ja-Bin; An, Gwang-Guk; Yang, Seung-Mo; Park, Hae-Soo; Chung, Woo-Seong; Hong, Jin-Pyo

    2016-02-18

    Perpendicularly magnetized tunnel junctions (p-MTJs) that contain synthetic antiferromagnetic (SAF) frames show promise as reliable building blocks to meet the demands of perpendicular magnetic anisotropy (PMA)-based spintronic devices. In particular, Co/Pd multilayer-based SAFs have been widely employed due to their outstanding PMA features. However, the widespread utilization of Co/Pd multilayer SAFs coupled with an adjacent CoFeB reference layer (RL) is still a challenge due to the structural discontinuity or intermixing that occurs during high temperature annealing. Thus, we address the thermally robust characteristics of Co/Pd multilayer SAFs by controlling a W layer as a potential buffer or capping layer. The W-capped Co/Pd multilayer SAF, which acts as a pinning layer, exhibited a wide-range plateau with sharp spin-flip and near-zero remanence at the zero field. Structural analysis of the W-capped multilayer SAF exhibited single-crystal-like c-axis oriented crystalline features after annealing at 400 °C, thereby demonstrating the applicability of these frames. In addition, when the W layer serving as a buffer layer in the Co/Pd multilayer SAF was coupled with a conventional CoFeB RL, higher annealing stability up to 425 °C and prominent antiferromagnetic coupling behavior were obtained.

  8. Thermally robust perpendicular Co/Pd-based synthetic antiferromagnetic coupling enabled by a W capping or buffer layer

    PubMed Central

    Lee, Ja-Bin; An, Gwang-Guk; Yang, Seung-Mo; Park, Hae-Soo; Chung, Woo-Seong; Hong, Jin-Pyo

    2016-01-01

    Perpendicularly magnetized tunnel junctions (p-MTJs) that contain synthetic antiferromagnetic (SAF) frames show promise as reliable building blocks to meet the demands of perpendicular magnetic anisotropy (PMA)-based spintronic devices. In particular, Co/Pd multilayer-based SAFs have been widely employed due to their outstanding PMA features. However, the widespread utilization of Co/Pd multilayer SAFs coupled with an adjacent CoFeB reference layer (RL) is still a challenge due to the structural discontinuity or intermixing that occurs during high temperature annealing. Thus, we address the thermally robust characteristics of Co/Pd multilayer SAFs by controlling a W layer as a potential buffer or capping layer. The W-capped Co/Pd multilayer SAF, which acts as a pinning layer, exhibited a wide-range plateau with sharp spin-flip and near-zero remanence at the zero field. Structural analysis of the W-capped multilayer SAF exhibited single-crystal-like c-axis oriented crystalline features after annealing at 400 °C, thereby demonstrating the applicability of these frames. In addition, when the W layer serving as a buffer layer in the Co/Pd multilayer SAF was coupled with a conventional CoFeB RL, higher annealing stability up to 425 °C and prominent antiferromagnetic coupling behavior were obtained. PMID:26887790

  9. Improving fatigue resistance of Pb(Zr,Ti)O3 thin films by using PbZrO3 buffer layers

    NASA Astrophysics Data System (ADS)

    Mensur Alkoy, Ebru; Uchiyama, Kiyoshi; Shiosaki, Tadashi; Alkoy, Sedat

    2006-05-01

    Ferroelectric Pb(Zr0.52Ti0.48)O3 (PZT) thin films with PbZrO3 (PZ) buffer layers were prepared on Pt(111)/Ti/SiO2/Si(100) substrates using a hybrid rf magnetron sputtering and sol-gel process. Texture of PZT films was found to depend on Pb content of PZ buffer layers. Buffered PZT films displayed comparable ferroelectric properties (2Pr=38-53 μC/cm2,2Ec=136-170 kV/cm) with unbuffered PZT. Asymmetric leakage current and fatigue behavior with superior fatigue resistance was observed in PZ buffered PZT compared to unbuffered films. PZ buffer layers were found to affect crystallization and texture of PZT, and act as a capacitive interface layer possibly blocking charge injection from electrodes.

  10. Atomically flat Ge buffer layers and alternating shutter growth of CaGe2 for large area germanane

    NASA Astrophysics Data System (ADS)

    Xu, Jinsong; Katoch, Jyoti; Ahmed, Adam; Pinchuk, Igor; Williams, Robert; McComb, David; Kawakami, Roland

    Germanane (GeH), which is converted from CaGe2 by soaking in HCl acid, has recently attracted interest because of its novel properties, such as large band gap (1.56eV), spin orbit coupling and predictions of high mobility (18000 cm2/Vs). Previously CaGe2 was successfully grown on Ge(111) substrates by molecular beam epitaxy (MBE) growth. But there were cracks between µm-sized islands, which is not desirable for scientific study and application, and limits the material quality. By growing atomically flat Ge buffer layers and using alternating shutter MBE growth, we are able to grow crack-free, large area films of CaGe2 films. Reflection high energy electron diffraction (RHEED) patterns of Ge buffer layer and CaGe2 indicates high quality two dimensional surfaces, which is further confirmed by atomic force microscopy (AFM), showing atomically flat and uniform Ge buffer layer and CaGe2. The appearance of Laue oscillation in X-ray diffraction (XRD) and Kiessig fringes in X-ray reflectivity (XRR) proves the uniformity of CaGe2 film and the smoothness of the interface. The high quality of CaGe2 film makes it promising to explore novel properties of GeH. Funded by NSF MRSEC DMR-1420451.

  11. Fabrication and electrochemical properties of insoluble fullerene-diamine adduct thin-films as buffer layer by alternate immersion process

    NASA Astrophysics Data System (ADS)

    Saito, Jo; Akiyama, Tsuyoshi; Suzuki, Atsushi; Oku, Takeo

    2017-01-01

    Insoluble fullerene-diamine adduct thin-films consisting of C60 and 1,2-diaminoethane were easily fabricated on an electrode by an alternate immersion process. Formation of the C60-diamine adduct films were confirmed using transmission absorption spectroscopy and atomic force microscopy. An inverted-type organic solar cells were fabricated by using the C60-diamine adduct film as the electron transport layer. The resultant photoelectric conversation performance of the solar cells suggested that photocurrent is generated via the photoexcitation of polythiophene. The result suggests that the present insoluble fullerene-diamine adduct films worked as buffer layer for organic thin-film solar cells.

  12. Enhanced Efficiency of Polymer Light-Emitting Diodes by Dispersing Dehydrated Nanotube Titanic Acid in the Hole-buffer Layer

    NASA Astrophysics Data System (ADS)

    Qian, L.; Xu, Z.; Teng, F.; Duan, X.-X.; Jin, Z.-S.; Du, Z.-L.; Li, F.-S.; Zheng, M.-J.; Wang, Y.-S.

    2007-06-01

    Efficiency of polymer light-emitting diodes (PLEDs) with poly(2-methoxy-5-(2-ethyl hexyloxy)- p-phenylene vinylene) (MEH-PPV) as an emitting layer was improved if a dehydrated nanotubed titanic acid (DNTA) doped hole-buffer layer polyethylene dioxythiophene (PEDOT) was used. Photoluminescence (PL) and Raman spectra indicated a stronger interaction between DNTA and sulfur atom in thiophene of PEDOT, which suppresses the chemical interaction between vinylene of MEH-PPV and thiophene of PEDOT. The interaction decreases the defect states in an interface region to result in enhancement in device efficiency, even though the hole transporting ability of PEDOT was decreased.

  13. The effects of the porous buffer layer and doping with dysprosium on internal stresses in the GaInP:Dy/por-GaAs/GaAs(100) heterostructures

    SciTech Connect

    Seredin, P. V.; Gordienko, N. N.; Glotov, A. V.; Zhurbina, I. A.; Domashevskaya, E. P.; Arsent'ev, I. N. Shishkov, M. V.

    2009-08-15

    In structures with a porous buffer layer, residual internal stresses caused by a mismatch between the crystal-lattice parameters of the epitaxial GaInP alloy and the GaAs substrate are redistributed to the porous layer that acts as a buffer and is conducive to disappearance of internal stresses. Doping of the epitaxial layer with dysprosium exerts a similar effect on the internal stresses in the film-substrate structure.

  14. Y1Ba2Cu3O(6+delta) growth on thin Y-enhanced SiO2 buffer layers on silicon

    NASA Technical Reports Server (NTRS)

    Robin, T.; Mesarwi, A.; Wu, N. J.; Fan, W. C.; Espoir, L.; Ignatiev, A.; Sega, R.

    1991-01-01

    SiO2 buffer layers as thin as 2 nm have been developed for use in the growth of Y1Ba2Cu3O(6+delta) thin films on silicon substrates. The SiO2 layers are formed through Y enhancement of silicon oxidation, and are highly stoichiometric. Y1Ba2Cu3O(6+delta) film growth on silicon with thin buffer layers has shown c orientation and Tc0 = 78 K.

  15. Enhancement of perpendicular magnetic anisotropy and coercivity in ultrathin Ru/Co/Ru films through the buffer layer engineering

    NASA Astrophysics Data System (ADS)

    Kolesnikov, Alexander G.; Stebliy, Maxim E.; Ognev, Alexey V.; Samardak, Alexander S.; Fedorets, Aleksandr N.; Plotnikov, Vladimir S.; Han, Xiufeng; Chebotkevich, Ludmila A.

    2016-10-01

    We present results on a study of the interplay between microstructure and the magnetic properties of ultrathin Ru/Co/Ru films with perpendicular magnetic anisotropy (PMA). To induce PMA in the Co layer, we experimentally determined thicknesses of the buffer and capping layers of Ru. The maximum value of PMA was observed for the Co thickness of 0.9 nm with the 3 nm thick capping layer. The effective anisotropy field (H eff) and coercive force (H c) of the Co layer are very sensitive to the Ru buffer layer thickness (t b). The values of H eff and H c increase approximately by two and ten times, correspondingly, when t b changes from 6 to 20 nm, owing to an increase in volume fraction of the crystalline phase as a result of the grains’ growth. PMA is found to be mainly enhanced by elastic strains induced by the lattice mismatch on the Ru/Co and Co/Ru interfaces, leading to the deformation of the Co lattice. The surface impact is determined to be less than 10% of the magneto-elastic contribution to the effective anisotropy. Observation of the magnetic domain structure by means of polar Kerr microscopy reveals that out-of-plane magnetization reversal occurs through the nucleation, growth, and annihilation of domains, where the average size drastically rises with the increasing t b.

  16. High rate buffer layer for IBAD MgO coated conductors

    DOEpatents

    Foltyn, Stephen R.; Jia, Quanxi; Arendt, Paul N.

    2007-08-21

    Articles are provided including a base substrate having a layer of an oriented material thereon, and, a layer of hafnium oxide upon the layer of an oriented material. The layer of hafnium oxide can further include a secondary oxide such as cerium oxide, yttrium oxide, lanthanum oxide, scandium oxide, calcium oxide and magnesium oxide. Such articles can further include thin films of high temperature superconductive oxides such as YBCO upon the layer of hafnium oxide or layer of hafnium oxide and secondary oxide.

  17. Chemically deposited La2Zr2O7 buffer layers for YBCO-coated conductors: film growth and microstructure

    NASA Astrophysics Data System (ADS)

    Molina, L.; Knoth, K.; Engel, S.; Holzapfel, B.; Eibl, O.

    2006-11-01

    An adequate buffer layer architecture is of great importance for YBa2Cu3O7-δ (YBCO)-coated conductor fabrication. We present a transmission electron microscopy (TEM) analysis of La2Zr2O7 (LZO) buffer layers on biaxially textured Ni-5 at.%W substrates for YBCO-coated conductors prepared by chemical solution deposition (CSD). The LZO thin films were heat-treated at 900 and 1050 °C respectively. Electron diffraction patterns, and bright and dark-field images were used to determine the microstructure, texture and the nanoporosity of the films. By x-ray diffraction the films were found to be [100] oriented and strongly biaxially textured. Although x-ray diffraction suggests an epitaxial growth of LZO on Ni it was shown by TEM that this was not the case. The grain size of the films is between 100 and 300 nm and therefore much smaller than the Ni grain size of 40 µm. Appropriate acquisition conditions for scanning electron microscopy (SEM) and TEM imaging are given to identify the nanogranularity of the films. For the film annealed at 1050 °C high-resolution SEM images clearly show a polycrystalline LZO microstructure and the grain size can readily be determined. Electron diffraction rings are more pronounced than for the film annealed at 900 °C, indicating a higher level of polycrystallinity in the film. SEM images of the film annealed at 900 °C yield no evidence of a polycrystalline microstructure; only single misoriented LZO grains separated by 500 nm are observed. Nanovoids 10-40 nm in size were found in the LZO buffer layers with a high density. The voids had approximately cuboid shape, indicating an anisotropy of the surface energy in LZO. The surface planes of the voids were identified as {111} lattice planes. Despite the nanoporosity, which is a typical feature of CSD-grown buffer layers, the LZO buffer layers act as efficient Ni diffusion barriers. Energy dispersive x-ray microanalysis (EDX) in the transmission electron microscope yielded the composition of

  18. Surface passivation and interface properties of bulk GaAs and epitaxial-GaAs/Ge using atomic layer deposited TiAlO alloy dielectric.

    PubMed

    Dalapati, G K; Chia, C K; Tan, C C; Tan, H R; Chiam, S Y; Dong, J R; Das, A; Chattopadhyay, S; Mahata, C; Maiti, C K; Chi, D Z

    2013-02-01

    High quality surface passivation on bulk-GaAs substrates and epitaxial-GaAs/Ge (epi-GaAs) layers were achieved by using atomic layer deposited (ALD) titanium aluminum oxide (TiAlO) alloy dielectric. The TiAlO alloy dielectric suppresses the formation of defective native oxide on GaAs layers. X-ray photoelectron spectroscopy (XPS) analysis shows interfacial arsenic oxide (As(x)O(y)) and elemental arsenic (As) were completely removed from the GaAs surface. Energy dispersive X-ray diffraction (EDX) analysis and secondary ion mass spectroscopy (SIMS) analysis showed that TiAlO dielectric is an effective barrier layer for reducing the out-diffusion of elemental atoms, enhancing the electrical properties of bulk-GaAs based metal-oxide-semiconductor (MOS) devices. Moreover, ALD TiAlO alloy dielectric on epi-GaAs with AlGaAs buffer layer realized smooth interface between epi-GaAs layers and TiAlO dielectric, yielding a high quality surface passivation on epi-GaAs layers, much sought-after for high-speed transistor applications on a silicon platform. Presence of a thin AlGaAs buffer layer between epi-GaAs and Ge substrates improved interface quality and gate dielectric quality through the reduction of interfacial layer formation (Ga(x)O(y)) and suppression of elemental out-diffusion (Ga and As). The AlGaAs buffer layer and TiAlO dielectric play a key role to suppress the roughening, interfacial layer formation, and impurity diffusion into the dielectric, which in turn largely enhances the electrical property of the epi-GaAs MOS devices.

  19. A nanoporous AlN layer patterned by anodic aluminum oxide and its application as a buffer layer in a GaN-based light-emitting diode.

    PubMed

    Chen, Lung-Chien; Wang, Chih-Kai; Huang, Jenn-Bin; Hong, Lu-Sheng

    2009-02-25

    This work investigates a nanoporous aluminum nitride (AlN) layer prepared using an anodic aluminum oxide (AAO) process and its application as a buffer layer for a GaN-based light-emitting diode (LED) fabricated on sapphire substrate. Following this AAO process, the average pore spacing and pore diameter of the nanoporous AlN layer were in the ranges 180-200 nm and 100-150 nm, respectively. The light output power of the GaN-based LED with a nanoporous AlN layer was about 53% higher than that of a GaN-based LED without a nanoporous AlN layer at an injection current of 20 mA. At an injection current of 80 mA, the light output power was increased by about 34%.

  20. Cd-free CIGS solar cells with buffer layer based on the In2S3 derivatives.

    PubMed

    Kim, Kihwan; Larina, Liudmila; Yun, Jae Ho; Yoon, Kyung Hoon; Kwon, HyukSang; Ahn, Byung Tae

    2013-06-21

    This study guided by device evaluations was conducted to reveal the reasons for the loss of the photo-generated carriers in CIGS cells with the buffer based on In2S3 derivatives. Chemical bath deposited Inx(OOH,S)y films have been employed as a Cd-free buffer layers. When compared to solar cells with CdS buffer layer, the Cu0.9(In0.7,Ga0.3)Se2.1 (Eg = 1.18 eV) cells with the Inx(OOH,S)y buffer exhibited strong voltage-dependent carrier collection and poor spectral response above 500 nm, presumably, due to energy barrier at the junction. In order to improve the charge collection by upward shift of the conduction band minimum of CIGS absorber, Inx(OOH,S)y/Cu0.9(In0.55,Ga0.45)Se2.1 (Eg = 1.30 eV) solar cells were also fabricated and their spectral responses were examined. When compared to the Cu0.9(In0.7,Ga0.3)Se2.1 cells, the improved spectral response and voltage dependent carrier collection were obtained. Nevertheless, considerable loss in charge collection above 500 nm was still observed. The efficiency reached 9.3% while the Cu0.9(In0.7,Ga0.3)Se2.1 cell exhibited only the efficiency of 3.4%. Finally, CIGS (Eg = 1.18 eV) solar cells with n-ZnO/i-ZnO/Inx(OOH,S)y/CdS/CIGS and n-ZnO/i-ZnO/CdS/Inx(OOH,S)y/CIGS configurations were fabricated. The influence of the TCO/buffer interface on the device characteristics was also addressed by means of comparison between the characteristics of two cells employing different interfaces. A 13.0% efficient cell has been achieved from n-ZnO/i-ZnO/CdS/Inx(OOH,S)y/CIGS configuration. The obtained data suggested that the limitation of the device efficiency was mainly related to the i-ZnO/Inx(OOH,S)y interface. The experimental results provide the knowledge base for further optimization of the interface properties to form high-quality p-n junction in the CIGS solar cells employing the CBD In2S3 buffer layer.

  1. Preparation of SmBiO3 buffer layer on YSZ substrate by an improved chemical solution deposition route

    NASA Astrophysics Data System (ADS)

    Zhu, Xiaolei; Pu, Minghua; Zhao, Yong

    2016-12-01

    A quick route for chemical solution deposition (CSD) has been developed to prepare SmBiO3 (SBO) layers on yttria stabilized zirconia (YSZ) substrates rapidly by using of solid state decomposition (SSD) technique. The proper conditions for volatilization of lactic acid, which as solvent in precursor coated layer, and SBO growth are 115°C for 30 min and 794°C for 60 min in flowing Ar gas. The coated layers are amorphous structure of mixture oxides and quasi-crystal structure of SBO before and after growth, respectively. The total time by this quick CSD route for organic solvent volatilization, salts decomposed and layer growth is not up to 2 h, which are much less than that needed for traditional CSD of over 10 h. SBO layer is directly epitaxial growth on YSZ substrate without any lattice rotation. SBO layer prepared by this quick route as well as that by traditional route are suitable for the growth of YBCO. The superconducting transition temperature and critical current density of the coated YBCO layer on SBO/YSZ obtained by this quick route are up to 90 K and 1.66 MA/cm2. These results may be the usable reference for continuous preparation of SBO buffer layer on IBAD-YSZ/Ni-based alloy tapes.

  2. Ferroelectric properties of multi-layer LiTaO 3 thin films with Ta IIO 5 buffer

    NASA Astrophysics Data System (ADS)

    Zhang, De-Yin; Peng, Wei-Dong; Li, Jin-Hua; Li, Kun; Huang, Da-Gui

    2007-12-01

    The new sol-gel derived multi-layer LiTaO 3 thin films with Ta IIO 5 buffer layer were prepared on Pt/Ti/SiO2/Si substrate using lithium ethoxide and tantalum ethoxide as starting materials. The sol of Ta IIO 5 was firstly covered on the substrate by spin coating at 6500rpm for 50s and then a rapid annealing at 650°C for 2min to form an about 20nm thick Ta IIO 5 buffer layer. Multi-layer LiTaO 3 thin films were made over Ta IIO 5 buffer by repeated spin coating at 4000rpm for 30s and then a rapid annealing process at 700°C for 3min. The spectrum of XRD show the crystalline orientation of thin film type Ta IIO 5 is different compared to powder type Ta IIO 5. The SEM micrograph of the cross section shows the prepared sample is uniform, smooth and crack-free on the surface and the thickness of LiTaO 3 thin film is 0.341μm. The ferroelectric hysteresis loop and leakage current of the prepared sample have been measured using Al/LiTaO 3/Ta IIO 5/Pt structure electrode by a ferroelectric material analyzer PLC-100. The remanent polarization and coercive field of the prepared sample polarized at 13V were 3.4μC/cm2 and 185kV/cm respectively. The leakage current of the prepared sample was 2.66x10 -7A at 71.43kV/cm .Experimental results show the prepared sample of LiTaO 3 thin film with Ta IIO 5 buffer has good ferroelectric properties. Ta IIO 5 buffer introduction between LiTaO 3 thin film and Pt substrate can effectively decrease the leakage current and improve the properties of uncooled LiTaO 3 infrared device.

  3. Crack-free thick (∼5 µm) α-Ga2O3 films on sapphire substrates with α-(Al,Ga)2O3 buffer layers

    NASA Astrophysics Data System (ADS)

    Oda, Masaya; Kaneko, Kentaro; Fujita, Shizuo; Hitora, Toshimi

    2016-12-01

    To obtain crack-free thick α-Ga2O3 films on sapphire substrates, effects and behaviors of buffer layers have been investigated. With the growth of an α-Ga2O3 layer, there appeared an unintentionally formed layer in the sample, which was associated with stress accumulation and could be the seed for crack generation. We obtained a thick (∼5 µm) α-Ga2O3 layer on a sapphire substrate with the insertion of α-(Al0.12Ga0.88)2O3/α-(Al0.02Ga0.98)2O3 buffer layers, and for this sample, we did not observe the intermediate layer, suggesting that the buffer layers were effective for eliminating the stress accumulation at the α-Ga2O3/sapphire interface region.

  4. Photovoltaic properties of Cu2ZnSnS4 cells fabricated using ZnSnO and ZnSnO/CdS buffer layers

    NASA Astrophysics Data System (ADS)

    Tajima, Shin; Umehara, Mitsutaro; Mise, Takahiro

    2016-11-01

    To improve the photovoltaic properties of Cu2ZnSnS4 (CZTS) photovoltaic cells, we investigated the use of novel buffer layer materials. We found that Zn1- x Sn x O y fabricated by atomic layer deposition functioned as an effective buffer layer. The short-circuit current density increased by 10% because of a decrease in the absorption loss in the short-wavelength region. With Zn0.70Sn0.30O y layers, the conversion efficiency was 5.7%. To reduce interface recombination, a thin CdS layer was inserted between the ZnSnO and CZTS layers. The CZTS cells fabricated using ZnSnO/CdS double buffer layers showed a high open-circuit voltage of 0.81 V.

  5. THz laser based on quasi-periodic AlGaAs superlattices

    SciTech Connect

    Malyshev, K V

    2013-06-30

    The use of quasi-periodic AlGaAs superlattices as an active element of a quantum cascade laser of terahertz range is proposed and theoretically investigated. A multi-colour emission, having from three to six peaks of optical gain, is found in Fibonacci, Thue-Morse, and figurate superlattices in electric fields of intensity F = 11 - 13 kV cm{sup -1} in the frequency range f = 2 - 4 THz. The peaks depend linearly on the electric field, retain the height of 20 cm{sup -1}, and strongly depend on the thickness of the AlGaAs-layers. (lasers)

  6. Molecular beam epitaxy growth of SrO buffer layers on graphite and graphene for the integration of complex oxides

    NASA Astrophysics Data System (ADS)

    Ahmed, Adam S.; Wen, Hua; Ohta, Taisuke; Pinchuk, Igor V.; Zhu, Tiancong; Beechem, Thomas; Kawakami, Roland K.

    2016-08-01

    We report the successful growth of high-quality SrO films on highly-ordered pyrolytic graphite (HOPG) and single-layer graphene by molecular beam epitaxy. The SrO layers have (001) orientation as confirmed by X-ray diffraction (XRD) while atomic force microscopy measurements show continuous pinhole-free films having rms surface roughness of <1.5 Å. Transport measurements of exfoliated graphene after SrO deposition show a strong dependence between the Dirac point and Sr oxidation. Subsequently, the SrO is leveraged as a buffer layer for more complex oxide integration via the demonstration of (001) oriented SrTiO3 grown atop a SrO/HOPG stack.

  7. Molecular beam epitaxy growth of SrO buffer layers on graphite and graphene for the integration of complex oxides

    SciTech Connect

    Ahmed, Adam S.; Wen, Hua; Ohta, Taisuke; Pinchuk, Igor V.; Zhu, Tiancong; Beechem, Thomas; Kawakami, Roland K.

    2016-04-27

    Here, we report the successful growth of high-quality SrO films on highly-ordered pyrolytic graphite (HOPG) and single-layer graphene by molecular beam epitaxy. The SrO layers have (001) orientation as confirmed by X-ray diffraction (XRD) while atomic force microscopy measurements show continuous pinhole-free films having rms surface roughness of <1.5 Å. Moreover, transport measurements of exfoliated graphene, after SrO deposition, show a strong dependence between the Dirac point and Sr oxidation. As a result, the SrO is leveraged as a buffer layer for more complex oxide integration via the demonstration of (001) oriented SrTiO3 grown atop a SrO/HOPG stack.

  8. Surface electronic structure of ZrB2 buffer layers for GaN growth on Si wafers

    NASA Astrophysics Data System (ADS)

    Yamada-Takamura, Yukiko; Bussolotti, Fabio; Fleurence, Antoine; Bera, Sambhunath; Friedlein, Rainer

    2010-08-01

    The electronic structure of epitaxial, predominantly single-crystalline thin films of zirconium diboride (ZrB2), a lattice-matching, conductive ceramic to GaN, grown on Si(111) was studied using angle-resolved ultraviolet photoelectron spectroscopy. The existence of Zr-derived surface states dispersing along the Γ¯-M¯ direction indicates a metallic character provided by a two-dimensional Zr-layer at the surface. Together with the measured work function, the results demonstrate that the surface electronic properties of such thin ZrB2(0001) buffer layers are comparable to those of the single crystals promising excellent conduction between nitride layers and the substrate in vertical light-emitting diodes on economic substrates.

  9. Microstructures of GaN Buffer Layers Grown on Si(111) Using Rapic Thermal Process Low-Pressure Metalorganic Chemical Vapor Deposition

    NASA Astrophysics Data System (ADS)

    Peng, Chen; Bo, Shen; Jian-Min, Zhu; Zhi-Zhong, Chen; Yu-Gang, Zhou; Shi-Yong, Xie; Rong, Zhang; Ping, Han; Shu-Lin, Gu; You-Dou, Zheng; Shu-Sheng, Jiang; Duan, Feng; Z, Huang C.

    2000-03-01

    Microstructures of GaN buffer layers grown on Si (111) substrates using rapid thermal process low-pressure metalorganic chemical vapor deposition are investigated by an atomic force microscope (AFM) and a high-resolution transmission electron microscope (HRTEM). AFM images show that the islands appear in the GaN buffer layer after annealing at high temperature. Cross-sectional HRTEM micrographs of the buffer region of these samples indicate that there are bunched steps on the surface of the Si substrate and a lot of domains in GaN misorienting each other with small angles. The boundaries of those domains locate near the bunched steps, and the regions of the film on a terrace between steps have the same crystal orientation. An amorphous-like layer, about 3 nm thick, can also be observed between the GaN buffer layer and the Si substrate.

  10. TEM study of dislocations structure in In0.82Ga0.18As/InP heterostructure with InGaAs as buffer layer

    NASA Astrophysics Data System (ADS)

    Zhao, Liang; Guo, Zuo-xing; Yuan, De-zeng; Wei, Qiu-lin; Zhao, Lei

    2016-05-01

    In order to improve the quality of detector, In x Ga1- x As ( x=0.82) buffer layer has been introduced in In0.82Ga0.18As/InP heterostructure. Dislocation behavior of the multilayer is analyzed through plane and cross section [110] by transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM). The dislocations are effectively suppressed in In x Ga1- x As ( x=0.82) buffer layer, and the density of dislocations in epilayer is reduced obviously. No lattice mismatch between buffer layer and epilayer results in no misfit dislocation (MD). The threading dislocations (TDs) are directly related to the multiplication of the MDs in buffer layer.

  11. The effect of employing the p/i buffer layers and in-situ hydrogen treatment for transparent a-Si:H solar cells.

    PubMed

    Lee, Da Jung; Yun, Sun Jin; Park, Min A; Lim, Jung Wook

    2014-05-01

    In this study, we describe the effects of various thicknesses of triple p/i buffer layers and hydrogen treatment on various performances in the fabrication of transparent a-Si:H solar cells. For the increment of buffer layer thickness, V(oc) increases steadily and J(sc) firstly increases and then decreases. The triple buffer layers also enhance the transmittance as well as conversion efficiency. For hydrogen plasma treatment, overall performances were enhanced with plasma power due to the passivation of dangling bonds at p/i interface. Therefore, the usage of triple buffer layers with proper treatment is beneficial to obtaining transparent a-Si:H solar cells with high quality.

  12. Superconducting, surface and interface properties of Ho(123) and Bi(2212) films on sapphire with cerium oxide buffer layers

    NASA Astrophysics Data System (ADS)

    Castro, L. F.; Suryanarayanan, R.; Das, A.; Bacca, E.; Gómez, M. E.; Lopera, W.; Prieto, P.; Kreisler, A.; Martin, J. C.

    1995-09-01

    We report on the X-ray diffraction, secondary ion mass spectrometry, and atomic force microscopy on Ho(123) and Bi(2212) films dc sputtered in pure oxygen atmosphere onto heated sapphire substrates with CeO 2 buffer layers. The films were c-axis oriented. The Ho(123) films had a T c of 88 K but had a relatively high room temperature resistivity of 400 μΩcm. The Bi(2212) films showed a broad transition and a low T c of 46 K. The data may be explained by a certain amount of Al diffusion and inhomogenous grain growth.

  13. Improved properties of barium strontium titanate thin films grown on copper foils by pulsed laser deposition using a self-buffered layer.

    SciTech Connect

    Liu, S.; Ma, B.; Narayanan, M.; Balachandran, U.

    2012-01-01

    Ba{sub 0.6}Sr{sub 0.4}TiO{sub 3} (BST) films were deposited by pulsed laser deposition on copper foils with low-temperature self-buffered layers. The deposition conditions included a low oxygen partial pressure and a temperature of 700 C to crystallize the films without the formation of secondary phases and substrate oxidation. The results from x-ray diffraction and scanning electron microscopy indicated that the microstructure of the BST films strongly depended on the growth temperature. The use of the self-buffered layer improved the dielectric properties of the deposited BST films. The leakage current density of the BST films on the copper foil was 4.4 x 10{sup -9} A cm{sup -2} and 3.3 x 10{sup -6} A cm{sup -2} with and without the self-buffered layer, respectively. The ferroelectric hysteresis loop for the BST thin film with buffer layer was slim, in contrast to the distorted loop observed for the film without the buffer layer. The permittivity (7 0 0) and dielectric loss tangent (0.013) of the BST film on the copper foil with self-buffered layer at room temperature were comparable to those of the film on metal and single-crystal substrates.

  14. Epitaxial growth of BaHfO3 buffer layer and its structure degeneration analysed by Raman spectrum.

    PubMed

    Zheng, Jiahui; Fan, Feng; Yan, Xiangfa; Lu, Yuming; Liang, Yu; Bai, Chuanyi; Liu, Zhiyong; Guo, Yanqun; Cai, Chuanbing

    2016-01-01

    BaHfO3 (BHO) has been proposed as a new cap layer material for YBa2Cu3O7-δ (YBCO) coated conductors. Highly c-axis oriented BHO cap layer has been deposited on ion-beam assisted deposition-MgO buffered Hastelloy tapes by direct-current-magnetron sputtering method. The epi-growth of BHO films combined with its properties is investigated in details. The degenerated cubic crystal structure of BHO film is confirmed by Raman spectrum analysis. XRD θ-2θ scan, φ-scan and ω-scan reveal an excellent c-axis alignment with good in-plane and out-of-plane textures for BHO cap layers. SEM and AFM investigations show BHO cap layer a dense and crack-free morphology. Subsequently pure c-axis orientation YBCO film was epitaxial grown on such BHO cap layer successfully, shown BaHfO3 a potential cap layer material for coated conductors.

  15. The role of hydrogenated amorphous silicon oxide buffer layer on improving the performance of hydrogenated amorphous silicon germanium single-junction solar cells

    NASA Astrophysics Data System (ADS)

    Sritharathikhun, Jaran; Inthisang, Sorapong; Krajangsang, Taweewat; Krudtad, Patipan; Jaroensathainchok, Suttinan; Hongsingtong, Aswin; Limmanee, Amornrat; Sriprapha, Kobsak

    2016-12-01

    Hydrogenated amorphous silicon oxide (a-Si1-xOx:H) film was used as a buffer layer at the p-layer (μc-Si1-xOx:H)/i-layer (a-Si1-xGex:H) interface for a narrow band gap hydrogenated amorphous silicon germanium (a-Si1-xGex:H) single-junction solar cell. The a-Si1-xOx:H film was deposited by plasma enhanced chemical vapor deposition (PECVD) at 40 MHz in a same processing chamber as depositing the p-type layer. An optimization of the thickness of the a-Si1-xOx:H buffer layer and the CO2/SiH4 ratio was performed in the fabrication of the a-Si1-xGex:H single junction solar cells. By using the wide band gap a-Si1-xOx:H buffer layer with optimum thickness and CO2/SiH4 ratio, the solar cells showed an improvement in the open-circuit voltage (Voc), fill factor (FF), and short circuit current density (Jsc), compared with the solar cells fabricated using the conventional a-Si:H buffer layer. The experimental results indicated the excellent potential of the wide-gap a-Si1-xOx:H buffer layers for narrow band gap a-Si1-xGex:H single junction solar cells.

  16. The effect of h-BN buffer layers in bilayer graphene on Co (111)

    NASA Astrophysics Data System (ADS)

    Li, Can; Liu, Yan; Zhang, Bin; Wang, Tao; Guo, Qing; Sheng, Kuang; Yin, You

    2015-05-01

    Understanding of the interface of Co/graphene is essential for applications of graphene-based devices, as well as in the process of graphene synthesis. In this paper, the Co/graphene interface, including five structures of bilayer graphene (BLG) on Co (111) surface with bilayer or monolayer BN buffer sheets, is investigated by using density functional theory calculations. The corresponding atomic and electronic structures and Mulliken charge populations are also analyzed. The bilayer BN sheets are found to be the thinnest insulator for the backside Co metal gate, which shields BLG from Co substrate pining, decreases the charges influenced by the substrate, and improves BLG transport mobility.

  17. Distortions to current-voltage curves of cigs cells with sputtered Zinc(Oxygen,Sulfur) buffer layers

    NASA Astrophysics Data System (ADS)

    Song, Tao

    Sputtered-deposited Zn(O,S) is an attractive alternative to CdS for Cu(In,Ga)Se 2 (CIGS) thin-film solar cells' buffer layer. It has a higher band gap and thus allows greater blue photon collection to achieve higher photon current. The primary goal of the thesis is to investigate the effects of the secondary barrier at the buffer-absorber interface on the distortions to current-voltage (J-V) curves of sputtered-Zn(O,S)/CIGS solar cells. A straightforward photodiode model is employed in the numerical simulation to explain the physical mechanisms of the experimental J-V distortions including J-V crossover and red kink. It is shown that the secondary barrier is influenced by both the internal material properties, such as the conduction-band offset (CBO) and the doping density of Zn(O,S), and the external conditions, such as the light intensity and operating temperature. A key parameter for the sputter deposition of Zn(O,S) has been the oxygen fraction in the argon beam. It is found that the CBO varies with the oxygen fraction in the argon beam at a fixed temperature. With a greater CBO (DeltaEC>0.3 eV), the resulting energy barrier limits the electron current flowing across the interface and thus leads to the J-V distortion. Two different ZnS targets, non-indium and indium-doped one, were used to deposit the Zn(O,S) buffer layer. At the same oxygen fraction in argon beam, a non-In-doped Zn(O,S) buffer with a smaller amount of doping forms a greater secondary barrier to limit the electron current due to the compensation of the Zn(O,S) buffer layer. In addition, the temperature-dependent J-V crossover can be explained by the temperature-dependent impact of the secondary barrier - at lower temperature in the dark, the maximum distortion-free barrier is reduced and results in a more serious current limitation, indicating a greater J-V crossover. It is also found that, under low-intensity illumination, there is a lower doping density of Zn(O,S) due to a smaller amount of

  18. Development of mid-frequency AC reactive magnetron sputtering for fast deposition of Y2O3 buffer layers

    NASA Astrophysics Data System (ADS)

    Xiong, Jie; Xia, Yudong; Xue, Yan; Zhang, Fei; Guo, Pei; Zhao, Xiaohui; Tao, Bowan

    2014-02-01

    A reel-to-reel magnetron sputtering system with mid-frequency alternating current (AC) power supply was used to deposit double-sided Y2O3 seed layer on biaxially textured Ni-5 at.%W tape for YBa2Cu3O7-δ coated conductors. A reactive sputtering process was carried out using two opposite symmetrical sputtering guns with metallic yttrium targets and water vapor for oxidizing the sputtered metallic atoms. The voltage control mode of the power supply was used and the influence of the cathode voltage and ArH2 pressure were systematically investigated. Subsequently yttrium-stabilized zirconia (YSZ) barrier and CeO2 cap layers were deposited on the Y2O3 buffered substrates in sequence, indicating high quality and uniform double-sided structure and surface morphology of such the architecture.

  19. DEVELOPMENT OF IN-SITU CONTROL DIAGNOSTICS FOR APPLICATION OF EPITAXIAL SUPERCONDUCTOR AND BUFFER LAYERS

    SciTech Connect

    B.C. Winkleman; T.V. Giel, Jr.; J. Cunningham

    1999-06-30

    The recent achievements of critical currents in excess of 1x10{sup 6}amp/cm{sup 2} at 77K in YBCO deposited over suitably textured buffer/substrate composites have stimulated interest in the potential fabrication of these coated conductors as wire. Numerous approaches and manufacturing schemes for producing coated conductor wire are currently being developed. Recently, under the U. S. Department of Energy (DOE's) sponsorship, the University of Tennessee Space Institute (UTSI) performed an extensive evaluation of leading coated conductor processing options. In general, it is our feeling that the science and chemistry that are being developed in the coated conductor wire program now need proper engineering evaluation to define the most viable options for a commercial fabrication process. All fabrication processes will need process control measurements. This report provides a specific review of the needs and available technologies for process control for many of the coated conductor processing options. This report also addresses generic process monitoring areas in which additional research and development is needed. The concentration is on the two different approaches for obtaining the textured substrates that have been identified as viable candidates. These are the Los Alamos National Laboratory's (LANL) ion-beam assisted deposition, called IBAD, to obtain a highly textured yttria-stabilized zirconia (YSZ) buffer on nickel alloy strips, and Oak Ridge National Laboratory's (ORNL) rolling assisted, bi-axially textured substrate option called RABiTS{trademark}.

  20. Development of in-situ control diagnostics for application of epitaxial superconductor and buffer layers

    SciTech Connect

    B.C. Winkleman; T.V. Giel; Jason Cunningham

    1999-07-30

    The recent achievements of critical currents in excess of 1 x 10{sup 6} amp/cm{sup 2} at 77 K in YBCO deposited over suitably textured buffer/substrate composites have stimulated interest in the potential fabrication of these coated conductors as wire. Numerous approaches and manufacturing schemes for producing coated conductor wire are currently being developed. Recently, under the US DOE's sponsorship, the University of Tennessee Space Institute performed an extensive evaluation of leading coated conductor processing options. In general, it is their feeling that the science and chemistry that are being developed in the coated conductor wire program now need proper engineering evaluation to define the most viable options for a commercial fabrication process. All fabrication processes will need process control measurements. This report provides a specific review of the needs and available technologies for process control for many of the coated conductor processing options. This report also addresses generic process monitoring areas in which additional research and development is needed. The concentration is on the two different approaches for obtaining the textured substrates that have been identified as viable candidates. These are the Los Alamos National Laboratory's ion-beam assisted deposition, called IBAD, to obtain a highly textured yttria-stabilized zirconia (YSZ) buffer on nickel alloy strips, and Oak Ridge National Laboratory's rolling assisted, bi-axially textured substrate option called RABiTS{trademark}.

  1. Study of the effects of GaN buffer layer quality on the dc characteristics of AlGaN/GaN high electron mobility transistors

    DOE PAGES

    Ahn, Shihyun; Zhu, Weidi; Dong, Chen; ...

    2015-04-21

    Here we studied the effect of buffer layer quality on dc characteristics of AlGaN/GaN high electron mobility (HEMTs). AlGaN/GaN HEMT structures with 2 and 5 μm GaN buffer layers on sapphire substrates from two different vendors with the same Al concentration of AlGaN were used. The defect densities of HEMT structures with 2 and 5 μm GaN buffer layer were 7 × 109 and 5 × 108 cm₋2, respectively, as measured by transmission electron microscopy. There was little difference in drain saturation current or in transfer characteristics in HEMTs on these two types of buffer. However, there was no dispersionmore » observed on the nonpassivated HEMTs with 5 μm GaN buffer layer for gate-lag pulsed measurement at 100 kHz, which was in sharp contrast to the 71% drain current reduction for the HEMT with 2 μm GaN buffer layer.« less

  2. Study of the effects of GaN buffer layer quality on the dc characteristics of AlGaN/GaN high electron mobility transistors

    SciTech Connect

    Ahn, Shihyun; Zhu, Weidi; Dong, Chen; Le, Lingcong; Hwang, Ya-Hsi; Kim, Byung-Jae; Ren, Fan; Pearton, Stephen J.; Lind, Aaron G.; Jones, Kevin S.; Kravchenko, I. I.; Zhang, Ming-Lan

    2015-04-21

    Here we studied the effect of buffer layer quality on dc characteristics of AlGaN/GaN high electron mobility (HEMTs). AlGaN/GaN HEMT structures with 2 and 5 μm GaN buffer layers on sapphire substrates from two different vendors with the same Al concentration of AlGaN were used. The defect densities of HEMT structures with 2 and 5 μm GaN buffer layer were 7 × 109 and 5 × 108 cm₋2, respectively, as measured by transmission electron microscopy. There was little difference in drain saturation current or in transfer characteristics in HEMTs on these two types of buffer. However, there was no dispersion observed on the nonpassivated HEMTs with 5 μm GaN buffer layer for gate-lag pulsed measurement at 100 kHz, which was in sharp contrast to the 71% drain current reduction for the HEMT with 2 μm GaN buffer layer.

  3. Evaluation of AlGaN/GaN high electron mobility transistors grown on ZrTi buffer layers with sapphire substrates

    SciTech Connect

    Ren, Fan; Pearton, Stephen J.; Ahn, Shihyun; Lin, Yi -Hsuan; Machuca, Francisco; Weiss, Robert; Welsh, Alex; McCartney, Martha R.; Smith, David J.; Kravchenko, Ivan I.

    2016-09-21

    Here, AlGaN/GaN high electron mobility transistors (HEMTs) have been grown on sapphire substrates, using ZrTi buffer layers to provide in-plane lattice-matching to hexagonal GaN. X-ray diffraction (XRD) as well as cross-section transmission electron microscopy (TEM) were used to assess the quality of the HEMT structure. The XRD 2θ scans showed full-width-at-half-maximum values of 0.16°, 0.07°, and 0.08° for ZrTi alloy, GaN buffer layer, and the entire HEMT structure, respectively. TEM studies of the GaN buffer layer and the AlN/ZrTi/AlN stack showed the importance of growing thin AlN buffer layers on the ZrTi layer prior to growth of the GaN buffer layer. The density of threading dislocations in the GaN channel layer of the HEMT structure was estimated to be in the 108 cm–2 range. The HEMT device exhibited a saturation drain current density of 820 mA/mm, and the channel of the fabricated HEMTs could be well modulated. A cutoff frequency (fT) of 8.9 GHz and a maximum frequency of oscillation (fmax) of 17.3 GHz were achieved for HEMTs with gate dimensions of 1 × 200 μm.

  4. Reel-to-reel deposition of epitaxial double-sided MgO buffer layers for coated conductors

    NASA Astrophysics Data System (ADS)

    Xue, Yan; Xiong, Jie; Zhang, Yahui; Zhang, Fei; Zhao, Rui-Peng; Hui, Wang; Wang, Quiling; Cheng, Guo; Zhao, Xiao-Hui; Tao, Bo-Wan

    2016-06-01

    We have successfully employed a double-sided process to deposit MgO buffer layers on both sides of amorphous Y2O3 surface for double-sided YBa2Cu3O7-δ (YBCO) coated conductors (CCs) for the first time, the structure of which is of great prospect to improve the performance and cut the production cost. The biaxial textures of MgO buffer layer are noticeably affected by the ion energy and film thickness, which is demonstrated by X-ray diffraction. The best biaxial texture of double-sided MgO films shows ω-scan of (002) MgO and Φ-scan of (220) MgO yield full width at half maximum values of 4° and 7.8° for one side, respectively, as well as 3.5° and 6.7° for the other side. The subsequent double-sided YBCO films are deposited on the as-prepared MgO template with entire critical current of over 300 A/cm for both sides.

  5. Graphene/nitrogen-functionalized graphene quantum dot hybrid broadband photodetectors with a buffer layer of boron nitride nanosheets.

    PubMed

    Tetsuka, Hiroyuki; Nagoya, Akihiro; Tamura, Shin-Ichi

    2016-12-01

    A high performance hybrid broadband photodetector with graphene/nitrogen-functionalized graphene quantum dots (NGQDs@GFET) is developed using boron nitride nanosheets (BN-NSs) as a buffer layer to facilitate the separation and transport of photoexcited carriers from the NGQD absorber. The NGQDs@GFET photodetector with the buffer layer of BN-NSs exhibits enhanced photoresponsivity and detectivity in the deep ultraviolet region of ca. 2.3 × 10(6) A W(-1) and ca. 5.5 × 10(13) Jones without the application of a backgate voltage. The high level of photoresponsivity persists into the near-infrared region (ca. 3.4 × 10(2) A W(-1) and 8.0 × 10(9) Jones). In addition, application in flexible photodetectors is demonstrated by the construction of a structure on a polyethylene terephthalate (PET) substrate. We further show the feasibility of using our flexible photodetectors towards the practical application of infrared photoreflectors. Together with the potential application of flexible photodetectors and infrared photoreflectors, the proposed hybrid photodetectors have potential for use in future graphene-based optoelectronic devices.

  6. Impact of buffer layer and Pt thickness on the interface structure and magnetic properties in (Co/Pt) multilayers

    NASA Astrophysics Data System (ADS)

    Bersweiler, M.; Dumesnil, K.; Lacour, D.; Hehn, M.

    2016-08-01

    The influence of Pt thickness on the interface structure (roughness / intermixing) and magnetic properties has been investigated for (Co / Pt) multilayers sputtered on a Pt or a thin oxide (MgO or AlO x ) buffer layer. When Pt thickness increases from 1.2 nm-2.2 nm, we observe that the effective anisotropy increases with the Pt thickness, simultaneously with the decrease of roughness, i.e. the occurrence of sharper interfaces. Perpendicular magnetic anisotropy (PMA) is still achieved on the oxide buffer layers, but with a lower effective anisotropy correlated to more perturbed interfaces. The detailed analysis of the saturation magnetization shows that: (i) M s is significantly enhanced in the case of rough/intermixed interfaces, which is attributed to and discussed in the framework of Pt induced polarization, (ii) the change in volume dipolar anisotropy is the main factor responsible for the reduction of K eff for systems grown on oxides. Beyond the major role of volume dipolar contribution that reduces PMA, a supplemental positive contribution promoting PMA can be invoked for rough interfaces and large M s (deposit on oxide). This contribution is consistent with a dipolar surface anisotropy term and increases for rough interfaces, in contrast to the Néel surface anisotropy. These opposite variations may interestingly lead to an enhanced anisotropy in (Co / Pt) stackings grown on oxides compared to systems deposited on Pt, i.e. with sharper interfaces.

  7. Impact of buffer layer and Pt thickness on the interface structure and magnetic properties in (Co/Pt) multilayers.

    PubMed

    Bersweiler, M; Dumesnil, K; Lacour, D; Hehn, M

    2016-08-24

    The influence of Pt thickness on the interface structure (roughness / intermixing) and magnetic properties has been investigated for (Co / Pt) multilayers sputtered on a Pt or a thin oxide (MgO or AlO x ) buffer layer. When Pt thickness increases from 1.2 nm-2.2 nm, we observe that the effective anisotropy increases with the Pt thickness, simultaneously with the decrease of roughness, i.e. the occurrence of sharper interfaces. Perpendicular magnetic anisotropy (PMA) is still achieved on the oxide buffer layers, but with a lower effective anisotropy correlated to more perturbed interfaces. The detailed analysis of the saturation magnetization shows that: (i) M s is significantly enhanced in the case of rough/intermixed interfaces, which is attributed to and discussed in the framework of Pt induced polarization, (ii) the change in volume dipolar anisotropy is the main factor responsible for the reduction of K eff for systems grown on oxides. Beyond the major role of volume dipolar contribution that reduces PMA, a supplemental positive contribution promoting PMA can be invoked for rough interfaces and large M s (deposit on oxide). This contribution is consistent with a dipolar surface anisotropy term and increases for rough interfaces, in contrast to the Néel surface anisotropy. These opposite variations may interestingly lead to an enhanced anisotropy in (Co / Pt) stackings grown on oxides compared to systems deposited on Pt, i.e. with sharper interfaces.

  8. Interface roughness of double buffer layer of GaN film grown on Si(1 1 1) substrate using GIXR analysis

    NASA Astrophysics Data System (ADS)

    Yamamoto, Y.; Yamabe, N.; Ohachi, T.

    2011-03-01

    A double buffer layer (DBL), interface reaction epitaxy (IRE) AlN/β-Si3N4/Si, grown by an IRE of β-Si3N4 and AlN films on Si, was fabricated to improve the crystalline quality of successively grown 30 nm GaN on a 30 nm AlN buffer layer using plasma-assisted molecular beam epitaxy (PA-MBE). The DBL was first prepared by surface nitridation of Si and successively prepared by IRE between the deposited Al and N atoms in β-Si3N4. Both the AlN buffer layer on the DBL and GaN film on the AlN buffer layer were grown by activity-modulation migration enhanced epitaxy (AM-MEE). Hetero epitaxial grown films of GaN(30 nm)/AlN buffer(30 nm)/DBL/Si(1 1 1) were prepared for analysis using a three layer model of grazing incidence-angle X-ray reflectivity (GIXR), which consisted of three layers of GaN, AlN buffer and Si and of the three interfaces of the GaN surface, GaN/AlN buffer and AlN buffer/DBL/Si. The nitridation temperature dependence of the interface roughness of the DBL was measured to be 0.5 and 0.6 nm, for nitridation temperatures of 780 and 830 °C, respectively. The full width at half maximum (FWHM) of rocking curve GaN(0 0 0 2) measured by X-ray diffraction (XRD) for nitridation temperatures of 780 and 830 °C were 58.2 and 55.2 arcmin, respectively.

  9. Graded-bandgap AlGaAs solar cells for AlGaAs/Ge cascade cells

    NASA Technical Reports Server (NTRS)

    Timmons, M. L.; Venkatasubramanian, R.; Colpitts, T. S.; Hills, J. S.; Hutchby, J. A.; Iles, P. A.; Chu, C. L.

    1991-01-01

    Some p/n graded-bandgap Al(x)Ga(1-x)As solar cells were fabricated and show AMO conversion efficiencies in excess of 15 percent without antireflection (AR) coatings. The emitters of these cells are graded between 0.008 is less than or equal to x is less than or equal to 0.02 during growth of 0.25 to 0.30 micron thick layers. The keys to achieving this performance were careful selection of organometallic sources and scrubbing oxygen and water vapor from the AsH3 source. Source selection and growth were optimized using time-resolved photoluminescence. Preliminary radiation-resistance measurements show AlGaAs cells degraded less than GaAs cells at high 1 MeV electron fluences, and AlGaAs cells grown on GaAs and Ge substrates degrade comparably.

  10. Device performance and lifetime of polymer:fullerene solar cells with UV-ozone-irradiated hole-collecting buffer layers.

    PubMed

    Lee, Seungsoo; Nam, Sungho; Lee, Hyena; Kim, Hwajeong; Kim, Youngkyoo

    2011-11-18

    We report the influence of UV-ozone irradiation of the hole-collecting buffer layers on the performance and lifetime of polymer:fullerene solar cells. UV-ozone irradiation was targeted at the surface of the poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) layers by varying the irradiation time up to 600 s. The change of the surface characteristics in the PEDOT:PSS after UV-ozone irradiation was measured by employing optical absorption spectroscopy, photoelectron yield spectroscopy, and contact angle measurements, while Raman and X-ray photoelectron spectroscopy techniques were introduced for more microscopic analysis. Results showed that the UV-ozone irradiation changed the chemical structure/composition of the surface of the PEDOT:PSS layers leading to the gradual increase of ionization potential with irradiation time in the presence of up-and-down variations in the contact angle (polarity). This surface property change was attributed to the formation of oxidative components, as evidenced by XPS and Auger electron images, which affected the sheet resistance of the PEDOT:PSS layers. Interestingly, device performance was slightly improved by short irradiation (up to 10 s), whereas it was gradually decreased by further irradiation. The short-duration illumination test showed that the lifetime of solar cells with the UV-ozone irradiated PEDOT:PSS layer was improved due to the protective role of the oxidative components formed upon UV-ozone irradiation against the attack of sulfonic acid groups in the PEDOT:PSS layer to the active layer.

  11. Ca/Alq3 hybrid cathode buffer layer for the optimization of organic solar cells based on a planar heterojunction

    NASA Astrophysics Data System (ADS)

    El Jouad, Z.; Barkat, L.; Stephant, N.; Cattin, L.; Hamzaoui, N.; Khelil, A.; Ghamnia, M.; Addou, M.; Morsli, M.; Béchu, S.; Cabanetos, C.; Richard-Plouet, M.; Blanchard, P.; Bernède, J. C.

    2016-11-01

    Use of efficient anode cathode buffer layer (CBL) is crucial to improve the efficiency of organic photovoltaic cells. Here we show that using a double CBL, Ca/Alq3, allows improving significantly cell performances. The insertion of Ca layer facilitates electron harvesting and blocks hole collection, leading to improved charge selectivity and reduced leakage current, whereas Alq3 blocks excitons. After optimisation of this Ca/Alq3 CBL using CuPc as electron donor, it is shown that it is also efficient when SubPc is substituted to CuPc in the cells. In that case we show that the morphology of the SubPc layer, and therefore the efficiency of the cells, strongly depends on the deposition rate of the SubPc film. It is necessary to deposit slowly (0.02 nm/s) the SubPc films because at higher deposition rate (0.06 nm/s) the films are porous, which induces leakage currents and deterioration of the cell performances. The SubPc layers whose formations are kinetically driven at low deposition rates are more uniform, whereas those deposited faster exhibit high densities of pinholes.

  12. UV-ozone-treated ultra-thin NaF film as anode buffer layer on organic light emitting devices.

    PubMed

    Chen, Yu-Cheng; Kao, Po-Ching; Chu, Sheng-Yuan

    2010-06-21

    An ultra-thin NaF film was thermally deposited between ITO and NPB as the buffer layer and then treated with the ultraviolet (UV) ozone, in the fabrication of organic light emitting diodes (ITO/NaF/NPB/Alq(3)/LiF/Al) to study its effect on hole-injection properties. The treatment drastically transforms the role of NaF film from hole-blocking to hole-injecting. This transformation is elucidated using hole-only devices, energy band measurement, surface energy, surface polarity, and X-ray photoelectron spectra. With the optimal thickness (3 nm) of the UV-ozone-treated NaF layer, the device performance is significantly improved, with a turn-on voltage, maximum luminance, and maximum current efficiency of 2.5 V, 15700 cd/m(2), and 4.9 cd/A, respectively. Results show that NaF film is not only a hole-blocking layer, but also a promising hole-injecting layer after UV-ozone treatment.

  13. Tailoring the magnetic anisotropy of CoFeB/MgO stacks onto W with a Ta buffer layer

    NASA Astrophysics Data System (ADS)

    Kaidatzis, Andreas; Bran, Cristina; Psycharis, Vasilios; Vázquez, Manuel; García-Martín, José Miguel; Niarchos, Dimitrios

    2015-06-01

    The emergence of perpendicular magnetic anisotropy (PMA) in CoFeB/MgO stacks deposited on W using a Ta buffer layer is studied as a function of Ta and CoFeB layer thickness and annealing temperature. It is shown that very thin Ta "dusting" layers (thickness between 0.3 and 1 nm) enhance PMA of CoFeB layers grown on top of W. We find that Ta thickness is a crucial factor affecting magnetic anisotropy and it needs to be scaled proportionally to CoFeB thickness for obtaining PMA. Stacks without Ta have in-plane anisotropy, verifying the "PMA-enhancing" role of Ta. The maximum effective PMA energy ( 3.6 ×106 erg/cm3) is obtained for a stack with 1.4 nm of CoFeB and 1 nm of Ta and after annealing at 350 °C . Besides, PMA can be obtained even at the as-deposited state for certain thicknesses. This W-based CoFeB/MgO system could enable the development of low power consumption, high density, and non-volatile magnetic memories.

  14. Self-assembled, aligned ZnO nanorod buffer layers for high-current-density, inverted organic photovoltaics.

    PubMed

    Rao, Arun D; Karalatti, Suresh; Thomas, Tiju; Ramamurthy, Praveen C

    2014-10-08

    Two different soft-chemical, self-assembly-based solution approaches are employed to grow zinc oxide (ZnO) nanorods with controlled texture. The methods used involve seeding and growth on a substrate. Nanorods with various aspect ratios (1-5) and diameters (15-65 nm) are grown. Obtaining highly oriented rods is determined by the way the substrate is mounted within the chemical bath. Furthermore, a preheat and centrifugation step is essential for the optimization of the growth solution. In the best samples, we obtain ZnO nanorods that are almost entirely oriented in the (002) direction; this is desirable since electron mobility of ZnO is highest along this crystallographic axis. When used as the buffer layer of inverted organic photovoltaics (I-OPVs), these one-dimensional (1D) nanostructures offer: (a) direct paths for charge transport and (b) high interfacial area for electron collection. The morphological, structural, and optical properties of ZnO nanorods are studied using scanning electron microscopy, X-ray diffraction, and ultraviolet-visible light (UV-vis) absorption spectroscopy. Furthermore, the surface chemical features of ZnO films are studied using X-ray photoelectron spectroscopy and contact angle measurements. Using as-grown ZnO, inverted OPVs are fabricated and characterized. For improving device performance, the ZnO nanorods are subjected to UV-ozone irradiation. UV-ozone treated ZnO nanorods show: (i) improvement in optical transmission, (ii) increased wetting of active organic components, and (iii) increased concentration of Zn-O surface bonds. These observations correlate well with improved device performance. The devices fabricated using these optimized buffer layers have an efficiency of ∼3.2% and a fill factor of 0.50; this is comparable to the best I-OPVs reported that use a P3HT-PCBM active layer.

  15. 19.5%-Efficient CuIn1-xGaxSe2 Photovoltaic Cells Using A Cd-Zn-S Buffer Layer

    SciTech Connect

    Bhattacharya. R. N.

    2008-01-01

    CuIn1-xGaxSe2 (CIGS) solar cell junctions prepared by chemical-bath-deposited (CBD) Zn1-xCdxS (CdZnS), ZnS, and CdS buffer layers are discussed. A 19.52%-efficient, CIGS-based, thin-film photovoltaic device has been fabricated using a single-layer CBD CdZnS buffer layer. The mechanism that creates extensive hydroxide and oxide impurities in CBD-ZnS and CBD-CdZnS thin films (compared to CBD-CdS thin film) is presented.

  16. High performance organic photovoltaics with zinc oxide and graphene oxide buffer layers

    NASA Astrophysics Data System (ADS)

    Mohd Yusoff, Abd Rashid Bin; Kim, Hyeong Pil; Jang, Jin

    2014-01-01

    We report air stable inverted organic photovoltaics (OPVs) incorporating graphene oxide (GO) and solution processed zinc oxide (ZnO) as hole transport and electron transport layers, respectively. Both the hole transport layer and the electron transport layer (HTL and ETL) are of advantage in high transparency and environmental stability. The use of GO and ZnO in poly(2,7-carbazole) derivative (PCDTBT):fullerene derivative (PC70BM)-based inverted OPVs leads to an improved device stability and enhanced high open circuit voltage (Voc) of 0.81 V, a short-circuit current density (Jsc) of 14.10 mA cm-2, and a fill factor (FF) of 54.44 along with a power conversion efficiency of 6.20%.

  17. Quantum transport modeling of the symmetric Fe/FeO0.5/MgO magnetic tunnel junction: the effects of correlations in the buffer layer.

    PubMed

    Timoshevskii, Vladimir; Hu, Yibin; Marcotte, Étienne; Guo, Hong

    2014-01-08

    We report ab initio simulations of quantum transport properties of Fe/MgO/Fe trilayer structures with FeO0.5 buffer iron oxide layer, where on-site Coulomb interaction is explicitly taken into account by local density approximation + Hubbard U approach. We show that on-site Coulomb repulsion in the iron-oxygen layer can cause a dramatic drop of the tunnel magnetoresistance of the system. We present an understanding of microscopic details of this phenomenon, connecting it to localization of electronic states of particular symmetry, which takes place in the buffer Fe-O layer, when on-site Coulomb repulsion is introduced. We further study the possible influence of the symmetry reduction in the buffer Fe-O layer on the transport properties of the Fe/MgO/Fe interface.

  18. Improved high temperature integration of Al{sub 2}O{sub 3} on MoS{sub 2} by using a metal oxide buffer layer

    SciTech Connect

    Son, Seokki; Choi, Moonseok; Kim, Dohyung; Choi, Changhwan; Yu, Sunmoon

    2015-01-12

    We deposited a metal oxide buffer layer before atomic layer deposition (ALD) of Al{sub 2}O{sub 3} onto exfoliated molybdenum disulfide (MoS{sub 2}) in order to accomplish enhanced integration. We demonstrate that even at a high temperature, functionalization of MoS{sub 2} by means of a metal oxide buffer layer can effectively provide nucleation sites for ALD precursors, enabling much better surface coverage of Al{sub 2}O{sub 3}. It is shown that using a metal oxide buffer layer not only allows high temperature ALD process, resulting in highly improved quality of Al{sub 2}O{sub 3}/MoS{sub 2} interface, but also leaves MoS{sub 2} intact.

  19. Efficiency enhancement of polymer solar cells by applying poly(vinylpyrrolidone) as a cathode buffer layer via spin coating or self-assembly.

    PubMed

    Wang, Haitao; Zhang, Wenfeng; Xu, Chenhui; Bi, Xianghong; Chen, Boxue; Yang, Shangfeng

    2013-01-01

    A non-conjugated polymer poly(vinylpyrrolidone) (PVP) was applied as a new cathode buffer layer in P3HT:PCBM bulk heterojunction polymer solar cells (BHJ-PSCs), by means of either spin coating or self-assembly, resulting in significant efficiency enhancement. For the case of incorporation of PVP by spin coating, power conversion efficiency (PCE) of the ITO/PEDOT:PSS/P3HT:PCBM/PVP/Al BHJ-PSC device (3.90%) is enhanced by 29% under the optimum PVP spin-coating speed of 3000 rpm, which leads to the optimum thickness of PVP layer of ~3 nm. Such an efficiency enhancement is found to be primarily due to the increase of the short-circuit current (J(sc)) (31% enhancement), suggesting that the charge collection increases upon the incorporation of a PVP cathode buffer layer, which originates from the conjunct effects of the formation of a dipole layer between P3HT:PCBM active layer and Al electrodes, the chemical reactions of PVP molecules with Al atoms, and the increase of the roughness of the top Al film. Incorporation of PVP layer by doping PVP directly into the P3HT:PCBM active layer leads to an enhancement of PCE by 13% under the optimum PVP doping ratio of 3%, and this is interpreted by the migration of PVP molecules to the surface of the active layer via self-assembly, resulting in the formation of the PVP cathode buffer layer. While the formation of the PVP cathode buffer layer is fulfilled by both fabrication methods (spin coating and self-assembly), the dependence of the enhancement of the device performance on the thickness of the PVP cathode buffer layer formed by self-assembly or spin coating is different, because of the different aggregation microstructures of the PVP interlayer.

  20. Evaluation of methods for application of epitaxial buffer and superconductor layers

    SciTech Connect

    1999-03-30

    The recent achievements of critical currents exceeding million amperes per square centimeter at 77K in YBCO deposited over suitably textured substrate have stimulated interest in the potential applications of coated conductors at high temperatures and in high magnetic fields. Currently, ion-beam assisted deposition (IBAD), and rolling assisted bi-axially textured substrate (RABiTS), represent two available options for obtaining textured substrates. For applying suitable coatings of buffer and high temperature superconductor (HTS) material over textured substrates, several options are available which include sputtering, electron-beam evaporation, laser ablation, electrophoresis, chemical vapor deposition (including metal organics chemical vapor deposition), sol-gel, metal organics decomposition, electrodeposition and aerosol/spray pyrolysis. A commercial continuous long-length wire/tape manufacturing scheme developed out of any suitable combination of the above techniques would consist of operations involving preparation of the substrate and application of buffer, HTS and passivation/insulation materials and special treatment steps such as post-annealing. These operations can be effected by various process parameters that can be classified into chemistry, materials, engineering and environmental related parameters. Under the DOE-sponsored program, to carry out an engineering evaluation, first, the process flow schemes were developed for various candidate options identifying the major operating steps, process conditions, and process streams. Next, to evaluate quantifiable parameters such as process severity (e.g. temperature and pressure), coating thickness and deposition rate for HTS material, achieved maximum J{sub c} value (for films >1{micro}m thick) and cost of chemical and material utilization efficiency, the multi-attribute method was used to determine attributes/merits for various parameters and candidate options. To determine similar attribute values for the

  1. Development of Production PVD-AIN Buffer Layer System and Processes to Reduce Epitaxy Costs and Increase LED Efficiency

    SciTech Connect

    Cerio, Frank

    2013-09-14

    The DOE has set aggressive goals for solid state lighting (SSL) adoption, which require manufacturing and quality improvements for virtually all process steps leading to an LED luminaire product. The goals pertinent to this proposed project are to reduce the cost and improve the quality of the epitaxial growth processes used to build LED structures. The objectives outlined in this proposal focus on achieving cost reduction and performance improvements over state-of-the-art, using technologies that are low in cost and amenable to high efficiency manufacturing. The objectives of the outlined proposal focus on cost reductions in epitaxial growth by reducing epitaxy layer thickness and hetero-epitaxial strain, and by enabling the use of larger, less expensive silicon substrates and would be accomplished through the introduction of a high productivity reactive sputtering system and an effective sputtered aluminum-nitride (AlN) buffer/nucleation layer process. Success of the proposed project could enable efficient adoption of GaN on-silicon (GaN/Si) epitaxial technology on 150mm silicon substrates. The reduction in epitaxy cost per cm{sup 2} using 150mm GaN-on-Si technology derives from (1) a reduction in cost of ownership and increase in throughput for the buffer deposition process via the elimination of MOCVD buffer layers and other throughput and CoO enhancements, (2) improvement in brightness through reductions in defect density, (3) reduction in substrate cost through the replacement of sapphire with silicon, and (4) reduction in non-ESD yield loss through reductions in wafer bow and temperature variation. The adoption of 150mm GaN/Si processing will also facilitate significant cost reductions in subsequent wafer fabrication manufacturing costs. There were three phases to this project. These three phases overlap in order to aggressively facilitate a commercially available production GaN/Si capability. In Phase I of the project, the repeatability of the performance

  2. Optimization of the ZnS Buffer Layer by Chemical Bath Deposition for Cu(In,Ga)Se2 Solar Cells.

    PubMed

    Jeon, Dong-Hwan; Hwang, Dae-Kue; Kim, Dae-Hwan; Kang, Jin-Kyu; Lee, Chang-Seop

    2016-05-01

    We evaluated a ZnS buffer layer prepared using a chemical bath deposition (CBD) process for application in cadmium-free Cu(In,Ga)Se2 (CIGS) solar cells. The ZnS buffer layer showed good transmittance (above 90%) in the spectral range from 300 to 800 nm and was non-toxic compared with the CdS buffer layers normally used in CIGS solar cells. The CBD process was affected by several deposition conditions. The deposition rate was dependent on the ammonia concentration (complexing agent). When the ammonia concentration was either too high or low, a decrease in the deposition rate was observed. In addition, post heat treatments at high temperatures had detrimental influences on the ZnS buffer layers because portions of the ZnS thin films were transformed into ZnO. With optimized deposition conditions, a CIGS solar cell with a ZnS buffer layer showed an efficiency of 14.18% with a 0.23 cm2 active area under 100 mW/cm2 illumination.

  3. Effect of rear-surface buffer layer on performance of lift-off Cu(In,Ga)Se2 solar cells

    NASA Astrophysics Data System (ADS)

    Aoyagi, Kenta; Tamura, Akihiro; Takakura, Hideyuki; Minemoto, Takashi

    2014-01-01

    The effect of an Au and MoOx rear-surface buffer layer inserted between Cu(In,Ga)Se2 (CIGS) and ZnO:Al on solar cell performances was examined. The lift-off CIGS solar cell without a rear-surface buffer layer showed particular characteristics of two series-connected diodes in the reverse direction, and its short-circuit current density was almost zero. In contrast, the Au or MoOx rear-surface buffer layer improved these characteristics. Although the lift-off CIGS solar cell with the Au rear-surface buffer layer showed shunt characteristics and low efficiency, the efficiency of the lift-off CIGS solar cell with the MoOx rear-surface buffer layer was approximately 50% of that of substrate-type CIGS solar cells. Diode parameters of lift-off CIGS solar cells were determined by fitting analysis of current density-voltage curves using a proposed new equivalent circuit model for lift-off CIGS solar cells.

  4. Evaluation of AlGaN/GaN high electron mobility transistors grown on ZrTi buffer layers with sapphire substrates

    DOE PAGES

    Ren, Fan; Pearton, Stephen J.; Ahn, Shihyun; ...

    2016-09-21

    Here, AlGaN/GaN high electron mobility transistors (HEMTs) have been grown on sapphire substrates, using ZrTi buffer layers to provide in-plane lattice-matching to hexagonal GaN. X-ray diffraction (XRD) as well as cross-section transmission electron microscopy (TEM) were used to assess the quality of the HEMT structure. The XRD 2θ scans showed full-width-at-half-maximum values of 0.16°, 0.07°, and 0.08° for ZrTi alloy, GaN buffer layer, and the entire HEMT structure, respectively. TEM studies of the GaN buffer layer and the AlN/ZrTi/AlN stack showed the importance of growing thin AlN buffer layers on the ZrTi layer prior to growth of the GaN buffermore » layer. The density of threading dislocations in the GaN channel layer of the HEMT structure was estimated to be in the 108 cm–2 range. The HEMT device exhibited a saturation drain current density of 820 mA/mm, and the channel of the fabricated HEMTs could be well modulated. A cutoff frequency (fT) of 8.9 GHz and a maximum frequency of oscillation (fmax) of 17.3 GHz were achieved for HEMTs with gate dimensions of 1 × 200 μm.« less

  5. Finding the lost open-circuit voltage in polymer solar cells by UV-ozone treatment of the nickel acetate anode buffer layer.

    PubMed

    Wang, Fuzhi; Sun, Gang; Li, Cong; Liu, Jiyan; Hu, Siqian; Zheng, Hua; Tan, Zhan'ao; Li, Yongfang

    2014-06-25

    Efficient polymer solar cells (PSCs) with enhanced open-circuit voltage (Voc) are fabricated by introducing solution-processed and UV-ozone (UVO)-treated nickel acetate (O-NiAc) as an anode buffer layer. According to X-ray photoelectron spectroscopy data, NiAc partially decomposed to NiOOH during the UVO treatment. NiOOH is a dipole species, which leads to an increase in the work function (as confirmed by ultraviolet photoemission spectroscopy), thus benefitting the formation of ohmic contact between the anode and photoactive layer and leading to increased Voc. In addition, the UVO treatment improves the wettability between the substrate and solvent of the active layer, which facilitates the formation of an upper photoactive layer with better morphology. Further, the O-NiAc layer can decrease the series resistance (Rs) and increase the parallel resistance (Rp) of the devices, inducing enhanced Voc in comparison with the as-prepared NiAc-buffered control devices without UVO treatment. For PSCs based on the P3HT:PCBM system, Voc increases from 0.50 to 0.60 V after the NiAc buffer layer undergoes UVO treatment. Similarly, in the P3HT:ICBA system, the Voc value of the device with a UVO-treated NiAc buffer layer increases from 0.78 to 0.88 V, showing an enhanced power conversion efficiency of 6.64%.

  6. Amphiphilic fullerene/ZnO hybrids as cathode buffer layers to improve charge selectivity of inverted polymer solar cells

    NASA Astrophysics Data System (ADS)

    Hu, Ting; Chen, Lie; Yuan, Kai; Chen, Yiwang

    2015-05-01

    Two types of novel fullerene derivative/ZnO hybrids were prepared by physically blending amphiphilic fullerene-end-capped poly(ethylene glycol) (C60-PEG) with ZnO nanocrystals (ZnO/C60-PEG) and by in situ grown ZnO from C60-PEG (ZnO@C60-PEG) at relatively low temperatures. The C60-PEG could act as n-doping on the ZnO while the PEG side chain of C60-PEG could passivate the defects of the ZnO at the same time, consequently increasing the lowest unoccupied molecular orbital (LUMO) level. Compared with the ZnO/C60-PEG by the physical blend approach, the ZnO@C60-PEG by the growth approach showed a more favorable morphology and higher electron mobility by developing a homogeneous network. As a consequence, the efficiency of the inverted polymer solar cells based on thieno[3,4-b]-thiophene/benzodithiophene (PTB7):[6,6]-phenyl C71-butyric acid methyl ester (PC71BM) is raised to 8.0% for the ZnO@C60-PEG cathode buffer layer and to 7.5% for the ZnO/C60-PEG cathode buffer layer with improved long-term stability.Two types of novel fullerene derivative/ZnO hybrids were prepared by physically blending amphiphilic fullerene-end-capped poly(ethylene glycol) (C60-PEG) with ZnO nanocrystals (ZnO/C60-PEG) and by in situ grown ZnO from C60-PEG (ZnO@C60-PEG) at relatively low temperatures. The C60-PEG could act as n-doping on the ZnO while the PEG side chain of C60-PEG could passivate the defects of the ZnO at the same time, consequently increasing the lowest unoccupied molecular orbital (LUMO) level. Compared with the ZnO/C60-PEG by the physical blend approach, the ZnO@C60-PEG by the growth approach showed a more favorable morphology and higher electron mobility by developing a homogeneous network. As a consequence, the efficiency of the inverted polymer solar cells based on thieno[3,4-b]-thiophene/benzodithiophene (PTB7):[6,6]-phenyl C71-butyric acid methyl ester (PC71BM) is raised to 8.0% for the ZnO@C60-PEG cathode buffer layer and to 7.5% for the ZnO/C60-PEG cathode buffer layer

  7. Magnetic anisotropy of crystalline Fe films grown on (001) GaAs substrates using Ge buffer layers

    NASA Astrophysics Data System (ADS)

    Bac, Seul-Ki; Lee, Hakjoon; Lee, Sangyeop; Choi, Seonghoon; Yoo, Taehee; Lee, Sanghoon; Liu, X.; Furdyna, J. K.

    2016-05-01

    Magnetic anisotropy of Fe films grown on (001) GaAs substrates using Ge buffer layers were investigated by planar Hall effect measurements. In addition to phenomena arising from dominant cubic symmetry of the Fe specimen, the study of angular dependence of magnetization reversal revealed breaking of this symmetry in the form of systematic asymmetric shifts of magnetic hysteresis loops around the <110 > crystallographic directions. We ascribe such symmetry breaking to an admixture of uniaxial anisotropy associated with the [100] direction in the Fe film. To determine the parameters associated with this uniaxial anisotropy, we quantitatively analyze the asymmetric shifts of the hysteresis loop centers from the <110 > directions. Even though the value of these parameters turns out to be relatively small compared to that of the cubic anisotropy (by about two orders of magnitude), they survive up to room temperature.

  8. Nano LaAlO3 buffer layer-assisted tunneling current in manganite p-n heterojunction

    NASA Astrophysics Data System (ADS)

    Ma, Jun-Jie; Wang, Deng-Jing; Huang, Hai-Lin; Wang, Ru-Wu; Li, Yun-Bao

    2015-10-01

    An oxide p-n heterojunction composed of a 150-nm La0.67Ca0.33MnO3 (LCMO) film, 0.05 wt% Nb doped SrTiO3 substrate (STON), and sandwiched 5-nm LaAlO3 (LAO) thin film is fabricated with the pulsed laser deposition technique and the interfacial transport properties are experimentally studied. The rectifying behavior of the junction is in agreement with Newman’s equation, indicating that tunneling is the dominant process for the carriers to pass through the interface while thermal emission is the dominant transport model of an LCMO/STON heterojunction with no LAO buffer layer. Project supported by the National Natural Science Foundation of China (Grant No. 10804089).

  9. Solvent effects of a dimethyldicyanoquinonediimine buffer layer as N-type material on the performance of organic photovoltaic cells.

    PubMed

    Yang, Eui Yeol; Oh, Se Young

    2014-08-01

    In the present work, we have fabricated organic photovoltaic cells consisting of ITO/PEDOT:PSS/P3HT:PCBM/DMDCNQI/Al using a dip-coating method with various solvent systems. We have investigated solvent effects (such as solubility, viscosity and vapor pressure) in deposition of a thin DMDCNQI buffer layer on the performance of organic photovoltaic cells. The solvent system which had low viscosity and good solubility properties, made a dense and uniform DMDCNQI ultra thin film, resulting in a high performance device. In particular, a prepared organic photovoltaic cell was fabricated using a cosolvent system (methanol:methylenechloride = 3:1) and showed a maximum power conversion efficiency of 4.53%.

  10. The 1.1 micrometer and visible emission semiconductor diode lasers. [(AlGa)As lasers

    NASA Technical Reports Server (NTRS)

    Ladany, I.; Nuese, C. J.; Kressel, H.

    1978-01-01

    In (AlGa)As, the first of three alloy systems studied, Continuous Wave (CW) operation was obtained at room temperature at a wavelength as low as 7260 A. Reliability in this system was studied in the incoherent mode. Zinc doped devices had significant degradation, whereas Ge or Ge plus Zi doped devices had none. The Al2O3 facet coatings were shown to significantly reduce facet deterioration in all types of lasers, longer wavelength units of that type having accumulated (at the time of writing) 22,000 hours with little if any degradation. A CL study of thin (AlGa)As layers revealed micro fluctuation in composition. A macro-scale fluctuation was observed by electroreflectance. An experimental and theoretical study of the effect of stripe width on the threshold current was carried out. Emission below 7000 A was obtained in VPE grown Ga(AsP) (In,Ga)P with CW operation at 10 C. Lasers and LED's were made by LPE in (InGa) (AsP). Laser thresholds of 5 kA/cm2 were obtained, while LED efficiences were on the order of 2%. Incoherent life test over 6000 hours showed no degradation.

  11. Air processed organic photovoltaic devices incorporating a MoOx anode buffer layer

    NASA Astrophysics Data System (ADS)

    Bovill, Edward S. R.; Griffin, Jonathan; Wang, Tao; Kingsley, James W.; Yi, Hunan; Iraqi, Ahmed; Buckley, Alastair R.; Lidzey, David G.

    2013-05-01

    Molybdenum oxide (MoOx) has been shown to act as an efficient hole extraction layer in organic photovoltaic (OPV) devices. However, exposing MoOx films to air is problematic as it is hygroscopic; the uptake of moisture having a negative impact on its electronic properties. Here, we use spectroscopic ellipsometry to characterise the uptake of water, and fabricate PCDTBT:PC70BM based OPVs to determine its effects on device performance. We then show that thermally annealing MoOx reduces its hygroscopicity, permitting it to be processed in air. Using this process, we create air-processsed OPVs having PCEs (power conversion efficiencies) of up to 5.36%.

  12. The effects of buffer layers on the performance and stability of flexible InGaZnO thin film transistors on polyimide substrates

    SciTech Connect

    Ok, Kyung-Chul; Park, Jin-Seong E-mail: jsparklime@hanyang.ac.kr; Ko Park, Sang-Hee; Kim, H. E-mail: jsparklime@hanyang.ac.kr; Hwang, Chi-Sun; Soo Shin, Hyun; Bae, Jonguk

    2014-02-10

    We demonstrated the fabrication of flexible amorphous indium gallium zinc oxide thin-film transistors (TFTs) on high-temperature polyimide (PI) substrates, which were debonded from the carrier glass after TFT fabrication. The application of appropriate buffer layers on the PI substrates affected the TFT performance and stability. The adoption of the SiN{sub x}/AlO{sub x} buffer layers as water and hydrogen diffusion barriers significantly improved the device performance and stability against the thermal annealing and negative bias stress, compared to single SiN{sub x} or SiO{sub x} buffer layers. The substrates could be bent down to a radius of curvature of 15 mm and the devices remained normally functional.

  13. Effect of dopent on the structural and optical properties of ZnS thin film as a buffer layer in solar cell application

    SciTech Connect

    Vashistha, Indu B. Sharma, S. K.; Sharma, Mahesh C.; Sharma, Ramphal

    2015-08-28

    In order to find the suitable alternative of toxic CdS buffer layer, deposition of pure ZnS and doped with Al by chemical bath deposition method have been reported. Further as grown pure and doped thin films have been annealed at 150°C. The structural and surface morphological properties have been characterized by X-Ray diffraction (XRD) and Atomic Force Microscope (AFM).The XRD analysis shows that annealed thin film has been polycrystalline in nature with sphalerite cubic crystal structure and AFM images indicate increment in grain size as well as growth of crystals after annealing. Optical measurement data give band gap of 3.5 eV which is ideal band gap for buffer layer for solar cell suggesting that the obtained ZnS buffer layer is suitable in a low-cost solar cell.

  14. Quality-enhanced AlN epitaxial films grown on c-sapphire using ZnO buffer layer for SAW applications

    NASA Astrophysics Data System (ADS)

    Fu, Sulei; Li, Qi; Gao, Shuang; Wang, Guangyue; Zeng, Fei; Pan, Feng

    2017-04-01

    AlN epitaxial films with a thin ZnO buffer layer were successfully deposited on c-sapphire by DC magnetron sputtering for surface acoustic wave (SAW) applications. The effect of ZnO buffer layer thickness on structural properties of AlN epitaxial films and the related SAW properties were investigated systematically. The results revealed that a thin ZnO buffer layer can significantly enhance the crystalline quality of AlN films and release the strain in AlN films. The AlN films were epitaxially grown on ZnO buffered-substrate with orientation relationship of (0001) [ 10 1 bar 0 ] AlN//(0001) [ 10 1 bar 0 ] ZnO//(0001) [2 bar 110 ] Al2O3. High frequency SAW devices with a center frequency of 1.4 GHz, a phase velocity of 5600 m/s were achieved on the obtained AlN films. The optimum ZnO buffer layer thickness was found to be 10 nm, resulting in high-quality epitaxial AlN films with a FWHM value of the rocking curve of 0.84°, nearly zero stress and low insertion loss of SAW devices. This work offers an effective approach to achieve high-quality AlN epitaxial films on sapphire substrates for the applications of AlN-based SAW devices.

  15. Effect of thermal annealing treatment with titanium chelate on buffer layer in inverted polymer solar cells

    NASA Astrophysics Data System (ADS)

    Liu, Zhiyong; Wang, Ning; Fu, Yan

    2016-12-01

    The solution processable electron extraction layer (EEL) is crucial for polymer solar cells (PSCs). Here, we investigated titanium (diisopropoxide) bis(2,4-pentanedionate) (TIPD) as an EEL and fabricated inverted PSCs with a blend of poly(3-hexylthiophene) (P3HT) and indene-C60 bisadduct (ICBA) acting as the photoactive layer, with a structure of ITO/TIPD/P3HT:ICBA/MoO3/Ag. After thermal annealing treatment at 150 °C for 15 min, the PSC performances increased from 3.85% to 6.84% and they achieve stable power conversion efficiency (PCE), with a similar PCE compared with TiO2 as an EEL by the vacuum evaporated method. Fourier transform infrared spectroscopy (FTIR) and ultraviolet photoelectron spectroscopy (UPS) confirmed that the TIPD decomposed and formed the Tidbnd O bond, and the energy level of the lowest unoccupied molecular orbital and the highest occupied molecular orbital increased. The space charge limited current (SCLC) measurements further confirmed the improvement in electron collection and the transport ability using TIPD as the EEL and thermal annealing.

  16. Understanding Coulomb Scattering Mechanism in Monolayer MoS2 Channel in the Presence of h-BN Buffer Layer.

    PubMed

    Joo, Min-Kyu; Moon, Byoung Hee; Ji, Hyunjin; Han, Gang Hee; Kim, Hyun; Lee, Gwanmu; Lim, Seong Chu; Suh, Dongseok; Lee, Young Hee

    2017-02-08

    As the thickness becomes thinner, the importance of Coulomb scattering in two-dimensional layered materials increases because of the close proximity between channel and interfacial layer and the reduced screening effects. The Coulomb scattering in the channel is usually obscured mainly by the Schottky barrier at the contact in the noise measurements. Here, we report low-temperature (T) noise measurements to understand the Coulomb scattering mechanism in the MoS2 channel in the presence of h-BN buffer layer on the silicon dioxide (SiO2) insulating layer. One essential measure in the noise analysis is the Coulomb scattering parameter (αSC) which is different for channel materials and electron excess doping concentrations. This was extracted exclusively from a 4-probe method by eliminating the Schottky contact effect. We found that the presence of h-BN on SiO2 provides the suppression of αSC twice, the reduction of interfacial traps density by 100 times, and the lowered Schottky barrier noise by 50 times compared to those on SiO2 at T = 25 K. These improvements enable us to successfully identify the main noise source in the channel, which is the trapping-detrapping process at gate dielectrics rather than the charged impurities localized at the channel, as confirmed by fitting the noise features to the carrier number and correlated mobility fluctuation model. Further, the reduction in contact noise at low temperature in our system is attributed to inhomogeneous distributed Schottky barrier height distribution in the metal-MoS2 contact region.

  17. RF-MBE growth of cubic AlN on MgO (001) substrates via 2-step c-GaN buffer layer

    NASA Astrophysics Data System (ADS)

    Kakuda, M.; Morikawa, S.; Kuboya, S.; Katayama, R.; Yaguchi, H.; Onabe, K.

    2013-09-01

    We fabricated cubic AlN (c-AlN) films on MgO (001) substrates via 2-step c-GaN buffer layer by radio-frequency-plasma-assisted molecular beam epitaxy (RF-MBE). The effect of low temperature c-GaN buffer layer on the surface flatness and crystal quality of c-AlN was investigated by AFM and XRD reciprocal space mapping analysis. We examined optical properties of the c-AlN film by spectroscopic ellipsometry. The absorption edge by the direct transition of the c-AlN film was 5.95 eV caused by the hexagonal phase incorporation.

  18. Effects of Varied Cleaning Methods on Ni-5% W Substrate for Dip-Coating of Water-based Buffer Layers: An X-ray Photoelectron Spectroscopy Study

    PubMed Central

    Narayanan, Vyshnavi; Bruneel, Els; Hühne, Ruben; van Driessche, Isabel

    2012-01-01

    This work describes various combinations of cleaning methods involved in the preparation of Ni-5% W substrates for the deposition of buffer layers using water-based solvents. The substrate has been studied for its surface properties using X-ray photoelectron spectroscopy (XPS). The contaminants in the substrates have been quantified and the appropriate cleaning method was chosen in terms of contaminants level and showing good surface crystallinity to further consider them for depositing chemical solution-based buffer layers for Y1Ba2Cu3Oy (YBCO) coated conductors.

  19. Growth of ZnO(0001) on GaN(0001)/4H-SiC buffer layers by plasma-assisted hybrid molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Adolph, David; Tingberg, Tobias; Ive, Tommy

    2015-09-01

    Plasma-assisted molecular beam epitaxy was used to grow ZnO(0001) layers on GaN(0001)/4H-SiC buffer layers deposited in the same growth chamber equipped with both N- and O-plasma sources. The GaN buffer layers were grown immediately before initiating the growth of ZnO. Using a substrate temperature of 445 °C and an O2 flow rate of 2.5 standard cubic centimeters per minute, we obtained ZnO layers with statistically smooth surfaces having a root-mean-square roughness of 0.3 nm and a peak-to-valley distance of 3 nm as revealed by atomic force microscopy. The full-width-at-half-maximum for x-ray rocking curves obtained across the ZnO(0002) and ZnO(10 1 bar 5) reflections was 198 and 948 arcsec, respectively. These values indicated that the mosaicity of the ZnO layer was comparable to the corresponding values of the underlying GaN buffer layer. Reciprocal space maps showed that the in-plane relaxation of the GaN and ZnO layers was 82% and 73%, respectively, and that the relaxation occurred abruptly during the growth. Room-temperature Hall-effect measurements revealed that the layers were inherently n-type and had an electron concentration of 1×1019 cm-3 and a Hall mobility of 51 cm2/V s.

  20. Nearly 4-Inch-Diameter Free-Standing GaN Wafer Fabricated by Hydride Vapor Phase Epitaxy with Pit-Inducing Buffer Layer

    NASA Astrophysics Data System (ADS)

    Sato, Tadashige; Okano, Shinya; Goto, Takenari; Yao, Takafumi; Seto, Ritsu; Sato, Akira; Goto, Hideki

    2013-08-01

    A free-standing GaN wafer was fabricated by depositing a GaN buffer that induced the formation of pits (hereafter, pit-inducing GaN buffer) on a low-temperature-grown GaN buffer on the sapphire substrate. A high-temperature-grown GaN layer was grown on the pit-inducing GaN buffer that induced the formation of pits on the high-temperature-grown GaN layer. The pit-inducing buffer suppresses crack formation in the thick GaN film thereby releasing growth stress. Thermal stress in GaN on a sapphire system is also discussed on the basis of calculations utilizing a bilayer model. We have succeeded in the fabrication of a nearly 4-in.-diameter free-standing GaN thick wafer with a pit-inducing GaN buffer by one-stop hydride vapor phase epitaxy, which will lead to a low-cost fabrication of free-standing GaN wafers.

  1. Thin-film encapsulation of organic electronic devices based on vacuum evaporated lithium fluoride as protective buffer layer

    NASA Astrophysics Data System (ADS)

    Peng, Yingquan; Ding, Sihan; Wen, Zhanwei; Xu, Sunan; Lv, Wenli; Xu, Ziqiang; Yang, Yuhuan; Wang, Ying; Wei, Yi; Tang, Ying

    2017-03-01

    Encapsulation is indispensable for organic thin-film electronic devices to ensure reliable operation and long-term stability. For thin-film encapsulating organic electronic devices, insulating polymers and inorganic metal oxides thin films are widely used. However, spin-coating of insulating polymers directly on organic electronic devices may destroy or introduce unwanted impurities in the underlying organic active layers. And also, sputtering of inorganic metal oxides may damage the underlying organic semiconductors. Here, we demonstrated that by utilizing vacuum evaporated lithium fluoride (LiF) as protective buffer layer, spin-coated insulating polymer polyvinyl alcohol (PVA), and sputtered inorganic material Er2O3, can be successfully applied for thin film encapsulation of copper phthalocyanine (CuPc)-based organic diodes. By encapsulating with LiF/PVA/LiF trilayer and LiF/Er2O3 bilayer films, the device lifetime improvements of 10 and 15 times can be achieved. These methods should be applicable for thin-film encapsulation of all kinds of organic electronic devices. Moisture-induced hole trapping, and Al top electrode oxidation are suggest to be the origins of current decay for the LiF/PVA/LiF trilayer and LiF/Er2O3 bilayer films encapsulated devices, respectively.

  2. Improved hole-injection and power efficiency of organic light-emitting diodes using an ultrathin cerium fluoride buffer layer

    NASA Astrophysics Data System (ADS)

    Lu, Hsin-Wei; Kao, Po-Ching; Chu, Sheng-Yuan

    2016-09-01

    In this study, the efficiency of organic light-emitting diodes (OLEDs) was enhanced by depositing a CeF3 film as an ultra-thin buffer layer between the ITO and NPB hole transport layer, with the structure configuration ITO/CeF3 (1 nm)/NPB (40 nm)/Alq3 (60 nm)/LiF (1 nm)/Al (150 nm). The enhancement mechanism was systematically investigated via several approaches. The work function increased from 4.8 eV (standard ITO electrode) to 5.2 eV (1-nm-thick UV-ozone treated CeF3 film deposited on the ITO electrode). The turn-on voltage decreased from 4.2 V to 4.0 V at 1 mA/cm2, the luminance increased from 7588 cd/m2 to 10820 cd/m2, and the current efficiency increased from 3.2 cd/A to 3.5 cd/A when the 1-nm-thick UV-ozone treated CeF3 film was inserted into the OLEDs.

  3. Direct charge carrier injection into Ga2O3 thin films using an In2O3 cathode buffer layer: their optical, electrical and surface state properties

    NASA Astrophysics Data System (ADS)

    Cui, W.; Zhao, X. L.; An, Y. H.; Guo, D. Y.; Qing, X. Y.; Wu, Z. P.; Li, P. G.; Li, L. H.; Cui, C.; Tang, W. H.

    2017-04-01

    Conductive Ga2O3 thin films with an In2O3 buffer layer have been prepared on c-plane sapphire substrates using a laser molecular beam epitaxy technique. The effects of the In2O3 buffer layer on the structure and optical, electrical and surface state properties of the Ga2O3 films have been studied. The change in conductivity of the thin films is attributed to different thicknesses of the In2O3 buffer layer, which determine the concentration of charge carriers injected into the upper Ga2O3 layer from the interface of the bilayer thin films. In addition, the increase in flat band voltage shift and capacitance values as the In2O3 buffer layer thickens are attributed to the increase in surface state density, which also contributes to the rapid shrinkage of the optical band gap of the Ga2O3. With transparency to visible light, high n-type conduction and the ability to tune the optical band gap and surface state density, we propose that Ga2O3/In2O3 bilayer thin film is an ideal n-type semiconductor for fabrication of transparent power devices, solar cell electrodes and gas sensors.

  4. Investigation of CdZnS Buffer Layers on the Performance of CuInGaSe2 and CuGaSe2 Solar Cells

    SciTech Connect

    Song, J.; Li, S. S.; Chen, L.; Noufi, R.; Anderson, T. J.; Crisalle, O. D.

    2006-01-01

    Cu(In,Ga)Se{sub 2} (CIGS) and CuGaSe{sub 2} (CGS) solar cells were fabricated using Cd{sub 1-x}Zn{sub x}S (CdZnS) buffer layers prepared by chemical bath deposition (CBD) with relative Zn compositions in the CBD bath values of X{sub bath} = 0 (i.e., pure CdS), 0.1, 0.2, 0.3, 0.4, and 0.5. The cell performance parameters of CIGS and CGS films treated with a KCN solution were investigated and compared to cells without KCN treatment. It was found that absorber films treated with KCN etching prior to the buffer CBD step show an improved cell performance for both the CIGS and CGS cells deposited with either CdS or CdZnS buffer layer. A CIGS cell with CdZnS buffer layer of X{sub bath} = 0.2 produced a 13% AM1.5G conversion efficiency with higher V{sub oc}, J{sub sc}, and FF values as compared to the CdZnS/CIGS cells with different Zn contents. Results of photo- J-V and quantum efficiency (QE) measurements reveal that the CGS cell with CdZnS buffer layer of X{sub bath} = 0.3 performed better than the CGS cell deposited with a pure CdS buffer layer. This result is suggested as a result of an increased photocurrent at shorter wavelengths and a more favorable conduction band-offset at the CdZnS/CGS junction.

  5. Long wavelength emitting GaInN quantum wells on metamorphic GaInN buffer layers with enlarged in-plane lattice parameter

    SciTech Connect

    Däubler, J. Passow, T.; Aidam, R.; Köhler, K.; Kirste, L.; Kunzer, M.; Wagner, J.

    2014-09-15

    Metamorphic (i.e., linear composition graded) GaInN buffer layers with an increased in-plane lattice parameter, grown by plasma-assisted molecular beam epitaxy, were used as templates for metal organic vapor phase epitaxy (MOVPE) grown GaInN/GaInN quantum wells (QWs), emitting in the green to red spectral region. A composition pulling effect was observed allowing considerable higher growth temperatures for the QWs for a given In composition. The internal quantum efficiency (IQE) of the QWs was determined by temperature and excitation power density dependent photoluminescence (PL) spectroscopy. An increase in IQE by a factor of two was found for green emitting QWs grown on metamorphic GaInN buffer compared to reference samples grown on standard GaN buffer layers. The ratio of room temperature to low temperature intensity PL of the red emitting QWs were found to be comparable to the PL efficiency of green emitting QWs, both grown on metamorphic GaInN buffers. The excitation density and well width dependence of the IQE indicate a reduction of the quantum confined Stark effect upon growth on GaInN buffer layers with increased in-plane lattice parameter.

  6. EXAMINATION OF DISLOCATIONS IN LATTICE-MISMATCHED GaInAs/BUFFER LAYER/GaAs FOR III-V PHOTOVOLTAICS

    SciTech Connect

    Levander, A.; Geisz, J.

    2007-01-01

    Dislocations act as sites for nonradiative electron/hole pair recombination, which reduces the effi ciency of photovoltaics. Lattice-matched materials can be grown on top of one another without forming a high density of dislocations. However, when the growth of lattice-mismatched (LMM) materials is attempted, many dislocations result from the relaxation of strain in the crystal structure. In an attempt to reduce the number of dislocations that propagate into a solar device when using LMM materials, a compositionally step-graded buffer is placed between the two LMM materials. In order to confi ne the dislocations to the buffer layer and therefore increase material quality and device effi ciency, the growth temperature and thickness of the buffer layer were varied. A GaInP compositionally graded buffer and GaInAs p-n junction were grown on a GaAs substrate in a metal-organic chemical vapor deposition (MOCVD) system. A multibeam optical stress sensor (MOSS) and X-ray diffraction (XRD) were used to characterize the strain in the epilayers. Electrical and optoelectronic properties were measured using a probe station and multimeter setup, solar simulator, and a quantum effi ciency instrument. It was determined that device functionality was highly dependent on the growth temperature of the graded buffer. As growth temperature increased, so did the dislocation density in the device despite an increase in the dislocation velocity, which should have increased the dislocation annihilation rate and the diffusion of dislocations to the edge of the crystal. The thickness of the graded buffer also affected device effi ciency with thinner samples performing poorly. The thinner graded buffer layers had high internal resistances from reduced carrier concentrations. In terms of effi ciency, the empirically derived recipe developed by the scientists at the National Renewable Energy Laboratory (NREL) produced the highest quality cells.

  7. High Cubic-Phase Purity InN on MgO (001) Using Cubic-Phase GaN as a Buffer Layer

    SciTech Connect

    Sanorpim, S.; Kuntharin, S.; Parinyataramas, J.; Yaguchi, H.; Iwahashi, Y.; Orihara, M.; Hijikata, Y.; Yoshida, S.

    2011-12-23

    High cubic-phase purity InN films were grown on MgO (001) substrates by molecular beam epitaxy with a cubic-phase GaN buffer layer. The cubic phase purity of the InN grown layers has been analyzed by high resolution X-ray diffraction, {mu}-Raman scattering and transmission electron microscopy. It is evidenced that the hexagonal-phase content in the InN overlayer much depends on hexagonal-phase content in the cubic-phase GaN buffer layer and increases with increasing the hexagonal-phase GaN content. From Raman scattering measurements, in addition, the InN layer with lowest hexagonal component (6%), only Raman characteristics of cubic TO{sub InN} and LO{sub InN} modes were observed, indicating a formation of a small amount of stacking faults, which does not affect on vibrational property.

  8. Mechanism insight into the effect of I/P buffer layer on the performance of NIP-type hydrogenated microcrystalline silicon solar cells

    NASA Astrophysics Data System (ADS)

    Bai, Lisha; Liu, Bofei; Zhao, Jing; Suo, Song; Hou, Guofu; Zhang, Dekun; Sun, Jian; Wei, Changchun; Zhao, Ying; Zhang, Xiaodan

    2015-05-01

    A simulation and experimental study on the effect of the buffer layer at the I/P interface on the performance of NIP-type hydrogenated microcrystalline silicon (μc-Si:H) single-junction solar cells is presented. Device-quality hydrogenated amorphous silicon (a-Si:H) material as a buffer layer at the I/P interface obviously improves the performance of NIP-type μc-Si:H single-junction solar cells. In addition to the well-known mechanism that an a-Si:H I/P buffer layer can reduce the recombination current density at I/P interfaces, the optically and electrically calibrated simulations and supporting experimental results in this study illustrate that the performance improvement also originates from the mitigation of the electric screening effect due to the reduced defect density at the I/P interfaces, which reinforces the bulk electric field. Integrating an optimized hydrogen profiling strategy and adding a-Si:H I/P buffer layer yielded an initial efficiency of 9.20% for μc-Si:H single-junction solar cells with an active area of 0.27 cm2. This study may provide new ideas of further improving the performance of NIP-type μc-Si:H single-junction solar cells by mitigating the electric screening effect.

  9. Improvement of photovoltaic efficiency of dye-sensitized solar cell by introducing highly transparent nanoporous TiO2 buffer layer.

    PubMed

    Kim, Yong Joo; Kim, Hark Jin; Lee, Mi Hyeon; Lim, Goo Il; Song, Hye Young; Choi, Young Sik; Park, Nam-Gyu; Lee, Chongmu; Lee, Wan In

    2010-01-01

    13 nm-sized highly-dispersible TiO2 nanoparticle was synthesized by solvothermal reaction of titanium isopropoxide in a basic condition with tetrabutylammonium hydroxide (TBAH). The prepared TiO2 nanoparticle was applied to fabrication of the transparent nanoporous TiO2 layer with 1.2 microm-thickness. By introducing this buffer layer between FTO and main TiO2 layer in the dye-sensitized solar cell (DSSC), the photovoltaic conversion efficiency was improved from 5.92% to 7.13%. Due to the excellent antireflective role of nanoporous TiO2 buffer layer, the transmittance of FTO glass was increased by 9.2%, and this seemed to be one of the major factors in enhancing photovoltaic conversion efficiency. Moreover, the presence of nanoporous TiO2 buffer layer induces excellent adhesion between FTO and main TiO2 layer, as well as it suppresses the back reaction by blocking direct contact between I3- and FTO electrode.

  10. Hydrothermal Growth and Application of ZnO Nanowire Films with ZnO and TiO2 Buffer Layers in Dye-Sensitized Solar Cells

    NASA Astrophysics Data System (ADS)

    Yang, Weiguang; Wan, Farong; Chen, Siwei; Jiang, Chunhua

    2009-12-01

    This paper reports the effects of the seed layers prepared by spin-coating and dip-coating methods on the morphology and density of ZnO nanowire arrays, thus on the performance of ZnO nanowire-based dye-sensitized solar cells (DSSCs). The nanowire films with the thick ZnO buffer layer (~0.8-1 μm thick) can improve the open circuit voltage of the DSSCs through suppressing carrier recombination, however, and cause the decrease of dye loading absorbed on ZnO nanowires. In order to further investigate the effect of TiO2 buffer layer on the performance of ZnO nanowire-based DSSCs, compared with the ZnO nanowire-based DSSCs without a compact TiO2 buffer layer, the photovoltaic conversion efficiency and open circuit voltage of the ZnO DSSCs with the compact TiO2 layer (~50 nm thick) were improved by 3.9-12.5 and 2.4-41.7%, respectively. This can be attributed to the introduction of the compact TiO2 layer prepared by sputtering method, which effectively suppressed carrier recombination occurring across both the film-electrolyte interface and the substrate-electrolyte interface.

  11. Power Conversion Efficiency and Device Stability Improvement of Inverted Perovskite Solar Cells by Using a ZnO:PFN Composite Cathode Buffer Layer.

    PubMed

    Jia, Xiaorui; Zhang, Lianping; Luo, Qun; Lu, Hui; Li, Xueyuan; Xie, Zhongzhi; Yang, Yongzhen; Li, Yan-Qing; Liu, Xuguang; Ma, Chang-Qi

    2016-07-20

    We have demonstrated in this article that both power conversion efficiency (PCE) and performance stability of inverted planar heterojunction perovskite solar cells can be improved by using a ZnO:PFN nanocomposite (PFN: poly[(9,9-bis(3'-(N,N-dimethylamion)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctyl)-fluorene]) as the cathode buffer layer (CBL). This nanocomposite could form a compact and defect-less CBL film on the perovskite/PC61BM surface (PC61BM: phenyl-C61-butyric acid methyl ester). In addition, the high conductivity of the nanocomposite layer makes it works well at a layer thickness of 150 nm. Both advantages of the composite layer are helpful in reducing interface charge recombination and improving device performance. The power conversion efficiency (PCE) of the best ZnO:PFN CBL based device was measured to be 12.76%, which is higher than that of device without CBL (9.00%), or device with ZnO (7.93%) or PFN (11.30%) as the cathode buffer layer. In addition, the long-term stability is improved by using ZnO:PFN composite cathode buffer layer when compare to that of the reference cells. Almost no degradation of open circuit voltage (VOC) and fill factor (FF) was found for the device having ZnO:PFN, suggesting that ZnO:PFN is able to stabilize the interface property and consequently improve the solar cell performance stability.

  12. Anisotropic structural and optical properties of semi-polar (11–22) GaN grown on m-plane sapphire using double AlN buffer layers

    PubMed Central

    Zhao, Guijuan; Wang, Lianshan; Yang, Shaoyan; Li, Huijie; Wei, Hongyuan; Han, Dongyue; Wang, Zhanguo

    2016-01-01

    We report the anisotropic structural and optical properties of semi-polar (11–22) GaN grown on m-plane sapphire using a three-step growth method which consisted of a low temperature AlN buffer layer, followed by a high temperature AlN buffer layer and GaN growth. By introducing double AlN buffer layers, we substantially improve the crystal and optical qualities of semi-polar (11–22) GaN, and significantly reduce the density of stacking faults and dislocations. The high resolution x-ray diffraction measurement revealed that the in-plane anisotropic structural characteristics of GaN layer are azimuthal dependent. Transmission electron microscopy analysis showed that the majority of dislocations in the GaN epitaxial layer grown on m-sapphire are the mixed-type and the orientation of GaN layer was rotated 58.4° against the substrate. The room temperature photoluminescence (PL) spectra showed the PL intensity and wavelength have polarization dependence along parallel and perpendicular to the [1–100] axis (polarization degrees ~ 0.63). The realization of a high polarization semi-polar GaN would be useful to achieve III-nitride based lighting emission device for displays and backlighting. PMID:26861595

  13. Application of biuret, dicyandiamide, or urea as a cathode buffer layer toward the efficiency enhancement of polymer solar cells.

    PubMed

    Zhao, Xuemei; Xu, Chenhui; Wang, Haitao; Chen, Fei; Zhang, Wenfeng; Zhao, Zhiqiang; Chen, Liwei; Yang, Shangfeng

    2014-03-26

    Three amino-containing small-molecule organic materials-biuret, dicyandiamide (DCDA), and urea-were successfully applied as novel cathode buffer layers (CBLs) in P3HT:PCBM bulk heterojunction polymer solar cells (BHJ-PSCs) for the first time, resulting in obvious efficiency enhancement. Under the optimized condition, the power conversion efficiencies (PCEs) of the CBL-incorporated BHJ-PSC devices are 3.84%, 4.25%, and 4.39% for biuret, DCDA, and urea, which are enhanced by ∼15%, ∼27%, and ∼31%, respectively, compared to the reference poly(3-hexylthiophene-2,5-diyl) : [6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PCBM) BHJ-PSC device without any CBL. The efficiency enhancement is primarily attributed to the increases of both short-circuit current density (Jsc) and fill factor (FF), for which the enhancement ratio is found to be sensitively dependent on the molecular structure of small-molecule organic materials. The surface morphologies and surface potential changes of the CBL-incorporated P3HT:PCBM photoactive layers were studied by atomic force microscopy and scanning Kelvin probe microscopy, respectively, suggesting the formation of an interfacial dipole layer between the photoactive layer and Al cathode, which may decrease the energy level offset between the work function of Al and the lowest unoccipoed molecular orbital level (LUMO) of the PCBM acceptor and consequently facilitate electron extraction by the Al cathode. The difference in the enhancement effect of biuret, DCDA, and urea is due to their difference on the work function matching with P3HT:PCBM. Besides, the coordination interaction between the lone-pair electrons on the N atoms of the amino (-NH2) group and the Al atoms may prohibit interaction between Al and the thiophene rings of P3HT, contributing to the efficiency enhancement of the CBL-incorporated devices as well. In this sense, the different CBL performance of biuret, DCDA, and urea is also proposed to partially originate from the

  14. Chemiluminescence flow biosensor for glucose using Mg-Al carbonate layered double hydroxides as catalysts and buffer solutions.

    PubMed

    Wang, Zhihua; Liu, Fang; Lu, Chao

    2012-01-01

    In this work, serving as supports in immobilizing luminol reagent, catalysts of luminol chemiluminescence (CL), and buffer solutions for the CL reaction, Mg-Al-CO(3) layered double hydroxides (LDHs) were found to trigger luminol CL in weak acid solutions (pH 5.8). The silica sol-gel with glucose oxidase and horseradish peroxidase was immobilized in the first half of the inside surface of a clear quartz tube, and luminol-hybrid Mg-Al-CO(3) LDHs were packed in the second half. Therefore, a novel CL flow-through biosensor for glucose was constructed in weak acid solutions. The CL intensity was linear with glucose concentration in the range of 0.005-1.0mM, and the detection limit for glucose (S/N=3) was 0.1 μM. The proposed biosensor exhibited excellent stability, high reproducibility and high selectivity for the determination of glucose and has been successfully applied to determine glucose in human plasma samples with satisfactory results. The success of this work has broken the bottleneck of the pH incompatibility between luminol CL and enzyme activity.

  15. Reduction of threading dislocation density for AlN epilayer via a highly compressive-stressed buffer layer

    NASA Astrophysics Data System (ADS)

    Huang, Jun; Niu, Mu Tong; Zhang, Ji Cai; Wang, Wei; wang, Jian Feng; Xu, Ke

    2017-02-01

    Crystalline qualities of three AlN films grown by cold-wall high temperature hydride vapor phase epitaxy (CW-HT-HVPE) on c-plane sapphire substrates, with different AlN buffer layers (BLs) deposited either by CW-HT-HVPE or by hot-wall low temperature hydride vapor phase epitaxy (HW-LT-HVPE), have been studied. The best film quality was obtained on a 500-nm-thick AlN BL grown by HW-LT-HVPE at 1000 ℃. In this case,the AlN epilayer has the lowest full-width at half-maximum (FWHM) values of the (0002) and (10-12) x-ray rocking curve peaks of 295 and 306 arcsec, respectively, corresponding to the screw and edge threading dislocation (TD) densities of 1.9×108 cm-2 and 5.2×108 cm-2. This improvement in crystal quality of the AlN film can be attributed to the high compressive-stress of BL grown by HW-LT-HVPE,which facilitate the inclination and annihilation of TDs.

  16. Characterization of Zn(O,S) Buffer Layers for Cu(In,Ga)Se2 Solar Cells.

    PubMed

    Choi, Ji Hyun; Jung, Sung Hee; Chung, Chee Won

    2016-05-01

    Zn(O,S) thin films were deposited using a ZnS target under Ar/O2 gases by radio-frequency magnetron sputtering. As the O2 concentration increased, the deposition rates of the Zn(O,S) films decreased due to increase of O-. The crystalline structure of Zn(O,S) was maintained at up to 0.6% O2, while the films became unstable at the condition exceeding 0.8% O2. This was attributed to incomplete nucleation and film growth on the substrate at the room temperature. Additionally, optical emission spectroscopy analysis indicated that an increased O- intensity at high O2 concentration was responsible for the slow deposition rate and increased oxygen concentration of the films. X-ray diffraction and scanning electron microscopy revealed the formation of a Zn(O,S) crystal structure with partial substitution of O for S and uniform and dense grains of the films. X-ray photoelectron spectroscopy showed that the Zn(O,S) films have a uniform composition of each element and consisted of a mixed crystal structure of Zn(O,S) with Zn-O bonding. Overall, the results of this study confirmed that Zn(O,S) films deposited by radio-frequency sputtering using Ar/O2 gas at room temperature can be applied to Cu(In,Ga)Se2 solar cells as a buffer layer.

  17. Barrier efficiency of sponge-like La2Zr2O7 buffer layers for YBCO-coated conductors

    NASA Astrophysics Data System (ADS)

    Molina, Leopoldo; Tan, Haiyan; Biermans, Ellen; Batenburg, Kees J.; Verbeeck, Jo; Bals, Sara; Van Tendeloo, Gustaaf

    2011-06-01

    Solution derived La2Zr2O7 films have drawn much attention for potential applications as thermal barriers or low-cost buffer layers for coated conductor technology. Annealing and coating parameters strongly affect the microstructure of La2Zr2O7, but different film processing methods can yield similar microstructural features such as nanovoids and nanometer-sized La2Zr2O7 grains. Nanoporosity is a typical feature found in such films and the implications for the functionality of the films are investigated by a combination of scanning transmission electron microscopy (STEM), electron energy-loss spectroscopy (EELS) and quantitative electron tomography. Chemical solution based La2Zr2O7 films deposited on flexible Ni-5 at.%W substrates with a {100}lang001rang biaxial texture were prepared for an in-depth characterization. A sponge-like structure composed of nanometer-sized voids is revealed by high-angle annular dark-field scanning transmission electron microscopy in combination with electron tomography. A three-dimensional quantification of nanovoids in the La2Zr2O7 film is obtained on a local scale. Mostly non-interconnected highly faceted nanovoids compromise more than one-fifth of the investigated sample volume. The diffusion barrier efficiency of a 170 nm thick La2Zr2O7 film is investigated by STEM-EELS, yielding a 1.8 ± 0.2 nm oxide layer beyond which no significant nickel diffusion can be detected and intermixing is observed. This is of particular significance for the functionality of YBa2Cu3O7 - δ coated conductor architectures based on solution derived La2Zr2O7 films as diffusion barriers.

  18. Characterization of ZrO2 buffer layers for sequentially evaporated Y-Ba-CuO on Si and Al2O3 substrates

    NASA Technical Reports Server (NTRS)

    Valco, George J.; Rohrer, Norman J.; Pouch, John J.; Warner, Joseph D.; Bhasin, Kul B.

    1988-01-01

    Thin film high temperature superconductors have the potential to change the microwave technology for space communications systems. For such applications it is desirable that the films be formed on substrates such as Al2O3 which have good microwave properties. The use of ZrO2 buffer layers between Y-Ba-Cu-O and the substrate has been investigated. These superconducting films have been formed by multilayer sequential electron beam evaporation of Cu, BaF2 and Y with subsequent annealing. The three layer sequence of Y/BaF2/Cu is repeated four times for a total of twelve layers. Such a multilayer film, approximately 1 micron thick, deposited directly on SrTiO3 and annealed at 900 C for 45 min produces a film with a superconducting onset of 93 K and critical temperature of 85 K. Auger electron spectroscopy in conjunction with argon ion sputtering was used to obtain the distribution of each element as a function of depth for an unannealed film, the annealed film on SrTiO3 and annealed films on ZrO2 buffer layers. The individual layers were apparent. After annealing, the bulk of the film on SrTiO3 is observed to be fairly uniform while films on the substrates with buffer layers are less uniform. The Y-Ba-Cu-O/ZrO2 interface is broad with a long Ba tail into the ZrO2, suggesting interaction between the film and the buffer layer. The underlying ZrO2/Si interface is sharper. The detailed Auger results are presented and compared with samples annealed at different temperatures and durations.

  19. Effect of AlN buffer layer properties on the morphology and polarity of GaN nanowires grown by molecular beam epitaxy

    SciTech Connect

    Brubaker, Matt D.; Rourke, Devin M.; Sanford, Norman A.; Bertness, Kris A.; Bright, Victor M.

    2011-09-01

    Low-temperature AlN buffer layers grown via plasma-assisted molecular beam epitaxy on Si (111) were found to significantly affect the subsequent growth morphology of GaN nanowires. The AlN buffer layers exhibited nanowire-like columnar protrusions, with their size, shape, and tilt determined by the AlN V/III flux ratio. GaN nanowires were frequently observed to adopt the structural characteristics of the underlying AlN columns, including the size and the degree of tilt. Piezoresponse force microscopy and polarity-sensitive etching indicate that the AlN films and the protruding columns have a mixed crystallographic polarity. Convergent beam electron diffraction indicates that GaN nanowires are Ga-polar, suggesting that Al-polar columns are nanowire nucleation sites for Ga-polar nanowires. GaN nanowires of low density could be grown on AlN buffers that were predominantly N-polar with isolated Al-polar columns, indicating a high growth rate for Ga-polar nanowires and suppressed growth of N-polar nanowires under typical growth conditions. AlN buffer layers grown under slightly N-rich conditions (V/III flux ratio = 1.0 to 1.3) were found to provide a favorable growth surface for low-density, coalescence-free nanowires.

  20. Capacitance-voltage and retention characteristics of Pt/SrBi2Ta2O9/HfO2/Si structures with various buffer layer thickness

    NASA Astrophysics Data System (ADS)

    Tang, M. H.; Sun, Z. H.; Zhou, Y. C.; Sugiyama, Y.; Ishiwara, H.

    2009-05-01

    The metal-ferroelectric-insulator-semiconductor (MFIS) structure diodes with SrBi2Ta2O9 (SBT) as ferroelectric thin film and HfO2 as insulating buffer layer were fabricated. The electrical properties of MFIS structure were investigated for different HfO2 buffer layer thickness. The experimental results show that the memory window extended significantly as the HfO2 layer thickness increased from 6 to 10 nm. It is also observed that the leakage current was reduced to about 10-10 A at applied voltage of 4 V, and the high and low capacitances remained distinguishable for over 8 h even if we extrapolate the measured data to 10 years.

  1. Thermal and Environmental Stability of Semi-Transparent Perovskite Solar Cells for Tandems Enabled by a Solution-Processed Nanoparticle Buffer Layer and Sputtered ITO Electrode.

    PubMed

    Bush, Kevin A; Bailie, Colin D; Chen, Ye; Bowring, Andrea R; Wang, Wei; Ma, Wen; Leijtens, Tomas; Moghadam, Farhad; McGehee, Michael D

    2016-05-01

    A sputtered oxide layer enabled by a solution-processed oxide nanoparticle buffer layer to protect underlying layers is used to make semi-transparent perovskite solar cells. Single-junction semi-transparent cells are 12.3% efficient, and mechanically stacked tandems on silicon solar cells are 18.0% efficient. The semi-transparent perovskite solar cell has a T 80 lifetime of 124 h when operated at the maximum power point at 100 °C without additional sealing in ambient atmosphere under visible illumination.

  2. High efficiency thin-film CuIn1-xGaxSe2 photovoltaic cells using a Cd1-xZnxS buffer layer

    NASA Astrophysics Data System (ADS)

    Bhattacharya, R. N.; Contreras, M. A.; Egaas, B.; Noufi, R. N.; Kanevce, A.; Sites, J. R.

    2006-12-01

    The authors have fabricated 19.52% thin-film CuIn1-xGaxSe2 (CIGS)-based photovoltaic devices using single layer chemical bath deposited Cd1-xZnxS (CdZnS) buffer layer. The efficiency equals the world record for any thin-film solar cell and is achieved with reduced optical absorption in the window layer. Using current-voltage, quantum efficiency, and capacitance-voltage measurements, the CIGS/CdZnS device parameters are directly compared with those of CIGS/CdS devices fabricated with equivalent absorbers.

  3. Structure and dielectric tunability of (Pb 0.5Ba 0.5)ZrO 3 thin films derived on (Sr 0.95La 0.05)TiO 3 buffer-layered substrates

    NASA Astrophysics Data System (ADS)

    Hao, Xihong; Zhai, Jiwei; Zhou, Jing; Yang, Jichun; Song, Xiwen; An, Shengli

    2010-02-01

    In present work, (Pb 0.5Ba 0.5)ZrO 3 (PBZ) thin films with a thickness of 840 nm were successfully fabricated on (Sr 0.95La 0.05)TiO 3 (SLT) buffer-layered Pt(1 1 1)/TiO 2/SiO 2/Si(1 0 0) substrates via the sol-gel technique. The effects of SLT buffer layer on the microstructure and electrical properties of PBZ thin films were investigated systemically. X-ray diffraction (XRD) and scanning electron microscopy (SEM) results indicated that PBZ thin films on SLT buffer-layered substrates showed a more uniform structure with a random orientation. Dielectric measurements illustrated that PBZ films with SLT buffer layer displayed larger dielectric constant, improved tunability and enhanced figure of merit (FOM). Moreover, leakage current of PBZ films was also reduced by SLT buffer layer.

  4. Reduced Dislocation Density in GaxIn1-xP Compositionally Graded Buffer Layers through Engineered Glide Plane Switch

    SciTech Connect

    Schulte, Kevin L.; France, Ryan M.; McMahon, William E.; Norman, Andrew G.; Guthrey, Harvey L.; Geisz, John F.

    2016-11-17

    In this work we develop control over dislocation glide dynamics in GaxIn1-xP compositionally graded buffer layers (CGBs) through control of CuPt ordering on the group-III sublattice. The ordered structure is metastable in the bulk, so any glissile dislocation that disrupts the ordered pattern will release stored energy, and experience an increased glide force. Here we show how this connection between atomic ordering and dislocation glide force can be exploited to control the threading dislocation density (TDD) in GaxIn1-xP CGBs. When ordered GaxIn1-xP is graded from the GaAs lattice constant to InP, the order parameter ..eta.. decreases as x decreases, and dislocation glide switches from one set of glide planes to the other. This glide plane switch (GPS) is accompanied by the nucleation of dislocations on the new glide plane, which typically leads to increased TDD. We develop control of the GPS position within a GaxIn1-xP CGB through manipulation of deposition temperature, surfactant concentration, and strain-grading rate. We demonstrate a two-stage GaxIn1-xP CGB from GaAs to InP with sufficiently low TDD for high performance devices, such as the 4-junction inverted metamorphic multi-junction solar cell, achieved through careful control the GPS position. Experimental results are analyzed within the context of a model that considers the force balance on dislocations on the two competing glide planes as a function of the degree of ordering.

  5. Reduced dislocation density in GaxIn1-xP compositionally graded buffer layers through engineered glide plane switch

    NASA Astrophysics Data System (ADS)

    Schulte, K. L.; France, R. M.; McMahon, W. E.; Norman, A. G.; Guthrey, H. L.; Geisz, J. F.

    2017-04-01

    In this work we develop control over dislocation glide dynamics in GaxIn1-xP compositionally graded buffer layers (CGBs) through control of CuPt ordering on the group-III sublattice. The ordered structure is metastable in the bulk, so any glissile dislocation that disrupts the ordered pattern will release stored energy, and experience an increased glide force. Here we show how this connection between atomic ordering and dislocation glide force can be exploited to control the threading dislocation density (TDD) in GaxIn1-xP CGBs. When ordered GaxIn1-xP is graded from the GaAs lattice constant to InP, the order parameter η decreases as x decreases, and dislocation glide switches from one set of glide planes to the other. This glide plane switch (GPS) is accompanied by the nucleation of dislocations on the new glide plane, which typically leads to increased TDD. We develop control of the GPS position within a GaxIn1-xP CGB through manipulation of deposition temperature, surfactant concentration, and strain-grading rate. We demonstrate a two-stage GaxIn1-xP CGB from GaAs to InP with sufficiently low TDD for high performance devices, such as the 4-junction inverted metamorphic multi-junction solar cell, achieved through careful control the GPS position. Experimental results are analyzed within the context of a model that considers the force balance on dislocations on the two competing glide planes as a function of the degree of ordering.

  6. Ultralow threading dislocation density in GaN epilayer on near-strain-free GaN compliant buffer layer and its applications in hetero-epitaxial LEDs

    PubMed Central

    Shih, Huan-Yu; Shiojiri, Makoto; Chen, Ching-Hsiang; Yu, Sheng-Fu; Ko, Chung-Ting; Yang, Jer-Ren; Lin, Ray-Ming; Chen, Miin-Jang

    2015-01-01

    High threading dislocation (TD) density in GaN-based devices is a long unresolved problem because of the large lattice mismatch between GaN and the substrate, which causes a major obstacle for the further improvement of next-generation high-efficiency solid-state lighting and high-power electronics. Here, we report InGaN/GaN LEDs with ultralow TD density and improved efficiency on a sapphire substrate, on which a near strain-free GaN compliant buffer layer was grown by remote plasma atomic layer deposition. This “compliant” buffer layer is capable of relaxing strain due to the absorption of misfit dislocations in a region within ~10 nm from the interface, leading to a high-quality overlying GaN epilayer with an unusual TD density as low as 2.2 × 105 cm−2. In addition, this GaN compliant buffer layer exhibits excellent uniformity up to a 6” wafer, revealing a promising means to realize large-area GaN hetero-epitaxy for efficient LEDs and high-power transistors. PMID:26329829

  7. Effect of Dual Cathode Buffer Layer on the Charge Carrier Dynamics of rrP3HT:PCBM Based Bulk Heterojunction Solar Cell.

    PubMed

    Singh, Ashish; Dey, Anamika; Das, Dipjyoti; Iyer, Parameswar Krishnan

    2016-05-04

    In bulk heterojunction (BHJ) solar cells, the buffer layer plays a vital role in enhancing the power conversion efficiency (PCE) by improving the charge carrier dynamics. A comprehensive understanding of the contacts is especially essential in order to optimize the performance of organic solar cells (OSCs). Although there are several fundamental reports on this subject, a proper correlation of the physical processes with experimental evidence at the photoactive layer and contact materials is essential. In this work, we incorporated three different additional buffer layers, namely, tris(8-hydroxyquinolinato) aluminum (Alq3), bathophenanthroline (BPhen) or bathocuproine (BCP) with LiF/Al as conventional cathode contact in both rrP3HT:PC61BM and rrP3HT:PC71BM blend BHJ solar cells and their corresponding photovoltaic performances were systematically correlated with their energy level diagram. The device with dual cathode buffer layer having ITO/PEDOT:PSS/blend polymer/BCP/LiF/Al configuration showed the best device performance with PCE, η = 4.96%, Jsc = 13.53 mA/cm(2), Voc = 0.60 V and FF= 61% for rrP3HT:PC71BM and PCE, η = 4.5% with Jsc = 13.3 mA/cm(2), Voc = 0.59 V and FF = 59% for rrP3HT:PC61BM. This drastic improvement in PCE in both the device configurations are due to the combined effects of better hole-blocking capacity of BCP and low work function provided by LiF/Al with the blend polymer. These results successfully explain the role of dual cathode buffer layers and their contribution to the PCE improvement and overall device performance with rrP3HT:PCBM based BHJ solar cell.

  8. Identification of the Chemical Bonding Prompting Adhesion of a-C:H Thin Films on Ferrous Alloy Intermediated by a SiCx:H Buffer Layer.

    PubMed

    Cemin, F; Bim, L T; Leidens, L M; Morales, M; Baumvol, I J R; Alvarez, F; Figueroa, C A

    2015-07-29

    Amorphous carbon (a-C) and several related materials (DLCs) may have ultralow friction coefficients that can be used for saving-energy applications. However, poor chemical bonding of a-C/DLC films on metallic alloys is expected, due to the stability of carbon-carbon bonds. Silicon-based intermediate layers are employed to enhance the adherence of a-C:H films on ferrous alloys, although the role of such buffer layers is not yet fully understood in chemical terms. The chemical bonding of a-C:H thin films on ferrous alloy intermediated by a nanometric SiCx:H buffer layer was analyzed by X-ray photoelectron spectroscopy (XPS). The chemical profile was inspected by glow discharge optical emission spectroscopy (GDOES), and the chemical structure was evaluated by Raman and Fourier transform infrared spectroscopy techniques. The nature of adhesion is discussed by analyzing the chemical bonding at the interfaces of the a-C:H/SiCx:H/ferrous alloy sandwich structure. The adhesion phenomenon is ascribed to specifically chemical bonding character at the buffer layer. Whereas carbon-carbon (C-C) and carbon-silicon (C-Si) bonds are formed at the outermost interface, the innermost interface is constituted mainly by silicon-iron (Si-Fe) bonds. The oxygen presence degrades the adhesion up to totally delaminate the a-C:H thin films. The SiCx:H deposition temperature determines the type of chemical bonding and the amount of oxygen contained in the buffer layer.

  9. Investigation of AlGaN/GaN high electron mobility transistor structures on 200-mm silicon (111) substrates employing different buffer layer configurations

    NASA Astrophysics Data System (ADS)

    Lee, H.-P.; Perozek, J.; Rosario, L. D.; Bayram, C.

    2016-11-01

    AlGaN/GaN high electron mobility transistor (HEMT) structures are grown on 200-mm diameter Si(111) substrates by using three different buffer layer configurations: (a) Thick-GaN/3 × {AlxGa1‑xN}/AlN, (b) Thin-GaN/3 × {AlxGa1‑xN}/AlN, and (c) Thin-GaN/AlN, so as to have crack-free and low-bow (<50 μm) wafer. Scanning electron microscopy, energy-dispersive X-ray spectroscopy, high resolution-cross section transmission electron microscopy, optical microscopy, atomic-force microscopy, cathodoluminescence, Raman spectroscopy, X-ray diffraction (ω/2θ scan and symmetric/asymmetric ω scan (rocking curve scan), reciprocal space mapping) and Hall effect measurements are employed to study the structural, optical, and electrical properties of these AlGaN/GaN HEMT structures. The effects of buffer layer stacks (i.e. thickness and content) on defectivity, stress, and two-dimensional electron gas (2DEG) mobility and 2DEG concentration are reported. It is shown that 2DEG characteristics are heavily affected by the employed buffer layers between AlGaN/GaN HEMT structures and Si(111) substrates. Particularly, we report that in-plane stress in the GaN layer affects the 2DEG mobility and 2DEG carrier concentration significantly. Buffer layer engineering is shown to be essential for achieving high 2DEG mobility (>1800 cm2/V•s) and 2DEG carrier concentration (>1.0 × 1013 cm‑2) on Si(111) substrates.

  10. Investigation of AlGaN/GaN high electron mobility transistor structures on 200-mm silicon (111) substrates employing different buffer layer configurations

    PubMed Central

    Lee, H.-P.; Perozek, J.; Rosario, L. D.; Bayram, C.

    2016-01-01

    AlGaN/GaN high electron mobility transistor (HEMT) structures are grown on 200-mm diameter Si(111) substrates by using three different buffer layer configurations: (a) Thick-GaN/3 × {AlxGa1−xN}/AlN, (b) Thin-GaN/3 × {AlxGa1−xN}/AlN, and (c) Thin-GaN/AlN, so as to have crack-free and low-bow (<50 μm) wafer. Scanning electron microscopy, energy-dispersive X-ray spectroscopy, high resolution-cross section transmission electron microscopy, optical microscopy, atomic-force microscopy, cathodoluminescence, Raman spectroscopy, X-ray diffraction (ω/2θ scan and symmetric/asymmetric ω scan (rocking curve scan), reciprocal space mapping) and Hall effect measurements are employed to study the structural, optical, and electrical properties of these AlGaN/GaN HEMT structures. The effects of buffer layer stacks (i.e. thickness and content) on defectivity, stress, and two-dimensional electron gas (2DEG) mobility and 2DEG concentration are reported. It is shown that 2DEG characteristics are heavily affected by the employed buffer layers between AlGaN/GaN HEMT structures and Si(111) substrates. Particularly, we report that in-plane stress in the GaN layer affects the 2DEG mobility and 2DEG carrier concentration significantly. Buffer layer engineering is shown to be essential for achieving high 2DEG mobility (>1800 cm2/V∙s) and 2DEG carrier concentration (>1.0 × 1013 cm−2) on Si(111) substrates. PMID:27869222

  11. Effect of AlN buffer layers on the structural and optoelectronic properties of InN/AlN/Sapphire heterostructures grown by MEPA-MOCVD

    NASA Astrophysics Data System (ADS)

    Indika, S. M. K.; Seidlitz, Daniel; Fali, Alireza; Cross, Brendan; Abate, Yohannes; Dietz, Nikolaus

    2016-09-01

    This contribution presents results on the structural and optoelectronic properties of InN layers grown on AlN/sapphire (0001) templates by Migration-Enhanced Plasma Assisted Metal Organic Chemical Vapor Deposition (MEPAMOCVD). The AlN nucleation layer (NL) was varied to assess the physical properties of the InN layers. For ex-situ analysis of the deposited structures, Raman spectroscopy, Atomic Force Microscopy (AFM), and Fourier Transform Infrared (FTIR) reflectance spectroscopy have been utilized. The structural and optoelectronic properties are assessed by Raman-E2 high FWHM values, surface roughness, free carrier concentrations, mobility of the free carriers, and high frequency dielectric function. This study focus on optimizing the AlN nucleation layer (e.g. temporal precursor exposure, nitrogen plasma exposure, plasma power and AlN buffer growth temperature) and its effect on the InN layer properties.

  12. Solution-processed nanocomposites containing molybdenum oxide and gold nanoparticles as anode buffer layers in plasmonic-enhanced organic photovoltaic devices.

    PubMed

    Tan, Kim-Shih; Chuang, Ming-Kai; Chen, Fang-Chung; Hsu, Chain-Shu

    2013-12-11

    Solution-processed nanocomposites containing molybdenum oxide (MoO3) and gold nanoparticles (Au NPs) have been used as anode buffer layers in organic photovoltaic devices (OPVs). The resulting devices exhibit a remarkable enhancement in power conversion efficiency after Au NPs were incorporated into the device. Such enhancements can be attributed to the localized surface plasmon resonance induced by the metallic nanostructures. We have also found that the rate of exciton generation and the probability of exciton dissociation were increased. Furthermore, the devices made of the MoO3 buffer layer containing Au NPs exhibited superior stability. This work opens up the possibility of fabricating OPVs with both high efficiency and a prolonged lifetime.

  13. Thirty-Day-Long Data Retention in Ferroelectric-Gate Field-Effect Transistors with HfO2 Buffer Layers

    NASA Astrophysics Data System (ADS)

    Takahashi, Kazuhiro; Aizawa, Koji; Park, Byung-Eun; Ishiwara, Hiroshi

    2005-08-01

    Metal-ferroelectric-insulator-semiconductor (MFIS) diodes and p-channel MFIS field-effect transistors (FETs) were fabricated and their electrical properties were characterized. These MFIS structures were formed using HfO2 as an insulating buffer layer, and SrBi2Ta2O9 (SBT) and (Bi,La)4Ti3O12 (BLT) as ferroelectric films. HfO2 buffer layers of about 8 nm physical thickness were deposited by ultrahigh-vacuum (UHV) electron-beam evaporation, then ferroelectric films of about 400 nm thickness were deposited by sol-gel spin coating. The fabricated p-channel MFIS-FETs with the SBT/HfO2 gate structure exhibited a drain current on/off ratio larger than 103 even after 30 days had elapsed. It was also found that the degradation of ferroelectricity was not pronounced even after applying 2.2× 1011 bipolar pulses.

  14. Growth of YBa sub 2 Cu sub 3 O sub 7 minus x thin films on Si with a CoSi sub 2 buffer layer

    SciTech Connect

    Luo, L.; Muenchausen, R.E.; Maggiore, C.J. ); Jimenez, J.R.; Schowalter, L.J. )

    1991-01-28

    By using the pulsed laser deposition technique, high-temperature superconducting YBa{sub 2}Cu{sub 3}O{sub 7{minus}{ital x}} (YBCO) films were grown on Si(001) with a 36 nm single-crystal {l angle}001{r angle} oriented CoSi{sub 2} buffer layer. The films, grown at a substrate temperature of {similar to}700 {degree}C, have a metallic resistive temperature dependence with zero resistance at 85 K. X-ray diffraction, scanning electron microscopy, and ion channeling studies show that the YBCO films are polycrystalline but are strongly {ital c}-axis oriented normal to the Si substrate. Diffusion at the interface between the YBCO film and silicide buffer layer was minimized. This is essential to the growth of high-temperature superconducting films on Si substrates.

  15. Optical, structural, and chemical properties of flash evaporated In{sub 2}S{sub 3} buffer layer for Cu(In,Ga)Se{sub 2} solar cells

    SciTech Connect

    Verma, Rajneesh; Chirila, Adrian; Guettler, Dominik; Perrenoud, Julian; Pianezzi, Fabian; Tiwari, Ayodhya N.; Datta, Debjit; Kumar, Satyendra; Mueller, Ulrich

    2010-10-15

    In{sub 2}S{sub 3} layers were deposited by flash evaporation technique with varying flash rates. The optical constants of layers based on Tauc-Lorentz model dielectric function were extracted from spectroscopic ellipsometry measurements. X-ray photoelectron spectroscopic investigation revealed the presence of oxygen impurity in as-deposited and air-annealed layers with traces of Na inclusion in the layer grown at high flash rate. The enhancement in crystalline arrangement of as-deposited layer after air annealing was confirmed by Raman spectroscopy. Rutherford backscattering measurements revealed the growth of off-stoichiometric layers at all flash rates. An analytical layer growth model has been proposed supporting the results obtained by various layer characterization techniques. The solar cells were prepared with flash evaporated In{sub 2}S{sub 3} buffer layers and their performances were compared with CdS reference solar cell. A significant gain in short-circuit current was obtained after air annealing of the complete device at 200 deg. C for 20 min. A maximum conversion efficiency of 12.6% was delivered by a high flash rate In{sub 2}S{sub 3} buffered cell with open-circuit voltage close to that of CdS reference cell. The improvement in device performance after air annealing treatment is explained by thermally enhanced Cu and oxygen diffusion from Cu(In,Ga)Se{sub 2} and i-ZnO to In{sub 2}S{sub 3} layer, respectively.

  16. A sputtered CdS buffer layer for co-electrodeposited Cu2ZnSnS4 solar cells with 6.6% efficiency.

    PubMed

    Tao, Jiahua; Zhang, Kezhi; Zhang, Chuanjun; Chen, Leilei; Cao, Huiyi; Liu, Junfeng; Jiang, Jinchun; Sun, Lin; Yang, Pingxiong; Chu, Junhao

    2015-06-28

    Cu2ZnSnS4 thin films with thicknesses ranging from 0.35 to 1.85 μm and micron-sized grains (0.5-1.5 μm) were synthesized using co-electrodeposited Cu-Zn-Sn-S precursors with different deposition times. Here we have introduced a sputtered CdS buffer layer for the development of CZTS solar cells for the first time, which enables breakthrough efficiencies up to 6.6%.

  17. Non-Stoichiometric Amorphous Indium Selenide Thin Films as a Buffer Layer for CIGS Solar Cells with Various Temperatures in Rapid Thermal Annealing.

    PubMed

    Yoo, Myoung Han; Kim, Nam-Hoon

    2016-05-01

    The conventional structure of most of copper indium gallium diselenide (Culn(1-x)Ga(x)Se2, CIGS) solar cells includes a CdS thin film as a buffer layer. Cd-free buffer layers have attracted great interest for use in photovoltaic applications to avoid the use of hazardous and toxic materials. The RF magnetron sputtering method was used with an InSe2 compound target to prepare the indium selenide precursor. Rapid thermal annealing (RTA) was conducted in ambient N2 gas to control the concentration of volatile Se from the precursor with a change in temperature. The nature of the RTA-treated indium selenide thin films remained amorphous under annealing temperatures of ≤ 700 degrees C. The Se concentration of the RTA-treated specimens demonstrated an opposite trend to the annealing temperature. The optical transmittance and band gap energies were 75.33% and 2.451-3.085 eV, respectively, and thus were suitable for the buffer layer. As the annealing temperature increased, the resistivity decreased by an order-of-magnitude from 10(4) to 10(1) Ω-cm. At lower Se concentrations, the conductivity abruptly changed from p-type to n-type without crystallite formation in the amorphous phase, with the carrier concentration in the order of 10(17) cm(-3).

  18. Investigations on crack generation mechanism and crack reduction by buffer layer insertion in thermal-plasma-jet crystallization of amorphous silicon films on glass substrate

    NASA Astrophysics Data System (ADS)

    Tanaka, Keisuke; Hayashi, Shohei; Morisaki, Seiji; Higashi, Seiichiro

    2015-01-01

    The crack generation mechanism and the effect of crack reduction by buffer SiO2 layer insertion in thermal-plasma-jet (TPJ) crystallization of an amorphous silicon film on a glass substrate have been investigated. The crack generation was clearly observed 13.7 s after TPJ irradiation using a high-speed camera, which indicates that cracks are generated not during heating, but during cooling. From the measurement and simulation of substrate deformations, it was clarified that the substrate deformed convexly during heating and it consequently deformed concavely after cooling owing to the substrate surface densification. This result indicated that the tensile stress generated by the concave deformation is the origin of cracks. The deposition of the buffer SiO2 layer generated compressive stress, which minimizes accumulation of tensile stress after TPJ annealing. The number of cracks in unit length significantly decreased owing to the decrease in tensile stress with the increase in the thickness of the buffer SiO2 layer.

  19. Improvement in performance and reliability with CF4 plasma pretreatment on the buffer oxide layer for low-temperature polysilicon thin-film transistor

    NASA Astrophysics Data System (ADS)

    Fan, Ching-Lin; Lin, Yi-Yan; Yang, Chun-Chieh

    2012-03-01

    This study applies CF4 plasma pretreatment to a buffer oxide layer to improve the performance of low-temperature polysilicon thin-film transistors (LTPS TFTs). Results show that the fluorine atoms piled up at the interface between the bulk channel and buffer oxide layer and accumulated in the bulk channel. The reduction of the trap states density by fluorine passivation can improve the electrical characteristics of the LTPS TFTs. It is found that the threshold voltage reduced from 4.32 to 3.03 V and the field-effect mobility increased from 29.71 to 45.65 cm2 V-1 S-1. In addition, the on current degradation and threshold voltage shift after stressing were significantly improved about 31% and 70%, respectively. We believe that the proposed CF4 plasma pretreatment on the buffer oxide layer can passivate the trap states and avoid the plasma induced damage on the polysilicon channel surface, resulting in the improvement in performance and reliability for LTPS-TFT mass production application on AMOLED displays with critical reliability requirement.

  20. MOCVD of BN and GaN thin films on silicon: new attempt of GaN growth with BN buffer layer

    NASA Astrophysics Data System (ADS)

    Boo, Jin-Hyo; Rohr, Carsten; Ho, Wilson

    1998-06-01

    Highly oriented polycrystalline h-BN thin films were deposited on silicon substrates in the temperature range of 600-900°C from the single molecular precursor of borane-triethylamine complex, (C 2H 5) 3N : BH 3, by supersonic jet assisted chemical vapor deposition. Hydrogen was used as carrier gas, and additional nitrogen was supplied by either ammonia through a nozzle or nitrogen via a remote microwave plasma. Hexagonal GaN films were also grown on Si(1 0 0) with h-BN buffer layers at temperatures between 550 and 750°C with dual supersonic molecular beam sources. Triethylgallium, (C 2H 5) 3Ga, and ammonia, NH 3, were used as precursors. Hydrogen was used as seeding gas for the precursors, providing a wide range of possible kinetic energies for the supersonic beams. The h-BN buffer layers and the GaN films were characterized in situ by Auger electron spectroscopy (AES), and ex situ by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and optical transmission. This is the first report of growing the h-BN films on silicon substrates from the single source precursor of borane-triethylamine complex and new attempts of GaN film growth on silicon with BN buffer layer.

  1. A CdSe thin film: a versatile buffer layer for improving the performance of TiO2 nanorod array:PbS quantum dot solar cells

    NASA Astrophysics Data System (ADS)

    Tan, Furui; Wang, Zhijie; Qu, Shengchun; Cao, Dawei; Liu, Kong; Jiang, Qiwei; Yang, Ying; Pang, Shan; Zhang, Weifeng; Lei, Yong; Wang, Zhanguo

    2016-05-01

    To fully utilize the multiple exciton generation effects in quantum dots and improve the overall efficiency of the corresponding photovoltaic devices, nanostructuralizing the electron conducting layer turns out to be a feasible strategy. Herein, PbS quantum dot solar cells were fabricated on the basis of morphologically optimized TiO2 nanorod arrays. By inserting a thin layer of CdSe quantum dots into the interface of TiO2 and PbS, a dramatic enhancement in the power conversion efficiency from 4.2% to 5.2% was realized and the resulting efficiency is one of the highest values for quantum dot solar cells based on nanostructuralized buffer layers. The constructed double heterojunction with a cascade type-II energy level alignment is beneficial for promoting photogenerated charge separation and reducing charge recombination, thereby responsible for the performance improvement, as revealed by steady-state analyses as well as ultra-fast photoluminescence and photovoltage decays. Thus this paper provides a good buffer layer to the community of quantum dot solar cells.To fully utilize the multiple exciton generation effects in quantum dots and improve the overall efficiency of the corresponding photovoltaic devices, nanostructuralizing the electron conducting layer turns out to be a feasible strategy. Herein, PbS quantum dot solar cells were fabricated on the basis of morphologically optimized TiO2 nanorod arrays. By inserting a thin layer of CdSe quantum dots into the interface of TiO2 and PbS, a dramatic enhancement in the power conversion efficiency from 4.2% to 5.2% was realized and the resulting efficiency is one of the highest values for quantum dot solar cells based on nanostructuralized buffer layers. The constructed double heterojunction with a cascade type-II energy level alignment is beneficial for promoting photogenerated charge separation and reducing charge recombination, thereby responsible for the performance improvement, as revealed by steady

  2. Tunable work function of a WO{sub x} buffer layer for enhanced photocarrier collection of pin-type amorphous silicon solar cells

    SciTech Connect

    Fang Liang; Baik, Seung Jae; Kang, Sang Jung; Seo, Jung Won; Jeon, Jin-Wan; Lim, Koeng Su; Kim, Jeong Won; Kim, Yoon Hak

    2011-05-15

    An in situ postdeposition ultraviolet treatment was proposed to improve the electrical properties of a tungsten oxide (WO{sub x}) buffer layer of pin-type amorphous silicon-based solar cell. Based on the x-ray and ultraviolet photoelectron spectroscopy and the activation energy measurements, it was found that the work function of WO{sub x} is tunable by ultraviolet light treatment, and the collection performance of solar cells incorporating WO{sub x} with the lower work function is further improved. Moreover, the optimal band alignment scheme for a window layer is discussed in terms of obtaining enhanced carrier collection without open circuit voltage degradation.

  3. Control of metamorphic buffer structure and device performance of In(x)Ga(1-x)As epitaxial layers fabricated by metal organic chemical vapor deposition.

    PubMed

    Nguyen, H Q; Yu, H W; Luc, Q H; Tang, Y Z; Phan, V T H; Hsu, C H; Chang, E Y; Tseng, Y C

    2014-12-05

    Using a step-graded (SG) buffer structure via metal-organic chemical vapor deposition, we demonstrate a high suitability of In0.5Ga0.5As epitaxial layers on a GaAs substrate for electronic device application. Taking advantage of the technique's precise control, we were able to increase the number of SG layers to achieve a fairly low dislocation density (∼10(6) cm(-2)), while keeping each individual SG layer slightly exceeding the critical thickness (∼80 nm) for strain relaxation. This met the demanded but contradictory requirements, and even offered excellent scalability by lowering the whole buffer structure down to 2.3 μm. This scalability overwhelmingly excels the forefront studies. The effects of the SG misfit strain on the crystal quality and surface morphology of In0.5Ga0.5As epitaxial layers were carefully investigated, and were correlated to threading dislocation (TD) blocking mechanisms. From microstructural analyses, TDs can be blocked effectively through self-annihilation reactions, or hindered randomly by misfit dislocation mechanisms. Growth conditions for avoiding phase separation were also explored and identified. The buffer-improved, high-quality In0.5Ga0.5As epitaxial layers enabled a high-performance, metal-oxide-semiconductor capacitor on a GaAs substrate. The devices displayed remarkable capacitance-voltage responses with small frequency dispersion. A promising interface trap density of 3 × 10(12) eV(-1) cm(-2) in a conductance test was also obtained. These electrical performances are competitive to those using lattice-coherent but pricey InGaAs/InP systems.

  4. Control of metamorphic buffer structure and device performance of InxGa1-xAs epitaxial layers fabricated by metal organic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Nguyen, H. Q.; Yu, H. W.; Luc, Q. H.; Tang, Y. Z.; Phan, V. T. H.; Hsu, C. H.; Chang, E. Y.; Tseng, Y. C.

    2014-12-01

    Using a step-graded (SG) buffer structure via metal-organic chemical vapor deposition, we demonstrate a high suitability of In0.5Ga0.5As epitaxial layers on a GaAs substrate for electronic device application. Taking advantage of the technique’s precise control, we were able to increase the number of SG layers to achieve a fairly low dislocation density (˜106 cm-2), while keeping each individual SG layer slightly exceeding the critical thickness (˜80 nm) for strain relaxation. This met the demanded but contradictory requirements, and even offered excellent scalability by lowering the whole buffer structure down to 2.3 μm. This scalability overwhelmingly excels the forefront studies. The effects of the SG misfit strain on the crystal quality and surface morphology of In0.5Ga0.5As epitaxial layers were carefully investigated, and were correlated to threading dislocation (TD) blocking mechanisms. From microstructural analyses, TDs can be blocked effectively through self-annihilation reactions, or hindered randomly by misfit dislocation mechanisms. Growth conditions for avoiding phase separation were also explored and identified. The buffer-improved, high-quality In0.5Ga0.5As epitaxial layers enabled a high-performance, metal-oxide-semiconductor capacitor on a GaAs substrate. The devices displayed remarkable capacitance-voltage responses with small frequency dispersion. A promising interface trap density of 3 × 1012 eV-1 cm-2 in a conductance test was also obtained. These electrical performances are competitive to those using lattice-coherent but pricey InGaAs/InP systems.

  5. Role of Arsenic During Aluminum Droplet Etching of Nanoholes in AlGaAs.

    PubMed

    Heyn, Christian; Zocher, Michel; Schnüll, Sandra; Hansen, Wolfgang

    2016-12-01

    Self-assembled nanoholes are drilled into (001) AlGaAs surfaces during molecular beam epitaxy (MBE) using local droplet etching (LDE) with Al droplets. It is known that this process requires a small amount of background arsenic for droplet material removal. The present work demonstrates that the As background can be supplied by both a small As flux to the surface as well as by the topmost As layer in an As-terminated surface reconstruction acting as a reservoir. We study the temperature-dependent evaporation of the As topmost layer with in situ electron diffraction and determine an activation energy of 2.49 eV. After thermal removal of the As topmost layer droplet etching is studied under well-defined As supply. We observe with decreasing As flux four regimes: planar growth, uniform nanoholes, non-uniform holes, and droplet conservation. The influence of the As supply is discussed quantitatively on the basis of a kinetic rate model.

  6. Role of Arsenic During Aluminum Droplet Etching of Nanoholes in AlGaAs

    NASA Astrophysics Data System (ADS)

    Heyn, Christian; Zocher, Michel; Schnüll, Sandra; Hansen, Wolfgang

    2016-09-01

    Self-assembled nanoholes are drilled into (001) AlGaAs surfaces during molecular beam epitaxy (MBE) using local droplet etching (LDE) with Al droplets. It is known that this process requires a small amount of background arsenic for droplet material removal. The present work demonstrates that the As background can be supplied by both a small As flux to the surface as well as by the topmost As layer in an As-terminated surface reconstruction acting as a reservoir. We study the temperature-dependent evaporation of the As topmost layer with in situ electron diffraction and determine an activation energy of 2.49 eV. After thermal removal of the As topmost layer droplet etching is studied under well-defined As supply. We observe with decreasing As flux four regimes: planar growth, uniform nanoholes, non-uniform holes, and droplet conservation. The influence of the As supply is discussed quantitatively on the basis of a kinetic rate model.

  7. Enhanced efficiency of inverted polymer solar cells by using solution-processed TiOx/CsOx cathode buffer layer.

    PubMed

    Zhou, Xiaodong; Fan, Xi; Sun, Xianke; Zhang, Yunli; Zhu, Ziqiang

    2015-01-01

    In this work, a double-buffer film of TiOx coated with CsOx (TiOx/CsOx) was solution prepared to be applied in poly(3-hexylthiophene):indene-C60 bisadduct (P3HT:ICBA) and P3HT:[6,6]-phenyl-C61-butyric acid methyl ester (PCBM) inverted polymer solar cells (PSCs). Compared with TiOx films and CsOx films, the TiOx/CsOx double-buffer film exhibited a favorable energy-level alignment among TiOx, CsOx, and the electron acceptor of PCBM or ICBA a better surface morphology; and an enhanced wetting and adhesion property with a contact angle of 21.0°, leading to a higher electron mobility of 5.52 × 10(-3) cm(2) V(-1)·s(-1). Moreover, the P3HT:ICBA and P3HT:PCBM photovoltaic devices with the double-buffer film showed the best power conversion efficiency up to 5.65% and 3.76%, respectively. Our results not only present that the double-buffer film is superior than the single film of TiOx and CsOx, but also imply that the solution-processed film has a potential to be generally used in roll-to-roll processed organic photovoltaic devices.

  8. Fabrication of CeO 2 buffer layer with high deposition rate on biaxially textured Ni-3%W substrate by electron beam evaporation

    NASA Astrophysics Data System (ADS)

    Lee, J. B.; Park, S. K.; Kim, B. J.; Lee, H. J.; Kim, S. S.; Moon, S. H.; Lee, H. G.; Hong, G. W.

    2011-11-01

    CeO2 has been used as a buffer layer of a coated conductor because of good chemical and structural compatibility with YBCO. But cracks were often observed at the surface for films thicker than 100 nm deposited at a high temperature because of a large difference in a thermal expansion coefficient between metal and CeO2. The deposition rate was limited to be slow for getting good epitaxy. In order to increase the film deposition rate, while maintaining the epitaxy till a final thickness, two-step deposition process was tested. The thin seed layer with a thickness less than 10 nm was deposited with a deposition rate of 3 Å/s, and the homo-epitaxial layer at a thickness more than 240 nm was deposited at a deposition rate of 30 Å/s. The resulting CeO2 films deposited at 600 °C showed a good texture with a Δφ of 5.3°, Δω of 4.2° and Ra of 2.2 nm. The two-step process may be option for a low cost buffer layer for Ni-3%W metal substrates for the coated conductor.

  9. Organic Solar Cells Based on WO2.72 Nanowire Anode Buffer Layer with Enhanced Power Conversion Efficiency and Ambient Stability.

    PubMed

    You, Longzhen; Liu, Bin; Liu, Tao; Fan, Bingbing; Cai, Yunhao; Guo, Lin; Sun, Yanming

    2017-04-12

    Tungsten oxide as an alternative to conventional acidic PEDOT:PSS has attracted much attention in organic solar cells (OSCs). However, the vacuum-processed WO3 layer and high-temperature sol-gel hydrolyzed WOX are incompatible with large-scale manufacturing of OSCs. Here, we report for the first time that a specific tungsten oxide WO2.72 (W18O49) nanowire can function well as the anode buffer layer. The nw-WO2.72 film exhibits a high optical transparency. The power conversion efficiency (PCE) of OSCs based on three typical polymer active layers PTB7:PC71BM, PTB7-Th:PC71BM, and PDBT-T1:PC71BM with nw-WO2.72 layer were improved significantly from 7.27 to 8.23%, from 8.44 to 9.30%, and from 8.45 to 9.09%, respectively compared to devices with PEDOT:PSS. Moreover, the photovoltaic performance of OSCs based on small molecule p-DTS(FBTTh2)2:PC71BM active layer was also enhanced with the incorporation of nw-WO2.72. The enhanced performance is mainly attributed to the improved short-circuit current density (Jsc), which benefits from the oxygen vacancies and the surface apophyses for better charge extraction. Furthermore, OSCs based on nw-WO2.72 show obviously improved ambient stability compared to devices with PEDOT:PSS layer. The results suggest that nw-WO2.72 is a promising candidate for the anode buffer layer materials in organic solar cells.

  10. Growth and characterization of GaAs, AlGaAs and their heterostructures by organometallic vapor phase epitaxy

    SciTech Connect

    Shealy, J.R.

    1983-01-01

    Organometallic Vapor Phase Epitaxy (OMVPE) is a cold wall vapor desposition technique using organometallic and/or hydride sources for the fabrication of a variety of epitaxial compound semiconductor alloys on suitable substrates. The use of the OMVPE process to produce high quality GaAs, AlGaAs, and their heterostructures on GaAs substrates using trimethygalium (TMG), trimethylalumium (TMA), and arsine is described. For GaAs epitaxial films, the unintentional residual donor sand acceptors have been identified using far-infrared photo-ionization data, and low temperature photoluminescence, respectively, and their concentrations have been evaluated using Hall data. For the growth of AlGaAs films, it was observed that poor quality films were obtained due to oxygen contamination of the layer during growth. A series of graded bandgap heterostructures and abrupt quantum well heterostructures were grown over a variety of growth conditions. Composition gradings were controlled over a full range of alloy compositions on distances as small as 500 - 1000 A, and a 40 A quantum well heterostructure was obtained at low growth temperatures (550/sup 0/C). Finally, results are presented on a few devices which incorporate metallurgical junctions and heterojunctions with the GaAs/AlGaAs system. These devices include a microwave vertical FET structure, graded bandgap solar cells, and light emitting diodes.

  11. Growth of Atomically Flat Ultra-Thin Ag Films on Si(111) by Introducing a √3 × √3-Ga Buffer Layer

    NASA Astrophysics Data System (ADS)

    He, Jie-Hui; Jiang, Li-Qun; Qiu, Jing-Lan; Chen, Lan; Wu, Ke-Hui

    2014-12-01

    It is known that, when Ag is deposited on Si(111)-7×7 substrates in a conventional growth procedure at room temperature, no atomically flat Ag film could be obtained. We use scanning tunneling microscopy and low-energy electron diffraction to investigate the growth of ultra-thin Ag films on the Si(111) substrates at room temperature. Our study reveals that, upon introducing a Si(111)-√3 × √3-Ga buffer layer, atomically flat Ag films can easily grow on Si(111) with a critical thickness of two monolayers. Moreover, Ag film growth follows a layer-by-layer mode with further deposition. This novel growth behavior of Ag can be explained in terms of a free electron model (i.e., particle in a box) and kinetic Monte Carlo simulations.

  12. Structure optimization of high indium content InGaAs/InP heterostructure for the growth of In0.82Ga0.18As buffer layer

    NASA Astrophysics Data System (ADS)

    Wei, Qiu-lin; Guo, Zuo-xing; Zhao, Lei; Zhao, Liang; Yuan, De-zeng; Miao, Guo-qing; Xia, Mao-sheng

    2016-11-01

    Microstructure and misfit dislocation behavior in In x Ga1- x As/InP heteroepitaxial materials grown by low pressure metal organic chemical vapor deposition (LP-MOCVD) were analyzed by high resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), atomic force microscopy (AFM), Raman spectroscopy and Hall effect measurements. To optimize the structure of In0.82Ga0.18As/InP heterostructure, the In x Ga1- x As buffer layer was grown. The residual strain of the In0.82Ga0.18As epitaxial layer was calculated. Further, the periodic growth pattern of the misfit dislocation at the interface was discovered and verified. Then the effects of misfit dislocation on the surface morphology and microstructure of the material were studied. It is found that the misfit dislocation of high indium (In) content In0.82Ga0.82As epitaxial layer has significant influence on the carrier concentration.

  13. AlGaAs diode pumped tunable chromium lasers

    DOEpatents

    Krupke, William F.; Payne, Stephen A.

    1992-01-01

    An all-solid-state laser system is disclosed wherein the laser is pumped in the longwave wing of the pump absorption band. By utilizing a laser material that will accept unusually high dopant concentrations without deleterious effects on the crystal lattice one is able to compensate for the decreased cross section in the wing of the absorption band, and the number of pump sources which can be used with such a material increases correspondingly. In a particular embodiment a chromium doped colquiriite-structure crystal such as Cr:LiSrAlF.sub.6 is the laser material. The invention avoids the problems associated with using AlGaInP diodes by doping the Cr:LiSrAlF.sub.6 heavily to enable efficient pumping in the longwave wing of the absorption band with more practical AlGaAs diodes.

  14. State diagnostics of RTD based on nanoscale multilayered AlGaAs heterostructures

    NASA Astrophysics Data System (ADS)

    Makeev, M. O.; Meshkov, S. A.; Sinyakin, V. Yu

    2016-08-01

    In the present work the problems of technical diagnostics of RTD based on nanoscale multilayered AlGaAs heterostructures are being solved. The technique and the algorithms of RTD functionality region developing are being considered.

  15. Functional solid additive modified PEDOT:PSS as an anode buffer layer for enhanced photovoltaic performance and stability in polymer solar cells

    PubMed Central

    Xu, Binrui; Gopalan, Sai-Anand; Gopalan, Anantha-Iyengar; Muthuchamy, Nallal; Lee, Kwang-Pill; Lee, Jae-Sung; Jiang, Yu; Lee, Sang-Won; Kim, Sae-Wan; Kim, Ju-Seong; Jeong, Hyun-Min; Kwon, Jin-Beon; Bae, Jin-Hyuk; Kang, Shin-Won

    2017-01-01

    Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) is most commonly used as an anode buffer layer in bulk-heterojunction (BHJ) polymer solar cells (PSCs). However, its hygroscopic and acidic nature contributes to the insufficient electrical conductivity, air stability and restricted photovoltaic (PV) performance for the fabricated PSCs. In this study, a new multifunctional additive, 2,3-dihydroxypyridine (DOH), has been used in the PEDOT: PSS buffer layer to obtain modified properties for PEDOT: PSS@DOH and achieve high PV performances. The electrical conductivity of PEDOT:PSS@DOH films was markedly improved compared with that of PEDOT:PSS. The PEDOT:PSS@DOH film exhibited excellent optical characteristics, appropriate work function alignment, and good surface properties in BHJ-PSCs. When a poly(3-hexylthiohpene):[6,6]-phenyl C61-butyric acid methyl ester blend system was applied as the photoactive layer, the power conversion efficiency of the resulting PSCs with PEDOT:PSS@DOH(1.0%) reached 3.49%, outperforming pristine PEDOT:PSS, exhibiting a power conversion enhancement of 20%. The device fabricated using PEDOT:PSS@DOH (1.0 wt%) also exhibited improved thermal and air stability. Our results also confirm that DOH, a basic pyridine derivative, facilitates adequate hydrogen bonding interactions with the sulfonic acid groups of PSS, induces the conformational transformation of PEDOT chains and contributes to the phase separation between PEDOT and PSS chains. PMID:28338088

  16. Functional solid additive modified PEDOT:PSS as an anode buffer layer for enhanced photovoltaic performance and stability in polymer solar cells

    NASA Astrophysics Data System (ADS)

    Xu, Binrui; Gopalan, Sai-Anand; Gopalan, Anantha-Iyengar; Muthuchamy, Nallal; Lee, Kwang-Pill; Lee, Jae-Sung; Jiang, Yu; Lee, Sang-Won; Kim, Sae-Wan; Kim, Ju-Seong; Jeong, Hyun-Min; Kwon, Jin-Beon; Bae, Jin-Hyuk; Kang, Shin-Won

    2017-03-01

    Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) is most commonly used as an anode buffer layer in bulk-heterojunction (BHJ) polymer solar cells (PSCs). However, its hygroscopic and acidic nature contributes to the insufficient electrical conductivity, air stability and restricted photovoltaic (PV) performance for the fabricated PSCs. In this study, a new multifunctional additive, 2,3-dihydroxypyridine (DOH), has been used in the PEDOT: PSS buffer layer to obtain modified properties for PEDOT: PSS@DOH and achieve high PV performances. The electrical conductivity of PEDOT:PSS@DOH films was markedly improved compared with that of PEDOT:PSS. The PEDOT:PSS@DOH film exhibited excellent optical characteristics, appropriate work function alignment, and good surface properties in BHJ-PSCs. When a poly(3-hexylthiohpene):[6,6]-phenyl C61-butyric acid methyl ester blend system was applied as the photoactive layer, the power conversion efficiency of the resulting PSCs with PEDOT:PSS@DOH(1.0%) reached 3.49%, outperforming pristine PEDOT:PSS, exhibiting a power conversion enhancement of 20%. The device fabricated using PEDOT:PSS@DOH (1.0 wt%) also exhibited improved thermal and air stability. Our results also confirm that DOH, a basic pyridine derivative, facilitates adequate hydrogen bonding interactions with the sulfonic acid groups of PSS, induces the conformational transformation of PEDOT chains and contributes to the phase separation between PEDOT and PSS chains.

  17. Reduction of the dark current in a P3HT-based organic photodiode with a ytterbium-fluoride buffer layer for electron transport

    NASA Astrophysics Data System (ADS)

    Lim, Seong Bin; Ji, Chan Hyuk; Kim, Kee Tae; Oh, Se Young

    2016-08-01

    Photodiodes are widely used to convert light into electrical signals. The conventional silicon (Si) based photodiodes boast high photoelectric conversion efficiency and detectivity. However, in general, inorganic-based photodiodes have low sensitivity at visible wavelengths due to their absorption of infrared wavelengths. Recently, electrical conducting polymer-based photodiodes have received significant attention due to their flexibility, low cost of production and high sensitivity at visible wavelength ranges. In the present work, we fabricated an organic photodiode (OPD) with a consisting of ITO/ NiO x / P3HT:PC60BM/ YbF3/Al structure. In the OPD, a yitterbium fluoride (YbF3) buffer layer was used as the electron transport layer. The OPD was analyzed by using optical-electrical measurements to determine its J-V, detectivity, and dynamic characteristics. We investigated the physical effects of the YbF3 buffer layer on the performance of OPD such as its carrier extraction, leakage current and ohmic characteristics.

  18. Functional solid additive modified PEDOT:PSS as an anode buffer layer for enhanced photovoltaic performance and stability in polymer solar cells.

    PubMed

    Xu, Binrui; Gopalan, Sai-Anand; Gopalan, Anantha-Iyengar; Muthuchamy, Nallal; Lee, Kwang-Pill; Lee, Jae-Sung; Jiang, Yu; Lee, Sang-Won; Kim, Sae-Wan; Kim, Ju-Seong; Jeong, Hyun-Min; Kwon, Jin-Beon; Bae, Jin-Hyuk; Kang, Shin-Won

    2017-03-24

    Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) is most commonly used as an anode buffer layer in bulk-heterojunction (BHJ) polymer solar cells (PSCs). However, its hygroscopic and acidic nature contributes to the insufficient electrical conductivity, air stability and restricted photovoltaic (PV) performance for the fabricated PSCs. In this study, a new multifunctional additive, 2,3-dihydroxypyridine (DOH), has been used in the PEDOT: PSS buffer layer to obtain modified properties for PEDOT: PSS@DOH and achieve high PV performances. The electrical conductivity of PEDOT:PSS@DOH films was markedly improved compared with that of PEDOT:PSS. The PEDOT:PSS@DOH film exhibited excellent optical characteristics, appropriate work function alignment, and good surface properties in BHJ-PSCs. When a poly(3-hexylthiohpene):[6,6]-phenyl C61-butyric acid methyl ester blend system was applied as the photoactive layer, the power conversion efficiency of the resulting PSCs with PEDOT:PSS@DOH(1.0%) reached 3.49%, outperforming pristine PEDOT:PSS, exhibiting a power conversion enhancement of 20%. The device fabricated using PEDOT:PSS@DOH (1.0 wt%) also exhibited improved thermal and air stability. Our results also confirm that DOH, a basic pyridine derivative, facilitates adequate hydrogen bonding interactions with the sulfonic acid groups of PSS, induces the conformational transformation of PEDOT chains and contributes to the phase separation between PEDOT and PSS chains.

  19. High-quality III-nitride films on conductive, transparent (2̅01)-oriented β-Ga2O3 using a GaN buffer layer

    PubMed Central

    Muhammed, M. M.; Roldan, M. A.; Yamashita, Y.; Sahonta, S.-L.; Ajia, I. A.; Iizuka, K.; Kuramata, A.; Humphreys, C. J.; Roqan, I. S.

    2016-01-01

    We demonstrate the high structural and optical properties of InxGa1−xN epilayers (0 ≤ x ≤ 23) grown on conductive and transparent (01)-oriented β-Ga2O3 substrates using a low-temperature GaN buffer layer rather than AlN buffer layer, which enhances the quality and stability of the crystals compared to those grown on (100)-oriented β-Ga2O3. Raman maps show that the 2″ wafer is relaxed and uniform. Transmission electron microscopy (TEM) reveals that the dislocation density reduces considerably (~4.8 × 107 cm−2) at the grain centers. High-resolution TEM analysis demonstrates that most dislocations emerge at an angle with respect to the c-axis, whereas dislocations of the opposite phase form a loop and annihilate each other. The dislocation behavior is due to irregular (01) β-Ga2O3 surface at the interface and distorted buffer layer, followed by relaxed GaN epilayer. Photoluminescence results confirm high optical quality and time-resolved spectroscopy shows that the recombination is governed by bound excitons. We find that a low root-mean-square average (≤1.5 nm) of InxGa1−xN epilayers can be achieved with high optical quality of InxGa1−xN epilayers. We reveal that (01)-oriented β-Ga2O3 substrate has a strong potential for use in large-scale high-quality vertical light emitting device design. PMID:27412372

  20. High-quality III-nitride films on conductive, transparent (2̅01)-oriented β-Ga2O3 using a GaN buffer layer

    NASA Astrophysics Data System (ADS)

    Muhammed, M. M.; Roldan, M. A.; Yamashita, Y.; Sahonta, S.-L.; Ajia, I. A.; Iizuka, K.; Kuramata, A.; Humphreys, C. J.; Roqan, I. S.

    2016-07-01

    We demonstrate the high structural and optical properties of InxGa1‑xN epilayers (0 ≤ x ≤ 23) grown on conductive and transparent (01)-oriented β-Ga2O3 substrates using a low-temperature GaN buffer layer rather than AlN buffer layer, which enhances the quality and stability of the crystals compared to those grown on (100)-oriented β-Ga2O3. Raman maps show that the 2″ wafer is relaxed and uniform. Transmission electron microscopy (TEM) reveals that the dislocation density reduces considerably (~4.8 × 107 cm‑2) at the grain centers. High-resolution TEM analysis demonstrates that most dislocations emerge at an angle with respect to the c-axis, whereas dislocations of the opposite phase form a loop and annihilate each other. The dislocation behavior is due to irregular (01) β-Ga2O3 surface at the interface and distorted buffer layer, followed by relaxed GaN epilayer. Photoluminescence results confirm high optical quality and time-resolved spectroscopy shows that the recombination is governed by bound excitons. We find that a low root-mean-square average (≤1.5 nm) of InxGa1‑xN epilayers can be achieved with high optical quality of InxGa1‑xN epilayers. We reveal that (01)-oriented β-Ga2O3 substrate has a strong potential for use in large-scale high-quality vertical light emitting device design.

  1. Electron density and currents of AlN/GaN high electron mobility transistors with thin GaN/AlN buffer layer

    SciTech Connect

    Bairamis, A.; Zervos, Ch.; Georgakilas, A.; Adikimenakis, A.; Kostopoulos, A.; Kayambaki, M.; Tsagaraki, K.; Konstantinidis, G.

    2014-09-15

    AlN/GaN high electron mobility transistor (HEMT) structures with thin GaN/AlN buffer layer have been analyzed theoretically and experimentally, and the effects of the AlN barrier and GaN buffer layer thicknesses on two-dimensional electron gas (2DEG) density and transport properties have been evaluated. HEMT structures consisting of [300 nm GaN/ 200 nm AlN] buffer layer on sapphire were grown by plasma-assisted molecular beam epitaxy and exhibited a remarkable agreement with the theoretical calculations, suggesting a negligible influence of the crystalline defects that increase near the heteroepitaxial interface. The 2DEG density varied from 6.8 × 10{sup 12} to 2.1 × 10{sup 13} cm{sup −2} as the AlN barrier thickness increased from 2.2 to 4.5 nm, while a 4.5 nm AlN barrier would result to 3.1 × 10{sup 13} cm{sup −2} on a GaN buffer layer. The 3.0 nm AlN barrier structure exhibited the highest 2DEG mobility of 900 cm{sup 2}/Vs for a density of 1.3 × 10{sup 13} cm{sup −2}. The results were also confirmed by the performance of 1 μm gate-length transistors. The scaling of AlN barrier thickness from 1.5 nm to 4.5 nm could modify the drain-source saturation current, for zero gate-source voltage, from zero (normally off condition) to 0.63 A/mm. The maximum drain-source current was 1.1 A/mm for AlN barrier thickness of 3.0 nm and 3.7 nm, and the maximum extrinsic transconductance was 320 mS/mm for 3.0 nm AlN barrier.

  2. Characterization of Sulfur Bonding in CdS:O Buffer Layers for CdTe-based Thin-Film Solar Cells.

    PubMed

    Duncan, Douglas A; Kephart, Jason M; Horsley, Kimberly; Blum, Monika; Mezher, Michelle; Weinhardt, Lothar; Häming, Marc; Wilks, Regan G; Hofmann, Timo; Yang, Wanli; Bär, Marcus; Sampath, Walajabad S; Heske, Clemens

    2015-08-05

    On the basis of a combination of X-ray photoelectron spectroscopy and synchrotron-based X-ray emission spectroscopy, we present a detailed characterization of the chemical structure of CdS:O thin films that can be employed as a substitute for CdS layers in thin-film solar cells. It is possible to analyze the local chemical environment of the probed elements, in particular sulfur, hence allowing insights into the species-specific composition of the films and their surfaces. A detailed quantification of the observed sulfur environments (i.e., sulfide, sulfate, and an intermediate oxide) as a function of oxygen content is presented, allowing a deliberate optimization of CdS:O thin films for their use as alternative buffer layers in thin-film photovoltaic devices.

  3. Space electric field concentrated effect for Zr:SiO2 RRAM devices using porous SiO2 buffer layer

    PubMed Central

    2013-01-01

    To improve the operation current lowing of the Zr:SiO2 RRAM devices, a space electric field concentrated effect established by the porous SiO2 buffer layer was investigated and found in this study. The resistive switching properties of the low-resistance state (LRS) and high-resistance state (HRS) in resistive random access memory (RRAM) devices for the single-layer Zr:SiO2 and bilayer Zr:SiO2/porous SiO2 thin films were analyzed and discussed. In addition, the original space charge limited current (SCLC) conduction mechanism in LRS and HRS of the RRAM devices using bilayer Zr:SiO2/porous SiO2 thin films was found. Finally, a space electric field concentrated effect in the bilayer Zr:SiO2/porous SiO2 RRAM devices was also explained and verified by the COMSOL Multiphysics simulation model. PMID:24330524

  4. Zero lattice mismatch and twin-free single crystalline ScN buffer layers for GaN growth on silicon

    SciTech Connect

    Lupina, L.; Zoellner, M. H.; Dietrich, B.; Capellini, G.; Niermann, T.; Lehmann, M.; Thapa, S. B.; Haeberlen, M.; Storck, P.; Schroeder, T.

    2015-11-16

    We report the growth of thin ScN layers deposited by plasma-assisted molecular beam epitaxy on Sc{sub 2}O{sub 3}/Y{sub 2}O{sub 3}/Si(111) substrates. Using x-ray diffraction, Raman spectroscopy, and transmission electron microscopy, we find that ScN films grown at 600 °C are single crystalline, twin-free with rock-salt crystal structure, and exhibit a direct optical band gap of 2.2 eV. A high degree of crystalline perfection and a very good lattice matching between ScN and GaN (misfit < 0.1%) makes the ScN/Sc{sub 2}O{sub 3}/Y{sub 2}O{sub 3} buffer system a very promising template for the growth of high quality GaN layers on silicon.

  5. Impact of thermal stability of poly(3,4-ethylenedioxythiophene): poly(4-styrenesulfonate) used as buffer layer in organic solar cells

    NASA Astrophysics Data System (ADS)

    Dang, Minh Trung; Cantú-Valle, Jesus; Hirsch, Lionel; Wantz, Guillaume

    2013-09-01

    We compared the performances of polymer-based photovoltaic devices prepared from different formulations of poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS). The PEDOT:PSS buffer layer is incorporated between the indium tin oxide (ITO) electrode and the active layer, which is composed of a blend of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). A highest efficiency of 3.86% (under AM1.5 solar illumination) was achieved for device prepared from a PEDOT:PSS trade-named high conductivity grade. However, annealing devices at a temperature over 120 °C results in decreased photovoltaic performance. This study shows that attention has to be paid to chemicals used to formulate high conductive PEDOT:PSS to become compatible with the production of solar cells involving thermal processing.

  6. High-efficiency cadmium-free Cu(In,Ga)Se{sub 2} thin-film solar cells with chemically deposited ZnS buffer layers

    SciTech Connect

    Nakada, Tokio; Furumi, Keisuke; Kunioka, Akio

    1999-10-01

    Cadmium-free Cu(In,Ga)Se{sub 2} (CIGS) thin-film solar cells with a MgF{sub 2}/ZnO:Al/CBD-ZnS/CIGS/Mo/SLG structure have been fabricated using chemical bath deposition (CBD)-ZnS buffer layers and high-quality CIGS absorber layers grown using molecular beam epitaxy (MBE) system. The use of CBD-ZnS, which is a wider band gap material than CBD-CdS, improved the quantum efficiency of fabricated cells at short wavelengths, leading to an increase in the short-circuit current. The best cell at present yielded an active area efficiency of 16.9% which is the highest value reported previously for Cd-free CIGS thin-film solar cells. The as-fabricated solar cells exhibited a reversible light-soaking effect under AM 1.5, 100 mW/cm{sup 2} illumination. This paper also presents a discussion of the issues relating to the use of the CBD-ZnS buffer material for improving device performance.

  7. Modification of electron states in CdTe absorber due to a buffer layer in CdTe/CdS solar cells

    SciTech Connect

    Fedorenko, Y. G. Major, J. D.; Pressman, A.; Phillips, L. J.; Durose, K.

    2015-10-28

    By application of the ac admittance spectroscopy method, the defect state energy distributions were determined in CdTe incorporated in thin film solar cell structures concluded on ZnO, ZnSe, and ZnS buffer layers. Together with the Mott-Schottky analysis, the results revealed a strong modification of the defect density of states and the concentration of the uncompensated acceptors as influenced by the choice of the buffer layer. In the solar cells formed on ZnSe and ZnS, the Fermi level and the energy position of the dominant deep trap levels were observed to shift closer to the midgap of CdTe, suggesting the mid-gap states may act as recombination centers and impact the open-circuit voltage and the fill factor of the solar cells. For the deeper states, the broadening parameter was observed to increase, indicating fluctuations of the charge on a microscopic scale. Such changes can be attributed to the grain-boundary strain and the modification of the charge trapped at the grain-boundary interface states in polycrystalline CdTe.

  8. Low-Temperature Solution-Processed SnO2 Nanoparticles as a Cathode Buffer Layer for Inverted Organic Solar Cells.

    PubMed

    Tran, Van-Huong; Ambade, Rohan B; Ambade, Swapnil B; Lee, Soo-Hyoung; Lee, In-Hwan

    2017-01-18

    SnO2 recently has attracted particular attention as a powerful buffer layer for organic optoelectronic devices due to its outstanding properties such as high electron mobility, suitable band alignment, and high optical transparency. Here, we report on facile low-temperature solution-processed SnO2 nanoparticles (NPs) in applications for a cathode buffer layer (CBL) of inverted organic solar cells (iOSCs). The conduction band energy of SnO2 NPs estimated by ultraviolet photoelectron spectroscopy was 4.01 eV, a salient feature that is necessary for an appropriate CBL. Using SnO2 NPs as CBL derived from a 0.1 M precursor concentration, P3HT:PC60BM-based iOSCs showed the best power conversion efficiency (PCE) of 2.9%. The iOSC devices using SnO2 NPs as CBL revealed excellent long-term device stabilities, and the PCE was retained at ∼95% of its initial value after 10 weeks in ambient air. These solution-processed SnO2 NPs are considered to be suitable for the low-cost, high throughput roll-to-roll process on a flexible substrate for optoelectronic devices.

  9. Effect of process temperature on structure and magnetic properties of perpendicularly magnetized D022-Mn3Ge thin films on a Cr buffer layer

    NASA Astrophysics Data System (ADS)

    Sugihara, Atsushi; Suzuki, Kazuya; Miyazaki, Terunobu; Mizukami, Shigemi

    2015-08-01

    We investigated the effect of post-annealing on the perpendicular magnetic anisotropy constant (Ku) and surface roughness (Ra) of Mn3Ge thin films grown at comparatively low temperatures (room temperature, 150, 200, and 250 °C) on Cr buffer layers. The films grown at ≥200 °C exhibit a D022-ordered crystal structure in an as-deposited state. The post-annealing process demonstrates differences in trends between the 200-°C-grown film and the 250-°C-grown film. The 200-°C-grown film displays significant degradation of Ku and an increase in Ra upon annealing at >300 °C because of its poor thermal durability, while the 250-°C-grown film is still intact even at 500 °C. The 250-°C-grown film post-annealed at 300 °C displays relatively high Ku while Ra remains low. It may be possible to grow D022-Mn3Ge with higher Ku and low Ra using a buffer-layer material with a lattice-matched crystal structure with D022-Mn3Ge and higher thermal durability than Cr.

  10. High-power single spatial mode AlGaAs channeled-substrate-planar semiconductor diode lasers for spaceborne communications

    NASA Technical Reports Server (NTRS)

    Connolly, J. C.; Carlin, D. B.; Ettenberg, M.

    1989-01-01

    A high power single spatial mode channeled substrate planar AlGaAs semiconductor diode laser was developed. The emission wavelength was optimized at 860 to 880 nm. The operating characteristics (power current, single spatial mode behavior, far field radiation patterns, and spectral behavior) and results of computer modeling studies on the performance of the laser are discussed. Reliability assessment at high output levels is included. Performance results on a new type of channeled substrate planar diode laser incorporating current blocking layers, grown by metalorganic chemical vapor deposition, to more effectively focus the operational current to the lasing region was demonstrated. The optoelectronic behavior and fabrication procedures for this new diode laser are discussed. The highlights include single spatial mode devices with up to 160 mW output at 8600 A, and quantum efficiencies of 70 percent (1 W/amp) with demonstrated operating lifetimes of 10,000 h at 50 mW.

  11. Distinguishing impurity concentrations in GaAs and AlGaAs using very shallow undoped heterostructures

    NASA Astrophysics Data System (ADS)

    Mak, W. Y.; Das Gupta, K.; Beere, H. E.; Farrer, I.; Sfigakis, F.; Ritchie, D. A.

    2010-12-01

    We have developed a method of fabricating very shallow, gateable, undoped two-dimensional electron gases (2DEG) and making very low resistivity contacts to these. We studied the evolution of mobility as a function of the depth of the 2DEG (from 310 to 30 nm). We extract quantitative information about the background impurity concentrations in GaAs and AlGaAs, the interface roughness, and the charge in the surface states. Surface charge sets an intrinsic limit to the mobility of very shallow 2DEGs. It is probably impossible to fabricate such shallow high-mobility 2DEGs using modulation doping due to the need to accommodate a spacer layer.

  12. An all chemical solution deposition approach for the growth of highly textured CeO2 cap layers on La2Zr2O7-buffered long lengths of biaxially textured Ni W substrates for YBCO-coated conductors

    NASA Astrophysics Data System (ADS)

    Engel, S.; Knoth, K.; Hühne, R.; Schultz, L.; Holzapfel, B.

    2005-10-01

    A reel-to-reel, dip coating process has been developed to continuously deposit epitaxial La2Zr2O7 (LZO) and CeO2 on 5 m long cube-textured {100} (001)Ni tapes. Recent results for La2Zr2O7 and CeO2 buffer layers deposited on long lengths of Ni substrate for the realization of YBa2Cu3O7-x (YBCO)-coated conductors are presented. The major achievement is the development of a new all chemical solution deposition (CSD) process leading to the formation of highly textured buffer layers at moderate annealing temperatures. Reproducible highly textured, dense and crack-free LZO buffer layers and CeO2 cap layers were obtained for annealing temperatures as low as 900 °C in a reducing atmosphere (Ar-5 at.%-H2). The thickness of the LZO buffer layers was determined to be (200 ± 10) nm per single coating; prepared cerium oxide layers showed a thickness of 60 nm ± 10 nm. Pulsed laser deposition (PLD) was used to grow YBCO films on these substrates. A Tc 0 of T = 90.5 K and ΔTc = 1.4 K was obtained on PLD-YBCO/CSD-CeO2 /CSD-LZO/Ni-5 at.% W, which shows the outstanding features of this new buffer layer architecture processed by CSD. The large layer thickness combined with low annealing temperatures is the main advantage of this new process for low-cost buffer layer deposition on Ni-RABiTS (rolling-assisted biaxially textured substrates).

  13. Incorporation of La in epitaxial SrTiO3 thin films grown by atomic layer deposition on SrTiO3-buffered Si (001) substrates

    NASA Astrophysics Data System (ADS)

    McDaniel, Martin D.; Posadas, Agham; Ngo, Thong Q.; Karako, Christine M.; Bruley, John; Frank, Martin M.; Narayanan, Vijay; Demkov, Alexander A.; Ekerdt, John G.

    2014-06-01

    Strontium titanate, SrTiO3 (STO), thin films incorporated with lanthanum are grown on Si (001) substrates at a thickness range of 5-25 nm. Atomic layer deposition (ALD) is used to grow the LaxSr1-xTiO3 (La:STO) films after buffering the Si (001) substrate with four-unit-cells of STO deposited by molecular beam epitaxy. The crystalline structure and orientation of the La:STO films are confirmed via reflection high-energy electron diffraction, X-ray diffraction, and cross-sectional transmission electron microscopy. The low temperature ALD growth (˜225 °C) and post-deposition annealing at 550 °C for 5 min maintains an abrupt interface between Si (001) and the crystalline oxide. Higher annealing temperatures (650 °C) show more complete La activation with film resistivities of ˜2.0 × 10-2 Ω cm for 20-nm-thick La:STO (x ˜ 0.15); however, the STO-Si interface is slightly degraded due to the increased annealing temperature. To demonstrate the selective incorporation of lanthanum by ALD, a layered heterostructure is grown with an undoped STO layer sandwiched between two conductive La:STO layers. Based on this work, an epitaxial oxide stack centered on La:STO and BaTiO3 integrated with Si is envisioned as a material candidate for a ferroelectric field-effect transistor.

  14. Inkjet printing of multiple Ce0.8Gd0.2O2 buffer layers on a Ni-5%W substrate

    NASA Astrophysics Data System (ADS)

    Mosiadz, M.; Tomov, R. I.; Hopkins, S. C.; Martin, G.; Holzapfel, B.; Glowacki, B. A.

    2010-06-01

    The successful inkjet printing of multiple cerium gadolinium oxide (Ce0.8Gd0.2O2) layers on highly textured Ni-5%W is reported using a stable ink, developing a solid-liquid interface comparable with that arising from dip coating. Two different approaches were used for the deposition of CGO layers using a 16-nozzle piezoelectric drop-on-demand print head. Two overlapping square arrays of droplets with constant volume and spacing were printed, with and without an intermediate CGO crystallization. The shortest possible heat treatment of the deposited layers was applied, potentially suitable for continuous large scale production. The results from X-ray diffraction show that the single phase Ce0.8Gd0.2O2 was obtained in all cases, but only the approach with intermediate CGO crystallization can produce a highly textured buffer layer. Optical micrographs and atomic force microscopy (AFM) also indicate the good quality of deposited films after heat treatment.

  15. Investigation of polycrystalline thin-film CuInSe{sub 2} solar cells based on ZnSe and ZnO buffer layers. Final report, February 16, 1992--November 15, 1995

    SciTech Connect

    Olsen, L C

    1996-06-01

    The major objective of this program was to determine the potential of ZnSe and ZnO buffer layers in solar cells based on CuInSe{sub 2} and related alloys. Experimental studies were carried out with CIS and CIGSS substrates. ZnSe films were deposited by a CVD process which involved the reaction of a zinc adduct and H{sub 2}Se. Al/ZnSe/CIS test cells were used for process development. Test cell performance aided in determining the optimum thickness for ZnSe buffer layers to be in the range of 150 {angstrom} to 200 {angstrom} for Siemens CIS material, and between 80 {angstrom} and 120 {angstrom} for the graded absorber material. If the buffer layers exceeded these values significantly, the short-circuit current would be reduced to zero. The best efficiency achieved for a ZnSe/CIS cell was an active area value of 9.2%. In general, deposition of a conductive ZnO film on top of a ZnSe/CIS structure resulted in either shunted or inflected I-V characteristics. Two approaches were investigated for depositing ZnO buffer layers, namely, chemical bath deposition and CVD. CVD ZnO buffer layers are grown by reacting a zinc adduct with tetrahydrofuran. Best results were obtained for ZnO buffer layers grown with a substrate temperature ca. 225--250 C. These studies concentrated on Siemens graded absorber material (CIGSS). ZnO/CIS solar cells have been fabricated by first depositing a ZnO buffer layer, followed by deposition of a low resistivity ZnO top contact layer and an Al/Ag collector grid. Several cells were fabricated with an area of 0.44 cm{sup 2} that have total area efficiencies greater than 11%. To date, the best performing ZnO/CIS cell had a total area efficiency of 11.3%. In general, the authors find that ZnO buffer layers should have a resistivity > 1,000 ohm-cm and have a thickness from 200 {angstrom} to 600 {angstrom}. CIS cells studies with ZnO buffer layers grown by CBD also show promise. Finally, simulation studies were carried out using the 1-D code, PC-1D.

  16. Tailoring Photoelectrochemical Performance and Stability of Cu(In,Ga)Se2 Photocathode via TiO2-Coupled Buffer Layers.

    PubMed

    Koo, Bonhyeong; Nam, Sung-Wook; Haight, Richard; Kim, Suncheul; Oh, Seungtaeg; Cho, Minhyung; Oh, Jihun; Lee, Jeong Yong; Ahn, Byung Tae; Shin, Byungha

    2017-02-15

    We report on the photoelectrochemical (PEC) performance and stability of Cu(In,Ga)Se2 (CIGS)-based photocathodes for photocatalytic hydrogen evolution from water. Various functional overlayers, such as CdS, TiO2, ZnxSnyOz, and a combination of the aforementioned, were applied on the CIGS to improve the performance and stability. We identified that the insertion of TiO2 overlayer on p-CIGS/n-buffer layers significantly improves the PEC performance. A multilayered photocathode consisting of CIGS/CdS/TiO2/Pt exhibited the best current-potential characteristics among the tested photocathodes, which demonstrates a power-saved efficiency of 2.63%. However, repeated linear sweep voltammetry resulted in degradation of performance. In this regard, we focused on the PEC durability issues through in-depth chemical characterization that revealed the degradation was attributed to atomic redistribution of elements constituting the photocathode, namely, in-diffusion of Pt catalysts, out-diffusion of elements from the CIGS, and removal of the metal-oxide layers; the best-performing CIGS/CdS/TiO2/Pt photocathode retained its initial performance until the TiO2 overlayer was removed. It was also found that the durability of CIGS photocathodes with a TiO2-coated metal-oxide buffer layer such as ZnxSnyOz was better than those with a TiO2-coated CdS, and the degradation mechanism was different, suggesting that the stability of a CIGS-based photocathode can be improved by careful design of the structure.

  17. Comparative Study of Zn(O,S) Buffer Layers and CIGS Solar Cells Fabricated by CBD, ALD, and Sputtering: Preprint

    SciTech Connect

    Ramanathan, K.; Mann, J.; Glynn, S.; Christensen, S.; Pankow, J.; Li, J.; Scharf, J.; Mansfield, L. M.; Contreras, M. A.; Noufi, R.

    2012-06-01

    Zn(O,S) thin films were deposited by chemical bath deposition (CBD), atomic layer deposition, and sputtering. Composition of the films and band gap were measured and found to follow the trends described in the literature. CBD Zn(O,S) parameters were optimized and resulted in an 18.5% efficiency cell that did not require post annealing, light soaking, or an undoped ZnO layer. Promising results were obtained with sputtering. A 13% efficiency cell was obtained for a Zn(O,S) emitter layer deposited with 0.5%O2. With further optimization of process parameters and an analysis of the loss mechanisms, it should be possible to increase the efficiency.

  18. High efficiency Cu(In,Ga)Se{sub 2} thin film solar cells without intermediate buffer layers

    SciTech Connect

    Ramanathan, K.; Wiesner, H.; Asher, S.; Niles, D.; Bhattacharya, R.N.; Keane, J.; Contreras, M.A.; Noufi, R.

    1998-09-01

    The nature of the interface between CuInGaSe{sub 2} (CIGS) and the chemical bath deposited CdS layer has been investigated. The authors show that heat-treating the absorbers in Cd- or Zn-containing solutions in the presence of ammonium hydroxide sets up an interfacial reaction with the possibility of an ion exchange occurring between Cd and Cu. The characteristics of devices made in this manner suggest that the reaction generates a thin, n-doped region in the absorber. The authors suggest that this aspect might be more important than the CdS layer in the formation of the junction. It is quite possible that the CdS/CuInSe{sub 2} device is a buried, shallow junction with a CdS window layer, rather than a heterojunction between CdS and CIGS. The authors use these ideas to develop methods for fabricating diodes without CdS or Cd.

  19. Improved performances of organic light-emitting diodes with mixed layer and metal oxide as anode buffer

    NASA Astrophysics Data System (ADS)

    Xue, Qin; Liu, Shouyin; Zhang, Shiming; Chen, Ping; Zhao, Yi; Liu, Shiyong

    2013-01-01

    We fabricated organic light-emitting devices (OLEDs) employing 2-methyl-9,10-di(2-naphthyl)-anthracene (MADN) as hole-transport material (HTM) instead of commonly used N,N'-bis-(1-naphthyl)-N,N'-diphenyl,1,1'-biphenyl-4,4'-diamine (NPB). After inserting a 0.9 nm thick molybdenum oxide (MoOx) layer at the indium tin oxide (ITO)/MADN interface and a 5 nm thick mixed layer at the organic/organic heterojunction interface, the power conversion efficiency of the device can be increased by 4-fold.

  20. AlGaAs phased array laser for optical communications

    NASA Technical Reports Server (NTRS)

    Carlson, N. W.

    1989-01-01

    Phased locked arrays of multiple AlGaAs diode laser emitters were investigated both in edge emitting and surface emitting configurations. CSP edge emitter structures, coupled by either evanescent waves or Y-guides, could not achieve the required powers (greater than or similar to 500 mW) while maintaining a diffraction limited, single lobed output beam. Indeed, although the diffraction limit was achieved in this type of device, it was at low powers and in the double lobed radiation pattern characteristic of out-of-phase coupling. Grating surface emitting (GSE) arrays were, therefore, investigated with more promising results. The incorporation of second order gratings in distribute Bragg reflector (DBR) structures allows surface emission, and can be configured to allow injection locking and lateral coupling to populate 2-D arrays that should be able to reach power levels commensurate with the needs of high performance, free space optical communications levels. Also, a new amplitude modulation scheme was developed for GSE array operation.

  1. Effects of annealing in Be/W and Be/C bilayers deposited on Si(0 0 1) substrates with Fe buffer layers

    NASA Astrophysics Data System (ADS)

    Schinteie, G.; Greculeasa, S. G.; Palade, P.; Lungu, G. A.; Porosnicu, C.; Jepu, I.; Lungu, C. P.; Filoti, G.; Kuncser, V.

    2015-02-01

    Atomic intermixing processes in relation to structural aspects and phase formation in Be based thin films subjected to different annealing treatments simulating the case of re-deposited layered structures on plasma facing components in nuclear fusion devices are reported. Accordingly, bilayers of Be/W and Be/C have been deposited on Si(0 0 1) substrates with Fe buffer layers. The Fe films have been prepared by radiofrequency sputtering and further processed by annealing in hydrogen atmosphere at 300 °C, for 90 min, at a pressure of 10 bars of H2. After the Be/W and Be/C bilayer deposition by means of thermionic vacuum arc method, annealing in vacuum at 600 °C, for 10 min has been applied to the complex structures. The influence of annealing on the phase composition and atomic intermixing processes in the complex structures has been studied by means of X-ray photoelectron spectroscopy (XPS) and conversion electron Mössbauer spectroscopy (CEMS). The layered structures present an oxidation gradient with oxide phases in the uppermost layers and non-oxidized phases in the lower layers, as observed from the XPS data. The CEMS results revealed that the as-deposited structures contain a main metallic Fe phase and secondary superparamagnetic Fe oxide phases at the Fe/Be interface, while annealed samples present a large contribution of Fe-Be and Fe-C mixtures. The annealing treatment induces considerable atomic interdiffusion, strongly dependent on the nature of the upper layer. In the case of Be/W system, the annealing provides a much rougher Be/W interface, while in case of the Be/C structure, the annealing treatment only homogenize the structure over the whole depth.

  2. Effect of TiO 2 buffer layer on the structural and optical properties of ZnO thin films deposited by E-beam evaporation and sol-gel method

    NASA Astrophysics Data System (ADS)

    Xu, Linhua; Shi, Linxing; Li, Xiangyin

    2008-12-01

    In this work, TiO 2 buffer layers were first deposited on Si substrates by electron beam evaporation, and then ZnO thin films were deposited on TiO 2 buffer layers by electron beam evaporation and a sol-gel method, respectively. The structural features and surface morphologies of these films were analyzed by X-ray diffraction (XRD) and a scanning probe microscope (SPM), respectively. The photoluminescence (PL) spectra were measured by a fluorophotometer. The analyses of the structures and surface morphologies showed that all the ZnO thin films were preferentially oriented along the c-axis perpendicular to the substrate surface; TiO 2 buffer layers increased the intensity of (0 0 2) diffraction peaks, made the grains denser and the surfaces of the films smoother. The photoluminescence spectra showed that TiO 2 buffer layers enhanced ultraviolet emissions and reduced visible emissions of the ZnO thin films to a large degree. All the results suggested that the use of TiO 2 buffer layers effectively improved the quality of ZnO thin films.

  3. Electrical properties of n-type GaSb substrates and p-type GaSb buffer layers for InAs/InGaSb superlattice infrared detectors

    SciTech Connect

    Mitchel, W. C. Haugan, H. J.; Mou, Shin; Brown, G. J.; Elhamri, S.; Berney, R.

    2015-09-15

    Lightly doped n-type GaSb substrates with p-type GaSb buffer layers are the preferred templates for growth of InAs/InGaSb superlattices used in infrared detector applications because of relatively high infrared transmission and a close lattice match to the superlattices. We report here temperature dependent resistivity and Hall effect measurements of bare substrates and substrate-p-type buffer layer structures grown by molecular beam epitaxy. Multicarrier analysis of the resistivity and Hall coefficient data demonstrate that high temperature transport in the substrates is due to conduction in both the high mobility zone center Γ band and the low mobility off-center L band. High overall mobility values indicate the absence of close compensation and that improved infrared and transport properties were achieved by a reduction in intrinsic acceptor concentration. Standard transport measurements of the undoped buffer layers show p-type conduction up to 300 K indicating electrical isolation of the buffer layer from the lightly n-type GaSb substrate. However, the highest temperature data indicate the early stages of the expected p to n type conversion which leads to apparent anomalously high carrier concentrations and lower than expected mobilities. Data at 77 K indicate very high quality buffer layers.

  4. Influence of a TiO{sub 2} buffer layer on the magnetic properties of anatase Co:TiO{sub 2} thin films

    SciTech Connect

    Gabor, M. S.; Petrisor, T. Jr.; Tiusan, C.; Hehn, M.; Vasile, B. S.; Petrisor, T.

    2012-04-15

    Our study addresses the influence of a TiO{sub 2} buffer layer on the morphological, structural, and magnetic properties of Co:TiO{sub 2} films grown on (001) SrTiO{sub 3} substrates by RF sputtering. We demonstrate that a direct correlation exist between the morphology, the Co heterogeneity, and the magnetic properties measured in the films. Correlated analysis by cross section transmission electron microscopy, energy dispersive x-ray, and x-ray photoemission spectroscopy reveals that the Co is not uniformly distributed in the film but concentrated in the surface clusters. Atomic force microscopy analysis illustrates that the unbuffered films present a large density of surface clusters. These clusters are not metallic Co but Co rich TiO{sub 2} anatase phase and they are accompanied by structural defects in the film: dislocations, small angle grain boundaries. Magnetometry analysis shows that the unbuffered films have a net ferromagnetic behavior, while in the buffered ones the ferromagnetism is quenched. Therefore, we conclude that the magnetism in unbuffered samples is related to the surface clusters and seems to have an extrinsic nature.

  5. Photovoltaic Performance and Interface Behaviors of Cu(In,Ga)Se2 Solar Cells with a Sputtered-Zn(O,S) Buffer Layer by High-Temperature Annealing.

    PubMed

    Wi, Jae-Hyung; Kim, Tae Gun; Kim, Jeong Won; Lee, Woo-Jung; Cho, Dae-Hyung; Han, Won Seok; Chung, Yong-Duck

    2015-08-12

    We selected a sputtered-Zn(O,S) film as a buffer material and fabricated a Cu(In,Ga)Se2 (CIGS) solar cell for use in monolithic tandem solar cells. A thermally stable buffer layer was required because it should withstand heat treatment during processing of top cell. Postannealing treatment was performed on a CIGS solar cell in vacuum at temperatures from 300-500 °C to examine its thermal stability. Serious device degradation particularly in VOC was observed, which was due to the diffusion of thermally activated constituent elements. The elements In and Ga tend to out-diffuse to the top surface of the CIGS, while Zn diffuses into the interface of Zn(O,S)/CIGS. Such rearrangement of atomic fractions modifies the local energy band gap and band alignment at the interface. The notch-shape induced at the interface after postannealing could function as an electrical trap during electron transport, which would result in the reduction of solar cell efficiency.

  6. Dark current reduction of small molecule organic photodetectors by controlling gap states of molybdenum oxide buffer layers

    NASA Astrophysics Data System (ADS)

    Kim, Seong Heon; Heo, Sung; Yun, Dong-Jin; Satoh, Ryu-ichi; Park, Gyeongsu; Kim, Kyu-Sik

    2016-09-01

    The gap states of the molybdenum-oxide (MoO x ) hole-extraction layer (HEL) in an organic photodetector (OPD) device, which originate from oxygen-vacancy defects, are controlled by appropriate plasma treatments on the MoO x layer. The density of MoO x gap states, investigated using X-ray photoelectron spectroscopy (XPS), is enhanced and depressed with Ar- and O2-plasma treatments, respectively. The dark current of an OPD with a MoO x HEL is considerably reduced by controlling the MoO x gap states using the plasma-treatment method. The mechanism of dark-current reduction may be interpreted by reduced gap states and by a suitable energy level bending and alignment.

  7. Fabrication of Sr silicate buffer layer on Si(100) substrate by pulsed laser deposition using a SrO target

    SciTech Connect

    Imanaka, Atsuhiro; Sasaki, Tsubasa; Hotta, Yasushi Satoh, Shin-ichi

    2014-09-01

    The authors fabricated 2 × 1 Sr-reconstructed Si(100) substrates using thin SrO layers, and used them to direct growth of crystalline perovskite oxide on Si. The SrO layers used to reconstruct the Si(100) substrates were grown by pulsed laser deposition from a SrO single crystal target, followed by postdeposition-annealing (PDA) of the SrO/Si(100) structure. In situ observations of reflective high-energy electron diffraction during PDA confirmed a 2 × 1 reconstruction of the Si surface and x-ray photoemission spectroscopy of the annealed samples confirmed the existence of Sr atoms in a silicate phase, which indicated that a 2 × 1 Sr-reconstructed Si surface was achieved. The optimal fabrication conditions were annealing at 720 °C for 1 min and an equivalent SrO layer thickness (ML{sub eq}) of 2.5 ML{sub eq}. The temperature condition was very narrow, at 720 ± 20 °C, for an acceptable product. Subsequently, the authors demonstrated the growth of crystalline SrTiO{sub 3} films on the 2 × 1 Sr-reconstructed Si(100) surfaces.

  8. Effects of the Buffer Layers on the Adhesion and Antimicrobial Properties of the Amorphous ZrAlNiCuSi Films

    NASA Astrophysics Data System (ADS)

    Chiang, Pai-Tsung; Chen, Guo-Ju; Jian, Sheng-Rui; Shih, Yung-Hui

    2011-06-01

    To extend the practical applications of the bulk metallic glasses (BMGs), the preparation of the metallic glass coatings on various substrates becomes an important research issue. Among the interfacial properties of the coatings, the adhesion between films and substrates is the most crucial. In this study, amorphous Zr61Al7.5Ni10Cu17.5Si4 (ZrAlNiCuSi) thin films were deposited on SUS304 stainless steel at various sputtering powers by DC sputtering. According to the scratch tests, the introduction of the Cr and Ti buffer layers effectively improves the adhesion between the amorphous thin films and substrate without changing the surface properties, such as roughness and morphology. The antimicrobial results show that the biological activities of these microbes, except Acinetobacter baumannii, are effectively suppressed during the test period.

  9. Improved mobility of AlGaN channel heterojunction material using an AlGaN/GaN composite buffer layer

    NASA Astrophysics Data System (ADS)

    Wen, Hui-Juan; Zhang, Jin-Cheng; Lu, Xiao-Li; Wang, Zhi-Zhe; Ha, Wei; Ge, Sha-Sha; Cao, Rong-Tao; Hao, Yue

    2014-03-01

    The quality of an AlGaN channel heterojunction on a sapphire substrate is massively improved by using an AlGaN/GaN composite buffer layer. We demonstrate an Al0.4Ga0.5N/Al0.18Ga0.82N heterojunction with a state-of-the-art mobility of 815 cm2/(V·s) and a sheet resistance of 890 Ω/□ under room temperature. The crystalline quality and the electrical properties of the AlGaN heterojunction material are analyzed by atomic force microscopy, high-resolution X-ray diffraction, and van der Pauw Hall and capacitance—voltage (C—V) measurements. The results indicate that the improved electrical properties should derive from the reduced surface roughness and low dislocation density.

  10. Recent Results on Growth of (211)B CdTe on (211)Si with Intermediate Ge and ZnTe Buffer Layers by Metalorganic Vapor-Phase Epitaxy

    NASA Astrophysics Data System (ADS)

    Shintri, Shashidhar; Rao, Sunil; Wijewarnasuriya, Priyalal; Trivedi, Sudhir; Bhat, Ishwara

    2012-10-01

    We report on the investigation of epitaxial cadmium telluride grown by metalorganic vapor-phase epitaxy (MOVPE) on (211)Si, with particular emphasis on studying the effect of changing the reactor parameters and thermal annealing conditions on the epilayer quality. The CdTe films were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), and x-ray diffraction (XRD). The best CdTe films were observed when the Te/Cd precursor partial pressure ratio was close to 3.1. It was also observed that, though annealing improved the crystal quality, a slight increase in surface roughness was observed. Similar attempts were made to improve the growth conditions of ZnTe intermediate buffer layer, which showed similar trends with changes in precursor flows.

  11. Modification of opto-electronic properties of ZnO by incorporating metallic tin for buffer layer in thin film solar cells

    SciTech Connect

    Deepu, D. R.; Jubimol, J.; Kartha, C. Sudha; Louis, Godfrey; Vijayakumar, K. P.; Kumar, K. Rajeev

    2015-06-24

    In this report, the effect of incorporation of metallic tin (Sn) on opto-electronic properties of ZnO thin films is presented. ZnO thin films were deposited through ‘automated chemical spray pyrolysis’ (CSP) technique; later different quantities of ‘Sn’ were evaporated on it and subsequently annealed. Vacuum annealing showed a positive effect on crystallinity of films. Creation of sub band gap levels due to ‘Sn’ diffusion was evident from the absorption and PL spectra. The tin incorporated films showed good photo response in visible region. Tin incorporated ZnO thin films seem to satisfy the desirable criteria for buffer layer in thin film solar cells.

  12. High performance planar p-i-n perovskite solar cells with crown-ether functionalized fullerene and LiF as double cathode buffer layers

    SciTech Connect

    Liu, Xiaodong; Zhou, Yi E-mail: songbo@suda.edu.cn Song, Bo E-mail: songbo@suda.edu.cn; Lei, Ming; Li, Yongfang E-mail: songbo@suda.edu.cn

    2015-08-10

    Double cathode buffer layers (CBLs) composed of fullerene derivative functionalized with a crown-ether end group in its side chain (denoted as PCBC) and a LiF layer were introduced between the PCBM acceptor layer and the top cathode in planar p-i-n perovskite solar cells (pero-SCs) based on CH{sub 3}NH{sub 3}PbI{sub 3−X}Cl{sub X}. The devices with the PCBC/LiF double CBLs showed significant improvements in power conversion efficiency (PCE) and long-term stability when compared to the device with LiF single CBL. Through optimizing the spin-coating speed of PCBC, a maximum PCE of 15.53% has been achieved, which is approximately 15% higher than that of the device with single LiF CBL. The remarkable improvement in PCE can be attributed to the formation of a better ohmic contact in the CBL between PCBC and LiF/Al electrode arising from the dipole moment of PCBC, leading to the enhanced fill factor and short-circuit current density (J{sub sc}). Besides the PCE, the long-term stability of the devices with PCBC interlayer is also superior to that of the device with LiF single CBL, which is due to the more effective protection for the perovskite/PCBM interface.

  13. High performance planar p-i-n perovskite solar cells with crown-ether functionalized fullerene and LiF as double cathode buffer layers

    NASA Astrophysics Data System (ADS)

    Liu, Xiaodong; Lei, Ming; Zhou, Yi; Song, Bo; Li, Yongfang

    2015-08-01

    Double cathode buffer layers (CBLs) composed of fullerene derivative functionalized with a crown-ether end group in its side chain (denoted as PCBC) and a LiF layer were introduced between the PCBM acceptor layer and the top cathode in planar p-i-n perovskite solar cells (pero-SCs) based on CH3NH3PbI3-XClX. The devices with the PCBC/LiF double CBLs showed significant improvements in power conversion efficiency (PCE) and long-term stability when compared to the device with LiF single CBL. Through optimizing the spin-coating speed of PCBC, a maximum PCE of 15.53% has been achieved, which is approximately 15% higher than that of the device with single LiF CBL. The remarkable improvement in PCE can be attributed to the formation of a better ohmic contact in the CBL between PCBC and LiF/Al electrode arising from the dipole moment of PCBC, leading to the enhanced fill factor and short-circuit current density (Jsc). Besides the PCE, the long-term stability of the devices with PCBC interlayer is also superior to that of the device with LiF single CBL, which is due to the more effective protection for the perovskite/PCBM interface.

  14. Single Junction InGaP/GaAs Solar Cells Grown on Si Substrates using SiGe Buffer Layers

    NASA Technical Reports Server (NTRS)

    Ringel, S. A.; Carlin, J. A.; Andre, C. L.; Hudait, M. K.; Gonzalez, M.; Wilt, D. M.; Clark, E. B.; Jenkins, P.; Scheiman, D.; Allerman, A.

    2002-01-01

    Single junction InGaP/GaAs solar cells displaying high efficiency and record high open circuit voltage values have been grown by metalorganic chemical vapor deposition on Ge/graded SiGe/Si substrates. Open circuit voltages as high as 980 mV under AM0 conditions have been verified to result from a single GaAs junction, with no evidence of Ge-related sub-cell photoresponse. Current AM0 efficiencies of close to 16% have been measured for a large number of small area cells, whose performance is limited by non-fundamental current losses due to significant surface reflection resulting from greater than 10% front surface metal coverage and wafer handling during the growth sequence for these prototype cells. It is shown that at the material quality currently achieved for GaAs grown on Ge/SiGe/Si substrates, namely a 10 nanosecond minority carrier lifetime that results from complete elimination of anti-phase domains and maintaining a threading dislocation density of approximately 8 x 10(exp 5) per square centimeter, 19-20% AM0 single junction GaAs cells are imminent. Experiments show that the high performance is not degraded for larger area cells, with identical open circuit voltages and higher short circuit current (due to reduced front metal coverage) values being demonstrated, indicating that large area scaling is possible in the near term. Comparison to a simple model indicates that the voltage output of these GaAs on Si cells follows ideal behavior expected for lattice mismatched devices, demonstrating that unaccounted for defects and issues that have plagued other methods to epitaxially integrate III-V cells with Si are resolved using SiGe buffers and proper GaAs nucleation methods. These early results already show the enormous and realistic potential of the virtual SiGe substrate approach for generating high efficiency, lightweight and strong III-V solar cells.

  15. Strain states of AlN/GaN-stress mitigating layer and their effect on GaN buffer layer grown by ammonia molecular beam epitaxy on 100-mm Si(111)

    NASA Astrophysics Data System (ADS)

    Ravikiran, L.; Radhakrishnan, K.; Dharmarasu, N.; Agrawal, M.; Munawar Basha, S.

    2013-09-01

    The effect of strain states of AlN/GaN-stress mitigating layer (SML) on buried crack density and its subsequent influence on the residual stresses in GaN buffer layers grown using ammonia-molecular beam epitaxy on 100-mm Si(111) substrate has been investigated. Different stages involved in the formation of buried cracks, which are crack initialization, growth of relaxed AlN layer, and subsequent lateral over growth, are identified using in-situ curvature measurements. While the increase of GaN thickness in AlN/GaN-SML enhanced its compressive strain relaxation and resulted in reduced buried crack spacing, the variation of AlN thickness did not show any effect on the crack spacing. Moreover, the decrease in the crack spacing (or increase in the buried crack density) was found to reduce the residual compression in 1st and 2nd GaN layers of AlN/GaN-SML structure. The higher buried crack density relaxed the compressive strain in 1st GaN layer, which further reduced its ability to compensate the tensile stress generated during substrate cool down, and hence resulted in lower residual compressive stress in 2nd GaN layer.

  16. Plasma versus thermal annealing for the Au-catalyst growth of ZnO nanocones and nanowires on Al-doped ZnO buffer layers

    NASA Astrophysics Data System (ADS)

    Güell, Frank; Martínez-Alanis, Paulina R.; Roso, Sergio; Salas-Pérez, Carlos I.; García-Sánchez, Mario F.; Santana, Guillermo; Marel Monroy, B.

    2016-06-01

    We successfully synthesized ZnO nanocones and nanowires over polycrystalline Al-doped ZnO (AZO) buffer layers on fused silica substrates by a vapor-transport process using Au-catalyst thin films. Different Au film thicknesses were thermal or plasma annealed in order to analyze their influence on the ZnO nanostructure growth morphology. Striking differences have been observed. Thermal annealing generates a distribution of Au nanoclusters and plasma annealing induces a fragmentation of the Au thin films. While ZnO nanowires are found in the thermal-annealed samples, ZnO nanocones and nanowires have been obtained on the plasma-annealed samples. Enhancement of the preferred c-axis (0001) growth orientation was demonstrated by x-ray diffraction when the ZnO nanocones and nanowires have been grown over the AZO buffer layer. The transmittance spectra of the ZnO nanocones and nanowires show a gradual increase from 375 to 900 nm, and photoluminescence characterization pointed out high concentration of defects leading to observation of a broad emission band in the visible range from 420 to 800 nm. The maximum emission intensity peak position of the broad visible band is related to the thickness of the Au-catalyst for the thermal-annealed samples and to the plasma power for the plasma-annealed samples. Finally, we proposed a model for the plasma versus thermal annealing of the Au-catalyst for the growth of the ZnO nanocones and nanowires. These results are promising for renewable energy applications, in particular for its potential application in solar cells.

  17. Assessment of Chemical Solution Synthesis and Properties of Gd2Zr2O7 Thin Films as Buffer Layers for Second-Generation High-Temperature Superconductor Wires (Postprint)

    DTIC Science & Technology

    2012-02-01

    due to differing chemical envi- ronment through the GZO layer, specifically caused by the variable carbon distribution. The performance of the MOD...deposition of lanthanum zirconate barrier layers applied to low-cost coated-conductor fabrication. J. Mater. Res. 19, 2117 (2004). 11. T. Aytug, M...cal solution deposition of lanthanum zirconate buffer layers on biaxially textured Ni–1.7% Fe–3% W alloy substrates for coated- conductor

  18. Impact of the deposition conditions of buffer and windows layers on lowering the metastability effects in Cu(In,Ga)Se2/Zn(S,O)-based solar cell

    NASA Astrophysics Data System (ADS)

    Naghavi, Negar; Hildebrandt, Thibaud; Bouttemy, Muriel; Etcheberry, Arnaud; Lincot, Daniel

    2016-02-01

    The highest and most reproducible (Cu(In,Ga)Se2 (CIGSe) based solar-cell efficiencies are obtained by use of a very thin n-type CdS layer deposited by chemical bath deposition (CBD). However because of both Cadmium's adverse environmental impact and the narrow bandgap of CdS (2.4-2.5 eV) one of the major objectives in the field of CIGSe technology remains the development and implementation in the production line of Cd-free buffer layers. The CBDZn( S,O) remains one the most studied buffer layer for replacing the CdS in Cu(In,Ga)Se2-based solar cells and has already demonstrated its potential to lead to high-efficiency solar cells up to 22.3%. However one of the key issue to implement a CBD-Zn(S,O) process in a CIGSe production line is the cells stability, which depends both on the deposition conditions of CBD-Zn(S,O) and on a good band alignment between CIGSe/Zn(S,O)/windows layers. The most common window layers applied in CIGSe solar cells consist of two layers : a thin (50-100 nm) and highly resistive i-ZnO layer deposited by magnetron sputtering and a transparent conducting 300-500 nm ZnO:Al layer. In the case of CBD-Zn(S,O) buffer layer, the nature and deposition conditions of both Zn(S,O) and the undoped window layer can strongly influence the performance and stability of cells. The present contribution will be specially focused on the effect of condition growth of CBD-Zn(S,O) buffer layers and the impact of the composition and deposition conditions of the undoped window layers such as ZnxMgyO or ZnxSnyO on the stability and performance of these solar cells.

  19. Electrical stabilities and memory mechanisms of organic bistable devices fabricated utilizing a poly(3,4-ethylene-dioxythiophene): Poly(styrenesulfonate) layer with a poly(methyl methacrylate) buffer layer

    NASA Astrophysics Data System (ADS)

    Min Son, Jung; Seung Song, Woo; Ho Yoo, Chan; Yeol Yun, Dong; Whan Kim, Tae

    2012-04-01

    Organic bistable devices (OBDs) based on a poly(3,4-ethylene-dioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) layer with a poly(methyl methacrylate) (PMMA) buffer layer were fabricated on indium-tin-oxide (ITO)-coated polyethylene terephthalate (PET) flexible substrates. Current-voltage curves for the Al/PEDOT:PSS/PMMA/ITO/PET device showed current bistabilities with an ON/OFF current ratio of 1 × 103, indicative of a significant enhancement of memory storage. The endurance number of the ON/OFF switchings for the OBDs was above 1 × 105 cycles showing high potential applications in read only memory devices. The memory mechanisms for the OBDs on the basis of oxidation and reduction operations were attributed to the filament processes.

  20. Large enhanced perpendicular magnetic anisotropy in CoFeB/MgO system with the typical Ta buffer replaced by an Hf layer

    NASA Astrophysics Data System (ADS)

    Liu, T.; Cai, J. W.; Sun, Li

    2012-09-01

    By systematically comparing the magnetic properties of the Ta/CoFeB/Ta and MgO/CoFeB/MgO structures with and without a submonolayer of MgO, Ta, V, Nb, Hf and W inserted in the middle of the CoFeB layer, we have proved that the observed perpendicular magnetic anisotropy (PMA) in Ta/CoFeB/MgO sandwiches is solely originated from the CoFeB/MgO interface with the Ta buffer acting to enhance the CoFeB/MgO interface anisotropy significantly. Moreover, replacing Ta with Hf causes the CoFeB/MgO interfacial PMA further enhanced by 35%, and the CoFeB layer with perpendicular magnetization has a much larger critical thickness accordingly, leaving a wider thickness margin for the CoFeB/MgO-based perpendicular magnetic tunnel junction optimization. Also the sputter deposited thin Hf films are amorphous with low surface roughness. These results will ensure the Hf/CoFeB/MgO more promising material system for PMA device development.

  1. Peculiarities of strain relaxation in linearly graded InxGa1-xAs/GaAs(001) metamorphic buffer layers grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Sorokin, S. V.; Klimko, G. V.; Sedova, I. V.; Sitnikova, A. A.; Kirilenko, D. A.; Baidakova, M. V.; Yagovkina, M. A.; Komissarova, T. A.; Belyaev, K. G.; Ivanov, S. V.

    2016-12-01

    This paper presents a comprehensive study of structural, optical and electrical properties of heterostructures with linearly graded InxGa1-xAs metamorphic buffer layers (MBLs) grown by molecular beam epitaxy on GaAs (001) substrates. The low density of threading dislocations (well below 106 cm-2) in 1-μm-thick In0.3Ga0.7As layers grown atop of the linearly graded InxGa1-xAs/GaAs MBLs has been confirmed by using transmission electron microscopy (TEM). X-ray diffraction (XRD) data demonstrate good agreement between the experimentally measured In step-back and its calculations in the frames of existing models. Combining the XRD reciprocal space maps (RSM) of the structures and the spatially-resolved selective area electron diffraction measurements by cross-sectional TEM in depth-profiled RSM diagrams allowed direct visualization of the strain relaxation dynamics during the MBL growth. Strong effect of the azimuth angle and the value of an unintentional initial miscut of nominally (001) oriented GaAs substrate on the strain relaxation dynamics was observed.

  2. New sulphide precursors for Zn(O,S) buffer layers in Cu(In,Ga)Se2 solar cells for faster reaction kinetics

    NASA Astrophysics Data System (ADS)

    Löckinger, Johannes; Nishiwaki, Shiro; Fuchs, Peter; Buecheler, Stephan; Romanyuk, Yaroslav E.; Tiwari, Ayodhya N.

    2016-08-01

    The development of a novel chemistry for the chemical bath deposition of Zn(O,S) buffer layers for Cu(In,Ga)Se2 (CIGS) solar cells is desired for a higher growth rate, hence reduced deposition time, while reducing simultaneously the required concentration of reactants. State-of-the-art recipes are based on thiourea as sulphide precursor requiring a high molarity of reactants and relatively long deposition times due to the slow decomposition rate of thiourea. In this contribution thioamide based sulphide precursors were investigated for their decomposition and growth behaviour. A co-solvent approach in an ethanolic/aqueous ammonia medium was evaluated omitting the need for additional complexants. By replacing thiourea with the investigated thioamides, homogeneous dense layers of around 30 nm were grown with a greatly decreased deposition time of 8 min compared to 25 min for thiourea. Likewise, the concentration of the sulphide precursor was 40-fold reduced. The photovoltaic performance as characterized by external quantum efficiency and current-voltage measurements, showed conversion efficiencies of 15% comparable to the thiourea based process.

  3. Internal stress and degradation in short-wavelength AlGaAs double-heterojunction devices

    NASA Technical Reports Server (NTRS)

    Ladany, I.; Furman, T. R.; Marinelli, D. P.

    1979-01-01

    Aging tests of incoherently operated zinc-doped double-heterojunction (DH) lasers designed for short-wavelength (0.71-0.72 micron) operation show that the introduction of buffer layers between the substrate and the DH structure leads to a drastic reduction in gradual degradation. This is attributed to a decrease in lattice mismatch stress.

  4. A proposed mechanism for investigating the effect of porous silicon buffer layer on TiO2 nanorods growth

    NASA Astrophysics Data System (ADS)

    Rahmani, N.; Dariani, R. S.; Rajabi, M.

    2016-03-01

    In this study, we have synthesized TiO2 nanorods (NRs) on silicon and porous silicon (PS) substrates by hydrothermal method. The PS substrates with different porosities were fabricated by electrochemical anodization on silicon. According to the field emission electron microscopy images, TiO2 NRs grown on PS substrates have a better growth compared to those grown on silicon. Also increasing substrate porosity leads to an increase in density of the NRs. Atomic force microscopy observation demonstrates that porous layer formation due to etching of silicon surface leads to an increase of its roughness. Results indicate surface roughness evolution with porosity increasing enhances TiO2 nucleation on substrate and thus increases TiO2 NRs density. We propose a growth mechanism to explain how we can control the local surface chemical potential and thus the nucleation and alignment of TiO2 NRs by surface roughness variation. Also, photoluminescence studies show a red-shift in band gap energy of NRs compared to that of common bulk TiO2.

  5. CdS and Cd-Free Buffer Layers on Solution Phase Grown Cu2ZnSn(SxSe1- x)4 :Band Alignments and Electronic Structure Determined with Femtosecond Ultraviolet Photoemission Spectroscopy

    SciTech Connect

    Haight, Richard; Barkhouse, Aaron; Wang, Wei; Yu, Luo; Shao, Xiaoyan; Mitzi, David; Hiroi, Homare; Sugimoto, Hiroki

    2013-12-02

    The heterojunctions formed between solution phase grown Cu2ZnSn(SxSe1- x)4(CZTS,Se) and a number of important buffer materials including CdS, ZnS, ZnO, and In2S3, were studied using femtosecond ultraviolet photoemission spectroscopy (fs-UPS) and photovoltage spectroscopy. With this approach we extract the magnitude and direction of the CZTS,Se band bending, locate the Fermi level within the band gaps of absorber and buffer and measure the absorber/buffer band offsets under flatband conditions. We will also discuss two-color pump/probe experiments in which the band bending in the buffer layer can be independently determined. Finally, studies of the bare CZTS,Se surface will be discussed including our observation of mid-gap Fermi level pinning and its relation to Voc limitations and bulk defects.

  6. Buffer Biology.

    ERIC Educational Resources Information Center

    Morgan, Kelly

    2000-01-01

    Presents a science experiment in which students test the buffering capacity of household products such as shampoo, hand lotion, fizzies candy, and cola. Lists the standards addressed in this experiment and gives an example of a student lab write-up. (YDS)

  7. Comparison of degradation and recaesiation between GaAs and AlGaAs photocathodes in an unbaked vacuum system.

    PubMed

    Feng, Cheng; Zhang, Yijun; Shi, Feng; Qian, Yunsheng; Cheng, Hongchang; Zhang, Junju; Liu, Xinxin; Zhang, Xiang

    2017-03-20

    The lifetime and reliability of a photocathode during operation are always raised problems and the photocathode performance depends on the vacuum condition. With the purpose of investigating the stability and reliability of a GaAs-based photocathode in a harsher vacuum environment, reflection-mode exponential-doped GaAs and AlGaAs photocathodes are metalorganic vapor-phase epitaxial grown and then (Cs, O) activated inside an unbaked vacuum chamber. The degraded photocurrents are compared after activation and recaesiations between GaAs and AlGaAs photocathdoes under illumination with an equal initial photocurrent and an equal optical flux, respectively. It is found that the performance on degradation and recaesiations between GaAs and AlGaAs photocathodes are different. In the unbaked vacuum system, the stability of an AlGaAs photocathode after (Cs, O) activation is always better than that of a GaAs photocathode. After multiple recaesiations, the photocurrent decay curves of the AlGaAs photocathode are nearly coincident, which means a nearly constant operational lifetime. Moreover, operational lifetime of an AlGaAs photocathode is longer than that of a GaAs photocathode, which further illuminates that AlGaAs photocathodes are superior to GaAs photocathodes in stability and repeatability under markedly harsher vacuum conditions.

  8. Structural and electrical properties of metal ferroelectric insulator semiconductor structure of Al/SrBi2Ta2O9/HfO2/Si using HfO2 as buffer layer

    NASA Astrophysics Data System (ADS)

    Roy, A.; Dhar, A.; Bhattacharya, D.; Ray, S. K.

    2008-05-01

    Ferroelectric SrBi2Ta2O9 (SBT) thin films have been deposited by the radio-frequency magnetron sputtering technique on bare p-Si as well as on HfO2 insulating buffer p-Si. XRD patterns revealed the formation of a well-crystallized SBT perovskite thin film on the HfO2 buffer layer. The electrical properties of the metal-ferroelectric-insulator-semiconductor (MFIS) structure were characterized by varying thicknesses of the HfO2 layer. The MFIS structure exhibits a maximum clockwise C-V memory window of 1.60 V when the thickness of the HfO2 layer was 12 nm with a lower leakage current density of 6.20 × 10-7 A cm-2 at a positive applied voltage of 7 V. However, the memory window reaches a maximum value of 0.7 V at a bias voltage of ±5 and then decreases due to charge injection in the case of the insulating buffer layer thickness of 3 nm. The density of oxide trapped charges at/near the buffer layer-ferroelectric interface is studied by the voltage stress method. Capacitance-voltage (C-V) and leakage current density (J-V) characteristics of the Al/SBT/HfO2/Si(1 0 0) capacitor indicate that the introduction of the HfO2 buffer layer prevents interfacial diffusion between the SBT thin film and the Si substrate effectively and improves the interface quality. Furthermore, the Al/SBT/HfO2/Si structures exhibit excellent retention characteristics, the high and low capacitance values clearly distinguishable for over 1 h and 30 min. This shows that the proposed Al/SrBi2Ta2O9/HfO2/Si structure is ideally suitable for high performance ferroelectric memories.

  9. Effect of surface modification of CeO2 buffer layers on Jc and defect microstructures of large-area YBCO thin films

    NASA Astrophysics Data System (ADS)

    Develos-Bagarinao, K.; Yamasaki, H.; Nakagawa, Y.

    2006-08-01

    High-quality CeO2 buffer layers are requisite for the successful growth of YBCO thin films with excellent properties on sapphire substrates. In this study, we evaluated the effect of surface modification of the CeO2 layers on the properties of the YBCO thin films prepared by large-area pulsed laser deposition (PLD), in particular the critical current density Jc and defect microstructure. High-temperature annealing (1050 °C) has been found to significantly smoothen the very rough and granular surfaces of the as-grown CeO2 layers (surface roughness rms~5-10 nm) to atomic flatness (rms~0.5 nm). However, a rather unique characteristic of the CeO2 layers deposited by large-area PLD is the development of pores when subjected to prolonged high-temperature annealing. For very short annealing periods (10-20 min), the surface morphology becomes atomically flat, along with the appearance of a high density of 'nanopores' that are ~40-100 nm in diameter and ~3-5 nm in depth. Extending the annealing period to 60 min or more results in the development of a surface subtended with enlarged pores ~0.2-0.5 µm in diameter. Compared with the YBCO thin films deposited on as-grown CeO2, YBCO thin films on annealed CeO2 exhibited better homogeneity of Jc and better crystalline texture. Among the YBCO thin films deposited on annealed CeO2, higher self-field and in-field Jc was obtained for YBCO thin films deposited on CeO2 with smooth surfaces but interspersed with nanopores. Investigation of the defect microstructure via the etch pit method in conjunction with atomic force microscopy (AFM) of the YBCO thin films revealed a high density of linear defects in the form of screw and edge dislocations, which correlated well with a high density of nanopores on annealed CeO2. Transmission electron microscopy (TEM) further confirmed the presence of threading dislocations clearly emanating from the nanopore sites. Angular dependence of Jc revealed enhanced flux pinning for YBCO thin films

  10. Large-roll growth of 25-inch hexagonal BN monolayer film for self-release buffer layer of free-standing GaN wafer

    PubMed Central

    Wu, Chenping; Soomro, Abdul Majid; Sun, Feipeng; Wang, Huachun; Huang, Youyang; Wu, Jiejun; Liu, Chuan; Yang, Xiaodong; Gao, Na; Chen, Xiaohong; Kang, Junyong; Cai, Duanjun

    2016-01-01

    Hexagonal boron nitride (h-BN) is known as promising 2D material with a wide band-gap (~6 eV). However, the growth size of h-BN film is strongly limited by the size of reaction chamber. Here, we demonstrate the large-roll synthesis of monolayer and controllable sub-monolayer h-BN film on wound Cu foil by low pressure chemical vapor deposition (LPCVD) method. By winding the Cu foil substrate into mainspring shape supported by a multi-prong quartz fork, the reactor size limit could be overcome by extending the substrate area to a continuous 2D curl of plane inward. An extremely large-size monolayer h-BN film has been achieved over 25 inches in a 1.2” tube. The optical band gap of h-BN monolayer was determined to be 6.0 eV. The h-BN film was uniformly transferred onto 2” GaN or 4” Si wafer surfaces as a release buffer layer. By HVPE method, overgrowth of thick GaN wafer over 200 μm has been achieved free of residual strain, which could provide high quality homo-epitaxial substrate. PMID:27756906

  11. Reduction in leakage current in AlGaN/GaN HEMT with three Al-containing step-graded AlGaN buffer layers on silicon

    NASA Astrophysics Data System (ADS)

    Yu, Xinxin; Ni, Jinyu; Li, Zhonghui; Zhou, Jianjun; Kong, Cen

    2014-05-01

    AlGaN/GaN high-electron-mobility transistor (HEMT) structures with two and three Al-containing step-graded AlGaN buffer layers (BLs) were grown on silicon (111) substrates by metal organic chemical vapor deposition. Considerable tensile stress was observed in the GaN grown with only two 0.8 µm AlGaN BLs, while a large in-plane compression in GaN grown with three 2.3 µm AlGaN BLs. The reverse gate leakage current in the HEMT with three AlGaN BLs was approximately 0.1 µA/mm, which was more than one order of magnitude smaller than that for the HEMT with two AlGaN BLs. A three-terminal off-state breakdown voltage of 265 V and a vertical gate-to-substrate breakdown voltage of 510 V were obtained in the HEMT with three AlGaN BLs. Detailed analysis was performed on the basis of the structural properties of AlGaN/GaN heterostructures.

  12. Large-roll growth of 25-inch hexagonal BN monolayer film for self-release buffer layer of free-standing GaN wafer

    NASA Astrophysics Data System (ADS)

    Wu, Chenping; Soomro, Abdul Majid; Sun, Feipeng; Wang, Huachun; Huang, Youyang; Wu, Jiejun; Liu, Chuan; Yang, Xiaodong; Gao, Na; Chen, Xiaohong; Kang, Junyong; Cai, Duanjun

    2016-10-01

    Hexagonal boron nitride (h-BN) is known as promising 2D material with a wide band-gap (~6 eV). However, the growth size of h-BN film is strongly limited by the size of reaction chamber. Here, we demonstrate the large-roll synthesis of monolayer and controllable sub-monolayer h-BN film on wound Cu foil by low pressure chemical vapor deposition (LPCVD) method. By winding the Cu foil substrate into mainspring shape supported by a multi-prong quartz fork, the reactor size limit could be overcome by extending the substrate area to a continuous 2D curl of plane inward. An extremely large-size monolayer h-BN film has been achieved over 25 inches in a 1.2” tube. The optical band gap of h-BN monolayer was determined to be 6.0 eV. The h-BN film was uniformly transferred onto 2” GaN or 4” Si wafer surfaces as a release buffer layer. By HVPE method, overgrowth of thick GaN wafer over 200 μm has been achieved free of residual strain, which could provide high quality homo-epitaxial substrate.

  13. High-performance tandem organic light-emitting diodes based on a buffer-modified p/n-type planar organic heterojunction as charge generation layer

    NASA Astrophysics Data System (ADS)

    Wu, Yukun; Sun, Ying; Qin, Houyun; Hu, Shoucheng; Wu, Qingyang; Zhao, Yi

    2017-04-01

    High-performance tandem organic light-emitting diodes (TOLEDs) were realized using a buffer-modified p/n-type planar organic heterojunction (OHJ) as charge generation layer (CGL) consisting of common organic materials, and the configuration of this p/n-type CGL was "LiF/N,N'-diphenyl-N,N'-bis(1-napthyl)-1,1'-biphenyl-4,4'-diamine (NPB)/4,7-diphenyl-1,10-phenanthroline (Bphen)/molybdenum oxide (MoOx)". The optimized TOLED exhibited a maximum current efficiency of 77.6 cd/A without any out-coupling techniques, and the efficiency roll-off was greatly improved compared to the single-unit OLED. The working mechanism of the p/n-type CGL was discussed in detail. It is found that the NPB/Bphen heterojunction generated enough charges under a forward applied voltage and the carrier extraction was a tunneling process. These results could provide a new method to fabricate high-performance TOLEDs.

  14. Ambient CdCl{sub 2} treatment on CdS buffer layer for improved performance of Sb{sub 2}Se{sub 3} thin film photovoltaics

    SciTech Connect

    Wang, Liang; Luo, Miao; Qin, Sikai; Liu, Xinsheng; Chen, Jie; Yang, Bo; Leng, Meiying; Xue, Ding-Jiang; Zhou, Ying; Gao, Liang; Song, Haisheng; Tang, Jiang

    2015-10-05

    Antimony selenide (Sb{sub 2}Se{sub 3}) is appealing as a promising light absorber because of its intrinsically benign grain boundaries, suitable band gap (∼1.1 eV), strong absorption coefficient, and relatively environmentally friendly constituents. Recently, we achieved a certified 5.6% efficiency Sb{sub 2}Se{sub 3} thin film solar cell with the assistance of ambient CdCl{sub 2} treatment on the CdS buffer layer. Here, we focused on investigating the underlying mechanism from a combined materials and device physics perspective applying current density-voltage (J-V) fitting analysis, atomic force microscope, X-ray photoelectron spectroscopy, fluorescence, and UV–Vis transmission spectroscopy. Our results indicated that ambient CdCl{sub 2} treatment on CdS film not only improved CdS grain size and quality, but also incorporated Cl and more O into the film, both of which can significantly improve the heterojunction quality and device performance of CdS/Sb{sub 2}Se{sub 3} solar cells.

  15. Integration and structural analysis of strain relaxed bi-epitaxial zinc oxide(0001) thin film with silicon(100) using titanium nitride buffer layer

    SciTech Connect

    Gupta, Pranav; Narayan, Jagdish

    2014-01-28

    Epitaxial growth of c-plane ZnO(0001) has been demonstrated on the Si(001) by using TiN as an intermediate buffer layer. Because of different out of plane symmetry of the substrate (Si/TiN) and the film (ZnO), two orientations of ZnO domains were obtained and the ZnO film growth is of bi-epitaxial nature. The ZnO thin film was observed to be nearly strain relaxed from X-ray and Raman measurements. The interface between the ZnO and TiN was investigated by transmission electron microscopy, and atomic arrangement has been modeled to understand the crystallographic orientation and structure of the domain/grain boundaries. Reaction at ZnO/TiN interface at higher growth temperature causing zinc titanate formation was observed. The grain boundary structure between the observed domains investigated by scanning transmission electron microscopy, revealed the ZnO(0001) planes to be contiguous across the grain boundary which is significant from the perspective of conduction electron scattering. In this configuration, the TiN (being electrically conductive) can be effectively used as an electrode for novel vertically integrated device applications (like light emitting diodes) directly on Si(100) substrate.

  16. Effect of different thickness crystalline SiC buffer layers on the ordering of MgB{sub 2} films probed by extended x-ray absorption fine structure

    SciTech Connect

    Putri, W. B. K.; Tran, D. H.; Kang, B.; Lee, O. Y.; Kang, W. N.; Miyanaga, T.; Yang, D. S.

    2014-03-07

    Extended X-ray absorption fine structure (EXAFS) spectroscopy is a powerful method to investigate the local structure of thin films. Here, we have studied EXAFS of MgB{sub 2} films grown on SiC buffer layers. Crystalline SiC buffer layers with different thickness of 70, 100, and 130 nm were deposited on the Al{sub 2}O{sub 3} (0001) substrates by using a pulsed laser deposition method, and then MgB{sub 2} films were grown on the SiC buffer layer by using a hybrid physical-chemical vapor deposition technique. Transition temperature of MgB{sub 2} film decreased with increasing thickness of SiC buffer layer. However, the T{sub c} dropping went no farther than 100 nm-thick-SiC. This uncommon behavior of transition temperature is likely to be created from electron-phonon interaction in MgB{sub 2} films, which is believed to be related to the ordering of MgB{sub 2} atomic bonds, especially in the ordering of Mg–Mg bonds. Analysis from Mg K-edge EXAFS measurements showed interesting ordering behavior of MgB{sub 2} films. It is noticeable that the ordering of Mg–B bonds is found to decrease monotonically with the increase in SiC thickness of the MgB{sub 2} films, while the opposite happens with the ordering in Mg–Mg bonds. Based on these results, crystalline SiC buffer layers in MgB{sub 2} films seemingly have evident effects on the alteration of the local structure of the MgB{sub 2} film.

  17. A nitrilo-tri-acetic-acid/acetic acid route for the deposition of epitaxial cerium oxide films as high temperature superconductor buffer layers

    SciTech Connect

    Thuy, T.T.; Lommens, P.; Narayanan, V.; Van de Velde, N.; De Buysser, K.; Herman, G.G.; Cloet, V.; Van Driessche, I.

    2010-09-15

    A water based cerium oxide precursor solution using nitrilo-tri-acetic-acid (NTA) and acetic acid as complexing agents is described in detail. This precursor solution is used for the deposition of epitaxial CeO{sub 2} layers on Ni-5at%W substrates by dip-coating. The influence of the complexation behavior on the formation of transparent, homogeneous solutions and gels has been studied. It is found that ethylenediamine plays an important role in the gelification. The growth conditions for cerium oxide films were Ar-5% gas processing atmosphere, a solution concentration level of 0.25 M, a dwell time of 60 min at 900 {sup o}C and 5-30 min at 1050 {sup o}C. X-ray diffraction (XRD), scanning electron microscope (SEM), atomic force microscopy (AFM), pole figures and spectroscopic ellipsometry were used to characterize the CeO{sub 2} films with different thicknesses. Attenuated total reflection-Fourier transform infrared (ATR-FTIR) was used to determine the carbon residue level in the surface of the cerium oxide film, which was found to be lower than 0.01%. Textured films with a thickness of 50 nm were obtained. - Graphical abstract: Study of the complexation and hydrolysis behavior of Ce{sup 4+} ions in the presence of nitrilo-tri-acetic acid and the subsequent development of an aqueous chemical solution deposition route suited for the processing of textured CeO{sub 2} buffer layers on Ni-W tapes.

  18. The effects of ultra-thin cerium fluoride film as the anode buffer layer on the electrical characteristics of organic light emitting diodes

    NASA Astrophysics Data System (ADS)

    Lu, Hsin-Wei; Tsai, Cheng-Che; Hong, Cheng-Shong; Kao, Po-Ching; Juang, Yung-Der; Chu, Sheng-Yuan

    2016-11-01

    In this study, the efficiency of organic light-emitting diodes (OLEDs) was enhanced by depositing a CeF3film as an ultra-thin buffer layer between the indium tin oxide (ITO) electrode and α-naphthylphenylbiphenyldiamine (NPB) hole transport layer, with the structure configuration ITO/CeF3 (0.5, 1, and 1.5 nm)/α-naphthylphenylbiphenyl diamine (NPB) (40 nm)/tris(8-hydroxyquinoline) aluminum (Alq3) (60 nm)/lithium fluoride (LiF) (1 nm)/Al (150 nm). The enhancement mechanism was systematically investigated via several approaches. The X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy results revealed the formation of the UV-ozone treated CeF3 film. The work function increased from 4.8 eV (standard ITO electrode) to 5.22 eV (0.5-nm-thick UV-ozone treated CeF3 film deposited on the ITO electrode). The surface roughness of the UV-ozone treated CeF3 film was smoother than that of the standard ITO electrode. Further, the UV-ozone treated CeF3 film increased both the surface energy and polarity, as determined from contact angle measurements. In addition, admittance spectroscopy measurements showed an increased capacitance and conductance of the OLEDs. Accordingly, the turn-on voltage decreased from 4.2 V to 3.6 V at 1 mA/cm2, the luminance increased from 7588 cd/m2 to 24760 cd/m2, and the current efficiency increased from 3.2 cd/A to 3.8 cd/A when the 0.5-nm-thick UV-ozone treated CeF3 film was inserted into the OLEDs.

  19. Buffer layers for coated conductors

    DOEpatents

    Stan, Liliana; Jia, Quanxi; Foltyn, Stephen R.

    2011-08-23

    A composite structure is provided including a base substrate, an IBAD oriented material upon the base substrate, and a cubic metal oxide material selected from the group consisting of rare earth zirconates and rare earth hafnates upon the IBAD oriented material. Additionally, an article is provided including a base substrate, an IBAD oriented material upon the base substrate, a cubic metal oxide material selected from the group consisting of rare earth zirconates and rare earth hafnates upon the IBAD oriented material, and a thick film upon the cubic metal oxide material. Finally, a superconducting article is provided including a base substrate, an IBAD oriented material upon the base substrate, a cubic metal oxide material selected from the group consisting of rare earth zirconates and rare earth hafnates upon the IBAD oriented material, and an yttrium barium copper oxide material upon the cubic metal oxide material.

  20. Cadmium-free copper indium gallium diselenide hybrid solar cells comprising a 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole buffer layer

    NASA Astrophysics Data System (ADS)

    Reinhard, Manuel; Simon, Christoph; Kuhn, Johannes; Bürkert, Linda; Cemernjak, Marco; Dimmler, Bernhard; Lemmer, Uli; Colsmann, Alexander

    2013-02-01

    Copper indium gallium diselenide (CIGS) solar cells are the most efficient thin film photovoltaic devices today. In this work, we investigate CIGS/organic hybrid solar cells comprising a semi-transparent metal top electrode and a wide band gap organic semiconductor as buffer layer. Depositing the organic semiconductor from solution, we fabricate Cd-free solar cells exhibiting about the same efficiency as their counterparts comprising CdS and significantly higher open-circuit voltages as compared to buffer-free devices. Although the organic molecules do not cover the CIGS surface homogeneously, their use enables prolonged charge carrier lifetimes according to impedance spectroscopy measurements.

  1. Preparation and properties of highly (100)-oriented Pb(Zr0.2Ti0.8)O3 thin film prepared by rf magnetron sputtering with a PbOx buffer layer

    NASA Astrophysics Data System (ADS)

    Wu, Jiagang; Zhu, Jiliang; Xiao, Dingquan; Zhu, Jianguo; Tan, Junzhe; Zhang, Qinglei

    2007-05-01

    A method for fabrication of highly (100)-oriented Pb(Zr0.2Ti0.8)O3 (PZT) thin films by rf magnetron sputtering with a special buffer of PbOx (RFMS-SBP) was developed. With this method, highly (100)-oriented Pb(Zr0.2Ti0.8)O3 thin films were prepared on the PbOx/Pt(111)/Ti/SiO2/Si(100) substrates, and the preferential (100) orientation of the Pb(Zr0.2Ti0.8)O3 film is 92%. The (100) orientation of the PbOx buffer layer leads to the (100) orientation of the PZT thin films, and the thickness of the buffer layer plays a significant role on the phase purity and electrical properties of the films. Highly (100)-oriented Pb(Zr0.2Ti0.8)O3 thin films with proper thickness of PbOx buffer layer possess good electrical properties with larger remnant polarization Pr (69.7 μC/cm2), lower coercive field Ec (92.4 kV/cm), and good pyroelectric coefficient at room temperature (2.6×10-8 C/cm2 K). The butterfly-shaped ɛ-E characteristic curve gives the evidence of the improved in-plane ferroelectric property in the films.

  2. Cd-free buffer layer materials on Cu2ZnSn(SxSe1-x)4: Band alignments with ZnO, ZnS, and In2S3

    NASA Astrophysics Data System (ADS)

    Barkhouse, D. Aaron R.; Haight, Richard; Sakai, Noriyuki; Hiroi, Homare; Sugimoto, Hiroki; Mitzi, David B.

    2012-05-01

    The heterojunctions formed between Cu2ZnSn(SxSe1-x)4 (CZTSSe) and three Cd-free n-type buffers, ZnS, ZnO, and In2S3, were studied using femtosecond ultraviolet photoemission and photovoltage spectroscopy. The electronic properties including the Fermi level location at the interface, band bending in the CZTSSe substrate, and valence and conduction band offsets were determined and correlated with device properties. We also describe a method for determining the band bending in the buffer layer and demonstrate this for the In2S3/CZTSSe system. The chemical bath deposited In2S3 buffer is found to have near optimal conduction band offset (0.15 eV), enabling the demonstration of Cd-free In2S3/CZTSSe solar cells with 7.6% power conversion efficiency.

  3. Reduced interface recombination in Cu{sub 2}ZnSnS{sub 4} solar cells with atomic layer deposition Zn{sub 1−x}Sn{sub x}O{sub y} buffer layers

    SciTech Connect

    Platzer-Björkman, C.; Frisk, C.; Larsen, J. K.; Ericson, T.; Li, S.-Y.; Scragg, J. J. S.; Keller, J.; Larsson, F.; Törndahl, T.

    2015-12-14

    Cu{sub 2}ZnSnS{sub 4} (CZTS) solar cells typically include a CdS buffer layer in between the CZTS and ZnO front contact. For sulfide CZTS, with a bandgap around 1.5 eV, the band alignment between CZTS and CdS is not ideal (“cliff-like”), which enhances interface recombination. In this work, we show how a Zn{sub 1−x}Sn{sub x}O{sub y} (ZTO) buffer layer can replace CdS, resulting in improved open circuit voltages (V{sub oc}) for CZTS devices. The ZTO is deposited by atomic layer deposition (ALD), with a process previously developed for Cu(In,Ga)Se{sub 2} solar cells. By varying the ALD process temperature, the position of the conduction band minimum of the ZTO is varied in relation to that of CZTS. A ZTO process at 95 °C is found to give higher V{sub oc} and efficiency as compared with the CdS reference devices. For a ZTO process at 120 °C, where the conduction band alignment is expected to be the same as for CdS, the V{sub oc} and efficiency is similar to the CdS reference. Further increase in conduction band minimum by lowering the deposition temperature to 80 °C shows blocking of forward current and reduced fill factor, consistent with barrier formation at the junction. Temperature-dependent current voltage analysis gives an activation energy for recombination of 1.36 eV for the best ZTO device compared with 0.98 eV for CdS. We argue that the V{sub oc} of the best ZTO devices is limited by bulk recombination, in agreement with a room temperature photoluminescence peak at around 1.3 eV for both devices, while the CdS device is limited by interface recombination.

  4. The direct growth of SrTiO 3 (100) layers on silicon (100) substrates; application as a buffer layer for the growth of DyBa 2Cu 3O 7- δ thin films

    NASA Astrophysics Data System (ADS)

    Méchin, L.; Gerritsma, G. J.; Garcia Lopez, J.

    1999-10-01

    Highly (100)-oriented SrTiO 3 thin films were sputtered on Si (100) substrates. After the optimization of the deposition conditions, the fraction of (110)-oriented material in the SrTiO 3 films was about 3%, but the rocking curve of the SrTiO 3 (200) peak was quite large (full width at half maximum (FWHM) ∼2.3°). Indeed grain boundaries crossing the whole SrTiO 3 film and an amorphous layer between Si and SrTiO 3 could be observed by transmission electron microscopy. DyBa 2Cu 3O 7- δ (DBCO) films were successively sputtered on the polycrystalline SrTiO 3 layers on Si. An Auger analysis revealed the presence of barium at the Si/SrTiO 3 interface that presumably diffused along the grain boundaries through SrTiO 3 to form barium silicates. By reducing both the DBCO deposition temperature and the SrTiO 3 thickness, we could prevent this diffusion and improve the electrical properties ( R300/ R100∼1 and Tc ( R=0) in the 40-60 K range). The specific problems for the growth of DBCO thin film on SrTiO 3-buffered silicon substrates by sputter deposition are finally pointed out.

  5. Aspects of the strontium oxide-copper oxide-titanium dioxide ternary system related to the deposition of strontium titanate and copper doped strontium titanate thin film buffer layers

    NASA Astrophysics Data System (ADS)

    Ayala, Alicia

    YBa2Cu3O7-delta (YBCO) coated conductors are promising materials for large-scale superconductivity applications. One version of a YBCO coated conductor is based on ion beam assisted deposition (IBAD) of magnesium oxide (MgO) onto polycrystalline metal substrates. SrTiO3 (STO) is often deposited by physical vapor deposition (PVD) methods as a buffer layer between the YBCO and IBAD MgO due to its chemical stability and lattice mismatch of only ˜1.5% with YBCO. In this work, some aspects of the stability of STO with respect to copper (Cu) and chemical solution deposition of STO on IBAD MgO templates were examined. Solubility limits of Cu in STO were established by processing Cu-doped STO powders by conventional bulk preparation techniques. The maximum solubility of Cu in STO was ˜1% as determined by transmission electron microscopy (TEM) and Rietveld refinements of x-ray diffraction (XRD) data. XRD analysis, performed in collaboration with NIST, on powder compositions on the STO/SrCuO 2 tie line did not identify any ternary phases. SrCu0.10Ti0.90Oy buffer layers were prepared by pulsed laser deposition (PLD) and CSD on IBAD MgO flexible metallic textured tapes. TEM analysis of a ˜100 nm thick SrCu0.10Ti 0.90Oy buffer layer deposited by PLD showed a smooth Cu-doped STO/MgO interface. A ˜600 nm thick YBCO film, deposited onto the SrCu 0.10Ti0.90Oy buffer by PLD, exhibited a T c of 87 K and critical current density (Jc) of ˜1 MA/cm 2. STO and Cu-doped STO thin films by CSD were ˜30 nm thick. The in plane alignment (FWHM) after deposition of the STO improved by ˜1° while it degraded by ˜2° with the SrCu0.05TiOy buffer. YBCO was deposited by PLD on the STO and SrCu0.05TiO y buffers. The in plane alignment (FWHM) of the YBCO with the STO buffer layer slightly improved while that of the YBCO with the SrCu0.05TiO y buffer layer remained constant. A goal of the CSD approach to fabrication of coated conductors is process simplicity. In this study, single layer

  6. Intermixing at the absorber-buffer layer interface in thin-film solar cells: The electronic effects of point defects in Cu(In,Ga)(Se,S)2 and Cu2ZnSn(Se,S)4 devices

    NASA Astrophysics Data System (ADS)

    Varley, J. B.; Lordi, V.

    2014-08-01

    We investigate point defects in the buffer layers CdS and ZnS that may arise from intermixing with Cu(In,Ga)(S,Se)2 (CIGS) or Cu2ZnSn(S,Se)4 (CZTS) absorber layers in thin-film photovoltaics. Using hybrid functional calculations, we characterize the electrical and optical behavior of Cu, In, Ga, Se, Sn, Zn, Na, and K impurities in the buffer. We find that In and Ga substituted on the cation site act as shallow donors in CdS and tend to enhance the prevailing n-type conductivity at the interface facilitated by Cd incorporation in CIGS, whereas they are deep donors in ZnS and will be less effective dopants. Substitutional In and Ga can favorably form complexes with cation vacancies (A-centers) which may contribute to the "red kink" effect observed in some CIGS-based devices. For CZTS absorbers, we find that Zn and Sn defects substituting on the buffer cation site are electrically inactive in n-type buffers and will not supplement the donor doping at the interface as in CIGS/CdS or ZnS devices. Sn may also preferentially incorporate on the S site as a deep acceptor in n-type ZnS, which suggests possible concerns with absorber-related interfacial compensation in CZTS devices with ZnS-derived buffers. Cu, Na, and K impurities are found to all have the same qualitative behavior, most favorably acting as compensating acceptors when substituting on the cation site. Our results suggest one beneficial role of K and Na incorporation in CIGS or CZTS devices is the partial passivation of vacancy-related centers in CdS and ZnS buffers, rendering them less effective interfacial hole traps and recombination centers.

  7. Effect of conductive TiN buffer layer on the growth of stoichiometric VO{sub 2} films and the out-of-plane insulator–metal transition properties

    SciTech Connect

    Mian, Md. Suruz; Okimura, Kunio

    2014-07-15

    A TiN buffer film is used with a conductive interfacial layer for stoichiometric vanadium dioxide (VO{sub 2}) film growth, creating a layered device with a VO{sub 2} insulator–metal transition. Low-temperature growth (<250 °C) of the VO{sub 2} film on a Ti layer on a Si substrate is achieved using inductively coupled plasma-assisted sputtering. It is found that Ti diffusion and oxidation degrades the VO{sub 2} film quality at higher temperatures, but the introduction of a TiN buffer layer suppresses the degradation and enables growth of a stoichiometric VO{sub 2} film even at 400 °C. The high resistance of the VO{sub 2} film grown on the TiN layer suggests the benefit of using the intrinsic insulator–metal transition of VO{sub 2}. The voltage-triggered switching properties of the layered devices are examined, and the cause of the high out-of-plane resistance in this layered structure is discussed based upon the dependence of the initial resistance as a function the electrode area.

  8. Effect of target power and composition on RE-Fe-B thin films with Cu and Nb buffer and cap layers

    SciTech Connect

    Castaldi, L.; Gibbs, M. R. J.; Davies, H. A.

    2006-11-01

    We report a systematic study of the structural, morphological, and magnetic properties of RE-Fe-B (RE=rare earth) films codeposited onto thermally oxidized Si substrates. The use of Cu and Nb buffer and cap layers was investigated. The deposition of the samples was performed by magnetron sputtering with the substrates held at 470 deg. C and using various Fe target power densities and fixed RE:Fe:B target power density. This was done in order to vary the growth rate and the Fe content of the films. The simultaneous increase of the deposition rate and Fe content influenced the c-axis texturing of the samples. For the Cu/RE:Fe:B/Cu films, as a consequence of the good perpendicular intrinisic coercivity ({approx}492 kA/m at 10 W) and very high remanent polarization ({approx}1.51 T at 110 W), very good perpendicular energy products were obtained at 10 W ({approx}133 kJ/m{sup 3}) and 110 W ({approx}136 kJ/m{sup 3}). The Nb/RE:Fe:B/Nb samples had the best combination of perpendicular energy product and intrinsic coercivity, with values of 150 kJ/m{sup 3} and 800 kA/m, respectively, for an iron target power of 20 W. This high energy product was retained up to target powers of 50 W in spite of the intrinsic coercivity decreasing rapidly with increasing power beyond 20 W, because of a marked increase in remanent polarization.

  9. A comparative study of the annealing behavior of Cu(In,Ga)(S,Se){sub 2} based solar cells with an indium sulfide buffer layer, partly submitted to wet chemical treatments

    SciTech Connect

    Hönes, C.; Hackenberg, J.; Zweigart, S.; Wachau, A.; Hergert, F.; Siebentritt, S.

    2015-03-07

    Indium sulfide thin films deposited via thermal evaporation from compound source material have been successfully utilized as a cadmium free buffer layer for Cu(In,Ga)Se{sub 2} based solar cells. However, high efficiencies are only reached after an additional annealing step. In this work, the annealing behavior of Cu(In,Ga)(S,Se){sub 2} based indium sulfide buffered solar cells is compared to the annealing behavior of similar cells, which were submitted to wet chemical treatments partly containing cadmium ions. Upon annealing a significant improvement of the initial solar cell characteristics is observed for the untreated cell and is related to the increase of activation energy for the carrier recombination process and a decrease of the ideality factor within the one diode model. It is shown here that this improvement can also be achieved by wet treatments of the absorber prior to buffer layer deposition. Upon annealing these treated cells still gain in collection length but lose open circuit voltage, which is explained here within a model including a highly p-doped absorber surface layer and supported by simulations showing that a decrease in doping density of such a surface layer would lead to the observed effects.

  10. First principles calculations of point defect diffusion in CdS buffer layers: Implications for Cu(In,Ga)(Se,S){sub 2} and Cu{sub 2}ZnSn(Se,S){sub 4}-based thin-film photovoltaics

    SciTech Connect

    Varley, J. B.; Lordi, V.; He, X.; Rockett, A.

    2016-01-14

    We investigate point defects in CdS buffer layers that may arise from intermixing with Cu(In,Ga)Se{sub 2} (CIGSe) or Cu{sub 2}ZnSn(S,Se){sub 4} (CZTSSe) absorber layers in thin-film photovoltaics (PV). Using hybrid functional calculations, we characterize the migration barriers of Cu, In, Ga, Se, Sn, Zn, Na, and K impurities and assess the activation energies necessary for their diffusion into the bulk of the buffer. We find that Cu, In, and Ga are the most mobile defects in CIGS-derived impurities, with diffusion expected to proceed into the buffer via interstitial-hopping and cadmium vacancy-assisted mechanisms at temperatures ∼400 °C. Cu is predicted to strongly favor migration paths within the basal plane of the wurtzite CdS lattice, which may facilitate defect clustering and ultimately the formation of Cu-rich interfacial phases as observed by energy dispersive x-ray spectroscopic elemental maps in real PV devices. Se, Zn, and Sn defects are found to exhibit much larger activation energies and are not expected to diffuse within the CdS bulk at temperatures compatible with typical PV processing temperatures. Lastly, we find that Na interstitials are expected to exhibit slightly lower activation energies than K interstitials despite having a larger migration barrier. Still, we find both alkali species are expected to diffuse via an interstitially mediated mechanism at slightly higher temperatures than enable In, Ga, and Cu diffusion in the bulk. Our results indicate that processing temperatures in excess of ∼400 °C will lead to more interfacial intermixing with CdS buffer layers in CIGSe devices, and less so for CZTSSe absorbers where only Cu is expected to significantly diffuse into the buffer.

  11. First principles calculations of point defect diffusion in CdS buffer layers: Implications for Cu(In,Ga)(Se,S)2 and Cu2ZnSn(Se,S)4-based thin-film photovoltaics

    NASA Astrophysics Data System (ADS)

    Varley, J. B.; Lordi, V.; He, X.; Rockett, A.

    2016-01-01

    We investigate point defects in CdS buffer layers that may arise from intermixing with Cu(In,Ga)Se2 (CIGSe) or Cu2ZnSn(S,Se)4 (CZTSSe) absorber layers in thin-film photovoltaics (PV). Using hybrid functional calculations, we characterize the migration barriers of Cu, In, Ga, Se, Sn, Zn, Na, and K impurities and assess the activation energies necessary for their diffusion into the bulk of the buffer. We find that Cu, In, and Ga are the most mobile defects in CIGS-derived impurities, with diffusion expected to proceed into the buffer via interstitial-hopping and cadmium vacancy-assisted mechanisms at temperatures ˜400 °C. Cu is predicted to strongly favor migration paths within the basal plane of the wurtzite CdS lattice, which may facilitate defect clustering and ultimately the formation of Cu-rich interfacial phases as observed by energy dispersive x-ray spectroscopic elemental maps in real PV devices. Se, Zn, and Sn defects are found to exhibit much larger activation energies and are not expected to diffuse within the CdS bulk at temperatures compatible with typical PV processing temperatures. Lastly, we find that Na interstitials are expected to exhibit slightly lower activation energies than K interstitials despite having a larger migration barrier. Still, we find both alkali species are expected to diffuse via an interstitially mediated mechanism at slightly higher temperatures than enable In, Ga, and Cu diffusion in the bulk. Our results indicate that processing temperatures in excess of ˜400 °C will lead to more interfacial intermixing with CdS buffer layers in CIGSe devices, and less so for CZTSSe absorbers where only Cu is expected to significantly diffuse into the buffer.

  12. Kinetic buffers.

    PubMed

    Alibrandi, Giuseppe; Fabbrizzi, Luigi; Licchelli, Maurizio; Puglisi, Antonio

    2015-01-12

    This paper proposes a new type of molecular device that is able to act as an inverse proton sponge to slowly decrease the pH inside a reaction vessel. This makes the automatic monitoring of the concentration of pH-sensitive systems possible. The device is a composite formed of an alkyl chloride, which kinetically produces acidity, and a buffer that thermodynamically modulates the variation in pH value. Profiles of pH versus time (pH-t plots) have been generated under various experimental conditions by computer simulation, and the device has been tested by carrying out automatic spectrophotometric titrations, without using an autoburette. To underline the wide variety of possible applications, this new system has been used to realize and monitor HCl uptake by a di-copper(II) bistren complex in a single run, in a completely automatic experiment.

  13. Effect of double-sided CaTiO3 buffer layers on the electrical properties of CaCu3Ti4O12 films on Pt /Ti/SiO2/Si substrates

    NASA Astrophysics Data System (ADS)

    Fang, Liang; Shen, Mingrong; Li, Zhenya

    2006-11-01

    The CaCu3Ti4O12 (CCTO) films with single- and double-sided CaTiO3 (CTO) buffer layers were grown on Pt /Ti/SiO2/Si substrates by pulsed laser deposition at 650°C, which was lower than the normal deposition temperature of the CCTO films. The CTO layer was used as seeding layer to improve the crystallization of the CCTO films and could enhance the dielectric properties of the multilayered films. In addition, the multilayered films exhibited low frequency dielectric relaxation and reduced leakage current density, which could be ascribed to the improved interfacial characteristics between the CTO layer and the electrode. The conduction mechanisms of the single layered and multilayered films were also discussed briefly.

  14. High Resistivity Molecular Beam Epitaxial AlGaAs for Device Applications.

    DTIC Science & Technology

    1980-02-01

    V MESFET technology requires, in part, the improvement of semi-insulating materials used in today’s device fabrication. The properties of currently...overall improvement in low temperature Hall mobility. Several techniques have been used to characterize AlGaAs properties. Basic determinations of impurity...available chromium-doped GaAs substrates impose restrictions on the performance of devices and monolithic circuits presently being produced in research

  15. Dielectric spectroscopy of Pb0.92La0.08Zr0.52Ti0.48O3 films on hastelloy substrates with and without LaNiO3 buffer layers

    NASA Astrophysics Data System (ADS)

    Narayanan, Manoj; Ma, Beihai; Balachandran, U. (Balu); Li, Wei

    2010-01-01

    Pb0.92La0.08Zr0.52Ti0.48O3 (PLZT) films were deposited by sol-gel synthesis on Hastelloy substrates with and without a LaNiO3 buffer. The dielectric properties were measured as a function of temperature and frequency to study the cause of dielectric degradation in PLZT films directly on hastelloy substrates. These measurements indicated an increased charge carrier activity in films without a buffer layer. We propose that a region of the film closer to the substrate surface is more oxygen deficient than the bulk and is responsible for the degradation in properties rather than the presence of a low parasitic secondary-phase interfacial layer such as NiOx.

  16. 1,3,5-Tris(phenyl-2-benzimidazole)-benzene cathode buffer layer thickness dependence in solution-processable organic solar cell based on 1,4,8,11,15,18,22,25-octahexylphthalocyanine

    NASA Astrophysics Data System (ADS)

    De Roméo Banoukepa, Gilles; Fujii, Akihiko; Shimizu, Yo; Ozaki, Masanori

    2015-04-01

    Studies on the insertion effects of a cathode buffer layer on bulk heterojunction organic solar cell based on 1,4,8,11,15,18,22,25-octahexylphthalocyanine (C6PcH2) and 1-(3-methoxy-carbonyl)-propyl-1-1-phenyl-(6,6)C61 (PCBM) by using 1,3,5-tris(phenyl-2-benzimidazole)-benzene (TPBi) as a cathode buffer layer material have been carried out. The external quantum efficiency and the short-circuit current markedly increased, resulting in the enhancement of the power conversion efficiency. The solar cell performance has been discussed from the atomic force microscopy, photoelectron yield spectroscopy and X-ray photoelectron spectroscopy measurements.

  17. Effects of substrate nitridation and buffer layer on the crystalline improvements of semi-polar InN(101¯3) crystal on GaAs(110) by MOVPE

    NASA Astrophysics Data System (ADS)

    Cho, H. C.; Togashi, R.; Murakami, H.; Kumagai, Y.; Koukitu, A.

    2013-03-01

    In this report, effects of ammonia nitridation and low temperature InN buffer growth were investigated to improve the crystalline quality of InN(101¯3) grown on GaAs(110) by metalorganic vapor phase epitaxy (MOVPE). InN(101¯3) single crystal including less than 0.1% of differently oriented domains was successfully grown by inserting low temperature InN buffer layer. The full width at half maximum (FWHM) values of InN(101¯3) epitaxial layer were drastically decreased from 89 arcmin to 55 arcmin after processing ammonia nitridation of GaAs(110) substrate surface. Furthermore, the FWHM value was decreased to 38 arcmin by increasing growth time, and the mechanism of dislocation annihilation happened during epitaxial growth was discussed.

  18. 2D SWIR image sensor with extended wavelength cutoff of 2.5 μm on InP/InGaAs epitaxial wafers with graded buffer layers

    NASA Astrophysics Data System (ADS)

    Mushini, Prabhu; Huang, Wei; Morales, Manuel; Brubaker, Robert; Nguyen, Thuc-Uyen; Dobies, Matt; Zhang, Wei; Gustus, William; Mathews, Gary; Endicter, Scott; Paik, Namwoong

    2016-05-01

    Two-dimensional photo detector arrays with a cutoff wavelength of 2.5 μm were fabricated on InP/InGaAs epitaxial wafers with graded buffer layers in a 320x256 geometry on a 12.5μm pitch. Novel growth and fabrication techniques were employed to fabricate these arrays and optimize the performance. The dark current of the detector was investigated for a wide range of temperatures. The fabricated detector array was mated with a ROIC and packaged with a multi-stage TEC and investigated further at the FPA level. The effect of the graded buffer layers on the sensor performance was investigated and the results were compared to other methods used to develop and fabricate 2D image sensors on extended wavelength materials.

  19. Spray-Pyrolyzed Three-Dimensional CuInS2 Solar Cells on Nanocrystalline-Titania Electrodes with Chemical-Bath-Deposited Inx(OH)ySz Buffer Layers

    NASA Astrophysics Data System (ADS)

    Nguyen, Duy-Cuong; Mikami, Yuki; Tsujimoto, Kazuki; Ryo, Toshihiro; Ito, Seigo

    2012-10-01

    Three-dimensional (3D) compound solar cells with the structure of have been fabricated by spray pyrolysis deposition of CuInS2 and chemical-bath deposition of Inx(OH)ySz for the light absorber and buffer layer, respectively. The effect of deposition and annealing conditions of Inx(OH)ySz on the photovoltaic properties of 3D CuInS2 solar cells was investigated. Inx(OH)ySz annealed in air ambient showed a better cell performance than those annealed in nitrogen ambient and without annealing. The improvement of the performance of cells with Inx(OH)ySz buffer layers annealed in air ambient is due to the increase in oxide concentration in the buffer layers [confirmed by X-ray photoelectron spectroscopy (XPS) measurement]. Among cells with Inx(OH)ySz buffer layers deposited for 1, 1.5, 1.75, and 2 h, that with Inx(OH)ySz deposited for 1.75 h showed the best cell performance. The best cell performance was observed for Inx(OH)ySz deposited for 1.75 h with annealing at 300 °C for 30 min in air ambient, and cell parameters were 22 mA cm-2 short-circuit photocurrent density, 0.41 V open-circuit voltage, 0.35 fill factor, and 3.2% conversion efficiency.

  20. Light-soaking effects and capacitance profiling in Cu(In,Ga)Se2 thin-film solar cells with chemical-bath-deposited ZnS buffer layers.

    PubMed

    Yu, Hye-Jung; Lee, Woo-Jung; Wi, Jae-Hyung; Cho, Dae-Hyung; Han, Won Seok; Chung, Yong-Duck; Kim, Tae-Soo; Song, Jung-Hoon

    2016-12-07

    We fabricated Cu(In,Ga)Se2 (CIGS) solar cells with chemical-bath deposited (CBD) ZnS buffer layers with different deposition times. The conversion efficiency and the fill factor of the CIGS solar cells reveal a strong dependence on the deposition time of CBD-ZnS films. In order to understand the detailed relationship between the heterojunction structure and the electronic properties of CIGS solar cells with different deposition times of CBD-ZnS films, capacitance-voltage (C-V) profiling measurements with additional laser illumination were performed. The light-soaking effects on CIGS solar cells with a CBD-ZnS buffer layer were investigated in detail using current density-voltage (J-V) and C-V measurements with several different lasers with different emission wavelengths. After light-soaking, the conversion efficiency changed significantly and the double diode feature in J-V curves disappeared. We explain that the major reason for the improvement of efficiency by light-soaking is due to the fact that negatively charged and highly defective vacancies in the CIGS absorber near the interface of CBD-ZnS/CIGS were formed and became neutral due to carriers generated by ultra-violet absorption in the buffer layer.

  1. A statistical approach for optimizing parameters for electrodeposition of indium (III) sulfide (In2S3) films, potential low-hazard buffer layers for photovoltaic applications

    NASA Astrophysics Data System (ADS)

    Mughal, Maqsood Ali

    Clean and environmentally friendly technologies are centralizing industry focus towards obtaining long term solutions to many large-scale problems such as energy demand, pollution, and environmental safety. Thin film solar cell (TFSC) technology has emerged as an impressive photovoltaic (PV) technology to create clean energy from fast production lines with capabilities to reduce material usage and energy required to manufacture large area panels, hence, lowering the costs. Today, cost ($/kWh) and toxicity are the primary challenges for all PV technologies. In that respect, electrodeposited indium sulfide (In2S3) films are proposed as an alternate to hazardous cadmium sulfide (CdS) films, commonly used as buffer layers in solar cells. This dissertation focuses upon the optimization of electrodeposition parameters to synthesize In2S3 films of PV quality. The work describe herein has the potential to reduce the hazardous impact of cadmium (Cd) upon the environment, while reducing the manufacturing cost of TFSCs through efficient utilization of materials. Optimization was performed through use of a statistical approach to study the effect of varying electrodeposition parameters upon the properties of the films. A robust design method referred-to as the "Taguchi Method" helped in engineering the properties of the films, and improved the PV characteristics including optical bandgap, absorption coefficient, stoichiometry, morphology, crystalline structure, thickness, etc. Current density (also a function of deposition voltage) had the most significant impact upon the stoichiometry and morphology of In2S3 films, whereas, deposition temperature and composition of the solution had the least significant impact. The dissertation discusses the film growth mechanism and provides understanding of the regions of low quality (for example, cracks) in films. In2S3 films were systematically and quantitatively investigated by varying electrodeposition parameters including bath

  2. High transmittance cadmium oxysulfide Cd(S,O) buffer layer grown by triton X-100 mediated chemical bath deposition for thin-film heterojunction solar cells

    NASA Astrophysics Data System (ADS)

    Ballipinar, Faruk; Rastogi, A. C.

    2017-01-01

    Polycrystalline 100-190 nm Cd(S,O) n-type semiconductor thin films of high transparency in the visible range are deposited by a surfactant Triton X-100 mediated chemical bath deposition process. The crystalline structure of the films revealed by X-ray diffraction data shows a cubic-CdO phase signified by (111) and (200) planes alongside the (002), (220), and (110) planes from hexagonal-CdS. The invariance of the 2θ position of the (002) CdS diffraction is interpreted in terms of the growth of the composite film essentially by the formation of a dilute interstitial alloy of CdO and CdS. This is confirmed by Raman spectra which, besides the CdS 1LO and 2LO modes at 300 and 600 cm-1, also show Raman lines from CdO at 1098 cm-1 and 952 cm-1 assigned as overtone of 2LO phonon modes and 556 cm-1 due to band crossing between LO and TO modes of CdO. Optical spectra of Cd(S,O) films show a median transmittance of >85% compared to ˜70% for CdS films in the 550-1000 nm wavelength range. The Cd(S,O) films show optical bandgap varying from 2.34 to 2.26 eV with increasing CdO fraction but retain high sub-bandgap transmission and sharp band edge threshold. The Cd(S,O) films thus offer an alternative to the CdS buffer layer in the heterojunction solar cells, which has major shortcoming of poor stability and high sub-bandgap absorption. The photoluminescence spectra of Cd(S,O) films show three green bands, of which one is the near band edge transition at 511.5 nm, the same as in CdS, the second band at 526.0 nm that red shifted from the CdS position is due to shallow donor-acceptor defects arising from structural change due to CdO, and the third band at 543.6 nm (2.28 eV) originates from direct band transition in CdO. The growth mechanism of Cd(S,O) films is described, which invokes that the Triton X-100 molecule modifies the microenvironment around adsorbed [Cd(NH3)4]2+ species, thereby inducing two concurrent reactions, one with SH- species that cause CdS formation and the

  3. AlGaAs ridge laser with 33% wall-plug efficiency at 100 °C based on a design of experiments approach

    NASA Astrophysics Data System (ADS)

    Fecioru, Alin; Boohan, Niall; Justice, John; Gocalinska, Agnieszka; Pelucchi, Emanuele; Gubbins, Mark A.; Mooney, Marcus B.; Corbett, Brian

    2016-04-01

    Upcoming applications for semiconductor lasers present limited thermal dissipation routes demanding the highest efficiency devices at high operating temperatures. This paper reports on a comprehensive design of experiment optimisation for the epitaxial layer structure of AlGaAs based 840 nm lasers for operation at high temperature (100 °C) using Technology Computer-Aided Design software. The waveguide thickness, Al content, doping level, and quantum well thickness were optimised. The resultant design was grown and the fabricated ridge waveguides were optimised for carrier injection and, at 100 °C, the lasers achieve a total power output of 28 mW at a current of 50 mA, a total slope efficiency 0.82 W A-1 with a corresponding wall-plug efficiency of 33%.

  4. In-situ analysis of optoelectronic properties of twin boundaries in AlGaAs by polarized cathodoluminescence spectroscopy in a TEM.

    PubMed

    Ohno, Yutaka

    2010-08-01

    Optoelectronic properties of nanoscale twin boundaries (TBs) in indirect-gap AlGaAs layers were studied by polarized cathodoluminescence spectroscopy in a transmission electron microscope. TBs arranged orderly in a short range, i.e. four or more parallel TBs arranged at regular intervals of nanometre length, emitted an intense monochromatic light polarized parallel to the boundaries. The intensity and the photon energy of the light were examined at different temperatures with different electron fluxes, and the origin of the light was discussed based on a twinning superlattice model. According to the study, it was suggested that the photon energy is tunable by controlling the intervals of TBs, without changing the crystal structure and the composition.

  5. Preparation and properties of highly (100)-oriented Pb(Zr{sub 0.2}Ti{sub 0.8})O{sub 3} thin film prepared by rf magnetron sputtering with a PbO{sub x} buffer layer

    SciTech Connect

    Wu, Jiagang; Zhu, Jiliang; Xiao, Dingquan; Zhu, Jianguo; Tan, Junzhe; Zhang, Qinglei

    2007-05-01

    A method for fabrication of highly (100)-oriented Pb(Zr{sub 0.2}Ti{sub 0.8})O{sub 3} (PZT) thin films by rf magnetron sputtering with a special buffer of PbO{sub x} (RFMS-SBP) was developed. With this method, highly (100)-oriented Pb(Zr{sub 0.2}Ti{sub 0.8})O{sub 3} thin films were prepared on the PbO{sub x}/Pt(111)/Ti/SiO{sub 2}/Si(100) substrates, and the preferential (100) orientation of the Pb(Zr{sub 0.2}Ti{sub 0.8})O{sub 3} film is 92%. The (100) orientation of the PbO{sub x} buffer layer leads to the (100) orientation of the PZT thin films, and the thickness of the buffer layer plays a significant role on the phase purity and electrical properties of the films. Highly (100)-oriented Pb(Zr{sub 0.2}Ti{sub 0.8})O{sub 3} thin films with proper thickness of PbO{sub x} buffer layer possess good electrical properties with larger remnant polarization P{sub r} (69.7 {mu}C/cm{sup 2}), lower coercive field E{sub c} (92.4 kV/cm), and good pyroelectric coefficient at room temperature (2.6x10{sup -8} C/cm{sup 2} K). The butterfly-shaped {epsilon}-E characteristic curve gives the evidence of the improved in-plane ferroelectric property in the films.

  6. Band alignments of different buffer layers (CdS, Zn(O,S), and In2S3) on Cu2ZnSnS4

    NASA Astrophysics Data System (ADS)

    Yan, Chang; Liu, Fangyang; Song, Ning; Ng, Boon K.; Stride, John A.; Tadich, Anton; Hao, Xiaojing

    2014-04-01

    The heterojunctions of different n-type buffers, i.e., CdS, Zn(O,S), and In2S3 on p-type Cu2ZnSnS4 (CZTS) were investigated using X-ray Photoelectron Spectroscopy (XPS) and Near Edge X-ray Absorption Fine Structure (NEXAFS) Measurements. The band alignment of the heterojunctions formed between CZTS and the buffer materials was carefully measured. The XPS data were used to determine the Valence Band Offsets (VBO) of different buffer/CZTS heterojunctions. The Conduction Band Offset (CBO) was calculated indirectly by XPS data and directly measured by NEXAFS characterization. The CBO of the CdS/CZTS heterojunction was found to be cliff-like with CBOXPS = -0.24 ± 0.10 eV and CBONEXAFS = -0.18 ± 0.10 eV, whereas those of Zn(O,S) and In2S3 were found to be spike-like with CBOXPS = 0.92 ± 0.10 eV and CBONEXAFS = 0.87 ± 0.10 eV for Zn(O,S)/CZTS and CBOXPS = 0.41 ± 0.10 eV for In2S3/CZTS, respectively. The CZTS photovoltaic device using the spike-like In2S3 buffer was found to yield a higher open circuit voltage (Voc) than that using the cliff-like CdS buffer. However, the CBO of In2S3/CZTS is slightly higher than the optimum level and thus acts to block the flow of light-generated electrons, significantly reducing the short circuit current (Jsc) and Fill Factor (FF) and thereby limiting the efficiency. Instead, the use of a hybrid buffer for optimization of band alignment is proposed.

  7. Structural and morphological properties of GaN buffer layers grown by ammonia molecular beam epitaxy on SiC substrates for AlGaN/GaN high electron mobility transistors

    SciTech Connect

    Corrion, A. L.; Poblenz, C.; Wu, F.; Speck, J. S.

    2008-05-01

    The impact of growth conditions on the surface morphology and structural properties of ammonia molecular beam epitaxy GaN buffers layers on SiC substrates was investigated. The threading dislocation (TD) density was found to decrease with decreasing NH{sub 3}:Ga flux ratio, which corresponded to an increase in surface roughness and reduction in residual compressive lattice mismatch stress. Furthermore, the dislocation density and compressive stress decreased for increasing buffer thickness. TD inclination was proposed to account for these observations. Optimized surface morphologies were realized at high NH{sub 3}:Ga flux ratios and were characterized by monolayer-high steps, spiral hillocks, and pyramidal mounds, with rms roughness of {approx}1.0 nm over 2x2 {mu}m{sup 2} atomic force microscopy images. Smooth surface morphologies were realized over a large range of growth temperatures and fluxes, and growth rates of up to 1 {mu}m/h were achieved. TD densities in the buffers as low as 3x10{sup 9} cm{sup -2} were demonstrated. These buffers were highly insulating and were used in recently reported AlGaN/GaN HEMTs with power densities of >11 W/mm at 4 and 10 GHz.

  8. Behavior of Photocarriers in the Light-Induced Metastable State in the p-n Heterojunction of a Cu(In,Ga)Se2 Solar Cell with CBD-ZnS Buffer Layer.

    PubMed

    Lee, Woo-Jung; Yu, Hye-Jung; Wi, Jae-Hyung; Cho, Dae-Hyung; Han, Won Seok; Yoo, Jisu; Yi, Yeonjin; Song, Jung-Hoon; Chung, Yong-Duck

    2016-08-31

    We fabricated Cu(In,Ga)Se2 (CIGS) solar cells with a chemical bath deposition (CBD)-ZnS buffer layer grown with varying ammonia concentrations in aqueous solution. The solar cell performance was degraded with increasing ammonia concentration, due to actively dissolved Zn atoms during CBD-ZnS precipitation. These formed interfacial defect states, such as hydroxide species in the CBD-ZnS film, and interstitial and antisite Zn defects at the p-n heterojunction. After light/UV soaking, the CIGS solar cell performance drastically improved, with a rise in fill factor. With the Zn-based buffer layer, the light soaking treatment containing blue photons induced a metastable state and enhanced the CIGS solar cell performance. To interpret this effect, we suggest a band structure model of the p-n heterojunction to explain the flow of photocarriers under white light at the initial state, and then after light/UV soaking. The determining factor is a p+ defect layer, containing an amount of deep acceptor traps, located near the CIGS surface. The p+ defect layer easily captures photoexcited electrons, and then when it becomes quasi-neutral, attracts photoexcited holes. This alters the barrier height and controls the photocurrent at the p-n junction, and fill factor values, determining the solar cell performance.

  9. Dependence of Device Characteristics of Bulk-Heterojunction Organic Thin-Film Solar Cells on Concentration of Glycerol and Sorbitol Addition in Pedot:. PSS Solutions for Fabricating Buffer Layers

    NASA Astrophysics Data System (ADS)

    Yamaki, Yusuke; Marumoto, Kazuhiro; Fujimori, Takuya; Mori, Tatsuo

    We have investigated the dependence of device characteristics of bulk-heterojunction organic thin-film solar cells on the concentration of glycerol and sorbitol addition in poly(3,4-ethylenedioxy thiophene):poly(4-styrene sulfonate) (PEDOT:PSS) solutions for fabricating buffer layers. The device structure is ITO/buffer/regioregular poly(3-hexylthiophene) (P3HT):[6,6]-phenyl C61-butyric acid methylester (PCBM)/Al. Glycerol addition is effective for increasing power conversion efficiency (PCE) from 1.25 to 1.41% because of the increase in short-circuit current density (Jsc) without decreasing open-circuit voltage (Voc). On the other hand, sorbitol addition decreases PCE from 1.25 to 1.04%, owing to the decrease in Voc. This difference in Voc behavior is ascribed to different work function of PEDOT:PSS with glycerol and sorbitol treatment.

  10. High-power AlGaAs channeled substrate planar diode lasers for spaceborne communications

    NASA Technical Reports Server (NTRS)

    Connolly, J. C.; Goldstein, B.; Pultz, G. N.; Slavin, S. E.; Carlin, D. B.; Ettenberg, M.

    1988-01-01

    A high power channeled substrate planar AlGaAs diode laser with an emission wavelength of 8600 to 8800 A was developed. The optoelectronic behavior (power current, single spatial and spectral behavior, far field characteristics, modulation, and astigmatism properties) and results of computer modeling studies on the performance of the laser are discussed. Lifetest data on these devices at high output power levels is also included. In addition, a new type of channeled substrate planar laser utilizing a Bragg grating to stabilize the longitudinal mode was demonstrated. The fabrication procedures and optoelectronic properties of this new diode laser are described.

  11. Photoluminescence of individual doped GaAs /AlGaAs nanofabricated quantum dots

    NASA Astrophysics Data System (ADS)

    Kalliakos, Sokratis; García, César Pascual; Pellegrini, Vittorio; Zamfirescu, Marian; Cavigli, Lucia; Gurioli, Massimo; Vinattieri, Anna; Pinczuk, Aron; Dennis, Brian S.; Pfeiffer, Loren N.; West, Ken W.

    2007-04-01

    Dilute arrays of GaAs /AlGaAs modulation-doped quantum dots with same sizes fabricated by electron beam lithography and low impact reactive ion etching exhibit highly uniform luminescence lines. Single quantum dots display spectral emission with peak energies and linewidths linked largely to the geometrical diameter of the dot and to the built-in electron population. Multicharged excitonic and biexcitonic emission intensities have activation energy of about 2meV. These results highlight the potential of high quality nanofabricated quantum dots for applications in areas that require fine control of optical emission.

  12. Photon pair sources in AlGaAs: from electrical injection to quantum state engineering

    NASA Astrophysics Data System (ADS)

    Autebert, C.; Boucher, G.; Boitier, F.; Eckstein, A.; Favero, I.; Leo, G.; Ducci, S.

    2015-11-01

    Integrated quantum photonics is a very active field of quantum information, communication, and processing. One of the main challenges to achieve massively parallel systems for complex operations is the generation, manipulation, and detection of many qubits within the same chip. Here, we present our last achievements on AlGaAs quantum photonic devices emitting nonclassical states of light at room temperature by spontaneous parametric down conversion (SPDC). The choice of this platform combines the advantages of a mature fabrication technology, a high nonlinear coefficient, a SPDC wavelength in the C-telecom band and the possibility of electrical injection.

  13. Towards III-V solar cells on Si: Improvement in the crystalline quality of Ge-on-Si virtual substrates through low porosity porous silicon buffer layer and annealing

    SciTech Connect

    Calabrese, Gabriele; Baricordi, Stefano; Bernardoni, Paolo; Fin, Samuele; Guidi, Vincenzo; Vincenzi, Donato

    2014-09-26

    A comparison between the crystalline quality of Ge grown on bulk Si and on a low porosity porous Si (pSi) buffer layer using low energy plasma enhanced chemical vapor deposition is reported. Omega/2Theta coupled scans around the Ge and Si (004) diffraction peaks show a reduction of the Ge full-width at half maximum (FWHM) of 22.4% in presence of the pSi buffer layer, indicating it is effective in improving the epilayer crystalline quality. At the same time atomic force microscopy analysis shows an increase in root means square roughness for Ge grown on pSi from 38.5 nm to 48.0 nm, as a consequence of the larger surface roughness of pSi compared to bulk Si. The effect of 20 minutes vacuum annealing at 580°C is also investigated. The annealing leads to a FWHM reduction of 23% for Ge grown on Si and of 36.5% for Ge on pSi, resulting in a FWHM of 101 arcsec in the latter case. At the same time, the RMS roughness is reduced of 8.8% and of 46.5% for Ge grown on bulk Si and on pSi, respectively. The biggest improvement in the crystalline quality of Ge grown on pSi with respect to Ge grown on bulk Si observed after annealing is a consequence of the simultaneous reorganization of the Ge epilayer and the buffer layer driven by energy minimization. A low porosity buffer layer can thus be used for the growth of low defect density Ge on Si virtual substrates for the successive integration of III-V multijunction solar cells on Si. The suggested approach is simple and fast –thus allowing for high throughput-, moreover is cost effective and fully compatible with subsequent wafer processing. Finally it does not introduce new chemicals in the solar cell fabrication process and can be scaled to large area silicon wafers.

  14. Electrical activation of carbon δ-doped (Al,Ga)As grown by metalorganic vapour-phase epitaxy

    NASA Astrophysics Data System (ADS)

    Li, G.; Petravić, M.; Jagadish, C.

    1997-04-01

    Carbon δ-doped (Al,Ga)As was grown by metalorganic vapour-phase epitaxy using trimethylaluminium (TMAl) or trimethylgallium (TMGa) as a doping precursor. The best C δ-doped Al 0.3Ga 0.7As has a peak hole density of 1.6 × 10 19 (1.4 × 10 19 for GaAs) cm -3 with a full hole profile width at half maximum of 85 Å (84 Å for GaAs). For C δ-doped Al 0.3Ga 0.7 As grown at 630°C, the use of TMGa as a doping precursor leads to both the sheet C atom density and the free hole density increasing with an increase in the total TMGa moles introduced during a δ-doping step. As a result, the electrical activation remains almost constant with the change of TMGa moles supplied. The sheet C atom density always increases with increasing supply of TMAl, but approaches its maximum value at an amount of TMAl of 6.4 × 10 -7 mol. The electrical activation reduces from > 90% to < 10% when the supply of TMAl increases from 2.1 × 10 -7 to 8 × 10 -7 mol. Regardless of the doping precursors, the hole density weakly decreases and the C atom density significantly increases with increasing growth temperature. Low growth temperatures are required for high electrical activation. Using optimised growth conditions, C δ-doped pipi doping superlattices with different average hole densities are fabricated to obtain C bulk-doped-like layers.

  15. Fabrication of Inverted Bulk-Heterojunction Organic Solar Cell with Ultrathin Titanium Oxide Nanosheet as an Electron-Extracting Buffer Layer

    NASA Astrophysics Data System (ADS)

    Itoh, Eiji; Maruyama, Yasutake; Fukuda, Katsutoshi

    2012-02-01

    The contributions and deposition conditions of ultrathin titania nanosheet (TN) crystallites were studied in an inverted bulk-heterojunction (BHJ) cell in indium tin oxide (ITO)/titania nanosheet/poly(3-hexylthiophene) (P3HT):phenyl-C61-butyric acid methylester (PCBM) active layer/MoOx/Ag multilayered photovoltaic devices. Only one or two layers of poly(diallyldimethylammonium chloride) (PDDA) and TN multilayered film deposited by the layer-by-layer deposition technique effectively decreased the leakage current and increased both open circuit voltage (VOC) and fill factor (FF), and power conversion efficiency (η) was increased nearly twofold by the insertion of two TN layers. The deposition of additional TN layers caused the reduction in FF, and the abnormal S-shaped curves above VOC for the devices with three and four TN layers were ascribed to the interfacial potential barrier at the ITO/TN interface and the series resistance across the multilayers of TN and PDDA. The performance of the BHJ cell with TN was markedly improved, and the S-shaped curves were eliminated following the the insertion of anatase-phase titanium dioxide between the ITO and TN layers owing to the decrease in the interfacial potential barrier.

  16. Non-activation ZnO array as a buffering layer to fabricate strongly adhesive metal-organic framework/PVDF hollow fiber membranes.

    PubMed

    Li, Wanbin; Meng, Qin; Li, Xiaonian; Zhang, Congyang; Fan, Zheng; Zhang, Guoliang

    2014-09-04

    A non-activation (NA) ZnO array is directly grown on a PVDF hollow fiber membrane. The defect-free MOF layers can be synthesized easily on the NA-ZnO array without any activation procedure. The array and MOF layers are strongly adhered to the hollow fiber membrane. The prepared ZIF membranes exhibit excellent gas separation performances.

  17. Domain matched epitaxial growth of (111) Ba{sub 0.5}Sr{sub 0.5}TiO{sub 3} thin films on (0001) Al{sub 2}O{sub 3} with ZnO buffer layer

    SciTech Connect

    Krishnaprasad, P. S. E-mail: mkj@cusat.ac.in; Jayaraj, M. K. E-mail: mkj@cusat.ac.in; Antony, Aldrin; Rojas, Fredy

    2015-03-28

    Epitaxial (111) Ba{sub 0.5}Sr{sub 0.5}TiO{sub 3} (BST) thin films have been grown by pulsed laser deposition on (0001) Al{sub 2}O{sub 3} substrate with ZnO as buffer layer. The x-ray ω-2θ, Φ-scan and reciprocal space mapping indicate epitaxial nature of BST thin films. The domain matched epitaxial growth of BST thin films over ZnO buffer layer was confirmed using Fourier filtered high resolution transmission electron microscope images of the film-buffer interface. The incorporation of ZnO buffer layer effectively suppressed the lattice mismatch and promoted domain matched epitaxial growth of BST thin films. Coplanar inter digital capacitors fabricated on epitaxial (111) BST thin films show significantly improved tunable performance over polycrystalline thin films.

  18. Characterization of Pt/Bi3.15Nd0.85Ti3O12/HfO2/Si structure using a hafnium oxide as buffer layer for ferroelectric-gate field effect transistors

    NASA Astrophysics Data System (ADS)

    Xie, Dan; Luo, Yafeng; Han, Xueguang; Ren, Tianling; Liu, Litian

    2009-12-01

    We have investigated the structural and electrical properties of metal-ferroelectric-insulator-semiconductor (MFIS) capacitors with Bi3.15Nd0.85Ti3O12 (BNdT) thin film deposited on Si and hafnium oxide (HfO2)/Si substrates. Microstructural analysis reveals the formation of well-crystallized BNdT perovskite film and good interface between BNdT film and HfO2 buffer layer. Pt/BNdT/HfO2/Si structure exhibits a memory window of 1.12 V at an operation voltage of 3.5 V. The width of memory window for the MFIS structure varies with increasing thickness of HfO2 layer, and 4-nm-thickness is optimum. The results from the fatigue test indicate a slight degradation of the memory window after 1010 switching cycles. These properties are encouraging for the development of ferroelectric memory transistors.

  19. Self-organization of dislocation-free, high-density, vertically aligned GaN nanocolumns involving InGaN quantum wells on graphene/SiO2 covered with a thin AlN buffer layer.

    PubMed

    Hayashi, Hiroaki; Konno, Yuta; Kishino, Katsumi

    2016-02-05

    We demonstrated the self-organization of high-density GaN nanocolumns on multilayer graphene (MLG)/SiO2 covered with a thin AlN buffer layer by RF-plasma-assisted molecular beam epitaxy. MLG/SiO2 substrates were prepared by the transfer of CVD graphene onto thermally oxidized SiO2/Si [100] substrates. Employing the MLG with an AlN buffer layer enabled the self-organization of high-density and vertically aligned nanocolumns. Transmission electron microscopy observation revealed that no threading dislocations, stacking faults, or twinning defects were included in the self-organized nanocolumns. The photoluminescence (PL) peak intensities of the self-organized GaN nanocolumns were 2.0-2.6 times higher than those of a GaN substrate grown by hydride vapor phase epitaxy. Moreover, no yellow luminescence or ZB-phase GaN emission was observed from the nanocolumns. An InGaN/GaN MQW and p-type GaN were integrated into GaN nanocolumns grown on MLG, displaying a single-peak PL emission at a wavelength of 533 nm. Thus, high-density nitride p-i-n nanocolumns were fabricated on SiO2/Si using the transferred MLG interlayer, indicating the possibility of developing visible nanocolumn LEDs on graphene/SiO2.

  20. Observation of hole injection boost via two parallel paths in Pentacene thin-film transistors by employing Pentacene: 4, 4″-tris(3-methylphenylphenylamino) triphenylamine: MoO{sub 3} buffer layer

    SciTech Connect

    Yan, Pingrui; Liu, Ziyang; Liu, Dongyang; Wang, Xuehui; Yue, Shouzhen; Zhao, Yi; Zhang, Shiming

    2014-11-01

    Pentacene organic thin-film transistors (OTFTs) were prepared by introducing 4, 4″-tris(3-methylphenylphenylamino) triphenylamine (m-MTDATA): MoO{sub 3}, Pentacene: MoO{sub 3}, and Pentacene: m-MTDATA: MoO{sub 3} as buffer layers. These OTFTs all showed significant performance improvement comparing to the reference device. Significantly, we observe that the device employing Pentacene: m-MTDATA: MoO{sub 3} buffer layer can both take advantage of charge transfer complexes formed in the m-MTDATA: MoO{sub 3} device and suitable energy level alignment existed in the Pentacene: MoO{sub 3} device. These two parallel paths led to a high mobility, low threshold voltage, and contact resistance of 0.72 cm{sup 2}/V s, −13.4 V, and 0.83 kΩ at V{sub ds} = − 100 V. This work enriches the understanding of MoO{sub 3} doped organic materials for applications in OTFTs.

  1. AlGaAs film growth using thermionic vacuum arc (TVA) and determination of its physical properties

    NASA Astrophysics Data System (ADS)

    Özen, Soner; Şenay, Volkan; Pat, Suat; Korkmaz, Şadan

    2015-06-01

    In this research, an AlGaAs film was deposited on a microscope slide by means of the thermionic vacuum arc (TVA) technique which is a novel plasma production technique. AlGaAs structures were grown by this deposition technique for the first time and this process occurred in a very short period of time. In order to characterize the produced film, nano-structural, nano-mechanical, optical, and surface properties were determined by field emission scanning electron microscope (FESEM), atomic force microscope (AFM), X-ray diffractometer (XRD) and interferometer. According to the results of the measurements, the mean thickness value of the produced film was obtained as 1.8 μm. The band gap value was determined as 2eV from the Kubelka-Munk plot. The refractive index value was obtained as approximately 3.4. Hardness value was determined as 2 GPa from the Oliver-Pharr method. All these values are consistent with the reported values in the literature for the AlGaAs films produced by different methods. TVA technique appeared as a suitable and promising technique for the production of AlGaAs films.

  2. Differential absorption lidar measurements of atmospheric water vapor using a pseudonoise code modulated AlGaAs laser. Thesis

    NASA Technical Reports Server (NTRS)

    Rall, Jonathan A. R.

    1994-01-01

    Lidar measurements using pseudonoise code modulated AlGaAs lasers are reported. Horizontal path lidar measurements were made at night to terrestrial targets at ranges of 5 and 13 km with 35 mW of average power and integration times of one second. Cloud and aerosol lidar measurements were made to thin cirrus clouds at 13 km altitude with Rayleigh (molecular) backscatter evident up to 9 km. Average transmitter power was 35 mW and measurement integration time was 20 minutes. An AlGaAs laser was used to characterize spectral properties of water vapor absorption lines at 811.617, 816.024, and 815.769 nm in a multipass absorption cell using derivative spectroscopy techniques. Frequency locking of an AlGaAs laser to a water vapor absorption line was achieved with a laser center frequency stability measured to better than one-fifth of the water vapor Doppler linewidth over several minutes. Differential absorption lidar measurements of atmospheric water vapor were made in both integrated path and range-resolved modes using an externally modulated AlGaAs laser. Mean water vapor number density was estimated from both integrated path and range-resolved DIAL measurements and agreed with measured humidity values to within 6.5 percent and 20 percent, respectively. Error sources were identified and their effects on estimates of water vapor number density calculated.

  3. Pressure-dependent DLTS (Deep Level Transient Spectroscopy) experiments on Si-doped AlGaAs

    NASA Astrophysics Data System (ADS)

    Farmer, J. W.; Hjalmarson, H. P.; Samara, G. A.

    Pressure dependent Deep Level Transient Spectroscopy (DLTS) experiments are used to measure the properties of the deep donors (DX-centers) responsible for the persistent photoconductivity effect in Si-doped AlGaAs. The sample dependence of the DLTS spectra shows evidence for a defect complex involved in the DX-center.

  4. Step buffer layer of Al0.25Ga0.75N/Al0.08Ga0.92N on P-InAlN gate normally-off high electron mobility transistors

    NASA Astrophysics Data System (ADS)

    Shrestha, Niraj M.; Li, Yiming; Chang, E. Y.

    2016-07-01

    Normally-off AlGaN/GaN high electron mobility transistors (HEMTs) are indispensable devices for power electronics as they can greatly simplify circuit designs in a cost-effective way. In this work, the electrical characteristics of p-type InAlN gate normally-off AlGaN/GaN HEMTs with a step buffer layer of Al0.25Ga0.75N/Al0.1Ga0.9N is studied numerically. Our device simulation shows that a p-InAlN gate with a step buffer layer allows the transistor to possess normally-off behavior with high drain current and high breakdown voltage simultaneously. The gate modulation by the p-InAlN gate and the induced holes appearing beneath the gate at the GaN/Al0.25Ga0.75N interface is because a hole appearing in the p-InAlN layer can effectively vary the threshold voltage positively. The estimated threshold voltage of the normally-off HEMTs explored is 2.5 V at a drain bias of 25 V, which is 220% higher than the conventional p-AlGaN normally-off AlGaN/GaN gate injection transistor (GIT). Concurrently, the maximum current density of the explored HEMT at a drain bias of 10 V slightly decreases by about 7% (from 240 to 223 mA mm-1). At a drain bias of 15 V, the current density reached 263 mA mm-1. The explored structure is promising owing to tunable positive threshold voltage and the maintenance of similar current density; notably, its breakdown voltage significantly increases by 36% (from 800 V, GIT, to 1086 V). The engineering findings of this study indicate that novel p-InAlN for both the gate and the step buffer layer can feature a high threshold voltage, large current density and high operating voltage for advanced AlGaN/GaN HEMT devices.

  5. Inverted polymer fullerene solar cells exceeding 10% efficiency with poly(2-ethyl-2-oxazoline) nanodots on electron-collecting buffer layers.

    PubMed

    Nam, Sungho; Seo, Jooyeok; Woo, Sungho; Kim, Wook Hyun; Kim, Hwajeong; Bradley, Donal D C; Kim, Youngkyoo

    2015-12-14

    Polymer solar cells have been spotlighted due to their potential for low-cost manufacturing but their efficiency is still less than required for commercial application as lightweight/flexible modules. Forming a dipole layer at the electron-collecting interface has been suggested as one of the more attractive approaches for efficiency enhancement. However, only a few dipole layer material types have been reported so far, including only one non-ionic (charge neutral) polymer. Here we show that a further neutral polymer, namely poly(2-ethyl-2-oxazoline) (PEOz) can be successfully used as a dipole layer. Inclusion of a PEOz layer, in particular with a nanodot morphology, increases the effective work function at the electron-collecting interface within inverted solar cells and thermal annealing of PEOz layer leads to a state-of-the-art 10.74% efficiency for single-stack bulk heterojunction blend structures comprising poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b']dithiophene-alt-3-fluorothieno[3,4-b]thiophene-2-carboxylate] as donor and [6,6]-phenyl-C71-butyric acid methyl ester as acceptor.

  6. Inverted polymer fullerene solar cells exceeding 10% efficiency with poly(2-ethyl-2-oxazoline) nanodots on electron-collecting buffer layers

    PubMed Central

    Nam, Sungho; Seo, Jooyeok; Woo, Sungho; Kim, Wook Hyun; Kim, Hwajeong; Bradley, Donal D. C.; Kim, Youngkyoo

    2015-01-01

    Polymer solar cells have been spotlighted due to their potential for low-cost manufacturing but their efficiency is still less than required for commercial application as lightweight/flexible modules. Forming a dipole layer at the electron-collecting interface has been suggested as one of the more attractive approaches for efficiency enhancement. However, only a few dipole layer material types have been reported so far, including only one non-ionic (charge neutral) polymer. Here we show that a further neutral polymer, namely poly(2-ethyl-2-oxazoline) (PEOz) can be successfully used as a dipole layer. Inclusion of a PEOz layer, in particular with a nanodot morphology, increases the effective work function at the electron-collecting interface within inverted solar cells and thermal annealing of PEOz layer leads to a state-of-the-art 10.74% efficiency for single-stack bulk heterojunction blend structures comprising poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene-alt-3-fluorothieno[3,4-b]thiophene-2-carboxylate] as donor and [6,6]-phenyl-C71-butyric acid methyl ester as acceptor. PMID:26656447

  7. Buffer Zone Fact Sheets

    EPA Pesticide Factsheets

    New requirements for buffer zones and sign posting contribute to soil fumigant mitigation and protection for workers and bystanders. The buffer provides distance between the pesticide application site and bystanders, reducing exposure risk.

  8. Effect of as Passivation on Vapor-Phase Epitaxial Growth of Ge on (211)Si as a Buffer Layer for CdTe Epitaxy

    DTIC Science & Technology

    2011-04-07

    to protect the Si surface from cross-contamination. Growth of thin Ge on As-passivated (211)Si was carried out next at 525C for various times, and...RMS roughness values of the films were around 0.5 nm and 1 nm, respectively, for Ge grown on Si with and without As passivation, indicating a slight...time periods of (a) 5 min and (b) 10 min. It can be seen that Ge grows layer-by- layer, resulting in a very thin Ge film . Fig. 4. SEM image of Ge

  9. Tungsten oxide buffer layers fabricated in an inert sol-gel process at room-temperature for blue organic light-emitting diodes.

    PubMed

    Höfle, Stefan; Bruns, Michael; Strässle, Stefan; Feldmann, Claus; Lemmer, Uli; Colsmann, Alexander

    2013-08-14

    WO3 deposition from tungsten ethoxide precursor solutions at room temperature is demonstrated. The W(OEt)6 precursor can be converted under inert conditions and hence avoids sample contamination with oxygen, opening a pathway to more stable devices. The stoichiometry of all WO3 layers and the optoelectronic performance of the respective SMOLEDs well match thermally evaporated WO3 and its corresponding SMOLEDs. The solution processed WO3 hole injection layers enable the fabrication of blue phosphorescent OLEDs with low onset voltage and current efficiencies of up to 14 cd A(-1) .

  10. High power master oscillator power amplifier (MOPA) AlGaAs laser for intersatellite communications

    NASA Technical Reports Server (NTRS)

    Cornwell, Donald M., Jr.

    1992-01-01

    A master oscillator power amplifier (MOPA) configuration has been developed using an anti-reflection-coated AlGaAs semiconductor broad area laser in a reflective amplifier mode. For CW injection, the MOPA produced 340 mW of diffraction-limited power. The semiconductor MOPA configuration also produced peak diffraction-limited powers of 360 mW and 320 mW for quaternary pulse position Q-PPM modulation rates of 50 Mbps and 325 Mbps, respectively, for a peak injected power of 100 mW. Angular beamsteering during modulation was minimized by collimating the injected beam. The diffraction-limited peak power was limited by the frequency chirp of the master oscillator and also by the coupling losses of the injected beam.

  11. AlGaAs growth by OMCVD using an excimer laser

    NASA Technical Reports Server (NTRS)

    Warner, Joseph D.; Wilt, David M.; Pouch, John J.; Aron, Paul R.

    1986-01-01

    AlGaAs has been grown on GaAs by laser assisted OMCVD using an excimer laser, wavelength 193 nm, and a Cambridge OMCVD reactor. Films were grown at temperatures of 450 and 500 C with the laser beam parallel to the surface and impinging onto the surface at 15 deg from parallel. The samples were heated by RF coils while the laser beam was perpendicular to the gas flow. Typical gas flow parameters are 12 slm of H2, 15 sccm of Ga(CH3)3, 13 sccm of Al(CH3)3, and a pressure of 250 mbar. The initial energy density of the beam at the surface was 40 mJ/sq cm, the pulse rate was 20 pps, and the growth time was 7 min. The films were analyzed by Auger electron spectroscopy for the aluminum concentration and by TEM for the surface morphology.

  12. Mg-compensation effect in GaN buffer layer for AlGaN/GaN high-electron-mobility transistors grown on 4H-SiC substrate

    NASA Astrophysics Data System (ADS)

    Ko, Kwangse; Lee, Kyeongjae; So, Byeongchan; Heo, Cheon; Lee, Kyungbae; Kwak, Taemyung; Han, Sang-Woo; Cha, Ho-Young; Nam, Okhyun

    2017-01-01

    The present study investigated the Mg doping effect in the gallium nitride (GaN) buffer layers (BLs) of AlGaN/GaN high-electron-mobility transistor (HEMT) structures grown on semi-insulating 4H-SiC substrates by metal organic chemical vapor deposition. When the Mg concentration was increased from 3 × 1017 to 8 × 1018 cm-3, the crystal quality slightly deteriorated, whereas electrical properties were significantly changed. The buffer leakage increased approximately 50 times from 0.77 to 39.2 nA at -50 V with the Mg doping concentration. The Mg-compensation effect and electron trapping effect were observed at Mg concentration of 3 × 1017 and 8 × 1018 cm-3, respectively, which were confirmed by an isolation leakage current test and low-temperature photoluminescence. When the BL was compensated, the two-dimensional electron gas (2DEG) mobility and sheet carrier concentration of the HEMTs were 1560 cm2 V-1 s-1 and 5.06 × 1012 cm-2, respectively. As a result, Mg-doped GaN BLs were demonstrated as a candidates of semi-insulating BLs for AlGaN/GaN HEMT.

  13. Large Memory Effect and High Carrier Mobility of Organic Field-Effect Transistors Using Semiconductor Colloidal Nano-Dots Dispersed in Polymer Buffer Layers

    NASA Astrophysics Data System (ADS)

    Kajimoto, Kaori; Kurokawa, Atsushi; Uno, Kazuyuki; Tanaka, Ichiro

    2011-02-01

    We fabricated organic memory field-effect transistors (FETs) using PbS colloidal nano-dots (NDs) dispersed in thin poly(methyl methacrylate) (PMMA) layers inserted between gate insulators (SiO2) and pentacene active layers as floating gates. The colloidal NDs were dispersed in chloroform solution with PMMA, and spin-coated on SiO2 surfaces. The fabricated memory FETs showed significantly large threshold voltage shifts of 64.5 V at maximum after a writing voltage of 100 V was applied to their control gates, and a maximum carrier mobility of 0.36 cm2 V-1 s-1, which was comparable to that of reference pentacene FETs without colloidal NDs, was obtained because of the improved crystallinity of the pentacene films.

  14. VIRTUAL FRAME BUFFER INTERFACE

    NASA Technical Reports Server (NTRS)

    Wolfe, T. L.

    1994-01-01

    Large image processing systems use multiple frame buffers with differing architectures and vendor supplied user interfaces. This variety of architectures and interfaces creates software development, maintenance, and portability problems for application programs. The Virtual Frame Buffer Interface program makes all frame buffers appear as a generic frame buffer with a specified set of characteristics, allowing programmers to write code which will run unmodified on all supported hardware. The Virtual Frame Buffer Interface converts generic commands to actual device commands. The virtual frame buffer consists of a definition of capabilities and FORTRAN subroutines that are called by application programs. The virtual frame buffer routines may be treated as subroutines, logical functions, or integer functions by the application program. Routines are included that allocate and manage hardware resources such as frame buffers, monitors, video switches, trackballs, tablets and joysticks; access image memory planes; and perform alphanumeric font or text generation. The subroutines for the various "real" frame buffers are in separate VAX/VMS shared libraries allowing modification, correction or enhancement of the virtual interface without affecting application programs. The Virtual Frame Buffer Interface program was developed in FORTRAN 77 for a DEC VAX 11/780 or a DEC VAX 11/750 under VMS 4.X. It supports ADAGE IK3000, DEANZA IP8500, Low Resolution RAMTEK 9460, and High Resolution RAMTEK 9460 Frame Buffers. It has a central memory requirement of approximately 150K. This program was developed in 1985.

  15. Néel temperature of Cr{sub 2}O{sub 3} in Cr{sub 2}O{sub 3}/Co exchange-coupled system: Effect of buffer layer

    SciTech Connect

    Pati, Satya Prakash E-mail: phy-satya@yahoo.co.in; Shimomura, Naoki; Nozaki, Tomohiro; Sahashi, Masashi; Shibata, Tatsuo

    2015-05-07

    The lattice parameter dependence of the Néel temperature T{sub N} of thin Cr{sub 2}O{sub 3} in a Cr{sub 2}O{sub 3}/Co exchange-coupled system is investigated. Lattice-mismatch-induced strain is generated in Cr{sub 2}O{sub 3} by using different buffer layers. The lattice parameters are determined from out-of-plane and in-plane X-ray diffraction measurements. The Néel temperature is detected by direct temperature-dependent magnetization measurement as well as the temperature-dependent interface exchange coupling energy. It is observed that in-plane lattice contraction can enhance T{sub N} in Cr{sub 2}O{sub 3}, which is consistent with theoretical calculations.

  16. Formation of a strontium buffer layer on Si(001) by pulsed-laser deposition through the Sr/Si(001)(2 × 3) surface reconstruction

    SciTech Connect

    Klement, D.; Spreitzer, M.; Suvorov, D.

    2015-02-16

    The formation of a ½ monolayer (ML) of strontium (Sr) on Si(001) represents the most widely used and effective passivation procedure for the epitaxial growth of strontium titanate (SrTiO{sub 3}) on Si with molecular beam epitaxy (MBE). In the present study, we demonstrate experimentally the possibility of preparing such a buffer layer with the pulsed-laser deposition (PLD) technique. In-situ analysis using reflection high-energy electron diffraction (RHEED) showed surface structure evolution from two-domain (2 × 1) + (1 × 2), exhibited by the bare silicon surface, to a (3 × 2) + (2 × 3) structure at 1/6 ML Sr coverage, which is then replaced by (1 × 2) + (2 × 1) structure at ¼ ML and maintained up to ½ ML coverage. In addition, two different processes for the removal of native silicon dioxide (SiO{sub 2}) layer were studied: thermal and Sr-induced deoxidation process. Annealing above 1100 °C proved to be the most efficient in terms of carbon contamination. The results highlight the possibilities of using the PLD technique for the synthesis of an epitaxial SrTiO{sub 3} layer on Si, needed for the integration of different functional oxides with a Si platform.

  17. Enhancing the orthorhombicity and antiferromagnetic-insulating state in epitaxial La0.67Ca0.33MnO3/NdGaO3(001) films by inserting a SmFeO3 buffer layer

    NASA Astrophysics Data System (ADS)

    Tan, Xuelian; Gao, Guanyin; Chen, Pingfan; Xu, Haoran; Zhi, Bowen; Jin, Feng; Chen, Feng; Wu, Wenbin

    2014-11-01

    Structural and magnetotransport properties of epitaxial La0.67Ca0.33MnO3(30 nm)/NdGaO3(001) [LCMO/NGO(001)] films are tuned by inserting an insulating SmFeO3 (SFO) buffer layer at various thicknesses (t). All the layers and the NGO substrates have the same Pbnm symmetry with the octahedra tilting about the b-axis, but different orthorhombicity (d). We found that as t increases, the fully strained (≤15 nm) or partially relaxed (30-60 nm) SFO layers can produce different d in the upper LCMO films. Correspondingly, the induced antiferromagnetic-insulating (AFI) state in LCMO is greatly enhanced with TAFI shifted from ˜250 K for t ≤ 15 nm to ˜263 K for t = 30-60 nm. We also show that the strain relaxation for t ≥ 30 nm is remarkably anisotropic, with a stable lattice constant a as that of the NGO substrates but increasing b of both SFO and LCMO layers. This indicates the octahedral coupling across the interfaces, leaving the strain along the a-axis accommodated by the octahedral tilts, while along the b-axis most probably by the octahedral deformations. The AFI state in the LCMO layer could be ascribed to the enhanced orthorhombicity with cooperatively increased Jahn-Teller-like distortions and tilting of the MnO6 octahedra. The results strongly suggest that the interfacial octahedral coupling plays a crucial role in epitaxial growth and in tuning functionalities of the perovskite oxide films.

  18. Spectroscopy analysis of graphene like deposition using DC unbalanced magnetron sputtering on γ‐Al{sub 2}O{sub 3} buffer layer

    SciTech Connect

    Aji, A. S. Darma, Y.

    2014-02-24

    In this work, graphene-like deposition using DC unbalanced magnetron-sputtering technique on γ‐Al{sub 2}O{sub 3} layer at low temperature has been systematically studied. The γ‐Al{sub 2}O{sub 3} was growth on silicon substrate using thermal evaporation of Al wire and continuing with dry oxidation of Al at 550 °C. Sputtering process were carried out using Fe-doped carbon pellet as a target by maintain the chamber pressure of 4.6×10{sup −2} Torr at substrate temperature of 300 °C for time deposition range of 1 to 4 hours. The quality of Al{sub 2}O{sub 3} on Si(100) and the characteristic of carbon thin film on γ‐Al{sub 2}O{sub 3} were analized by mean XRD, opctical microscopy, EDAX, FTIR, and Raman spectra. XRD and optical microscopy analysis shows that Al{sub 2}O{sub 3} film is growth uniformly on Si substrate and forming the γ phase of Al{sub 2}O{sub 3}. Raman and FTIR spectra confirm the formation of graphene like carbon layer on Al{sub 2}O{sub 3}. Additionally, thermal annealing for some sample series have been performed to study their structural stability. The change of atomic structure due to thermal annealing were analized by XRD spectra. The quality and the number of graphene layers are investigated by using Raman spectra peaks analysis.

  19. AlGaAs top solar cell for mechanical attachment in a multi-junction tandem concentrator solar cell stack

    NASA Technical Reports Server (NTRS)

    Dinetta, L. C.; Hannon, M. H.; Mcneely, J. B.; Barnett, A. M.

    1991-01-01

    The AstroPower self-supporting, transparent AlGaAs top solar cell can be stacked upon any well-developed bottom solar cell for improved system performance. This is an approach to improve the performance and scale of space photovoltaic power systems. Mechanically stacked tandem solar cell concentrator systems based on the AlGaAs top concentrator solar cell can provide near term efficiencies of 36 percent (AMO, 100x). Possible tandem stack efficiencies greater than 38 percent (100x, AMO) are feasible with a careful selection of materials. In a three solar cell stack, system efficiencies exceed 41 percent (100x, AMO). These device results demonstrate a practical solution for a state-of-the-art top solar cell for attachment to an existing, well-developed solar cell.

  20. Quality-enhanced In{sub 0.3}Ga{sub 0.7}As film grown on GaAs substrate with an ultrathin amorphous In{sub 0.6}Ga{sub 0.4}As buffer layer

    SciTech Connect

    Gao, Fangliang; Li, Guoqiang

    2014-01-27

    Using low-temperature molecular beam epitaxy, amorphous In{sub 0.6}Ga{sub 0.4}As layers have been grown on GaAs substrates to act as buffer layers for the subsequent epitaxial growth of In{sub 0.3}Ga{sub 0.7}As films. It is revealed that the crystallinity of as-grown In{sub 0.3}Ga{sub 0.7}As films is strongly affected by the thickness of the large-mismatched amorphous In{sub 0.6}Ga{sub 0.4}As buffer layer. Given an optimized thickness of 2 nm, this amorphous In{sub 0.6}Ga{sub 0.4}As buffer layer can efficiently release the misfit strain between the In{sub 0.3}Ga{sub 0.7}As epi-layer and the GaAs substrate, trap the threading and misfit dislocations from propagating to the following In{sub 0.3}Ga{sub 0.7}As epi-layer, and reduce the surface fluctuation of the as-grown In{sub 0.3}Ga{sub 0.7}As, leading to a high-quality In{sub 0.3}Ga{sub 0.7}As film with competitive crystallinity to that grown on GaAs substrate using compositionally graded In{sub x}Ga{sub 1-x}As metamorphic buffer layers. Considering the complexity of the application of the conventional In{sub x}Ga{sub 1-x}As graded buffer layers, this work demonstrates a much simpler approach to achieve high-quality In{sub 0.3}Ga{sub 0.7}As film on GaAs substrate and, therefore, is of huge potential for the InGaAs-based high-efficiency photovoltaic industry.

  1. Structural, Electrical, and Optical Properties of ZnO Film Used as Buffer Layer for CIGS Thin-Film Solar Cell.

    PubMed

    Choi, Eun Chang; Cha, Ji-Hyun; Jung, Duk-Young; Hong, Byungyou

    2016-05-01

    The CuIn(x)Ga(1-x)Se2 (CIGS) using the solution-based fabrication method is attractive for thin film solar cells because of its possibilities for large-area and low-cost production. ZnO films between transparent conductive oxide (TCO) and the CdS films can improve the performances of CIGS thin-film solar cells. In this study, we investigated the characteristics of ZnO film between TCO and CIGS layers in a solar cell (AZO/ZnO/CdS/CIGS/Mo), which were deposited at various thicknesses to investigate the role of the films in CIGS solar cells. It was confirmed that the conversion efficiency of a CIGS solar cell depends on the ZnO film. For a ZnO film thickness of 80 nm, the highest power conversion efficiency that a solar cell achieved was J(sc) of 18.73 mA/cm2.

  2. Recent advances in polymer solar cells: realization of high device performance by incorporating water/alcohol-soluble conjugated polymers as electrode buffer layer.

    PubMed

    He, Zhicai; Wu, Hongbin; Cao, Yong

    2014-02-01

    This Progress Report highlights recent advances in polymer solar cells with special attention focused on the recent rapid-growing progress in methods that use a thin layer of alcohol/water-soluble conjugated polymers as key component to obtain optimized device performance, but also discusses novel materials and device architectures made by major prestigious institutions in this field. We anticipate that due to drastic improvements in efficiency and easy utilization, this method opens up new opportunities for PSCs from various material systems to improve towards 10% efficiency, and many novel device structures will emerge as suitable architectures for developing the ideal roll-to-roll type processing of polymer-based solar cells.

  3. Mechanism for persistent hexagonal island formation in AlN buffer layer during growth on Si (111) by plasma-assisted molecular beam epitaxy

    SciTech Connect

    Hsu, K.-Y.; Chung, H.-C.; Liu, C.-P.; Tu, L.-W.

    2007-05-21

    The characteristics of structure and morphology of AlN grown by a growth interruption method on Si (111) with plasma-assisted molecular beam epitaxy are investigated. It is found that the growth interruption method would improve the surface flatness of the AlN layer without the formation of Al droplets. However, AlN hexagonal islands were present and persistent throughout the entire growth owing to effective strain relaxation and Eherlich-Schowebel barrier effect of preexistent surface islands grown on higher terraces of the Si substrate. The density of threading dislocations underneath the hexagonal islands is much less than elsewhere in the film, which is presumably due to dislocation annihilation during the island growth process.

  4. Organellar calcium buffers.

    PubMed

    Prins, Daniel; Michalak, Marek

    2011-03-01

    Ca(2+) is an important intracellular messenger affecting many diverse processes. In eukaryotic cells, Ca(2+) storage is achieved within specific intracellular organelles, especially the endoplasmic/sarcoplasmic reticulum, in which Ca(2+) is buffered by specific proteins known as Ca(2+) buffers. Ca(2+) buffers are a diverse group of proteins, varying in their affinities and capacities for Ca(2+), but they typically also carry out other functions within the cell. The wide range of organelles containing Ca(2+) and the evidence supporting cross-talk between these organelles suggest the existence of a dynamic network of organellar Ca(2+) signaling, mediated by a variety of organellar Ca(2+) buffers.

  5. Effect of process pressure and substrate temperature on CdS buffer layers deposited by using RF sputtering for Cu(In,Ga)Se2 solar cells

    NASA Astrophysics Data System (ADS)

    Choi, Ji Hyun; Jung, Sung Hee; Chung, Chee Won

    2016-02-01

    The characteristics of CdS films deposited on Cu(In,Ga)Se2(CIGS)/Mo/glass and glass substrates by using RF magnetron sputtering were investigated. The deposition pressure and the substrate temperature were selected as key parameters to examine the electrical, compositional and optical properties of the films. As the deposition pressure was increased, the resistivity increased while the carrier concentration decreased owing to a stoichiometric change and Cd-O incorporation at high pressure. Field-emission scanning electron microscopy(FE-SEM) revealed that the CdS films on CIGS/Mo became denser as the pressure was increased, which was responsible for the high transmittance of the film deposited at high pressure. As the substrate temperature was increased, the deposition rate decreased, which could be explained by using Langmuir theory. As the temperature was increased from room temperature to 573 K, the resistivity increased and the carrier concentration decreased, which was attributed to an increase in [S]/[Cd] ratio. In addition, as the temperature was increased, the small grains were agglomerated to form larger grains due to the increase in the activity of grains at high temperature. CdS films were confirmed to be uniformly deposited on the CIGS layer by using RF sputtering. The large amount of interdiffusion between the CIGS and the CdS films deposited at a high substrate temperature were observed by using X-ray photoelectron spectroscopy.

  6. Common data buffer

    NASA Technical Reports Server (NTRS)

    Byrne, F.

    1981-01-01

    Time-shared interface speeds data processing in distributed computer network. Two-level high-speed scanning approach routes information to buffer, portion of which is reserved for series of "first-in, first-out" memory stacks. Buffer address structure and memory are protected from noise or failed components by error correcting code. System is applicable to any computer or processing language.

  7. Multi-user quantum key distribution with entangled photons from an AlGaAs chip

    NASA Astrophysics Data System (ADS)

    Autebert, C.; Trapateau, J.; Orieux, A.; Lemaître, A.; Gomez-Carbonell, C.; Diamanti, E.; Zaquine, I.; Ducci, S.

    2016-12-01

    In view of real-world applications of quantum information technologies, the combination of miniature quantum resources with existing fibre networks is a crucial issue. Among such resources, on-chip entangled photon sources play a central role for applications spanning quantum communications, computing and metrology. Here, we use a semiconductor source of entangled photons operating at room temperature in conjunction with standard telecom components to demonstrate multi-user quantum key distribution, a core protocol for securing communications in quantum networks. The source consists of an AlGaAs chip-emitting polarisation entangled photon pairs over a large bandwidth in the main telecom band around 1550 nm without the use of any off-chip compensation or interferometric scheme; the photon pairs are directly launched into a dense wavelength division multiplexer (DWDM) and secret keys are distributed between several pairs of users communicating through different channels. We achieve a visibility measured after the DWDM of 87% and show long-distance key distribution using a 50-km standard telecom fibre link between two network users. These results illustrate a promising route to practical, resource-efficient implementations adapted to quantum network infrastructures.

  8. Quasiperiodic AlGaAs superlattices for neuromorphic networks and nonlinear control systems

    SciTech Connect

    Malyshev, K. V.

    2015-01-28

    The application of quasiperiodic AlGaAs superlattices as a nonlinear element of the FitzHugh–Nagumo neuromorphic network is proposed and theoretically investigated on the example of Fibonacci and figurate superlattices. The sequences of symbols for the figurate superlattices were produced by decomposition of the Fibonacci superlattices' symbolic sequences. A length of each segment of the decomposition was equal to the corresponding figurate number. It is shown that a nonlinear network based upon Fibonacci and figurate superlattices provides better parallel filtration of a half-tone picture; then, a network based upon traditional diodes which have cubic voltage-current characteristics. It was found that the figurate superlattice F{sup 0}{sub 11}(1) as a nonlinear network's element provides the filtration error almost twice less than the conventional “cubic” diode. These advantages are explained by a wavelike shape of the decreasing part of the quasiperiodic superlattice's voltage-current characteristic, which leads to multistability of the network's cell. This multistability promises new interesting nonlinear dynamical phenomena. A variety of wavy forms of voltage-current characteristics opens up new interesting possibilities for quasiperiodic superlattices and especially for figurate superlattices in many areas—from nervous system modeling to nonlinear control systems development.

  9. Quasiperiodic AlGaAs superlattices for neuromorphic networks and nonlinear control systems

    NASA Astrophysics Data System (ADS)

    Malyshev, K. V.

    2015-01-01

    The application of quasiperiodic AlGaAs superlattices as a nonlinear element of the FitzHugh-Nagumo neuromorphic network is proposed and theoretically investigated on the example of Fibonacci and figurate superlattices. The sequences of symbols for the figurate superlattices were produced by decomposition of the Fibonacci superlattices' symbolic sequences. A length of each segment of the decomposition was equal to the corresponding figurate number. It is shown that a nonlinear network based upon Fibonacci and figurate superlattices provides better parallel filtration of a half-tone picture; then, a network based upon traditional diodes which have cubic voltage-current characteristics. It was found that the figurate superlattice F011(1) as a nonlinear network's element provides the filtration error almost twice less than the conventional "cubic" diode. These advantages are explained by a wavelike shape of the decreasing part of the quasiperiodic superlattice's voltage-current characteristic, which leads to multistability of the network's cell. This multistability promises new interesting nonlinear dynamical phenomena. A variety of wavy forms of voltage-current characteristics opens up new interesting possibilities for quasiperiodic superlattices and especially for figurate superlattices in many areas—from nervous system modeling to nonlinear control systems development.

  10. Buffer Therapy for Cancer

    PubMed Central

    Ribeiro, Maria de Lourdes C; Silva, Ariosto S.; Bailey, Kate M.; Kumar, Nagi B.; Sellers, Thomas A.; Gatenby, Robert A.; Ibrahim-Hashim, Arig; Gillies, Robert J.

    2013-01-01

    Oral administration of pH buffers can reduce the development of spontaneous and experimental metastases in mice, and has been proposed in clinical trials. Effectiveness of buffer therapy is likely to be affected by diet, which could contribute or interfere with the therapeutic alkalinizing effect. Little data on food pH buffering capacity was available. This study evaluated the pH and buffering capacity of different foods to guide prospective trials and test the effect of the same buffer (lysine) at two different ionization states. Food groups were derived from the Harvard Food Frequency Questionnaire. Foods were blended and pH titrated with acid from initial pH values until 4.0 to determine “buffering score”, in mmol H+/pH unit. A “buffering score” was derived as the mEq H+ consumed per serving size to lower from initial to a pH 4.0, the postprandial pH of the distal duodenum. To differentiate buffering effect from any metabolic byproduct effects, we compared the effects of oral lysine buffers prepared at either pH 10.0 or 8.4, which contain 2 and 1 free base amines, respectively. The effect of these on experimental metastases formation in mice following tail vein injection of PC-3M prostate cancer cells were monitored with in vivo bioluminescence. Carbohydrates and dairy products’ buffering score varied between 0.5 and 19. Fruits and vegetables showed a low to zero buffering score. The score of meats varied between 6 and 22. Wine and juices had negative scores. Among supplements, sodium bicarbonate and Tums® had the highest buffering capacities, with scores of 11 and 20 per serving size, respectively. The “de-buffered” lysine had a less pronounced effect of prevention of metastases compared to lysine at pH 10. This study has demonstrated the anti-cancer effects of buffer therapy and suggests foods that can contribute to or compete with this approach to manage cancer. PMID:24371544

  11. Ni-based anode-supported Al2O3-doped-Y2O3-stabilized ZrO2 thin electrolyte solid oxide fuel cells with Y2O3-stabilized ZrO2 buffer layer

    NASA Astrophysics Data System (ADS)

    Lei, Libin; Bai, Yaohui; Liu, Jiang

    2014-02-01

    In order to reduce the sintering temperature of Ni-based anode-supported thin 8 mol% yttria-stabilized zirconia (YSZ) elsectrolyte solid oxide fuel cells (SOFCs), alumina, with a weight percent of 1, 3, 5, and 7, is respectively doped into YSZ as sintering aid. A pure YSZ buffer layer is introduced between the Al2O3-doped-YSZ electrolyte and Ni-YSZ anode, to prevent Al2O3 and NiO from forming non-conductive spinel NiAl2O4. The experimental results show that doping proper amount of Al2O3 doping can reduce the sintering temperature of YSZ, e.g., 1 wt.% doping decreases the temperature from 1673 K to 1573 K. Anode-supported SOFCs are prepared with Al2O3-doped-YSZ electrolytes sintered at different temperatures. Electrochemical characterization of the SOFCs shows that the single cell with 1 wt.% alumina-doped YSZ electrolyte sintered at 1573 K gives the highest output. The effect of alumina doping on sintering behavior and electrical performance of YSZ is discussed in detail.

  12. The action mechanism of TiO{sub 2}:NaYF{sub 4}:Yb{sup 3+},Tm{sup 3+} cathode buffer layer in highly efficient inverted organic solar cells

    SciTech Connect

    Liu, Chunyu; Chen, Huan; Zhao, Dan; Shen, Liang; He, Yeyuan; Guo, Wenbin E-mail: chenwy@jlu.edu.cn; Chen, Weiyou E-mail: chenwy@jlu.edu.cn

    2014-08-04

    We report the fabrication and characteristics of organic solar cells with 6.86% power conversion efficiency (PCE) by doping NaYF{sub 4}:Yb{sup 3+},Tm{sup 3+} into TiO{sub 2} cathode buffer layer. The dependence of devices performance on doping concentration of NaYF{sub 4}:Yb{sup 3+},Tm{sup 3+} is investigated. Results indicate that short-circuit current density (J{sub sc}) has an apparent improvement, leading to an enhancement of 22.7% in PCE for the optimized doping concentration of 0.05 mmol ml{sup −1} compared to the control devices. NaYF{sub 4}:Yb{sup 3+},Tm{sup 3+} nanoparticles (NPs) can play threefold roles, one is that the incident light in visible region can be scattered by NaYF{sub 4} NPs, the second is that solar irradiation in infrared region can be better utilized by Up-conversion effect of Yb{sup 3+} and Tm{sup 3+} ions, the third is that electron transport property in TiO{sub 2} thin film can be greatly improved.

  13. Rapid screening buffer layers in photovoltaics

    SciTech Connect

    List, III, Frederick Alyious; Tuncer, Enis

    2014-09-09

    An apparatus and method of testing electrical impedance of a multiplicity of regions of a photovoltaic surface includes providing a multi-tipped impedance sensor with a multiplicity of spaced apart impedance probes separated by an insulating material, wherein each impedance probe includes a first end adapted for contact with a photovoltaic surface and a second end in operable communication with an impedance measuring device. The multi-tipped impedance sensor is used to contact the photovoltaic surface and electrical impedance of the photovoltaic material is measured between individual first ends of the probes to characterize the quality of the photovoltaic surface.

  14. DLTS study of deep centers created by Ar-ion bombardment in n- and p-type MBE AlGaAs

    NASA Astrophysics Data System (ADS)

    Kaniewska, M.; Sadowski, J.; Guziewicz, M.

    2004-07-01

    The thermal emission rate of dominant traps in molecular beam epitaxial n- and p-type AlGaAs subjected to Ar-ion beam etching has been studied by deep level transient spectroscopy. Emission signatures were determined and compared with results obtained by other authors for irradiation induced and grown-in defects in GaAs and AlGaAs. The most significant result of this study is the observation that the process-induced defects in n- as well as p-type AlGaAs exhibit emission signatures, which are characteristic of native defects found in GaAs. The effect is discussed in terms of a compensation effect and related band bending.

  15. A three solar cell system based on a self-supporting, transparent AlGaAs top solar cell

    NASA Technical Reports Server (NTRS)

    Negley, Gerald H.; Rhoads, Sandra L.; Terranova, Nancy E.; Mcneely, James B.; Barnett, Allen M.

    1989-01-01

    Development of a three solar cell stack can lead to practical efficiencies greater than 30 percent (1x,AM0). A theoretical efficiency limitation of 43.7 percent at AM0 and one sun is predicted by this model. Including expected losses, a practical system efficiency of 36.8 percent is anticipated. These calculations are based on a 1.93eV/1.43eV/0.89eV energy band gap combination. AlGaAs/GaAs/GaInAsP materials can be used with a six-terminal wiring configuration. The key issues for multijunction solar cells are the top and middle solar cell performance and the sub-bandgap transparency. AstroPower has developed a technique to fabricate AlGaAs solar cells on rugged, self-supporting, transparent AlGaAs substrates. Top solar cell efficiencies greater than 11 percent AM0 have been achieved. State-of-the-art GaAs or InP devices will be used for the middle solar cell. GaInAsP will be used to fabricate the bottom solar cell. This material is lattice-matched to InP and offers a wide range of bandgaps for optimization of the three solar cell stack. Liquid phase epitaxy is being used to grow the quaternary material. Initial solar cells have shown open-circuit voltages of 462 mV for a bandgap of 0.92eV. Design rules for the multijunction three solar cell stack are discussed. The progress in the development of the self-supporting AlGaAs top solar cell and the GaInAsP bottom solar cell is presented.

  16. Interface induced uniaxial magnetic anisotropy in amorphous CoFeB films on AlGaAs(001).

    PubMed

    Hindmarch, A T; Kinane, C J; MacKenzie, M; Chapman, J N; Henini, M; Taylor, D; Arena, D A; Dvorak, J; Hickey, B J; Marrows, C H

    2008-03-21

    We demonstrate an isolated magnetic interface anisotropy in amorphous CoFeB films on (Al)GaAs(001), similar to that in epitaxial films but without a magnetocrystalline anisotropy term. The direction of the easy axis corresponds to that due to the interfacial interaction proposed for epitaxial films. We show that the anisotropy is determined by the relative orbital component of the atomic magnetic moments. Charge transfer is ruled out as the origin of the interface anisotropy, and it is postulated that the spin-orbit interaction in the semiconductor is crucial in determining the magnetic anisotropy.

  17. Aspects of the SrO-CuO-TiO2 Ternary System Related to the Deposition of SrTiO3 and Copper-Doped SrTiO3 Thin-Film Buffer Layers

    SciTech Connect

    Ayala, Alicia

    2004-12-20

    YBa2Cu3O27-δ (YBCO) coated conductors are promising materials for large-scale superconductivity applications. One version of a YBCO coated conductor is based on ion beam assisted deposition (IBAD) of magnesium oxide (MgO) onto polycrystalline metal substrates. SrTiO3 (STO) is often deposited by physical vapor deposition (PVD) methods as a buffer layer between the YBCO and IBAD MgO due to its chemical stability and lattice mismatch of only ~1.5% with YBCO. In this work, some aspects of the stability of STO with respect to copper (Cu) and chemical solution deposition of STO on IBAD MgO templates were examined. Solubility limits of Cu in STO were established by processing Cu-doped STO powders by conventional bulk preparation techniques. The maximum solubility of Cu in STO was ~1% as determined by transmission electron microscopy (TEM) and Rietveld refinements of x-ray diffraction (XRD) data. XRD analysis, performed in collaboration with NIST, on powder compositions on the STO/SrCuO2 tie line did not identify any ternary phases. SrCu0.10T0.90Oy buffer layers were prepared by pulsed laser deposition (PLD) and CSD on IBAD MgO flexible metallic textured tapes. TEM analysis of a ~100 nm thick SrCu0.10Ti0.90Oy buffer layer deposited by PLD showed a smooth Cu-doped STO/MgO interface. A ~600 nm thick YBCO film, deposited onto the SrCu0.10Ti0.90Oy buffer by PLD, exhibited a Tc of 87 K and critical current density (Jc) of ~1 MA/cm2. STO and Cu-doped STO thin films by CSD were ~30 nm thick. The in plane alignment (FWHM) after deposition of the STO improved by ~1° while it degraded by ~2° with the SrCu0.05TiOy buffer. YBCO was deposited by PLD on the STO and SrCu0.05TiOy buffers. The in plane alignment (FWHM) of the YBCO with the STO buffer layer

  18. Intermixing at the absorber-buffer layer interface in thin-film solar cells: The electronic effects of point defects in Cu(In,Ga)(Se,S){sub 2} and Cu{sub 2}ZnSn(Se,S){sub 4} devices

    SciTech Connect

    Varley, J. B.; Lordi, V.

    2014-08-14

    We investigate point defects in the buffer layers CdS and ZnS that may arise from intermixing with Cu(In,Ga)(S,Se){sub 2} (CIGS) or Cu{sub 2}ZnSn(S,Se){sub 4} (CZTS) absorber layers in thin-film photovoltaics. Using hybrid functional calculations, we characterize the electrical and optical behavior of Cu, In, Ga, Se, Sn, Zn, Na, and K impurities in the buffer. We find that In and Ga substituted on the cation site act as shallow donors in CdS and tend to enhance the prevailing n-type conductivity at the interface facilitated by Cd incorporation in CIGS, whereas they are deep donors in ZnS and will be less effective dopants. Substitutional In and Ga can favorably form complexes with cation vacancies (A-centers) which may contribute to the “red kink” effect observed in some CIGS-based devices. For CZTS absorbers, we find that Zn and Sn defects substituting on the buffer cation site are electrically inactive in n-type buffers and will not supplement the donor doping at the interface as in CIGS/CdS or ZnS devices. Sn may also preferentially incorporate on the S site as a deep acceptor in n-type ZnS, which suggests possible concerns with absorber-related interfacial compensation in CZTS devices with ZnS-derived buffers. Cu, Na, and K impurities are found to all have the same qualitative behavior, most favorably acting as compensating acceptors when substituting on the cation site. Our results suggest one beneficial role of K and Na incorporation in CIGS or CZTS devices is the partial passivation of vacancy-related centers in CdS and ZnS buffers, rendering them less effective interfacial hole traps and recombination centers.

  19. Buffers more than buffering agent: introducing a new class of stabilizers for the protein BSA.

    PubMed

    Gupta, Bhupender S; Taha, Mohamed; Lee, Ming-Jer

    2015-01-14

    In this study, we have analyzed the influence of four biological buffers on the thermal stability of bovine serum albumin (BSA) using dynamic light scattering (DLS). The investigated buffers include 4-(2-hydroxyethyl)piperazine-1-ethanesulfonic acid (HEPES), 4-(2-hydroxyethyl)-1-piperazine-propanesulfonic acid (EPPS), 4-(2-hydroxyethyl)piperazine-1-ethanesulfonic acid sodium salt (HEPES-Na), and 4-morpholinepropanesulfonic acid sodium salt (MOPS-Na). These buffers behave as a potential stabilizer for the native structure of BSA against thermal denaturation. The stabilization tendency follows the order of MOPS-Na > HEPES-Na > HEPES ≫ EPPS. To obtain an insight into the role of hydration layers and peptide backbone in the stabilization of BSA by these buffers, we have also explored the phase transition of a thermoresponsive polymer, poly(N-isopropylacrylamide (PNIPAM)), a model compound for protein, in aqueous solutions of HEPES, EPPS, HEPES-Na, and MOPS-Na buffers at different concentrations. It was found that the lower critical solution temperatures (LCST) of PNIPAM in the aqueous buffer solutions substantially decrease with increase in buffer concentration. The mechanism of interactions between these buffers and protein BSA was probed by various techniques, including UV-visible, fluorescence, and FTIR. The results of this series of studies reveal that the interactions are mainly governed by the influence of the buffers on the hydration layers surrounding the protein. We have also explored the possible binding sites of BSA with these buffers using a molecular docking technique. Moreover, the activities of an industrially important enzyme α-chymotrypsin (α-CT) in 0.05 M, 0.5 M, and 1.0 M of HEPES, EPPS, HEPES-Na, and MOPS-Na buffer solutions were analyzed at pH = 8.0 and T = 25 °C. Interestingly, the activities of α-CT were found to be enhanced in the aqueous solutions of these investigated buffers. Based upon the Jones-Dole viscosity parameters, the

  20. Buffered Electrochemical Polishing of Niobium

    SciTech Connect

    Gianluigi Ciovati; Tian, Hui; Corcoran, Sean

    2011-03-01

    The standard preparation of superconducting radio-frequency (SRF) cavities made of pure niobium include the removal of a 'damaged' surface layer, by buffered chemical polishing (BCP) or electropolishing (EP), after the cavities are formed. The performance of the cavities is characterized by a sharp degradation of the quality factor when the surface magnetic field exceeds about 90 mT, a phenomenon referred to as 'Q-drop.' In cavities made of polycrystalline fine grain (ASTM 5) niobium, the Q-drop can be significantly reduced by a low-temperature (? 120 °C) 'in-situ' baking of the cavity if the chemical treatment was EP rather than BCP. As part of the effort to understand this phenomenon, we investigated the effect of introducing a polarization potential during buffered chemical polishing, creating a process which is between the standard BCP and EP. While preliminary results on the application of this process to Nb cavities have been previously reported, in this contribution we focus on the characterization of this novel electrochemical process by measuring polarization curves, etching rates, surface finish, electrochemical impedance and the effects of temperature and electrolyte composition. In particular, it is shown that the anodic potential of Nb during BCP reduces the etching rate and improves the surface finish.

  1. INTERNATIONAL CONFERENCE ON SEMICONDUCTOR INJECTION LASERS SELCO-87: Line width of a single longitudinal mode emitted by an AlGaAs heterojunction laser

    NASA Astrophysics Data System (ADS)

    Bogatov, Alexandr P.; Eliseev, P. G.; Luk'yanov, S. A.; Pak, G. T.; Petrakova, T. V.

    1988-11-01

    A nonmonotonic dependence of the emission line width on the power was observed for a single longitudinal mode of an AlGaAs heterojunction laser. This behavior could be due to the dependence of the waveguide coefficient of the amplitude-phase coupling on the nature of operation of the laser.

  2. CHEMICAL SOLUTION DEPOSITION BASED OXIDE BUFFERS AND YBCO COATED CONDUCTORS

    SciTech Connect

    Paranthaman, Mariappan Parans

    2011-01-01

    We have reviewed briefly the growth of buffer and high temperature superconducting oxide thin films using a chemical solution deposition (CSD) method. In the Rolling-Assisted Biaxially Textured Substrates (RABiTS) process, developed at Oak Ridge National Laboratory, utilizes the thermo mechanical processing to obtain the flexible, biaxially oriented copper, nickel or nickel-alloy substrates. Buffers and Rare Earth Barium Copper Oxide (REBCO) superconductors have been deposited epitaxially on the textured nickel alloy substrates. The starting substrate serves as a template for the REBCO layer, which has substantially fewer weak links. Buffer layers play a major role in fabricating the second generation REBCO wire technology. The main purpose of the buffer layers is to provide a smooth, continuous and chemically inert surface for the growth of the REBCO film, while transferring the texture from the substrate to the superconductor layer. To achieve this, the buffer layers need to be epitaxial to the substrate, i.e. they have to nucleate and grow in the same bi-axial texture provided by the textured metal foil. The most commonly used RABiTS multi-layer architectures consist of a starting template of biaxially textured Ni-5 at.% W (Ni-W) substrate with a seed (first) layer of Yttrium Oxide (Y2O3), a barrier (second) layer of Yttria Stabilized Zirconia (YSZ), and a Cerium Oxide (CeO2) cap (third) layer. These three buffer layers are generally deposited using physical vapor deposition (PVD) techniques such as reactive sputtering. On top of the PVD template, REBCO film is then grown by a chemical solution deposition. This article reviews in detail about the list of oxide buffers and superconductor REBCO films grown epitaxially on single crystal and/or biaxially textured Ni-W substrates using a CSD method.

  3. Buffer architecture for biaxially textured structures and method of fabricating same

    DOEpatents

    Norton, David P.; Park, Chan; Goyal, Amit

    2004-04-06

    The invention relates to an article with an improved buffer layer architecture comprising a substrate having a metal surface, and an epitaxial buffer layer on the surface of the substrate. The epitaxial buffer layer comprises at least one of the group consisting of ZrO.sub.2, HfO.sub.2, and compounds having at least one of Ca and a rare earth element stabilizing cubic phases of ZrO.sub.2 and/or HfO.sub.2. The article can also include a superconducting layer deposited on the epitaxial buffer layer. The article can also include an epitaxial capping layer between the epitaxial buffer layer and the superconducting layer. A method for preparing an epitaxial article comprises providing a substrate with a metal surface, depositing on the metal surface an epitaxial buffer layer comprising at least one material selected from the group consisting of ZrO.sub.2, HfO.sub.2, and compounds having at least one of Ca and a rare earth element stabilizing cubic phases of at least one of ZrO.sub.2 and HfO.sub.2. The epitaxial layer depositing step occurs in a vacuum with a background pressure of no more than 1.times.10.sup.-5 Torr. The method can further comprise depositing a superconducting layer on the epitaxial layer, and depositing an epitaxial capping layer between the epitaxial buffer layer and the superconducting layer.

  4. Transmitter release modulation by intracellular Ca2+ buffers in facilitating and depressing nerve terminals of pyramidal cells in layer 2/3 of the rat neocortex indicates a target cell-specific difference in presynaptic calcium dynamics

    PubMed Central

    Rozov, A; Burnashev, N; Sakmann, B; Neher, E

    2001-01-01

    In connections formed by nerve terminals of layer 2/3 pyramidal cells onto bitufted interneurones in young (postnatal day (P)14–15) rat somatosensory cortex, the efficacy and reliability of synaptic transmission were low. At these connections release was facilitated by paired-pulse stimulation (at 10 Hz). In connections formed by terminals of layer 2/3 pyramids with multipolar interneurones efficacy and reliability were high and release was depressed by paired-pulse stimulation. In both types of terminal, however, the voltage-dependent Ca2+ channels that controlled transmitter release were predominantly of the P/Q- and N-subtypes. The relationship between unitary EPSP amplitude and extracellular calcium concentration ([Ca2+]o) was steeper for facilitating than for depressing terminals. Fits to a Hill equation with nH= 4 indicated that the apparent KD of the Ca2+ sensor for vesicle release was two- to threefold lower in depressing terminals than in facilitating ones. Intracellular loading of pyramidal neurones with the fast and slowly acting Ca2+ buffers BAPTA and EGTA differentially reduced transmitter release in these two types of terminal. Unitary EPSPs evoked by pyramidal cell stimulation in bitufted cells were reduced by presynaptic BAPTA and EGTA with half-effective concentrations of ∼0.1 and ∼1 mm, respectively. Unitary EPSPs evoked in multipolar cells were reduced to one-half of control at higher concentrations of presynaptic BAPTA and EGTA (∼0.5 and ∼7 mm, respectively). Frequency-dependent facilitation of EPSPs in bitufted cells was abolished by EGTA at concentrations of > 0.2 mm, suggesting that accumulation of free Ca2+ is essential for facilitation in the terminals contacting bitufted cells. In contrast, facilitation was unaffected or even slightly increased in the terminals loaded with BAPTA in the concentration range 0.02–0.5 mm. This is attributed to partial saturation of exogenously added BAPTA. However, BAPTA at concentrations > 1 mm

  5. Measuring the Degeneracy of Discrete Energy Levels Using a GaAs /AlGaAs Quantum Dot

    NASA Astrophysics Data System (ADS)

    Hofmann, A.; Maisi, V. F.; Gold, C.; Krähenmann, T.; Rössler, C.; Basset, J.; Märki, P.; Reichl, C.; Wegscheider, W.; Ensslin, K.; Ihn, T.

    2016-11-01

    We demonstrate an experimental method for measuring quantum state degeneracies in bound state energy spectra. The technique is based on the general principle of detailed balance and the ability to perform precise and efficient measurements of energy-dependent tunneling-in and -out rates from a reservoir. The method is realized using a GaAs /AlGaAs quantum dot allowing for the detection of time-resolved single-electron tunneling with a precision enhanced by a feedback control. It is thoroughly tested by tuning orbital and spin degeneracies with electric and magnetic fields. The technique also lends itself to studying the connection between the ground-state degeneracy and the lifetime of the excited states.

  6. Optical reflection from the Bragg lattice of AsSb metal nanoinclusions in an AlGaAs matrix

    SciTech Connect

    Ushanov, V. I.; Chaldyshev, V. V.; Preobrazhenskii, V. V.; Putyato, M. A.; Semyagin, B. R.

    2013-08-15

    The optical properties of metal-semiconductor metamaterials based on an AlGaAs matrix are studied. The specific feature of these materials is that there are As and AsSb nanoinclusion arrays which modify the dielectric properties of the material. These nanoinclusions are randomly arranged in the medium or form a Bragg structure with a reflectance peak at a wavelength close to 750 nm, corresponding to the transparency region of the matrix. The reflectance spectra are studied for s- and p-polarized light at different angles of incidence. It is shown that (i) As nanoinclusion arrays only slightly influence the optical properties of the medium in the wavelength range 700-900 nm, (ii) chaotic AsSb nanoinclusion arrays cause strong scattering of light, and (iii) the spatial periodicity in the arrangement of AsSb nanoinclusions is responsible for Bragg resonance in the optical reflection.

  7. Valuation of forested buffers

    NASA Astrophysics Data System (ADS)

    Basnyat, Prakash

    The research concentrated on two fronts: (1) defining relationships between land use complex and nitrate and sediment concentrations; and (2) developing a method for assessing the extent of potential and water quality improvements available through land management options and their associated costs. In this work, selected basins of the Fish River (Alabama) were delineated, land use/land cover types were classified, and "contributing zones" were delineated using Geographic Information System (GIS) and Remote Sensing (RS) analytical tools. Water samples collected from these basins were analyzed for their nutrient contents. Based on measured nitrate and sediment concentrations in basin streams, a linkage model was developed. This linkage model relates land use/land cover with the pollution levels in the stream. The linkage model was evaluated at three different scales: (1) the basin scale; (2) the contributing zone scale; and (3) the stream buffer/riparian zone scale. The contributing zone linkage model suggests that forests act as a sink or transformation zone. Residential/urban/built-up areas were identified as the strongest contributors of nitrate in the contributing zones model and active agriculture was identified as the second largest contributor. Regression results for the "land use/land cover diversity" model (stream buffer/riparian zone scale) suggest that areas that are close (adjacent) to the stream and any disturbances in these areas will have major impacts on stream water quality. The economic model suggests the value of retiring lands from agricultural land uses to forested buffers varies from 0 to 3067 per hectare, depending on the types of crops currently grown. Along with conversion costs, this land value forms the basis for estimates of the costs of land management options for improving (or maintaining) water quality throughout the study area. The model also shows the importance of stream-side management zones, which are key to maintenance of stream

  8. Band alignments of different buffer layers (CdS, Zn(O,S), and In{sub 2}S{sub 3}) on Cu{sub 2}ZnSnS{sub 4}

    SciTech Connect

    Yan, Chang; Liu, Fangyang; Song, Ning; Hao, Xiaojing; Ng, Boon K.; Stride, John A.; Tadich, Anton

    2014-04-28

    The heterojunctions of different n-type buffers, i.e., CdS, Zn(O,S), and In{sub 2}S{sub 3} on p-type Cu{sub 2}ZnSnS{sub 4} (CZTS) were investigated using X-ray Photoelectron Spectroscopy (XPS) and Near Edge X-ray Absorption Fine Structure (NEXAFS) Measurements. The band alignment of the heterojunctions formed between CZTS and the buffer materials was carefully measured. The XPS data were used to determine the Valence Band Offsets (VBO) of different buffer/CZTS heterojunctions. The Conduction Band Offset (CBO) was calculated indirectly by XPS data and directly measured by NEXAFS characterization. The CBO of the CdS/CZTS heterojunction was found to be cliff-like with CBO{sub XPS} = −0.24 ± 0.10 eV and CBO{sub NEXAFS} = −0.18 ± 0.10 eV, whereas those of Zn(O,S) and In{sub 2}S{sub 3} were found to be spike-like with CBO{sub XPS} = 0.92 ± 0.10 eV and CBO{sub NEXAFS} = 0.87 ± 0.10 eV for Zn(O,S)/CZTS and CBO{sub XPS} = 0.41 ± 0.10 eV for In{sub 2}S{sub 3}/CZTS, respectively. The CZTS photovoltaic device using the spike-like In{sub 2}S{sub 3} buffer was found to yield a higher open circuit voltage (Voc) than that using the cliff-like CdS buffer. However, the CBO of In{sub 2}S{sub 3}/CZTS is slightly higher than the optimum level and thus acts to block the flow of light-generated electrons, significantly reducing the short circuit current (Jsc) and Fill Factor (FF) and thereby limiting the efficiency. Instead, the use of a hybrid buffer for optimization of band alignment is proposed.

  9. Effects of surface barrier layer in AlGaAs/GaAs solar cells

    NASA Astrophysics Data System (ADS)

    Urabe, Hiroyuki; Kuramoto, Makoto; Nakano, Tomohiro; Kawaharazuka, Atsushi; Makimoto, Toshiki; Horikoshi, Yoshiji

    2015-09-01

    In this paper, we report the effects of surface barrier layers on the characteristics of AlGaAs/GaAs solar cells. The external quantum efficiency (EQE) spectra for AlGaAs barrier samples with different barrier layer AlAs fractions and thickness of the surface barrier layer were measured to increase the solar cell efficiency. The results show that the surface barrier layer is effective to block diffusing photoexcited electrons to the surface while the thicker barrier layer absorbs higher energy photons to generate carriers which recombine at the surface. The optimal surface barrier structure is a 50 nm thick Al0.7Ga0.3As.

  10. The buffer effect in neutral electrolyte supercapacitors

    NASA Astrophysics Data System (ADS)

    Vindt, Steffen T.; Skou, Eivind M.

    2016-02-01

    The observation that double-layer capacitors based on neutral aqueous electrolytes can have significantly wider usable potential windows than those based on acidic or alkaline electrolytes is studied. This effect is explained by a local pH change taking place at the electrode surfaces, leading to a change in the redox potential of water in opposite directions on the two electrodes, resulting in the wider stability window. The magnitude of this effect is suggested to be dependent on the buffer capacity, rather than the intrinsic pH value of the electrolyte. This is confirmed by studying the impact of addition of a buffer to such systems. It is shown that a 56 % higher dynamic storage capacity may be achieved, simply by controlling the buffer capacity of the electrolyte. The model system used, is based on a well-known commercial activated carbon (NORIT™ A SUPRA) as the electrode material, aqueous potassium nitrate as the electrolyte and potassium phosphates as the buffer system.

  11. Buffer Capacity: An Undergraduate Laboratory Experiment.

    ERIC Educational Resources Information Center

    Russo, Steven O.; Hanania, George I. H.

    1987-01-01

    Describes a quantitative experiment designed to demonstrate buffer action and the measurement of buffer capacity. Discusses how to make acetate buffers, determine their buffer capacity, plot the capacity/pH curve, and interpret the data obtained. (TW)

  12. The influence of Sb doping on the growth and electronic properties of GaAs(100) and AlGaAs(100)

    NASA Technical Reports Server (NTRS)

    Jamison, K. D.; Chen, H. C.; Bensaoula, A.; Lim, W.; Trombetta, L.

    1989-01-01

    Isoelectronic doping using antimony has been shown to reduce traps and improve material properties during epitaxial growth of Si doped GaAs(100) and AlGaAs(100). In this study, the effect of the antimony dopant on the optimal growth temperature is examined with the aim of producing high-quality heterostructures at lower temperatues. High-quality films of GaAs and AlGaAs have been grown by molecular-beam epitaxy at the normal growth temperatures of 610 and 700 C, respectively, and 50-100 C below this temperature using varying small amounts of Sb as a dopant. Electrical properties of the films were then examined using Hall mobility measurements and deep-level transient spectroscopy.

  13. Virtual Frame Buffer Interface Program

    NASA Technical Reports Server (NTRS)

    Wolfe, Thomas L.

    1990-01-01

    Virtual Frame Buffer Interface program makes all frame buffers appear as generic frame buffer with specified set of characteristics, allowing programmers to write codes that run unmodified on all supported hardware. Converts generic commands to actual device commands. Consists of definition of capabilities and FORTRAN subroutines called by application programs. Developed in FORTRAN 77 for DEC VAX 11/780 or DEC VAX 11/750 computer under VMS 4.X.

  14. Buffer capacity of biologics--from buffer salts to buffering by antibodies.

    PubMed

    Karow, Anne R; Bahrenburg, Sven; Garidel, Patrick

    2013-01-01

    Controlling pH is essential for a variety of biopharmaceutical process steps. The chemical stability of biologics such as monoclonal antibodies is pH-dependent and slightly acidic conditions are favorable for stability in a number of cases. Since control of pH is widely provided by added buffer salts, the current study summarizes the buffer characteristics of acetate, citrate, histidine, succinate, and phosphate buffers. Experimentally derived values largely coincide with values calculated from a model that had been proposed in 1922 by van Slyke. As high concentrated protein formulations become more and more prevalent for biologics, the self-buffering potential of proteins becomes of relevance. The current study provides information on buffer characteristics for pH ranges down to 4.0 and up to 8.0 and shows that a monoclonal antibody at 50 mg/mL exhibits similar buffer capacity as 6 mM citrate or 14 mM histidine (pH 5.0-6.0). Buffer capacity of antibody solutions scales linearly with protein concentration up to more than 200 mg/mL. At a protein concentration of 220 mg/mL, the buffer capacity resembles the buffer capacity of 30 mM citrate or 50 mM histidine (pH 5.0-6.0). The buffer capacity of monoclonal antibodies is practically identical at the process relevant temperatures 5, 25, and 40°C. Changes in ionic strength of ΔI=0.15, in contrast, can alter the buffer capacity up to 35%. In conclusion, due to efficient self-buffering by antibodies in the pH range of favored chemical stability, conventional buffer excipients could be dispensable for pH stabilization of high concentrated protein solutions.

  15. CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES: Effects of LSMO Buffer Layer on Crystalline Orientation and Ferroelectric Properties of Bi2.9Pr0.9Ti3O12 Thin Films Prepared by Radio-Frequency Magnetron Sputtering

    NASA Astrophysics Data System (ADS)

    Wu, Yun-Yi; Zhang, Duan-Ming; Yu, Jun; Zheng, Chao-Dan; Wang, Yun-Bo

    2008-11-01

    Ferroelectric Bi2.9Pr0.9Ti3O12/La0.67Sr0.33MnO3 (BPT/LSMO) films are fabricated on Pt(111)/TiO2/SiO2/Si substrates by rf-magnetron sputtering method. The influences of the LSMO deposition conditions and LSMO layer thickness on properties of BPT thin films are studied. The LSMO layer deposited at 300° C and 450σ C favours preferred (117) orientation of BPT films, while deposited at 600° C for LSMO layer leads to strong (111)-preferred orientation of BPT film. With the LSMO buffer layer, the films exhibit improved ferroelectric properties and Pt/BPT/LSMO(20nm)/Pt capacitor shows the largest remnant polarization Pr of 18.4 μC/cm2 at 14 V. A similar change in dielectric constant with the increase of LSMO layer thickness is also observed and the highest dielectric constant of 342.7 is obtained for the Pt/BPT/LSMO(20 nm)/Pt film. Compared with the Pt/BPT/Pt film, the Pt/BPT/LSMO/Pt films exhibit better fatigue endurance after 5 × 109 switching cycles. Moreover, the LSMO layer has apparent effect on leakage current density and the Pt/BPT/LSMO(20 nm)/Pt film exhibits the lowest leakage current density.

  16. Effect of buffer structures on AlGaN/GaN high electron mobility transistor reliability

    SciTech Connect

    Liu, L.; Xi, Y. Y.; Ren, F.; Pearton, S. J.; Laboutin, O.; Cao, Yu; Johnson, Wayne J.; Kravchenko, Ivan I

    2012-01-01

    AlGaN/GaN high electron mobility transistors (HEMTs) with three different types of buffer layers, including a GaN/AlGaN composite layer, or 1 or 2 lm GaN thick layers, were fabricated and their reliability compared. The HEMTs with the thick GaN buffer layer showed the lowest critical voltage (Vcri) during off-state drain step-stress, but this was increased by around 50% and 100% for devices with the composite AlGaN/GaN buffer layers or thinner GaN buffers, respectively. The Voff - state for HEMTs with thin GaN and composite buffers were 100 V, however, this degraded to 50 60V for devices with thick GaN buffers due to the difference in peak electric field near the gate edge. A similar trend was observed in the isolation breakdown voltage measurements, with the highest Viso achieved based on thin GaN or composite buffer designs (600 700 V), while a much smaller Viso of 200V was measured on HEMTs with the thick GaN buffer layers. These results demonstrate the strong influence of buffer structure and defect density on AlGaN/GaN HEMT performance and reliability.

  17. Ring Buffered Network Bus

    NASA Technical Reports Server (NTRS)

    1997-01-01

    This report describes the research effort to demonstrate the integration of a data sharing technology, Ring Buffered Network Bus, in development by Dryden Flight Research Center, with an engine simulation application, the Java Gas Turbine Simulator, in development at the University of Toledo under a grant from the Glenn Research Center. The objective of this task was to examine the application of the RBNB technologies as a key component in the data sharing, health monitoring and system wide modeling elements of the NASA Aviation Safety Program (AVSP) [Golding, 1997]. System-wide monitoring and modeling of aircraft and air safety systems will require access to all data sources which are relative factors when monitoring or modeling the national airspace such as radar, weather, aircraft performance, engine performance, schedule and planning, airport configuration, flight operations, etc. The data sharing portion of the overall AVSP program is responsible for providing the hardware and software architecture to access and distribute data, including real-time flight operations data, among all of the AVSP elements. The integration of an engine code capable of numerically "flying" through recorded flight paths and weather data using a software tool that allows for distributed access of data to this engine code demonstrates initial steps toward building a system capable of monitoring and modeling the National Airspace.

  18. Oracle Log Buffer Queueing

    SciTech Connect

    Rivenes, A S

    2004-12-08

    The purpose of this document is to investigate Oracle database log buffer queuing and its affect on the ability to load data using a specialized data loading system. Experiments were carried out on a Linux system using an Oracle 9.2 database. Previous experiments on a Sun 4800 running Solaris had shown that 100,000 entities per minute was an achievable rate. The question was then asked, can we do this on Linux, and where are the bottlenecks? A secondary question was also lurking, how can the loading be further scaled to handle even higher throughput requirements? Testing was conducted using a Dell PowerEdge 6650 server with four CPUs and a Dell PowerVault 220s RAID array with 14 36GB drives and 128 MB of cache. Oracle Enterprise Edition 9.2.0.4 was used for the database and Red Hat Linux Advanced Server 2.1 was used for the operating system. This document will detail the maximum observed throughputs using the same test suite that was used for the Sun tests. A detailed description of the testing performed along with an analysis of bottlenecks encountered will be made. Issues related to Oracle and Linux will also be detailed and some recommendations based on the findings.

  19. Mechanisms of buffer therapy resistance.

    PubMed

    Bailey, Kate M; Wojtkowiak, Jonathan W; Cornnell, Heather H; Ribeiro, Maria C; Balagurunathan, Yoganand; Hashim, Arig Ibrahim; Gillies, Robert J

    2014-04-01

    Many studies have shown that the acidity of solid tumors contributes to local invasion and metastasis. Oral pH buffers can specifically neutralize the acidic pH of tumors and reduce the incidence of local invasion and metastatic formation in multiple murine models. However, this effect is not universal as we have previously observed that metastasis is not inhibited by buffers in some tumor models, regardless of buffer used. B16-F10 (murine melanoma), LL/2 (murine lung) and HCT116 (human colon) tumors are resistant to treatment with lysine buffer therapy, whereas metastasis is potently inhibited by lysine buffers in MDA-MB-231 (human breast) and PC3M (human prostate) tumors. In the current work, we confirmed that sensitive cells utilized a pH-dependent mechanism for successful metastasis supported by a highly glycolytic phenotype that acidifies the local tumor microenvironment resulting in morphological changes. In contrast, buffer-resistant cell lines exhibited a pH-independent metastatic mechanism involving constitutive secretion of matrix degrading proteases without elevated glycolysis. These results have identified two distinct mechanisms of experimental metastasis, one of which is pH-dependent (buffer therapy sensitive cells) and one which is pH-independent (buffer therapy resistant cells). Further characterization of these models has potential for therapeutic benefit.

  20. Influence of buffer-layer construction and substrate orientation on the electron mobilities in metamorphic In{sup 0.70}Al{sup 0.30}As/In{sup 0.76}Ga{sup 0.24}As/In{sup 0.70}Al{sup 0.30}As structures on GaAs substrates

    SciTech Connect

    Kulbachinskii, V. A.; Oveshnikov, L. N.; Lunin, R. A.; Yuzeeva, N. A.; Galiev, G. B.; Klimov, E. A.; Pushkarev, S. S.; Maltsev, P. P.

    2015-07-15

    The influence of construction of the buffer layer and misorientation of the substrate on the electrical properties of In{sup 0.70}Al{sup 0.30}As/In{sup 0.76}Ga{sup 0.24}As/In{sup 0.70}Al{sup 0.30}As quantum wells on a GaAs substrate is studied. The temperature dependences (in the temperature range of 4.2 K < T < 300 K) and field dependences (in magnetic fields as high as 6 T) of the sample resistances are measured. Anisotropy of the resistances in different crystallographic directions is detected; this anisotropy depends on the substrate orientation and construction of the metamorphic buffer layer. In addition, the Hall effect and the Shubnikov–de Haas effect are studied. The Shubnikov–de Haas effect is used to determine the mobilities of electrons separately in several occupied dimensionally quantized subbands in different crystallographic directions. The calculated anisotropy of mobilities is in agreement with experimental data on the anisotropy of the resistances.

  1. Selective-area growth and magnetic characterization of MnAs/AlGaAs nanoclusters on insulating Al{sub 2}O{sub 3} layers crystallized on Si(111) substrates

    SciTech Connect

    Sakita, Shinya; Hara, Shinjiro; Elm, Matthias T.; Klar, Peter J.

    2016-01-25

    We report on selective-area metal-organic vapor phase epitaxy and magnetic characterization of coupled MnAs/AlGaAs nanoclusters formed on thin Al{sub 2}O{sub 3} insulating layers crystallized on Si(111) substrates. Cross-sectional transmission electron microscopy reveals that poly-crystalline γ-Al{sub 2}O{sub 3} grains are formed after an annealing treatment of the amorphous Al{sub 2}O{sub 3} layers deposited by atomic layer deposition on Si(111) substrates. The 〈111〉 direction of the γ-Al{sub 2}O{sub 3} grains tends to be oriented approximately parallel to the 〈111〉 direction of the Si substrate. We observe that hexagonal MnAs nanoclusters on AlGaAs buffer layers grown by selective-area metal-organic vapor phase epitaxy on partially SiO{sub 2}-masked Al{sub 2}O{sub 3} insulator crystallized on Si(111) substrates are oriented with the c-axis along the 〈111〉 direction of the substrates, but exhibit a random in-plane orientation. A likely reason is the random orientation of the poly-crystalline γ-Al{sub 2}O{sub 3} grains in the Al{sub 2}O{sub 3} layer plane. Magnetic force microscopy studies at room temperature reveal that arrangements of coupled MnAs nanoclusters exhibit a complex magnetic domain structure. Such arrangements of coupled MnAs nanoclusters may also show magnetic random telegraph noise, i.e., jumps between two discrete resistance levels, in a certain temperature range, which can be explained by thermally activated changes of the complex magnetic structure of the nanocluster arrangements.

  2. Excitation and de-excitation mechanisms of Er-doped GaAs and AlGaAs

    NASA Astrophysics Data System (ADS)

    Elsaesser, David W.

    1992-12-01

    Electrical and optical characterization have been performed on GaAs and Al(x)Ga(1-x)As samples doped with Er either by ion implantation or during Molecular Beam Epitaxial (MBE) growth. Deep Level Transient Spectroscopy (DLTS) and Temperature-Dependent Hall Effect (TDH) measurements indicated the presence of two hole traps in Er-doped GaAs, at 35 and 360 meV above the valence band maximum. The former (shallower) center was thought to be due to Er substituting for a Ga atom (ErGa) and giving rise to an isoelectronic impurity potential. The second center was attributed to an Er atom occupying an interstitial position (Er(i)). Annealing studies performed on Er-implanted GaAs indicated that the ErGa center preferentially formed at higher annealing temperatures (greater than 850 C), with the Er(i) reaching a maximum concentration at an annealing temperature of around 750 C. Optical characterization performed by Photoluminescence (PL) measurements showed that the Er(i) center gave a much stronger Er-related intra-4f shell emission. Mechanisms for the excitation of the 4f shells of these two centers are discussed. Similar optically active Eri centers may be forming in AlGaAs.

  3. AlGaAs top solar cell for mechanical attachment in a multi-junction tandem concentrator solar cell stack

    NASA Technical Reports Server (NTRS)

    Dinetta, L. C.; Hannon, M. H.; Cummings, J. R.; Mcneeley, J. B.; Barnett, Allen M.

    1990-01-01

    Free-standing, transparent, tunable bandgap AlxGa1-xAs top solar cells have been fabricated for mechanical attachment in a four terminal tandem stack solar cell. Evaluation of the device results has demonstrated 1.80 eV top solar cells with efficiencies of 18 percent (100 X, and AM0) which would yield stack efficiencies of 31 percent (100 X, AM0) with a silicon bottom cell. When fully developed, the AlxGa1-xAs/Si mechanically-stacked two-junction solar cell concentrator system can provide efficiencies of 36 percent (AM0, 100 X). AlxGa1-xAs top solar cells with bandgaps from 1.66 eV to 2.08 eV have been fabricated. Liquid phase epitaxy (LPE) growth techniques have been used and LPE has been found to yield superior AlxGa1-xAs material when compared to molecular beam epitaxy and metal-organic chemical vapor deposition. It is projected that stack assembly technology will be readily applicable to any mechanically stacked multijunction (MSMJ) system. Development of a wide bandgap top solar cell is the only feasible method for obtaining stack efficiencies greater than 40 percent at AM0. System efficiencies of greater than 40 percent can be realized when the AlGaAs top solar cell is used in a three solar cell mechanical stack.

  4. Electrodialysis operation with buffer solution

    DOEpatents

    Hryn, John N.; Daniels, Edward J.; Krumdick, Greg K.

    2009-12-15

    A new method for improving the efficiency of electrodialysis (ED) cells and stacks, in particular those used in chemical synthesis. The process entails adding a buffer solution to the stack for subsequent depletion in the stack during electrolysis. The buffer solution is regenerated continuously after depletion. This buffer process serves to control the hydrogen ion or hydroxide ion concentration so as to protect the active sites of electrodialysis membranes. The process enables electrodialysis processing options for products that are sensitive to pH changes.

  5. Programmable pH buffers

    DOEpatents

    Gough, Dara Van; Huber, Dale L.; Bunker, Bruce C.; Roberts, Mark E.

    2017-01-24

    A programmable pH buffer comprises a copolymer that changes pK.sub.a at a lower critical solution temperature (LCST) in water. The copolymer comprises a thermally programmable polymer that undergoes a hydrophobic-to-hydrophilic phase change at the LCST and an electrolytic polymer that exhibits acid-base properties that are responsive to the phase change. The programmable pH buffer can be used to sequester CO.sub.2 into water.

  6. Crystallographic tilt and in-plane anisotropies of an a-plane InGaN/GaN layered structure grown by MOCVD on r-plane sapphire using a ZnO buffer

    NASA Astrophysics Data System (ADS)

    Liu, H. F.; Liu, W.; Guo, S.; Chi, D. Z.

    2016-03-01

    High-resolution x-ray diffraction (HRXRD) was used to investigate the crystallographic tilts and structural anisotropies in epitaxial nonpolar a-plane InGaN/GaN grown by metal-organic chemical vapor deposition on r-plane sapphire using a ZnO buffer. The substrate had an unintentional miscut of 0.14° towards its [-4 2 2 3] axis. However, HRXRD revealed a tilt of 0.26° (0.20°) between the ZnO (GaN) (11-20) and the Al2O3 (1-102) atomic planes, with the (11-20) axis of ZnO (GaN) tilted towards its c-axis, which has a difference of 163° in azimuth from that of the substrate’s miscut. Excess broadenings in the GaN/ZnO (11-20) rocking curves (RCs) were observed along its c-axis. Specific analyses revealed that partial dislocations and anisotropic in-plane strains, rather than surface-related effects, wafer curvature or stacking faults, are the dominant factors for the structural anisotropy. The orientation of the partial dislocations is most likely affected by the miscut of the substrate, e.g. via tilting of the misfit dislocation gliding planes created during island coalescences. Their Burgers vector components in the growth direction, in turn, gave rise to crystallographic tilts in the same direction as that of the excess RC-broadenings.

  7. Quantum-well intermixing for the control of second-order nonlinear effects in AlGaAs multiple-quantum-well waveguides.

    PubMed

    Street, M W; Whitbread, N D; Hutchings, D C; Arnold, J M; Marsh, J H; Aitchison, J S; Kennedy, G T; Sibbett, W

    1997-11-01

    We present experimental evidence to demonstrate the feasibility of a promising new quasi-phase-matching technique in AlGaAs multiple-quantum-well waveguides. Non-phase-matched second-harmonic-generation measurements indicate that, for sub-half-bandgap excitation near 1.5 microm , quantum-well intermixing by impurity-free vacancy disordering results in a reduction of the nonlinear susceptibility chi((2))(zxy) (~340 pm/V) by 17%. Relatively low intermixed waveguide losses, and the high spatial resolution of the impurity-free vacancy disordering process, suggest that periodic intermixing along the direction of propagation should lead to useful frequency-conversion efficiencies.

  8. Buffer Gas Acquisition and Storage

    NASA Technical Reports Server (NTRS)

    Parrish, Clyde F.; Lueck, Dale E.; Jennings, Paul A.; Callahan, Richard A.; Delgado, H. (Technical Monitor)

    2001-01-01

    The acquisition and storage of buffer gases (primarily argon and nitrogen) from the Mars atmosphere provides a valuable resource for blanketing and pressurizing fuel tanks and as a buffer gas for breathing air for manned missions. During the acquisition of carbon dioxide (CO2), whether by sorption bed or cryo-freezer, the accompanying buffer gases build up in the carbon dioxide acquisition system, reduce the flow of CO2 to the bed, and lower system efficiency. It is this build up of buffer gases that provide a convenient source, which must be removed, for efficient capture Of CO2 Removal of this buffer gas barrier greatly improves the charging rate of the CO2 acquisition bed and, thereby, maintains the fuel production rates required for a successful mission. Consequently, the acquisition, purification, and storage of these buffer gases are important goals of ISRU plans. Purity of the buffer gases is a concern e.g., if the CO, freezer operates at 140 K, the composition of the inert gas would be approximately 21 percent CO2, 50 percent nitrogen, and 29 percent argon. Although there are several approaches that could be used, this effort focused on a hollow-fiber membrane (HFM) separation method. This study measured the permeation rates of CO2, nitrogen (ND, and argon (Ar) through a multiple-membrane system and the individual membranes from room temperature to 193K and 10 kpa to 300 kPa. Concentrations were measured with a gas chromatograph that used a thermoconductivity (TCD) detector with helium (He) as the carrier gas. The general trend as the temperature was lowered was for the membranes to become more selective, In addition, the relative permeation rates between the three gases changed with temperature. The end result was to provide design parameters that could be used to separate CO2 from N2 and Ar.

  9. Buffer gas acquisition and storage

    NASA Astrophysics Data System (ADS)

    Parrish, Clyde F.; Lueck, Dale E.; Jennings, Paul A.

    2001-02-01

    The acquisition and storage of buffer gases (primarily argon and nitrogen) from the Mars atmosphere provides a valuable resource for blanketing and pressurizing fuel tanks and as a buffer gas for breathing air for manned missions. During the acquisition of carbon dioxide (CO2), whether by sorption bed or cryo-freezer, the accompanying buffer gases build up in the carbon dioxide acquisition system, reduce the flow of CO2 to the bed, and lower system efficiency. It is this build up of buffer gases that provide a convenient source, which must be removed, for efficient capture of CO2. Removal of this buffer gas barrier greatly improves the charging rate of the CO2 acquisition bed and, thereby, maintains the fuel production rates required for a successful mission. Consequently, the acquisition, purification, and storage of these buffer gases are important goals of ISRU plans. Purity of the buffer gases is a concern e.g., if the CO2 freezer operates at 140 K, the composition of the inert gas would be approximately 21 percent CO2, 50 percent nitrogen, and 29 percent argon. Although there are several approaches that could be used, this effort focused on a hollow-fiber membrane (HFM) separation method. This study measured the permeation rates of CO2, nitrogen (N2), and argon (Ar) through a multiple-membrane system and the individual membranes from room temperature to 193 K and 10 kPa to 300 kPa. Concentrations were measured with a gas chromatograph. The end result was data necessary to design a system that could separate CO2, N2, and Ar. .

  10. A highly selective, chlorofluorocarbon-free GaAs on AlGaAs etch

    SciTech Connect

    Smith, L.E. . Solid State Technology Center)

    1993-07-01

    A highly selective reactive ion etching process using SiCl[sub 4], CF[sub 4], O[sub 2], and He is reported. The selectivity of the etch, which is adjustable, ranges from 308:1 to 428:1 for GaAs to Al[sub 0.11]Ga[sub 0.89]As. This variability in selectivity is achieved by adjusting the helium flow rate. One very attractive feature of this etch is that it uses no chlorofluorocarbons and therefore complies with future bans on these substances imposed at both federal and corporate levels. The etch is demonstrated on a GaAs field effect transistor structure with an underlying Al[sub 0.11]Ga[sub 0.89]As stop-etch layer. The etch can be used for both anisotropic and isotropic applications.

  11. Giant energy harvesting potential in (100)-oriented 0.68PbMg1/3Nb2/3O3-0.32PbTiO3 with Pb(Zr0.3Ti0.7)O3/PbOx buffer layer and (001)-oriented 0.67PbMg1/3Nb2/3O3-0.33PbTiO3 thin films

    NASA Astrophysics Data System (ADS)

    Vats, Gaurav; Kushwaha, Himmat Singh; Vaish, Rahul; Madhar, Niyaz Ahamad; Shahabuddin, Mohammed; Parakkandy, Jafar M.; Batoo, Khalid Mujasam

    2014-11-01

    This work emphasis on the competence of (100)-oriented PMN-PT buffer layered (0.68PbMg1/3Nb2/3O3-0.32PbTiO3 with Pb(Zr0.3Ti0.7)O3/PbOx buffer layer) and (001)-oriented PMN-PT (0.67PbMg1/3Nb2/3O3-0.33PbTiO3) for low grade thermal energy harvesting using Olsen cycle. Our analysis (based on well-reported experiments in literature) reveals that these films show colossal energy harnessing possibility. Both the films are found to have maximum harnessable energy densities (PMN-PT buffer layered: 8 MJ/m3; PMN-PT: 6.5 MJ/m3) in identical ambient conditions of 30-150°C and 0-600 kV/cm. This energy harnessing plausibility is found to be nearly five times higher than the previously reported values to date.

  12. Free flow cell electrophoresis using zwitterionic buffer

    NASA Technical Reports Server (NTRS)

    Rodkey, R. Scott

    1990-01-01

    Studies of a zwitterionic buffer formulated for cell electrophoresis were done using the McDonnell-Douglas Continuous Flow Electrophoresis System. Standard buffers were analyzed for their stability in the electrical field and the results showed that both buffers tested were inherently unstable. Further, titration studies showed that the standards buffers buffered poorly at the pH employed for electrophoresis. The zwitterionic buffer buffered well at its nominal pH and was shown to be stable in the electrical field. Comparative studies of the buffer with standard cell separation buffers using formalin fixed rabbit and goose red blood cells showed that the zwitterionic buffer gave better resolution of the fixed cells. Studies with viable hybridoma cells showed that buffer Q supported cell viability equal to Hank's Balanced Salt Solution and that hybridoma cells in different stages of the growth cycle demonstrated reproducible differences in electrophoretic mobility.

  13. AlGaAs 55Fe X-ray radioisotope microbattery

    PubMed Central

    Butera, S.; Whitaker, M. D. C.; Lioliou, G.; Barnett, A. M.

    2016-01-01

    This paper describes the performance of a fabricated prototype Al0.2Ga0.8As 55Fe radioisotope microbattery photovoltaic cells over the temperature range −20 °C to 50 °C. Two 400 μm diameter p+-i-n+ (3 μm i-layer) Al0.2Ga0.8As mesa photodiodes were used as conversion devices in a novel X-ray microbattery prototype. The changes of the key microbattery parameters were analysed in response to temperature: the open circuit voltage, the maximum output power and the internal conversion efficiency decreased when the temperature was increased. At −20 °C, an open circuit voltage and a maximum output power of 0.2 V and 0.04 pW, respectively, were measured per photodiode. The best internal conversion efficiency achieved for the fabricated prototype was only 0.95% at −20 °C. PMID:27922093

  14. AlGaAs 55Fe X-ray radioisotope microbattery

    NASA Astrophysics Data System (ADS)

    Butera, S.; Whitaker, M. D. C.; Lioliou, G.; Barnett, A. M.

    2016-12-01

    This paper describes the performance of a fabricated prototype Al0.2Ga0.8As 55Fe radioisotope microbattery photovoltaic cells over the temperature range ‑20 °C to 50 °C. Two 400 μm diameter p+-i-n+ (3 μm i-layer) Al0.2Ga0.8As mesa photodiodes were used as conversion devices in a novel X-ray microbattery prototype. The changes of the key microbattery parameters were analysed in response to temperature: the open circuit voltage, the maximum output power and the internal conversion efficiency decreased when the temperature was increased. At ‑20 °C, an open circuit voltage and a maximum output power of 0.2 V and 0.04 pW, respectively, were measured per photodiode. The best internal conversion efficiency achieved for the fabricated prototype was only 0.95% at ‑20 °C.

  15. Influence of glyphosate on the copper dissolution in phosphate buffer

    NASA Astrophysics Data System (ADS)

    Coutinho, C. F. B.; Silva, M. O.; Machado, S. A. S.; Mazo, L. H.

    2007-01-01

    The electrochemical behavior of copper microelectrode in phosphate buffer in the presence of glyphosate was investigated by electrochemical techniques. It was observed that the additions of glyphosate in the phosphate buffer increased the anodic current of copper microelectrode and the electrochemical dissolution was observed. This phenomenon could be associated with the Cu(II) complexation by glyphosate forming a soluble complex. Physical characterization of the surface showed that, in absence of glyphosate, an insoluble layer covered the copper surface; on the other hand, in presence of glyphosate, it was observed a corroded copper surface with the formation of glyphosate complex in solution.

  16. Buffering in cyclic gene networks

    NASA Astrophysics Data System (ADS)

    Glyzin, S. D.; Kolesov, A. Yu.; Rozov, N. Kh.

    2016-06-01

    We consider cyclic chains of unidirectionally coupled delay differential-difference equations that are mathematical models of artificial oscillating gene networks. We establish that the buffering phenomenon is realized in these system for an appropriate choice of the parameters: any given finite number of stable periodic motions of a special type, the so-called traveling waves, coexist.

  17. Raman study of CeO2 texture as a buffer layer in the CeO2/La2Zr2O7/Ni architecture for coated conductors.

    PubMed

    Jiménez, C; Caroff, T; Bartasyte, A; Margueron, S; Abrutis, A; Chaix-Pluchery, O; Weiss, F

    2009-04-01

    The CeO(2)/La(2)Zr(2)O(7)/Ni piled-up structure is a very promising architecture for YBa(2)Cu(3)O(7) (YBCO) coated conductors. We have grown YBCO/CeO(2)/LZO/Ni epitaxial structures by metalorganic decomposition (MOD) and metalorganic chemical vapor deposition (MOCVD) methods. The crystallographic quality of the CeO(2) layer is not well determined by conventional X-ray diffraction (XRD) due to the superposition of LZO and CeO(2) reflections. An alternative simple Raman spectroscopy analysis of the crystalline quality of the CeO(2) films is proposed. The F(2g) Raman mode of CeO(2) can be quantified either by using two polarization configurations (crossed or parallel) or at two different rotation angles around the normal axis (0 degrees and 45 degrees ) to obtain information about the sample texture. The sample texture can be determined via a quality factor (referred to as the Raman intensity ratio, RIR) consisting of calculating the ratio of the integrated intensity of the CeO(2) F(2g) mode at 0 degrees and 45 degrees in parallel polarization. This factor correlates with superconducting performance and the technique can be used as an on-line nondestructive characterization method.

  18. In situ metalorganic growth control of GaAlAs thick layers using 1.32 μm laser reflectometry

    NASA Astrophysics Data System (ADS)

    Kuszelewicz, R.; Rafflé, Y.; Azoulay, R.; Dugrand, L.; Le Roux, G.

    1995-02-01

    We report on the use of in situ reflectometry using 1.32 μm laser light to monitor the metalorganic growth of thick GaAlAs layers. With respect to the particular growth conditions, the calibration of effective indices was carried out for bulk as well as multi quantum well layers. This allowed in situ measurements of large thickness layers, Al concentration determination of AlGaAS layers, and metal-semiconductor-field effect transistor (MESFET) structure monitoring with highly improved precision and reproducibility.

  19. Propagation of misfit dislocations from buffer/Si interface into Si

    DOEpatents

    Liliental-Weber, Zuzanna; Maltez, Rogerio Luis; Morkoc, Hadis; Xie, Jinqiao

    2011-08-30

    Misfit dislocations are redirected from the buffer/Si interface and propagated to the Si substrate due to the formation of bubbles in the substrate. The buffer layer growth process is generally a thermal process that also accomplishes annealing of the Si substrate so that bubbles of the implanted ion species are formed in the Si at an appropriate distance from the buffer/Si interface so that the bubbles will not migrate to the Si surface during annealing, but are close enough to the interface so that a strain field around the bubbles will be sensed by dislocations at the buffer/Si interface and dislocations are attracted by the strain field caused by the bubbles and move into the Si substrate instead of into the buffer epi-layer. Fabrication of improved integrated devices based on GaN and Si, such as continuous wave (CW) lasers and light emitting diodes, at reduced cost is thereby enabled.

  20. An integrated recirculating optical buffer.

    PubMed

    Park, Hyundai; Mack, John P; Bluementhal, Daniel J; Bowers, John E

    2008-07-21

    This paper reports an integrated optical buffer consisting of a low loss silicon waveguide delay line and a silicon evanescent gate matrix switch. The integrated device demonstrates an error free operation at 40 Gb/s data rate with a packet delay of 1.1 ns. This demonstration also highlights the silicon evanescent device platform to realize new types of photonic integrated devices by combining the low loss silicon passive components with the silicon evanescent photonic active devices.