Parametrization of optical properties of indium-tin-oxide thin films by spectroscopic ellipsometry: Substrate interfacial reactivity

NASA Astrophysics Data System (ADS)

Losurdo, M.; Giangregorio, M.; Capezzuto, P.; Bruno, G.; de Rosa, R.; Roca, F.; Summonte, C.; Plá, J.; Rizzoli, R.

2002-01-01

Indium-tin-oxide (ITO) films deposited by sputtering and e-gun evaporation on both transparent (Corning glass) and opaque (c-Si, c-Si/SiO2) substrates and in c-Si/a-Si:H/ITO heterostructures have been analyzed by spectroscopic ellipsometry (SE) in the range 1.5-5.0 eV. Taking the SE advantage of being applicable to absorbent substrate, ellipsometry is used to determine the spectra of the refractive index and extinction coefficient of the ITO films. The effect of the substrate surface on the ITO optical properties is focused and discussed. To this aim, a parametrized equation combining the Drude model, which considers the free-carrier response at the infrared end, and a double Lorentzian oscillator, which takes into account the interband transition contribution at the UV end, is used to model the ITO optical properties in the useful UV-visible range, whatever the substrate and deposition technique. Ellipsometric analysis is corroborated by sheet resistance measurements.

Optical constants of wurtzite ZnS thin films determined by spectroscopic ellipsometry

NASA Astrophysics Data System (ADS)

Ong, H. C.; Chang, R. P. H.

2001-11-01

The complex dielectric functions of wurtzite ZnS thin films grown on (0001) Al2O3 have been determined by using spectroscopic ellipsometry over the spectral range of 1.33-4.7 eV. Below the band gap, the refractive index n is found to follow the first-order Sellmeir dispersion relationship n2(λ)=1+2.22λ2/(λ2-0.0382). Strong and well-defined free excitonic features located above the band edge are clearly observed at room temperature. The intrinsic optical parameters of wurtzite ZnS such as band gaps and excitonic binding energies have been determined by fitting the absorption spectrum using a modified Elliott expression together with Lorentizan broadening. Both parameters are found to be larger than their zinc blende counterparts.

Characterization by spectroscopic Ellipsometry, the physical properties of silver nanoparticles.

NASA Astrophysics Data System (ADS)

Coanga, Jean-Maurice

2013-04-01

Physicists are able to change their minds through their experiments. I think it is time to go kick the curse and go further in research if we want a human future. I work in the Nano-Optics and Plasmonics research. I defined with ellipsomètrie the structure of new type of Nano particles of silver. It's same be act quickly to replace the old dirty leaded electronic-connexion chip and by the other hand to find a new way for the heath care of cancer disease by nanoparticles the next killers of bad cells. Silver nanoparticle layers are obtained by Spark Plasma Sintering are investigated as an alternative to lead alloy based material for solder joint in power mechatronics modules. These layers are characterized by mean of conventional techniques that is the dilatometry technique, the resistivity measurement through the van der Pauw method, and the flash laser technique. Furthermore, the nanoparticles of silver layer are deeply studied by UV-Visible spectroscopic ellipsometry. Spectroscopic angles parameters are determined in function of temperature and dielectric constants are deduced and analyzed through an optical model which takes into account a Drude and a Lorentz component within the Bruggeman effective medium approximation (EMA). The relaxation times and the electrical conductivity are plot in function of temperature. The obtained electrical conductivity give significant result in good agreement to those reported by four points electrical measurement method.

Solid-state dewetting of thin Au films studied with real-time, in situ spectroscopic ellipsometry

NASA Astrophysics Data System (ADS)

Magnozzi, M.; Bisio, F.; Canepa, M.

2017-11-01

We report the design and testing of a small, high vacuum chamber that allows real-time, in situ spectroscopic ellipsometry (SE) measurements; the chamber was designed to be easily inserted within the arms of a commercial ellipsometer. As a test application, we investigated the temperature-induced solid-state dewetting of thin (20 to 8 nm) Au layers on Si wafers. In situ SE measurements acquired in real time during the heating of the samples reveal features that can be related to the birth of a localized surface plasmon resonance (LSPR), and demonstrate the presence of a temperature threshold for the solid-state dewetting.

Observation of Frenkel and charge transfer excitons in pentacene single crystals using spectroscopic generalized ellipsometry

NASA Astrophysics Data System (ADS)

Qi, Dongchen; Su, Haibin; Bastjan, M.; Jurchescu, O. D.; Palstra, T. M.; Wee, Andrew T. S.; Rübhausen, M.; Rusydi, A.

2013-09-01

We report on the emerging and admixture of Frenkel and charge transfer (CT) excitons near the absorption onset in pentacene single crystals. Using high energy-resolution spectroscopic generalized ellipsometry with in-plane polarization dependence, the excitonic nature of three lowest lying excitations is discussed. Their distinct polarization dependence strongly indicates the presence of both Frenkel and CT types of excitons near the excitation onset. In particular, the peculiar polarization behavior of the second excitation can only be rationalized by taking into account the inherent CT transition dipole moment. This observation has important implications for the pentacene-based optoelectronic devices.

Spectroscopic ellipsometry analysis of nanocrystalline silicon carbide obtained at low temperature

NASA Astrophysics Data System (ADS)

Kerdiles, S.; Madelon, R.; Rizk, R.

2001-12-01

Thin films of silicon carbide obtained by hydrogen-reactive magnetron sputtering with various substrate temperatures TS (100-600 °C) were analysed by transmission electron microscopy (TEM) and spectroscopic ellipsometry (SE). The TEM images show evidence of the growth of hydrogenated nanocrystalline silicon carbide (nc-SiC:H) deposited at TS as low as 300 °C, with an average grain size of 4-5 nm. The SE spectra were reproduced by using the Forouhi-Bloomer model and assuming a 7 nm thick overlayer with a void fraction of 45%. The observed increase of the refractive index with TS is assigned to the improvement of both crystallinity and compactness of the layer. The expected increase of the optical gap seems to be offset by the drop of hydrogen content, leaving the gap unchanged. The fabrication and characteristics of nc-SiC:H/c-Si diode are finally described and the data indicate a good rectifying behaviour, together with a low leakage current.

Optical constants of electroplated gold from spectroscopic ellipsometry

NASA Astrophysics Data System (ADS)

Synowicki, R. A.; Herzinger, Craig M.; Hall, James T.; Malingowski, Andrew

2017-11-01

The optical constants of an opaque electroplated gold film (Laser Gold from Epner Technology Inc.), were determined by spectroscopic ellipsometry at room temperature over the spectral range from 0.142 μm in the vacuum ultraviolet to 36 μm in the infrared (photon energy range 0.034-8.75 eV). Data from two separate ellipsometer instruments covering different spectral ranges were analyzed simultaneously. The optical constants n&k or ε1&ε2 were determined by fitting an oscillator dispersion model combining Drude, Gaussian, and Sellmeier dispersion functions to the experimental Ψ and Δ data. The data were analyzed using both an ideal bulk substrate model and a simple overlayer model to account for surface roughness. Including the optical surface roughness layer improved ellipsometric data fits in the UV, and using a separate Drude function for the surface layer improved fits in the infrared. The surface roughness was also characterized using an Atomic Force Microscope. Using an oscillator dispersion model for the optical constants determined in this work allows for more realistic extrapolation to longer infrared wavelengths. Extending optical constants out to 50 μm and beyond is important for calibrating far-infrared reflectance measurements. Applications include understanding the thermal performance of cryogenic space-based instruments, such as the James Webb Space Telescope (JWST).

Modeling the transport properties of epitaxially grown thermoelectric oxide thin films using spectroscopic ellipsometry

NASA Astrophysics Data System (ADS)

Sarath Kumar, S. R.; Abutaha, Anas I.; Hedhili, M. N.; Alshareef, H. N.

2012-01-01

The influence of oxygen vacancies on the transport properties of epitaxial thermoelectric (Sr,La)TiO3 thin films is determined using electrical and spectroscopic ellipsometry (SE) measurements. Oxygen vacancy concentration was varied by ex-situ annealing in Ar and Ar/H2. All films exhibited degenerate semiconducting behavior, and electrical conductivity decreased (258-133 S cm-1) with increasing oxygen content. Similar decrease in the Seebeck coefficient is observed and attributed to a decrease in effective mass (7.8-3.2 me), as determined by SE. Excellent agreement between transport properties deduced from SE and direct electrical measurements suggests that SE is an effective tool for studying oxide thin film thermoelectrics.

Monitoring the layer-by-layer self-assembly of graphene and graphene oxide by spectroscopic ellipsometry.

PubMed

Zhou, Kai-Ge; Chang, Meng-Jie; Wang, Hang-Xing; Xie, Yu-Long; Zhang, Hao-Li

2012-01-01

Thin films of graphene oxide, graphene and copper (II) phthalocyanine dye have been successfully fabricated by electrostatic layer-by-layer (LbL) assembly approach. We present the first variable angle spectroscopic ellipsometry (VASE) investigation on these graphene-dye hybrid thin films. The thickness evaluation suggested that our LbL assembly process produces highly uniform and reproducible thin films. We demonstrate that the refractive indices of the graphene-dye thin films undergo dramatic variation in the range close to the absorption of the dyes. This investigation provides new insight to the optical properties of graphene containing thin films and shall help to establish an appropriate optical model for graphene-based hybrid materials.

FTIR and Vis-FUV real time spectroscopic ellipsometry studies of polymer surface modifications during ion beam bombardment

NASA Astrophysics Data System (ADS)

Laskarakis, A.; Gravalidis, C.; Logothetidis, S.

2004-02-01

The continuously increasing application of polymeric materials in many scientific and technological fields has motivated an extensive use of polymer surface treatments, which modify the physical and chemical properties of polymer surfaces leading to surface activation and promotion of the surface adhesion. Fourier transform IR spectroscopic ellipsometry (FTIRSE) and phase modulated ellipsometry (PME) in the IR and Vis-FUV spectral regions respectively have been employed for in situ and real time monitoring of the structural changes on the polymer surface obtained by Ar + ion bombardment. The polymers were industrially supplied polyethylene terephthalate (PET) and polyethylene naphthalate (PEN) membranes. The Ar + ion bombardment has found to change the chemical bonding of the films and especially the amount of the CO, C-C and CC groups. The detailed study of the FTIRSE spectra reveals important information about the effect of the Ar + ion bombardment on each of the above bonding groups. Also, the modification of the characteristic features, attributed to electronic transitions in specific bonds of PET and PEN macromolecules, has been studied using PME.

Spectroscopic ellipsometry study of N+ ion-implanted ethylene-norbornene films

NASA Astrophysics Data System (ADS)

Šiljegović, M.; Kačarević-Popović, Z. M.; Stchakovsky, M.; Radosavljević, A. N.; Korica, S.; Novaković, M.; Popović, M.

2014-05-01

The optical properties of 150 keV N+ implanted ethylene-norbornene (TOPAS 6017S-04) copolymer were investigated using phase modulated spectroscopic ellipsometry (PMSE) and ultraviolet-visible (UV-Vis) spectroscopy in the ranges of 0.6-6.5 eV and of 1.5-6.2 eV, respectively. The single-effective-oscillator model was used to fit the calculated data to the experimental ellipsometric spectra. The results show that the oscillator and dispersion energies decrease with increasing ion fluence up to 1015 cm-2, and then these parameters increase with further fluence increasing. Analysis of the UV-Vis absorption spectra revealed the presence of indirect electronic transitions with the band gap energy in the range of 1.3 to 2.8 eV. It was found that both the band gap energy and the energy width of the distribution of localized band tail states decrease, while the values of Tauc coefficient increase with increasing the ion fluence. From the ellipsometric data we found that the real part of the dielectric function increased about 7% after irradiation with 1015 cm-2, and decreased about 10% in samples modified with 1016 cm-2.

Optical properties of LiGaS2: an ab initio study and spectroscopic ellipsometry measurement

NASA Astrophysics Data System (ADS)

Atuchin, V. V.; Lin, Z. S.; Isaenko, L. I.; Kesler, V. G.; Kruchinin, V. N.; Lobanov, S. I.

2009-11-01

Electronic and optical properties of lithium thiogallate crystal, LiGaS2, have been investigated by both experimental and theoretical methods. The plane-wave pseudopotential method based on DFT theory has been used for band structure calculations. The electronic parameters of Ga 3d orbitals have been corrected by the DFT+U methods to be consistent with those measured with x-ray photoemission spectroscopy. Evolution of optical constants of LiGaS2 over a wide spectral range was determined by developed first-principles theory and dispersion curves were compared with optical parameters defined by spectroscopic ellipsometry in the photon energy range 1.2-5.0 eV. Good agreement has been achieved between theoretical and experimental results.

Spectroscopic ellipsometry study of Cu2ZnSnS4 bulk poly-crystals

NASA Astrophysics Data System (ADS)

Levcenko, S.; Hajdeu-Chicarosh, E.; Garcia-Llamas, E.; Caballero, R.; Serna, R.; Bodnar, I. V.; Victorov, I. A.; Guc, M.; Merino, J. M.; Pérez-Rodriguez, A.; Arushanov, E.; León, M.

2018-04-01

The linear optical properties of Cu2ZnSnS4 bulk poly-crystals have been investigated using spectroscopic ellipsometry in the range of 1.2-4.6 eV at room temperature. The characteristic features identified in the optical spectra are explained by using the Adachi analytical model for the interband transitions at the corresponding critical points in the Brillouin zone. The experimental data have been modeled over the entire spectral range taking into account the lowest E0 transition near the fundamental absorption edge and E1A and E1B higher energy interband transitions. In addition, the spectral dependences of the refractive index, extinction coefficient, absorption coefficient, and normal-incidence reflectivity values have been accurately determined and are provided since they are essential data for the design of Cu2ZnSnS4 based optoelectronic devices.

Characterization of anisotropically shaped silver nanoparticle arrays via spectroscopic ellipsometry supported by numerical optical modeling

NASA Astrophysics Data System (ADS)

Gkogkou, Dimitra; Shaykhutdinov, Timur; Oates, Thomas W. H.; Gernert, Ulrich; Schreiber, Benjamin; Facsko, Stefan; Hildebrandt, Peter; Weidinger, Inez M.; Esser, Norbert; Hinrichs, Karsten

2017-11-01

The present investigation aims to study the optical response of anisotropic Ag nanoparticle arrays deposited on rippled silicon substrates by performing a qualitative comparison between experimental and theoretical results. Spectroscopic ellipsometry was used along with numerical calculations using finite-difference time-domain (FDTD) method and rigorous coupled wave analysis (RCWA) to reveal trends in the optical and geometrical properties of the nanoparticle array. Ellipsometric data show two resonances, in the orthogonal x and y directions, that originate from localized plasmon resonances as demonstrated by the calculated near-fields from FDTD calculations. The far-field calculations by RCWA point to decoupled resonances in x direction and possible coupling effects in y direction, corresponding to the short and long axis of the anisotropic nanoparticles, respectively.

Non-destructive characterization of corroded glass surfaces by spectroscopic ellipsometry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kaspar, Tiffany C.; Reiser, Joelle T.; Ryan, Joseph V.

Characterization of the alteration layers that form on glass surfaces during corrosion processes provides valuable information on both the mechanisms and rate of glass alteration. In recent years, state-of-the-art materials and surface characterization techniques have been employed to study various aspects of the alteration layers that result from corrosion. In most cases, these techniques are destructive and thus can only be employed at the end of the corrosion experiment. We show that the alteration layers can be investigated by non-destructive spectroscopic ellipsometry (SE), which provides pertinent information on alteration layer thickness, morphology, and, through correlation of the index of refraction,more » porosity. SE measurements of silicate glass coupons altered in aqueous solutions of pH 3, 5, 7, 9, and 11 at 90 °C for 7 days are compared to cross-sectional secondary electron microscopy images. In most cases, quantitative agreement of the alteration layer thickness is obtained. The fractional porosity calculated from the index of refraction is lower than the porosity calculated from elemental analysis of the aqueous solutions, indicating that the alteration layer has compacted during corrosion or the subsequent supercritical CO 2 drying process. Our results confirm the utility of performing non-destructive SE measurements on corroded glass surfaces.« less

Non-destructive characterization of corroded glass surfaces by spectroscopic ellipsometry

DOE PAGES

Kaspar, Tiffany C.; Reiser, Joelle T.; Ryan, Joseph V.; ...

2017-11-03

Characterization of the alteration layers that form on glass surfaces during corrosion processes provides valuable information on both the mechanisms and rate of glass alteration. In recent years, state-of-the-art materials and surface characterization techniques have been employed to study various aspects of the alteration layers that result from corrosion. In most cases, these techniques are destructive and thus can only be employed at the end of the corrosion experiment. We show that the alteration layers can be investigated by non-destructive spectroscopic ellipsometry (SE), which provides pertinent information on alteration layer thickness, morphology, and, through correlation of the index of refraction,more » porosity. SE measurements of silicate glass coupons altered in aqueous solutions of pH 3, 5, 7, 9, and 11 at 90 °C for 7 days are compared to cross-sectional secondary electron microscopy images. In most cases, quantitative agreement of the alteration layer thickness is obtained. The fractional porosity calculated from the index of refraction is lower than the porosity calculated from elemental analysis of the aqueous solutions, indicating that the alteration layer has compacted during corrosion or the subsequent supercritical CO 2 drying process. Our results confirm the utility of performing non-destructive SE measurements on corroded glass surfaces.« less

Role of an Oxidant Mixture as Surface Modifier of Porous Silicon Microstructures Evaluated by Spectroscopic Ellipsometry

PubMed Central

Montiel-González, Zeuz; Escobar, Salvador; Nava, Rocío; del Río, J. Antonio; Tagüeña-Martínez, Julia

2016-01-01

Current research on porous silicon includes the construction of complex structures with luminescent and/or photonic properties. However, their preparation with both characteristics is still challenging. Recently, our group reported a possible method to achieve that by adding an oxidant mixture to the electrolyte used to produce porous silicon. This mixture can chemically modify their microstructure by changing the thickness and surface passivation of the pore walls. In this work, we prepared a series of samples (with and without oxidant mixture) and we evaluated the structural differences through their scanning electron micrographs and their optical properties determined by spectroscopic ellipsometry. The results showed that ellipsometry is sensitive to slight variations in the porous silicon structure, caused by changes in their preparation. The fitting process, based on models constructed from the features observed in the micrographs, allowed us to see that the mayor effect of the oxidant mixture is on samples of high porosity, where the surface oxidation strongly contributes to the skeleton thinning during the electrochemical etching. This suggests the existence of a porosity threshold for the action of the oxidant mixture. These results could have a significant impact on the design of complex porous silicon structures for different optoelectronic applications. PMID:27097767

Role of an Oxidant Mixture as Surface Modifier of Porous Silicon Microstructures Evaluated by Spectroscopic Ellipsometry.

PubMed

Montiel-González, Zeuz; Escobar, Salvador; Nava, Rocío; del Río, J Antonio; Tagüeña-Martínez, Julia

2016-04-21

Current research on porous silicon includes the construction of complex structures with luminescent and/or photonic properties. However, their preparation with both characteristics is still challenging. Recently, our group reported a possible method to achieve that by adding an oxidant mixture to the electrolyte used to produce porous silicon. This mixture can chemically modify their microstructure by changing the thickness and surface passivation of the pore walls. In this work, we prepared a series of samples (with and without oxidant mixture) and we evaluated the structural differences through their scanning electron micrographs and their optical properties determined by spectroscopic ellipsometry. The results showed that ellipsometry is sensitive to slight variations in the porous silicon structure, caused by changes in their preparation. The fitting process, based on models constructed from the features observed in the micrographs, allowed us to see that the mayor effect of the oxidant mixture is on samples of high porosity, where the surface oxidation strongly contributes to the skeleton thinning during the electrochemical etching. This suggests the existence of a porosity threshold for the action of the oxidant mixture. These results could have a significant impact on the design of complex porous silicon structures for different optoelectronic applications.

Spectroscopic and microscopic investigation of MBE-grown CdTe (211)B epitaxial thin films on GaAs (211)B substrates

NASA Astrophysics Data System (ADS)

Özden, Selin; Koc, Mumin Mehmet

2018-03-01

CdTe epitaxial thin films, for use as a buffer layer for HgCdTe defectors, were grown on GaAs (211)B using the molecular beam epitaxy method. Wet chemical etching (Everson method) was applied to the epitaxial films using various concentrations and application times to quantify the crystal quality and dislocation density. Surface characterization of the epitaxial films was achieved using Atomic force microscopy and Scanning electron microscopy (SEM) before and after each treatment. The Energy Dispersive X-Ray apparatus of SEM was used to characterize the chemical composition. Untreated CdTe films show smooth surface characteristics with root mean square (RMS) roughnesses of 1.18-3.89 nm. The thicknesses of the CdTe layers formed were calculated via FTIR spectrometry and obtained by ex situ spectroscopic ellipsometry. Raman spectra were obtained for various temperatures. Etch pit densities (EPD) were measured, from which it could be seen that EPD changes between 1.7 × 108 and 9.2 × 108 cm-2 depending on the concentration of the Everson etch solution and treatment time. Structure, shape and depth of pits resulting from each etch pit implementation were also evaluated. Pit widths varying between 0.15 and 0.71 µm with heights varying between 2 and 80 nm were observed. RMS roughness was found to vary by anything from 1.56 to 26 nm.

Low temperature plasma enhanced CVD epitaxial growth of silicon on GaAs: a new paradigm for III-V/Si integration

NASA Astrophysics Data System (ADS)

Cariou, Romain; Chen, Wanghua; Maurice, Jean-Luc; Yu, Jingwen; Patriarche, Gilles; Mauguin, Olivia; Largeau, Ludovic; Decobert, Jean; Roca I Cabarrocas, Pere

2016-05-01

The integration of III-V semiconductors with silicon is a key issue for photonics, microelectronics and photovoltaics. With the standard approach, namely the epitaxial growth of III-V on silicon, thick and complex buffer layers are required to limit the crystalline defects caused by the interface polarity issues, the thermal expansion, and lattice mismatches. To overcome these problems, we have developed a reverse and innovative approach to combine III-V and silicon: the straightforward epitaxial growth of silicon on GaAs at low temperature by plasma enhanced CVD (PECVD). Indeed we show that both GaAs surface cleaning by SiF4 plasma and subsequent epitaxial growth from SiH4/H2 precursors can be achieved at 175 °C. The GaAs native oxide etching is monitored with in-situ spectroscopic ellipsometry and Raman spectroscopy is used to assess the epitaxial silicon quality. We found that SiH4 dilution in hydrogen during deposition controls the layer structure: the epitaxial growth happens for deposition conditions at the transition between the microcrystalline and amorphous growth regimes. SIMS and STEM-HAADF bring evidences for the interface chemical sharpness. Together, TEM and XRD analysis demonstrate that PECVD enables the growth of high quality relaxed single crystal silicon on GaAs.

Characterization of Free-Standing Nano-Membranes by Using Ellipsometry

NASA Astrophysics Data System (ADS)

Park, Sungmo; Lee, Changho; An, Ilsin; Kim, Min-Su; Park, Jin-Goo; Ahn, Jin-ho

2018-04-01

The thickness of the pellicle is only a few tens of microns in extreme ultraviolet lithography (EUVL). This is because the absorption loss by the pellicle is high. Thus, the thickness and contamination on the surface of the EUVL pellicle are important factors for controlling the transmission of EUV light. In this work, we fabricate ultra-thin silicon-nitride membranes for EUVL pellicles and use micro-spot spectroscopic ellipsometry and imaging ellipsometry for characterization. We successfully deduce not only the thickness but also the optical function of the membrane. However, we found that some precautions were required for accurate measurement of the free-standing thin membranes by using ellipsometry. Issues related to the vibration of the membrane and the sensitivity of the measurement are discussed.

Optical properties of a nanostructured glass-based film using spectroscopic ellipsometry

DOE PAGES

Jellison, G. E.; Aytug, T.; Lupini, A. R.; ...

2015-12-22

Nanostructured glass films, which are fabricated using spinodally phase-separated low-alkali glasses, have several interesting and useful characteristics, including being robust, non-wetting and antireflective. Spectroscopic ellipsometry measurements have been performed on one such film and its optical properties were analyzed using a 5-layer structural model of the near-surface region. Since the glass and the film are transparent over the spectral region of the measurement, the Sellmeier model is used to parameterize the dispersion in the refractive index. To simulate the variation of the optical properties of the film over the spot size of the ellipsometer (~ 3 × 5 mm), themore » Sellmeier amplitude is convoluted using a Gaussian distribution. The transition layers between the ambient and the film and between the film and the substrate are modeled as graded layers, where the refractive index varies as a function of depth. These layers are modeled using a two-component Bruggeman effective medium approximation where the two components are the layer above and the layer below. Lastly, the fraction is continuous through the transition layer and is modelled using the incomplete beta function.« less

Materials, structures, and devices for high-speed electronics

NASA Technical Reports Server (NTRS)

Woollam, John A.; Snyder, Paul G.

1992-01-01

Advances in materials, devices, and instrumentation made under this grant began with ex-situ null ellipsometric measurements of simple dielectric films on bulk substrates. Today highly automated and rapid spectroscopic ellipsometers are used for ex-situ characterization of very complex multilayer epitaxial structures. Even more impressive is the in-situ capability, not only for characterization but also for the actual control of the growth and etching of epitaxial layers. Spectroscopic ellipsometry has expanded from the research lab to become an integral part of the production of materials and structures for state of the art high speed devices. Along the way, it has contributed much to our understanding of the growth characteristics and material properties. The following areas of research are summarized: Si3N4 on GaAs, null ellipsometry; diamondlike carbon films; variable angle spectroscopic ellipsometry (VASE) development; GaAs-AlGaAs heterostructures; Ta-Cu diffusion barrier films on GaAs; GaAs-AlGaAs superlattices and multiple quantum wells; superconductivity; in situ elevated temperature measurements of III-V's; optical constants of thermodynamically stable InGaAs; doping dependence of optical constants of GaAs; in situ ellipsometric studies of III-V epitaxial growth; photothermal spectroscopy; microellipsometry; and Si passivation and Si/SiGe strained-layer superlattices.

Characterization of multilayer GaAs/AlGaAs transistor structures by variable angle spectroscopic ellipsometry

NASA Technical Reports Server (NTRS)

Merkel, Kenneth G.; Snyder, Paul G.; Woollam, John A.; Alterovitz, Samuel; Rai, A. K.

1989-01-01

Variable angle of incidence spectroscopic ellipsometry (VASE) has been implemented as a means of determining layer thickness, alloy composition, and growth quality of GaAs/AlGaAs samples composed of relatively thick layers as well as superlattices. The structures studied in this work contained GaAs/AlGaAs multilayers with a superlattice 'barrier' and were grown for later formation of modulation-doped field effect transistors (MODFETs). Sample modeling was performed by treating the superlattice as a bulk AlGaAs layer of unknown composition. Extremely good data fits were realized when five layer thicknesses and two alloy ratios were allowed to vary in a regression analysis. Room temperature excitonic effects associated with the e-hh(1), e-lh(1) and e-hh(2) transitions were observed in the VASE data.

Analyzing optical properties of thin vanadium oxide films through semiconductor-to-metal phase transition using spectroscopic ellipsometry

NASA Astrophysics Data System (ADS)

Sun, Jianing; Pribil, Greg K.

2017-11-01

We investigated the optical behaviors of vanadium dioxide (VO2) films through the semiconductor-to-metal (STM) phase transition using spectroscopic ellipsometry. Correlations between film thickness and refractive index were observed resulting from the absorbing nature of these films. Simultaneously analyzing data at multiple temperatures using Kramers-Kronig consistent oscillator models help identify film thickness. Nontrivial variations in resulting optical constants were observed through STM transition. As temperature increases, a clear increase is observed in near infrared absorption due to Drude losses that accompany the transition from semiconducting to metallic phases. Thin films grown on silicon and sapphire substrate present different optical properties and thermal hysteresis due to lattice stress and compositional differences.

Electronic structure of HxVO2 probed with in-situ spectroscopic ellipsometry

NASA Astrophysics Data System (ADS)

Kim, So Yeun; Sandilands, Luke J.; Kang, Taedong; Son, Jaeseok; Sohn, C. H.; Yoon, Hyojin; Son, Junwoo; Moon, S. J.; Noh, T. W.

Vanadium dioxide (VO2) undergoes a metal-to-insulator transition (MIT) near 340K. Despite extensive studies on this material, the role of electron-electron correlation and electron-lattice interactions in driving this MIT is still under debate. Recently, it was demonstrated that hydrogen can be reversibly absorbed into VO2 thin film without destroying the lattice framework. This H-doping allows systematic control of the electron density and lattice structure which in turn leads to a insulator (VO2) - metal (HxVO2) - insulator (HVO2) phase modulation. To better understand the phase modulation of HxVO2, we used in-situ spectroscopic ellipsometry to monitor the electronic structure during the hydrogenization process, i.e. we measured the optical conductivity of HxVO2 while varying x. Starting in the high temperature rutile metallic phase of VO2, we observed a large change in the electronic structure upon annealing in H gas at 370K: the low energy conductivity is continuously suppressed, consistent with reported DC resistivity data, while the conductivity peaks at high energy show strong changes in energy and spectral weight. The implications of our results for the MIT in HxVO2 will be discussed.

Optical constants of neat liquid-chemical warfare agents and related materials measured by infrared spectroscopic ellipsometry

NASA Astrophysics Data System (ADS)

Yang, C. S.-C.; Williams, B. R.; Hulet, M. S.; Tiwald, T. E.; Miles, R. W., Jr.; Samuels, A. C.

2011-05-01

We studied various liquids using a vertical attenuated total reflection (ATR) liquid sampling assembly in conjunction with Infrared Variable Angle Spectroscopic Ellipsometry (IR-VASE), to determine the infrared optical constants of several bulk liquids related to chemical warfare. The index of refraction, n, and the extinction coefficient, k, of isopropyl methylphosphonofluoridate (Sarin or GB), isopropyl alcohol (IPA) (a precursor of GB), and dimethyl methylphosphonate (DMMP)-a commonly employed simulant for GB, measured by our vertical ATR IR-VASE setup are closely matched to those found in other studies. We also report the optical constants of cyclohexyl methylphosphonofluoridate (GF), 2-(diisopropylamino)ethyl methylphosphonothioate (VX), bis-(2-chloroethyl) sulfide (HD), and 2-chlorovinyl dichloroarsine (L, Lewisite). The ATR IR-VASE technique affords an accurate measurement of the optical constants of these hazardous compounds.

Photomask CD and LER characterization using Mueller matrix spectroscopic ellipsometry

NASA Astrophysics Data System (ADS)

Heinrich, A.; Dirnstorfer, I.; Bischoff, J.; Meiner, K.; Ketelsen, H.; Richter, U.; Mikolajick, T.

2014-10-01

Critical dimension and line edge roughness on photomask arrays are determined with Mueller matrix spectroscopic ellipsometry. Arrays with large sinusoidal perturbations are measured for different azimuth angels and compared with simulations based on rigorous coupled wave analysis. Experiment and simulation show that line edge roughness leads to characteristic changes in the different Mueller matrix elements. The influence of line edge roughness is interpreted as an increase of isotropic character of the sample. The changes in the Mueller matrix elements are very similar when the arrays are statistically perturbed with rms roughness values in the nanometer range suggesting that the results on the sinusoidal test structures are also relevant for "real" mask errors. Critical dimension errors and line edge roughness have similar impact on the SE MM measurement. To distinguish between both deviations, a strategy based on the calculation of sensitivities and correlation coefficients for all Mueller matrix elements is shown. The Mueller matrix elements M13/M31 and M34/M43 are the most suitable elements due to their high sensitivities to critical dimension errors and line edge roughness and, at the same time, to a low correlation coefficient between both influences. From the simulated sensitivities, it is estimated that the measurement accuracy has to be in the order of 0.01 and 0.001 for the detection of 1 nm critical dimension error and 1 nm line edge roughness, respectively.

Determination of doping effects on Si and GaAs bulk samples properties by photothermal investigations

NASA Astrophysics Data System (ADS)

Abroug, Sameh; Saadallah, Faycel; Yacoubi, Noureddine

2007-11-01

The knowledge of doping effects on optical and thermal properties of semiconductors is crucial for the development of opto-electronic compounds. The purpose of this work is to investigate these effects by mirage effect technique and spectroscopic ellipsometry SE. The near gap optical spectra are obtained from photothermal signal for differently doped Si and GaAs bulk samples. However, the above bandgap absorption is determined from SE. These spectra show that absorption in the near IR increases with dopant density and also the bandgap shifts toward low energies. This behavior is due to free carrier absorption which could be obtained by subtracting phonon-assisted absorption from the measured spectrum. This carrier absorption is related to the dopant density through a semi-empirical model. We have also used the photothermal signal phase to measure the influence of doping on thermal diffusivity.

Spectroscopic ellipsometry of columnar porous Si thin films and Si nanowires

NASA Astrophysics Data System (ADS)

Fodor, Bálint; Defforge, Thomas; Agócs, Emil; Fried, Miklós; Gautier, Gaël; Petrik, Péter

2017-11-01

Columnar mesoporous Si thin films and dense nanowire (SiNW) carpets were investigated by spectroscopic ellipsometry in the visible-near-infrared wavelength range. Porous Si layers were formed by electrochemical etching while structural anisotropy was controlled by the applied current. Layers of highly oriented SiNWs, with length up to 4.1 μm were synthesized by metal-assisted chemical etching. Ellipsometric spectra were fitted with different multi-layered, effective medium approximation-based (EMA) models. Isotropic, in-depth graded, anisotropic and hybrid EMA models were investigated with the help of the root mean square errors obtained from the fits. Ellipsometric-fitted layer thicknesses were also cross-checked by scanning electron microscopy showing an excellent agreement. Furthermore, in the case of mesoporous silicon, characterization also revealed that, at low current densities (<100 mA/cm2), in-depth inhomogeneity shows a more important feature in the ellipsometric spectra than anisotropy. On the other hand, at high current densities (>100 mA/cm2) this behavior turns around, and anisotropy becomes the dominant feature describing the spectra. Characterization of SiNW layers showed a very high geometrical anisotropy. However, the highest fitted geometrical anisotropy was obtained for the layer composed of ∼1 μm long SiNWs indicating that for thicker layers, collapse of the nanowires occurs.

Enhanced sensitivity to dielectric function and thickness of absorbing thin films by combining total internal reflection ellipsometry with standard ellipsometry and reflectometry

NASA Astrophysics Data System (ADS)

Lizana, A.; Foldyna, M.; Stchakovsky, M.; Georges, B.; Nicolas, D.; Garcia-Caurel, E.

2013-03-01

High sensitivity of spectroscopic ellipsometry and reflectometry for the characterization of thin films can strongly decrease when layers, typically metals, absorb a significant fraction of the light. In this paper, we propose a solution to overcome this drawback using total internal reflection ellipsometry (TIRE) and exciting a surface longitudinal wave: a plasmon-polariton. As in the attenuated total reflectance technique, TIRE exploits a minimum in the intensity of reflected transversal magnetic (TM) polarized light and enhances the sensitivity of standard methods to thicknesses of absorbing films. Samples under study were stacks of three films, ZnO : Al/Ag/ZnO : Al, deposited on glass substrates. The thickness of the silver layer varied from sample to sample. We performed measurements with a UV-visible phase-modulated ellipsometer, an IR Mueller ellipsometer and a UV-NIR reflectometer. We used the variance-covariance formalism to evaluate the sensitivity of the ellipsometric data to different parameters of the optical model. Results have shown that using TIRE doubled the sensitivity to the silver layer thickness when compared with the standard ellipsometry. Moreover, the thickness of the ZnO : Al layer below the silver layer can be reliably quantified, unlike for the fit of the standard ellipsometry data, which is limited by the absorption of the silver layer.

Dielectric functions, chemical and atomic compositions of the near surface layers of implanted GaAs by In+ ions

NASA Astrophysics Data System (ADS)

Kulik, M.; Kołodyńska, D.; Bayramov, A.; Drozdziel, A.; Olejniczak, A.; Żuk, J.

2018-06-01

The surfaces of (100) GaAs were irradiated with In+ ions. The implanted samples were isobaric annealed at 800 °C and then of dielectric function, the surface atomic concentrations of atoms and also the chemical composition of the near surface layers in these implanted semiconductor samples were obtained. The following investigation methods were used: spectroscopic ellipsometry (SE), Rutherford backscattering spectrometry analyses (RBSA) and X-ray photoelectron spectroscopy (XPS) in the study of the above mentioned quantities, respectively. The change of the shape spectra of the dielectric functions at about 3.0 eV phonon energy, diffusion of In+ ions as well as chemical composition changes were observed after ion implantation and the thermal treatment. Due to displacement of Ga ions from GaAs by the In+ ions the new chemical compound InAs was formed. The relative amounts Ga2O3 and As2O3 ratio increase in the native oxide layers with the fluences increase after the thermal treatment of the samples. Additionally, it was noticed that the quantities of InO2 increase with the increasing values of the irradiated ions before thermal treatment.

Spectroscopic imaging ellipsometry for automated search of flakes of mono- and n-layers of 2D-materials

NASA Astrophysics Data System (ADS)

Funke, S.; Wurstbauer, U.; Miller, B.; Matković, A.; Green, A.; Diebold, A.; Röling, C.; Thiesen, P. H.

2017-11-01

Spectroscopic imaging ellipsometry (SIE) is used to localize and characterize flakes of conducting, semi-conducting and insulating 2D-materials. Although the research in the field of monolayers of 2D-materials increased the last years, it is still challenging to look for small flakes and distinguish between different layer numbers. Special substrates are used to enhance optical contrast for the conventional light microscopy (LM). In case when other functional support from the substrate is essential, an additional transfer step needs to be employed, bringing the drawbacks as contamination, cracking and wrinkling of the 2D materials. Furthermore it is time-consuming and not yet fully automatically to search for monolayers by contrast with the LM. Here we present a method, that is able to automatically localize regions with desired thicknesses, e.g. monolayers, of the different materials on arbitrary substrates.

Atomic Force Microscopy and Spectroscopic Ellipsometry combined analysis of Small Ubiquitin-like Modifier adsorption on functional monolayers

NASA Astrophysics Data System (ADS)

Solano, Ilaria; Parisse, Pietro; Gramazio, Federico; Ianeselli, Luca; Medagli, Barbara; Cavalleri, Ornella; Casalis, Loredana; Canepa, Maurizio

2017-11-01

The comprehension of mechanisms of interaction between functional layers and proteins is relevant for the development of sensitive and precise biosensors. Here we report our study which combines Atomic Force Microscopy and Spectroscopic Ellipsometry to investigate the His-Ni-NTA mediated interaction between 6His-tagged Small Ubiquitin-like Modifier (SUMO) protein with self assembled monolayers of NTA terminated alkanethiols. The use of AFM-based nanolithograhic tools and the analysis of ellipsometric spectra in situ and ex situ provided us a solid method to disentangle the effects of Ni(II)-mediated interaction between the NTA layer and the 6His-tagged SUMO and to accurately determine in physiological condition the thickness value of the SUMO layer. This investigation is a first step towards the study of layered systems of greater complexity of which the NTA/6His-tagged SUMO is a prototypical example.

Atomic oxygen effects on thin film space coatings studied by spectroscopic ellipsometry, atomic force microscopy, and laser light scattering

NASA Technical Reports Server (NTRS)

Synowicki, R. A.; Hale, Jeffrey S.; Woollam, John A.

1992-01-01

The University of Nebraska is currently evaluating Low Earth Orbit (LEO) simulation techniques as well as a variety of thin film protective coatings to withstand atomic oxygen (AO) degradation. Both oxygen plasma ashers and an electron cyclotron resonance (ECR) source are being used for LEO simulation. Thin film coatings are characterized by optical techniques including Variable Angle Spectroscopic Ellipsometry, Optical spectrophotometry, and laser light scatterometry. Atomic Force Microscopy (AFM) is also used to characterize surface morphology. Results on diamondlike carbon (DLC) films show that DLC degrades with simulated AO exposure at a rate comparable to Kapton polyimide. Since DLC is not as susceptible to environmental factors such as moisture absorption, it could potentially provide more accurate measurements of AO fluence on short space flights.

Spectroscopic Ellipsometry Studies of Ag and ZnO Thin Films and Their Interfaces for Thin Film Photovoltaics

NASA Astrophysics Data System (ADS)

Sainju, Deepak

Many modern optical and electronic devices, including photovoltaic devices, consist of multilayered thin film structures. Spectroscopic ellipsometry (SE) is a critically important characterization technique for such multilayers. SE can be applied to measure key parameters related to the structural, optical, and electrical properties of the components of multilayers with high accuracy and precision. One of the key advantages of this non-destructive technique is its capability of monitoring the growth dynamics of thin films in-situ and in real time with monolayer level precision. In this dissertation, the techniques of SE have been applied to study the component layer materials and structures used as back-reflectors and as the transparent contact layers in thin film photovoltaic technologies, including hydrogenated silicon (Si:H), copper indium-gallium diselenide (CIGS), and cadmium telluride (CdTe). The component layer materials, including silver and both intrinsic and doped zinc oxide, are fabricated on crystalline silicon and glass substrates using magnetron sputtering techniques. These thin films are measured in-situ and in real time as well as ex-situ by spectroscopic ellipsometry in order to extract parameters related to the structural properties, such as bulk layer thickness and surface roughness layer thickness and their time evolution, the latter information specific to real time measurements. The index of refraction and extinction coefficient or complex dielectric function of a single unknown layer can also be obtained from the measurement versus photon energy. Applying analytical expressions for these optical properties versus photon energy, parameters that describe electronic transport, such as electrical resistivity and electron scattering time, can be extracted. The SE technique is also performed as the sample is heated in order to derive the effects of annealing on the optical properties and derived electrical transport parameters, as well as the

Optical properties of thickness-controlled MoS2 thin films studied by spectroscopic ellipsometry

NASA Astrophysics Data System (ADS)

Li, Dahai; Song, Xiongfei; Xu, Jiping; Wang, Ziyi; Zhang, Rongjun; Zhou, Peng; Zhang, Hao; Huang, Renzhong; Wang, Songyou; Zheng, Yuxiang; Zhang, David Wei; Chen, Liangyao

2017-11-01

As a promising candidate for applications in future electronic and optoelectronic devices, MoS2 has been a research focus in recent years. Therefore, investigating its optical properties is of practical significance. Here we synthesized different MoS2 thin films with quantitatively controlled thickness and sizable thickness variation, which is vital to find out the thickness-dependent regularity. Afterwards, several characterization methods, including X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), Raman spectroscopy, photoluminescence (PL), optical absorption spectra, and spectroscopic ellipsometry (SE), were systematically performed to character the optical properties of as-grown samples. Accurate dielectric constants of MoS2 are obtained by fitting SE data using point-by-point method, and precise energies of interband transitions are directly extracted from the Lorentz dispersion model. We assign these energies to different interband electronic transitions between the valence bands and conduction bands in the Brillouin zone. In addition, the intrinsic physical mechanisms existing in observed phenomena are discussed in details. Results derived from this work are reliable and provide a better understanding of MoS2, which can be expected to help people fully employ its potential for wider applications.

Characterization of SiGe/Ge heterostructures and graded layers using variable angle spectroscopic ellipsometry

NASA Technical Reports Server (NTRS)

Croke, E. T.; Wang, K. L.; Heyd, A. R.; Alterovitz, S. A.; Lee, C. H.

1996-01-01

Variable angle spectroscopic ellipsometry (VASE) has been used to characterize Si(x)Ge(1-x)/Ge superlattices (SLs) grown on Ge substrates and thick Si(x)Ge(1-x)/Ge heterostructures grown on Si substrates. Our VASE analysis yielded the thicknesses and alloy compositions of all layers within the optical penetration depth of the surface. In addition, strain effects were observed in the VASE results for layers under both compressive and tensile strain. Results for the SL structures were found to be in close agreement with high resolution x-ray diffraction measurements made on the same samples. The VASE analysis has been upgraded to characterize linearly graded Si(x)Ge(1-x) buffer layers. The algorithm has been used to determine the total thickness of the buffer layer along with the start and end alloy composition by breaking the total thickness into many (typically more than 20) equal layers. Our ellipsometric results for 1 (mu)m buffer layers graded in the ranges 0.7 less than or = x less than or = 1.0, and 0.5 less than or = x less than or = 1.0 are presented, and compare favorably with the nominal values.

Evaluation of the dielectric function of colloidal Cd1 - xHgxTe quantum dot films by spectroscopic ellipsometry

NASA Astrophysics Data System (ADS)

Bejaoui, A.; Alonso, M. I.; Garriga, M.; Campoy-Quiles, M.; Goñi, A. R.; Hetsch, F.; Kershaw, S. V.; Rogach, A. L.; To, C. H.; Foo, Y.; Zapien, J. A.

2017-11-01

We report on the investigation by spectroscopic ellipsometry of films containing Cd1 - xHgxTe alloy quantum dots (QDs). The alloy QDs were fabricated from colloidal CdTe QDs grown by an aqueous synthesis process followed by an ion-exchange step in which Hg2+ ions progressively replace Cd2+. For ellipsometric studies, several films were prepared on glass substrates using layer-by-layer (LBL) deposition. The contribution of the QDs to the measured ellipsometric spectra is extracted from a multi-sample, transmission and multi- angle-of-incidence ellipsometric data analysis fitted using standard multilayer and effective medium models that include surface roughness effects, modeled by an effective medium approximation. The relationship of the dielectric function of the QDs retrieved from these studies to that of the corresponding II-VI bulk material counterparts is presented and discussed.

Spectroscopic ellipsometry studies on ZnCdO thin films with different Cd concentrations grown by pulsed laser deposition

NASA Astrophysics Data System (ADS)

Chen, Shuai; Li, Qingxuan; Ferguson, Ian; Lin, Tao; Wan, Lingyu; Feng, Zhe Chuan; Zhu, Liping; Ye, Zhizhen

2017-11-01

A set of Zn1-xCdxO thin films with different Cd concentrations was deposited on quartz substrates by Pulsed Laser Deposition (PLD). The properties of these films were investigated by variable angle and temperature dependent spectroscopic ellipsometry (SE). The experimental Zn1-xCdxO thin films showed a red shift in the absorption edge with increasing Cd contents at room temperature. For ZnCdO films with the similar Cd concentration, it has been found that the film thickness has important effects on the optical constants (n, k). The variations of optical constants (n, k) and the band gap, E0, with temperature (T) in 25 °C-600 °C for a typical Zn0.95Cd0.05O sample were obtained. The E0 vs T relationship is described by a T- quadratic equation.

Water Vapor Uptake of Ultrathin Films of Biologically Derived Nanocrystals: Quantitative Assessment with Quartz Crystal Microbalance and Spectroscopic Ellipsometry.

PubMed

Niinivaara, Elina; Faustini, Marco; Tammelin, Tekla; Kontturi, Eero

2015-11-10

Despite the relevance of water interactions, explicit analysis of vapor adsorption on biologically derived surfaces is often difficult. Here, a system was introduced to study the vapor uptake on a native polysaccharide surface; namely, cellulose nanocrystal (CNC) ultrathin films were examined with a quartz crystal microbalance with dissipation monitoring (QCM-D) and spectroscopic ellipsometry (SE). A significant mass uptake of water vapor by the CNC films was detected using the QCM-D upon increasing relative humidity. In addition, thickness changes proportional to changes in relative humidity were detected using SE. Quantitative analysis of the results attained indicated that in preference to being soaked by water at the point of hydration each individual CNC in the film became enveloped by a 1 nm thick layer of adsorbed water vapor, resulting in the detected thickness response.

Spectroscopic ellipsometry investigation of the optical properties of graphene oxide dip-coated on magnetron sputtered gold thin films

NASA Astrophysics Data System (ADS)

Politano, Grazia Giuseppina; Vena, Carlo; Desiderio, Giovanni; Versace, Carlo

2018-02-01

Despite intensive investigations on graphene oxide-gold nanocomposites, the interaction of graphene oxide sheets with magnetron sputtered gold thin films has not been studied yet. The optical constants of graphene oxide thin films dip-coated on magnetron sputtered gold thin films were determined by spectroscopic ellipsometry in the [300-1000] wavelength range. Moreover, the morphologic properties of the samples were investigated by SEM analysis. Graphene oxide absorbs mainly in the ultraviolet region, but when it is dip-coated on magnetron sputtered gold thin films, its optical constants show dramatic changes, becoming absorbing in the visible region, with a peak of the extinction coefficient at 3.1 eV. Using magnetron sputtered gold thin films as a substrate for graphene oxide thin films could therefore be the key to enhance graphene oxide optical sheets' properties for several technological applications, preserving their oxygen content and avoiding the reduction process.

Thermal treatment effects imposed on solid DNA cationic lipid complex with hexadecyltrimethylammonium chloride, observed by variable angle spectroscopic ellipsometry

NASA Astrophysics Data System (ADS)

Nizioł, Jacek

2014-12-01

DNA cationic lipid complexes are materials of properties required for applications in organic electronics and optoelectronics. Often, their thermal stability demonstrated by thermogravimetry is cited in the literature as important issue. However, little is known about processes occurring in heated solid DNA cationic lipid complexes. In frame of this work, thin films of Deoxyribonucleic acid-hexadecyltrimethylammonium chloride (DNA-CTMA) were deposited on silicon wafers. Samples were thermally annealed, and simultaneously, their optical functions were measured by spectroscopic ellipsometry. At lower temperatures, thermal expansion coefficient of solid DNA-CTMA was negative, but at higher temperatures positive. Thermally induced modification of absorption spectrum in UV-vis was observed. It occurred at a range of temperatures higher than this of DNA denaturation in solution. The observed phenomenon was irreversible, at least in time scale of the experiment (one day).

Interplay of hydrogen and deposition temperature in optical properties of hot-wire deposited a-Si:H Films: Ex situ spectroscopic ellipsometry studies

NASA Astrophysics Data System (ADS)

Gupta, S.; Weiner, B. R.; Morell, G.

2005-11-01

High-quality hydrogenated amorphous silicon (a-Si:H) thin films were grown by hot-wire chemical vapor deposition on glass (Corning 7059) using silane with relatively high hydrogen albeit avoiding the formation of microcrystalline hydrogenated silicon. They were grown as a function of substrate temperature (TS) ranging from 50 to 515 °C resulting in the corresponding hydrogen concentration [CH] variation from 20.0 to 0.2 at. %. They are optically examined ex situ using spectroscopic phase modulated ellipsometry from near IR to near UV (i.e., 1.5-5.0 eV) obtaining pseudo-dielectric function (<ɛr(E)>,<ɛi(E)>) for investigating the role of hydrogen in network disorder. The raw ellipsometry data were modeled using Bruggeman effective medium theory and the dispersion relations for the amorphous semiconductors. A two-layer model consisting of a top surface roughness layer (dS) containing an effective medium mix of 50% a-Si:H and 50% voids and a single ``bulk'' layer (dB) of 100% a-Si:H was used to simulate the data reasonably well. We performed these simulations by nonlinear least-square regression analysis and it was possible to estimate the true dielectric function, energy band gap (Eg), film thickness (dSE), bulk void fraction, surface roughness layer (dS), and confidence limits (χ2). Moreover, it is shown that the Tauc-Lorentz model fits the ellipsometry data reasonably well and helps elucidating the layered structure of a-Si:H thin films. We also compared the optical band gap determined using ellipsometry modeling and the Tauc gap. We discuss the variation of the deduced parameters in terms of role of TS (T role) or of hydrogen (H role) yielding possible physical meaning and found an agreement with the excitation dependent Raman spectroscopy results reported earlier [S. Gupta, R. S. Katiyar, G. Morell, S. Z. Weisz, and J. Balberg, Appl. Phys. Lett. 75, 2803 (1999)]. Atomic force microscopy was also used to validate the simulations. These analyses led to a

Effect of Ta concentration on the refractive index of TiO{sub 2}:Ta studied by spectroscopic ellipsometry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nurfani, Eka, E-mail: ekanurfani@gmail.com; Kurniawan, Robi; Muhammady, Shibghatullah

2016-04-19

We have investigated optical properties of Ta-doped TiO{sub 2} thin film on LaAlO{sub 3} (LAO) substrate using Spectroscopic Ellipsometry (SE) at room temperature. Amplitude ratio Ψ and phase difference L1 between p- and s- polarized light waves are obtained by multiple incident angles measurement (60°, 70°, and 80°) at energy range of 0.5 – 6.5 eV. In order to obtain optical properties for every Ta concentrations (0.01, 0.4, and 5 at. %), multilayer modelling was performed simultaneously by using Drude-Lorentz model. Refractive index and optical dispersion parameters were determined by Wemple-DiDomenico relation. In general, refractive index at zero photon energymore » n(0) increases by increasing Ta concentration. Furthermore, optical band gap shows a significant increasing due to presence of Ta dopant. In addition, other optical constants are discussed as well.« less

Measurement of InAsSb bandgap energy and InAs/InAsSb band edge positions using spectroscopic ellipsometry and photoluminescence spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Webster, P. T.; Riordan, N. A.; Liu, S.

2015-12-28

The structural and optical properties of lattice-matched InAs{sub 0.911}Sb{sub 0.089} bulk layers and strain-balanced InAs/InAs{sub 1−x}Sb{sub x} (x ∼ 0.1–0.4) superlattices grown on (100)-oriented GaSb substrates by molecular beam epitaxy are examined using X-ray diffraction, spectroscopic ellipsometry, and temperature dependent photoluminescence spectroscopy. The photoluminescence and ellipsometry measurements determine the ground state bandgap energy and the X-ray diffraction measurements determine the layer thickness and mole fraction of the structures studied. Detailed modeling of the X-ray diffraction data is employed to quantify unintentional incorporation of approximately 1% Sb into the InAs layers of the superlattices. A Kronig-Penney model of the superlattice miniband structure ismore » used to analyze the valence band offset between InAs and InAsSb, and hence the InAsSb band edge positions at each mole fraction. The resulting composition dependence of the bandgap energy and band edge positions of InAsSb are described using the bandgap bowing model; the respective low and room temperature bowing parameters for bulk InAsSb are 938 and 750 meV for the bandgap, 558 and 383 meV for the conduction band, and −380 and −367 meV for the valence band.« less

Combined ellipsometry and refractometry technique for characterisation of liquid crystal based nanocomposites.

PubMed

Warenghem, Marc; Henninot, Jean François; Blach, Jean François; Buchnev, Oleksandr; Kaczmarek, Malgosia; Stchakovsky, Michel

2012-03-01

Spectroscopic ellipsometry is a technique especially well suited to measure the effective optical properties of a composite material. However, as the sample is optically thick and anisotropic, this technique loses its accuracy for two reasons: anisotropy means that two parameters have to be determined (ordinary and extraordinary indices) and optically thick means a large order of interference. In that case, several dielectric functions can emerge out of the fitting procedure with a similar mean square error and no criterion to discriminate the right solution. In this paper, we develop a methodology to overcome that drawback. It combines ellipsometry with refractometry. The same sample is used in a total internal reflection (TIR) setup and in a spectroscopic ellipsometer. The number of parameters to be determined by the fitting procedure is reduced in analysing two spectra, the correct final solution is found by using the TIR results both as initial values for the parameters and as check for the final dielectric function. A prefitting routine is developed to enter the right initial values in the fitting procedure and so to approach the right solution. As an example, this methodology is used to analyse the optical properties of BaTiO(3) nanoparticles embedded in a nematic liquid crystal. Such a methodology can also be used to analyse experimentally the validity of the mixing laws, since ellipsometry gives the effective dielectric function and thus, can be compared to the dielectric function of the components of the mixture, as it is shown on the example of BaTiO(3)/nematic composite.

Multichannel Spectroscopic Ellipsometry for CdTe Photovoltaics: from Materials and Interfaces to Solar Cells

NASA Astrophysics Data System (ADS)

Koirala, Prakash

Spectroscopic ellipsometry (SE) in the mid-infrared to ultraviolet range has been implemented in order to develop and evaluate optimization procedures for CdTe solar cells at the different stages of fabrication. In this dissertation research, real time SE (RT-SE) has been applied during the fabrication of the as-deposited CdS/CdTe solar cell. Two areas of background research were addressed before undertaking the challenging RT-SE analysis procedures. First, optical functions were parameterized versus temperature for the glass substrate and its overlayers, including three different SnO2 layers. This database has applications not only for RT-SE analysis but also for on-line monitoring of the coated glass itself at elevated temperature. Second, post-deposition modifications of substrate have been studied by infrared spectroscopic ellipsometry (IR-SE) prior to the RT-SE analysis in order to evaluate the need for such modification in the analysis. With support from these background studies, RT-SE has been implemented in analyses of the evolution of the thin film structural properties during sputter deposition of polycrystalline CdS/CdTe solar cells on the transparent conducting oxide (TCO) coated glass substrates. The real time optical spectra collected during CdS/CdTe deposition were analyzed using the optical property database for all substrate components as a function of measurement temperature. RT-SE enables characterization of the filling process of the surface roughness modulations on the top-most SnO2 substrate layer, commonly referred to as the high resistivity transparent (HRT) layer. In this filling process, the optical properties of this surface layer are modified in accordance with an effective medium theory. In addition to providing information on interface formation to the substrate during film growth, RT-SE also provides information on the bulk layer CdS growth, its surface roughness evolution, as well as overlying CdTe interface formation and bulk layer

Jet Fuel Thermal Stability Investigations Using Ellipsometry

NASA Technical Reports Server (NTRS)

Nash, Leigh; Vasu, Subith S.; Klettlinger, Jennifer Lindsey

2017-01-01

Jet fuels are typically used for endothermic cooling in practical engines where their thermal stability is very important. In this work the thermal stability of Sasol IPK (a synthetic jet fuel) with varying levels of naphthalene has been studied on stainless steel substrates using spectroscopic ellipsometry in the temperature range 385-400 K. Ellipsometry is an optical technique that measures the changes in a light beam’s polarization and intensity after it reflects off of a thin film to determine the film’s thickness and optical properties. All of the tubes used were rated as thermally unstable by the color standard portion of the Jet Fuel Thermal Oxidation Test, and this was confirmed by the deposit thicknesses observed using ellipsometry. A new amorphous model on a stainless steel substrate was used to model the data and obtain the results. It was observed that, as would be expected, increasing the temperature of the tube increased the overall deposit amount for a constant concentration of naphthalene. The repeatability of these measurements was assessed using multiple trials of the same fuel at 385 K. Lastly, the effect of increasing the naphthalene concentration in the fuel at a constant temperature was found to increase the deposit thickness.In conclusion, ellipsometry was used to investigate the thermal stability of jet fuels on stainless steel substrate. The effects of increasing temperature and addition of naphthalene on stainless steel tubes with Sasol IPK fuel were investigated. It was found, as expected, that increasing temperature lead to an increase in deposit thickness. It wasAmerican Institute of Aeronautics and Astronautics6also found that increasing amounts of naphthalene increased the maximum deposit thickness. The repeatability of these measurements was investigated using multiple tests at the same conditions. The present work provides as a better quantitative tool compared to the widely used JFTOT technique. Future work will expand on the

Spectroscopic Ellipsometry Measurements of Wurtzite Gallium Nitride Surfaces as a Function of Buffered Oxide Etch Substrate Submersion

NASA Astrophysics Data System (ADS)

Szwejkowski, Chester; Constantin, Costel; Duda, John; Hopkins, Patrick; Optical Studies of GaN interfaces Collaboration

2013-03-01

Gallium nitride (GaN) is considered the most important semiconductor after the discovery of silicon. Understanding the optical properties of GaN surfaces is imperative in determining the utility and applicability of this class of materials to devices. In this work, we present preliminary results of spectroscopic ellipsometry measurements as a function of surface root mean square (RMS). We used commercially available 5mm x 5mm, one side polished GaN (3-7 μm)/Sapphire (430 μm) substrates that have a wurtzite crystal structure and they are slightly n-type doped. The GaN substrates were cleaned with Acetone (20 min)/Isopropanol(20 min)/DI water (20 min) before they were submerged into Buffered Oxide Etch (BOE) for 10s - 60s steps. This BOE treatment produced RMS values of 1-30 nm as measured with an atomic force microscope. Preliminary qualitative ellipsometric measurements show that the complex refractive index and the complex dielectric function decrease with an increase of RMS. More measurements need to be done in order to provide explicit quantitative results. This work was supported by the 4-VA Collaborative effort between James Madison University and University of Virginia.

Superlattice Intermediate Band Solar Cell on Gallium Arsenide

DTIC Science & Technology

2015-02-09

18  APPENDIX: Methodology for Calculaton of Minband Energies and Absorption Coefficient of a Superlattice...4 Figure 3. Absorption coefficient extracted from spectroscopic ellipsometry measurements of a... coefficient of a 30 period GaAs0.98N0.02 (3nm)/ Al0.20Ga0.80As (3nm) Superlattice following the methodology developed in

Characterization of High Ge Content SiGe Heterostructures and Graded Alloy Layers Using Spectroscopic Ellipsometry

NASA Technical Reports Server (NTRS)

Heyd, A. R.; Alterovitz, S. A.; Croke, E. T.

1995-01-01

Si(x)Ge(1-x)heterostructures on Si substrates have been widely studied due to the maturity of Si technology. However, work on Si(x)Ge)1-x) heterostructures on Ge substrates has not received much attention. A Si(x)Ge(1-x) layer on a Si substrate is under compressive strain while Si(x)Ge(1-x) on Ge is under tensile strain; thus the critical points will behave differently. In order to accurately characterize high Ge content Si(x)Ge(1-x) layers the energy shift algorithm used to calculate alloy compositions, has been modified. These results have been used along with variable angle spectroscopic ellipsometry (VASE) measurements to characterize Si(x)Ge(1-x)/Ge superlattices grown on Ge substrates. The results agree closely with high resolution x-ray diffraction measurements made on the same samples. The modified energy shift algorithm also allows the VASE analysis to be upgraded in order to characterize linearly graded layers. In this work VASE has been used to characterize graded Si(x)Ge(1-x) layers in terms of the total thickness, and the start and end alloy composition. Results are presented for a 1 micrometer Si(x)Ge(1-x) layer linearly graded in the range 0.5 less than or equal to x less than or equal to 1.0.

Optical properties of ultrathin CIGS films studied by spectroscopic ellipsometry assisted by chemical engineering

NASA Astrophysics Data System (ADS)

Loubat, Anaïs; Eypert, Céline; Mollica, Fabien; Bouttemy, Muriel; Naghavi, Negar; Lincot, Daniel; Etcheberry, Arnaud

2017-11-01

CIGS (Cu(In1-x,Gax)Se2) based devices are very efficient for photovoltaic conversion. A non-destructive optical study of CIGS is an important challenge as for evaluation of the material quality, and for device modeling. Spectroscopic Ellipsometry (SE) is well adapted for a quantitative characterization only if the handicaps of the roughness limitation, the oxidized surface, or the compositional gradient are minimized. For this SE study, ungraded and thin CIGS samples are prepared with GGI (x) ratio (=[Ga]/([Ga] + [In])) ranging from 0.15 to 0.60. Thanks to chemical engineering based on acidic bromine solution etching and/or HCl de-oxidation, the SE experiments are performed on flattened surfaces, and also, on as grown de-oxidized samples. Using assumptions based on XPS, AFM and SEM complementary characterizations, we give proof of oxide free flattening surfaces and chemical homogeneity in depth. Using these observations, the SE data are modeled on the basis of a three layer model using an Adachi/Tauc-Lorentz formula for the CIGS dispersion. The optical gap values are determined in good agreement with the x ratio measured by the other characterization techniques. SE is able to well estimate the thickness and roughness variations on each sample. Furthermore, the CIGS optical constant extracted on such reference flat surfaces are then applied to the as grown-de-oxidized surfaces, enabling to describe the SE data obtained on rougher surfaces. A complete consistency of the proposed model is shown as well as the capability of SE to be sensitive to the chemistry of the surface.

Spectroscopic Ellipsometry Studies of Thin Film a-Si:H Solar Cell Fabrication by Multichamber Deposition in the n-i-p Substrate Configuration

NASA Astrophysics Data System (ADS)

Dahal, Lila Raj

Real time spectroscopic ellipsometry (RTSE), and ex-situ mapping spectroscopic ellipsometry (SE) are powerful characterization techniques capable of performance optimization and scale-up evaluation of thin film solar cells used in various photovoltaics technologies. These non-invasive optical probes employ multichannel spectral detection for high speed and provide high precision parameters that describe (i) thin film structure, such as layer thicknesses, and (ii) thin film optical properties, such as oscillator variables in analytical expressions for the complex dielectric function. These parameters are critical for evaluating the electronic performance of materials in thin film solar cells and also can be used as inputs for simulating their multilayer optical performance. In this Thesis, the component layers of thin film hydrogenated silicon (Si:H) solar cells in the n-i-p or substrate configuration on rigid and flexible substrate materials have been studied by RTSE and ex-situ mapping SE. Depositions were performed by magnetron sputtering for the metal and transparent conducting oxide contacts and by plasma enhanced chemical vapor deposition (PECVD) for the semiconductor doped contacts and intrinsic absorber layers. The motivations are first to optimize the thin film Si:H solar cell in n-i-p substrate configuration for single-junction small-area dot cells and ultimately to scale-up the optimized process to larger areas with minimum loss in device performance. Deposition phase diagrams for both i- and p -layers on 2" x 2" rigid borosilicate glass substrate were developed as functions of the hydrogen-to-silane flow ratio in PECVD. These phase diagrams were correlated with the performance parameters of the corresponding solar cells, fabricated in the Cr/Ag/ZnO/n/i/ p/ITO structure. In both cases, optimization was achieved when the layers were deposited in the protocrystalline phase. Identical solar cell structures were fabricated on 6" x 6" borosilicate glass with

Characterization of Si (sub X)Ge (sub 1-x)/Si Heterostructures for Device Applications Using Spectroscopic Ellipsometry

NASA Technical Reports Server (NTRS)

Sieg, R. M.; Alterovitz, S. A.; Croke, E. T.; Harrell, M. J.; Tanner, M.; Wang, K. L.; Mena, R. A.; Young, P. G.

1993-01-01

Spectroscopic ellipsometry (SE) characterization of several complex Si (sub X)Ge (sub 1-x)/Si heterostructures prepared for device fabrication, including structures for heterojunction bipolar transistors (HBT), p-type and n-type heterostructure modulation doped field effect transistors, has been performed. We have shown that SE can simultaneously determine all active layer thicknesses, Si (sub X)Ge (sub 1-x) compositions, and the oxide overlayer thickness, with only a general knowledge of the structure topology needed a priori. The characterization of HBT material included the SE analysis of a Si (sub X)Ge (sub 1-x) layer deeply buried (600 nanometers) under the silicon emitter and cap layers. In the SE analysis of n-type heterostructures, we examined for the first time a silicon layer under tensile strain. We found that an excellent fit can be obtained using optical constants of unstrained silicon to represent the strained silicon conduction layer. We also used SE to measure lateral sample homogeneity, providing quantitative identification of the inhomogeneous layer. Surface overlayers resulting from prior sample processing were also detected and measured quantitatively. These results should allow SE to be used extensively as a non-destructive means of characterizing Si (sub X)Ge (sub 1-x)/Si heterostructures prior to device fabrication and testing.

Characterization of thermochromic VO2 (prepared at 250 °C) in a wide temperature range by spectroscopic ellipsometry

NASA Astrophysics Data System (ADS)

Houska, J.; Kolenaty, D.; Rezek, J.; Vlcek, J.

2017-11-01

The paper deals with thermochromic VO2 prepared by reactive high-power impulse magnetron sputtering and characterized by spectroscopic ellipsometry. We focus on the dispersion of optical constants in a wide temperature range and on the transmittance predicted using the optical constants. While the thermochromic behavior of VO2 in itself has been reported previously (particularly above the room temperature, RT), in this paper we present (i) optical properties achieved at a low deposition temperature of 250 °C and without any substrate bias voltage (which dramatically increases the application potential of the coating) and (ii) changes of these properties not only above but also below RT (down to -30 °C). The properties include very low (for VO2) extinction coefficient at RT (0.10 at 550 nm), low transition temperature of around or even below 50 °C (compared to the frequently cited 68 °C) and high modulation of the predicted infrared transmittance (e.g. 39% at -30 °C, 30% at RT and 3.4% above the transition temperature at 2000 nm for a 100 nm thick coating on glass). The results are important for the design of thermochromic coatings, and pathways for their preparation under industry-friendly conditions, for various technological applications.

Composition and temperature dependent optical properties of AlxGa1-xN alloy by spectroscopic ellipsometry

NASA Astrophysics Data System (ADS)

Liu, Yao; Li, Qing Xuan; Wan, Ling Yu; Kucukgok, Bahadir; Ghafari, Ehsan; Ferguson, Ian T.; Zhang, Xiong; Wang, Shuchang; Feng, Zhe Chuan; Lu, Na

2017-11-01

A series of AlxGa1-xN/AlN/Sapphire films with x = 0.35-0.75 and different thickness of epi-layer were prepared by metalorganic chemical vapor deposition (MOCVD). Spectroscopic ellipsometry (SE) was used to study the temperature-dependent refractive indices and optical bandgaps of the AlxGa1-xN films ranging from 300 to 823 K. Parametric semiconductor (PSEMI) models were used to describe the dielectric functions of AlGaN/AlN layers. The fitting results of refractive index, energy bandgap, thickness and surface roughness at 300 K are in good agreement with photoluminescence (PL), scanning electron microscopy (SEM) measurements and the existing literature. Our finding indicates that the crystal quality of the samples with x = 0.47 and 0.60 are better than those with x = 0.35 and 0.75. As the temperature rises, the increasing of refractive index for the low Al content AlxGa1-xN layers is stronger than that of high Al content in the transparent region, and the reduction of bandgap with high Al content is larger than that of low Al content. For all the samples (x = 0.35-0.75), an analytical expression for temperature-dependent refractive index in the wavelength range of 195-1650 nm was obtained using the Sellmeier law, and the quantitative analysis of the SE-derived temperature-dependent bandgap was conducted by using the Bose-Einstein equation.

Surface roughness estimation of MBE grown CdTe/GaAs(211)B by ex-situ spectroscopic ellipsometry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Karakaya, Merve, E-mail: mervegunnar@iyte.edu.tr; Bilgilisoy, Elif; Arı, Ozan

Spectroscopic ellipsometry (SE) ranging from 1.24 eV to 5.05 eV is used to obtain the film thickness and optical properties of high index (211) CdTe films. A three-layer optical model (oxide/CdTe/GaAs) was chosen for the ex-situ ellipsometric data analysis. Surface roughness cannot be determined by the optical model if oxide is included. We show that roughness can be accurately estimated, without any optical model, by utilizing the correlation between SE data (namely the imaginary part of the dielectric function, or phase angle, ψ) and atomic force microscopy (AFM) roughness. and ψ values at 3.31 eV, which corresponds to E{sub 1}more » critical transition energy of CdTe band structure, are chosen for the correlation since E{sub 1} gives higher resolution than the other critical transition energies. On the other hand, due to the anisotropic characteristic of (211) oriented CdTe surfaces, SE data ( and ψ) shows varieties for different azimuthal angle measurements. For this reason, in order to estimate the surface roughness by considering these correlations, it is shown that SE measurements need to be taken at the same surface azimuthal angle. Estimating surface roughness in this manner is an accurate way to eliminate cumbersome surface roughness measurement by AFM.« less

Nondestructive characterization of textured a-Si:H/c-Si heterojunction solar cell structures with nanometer-scale a-Si:H and In2O3:Sn layers by spectroscopic ellipsometry

NASA Astrophysics Data System (ADS)

Matsuki, Nobuyuki; Fujiwara, Hiroyuki

2013-07-01

Nanometer-scale hydrogenated amorphous silicon (a-Si:H) layers formed on crystalline silicon (c-Si) with pyramid-shaped textures have been characterized by spectroscopic ellipsometry (SE) using a tilt angle measurement configuration, in an attempt to establish a nondestructive method for the structural characterization of the a-Si:H/c-Si heterojunction solar cells. By applying an a-Si:H dielectric function model developed recently, the thickness and SiH2 content of the a-Si:H layer have been determined even on the textured substrates. Furthermore, from the SE analysis incorporating the Drude model, the carrier properties of the In2O3:Sn layers in the textured solar-cell structure have been characterized.

The optical properties of transferred graphene and the dielectrics grown on it obtained by ellipsometry

NASA Astrophysics Data System (ADS)

Kasikov, Aarne; Kahro, Tauno; Matisen, Leonard; Kodu, Margus; Tarre, Aivar; Seemen, Helina; Alles, Harry

2018-04-01

Graphene layers grown by chemical vapour deposition (CVD) method and transferred from Cu-foils to the oxidized Si-substrates were investigated by spectroscopic ellipsometry (SE), Raman and X-Ray Photoelectron Spectroscopy (XPS) methods. The optical properties of transferred CVD graphene layers do not always correspond to the ones of the exfoliated graphene due to the contamination from the chemicals used in the transfer process. However, the real thickness and the mean properties of the transferred CVD graphene layers can be found using ellipsometry if a real thickness of the SiO2 layer is taken into account. The pulsed laser deposition (PLD) and atomic layer deposition (ALD) methods were used to grow dielectric layers on the transferred graphene and the obtained structures were characterized using optical methods. The approach demonstrated in this work could be useful for the characterization of various materials grown on graphene.

Characterization of an active metasurface using terahertz ellipsometry

DOE PAGES

Karl, Nicholas; Heimbeck, Martin S.; Everitt, Henry O.; ...

2017-11-06

Switchable metasurfaces fabricated on a doped epi-layer have become an important platform for developing techniques to control terahertz (THz) radiation, as a DC bias can modulate the transmission characteristics of the metasurface. To model and understand this performance in new device configurations accurately, a quantitative understanding of the bias-dependent surface characteristics is required. In this work, we perform THz variable angle spectroscopic ellipsometry on a switchable metasurface as a function of DC bias. By comparing these data with numerical simulations, we extract a model for the response of the metasurface at any bias value. Using this model, we predict amore » giant bias-induced phase modulation in a guided wave configuration. Lastly, these predictions are in qualitative agreement with our measurements, offering a route to efficient modulation of THz signals.« less

The study of genomic DNA adsorption and subsequent interactions using total internal reflection ellipsometry.

PubMed

Nabok, Alexei; Tsargorodskaya, Anna; Davis, Frank; Higson, Séamus P J

2007-10-31

The adsorption of genomic DNA and subsequent interactions between adsorbed and solvated DNA was studied using a novel sensitive optical method of total internal reflection ellipsometry (TIRE), which combines spectroscopic ellipsometry with surface plasmon resonance (SPR). Single strands of DNA of two species of fish (herring and salmon) were electrostatically adsorbed on top of polyethylenimine films deposited upon gold coated glass slides. The ellipsometric spectra were recorded and data fitting utilized to extract optical parameters (thickness and refractive index) of adsorbed DNA layers. The further adsorption of single stranded DNA from an identical source, i.e. herring ss-DNA on herring ss-DNA or salmon ss-DNA on salmon ss-DNA, on the surface was observed to give rise to substantial film thickness increases at the surface of about 20-21 nm. Conversely adsorption of DNA from alternate species, i.e. salmon ss-DNA on herring ss-DNA or herring ss-DNA on salmon ss-DNA, yielded much smaller changes in thickness of 3-5 nm. AFM studies of the surface roughness of adsorbed layers were in line with the TIRE data.

Study of Receptor-Chaperone Interactions Using the Optical Technique of Spectroscopic Ellipsometry

PubMed Central

Kriechbaumer, Verena; Tsargorodskaya, Anna; Mustafa, Mohd K.; Vinogradova, Tatiana; Lacey, Joanne; Smith, David P.; Abell, Benjamin M.; Nabok, Alexei

2011-01-01

This work describes a detailed quantitative interaction study between the novel plastidial chaperone receptor OEP61 and isoforms of the chaperone types Hsp70 and Hsp90 using the optical method of total internal reflection ellipsometry (TIRE). The receptor OEP61 was electrostatically immobilized on a gold surface via an intermediate layer of polycations. The TIRE measurements allowed the evaluation of thickness changes in the adsorbed molecular layers as a result of chaperone binding to receptor proteins. Hsp70 chaperone isoforms but not Hsp90 were shown to be capable of binding OEP61. Dynamic TIRE measurements were carried out to evaluate the affinity constants of the above reactions and resulted in clear discrimination between specific and nonspecific binding of chaperones as well as differences in binding properties between the highly similar Hsp70 isoforms. PMID:21767504

Tunable optical properties of plasmonic Au/Al2O3 nanocomposite thin films analyzed by spectroscopic ellipsometry accounting surface characteristics.

PubMed

Jaiswal, Jyoti; Mourya, Satyendra; Malik, Gaurav; Chandra, Ramesh

2018-05-01

In the present work, we have fabricated plasmonic gold/alumina nanocomposite (Au/Al 2 O 3 NC) thin films on a glass substrate at room temperature by RF magnetron co-sputtering. The influence of the film thickness (∼10-40  nm) on the optical and other physical properties of the samples was investigated and correlated with the structural and compositional properties. The X-ray diffractometer measurement revealed the formation of Au nanoparticles with average crystallite size (5-9.2 nm) embedded in an amorphous Al 2 O 3 matrix. The energy-dispersive X ray and X-ray photoelectron spectroscopy results confirmed the formation of Au/Al 2 O 3 NC quantitatively and qualitatively and it was observed that atomic% of Au increased by increasing thickness. The optical constants of the plasmonic Au/Al 2 O 3 NC thin films were examined by variable angle spectroscopic ellipsometry in the wide spectral range of 246-1688 nm, accounting the surface characteristics in the optical stack model, and the obtained results are expected to be unique. Additionally, a thickness-dependent blueshift (631-590 nm) of surface plasmon resonance peak was observed in the absorption spectra. These findings of the plasmonic Au/Al 2 O 3 NC films may allow the design and fabrication of small, compact, and efficient devices for optoelectronic and photonic applications.

Study of receptor-chaperone interactions using the optical technique of spectroscopic ellipsometry.

PubMed

Kriechbaumer, Verena; Tsargorodskaya, Anna; Mustafa, Mohd K; Vinogradova, Tatiana; Lacey, Joanne; Smith, David P; Abell, Benjamin M; Nabok, Alexei

2011-07-20

This work describes a detailed quantitative interaction study between the novel plastidial chaperone receptor OEP61 and isoforms of the chaperone types Hsp70 and Hsp90 using the optical method of total internal reflection ellipsometry (TIRE). The receptor OEP61 was electrostatically immobilized on a gold surface via an intermediate layer of polycations. The TIRE measurements allowed the evaluation of thickness changes in the adsorbed molecular layers as a result of chaperone binding to receptor proteins. Hsp70 chaperone isoforms but not Hsp90 were shown to be capable of binding OEP61. Dynamic TIRE measurements were carried out to evaluate the affinity constants of the above reactions and resulted in clear discrimination between specific and nonspecific binding of chaperones as well as differences in binding properties between the highly similar Hsp70 isoforms. Copyright © 2011 Biophysical Society. Published by Elsevier Inc. All rights reserved.

Optical gradients in a-Si:H thin films detected using real-time spectroscopic ellipsometry with virtual interface analysis

NASA Astrophysics Data System (ADS)

Junda, Maxwell M.; Karki Gautam, Laxmi; Collins, Robert W.; Podraza, Nikolas J.

2018-04-01

Virtual interface analysis (VIA) is applied to real time spectroscopic ellipsometry measurements taken during the growth of hydrogenated amorphous silicon (a-Si:H) thin films using various hydrogen dilutions of precursor gases and on different substrates during plasma enhanced chemical vapor deposition. A procedure is developed for optimizing VIA model configurations by adjusting sampling depth into the film and the analyzed spectral range such that model fits with the lowest possible error function are achieved. The optimal VIA configurations are found to be different depending on hydrogen dilution, substrate composition, and instantaneous film thickness. A depth profile in the optical properties of the films is then extracted that results from a variation in an optical absorption broadening parameter in a parametric a-Si:H model as a function of film thickness during deposition. Previously identified relationships are used linking this broadening parameter to the overall shape of the optical properties. This parameter is observed to converge after about 2000-3000 Å of accumulated thickness in all layers, implying that similar order in the a-Si:H network can be reached after sufficient thicknesses. In the early stages of growth, however, significant variations in broadening resulting from substrate- and processing-induced order are detected and tracked as a function of bulk layer thickness yielding an optical property depth profile in the final film. The best results are achieved with the simplest film-on-substrate structures while limitations are identified in cases where films have been deposited on more complex substrate structures.

X-ray photoelectron spectroscopic study of the oxide removal mechanism of GaAs /100/ molecular beam epitaxial substrates in in situ heating

NASA Technical Reports Server (NTRS)

Vasquez, R. P.; Lewis, B. F.; Grunthaner, F. J.

1983-01-01

A standard cleaning procedure for GaAs (100) molecular beam epitaxial (MBE) substrates is a chemical treatment with a solution of H2SO4/H2O2/H2O, followed by in situ heating prior to MBE growth. X-ray photoelectron spectroscopic (XPS) studies of the surface following the chemical treatment show that the oxidized As is primarily As(+ 5). Upon heating to low temperatures (less than (350 C) the As(+ 5) oxidizes the substrate to form Ga2O3 and elemental As, and the As(+ 5) is reduced to As(+ 3) in the process. At higher temperatures (500 C), the As(+ 3) and elemental As desorb, while the Ga(+ 3) begins desorbing at about 600 C.

Spectrally resolved localized states in GaAs 1– xBi x

DOE PAGES

Christian, Theresa M.; Alberi, Kirstin; Beaton, Daniel A.; ...

2017-02-01

In this study, the role of localized states and their influence on the broader band structure remains a crucial question in understanding the band structure evolution in GaAs 1-xBi x. Here in this work, we present clear spectroscopic observations of recombination at several localized states in GaAs 1-xBi x. Sharp and recognizable photoluminescence features appear in multiple samples and redshift as a function of GaBi fraction between x = 0.16% and 0.4% at a linearized rate of 34 meV per % Bi, weaker than the redshift associated with band-to-band recombination. Interpreting these results in terms of radiative recombination between localizedmore » holes and free electrons sheds light on the relative movement of the conduction band minimum and the characteristics of localized bismuth-related trap states in GaAs 1-xBi x alloys.« less

Protein adsorption on thin films of carbon and carbon nitride monitored with in situ ellipsometry.

PubMed

Berlind, T; Tengvall, P; Hultman, L; Arwin, H

2011-03-01

Thin films of amorphous carbon and amorphous, graphitic and fullerene-like carbon nitride were deposited by reactive magnetron sputtering and optically characterized with spectroscopic ellipsometry. Complementary studies using scanning electron microscopy and atomic force microscopy were performed. The films were exposed to human serum albumin (HSA) and the adsorption was monitored in situ using dynamic ellipsometry. From the ellipsometric data the adsorbed amount of proteins was quantified in terms of surface mass density using de Feijter's model. The results indicate larger adsorption of proteins onto the amorphous films compared to the films with a more textured structure. Complementary studies with 125I-labeled HSA showed an apparent protein adsorption up to six times larger compared to the ellipsometry measurement. In addition, the four types of films were incubated in blood plasma followed by exposure to anti-fibrinogen, anti-HMWK or anti-C3c, revealing the materials' response to complement and contact activation. The amorphous and graphitic carbon nitride exhibit rather high immune activity compared to a titanium reference, whereas the amorphous carbon and the fullerene-like CNx show less immune complement deposition. Compared to the reference, all films exhibit indications of a stronger ability to initiate the intrinsic pathway of coagulation. Finally, the surfaces' bone-bonding ability was investigated by examination of their ability to form calcium phosphate crystals in a simulated body fluid, with a-CNx depositing most calcium phosphate after 21 days of incubation. Copyright © 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

In-situ ellipsometric studies of optical and surface properties of GaAs(100) at elevated temperatures

NASA Technical Reports Server (NTRS)

Yao, Huade; Snyder, Paul G.

1991-01-01

A rotating-polarizer ellipsometer was attached to an ultrahigh vacuum (UHV) chamber. A GaAs(100) sample was introduced into the UHV chamber and heated at anumber of fixed elevated temperatures, without arsenic overpressure. In-situ spectroscopic ellipsometric (SE) measurements were taken, through a pair of low-strain quartz windows, to monitor the surface changes and measure the pseudodielectric functions at elevated temperatures. Real-time data from GaAs surface covered with native oxide showed clearly the evolution of oxide desorption at approximately 580 C. In addition, surface degradation was found before and after the oxide desorption. An oxide free and smooth GaAs surface was obtained by depositing an arsenic protective coating onto a molecular beam epitaxy grown GaAs surface. The arsenic coating was evaporated immediately prior to SE measurements. A comparison showed that our room temperature data from this GaAs surface, measured in the UHV, are in good agreement with those in the literature obtained by wet-chemical etching. The surface also remained clean and smooth at higher temperatures, so that reliable temperature-dependent dielectric functions were obtained.

Spectroscopic Ellipsometry Studies of Thin Film a-Si:H/nc-Si:H Micromorph Solar Cell Fabrication in the p-i-n Superstrate Configuration

NASA Astrophysics Data System (ADS)

Huang, Zhiquan

Spectroscopic ellipsometry (SE) is a non-invasive optical probe that is capable of accurately and precisely measuring the structure of thin films, such as their thicknesses and void volume fractions, and in addition their optical properties, typically defined by the index of refraction and extinction coefficient spectra. Because multichannel detection systems integrated into SE instrumentation have been available for some time now, the data acquisition time possible for complete SE spectra has been reduced significantly. As a result, real time spectroscopic ellipsometry (RTSE) has become feasible for monitoring thin film nucleation and growth during the deposition of thin films as well as during their removal in processes of thin film etching. Also because of the reduced acquisition time, mapping SE is possible by mounting an SE instrument with a multichannel detector onto a mechanical translation stage. Such an SE system is capable of mapping the thin film structure and its optical properties over the substrate area, and thereby evaluating the spatial uniformity of the component layers. In thin film photovoltaics, such structural and optical property measurements mapped over the substrate area can be applied to guide device optimization by correlating small area device performance with the associated local properties. In this thesis, a detailed ex-situ SE study of hydrogenated amorphous silicon (a-Si:H) thin films and solar cells prepared by plasma enhanced chemical vapor deposition (PECVD) has been presented. An SE analysis procedure with step-by-step error minimization has been applied to obtain accurate measures of the structural and optical properties of the component layers of the solar cells. Growth evolution diagrams were developed as functions of the deposition parameters in PECVD for both p-type and n-type layers to characterize the regimes of accumulated thickness over which a-Si:H, hydrogenated nanocrystalline silicon (nc-Si:H) and mixed phase (a

Perspective: Optical measurement of feature dimensions and shapes by scatterometry

NASA Astrophysics Data System (ADS)

Diebold, Alain C.; Antonelli, Andy; Keller, Nick

2018-05-01

The use of optical scattering to measure feature shape and dimensions, scatterometry, is now routine during semiconductor manufacturing. Scatterometry iteratively improves an optical model structure using simulations that are compared to experimental data from an ellipsometer. These simulations are done using the rigorous coupled wave analysis for solving Maxwell's equations. In this article, we describe the Mueller matrix spectroscopic ellipsometry based scatterometry. Next, the rigorous coupled wave analysis for Maxwell's equations is presented. Following this, several example measurements are described as they apply to specific process steps in the fabrication of gate-all-around (GAA) transistor structures. First, simulations of measurement sensitivity for the inner spacer etch back step of horizontal GAA transistor processing are described. Next, the simulated metrology sensitivity for sacrificial (dummy) amorphous silicon etch back step of vertical GAA transistor processing is discussed. Finally, we present the application of plasmonically active test structures for improving the sensitivity of the measurement of metal linewidths.

Spectroscopic ellipsometry for analysis of polycrystalline thin-film photovoltaic devices and prediction of external quantum efficiency

NASA Astrophysics Data System (ADS)

Ibdah, Abdel-Rahman; Koirala, Prakash; Aryal, Puruswottam; Pradhan, Puja; Marsillac, Sylvain; Rockett, Angus A.; Podraza, Nikolas J.; Collins, Robert W.

2017-11-01

Complete polycrystalline thin-film photovoltaic (PV) devices employing CuIn1-xGaxSe2/CdS and CdS/CdTe heterojunctions have been studied by ex situ spectroscopic ellipsometry (SE). In this study, layer thicknesses have been extracted along with photon energy independent parameters such as compositions that describe the dielectric function spectra ε(E) of the individual layers. For accurate ex situ SE analysis of these PV devices, a database of ε(E) spectra is required for all thin film component materials used in each of the two absorber technologies. When possible, database measurements are performed by applying SE in situ immediately after deposition of the thin film materials and after cooling to room temperature in order to avoid oxidation and surface contamination. Determination of ε(E) from the resulting in situ SE data requires structural information that can be obtained from analysis of SE data acquired in real time during the deposition process. From the results of ex situ analysis of the complete CuIn1-xGaxSe2 (CIGS) and CdTe PV devices, the deduced layer thicknesses in combination with the parameters describing ε(E) can be employed in further studies that simulate the external quantum efficiency (EQE) spectra of the devices. These simulations have been performed here by assuming that all electron-hole pairs generated within the active layers, i.e. layers incorporating a dominant absorber component (either CIGS or CdTe), are separated and collected. The active layers may include not only the bulk absorber but also window and back contact interface layers, and individual current contributions from these layers have been determined in the simulations. In addition, the ex situ SE analysis results enable calculation of the absorbance spectra for the inactive layers and the overall reflectance spectra, which lead to quantification of all optical losses in terms of a current density deficit. Mapping SE can be performed given the high speed of multichannel

Case study on the dynamics of ultrafast laser heating and ablation of gold thin films by ultrafast pump-probe reflectometry and ellipsometry

NASA Astrophysics Data System (ADS)

Pflug, T.; Wang, J.; Olbrich, M.; Frank, M.; Horn, A.

2018-02-01

To increase the comprehension of ultrafast laser ablation, the ablation process has to be portrayed with sufficient temporal resolution. For example, the temporal modification of the complex refractive index {\\tilde{n}} and the relative reflectance of a sample material after irradiation with ultrafast single-pulsed laser radiation can be measured with a pump-probe setup. This work describes the construction and validation of a pump-probe setup enabling spatially, temporally, and spectroscopically resolved Brewster angle microscopy, reflectometry, ellipsometry, and shadow photography. First pump-probe reflectometry and ellipsometry measurements are performed on gold at λ _{probe}= 440 nm and three fluences of the single-pulsed pump radiation at λ _{pump}= 800 nm generating no, gentle, and strong ablation. The relative reflectance overall increases at no and gentle ablation. At strong ablation, the relative reflectance locally decreases, presumable caused by emitted thermal electrons, ballistic electrons, and ablating material. The refractive index n is slightly decreasing after excitation, while the extinction coefficient k is increasing.

Temperature dependent optical properties of ZnO thin film using ellipsometry and photoluminescence

NASA Astrophysics Data System (ADS)

Bouzourâa, M.-B.; Battie, Y.; Dalmasso, S.; Zaïbi, M.-A.; Oueslati, M.; En Naciri, A.

2018-05-01

We report the temperature dependence of the dielectric function, the exciton binding energy and the electronic transitions of crystallized ZnO thin film using spectroscopic ellipsometry (SE) and photoluminescence (PL). ZnO layers were prepared by sol-gel method and deposited on crystalline silicon (Si) by spin coating technique. The ZnO optical properties were determined between 300 K and 620 K. Rigorous study of optical responses was achieved in order to demonstrate the quenching exciton of ZnO as a function of temperature. Numerical technique named constrained cubic splines approximation (CCS), Tauc-Lorentz (TL) and Tanguy dispersion models were selected for the ellipsometry data modeling in order to obtain the dielectric function of ZnO. The results reveals that the exciton bound becomes widely flattening at 470 K on the one hand, and on the other that the Tanguy dispersion law is more appropriate for determining the optical responses of ZnO thin film in the temperature range of 300 K-420 K. The Tauc-Lorentz, for its part, reproduces correctly the ZnO dielectric function in 470 K-620 K temperature range. The temperature dependence of the electronic transition given by SE and PL shows that the exciton quenching was observed in 420 K-∼520 K temperature range. This quenching effect can be explained by the equilibrium between the Coulomb force of exciton and its kinetic energy in the film. The kinetic energy was found to induce three degrees of freedom of the exciton.

Effects of oxygen partial pressure, deposition temperature, and annealing on the optical response of CdS:O thin films as studied by spectroscopic ellipsometry

NASA Astrophysics Data System (ADS)

Junda, Maxwell M.; Grice, Corey R.; Subedi, Indra; Yan, Yanfa; Podraza, Nikolas J.

2016-07-01

Ex-situ spectroscopic ellipsometry measurements are made on radio frequency magnetron sputtered oxygenated cadmium sulfide (CdS:O) thin films. Films are deposited onto glass substrates at room temperature and at 270 °C with varying oxygen to total gas flow ratios in the sputtering ambient. Ellipsometric spectra from 0.74 to 5.89 eV are collected before and after annealing at 607 °C to simulate the thermal processes during close-space sublimation of overlying cadmium telluride in that solar cell configuration. Complex dielectric function (ɛ = ɛ1 + iɛ2) spectra are extracted for films as a function of oxygen gas flow ratio, deposition temperature, and post-deposition annealing using a parametric model accounting for critical point transitions and an Urbach tail for sub-band gap absorption. The results suggest an inverse relationship between degree of crystallinity and oxygen gas flow ratio, whereas annealing is shown to increase crystallinity in all samples. Direct band gap energies are determined from the parametric modeling of ɛ and linear extrapolations of the square of the absorption coefficient. As-deposited samples feature a range of band gap energies whereas annealing is shown to result in gap energies ranging only from 2.40 to 2.45 eV, which is close to typical band gaps for pure cadmium sulfide.

EBIC spectroscopy - A new approach to microscale characterization of deep levels in semi-insulating GaAs

NASA Technical Reports Server (NTRS)

Li, C.-J.; Sun, Q.; Lagowski, J.; Gatos, H. C.

1985-01-01

The microscale characterization of electronic defects in (SI) GaAs has been a challenging issue in connection with materials problems encountered in GaAs IC technology. The main obstacle which limits the applicability of high resolution electron beam methods such as Electron Beam-Induced Current (EBIC) and cathodoluminescence (CL) is the low concentration of free carriers in semiinsulating (SI) GaAs. The present paper provides a new photo-EBIC characterization approach which combines the spectroscopic advantages of optical methods with the high spatial resolution and scanning capability of EBIC. A scanning electron microscope modified for electronic characterization studies is shown schematically. The instrument can operate in the standard SEM mode, in the EBIC modes (including photo-EBIC and thermally stimulated EBIC /TS-EBIC/), and in the cathodo-luminescence (CL) and scanning modes. Attention is given to the use of CL, Photo-EBIC, and TS-EBIC techniques.

Growth features and spectroscopic structure investigations of nanoprofiled AlN films formed on misoriented GaAs substrates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Seredin, P. V., E-mail: paul@phys.vsu.ru; Goloshchapov, D. L.; Lenshin, A. S.

Nanostructured aluminum-nitride films are formed by reactive ion-plasma sputtering onto GaAs substrates with different orientations. The properties of the films are studied via structural analysis, atomic force microscopy, and infrared and visible–ultraviolet spectroscopy. The aluminum-nitride films can have a refractive index in the range of 1.6–4.0 at a wavelength of ~250 nm and an optical band gap of ~5 eV. It is shown that the morphology, surface composition, and optical characteristics of AlN/GaAs heterophase systems can be controlled using misoriented GaAs substrates.

Band gap of corundumlike α -Ga2O3 determined by absorption and ellipsometry

NASA Astrophysics Data System (ADS)

Segura, A.; Artús, L.; Cuscó, R.; Goldhahn, R.; Feneberg, M.

2017-07-01

The electronic structure near the band gap of the corundumlike α phase of Ga2O3 has been investigated by means of optical absorption and spectroscopic ellipsometry measurements in the ultraviolet (UV) range (400-190 nm). The absorption coefficient in the UV region and the imaginary part of the dielectric function exhibit two prominent absorption thresholds with wide but well-defined structures at 5.6 and 6.3 eV which have been ascribed to allowed direct transitions from crystal-field split valence bands to the conduction band. Excitonic effects with large Gaussian broadening are taken into account through the Elliott-Toyozawa model, which yields an exciton binding energy of 110 meV and direct band gaps of 5.61 and 6.44 eV. The large broadening of the absorption onset is related to the slightly indirect character of the material.

Characterisation of slab waveguides, fabricated in CaF2 and Er-doped tungsten-tellurite glass by MeV energy N+ ion implantation, using spectroscopic ellipsometry and m-line spectroscopy

NASA Astrophysics Data System (ADS)

Bányász, I.; Berneschi, S.; Lohner, T.; Fried, M.; Petrik, P.; Khanh, N. Q.; Zolnai, Z.; Watterich, A.; Bettinelli, M.; Brenci, M.; Nunzi-Conti, G.; Pelli, S.; Righini, G. C.; Speghini, A.

2010-05-01

Slab waveguides were fabricated in Er-doped tungsten-tellurite glass and CaF2 crystal samples via ion implantation. Waveguides were fabricated by implantation of MeV energy N+ ions at the Van de Graaff accelerator of the Research Institute for Particle and Nuclear Physics, Budapest, Hungary. Part of the samples was annealed. Implantations were carried out at energies of 1.5 MeV (tungsten-tellurite glass) and 3.5 MeV (CaF2). The implanted doses were between 5 x 1012 and 8 x 1016 ions/cm2. Refractive index profile of the waveguides was measured using SOPRA ES4G and Woollam M-2000DI spectroscopic ellipsometers at the Research Institute for Technical Physics and Materials Science, Budapest. Functionality of the waveguides was tested using a home-made instrument (COMPASSO), based on m-line spectroscopy and prism coupling technique, which was developed at the Materials and Photonics Devices Laboratory (MDF Lab.) of the Institute of Applied Physics in Sesto Fiorentino, Italy. Results of both types of measurements were compared to depth distributions of nuclear damage in the samples, calculated by SRIM 2007 code. Thicknesses of the guiding layer and of the implanted barrier obtained by spectroscopic ellipsometry correspond well to SRIM simulations. Irradiationinduced refractive index modulation saturated around a dose of 8 x 1016 ions/cm2 in tungsten-tellurite glass. Annealing of the implanted waveguides resulted in a reduction of the propagation loss, but also reduced the number of supported guiding modes at the lower doses. We report on the first working waveguides fabricated in an alkali earth halide crystal implanted by MeV energy medium-mass ions.

InP and GaAs characterization with variable stoichiometry obtained by molecular spray

NASA Technical Reports Server (NTRS)

Massies, J.; Linh, N. T.; Olivier, J.; Faulconnier, P.; Poirier, R.

1979-01-01

Both InP and GaAs surfaces were studied in parallel. A molecular spray technique was used to obtain two semiconductor surfaces with different superficial compositions. The structures of these surfaces were examined by electron diffraction. Electron energy loss was measured spectroscopically in order to determine surface electrical characteristics. The results are used to support conclusions relative to the role of surface composition in establishing a Schottky barrier effect in semiconductor devices.

Optical Metrology for Directed Self-assembly Patterning Using Mueller Matrix Spectroscopic Ellipsometry Based Scatterometry

NASA Astrophysics Data System (ADS)

Dixit, Dhairya J.

The semiconductor industry continues to drive patterning solutions that enable devices with higher memory storage capacity, faster computing performance, lower cost per transistors, and higher transistor density. These developments in the field of semiconductor manufacturing along with the overall minimization of the size of transistors require cutting-edge metrology tools for characterization. Directed self-assembly (DSA) patterning process can be used to fabricate nanoscale line-space patterns and contact holes via thermodynamically driven micro-phase separation of block copolymer (BCP) films with boundary constraints from guiding templates. Its main advantages are high pattern resolution (~10 nm), high throughput, no requirement of a high-resolution mask, and compatibility with standard fab-equipment and processes. Although research into DSA patterning has demonstrated a high potential as a nanoscale patterning process, there are critical challenges that must be overcome before transferring DSA into high volume manufacturing, including achievement of low defect density and high process stability. For this, advances in critical dimension (CD) and overlay measurement as well as rapid defect characterization are required. Both scatterometry and critical dimension-scanning electron microscopy (CD-SEM) are routinely used for inline dimensional metrology. CD-SEM inspection is limited, as it does not easily provide detailed line-shape information, whereas scatterometry has the capability of measuring important feature dimensions including: line-width, line-shape, sidewall-angle, and thickness of the patterned samples quickly and non-destructively. The present work describes the application of Mueller matrix spectroscopic ellipsometry (MMSE) based scatterometry to optically characterize DSA patterned line- space grating and contact hole structures fabricated with phase-separated polystyrene-b-polymethylmethacrylate (PS-b-PMMA) at various integration steps of BCP DSA

Design and fabrication of six-volt vertically-stacked GaAs photovoltaic power converter

PubMed Central

Zhao, Yongming; Sun, Yurun; He, Yang; Yu, Shuzhen; Dong, Jianrong

2016-01-01

A six-volt vertically-stacked, high current GaAs photovoltaic power converter (PPC) has been designed and fabricated to produce output power over 1 W under monochromatic illumination. An N++-GaAs/P++-AlGaAs tunnel junctions (TJs) structure has been used for connecting each sub-cell in this vertically-stacked PPC device. The thickness of the each GaAs sub-cell has been derived based on the calculation of absorption depth of photons with a wavelength of 808 nm using absorption coefficient obtained from ellipsometry measurements. The devices were characterized under non-uniform CW laser illumination at 808 nm with incident power up to 4.1 W. A maximum conversion efficiency of 50.2% was achieved at 0.3 W under non-uniform (coupled in optical fiber) monochromatic illumination, dropping to 42.5% at 4.1 W. The operating voltage at the maximum power point is 5.5–6.0 V, depending on the incident laser power, and an output electrical power output of 1.3 W can be extracted at a laser power of 2.9 W and the maximum electrical power output amounts to 1.72 W. The external quantum efficiency (EQE) measurement indicates that the performance of PPC can be further improved by refining the design of the thickness of sub-cells and improving TJs. PMID:27901079

Broadband optical properties of graphene and HOPG investigated by spectroscopic Mueller matrix ellipsometry

NASA Astrophysics Data System (ADS)

Song, Baokun; Gu, Honggang; Zhu, Simin; Jiang, Hao; Chen, Xiuguo; Zhang, Chuanwei; Liu, Shiyuan

2018-05-01

Optical properties of mono-graphene fabricated by chemical vapor deposition (CVD) and highly oriented pyrolytic graphite (HOPG) are comparatively studied by Mueller matrix ellipsometry (MME) over an ultra-wide energy range of 0.73-6.42 eV. A multilayer stacking model is constructed to describe the CVD mono-graphene, in which the roughness of the glass substrate and the water adsorption on the graphene are considered. We introduce a uniaxial anisotropic dielectric model to parameterize the optical constants of both the graphene and the HOPG. With the established models, broadband optical constants of the graphene and the HOPG are determined from the Mueller matrix spectra based on a point-by-point method and a non-linear regression method, respectively. Two significant absorption peaks at 4.75 eV and 6.31 eV are observed in the extinction coefficient spectra of the mono-graphene, which can be attributed to the von-Hove singularity (i.e., the π-to-π∗ exciton transition) near the M point and the σ-to-σ∗ exciton transition near the Γ point of the Brillouin zone, respectively. Comparatively, only a major absorption peak at 4.96 eV appears in the ordinary extinction coefficient spectra of the HOPG, which is mainly formed by the π-to-π∗ interband transition.

Single-shot Ellipsometry of Shocked Iron to 275 GPa

NASA Astrophysics Data System (ADS)

Grant, Sean; Ao, Tommy; Bernstein, Aaron; Davis, Jean-Paul; Ditmire, Todd; Dolan, Daniel; Lin, Jung-Fu; Porwitzky, Andrew; Seagle, Christopher

2017-06-01

We have studied the properties of iron under shock conditions using time-resolved ellipsometry, a technique that probes the dielectric value of materials under dynamic conditions, on the STAR gas gun facility at Sandia National Laboratories. We performed experiments on a two-stage gas gun ranging from the α - ɛ transition (75 GPa) to the solid-liquid transition (275 GPa). For the first time, we report the dielectric results of shocked iron at those conditions. In addition, the time-resolved ellipsometry diagnostic is being implemented on the Sandia pulsed power Z-machine. The goal of upcoming Z experiments will be to employ the ``shock-ramp'' technique to reach pressure and temperature conditions relevant to the Earth core, and to use ellipsometry to obtain the iron electric conductivities needed for benchmarking material models. Sandia National Laboratories is a multi-mission laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. SAND2017-1952 A.

Wavelength dependent in-plane birefringence of transparent flexible films determined by using transmission ellipsometry

NASA Astrophysics Data System (ADS)

Yang, Sung Mo; Hong, Sera; Kim, Sang Youl

2018-05-01

We introduce a simple method to determine the in-plane birefringence of transparent flexible films by using transmission spectroscopic ellipsometry. The pseudo-ellipsometric constants which can represent their sample azimuthal angle dependent characteristics are introduced. The effect of in-plane birefringence and sample azimuthal angle on the pseudo ellipsometric constants is calculated using Jones matrix formalism, and the observed sample azimuthal angle dependence of measured pseudo-ellipsometric data is well understood. Wavelength dependence of in-plane birefringence is expressed in terms of the Sellmeier dispersion equation. The best fit pseudo-ellipsometric spectra to the measured ones at the sample azimuthal angles of every 15° from 0 to 90° are searched. The dispersion coefficients of the Sellmeier equation and the azimuthal angle of the optic axis are determined for polycarbonate (PC), poly(ethylene naphthalate) (PEN), poly(ethylene terephthalate) (PET), polyimide (PI), and colorless polyimide (CPI) films.

Microprocessor design for GaAs technology

NASA Astrophysics Data System (ADS)

Milutinovic, Veljko M.

Recent advances in the design of GaAs microprocessor chips are examined in chapters contributed by leading experts; the work is intended as reading material for a graduate engineering course or as a practical R&D reference. Topics addressed include the methodology used for the architecture, organization, and design of GaAs processors; GaAs device physics and circuit design; design concepts for microprocessor-based GaAs systems; a 32-bit GaAs microprocessor; a 32-bit processor implemented in GaAs JFET; and a direct coupled-FET-logic E/D-MESFET experimental RISC machine. Drawings, micrographs, and extensive circuit diagrams are provided.

Analysis of Toxic Amyloid Fibril Interactions at Natively Derived Membranes by Ellipsometry

PubMed Central

Smith, Rachel A. S.; Nabok, Aleksey; Blakeman, Ben J. F.; Xue, Wei-Feng; Abell, Benjamin; Smith, David P.

2015-01-01

There is an ongoing debate regarding the culprits of cytotoxicity associated with amyloid disorders. Although small pre-fibrillar amyloid oligomers have been implicated as the primary toxic species, the fibrillar amyloid material itself can also induce cytotoxicity. To investigate membrane disruption and cytotoxic effects associated with intact and fragmented fibrils, the novel in situ spectroscopic technique of Total Internal Reflection Ellipsometry (TIRE) was used. Fibril lipid interactions were monitored using natively derived whole cell membranes as a model of the in vivo environment. We show that fragmented fibrils have an increased ability to disrupt these natively derived membranes by causing a loss of material from the deposited surface when compared with unfragmented fibrils. This effect was corroborated by observations of membrane disruption in live cells, and by dye release assay using synthetic liposomes. Through these studies we demonstrate the use of TIRE for the analysis of protein-lipid interactions on natively derived lipid surfaces, and provide an explanation on how amyloid fibrils can cause a toxic gain of function, while entangled amyloid plaques exert minimal biological activity. PMID:26172440

In Situ Infrared Ellipsometry for Protein Adsorption Studies on Ultrathin Smart Polymer Brushes in Aqueous Environment

DOE PAGES

Kroning, Annika; Furchner, Andreas; Aulich, Dennis; ...

2015-02-10

The protein-adsorbing and -repelling properties of various smart nanometer-thin polymer brushes with high potential for biosensing and biomedical applications are studied by in-situ infrared-spectroscopic ellipsometry (IRSE). IRSE as a highly sensitive non-destructive technique allows us to investigate protein adsorption on polymer brushes in aqueous environment in dependence of external stimuli like temperature and pH. These stimuli are, for instance, relevant in switchable mixed brushes containing poly(N-isopropyl acrylamide) and poly(acrylic acid), respectively. We use such brushes as model surfaces for controlling protein adsorption of human serum albumin and human fibrinogen. IRSE can distinguish between polymer-specific vibrational bands, which yield insights intomore » the hydration state of the brushes, and changes in the protein-specific amide bands, which are related to changes of the protein secondary structure.« less

User oriented end-station on VUV pump-probe magneto-optical ellipsometry at ELI beamlines

NASA Astrophysics Data System (ADS)

Espinoza, Shirly; Neuber, Gerd; Brooks, Christopher D.; Besner, Bastian; Hashemi, Maryam; Rübhausen, Michael; Andreasson, Jakob

2017-11-01

A state of the art ellipsometer for user operations is being implemented at ELI Beamlines in Prague, Czech Republic. It combines three of the most promising and exotic forms of ellipsometry: VUV, pump-probe and magneto-optical ellipsometry. This new ellipsometer covers a spectral operational range from the NIR up to the VUV, with high through-put between 1 and 40 eV. The ellipsometer also allows measurements of magneto-optical spectra with a 1 kHz switchable magnetic field of up to 1.5 T across the sample combining ellipsometry and Kerr spectroscopy measurements in an unprecedented spectral range. This form of generalized ellipsometry enables users to address diagonal and off-diagonal components of the dielectric tensor within one measurement. Pump-probe measurements enable users to study the dynamic behaviour of the dielectric tensor in order to resolve the time-domain phenomena in the femto to 100 ns range.

Ellipsometry with polarisation analysis at cryogenic temperatures inside a vacuum chamber

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bauer, S.; Grees, B.; Spitzer, D.

2013-12-15

In this paper we describe a new variant of null ellipsometry to determine thicknesses and optical properties of thin films on a substrate at cryogenic temperatures. In the PCSA arrangement of ellipsometry the polarizer and the compensator are placed before the substrate and the analyzer after it. Usually, in the null ellipsometry the polarizer and the analyzer are rotated to find the searched minimum in intensity. In our variant we rotate the polarizer and the compensator instead, both being placed in the incoming beam before the substrate. Therefore the polarisation analysis of the reflected beam can be realized by anmore » analyzer at fixed orientation. We developed this method for investigations of thin cryogenic films inside a vacuum chamber where the analyzer and detector had to be placed inside the cold shield at a temperature of T≈ 90 K close to the substrate. All other optical components were installed at the incoming beam line outside the vacuum chamber, including all components which need to be rotated during the measurements. Our null ellipsometry variant has been tested with condensed krypton films on a highly oriented pyrolytic graphite substrate (HOPG) at a temperature of T≈ 25 K. We show that it is possible to determine the indices of refraction of condensed krypton and of the HOPG substrate as well as thickness of krypton films with reasonable accuracy.« less

Excitation and De-Excitation Mechanisms of Er-Doped GaAs and A1GaAs.

DTIC Science & Technology

1992-12-01

AD-A258 814 EXCITATION AND DE -EXCITATION MECHANISMS OF Er-DOPED GaAs AND A1GaAs DISSERTATION David W. Elsaesser, Captain, USAF DTICY. ft £ICTE’’ )AN...0 8 1993U -o Wo- .%Approved for public release; Distribution unlimited 93 1 04 022 AFIT/DS/ENP/92-5 EXCITATION AND DE -EXCITATION MECHANISMS OF Er...public release; Distribution unlimited AFIT/DS/ENP/92D-005 EXCITATION AND DE -EXCITATION MECHANISMS OF Er-DOPED GaAs AND A1GaAs 4 toFlor -- David W

GaAs Computer Technology

DTIC Science & Technology

1992-01-07

AD-A259 259 FASTC-ID FOREIGN AEROSPACE SCIENCE AND TECHNOLOGY CENTER GaAs COMPUTER TECHNOLOGY (1) by Wang Qiao-yu 93-00999 Distrir bution t,,,Nm ted...FASTC- ID(RS)T-0310-92 HUMAN TRANSLATION FASTC-ID(RS)T-0310-92 7 January 1993 GaAs COMPUTER TECHNOLOGY (1) By: Wang Qiao-yu English pages: 6 Source...the best quality copy available. j C] " ------ GaAs Computer Technology (1) Wang Qiao-yu (Li-Shan Microelectronics Institute) Abstract: The paper

GaAs shallow-homojunction solar cells

NASA Technical Reports Server (NTRS)

Fan, J. C. C.

1981-01-01

The feasibility of fabricating space resistant, high efficiency, light weight, low cost GaAs shallow homojunction solar cells for space application is investigated. The material preparation of ultrathin GaAs single crystal layers, and the fabrication of efficient GaAs solar cells on bulk GaAs substrates are discussed. Considerable progress was made in both areas, and conversion efficiency about 16% AMO was obtained using anodic oxide as a single layer antireflection coating. A computer design shows that even better cells can be obtained with double layer antireflection coating. Ultrathin, high efficiency solar cells were obtained from GaAs films prepared by the CLEFT process, with conversion efficiency as high as 17% at AMI from a 10 micrometers thick GaAs film. A organometallic CVD was designed and constructed.

Insulators obtained by electron cyclotron resonance plasmas on Si or GaAs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Diniz, J.A.; Doi, I.; Swart, J.W

2003-03-15

Silicon oxynitride (SiO{sub x}N{sub y}) and nitride (SiN{sub x}) insulators have been deposited or grown (with or without silane in the gas mixture, respectively) by electron cyclotron resonance (ECR) plasmas on Si and/or GaAs substrates at room temperature (20 deg. C) and low pressures (up to 10 mTorr). Chemical bonding characteristics of the SiO{sub x}N{sub y} and SiN{sub x} films were evaluated using Fourier transform infrared spectrometry (FTIR). The profile measurements determined the film thickness, the deposition (or oxidation) rate and the etch rates in buffered HF (BHF). The refractive indexes and the thicknesses were determined by ellipsometry. The effectivemore » interface charge densities were determined by capacitance-voltage (C-V) measurements. With these processes and analyses, different films were obtained and optimized. Suitable gate insulators for metal-insulator-semiconductor (MIS) devices with low interface charge densities were developed: (a) SiN{sub x} films deposited by ECR-chemical vapor deposition (ECR-PECVD) on GaAs substrates; (b) SiO{sub x}N{sub y} insulators obtained by low-energy molecular nitrogen ion ({sup 28}N{sub 2}{sup +}) implantation (energy of 5 keV and dose of 1x10{sup 15}/cm{sup 2}) in Si substrates prior to high-density O{sub 2} ECR plasma oxidation; and (c) SiO{sub x}N{sub y} insulators grown (without silane in the gas mixture) by O{sub 2}/N{sub 2}/Ar ECR plasma 'oxynitridation'. Furthermore, some SiN{sub x} films also present very good masking characteristics for local oxidation of silicon process.« less

Genesis Silicon Carbide Concentrator Target 60003 Preliminary Ellipsometry Mapping Results

NASA Technical Reports Server (NTRS)

Calaway, M. J.; Rodriquez, M. C.; Stansbery, E. K.

2007-01-01

The Genesis concentrator was custom designed to focus solar wind ions primarily for terrestrial isotopic analysis of O-17/O-16 and O-18/O-16 to +/-1%, N-15/N-14 to +/-1%, and secondarily to conduct elemental and isotopic analysis of Li, Be, and B. The circular 6.2 cm diameter concentrator target holder was comprised of four quadrants of highly pure semiconductor materials that included one amorphous diamond-like carbon, one C-13 diamond, and two silicon carbide (SiC). The amorphous diamond-like carbon quadrant was fractured upon impact at Utah Test and Training Range (UTTR), but the remaining three quadrants survived fully intact and all four quadrants hold an important collection of solar wind. The quadrants were removed from the target holder at NASA Johnso n Space Center Genesis Curation Laboratory in April 2005, and have been housed in stainless steel containers under continual nitrogen purge since time of disintegration. In preparation for allocation of a silicon carbide target for oxygen isotope analyses at UCLA, the two SiC targets were photographed for preliminary inspection of macro particle contamination from the hard non-nominal landing as well as characterized by spectroscopic ellipsometry to evaluate thin film contamination. This report is focused on Genesis SiC target sample number 60003.

Real Time Spectroscopic Ellipsometry Analysis of First Stage CuIn1-xGaxSe₂ Growth: Indium-Gallium Selenide Co-Evaporation.

PubMed

Pradhan, Puja; Aryal, Puruswottam; Attygalle, Dinesh; Ibdah, Abdel-Rahman; Koirala, Prakash; Li, Jian; Bhandari, Khagendra P; Liyanage, Geethika K; Ellingson, Randy J; Heben, Michael J; Marsillac, Sylvain; Collins, Robert W; Podraza, Nikolas J

2018-01-16

Real time spectroscopic ellipsometry (RTSE) has been applied for in-situ monitoring of the first stage of copper indium-gallium diselenide (CIGS) thin film deposition by the three-stage co-evaporation process used for fabrication of high efficiency thin film photovoltaic (PV) devices. The first stage entails the growth of indium-gallium selenide (In 1- x Ga x )₂Se₃ (IGS) on a substrate of Mo-coated soda lime glass maintained at a temperature of 400 °C. This is a critical stage of CIGS deposition because a large fraction of the final film thickness is deposited, and as a result precise compositional control is desired in order to achieve the optimum performance of the resulting CIGS solar cell. RTSE is sensitive to monolayer level film growth processes and can provide accurate measurements of bulk and surface roughness layer thicknesses. These in turn enable accurate measurements of the bulk layer optical response in the form of the complex dielectric function ε = ε₁ - iε₂, spectra. Here, RTSE has been used to obtain the (ε₁, ε₂) spectra at the measurement temperature of 400 °C for IGS thin films of different Ga contents ( x ) deduced from different ranges of accumulated bulk layer thickness during the deposition process. Applying an analytical expression in common for each of the (ε₁, ε₂) spectra of these IGS films, oscillator parameters have been obtained in the best fits and these parameters in turn have been fitted with polynomials in x . From the resulting database of polynomial coefficients, the (ε₁, ε₂) spectra can be generated for any composition of IGS from the single parameter, x . The results have served as an RTSE fingerprint for IGS composition and have provided further structural information beyond simply thicknesses, for example information related to film density and grain size. The deduced IGS structural evolution and the (ε₁, ε₂) spectra have been interpreted as well in relation to observations from scanning

Variable angle spectroscopic ellipsometric characterization of HfO2 thin film

NASA Astrophysics Data System (ADS)

Kumar, M.; Kumari, N.; Karar, V.; Sharma, A. L.

2018-02-01

Hafnium Oxide film was deposited on BK7 glass substrate using reactive oxygenated E-Beam deposition technique. The film was deposited using in-situ quartz crystal thickness monitoring to control the film thickness and rate of evaporation. The thin film was grown with a rate of deposition of 0.3 nm/s. The coated substrate was optically characterized using spectrophotometer to determine its transmission spectra. The optical constants as well as film thickness of the hafnia film were extracted by variable angle spectroscopic ellipsometry with Cauchy fitting at incidence angles of 65˚, 70˚ and 75˚.

GaAs MOEMS Technology

DOE Office of Scientific and Technical Information (OSTI.GOV)

SPAHN, OLGA B.; GROSSETETE, GRANT D.; CICH, MICHAEL J.

2003-03-01

Many MEMS-based components require optical monitoring techniques using optoelectronic devices for converting mechanical position information into useful electronic signals. While the constituent piece-parts of such hybrid opto-MEMS components can be separately optimized, the resulting component performance, size, ruggedness and cost are substantially compromised due to assembly and packaging limitations. GaAs MOEMS offers the possibility of monolithically integrating high-performance optoelectronics with simple mechanical structures built in very low-stress epitaxial layers with a resulting component performance determined only by GaAs microfabrication technology limitations. GaAs MOEMS implicitly integrates the capability for radiation-hardened optical communications into the MEMS sensor or actuator component, a vitalmore » step towards rugged integrated autonomous microsystems that sense, act, and communicate. This project establishes a new foundational technology that monolithically combines GaAs optoelectronics with simple mechanics. Critical process issues addressed include selectivity, electrochemical characteristics, and anisotropy of the release chemistry, and post-release drying and coating processes. Several types of devices incorporating this novel technology are demonstrated.« less

LEC GaAs for integrated circuit applications

NASA Technical Reports Server (NTRS)

Kirkpatrick, C. G.; Chen, R. T.; Homes, D. E.; Asbeck, P. M.; Elliott, K. R.; Fairman, R. D.; Oliver, J. D.

1984-01-01

Recent developments in liquid encapsulated Czochralski techniques for the growth of semiinsulating GaAs for integrated circuit applications have resulted in significant improvements in the quality and quantity of GaAs material suitable for device processing. The emergence of high performance GaAs integrated circuit technologies has accelerated the demand for high quality, large diameter semiinsulating GaAs substrates. The new device technologies, including digital integrated circuits, monolithic microwave integrated circuits and charge coupled devices have largely adopted direct ion implantation for the formation of doped layers. Ion implantation lends itself to good uniformity and reproducibility, high yield and low cost; however, this technique also places stringent demands on the quality of the semiinsulating GaAs substrates. Although significant progress was made in developing a viable planar ion implantation technology, the variability and poor quality of GaAs substrates have hindered progress in process development.

Design optimization of GaAs betavoltaic batteries

NASA Astrophysics Data System (ADS)

Chen, Haiyanag; Jiang, Lan; Chen, Xuyuan

2011-06-01

GaAs junctions are designed and fabricated for betavoltaic batteries. The design is optimized according to the characteristics of GaAs interface states and the diffusion length in the depletion region of GaAs carriers. Under an illumination of 10 mCi cm-2 63Ni, the open circuit voltage of the optimized batteries is about ~0.3 V. It is found that the GaAs interface states induce depletion layers on P-type GaAs surfaces. The depletion layer along the P+PN+ junction edge isolates the perimeter surface from the bulk junction, which tends to significantly reduce the battery dark current and leads to a high open circuit voltage. The short circuit current density of the optimized junction is about 28 nA cm-2, which indicates a carrier diffusion length of less than 1 µm. The overall results show that multi-layer P+PN+ junctions are the preferred structures for GaAs betavoltaic battery design.

Discrete retardance second harmonic generation ellipsometry.

PubMed

Dehen, Christopher J; Everly, R Michael; Plocinik, Ryan M; Hedderich, Hartmut G; Simpson, Garth J

2007-01-01

A new instrument was constructed to perform discrete retardance nonlinear optical ellipsometry (DR-NOE). The focus of the design was to perform second harmonic generation NOE while maximizing sample and application flexibility and minimizing data acquisition time. The discrete retardance configuration results in relatively simple computational algorithms for performing nonlinear optical ellipsometric analysis. NOE analysis of a disperse red 19 monolayer yielded results that were consistent with previously reported values for the same surface system, but with significantly reduced acquisition times.

GaAs Monolithic Microwave Subsystem Technology Base

DTIC Science & Technology

1980-01-01

To provide a captive source of reliable, high-quality GaAs substrates, a new crystal growth and substrate preparation facility which utilizes a high...Symp. GaAs and Related Compounds, Inst. Phys. Conf. Ser. 24, 6. 20. Wood, Woodcock and Harris (1978) GaAs and Related Compounds, Inst. Phys. Conf

Investigation of the dielectric function of solution-processed InGaZnO films using ellipsometry.

PubMed

Kim, Tae Jung; Yoon, Jae Jin; Hwang, Soo Min; Choi, Jun Hyuk; Hwang, Soon Yong; Ghong, Tae Ho; Barange, Nilesh; Kim, Jun Young; Kim, Young Dong; Joo, Jinho

2012-07-01

The optical properties of InGaZnO (IGZO) films grown through the sol-gel process as a function of sintering time were investigated with spectroscopic ellipsometry (SE). The IGZO precursor sol was prepared by mixing In nitrate, Ga nitrate, and Zn acetate at a molar ratio of In:Ga:Zn = 3:1:1. The solution was deposited on a SiO2/Si substrate via spin coating. Sintering was performed at 400 degrees C for 1-15 h in an ambient atmosphere. The optical properties were measured over the range 1.12-6.52 eV via variable angle SE, at room temperature. The angle of incidence was varied from 50 to 70 degrees in 5 degree steps. To extract the pure optical properties of IGZO, multilayer-structure calculation with Tauc-Lorentz dispersion relation for IGZO was performed. The changes in the dielectric function of the IGZO films with varying sintering time were observed. The resultant optical properties can be related to the concentration of oxygen vacancies in the material, which can be controlled by the sintering time.

Compound semiconductor detectors for X-ray astronomy: Spectroscopic measurements and material characterization

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bavdaz, M.; Kraft, S.; Peacock, A.

1998-12-31

The use of some specific compound semiconductors in the fabrication of high energy X-ray detectors shows significant potential for X-ray astrophysics space missions. The authors are currently investigating three high purity crystals--CdZnTe, GaAs and TlBr--as the basis for future hard X-ray detectors (above 10 keV). In this paper the authors present the first results on CdZnTe and GaAs based detectors and evaluate the factors currently still constraining the performance. Energy resolutions (FWHM) of 0.9 keV and 1.1 keV at 14 keV and 60 keV, respectively, have been obtained with an epitaxial GaAs detector, while 0.7 keV and 1.5 keV FWHMmore » were measured at the same energies with a CdZnTe detector. Based on these results it is clear, that the next generation of X-ray astrophysics missions now in the planning phase may well consider extending the photon energy range up to {approximately} 100 keV by use of efficient detectors with reasonable spectroscopic capabilities.« less

Jet Fuel Thermal Stability Investigations using Ellipsometry

NASA Technical Reports Server (NTRS)

Nash, Leigh; Klettlinger, Jennifer; Vasu, Subith

2017-01-01

Ellipsometry is an optical technique used to measure the thickness of thin films. This technique was used to measure the thickness of deposits created by heated jet fuel, specifically Sasol IPK on stainless steel tubes. A new amorphous model was used to iteratively determine the film thickness. This method was found to be repeatable, and the thickness of deposit increased with increasing temperature and increasing concentration of naphthalene.

In-situ ellipsometry: applications to thin film research, development, and production

NASA Astrophysics Data System (ADS)

Kief, Mark T.

1999-07-01

Many industries including the optics industry, semiconductor industry, and magnetic storage industry are deeply rooted in the science and technology of the film materials and thin film based devices. Research in novel thin film systems and the engineering of artificial structures increasingly requires a control on the atomic scale in both thickness and lateral order. Development of the deposition and fabrication processes for these thin film structures requires technical sophistication and efficiency combined with an understanding of the multi-faceted process interactions. The production of these materials necessitates a remarkable degree of control to minimize scrap and assure good performance. Furthermore, in today's industry these operations must occur at an ever accelerating pace. In this article, we will review one technique which can make these challenges more tractable-- insitu ellipsometry. This is a very powerful tool which is capable of characterizing thin film processes in real-time. We review the art and illustrate with novel applications to metal thin film growth. In addition, we will illustrate how information obtained with insitu ellipsometry can predict the end use thin film properties such as the transport properties. In conclusion, further advances in insitu ellipsometry and its applications will be discussed in terms of needs and trends as a tool for thin film research, development and production.

In-situ ellipsometry: applications to thin film research, development, and production

NASA Astrophysics Data System (ADS)

Kief, M. T.

1999-07-01

Many industries including the optics industry, semiconductor industry, and magnetic storage industry are deeply rooted in the science and technology of thin film materials and thin film based devices. Research in novel thin film systems and the engineering of artificial structures increasingly requires a control on the atomic scale in both thickness and lateral order. Development of the deposition and fabrication processes for these thin film structures requires technical sophistication and efficiency combined with an understanding of the multi-faceted process interactions. The production of these materials necessitates a remarkable degree of control to minimize scrap and assure good performance. Furthermore, in today's industry these operations must occur at an ever accelerating pace. In this article, we will review one technique which can make these challenges more tractable - insitu ellipsometry. This is a very powerful tool which is capable of characterizing thin film processes in real-time. We review the art and illustrate with novel applications to metal thin film growth. In addition, we will illustrate how information obtained with insitu ellipsometry can predict the end use thin film properties such as the transport properties. In conclusion, further advances in insitu ellipsometry and its applications will be discussed in terms of needs and trends as a tool for thin film research, development and production.

New Passivation Methods of GaAs.

DTIC Science & Technology

1980-01-01

Fabrication of Thin Nitride Layers on GaAs 33 - 35 CHAPTER 7 Passivation of InGaAsP 36 - 37 CHAPTER 8 Emulsions on GaAs Surfaces 38 - 42 APPENDIX...not yet given any useful results. The deposition of SiO2 by using emulsions is pursued and first results on the possibility of GaAs doping are...glycol-tartaric acid based aqueous solution was used in order to anodically oxidise the gate notch after the source and drain ohmic contacts were formed

Magneto-ellipsometry as a powerful technique for investigating magneto-optical structures properties

NASA Astrophysics Data System (ADS)

Maximova, Olga; Kosyrev, Nikolay; Yakovlev, Ivan; Shevtsov, Dmitriy; Lyaschenko, Sergey; Varnakov, Sergey; Ovchinnikov, Sergey

2017-10-01

In this work we report on new magneto-ellipsometry set-up that allows to grow thin films and nanostructures by ultrahigh vacuum thermal evaporation as well as to conduct in situ measurements during the growth in order to analyze and control nanostructures properties. Ellipsometry and transverse magneto-optical Kerr effect measurements can be performed in situ inside this set-up. A uniform magnetic field of high intensity (more than 1 kOe) can be applied to samples inside the vacuum chamber. Also, we report on the developed method of data interpretation that is the base of the set-up software. Thus, we present a powerful tool for nanostructures synthesis and characterization.

Multiple-layered effective medium approximation approach to modeling environmental effects on alumina passivated highly porous silicon nanostructured thin films measured by in-situ Mueller matrix ellipsometry

NASA Astrophysics Data System (ADS)

Mock, Alyssa; Carlson, Timothy; VanDerslice, Jeremy; Mohrmann, Joel; Woollam, John A.; Schubert, Eva; Schubert, Mathias

2017-11-01

Optical changes in alumina passivated highly porous silicon slanted columnar thin films during controlled exposure to toluene vapor are reported. Electron-beam evaporation glancing angle deposition and subsequent atomic layer deposition are utilized to deposit alumina passivated nanostructured porous silicon thin films. In-situ Mueller matrix generalized spectroscopic ellipsometry in an environmental cell is then used to determine changes in optical properties of the nanostructured thin films by inspection of individual Mueller matrix elements, each of which exhibit sensitivity to adsorption. The use of a multiple-layered effective medium approximation model allows for accurate description of the inhomogeneous nature of toluene adsorption onto alumina passivated highly porous silicon slanted columnar thin films.

Phosphine Functionalization GaAs(111)A Surfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Traub, M.; Biteen, J; Michalak, D

Phosphorus-functionalized GaAs surfaces have been prepared by exposure of Cl-terminated GaAs(111)A surfaces to triethylphosphine (PEt3) or trichlorophosphine (PCl3), or by the direct functionalization of the native-oxide terminated GaAs(111)A surface with PCl3. The presence of phosphorus on each functionalized surface was confirmed by X-ray photoelectron spectroscopy. High-resolution, soft X-ray photoelectron spectroscopy was used to evaluate the As and Ga 3d regions of such surfaces. On PEt3 treated surfaces, the Ga 3d spectra exhibited a bulk Ga peak as well as peaks that were shifted to 0.35, 0.92 and 1.86 eV higher binding energy. These peaks were assigned to residual Cl-terminated Gamore » surface sites, surficial Ga2O and surficial Ga2O3, respectively. For PCl3-treated surfaces, the Ga 3d spectra displayed peaks ascribable to bulk Ga(As), Ga2O, and Ga2O3, as well as a peak shifted 0.30 eV to higher binding energy relative to the bulk signal. A peak corresponding to Ga(OH)3, observed on the Cl-terminated surface, was absent from all of the phosphine-functionalized surfaces. After reaction of the Cl-terminated GaAs(111)A surface with PCl3 or PEt3, the As 3d spectral region was free of As oxides and As0. Although native oxide-terminated GaAs surfaces were free of As oxides after reaction with PCl3, such surfaces contained detectable amounts of As0. Photoluminescence measurements indicted that phosphine-functionalized surfaces prepared from Cl-terminated GaAs(111)A surfaces had better electrical properties than the native-oxide capped GaAs(111)A surface, while the native-oxide covered surface treated with PCl3 showed no enhancement in PL intensity.« less

Nitridation of porous GaAs by an ECR ammonia plasma

NASA Astrophysics Data System (ADS)

Naddaf, M.; Hullavarad, S. S.; Ganesan, V.; Bhoraskar, S. V.

2006-02-01

The effect of surface porosity of GaAs on the nature of growth of GaN, by use of plasma nitridation of GaAs, has been investigated. Porous GaAs samples were prepared by anodic etching of n-type (110) GaAs wafers in HCl solution. Nitridation of porous GaAs samples were carried out by using an electron-cyclotron resonance-induced ammonia plasma. The formation of mixed phases of GaN was investigated using the grazing angle x-ray diffraction method. A remarkable improvement in the intensity of photoluminescence (PL) compared with that of GaN synthesized by direct nitriding of GaAs surface has been observed. The PL intensity of nitrided porous GaAs at the temperature of 380 °C was found to be about two orders of magnitude higher as compared with the directly nitrided GaAs at the temperature of 500 °C. The changes in the morphology of nitrided porous GaAs have been investigated using both scanning electron microscopy and atomic force microscopy.

GaAs VLSI technology and circuit elements for DSP

NASA Astrophysics Data System (ADS)

Mikkelson, James M.

1990-10-01

Recent progress in digital GaAs circuit performance and complexity is presented to demonstrate the current capabilities of GaAs components. High density GaAs process technology and circuit design techniques are described and critical issues for achieving favorable complexity speed power and cost tradeoffs are reviewed. Some DSP building blocks are described to provide examples of what types of DSP systems could be implemented with present GaAs technology. DIGITAL GaAs CIRCUIT CAPABILITIES In the past few years the capabilities of digital GaAs circuits have dramatically increased to the VLSI level. Major gains in circuit complexity and power-delay products have been achieved by the use of silicon-like process technologies and simple circuit topologies. The very high speed and low power consumption of digital GaAs VLSI circuits have made GaAs a desirable alternative to high performance silicon in hardware intensive high speed system applications. An example of the performance and integration complexity available with GaAs VLSI circuits is the 64x64 crosspoint switch shown in figure 1. This switch which is the most complex GaAs circuit currently available is designed on a 30 gate GaAs gate array. It operates at 200 MHz and dissipates only 8 watts of power. The reasons for increasing the level of integration of GaAs circuits are similar to the reasons for the continued increase of silicon circuit complexity. The market factors driving GaAs VLSI are system design methodology system cost power and reliability. System designers are hesitant or unwilling to go backwards to previous design techniques and lower levels of integration. A more highly integrated system in a lower performance technology can often approach the performance of a system in a higher performance technology at a lower level of integration. Higher levels of integration also lower the system component count which reduces the system cost size and power consumption while improving the system reliability

Spectral ellipsometry studying of iron's optical and electronic properties

NASA Astrophysics Data System (ADS)

Chernukha, Yevheniia; Stashchuk, Vasyl S.; Polianska, Olena; Oshtuk, Olexsandr

2014-05-01

Fe's optical and electronic properties were investigated at room temperature in different structural states. The sample's surface was explored in wide spectral range λ = 0,23-17,0 μm (E = 4,96 - 0,07 еV ) by the Beatty's spectral ellipsometry method. While an experiment was carried out ellipsometry parameters Δ and ψ were measure near the principal angle of incidence. The refraction index R , permittivity Ɛ and optical conductivity σ( hν ) , that is proportional to the interband density of electronic states, were calculated using these parameters. Fe's optical conductivities in liquid, amorphous and crystalline states were compared in this work. The optical conductivity was calculated using the published data of the iron's density of electronic states in crystalline, amorphous and liquid states for the comparison of the experimental and theoretical results. It is shown that, at structural transformations "amorphous, liquid state- crystalline state", the optical properties of metallic iron are determined, in the first turn, by the nearest neighborhood, and the electronic structure is not subjected to significant modifications.

Three-dimensional lattice rotation in GaAs nanowire growth on hydrogen-silsesquioxane covered GaAs (001) using molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Tran, Dat Q.; Pham, Huyen T.; Higashimine, Koichi; Oshima, Yoshifumi; Akabori, Masashi

2018-05-01

We report on crystallographic behaviors of inclined GaAs nanowires (NWs) self-crystallized on GaAs (001) substrate. The NWs were grown on hydrogen-silsesquioxane (HSQ) covered substrates using molecular beam epitaxy (MBE). Commonly, the epitaxial growth of GaAs < 111>B (B-polar) NWs is prominently observed on GaAs (001); however, we yielded a remarkable number of epitaxially grown GaAs < 111>A (A-polar) NWs in addition to the majorly obtained B-polar NWs. Such NW orientations are always accompanied by a typical inclined angle of 35° from (001) plane. NWs with another inclined angle of 74° were additionally observed and attributed to be < 111>-oriented, not in direct epitaxial relation with the substrate. Such 74° NWs' existence is related to first-order three-dimensional (3D) lattice rotation taking place at the very beginning of the growth. It turns out that spatially 60° lattice rotation around < 111> directions at GaAs seeds is essentially in charge of A- and B-polar 74° NWs. Transmission electron microscope observations reveal a high density of twinning in the B-polar NWs and twin-free characteristic in the A-polar NWs.

In situ monitoring of atomic layer epitaxy via optical ellipsometry

NASA Astrophysics Data System (ADS)

Lyzwa, F.; Marsik, P.; Roddatis, V.; Bernhard, C.; Jungbauer, M.; Moshnyaga, V.

2018-03-01

We report on the use of time-resolved optical ellipsometry to monitor the deposition of single atomic layers with subatomic sensitivity. Ruddlesden-Popper thin films of SrO(SrTiO3) n=4 were grown by means of metalorganic aerosol deposition in the atomic layer epitaxy mode on SrTiO3(1 0 0), LSAT(1 0 0) and DyScO3(1 1 0) substrates. The measured time dependences of ellipsometric angles, Δ(t) and Ψ(t), were described by using a simple optical model, considering the sequence of atomic layers SrO and TiO2 with corresponding bulk refractive indices. As a result, valuable online information on the atomic layer epitaxy process was obtained. Ex situ characterization techniques, i.e. transmission electron microscopy, x-ray diffraction and x-ray reflectometry verify the crystal structure and confirm the predictions of optical ellipsometry.

The electronic and optical properties of quaternary GaAs1-x-y N x Bi y alloy lattice-matched to GaAs: a first-principles study.

PubMed

Ma, Xiaoyang; Li, Dechun; Zhao, Shengzhi; Li, Guiqiu; Yang, Kejian

2014-01-01

First-principles calculations based on density functional theory have been performed for the quaternary GaAs1-x-y N x Bi y alloy lattice-matched to GaAs. Using the state-of-the-art computational method with the Heyd-Scuseria-Ernzerhof (HSE) hybrid functional, electronic, and optical properties were obtained, including band structures, density of states (DOSs), dielectric function, absorption coefficient, refractive index, energy loss function, and reflectivity. It is found that the lattice constant of GaAs1-x-y N x Bi y alloy with y/x =1.718 can match to GaAs. With the incorporation of N and Bi into GaAs, the band gap of GaAs1-x-y N x Bi y becomes small and remains direct. The calculated optical properties indicate that GaAs1-x-y N x Bi y has higher optical efficiency as it has less energy loss than GaAs. In addition, it is also found that the electronic and optical properties of GaAs1-x-y N x Bi y alloy can be further controlled by tuning the N and Bi compositions in this alloy. These results suggest promising applications of GaAs1-x-y N x Bi y quaternary alloys in optoelectronic devices.

Sensing of Streptococcus mutans by microscopic imaging ellipsometry

NASA Astrophysics Data System (ADS)

Khaleel, Mai Ibrahim; Chen, Yu-Da; Chien, Ching-Hang; Chang, Yia-Chung

2017-05-01

Microscopic imaging ellipsometry is an optical technique that uses an objective and sensing procedure to measure the ellipsometric parameters Ψ and Δ in the form of microscopic maps. This technique is well known for being noninvasive and label-free. Therefore, it can be used to detect and characterize biological species without any impact. Microscopic imaging ellipsometry was used to measure the optical response of dried Streptococcus mutans cells on a glass substrate. The ellipsometric Ψ and Δ maps were obtained with the Optrel Multiskop system for specular reflection in the visible range (λ=450 to 750 nm). The Ψ and Δ images at 500, 600, and 700 nm were analyzed using three different theoretical models with single-bounce, two-bounce, and multibounce light paths to obtain the optical constants and height distribution. The obtained images of the optical constants show different aspects when comparing the single-bounce analysis with the two-bounce or multibounce analysis in detecting S. mutans samples. Furthermore, the height distributions estimated by two-bounce and multibounce analyses of S. mutans samples were in agreement with the thickness values measured by AFM, which implies that the two-bounce and multibounce analyses can provide information complementary to that obtained by a single-bounce light path.

Design and fabrication of GaAs OMIST photodetector

NASA Astrophysics Data System (ADS)

Kang, Xuejun; Lin, ShiMing; Liao, Qiwei; Gao, Junhua; Liu, Shi'an; Cheng, Peng; Wang, Hongjie; Zhang, Chunhui; Wang, Qiming

1998-08-01

We designed and fabricated GaAs OMIST (Optical-controlled Metal-Insulator-Semiconductor Thyristor) device. Using oxidation of AlAs layer that is grown by MBE forms the Ultra- Thin semi-Insulating layer (UTI) of the GAAS OMIST. The accurate control and formation of high quality semi-insulating layer (AlxOy) are the key processes for fabricating GaAs OMIST. The device exhibits a current-controlled negative resistance region in its I-V characteristics. When illuminated, the major effect of optical excitation is the reduction of the switching voltage. If the GaAs OMIST device is biased at a voltage below its dark switching voltage Vs, sufficient incident light can switch OMIST from high impedance low current 'off' state to low impedance high current 'on' state. The absorbing material of OMIST is GaAS, so if the wavelength of incident light within 600 to approximately 850 nm can be detected effectively. It is suitable to be used as photodetector for digital optical data process. The other attractive features of GaAs OMIST device include suitable conducted current, switching voltage and power levels for OEIC, high switch speed and high sensitivity to light or current injection.

Characteristics of GaAs with inverted thermal conversion

NASA Technical Reports Server (NTRS)

Kang, C. H.; Lagowski, J.; Gatos, H. C.

1987-01-01

GaAs crystals exhibiting inverted thermal conversion (ITC) of resistivity were investigated in conjunction with standard semiinsulating (SI) GaAs regarding characteristics important in device processing. It was established that dislocation density and Si implant activation are unaffected by transformation to the ITC state. However, in ITC GaAs the controlled increase of the EL2 (native midgap donor) concentration during annealing makes it possible to attain resistivities one order of magnitude greater (e.g., about 10 to the 9th ohm cm of 300 K) than those attained in standard SI GaAs (e.g., 10 to the 7th-10 to the 8th ohm cm).

Electrodeposition of Metal on GaAs Nanowires

NASA Astrophysics Data System (ADS)

Liu, Chao; Einabad, Omid; Watkins, Simon; Kavanagh, Karen

2010-10-01

Copper (Cu) electrical contacts to freestanding gallium arsenide (GaAs) nanowires have been fabricated via electrodeposition. The nanowires are zincblende (111) oriented grown epitaxially on n-type Si-doped GaAs (111)B substrates by gold-catalyzed Vapor Liquid Solid (VLS) growth in a metal organic vapour phase epitaxy (MOVPE) reactor. The epitaxial electrodeposition process, based on previous work with bulk GaAs substrates, consists of a substrate oxide pre-etch in dilute ammonium-hydroxide carried out prior to galvanostatic electrodeposition in a pure Cu sulphate aqueous electrolyte at 20-60^oC. For GaAs nanowires, we find that Cu or Fe has a preference for growth on the gold catalyst avoiding the sidewalls. After removing gold, both metals still prefer to grow only on top of the nanowire, which has the largest potential field.

GaAs Solar Cell Radiation Handbook

NASA Technical Reports Server (NTRS)

Anspaugh, B. E.

1996-01-01

The handbook discusses the history of GaAs solar cell development, presents equations useful for working with GaAs solar cells, describes commonly used instrumentation techniques for assessing radiation effects in solar cells and fundamental processes occurring in solar cells exposed to ionizing radiation, and explains why radiation decreases the electrical performance of solar cells. Three basic elements required to perform solar array degradation calculations: degradation data for GaAs solar cells after irradiation with 1 MeV electrons at normal incidence; relative damage coefficients for omnidirectional electron and proton exposure; and the definition of the space radiation environment for the orbit of interest, are developed and used to perform a solar array degradation calculation.

Real Time Spectroscopic Ellipsometry Analysis of First Stage CuIn1−xGaxSe2 Growth: Indium-Gallium Selenide Co-Evaporation

PubMed Central

Pradhan, Puja; Aryal, Puruswottam; Attygalle, Dinesh; Ibdah, Abdel-Rahman; Koirala, Prakash; Li, Jian; Bhandari, Khagendra P.; Liyanage, Geethika K.; Ellingson, Randy J.; Heben, Michael J.; Marsillac, Sylvain; Collins, Robert W.; Podraza, Nikolas J.

2018-01-01

Real time spectroscopic ellipsometry (RTSE) has been applied for in-situ monitoring of the first stage of copper indium-gallium diselenide (CIGS) thin film deposition by the three-stage co-evaporation process used for fabrication of high efficiency thin film photovoltaic (PV) devices. The first stage entails the growth of indium-gallium selenide (In1−xGax)2Se3 (IGS) on a substrate of Mo-coated soda lime glass maintained at a temperature of 400 °C. This is a critical stage of CIGS deposition because a large fraction of the final film thickness is deposited, and as a result precise compositional control is desired in order to achieve the optimum performance of the resulting CIGS solar cell. RTSE is sensitive to monolayer level film growth processes and can provide accurate measurements of bulk and surface roughness layer thicknesses. These in turn enable accurate measurements of the bulk layer optical response in the form of the complex dielectric function ε = ε1 − iε2, spectra. Here, RTSE has been used to obtain the (ε1, ε2) spectra at the measurement temperature of 400 °C for IGS thin films of different Ga contents (x) deduced from different ranges of accumulated bulk layer thickness during the deposition process. Applying an analytical expression in common for each of the (ε1, ε2) spectra of these IGS films, oscillator parameters have been obtained in the best fits and these parameters in turn have been fitted with polynomials in x. From the resulting database of polynomial coefficients, the (ε1, ε2) spectra can be generated for any composition of IGS from the single parameter, x. The results have served as an RTSE fingerprint for IGS composition and have provided further structural information beyond simply thicknesses, for example information related to film density and grain size. The deduced IGS structural evolution and the (ε1, ε2) spectra have been interpreted as well in relation to observations from scanning electron microscopy, X

Crystal growth of device quality GaAs in space

NASA Technical Reports Server (NTRS)

Gatos, H. C.; Lagowski, J.

1979-01-01

The optimization of space processing of GaAs is described. The detailed compositional, structural, and electronic characterization of GaAs on a macro- and microscale and the relationships between growth parameters and the properties of GaAs are among the factors discussed. The key parameters limiting device performance are assessed.

Comparison null imaging ellipsometry using polarization rotator

NASA Astrophysics Data System (ADS)

Park, Sungmo; Kim, Eunsung; Kim, Jiwon; An, Ilsin

2018-05-01

In this study, two-reflection imaging ellipsometry is carried out to compare the changes in polarization states between two samples. By using a polarization rotator, the parallel and perpendicular components of polarization are easily switched between the two samples being compared. This leads to an intensity image consisting of null and off-null points depending on the difference in optical characteristics between the two samples. This technique does not require any movement of optical elements for nulling and can be used to detect defects or surface contamination for quality control of samples.

Spectroscopic vector analysis for fast pattern quality monitoring

NASA Astrophysics Data System (ADS)

Sohn, Younghoon; Ryu, Sungyoon; Lee, Chihoon; Yang, Yusin

2018-03-01

In semiconductor industry, fast and effective measurement of pattern variation has been key challenge for assuring massproduct quality. Pattern measurement techniques such as conventional CD-SEMs or Optical CDs have been extensively used, but these techniques are increasingly limited in terms of measurement throughput and time spent in modeling. In this paper we propose time effective pattern monitoring method through the direct spectrum-based approach. In this technique, a wavelength band sensitive to a specific pattern change is selected from spectroscopic ellipsometry signal scattered by pattern to be measured, and the amplitude and phase variation in the wavelength band are analyzed as a measurement index of the pattern change. This pattern change measurement technique is applied to several process steps and verified its applicability. Due to its fast and simple analysis, the methods can be adapted to the massive process variation monitoring maximizing measurement throughput.

Characterisation of semi-insulating GaAs

NASA Technical Reports Server (NTRS)

Walukiewicz, W.; Pawlowicz, L.; Lagowski, J.; Gatos, H. C.

1982-01-01

Hole and electron mobilities as functions of temperature and ionised impurity concentration are calculated for GaAs. It is shown that these calculations, when used to analyse electrical properties of semi-insulating GaAs, enable an assessment of the Fermi energy position and ionised impurity concentration to be made. In contrast to previous work, the analysis does not require any phenomenological assumptions.

Technology requirements for GaAs photovoltaic arrays

NASA Technical Reports Server (NTRS)

Scott-Monck, J.; Rockey, D.

1981-01-01

An analysis based on percent GaAs solar cell weight and cost is performed to assess the utility of this cell for future space missions. It is shown that the GaAs substrate cost and the end-of-life (EOL) advantage the cell can provide over the space qualified silicon solar cell are the dominant factors determining potential use. Examples are presented to show that system level advantages resulting from reduction in solar panel area may warrant the use of GaAs at its current weight and projected initial cost provided the EOL advantage over silicon is at least 20 percent.

Crystal Growth of Device Quality Gaas in Space

NASA Technical Reports Server (NTRS)

Gatos, H. C.

1985-01-01

The GaAs research evolves about these key thrust areas. The overall program combines: (1) studies of crystal growth on novel approaches to engineering of semiconductor material (i.e., GaAs and related compounds); (2) investigation and correlation of materials properties and electronic characteristics on a macro- and microscale; and (3) investigation of electronic properties and phenomena controlling device applications and device performance. This effort is aimed at the essential ground-based program which would insure successful experimentation with and eventually processing of GaAs in near zero gravity environment. It is believed that this program addresses in a unique way materials engineering aspects which bear directly on the future exploitation of the potential of GaAs and related materials in device and systems applications.

Crystal growth of device quality GaAs in space

NASA Technical Reports Server (NTRS)

Gatos, H. C.; Lagowski, J.

1984-01-01

The crystal growth, device processing and device related properties and phenomena of GaAs are investigated. Our GaAs research evolves about these key thrust areas. The overall program combines: (1) studies of crystal growth on novel approaches to engineering of semiconductor materials (i.e., GaAs and related compounds); (2) investigation and correlation of materials properties and electronic characteristics on a macro- and microscale; (3) investigation of electronic properties and phenomena controlling device applications and device performance. The ground based program is developed which would insure successful experimentation with and eventually processing of GaAs in a near zero gravity environment.

Supernormal hardness increase of dilute Ga(As, N) thin films

NASA Astrophysics Data System (ADS)

Berggren, Jonas; Hanke, Michael; Luna, Esperanza; Trampert, Achim

2017-03-01

Hardness of epitaxial GaAs1-xNx films on GaAs(001) with different film thicknesses, varying from 80 to 700 nm, and nitrogen compositions x between zero (pure GaAs) and 0.031, were studied by means of nano-indentation. As a result, a disproportionate and monotonic increase by 17% in hardness was proved in the dilute range from GaAs to GaAs0.969N0.031. We are tracing this observation to solid solution strengthening, an extrinsic effect based on dislocation pinning due to interstitial nitrogen. On the other hand, intrinsic effects related to different electronegativities of As and N (i.e., altered bonding conditions) could be ruled out. Furthermore, in tensilely strained GaAs1-xNx layers, the appearance of cracks acts as the main strain relieving mechanism. A correlation between cracking and hardness reduction is investigated and discussed as a further relaxation pathway.

Ellipsometry study of optical parameters of AgIn5S8 crystals

NASA Astrophysics Data System (ADS)

Isik, Mehmet; Gasanly, Nizami

2015-12-01

AgIn5S8 crystals grown by Bridgman method were characterized for optical properties by ellipsometry measurements. Spectral dependence of optical parameters; real and imaginary parts of the pseudodielectric function, pseudorefractive index, pseudoextinction coefficient, reflectivity and absorption coefficient were obtained from ellipsometry experiments carried out in the 1.2-6.2 eV range. Direct band gap energy of 1.84 eV was found from the analysis of absorption coefficient vs. photon energy. The oscillator energy, dispersion energy and zero-frequency refractive index, high-frequency dielectric constant values were found from the analysis of the experimental data using Wemple-DiDomenico and Spitzer-Fan models. Crystal structure and atomic composition ratio of the constituent elements in the AgIn5S8 crystal were revealed from structural characterization techniques of X-ray diffraction and energy dispersive spectroscopy.

Doping assessment in GaAs nanowires.

PubMed

Goktas, N Isik; Fiordaliso, E M; LaPierre, R R

2018-06-08

Semiconductor nanowires (NWs) are a candidate technology for future optoelectronic devices. One of the critical issues in NWs is the control of impurity doping for the formation of p-n junctions. In this study, beryllium (p-type dopant) and tellurium (n-type dopant) in self-assisted GaAs NWs was studied. The GaAs NWs were grown on (111) Si by molecular beam epitaxy using the self-assisted method. The dopant incorporation in the self-assisted GaAs NWs was investigated using Raman spectroscopy, photoluminescence, secondary ion mass spectrometry and electron holography. Be-doped NWs showed similar carrier concentration as compared to thin film (TF) standards. However, Te-doped NWs showed at least a one order of magnitude lower carrier concentration as compared to TF standards. Dopant incorporation mechanisms in NWs are discussed.

Doping assessment in GaAs nanowires

NASA Astrophysics Data System (ADS)

Isik Goktas, N.; Fiordaliso, E. M.; LaPierre, R. R.

2018-06-01

Semiconductor nanowires (NWs) are a candidate technology for future optoelectronic devices. One of the critical issues in NWs is the control of impurity doping for the formation of p–n junctions. In this study, beryllium (p-type dopant) and tellurium (n-type dopant) in self-assisted GaAs NWs was studied. The GaAs NWs were grown on (111) Si by molecular beam epitaxy using the self-assisted method. The dopant incorporation in the self-assisted GaAs NWs was investigated using Raman spectroscopy, photoluminescence, secondary ion mass spectrometry and electron holography. Be-doped NWs showed similar carrier concentration as compared to thin film (TF) standards. However, Te-doped NWs showed at least a one order of magnitude lower carrier concentration as compared to TF standards. Dopant incorporation mechanisms in NWs are discussed.

Reflectometry-Ellipsometry Reveals Thickness, Growth Rate, and Phase Composition in Oxidation of Copper.

PubMed

Diaz Leon, Juan J; Fryauf, David M; Cormia, Robert D; Zhang, Min-Xian Max; Samuels, Kathryn; Williams, R Stanley; Kobayashi, Nobuhiko P

2016-08-31

The oxidation of copper is a complicated process. Copper oxide develops two stable phases at room temperature and standard pressure (RTSP): cuprous oxide (Cu2O) and cupric oxide (CuO). Both phases have different optical and electrical characteristics that make them interesting for applications such as solar cells or resistive switching devices. For a given application, it is necessary to selectively control oxide thickness and cupric/cuprous oxide phase volume fraction. The thickness and composition of a copper oxide film growing on the surface of copper widely depend on the characteristics of as-deposited copper. In this Research Article, two samples, copper films prepared by two different deposition techniques, electron-beam evaporation and sputtering, were studied. As the core part of the study, the formation of the oxidized copper was analyzed routinely over a period of 253 days using spectroscopic polarized reflectometry-spectroscopic ellipsometry (RE). An effective medium approximation (EMA) model was used to fit the RE data. The RE measurements were complemented and validated by using X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and X-ray diffraction (XRD). Our results show that the two samples oxidized under identical laboratory ambient conditions (RTSP, 87% average relative humidity) developed unique oxide films following an inverse-logarithmic growth rate with thickness and composition different from each other over time. Discussion is focused on the ability of RE to simultaneously extract thickness (i.e., growth rate) and composition of copper oxide films and on plausible physical mechanisms responsible for unique oxidation habits observed in the two copper samples. It appears that extended surface characteristics (i.e., surface roughness and grain boundaries) and preferential crystalline orientation of as-deposited polycrystalline copper films control the growth kinetics of the copper oxide film. Analysis based on a noncontact

ELLIPSOMETRY OF ELECTROCHEMICAL SURFACE LAYERS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Muller, R.H.

1977-06-01

Ellipsometry is concerned with the analysis and interpretation of changes in the state of polarization caused by reflection. The technique has found increasing interest in recent years for the measurement of thin films because it is unusually sensitive, disturbs the object minimally and can be applied to surfaces contained in any optically transparent medium. Film thicknesses amenable to measurement range from fractional monoatomic coverage to microscopic thicknesses. The measurement of changes in the state of polarization of light due to reflection provides an unusually sensitive tool for observing surface layers in any optically transparent environment. A fast, self-compensating ellipsometer hasmore » been used to observe the electrochemical formation of reacted surface layers. The optical effect of mass-transport boundary layers and component imperfections have been taken into account in the interpretation of results.« less

GaAs photoconductive semiconductor switch

DOEpatents

Loubriel, Guillermo M.; Baca, Albert G.; Zutavern, Fred J.

1998-01-01

A high gain, optically triggered, photoconductive semiconductor switch (PCSS) implemented in GaAs as a reverse-biased pin structure with a passivation layer above the intrinsic GaAs substrate in the gap between the two electrodes of the device. The reverse-biased configuration in combination with the addition of the passivation layer greatly reduces surface current leakage that has been a problem for prior PCSS devices and enables employment of the much less expensive and more reliable DC charging systems instead of the pulsed charging systems that needed to be used with prior PCSS devices.

Structure of high-index GaAs surfaces - the discovery of the stable GaAs(2511) surface

NASA Astrophysics Data System (ADS)

Jacobi, K.; Geelhaar, L.; Márquez, J.

We present a brief overview of surface structures of high-index GaAs surfaces, putting emphasis on recent progress in our own laboratory. By adapting a commercial scanning tunneling microscope (STM) to our molecular beam epitaxy and ultra high vacuum analysis chamber system, we have been able to atomically resolve the GaAs( {1} {1} {3})B(8 ×1), (114)Aα2(2×1), (137), (3715), and (2511) surface structures. In cooperation with P. Kratzer and M. Scheffler from the Theory Department of the Fritz-Haber Institute we determined the structure of some of these surfaces by comparing total-energy calculations and STM image simulations with the atomically resolved STM images. We present the results for the {112}, {113}, and {114} surfaces. Then we describe what led us to proceed into the inner parts of the stereographic triangle and to discover the hitherto unknown stable GaAs(2511) surface.

Electrode pattern design for GaAs betavoltaic batteries

NASA Astrophysics Data System (ADS)

Haiyang, Chen; Jianhua, Yin; Darang, Li

2011-08-01

The sensitivities of betavoltaic batteries and photovoltaic batteries to series and parallel resistance are studied. Based on the study, an electrode pattern design principle of GaAs betavoltaic batteries is proposed. GaAs PIN junctions with and without the proposed electrode pattern are fabricated and measured under the illumination of 63Ni. Results show that the proposed electrode can reduce the backscattering and shadowing for the beta particles from 63Ni to increase the GaAs betavoltaic battery short circuit currents effectively but has little impact on the fill factors and ideal factors.

GaAs core--shell nanowires for photovoltaic applications.

PubMed

Czaban, Josef A; Thompson, David A; LaPierre, Ray R

2009-01-01

We report the use of Te as an n-type dopant in GaAs core-shell p-n junction nanowires for use in photovoltaic devices. Te produced significant change in the morphology of GaAs nanowires grown by the vapor-liquid-solid process in a molecular beam epitaxy system. The increase in radial growth of nanowires due to the surfactant effect of Te had a significant impact on the operating characteristics of photovoltaic devices. A decrease in solar cell efficiency occurred when the Te-doped GaAs growth duration was increased.

Understanding and Curing Structural Defects in Colloidal GaAs Nanocrystals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Srivastava, Vishwas; Liu, Wenyong; Janke, Eric M.

2017-02-22

Nearly three decades since the first report on the synthesis of colloidal GaAs nanocrystals (NCs), the preparation and properties of this material remain highly controversial. Traditional synthetic routes either fail to produce the GaAs phase or result in materials that do not show expected optical properties such as excitonic transitions. In this work, we demonstrate a variety of synthetic routes toward crystalline GaAs NCs. By using a combination of Raman, EXAFS and transient absorption spectroscopies, we conclude that unusual optical properties of 2 colloidal GaAs NCs can be related to the presence of vacancies and lattice disorder. We introduce novelmore » molten salt based annealing approach to alleviate these structural defects and show the emergence of size-dependent excitonic transitions in colloidal GaAs quantum dots.« less

GaAs homojunction solar cell development

NASA Technical Reports Server (NTRS)

Flood, D. J.; Swartz, C. K.; Hart, R. E., Jr.

1980-01-01

The Lincoln Laboratory n(+)/p/p(+) GaAs shallow homojunction cell structure was successfully demonstrated on 2 by 2 cm GaAs substrates. Air mass zero efficiencies of the seven cells produced to date range from 13.6 to 15.6 percent. Current voltage (I-V) characteristics, spectral response, and measurements were made on all seven cells. Preliminary analysis of 1 MeV electron radiation damage data indicate excellent radiation resistance for these cells.

Characterization on Smart Optics Using Ellipsometry

NASA Technical Reports Server (NTRS)

Song, Kyo D.

2002-01-01

Recently, NASA Langley Research Center developed a smart active optical concept to filter narrow band pass or to control optical intensity. To characterize developed smart optics materials, we have measured thickness and reflection properties of the materials using a WVASE32 ellipsometry. This project allowed us to: (1) prepare the smart optical materials for measurement of thickness and optical properties at NASA Langley Research Center; (2) measure thickness and optical properties of the smart optical materials; (3) evaluate the measured properties in terms of applications for narrow band-pass filters. The outcomes of this research provide optical properties and physical properties of the smart optics on a selected spectral range. The applications of this development were used for field-controlled spectral smart filters.

Spectroscopic characterization of III-V semiconductor nanomaterials

NASA Astrophysics Data System (ADS)

Crankshaw, Shanna Marie

through a novel spectroscopic technique first formulated for the rather different purpose of dispersion engineering for slow-light schemes. The frequency-resolved technique combined with the unusual (110) quantum wells in a furthermore atypical waveguide experimental geometry has revealed fascinating behavior of electron spin splitting which points to the possibility of optically orienting electron spins with linearly polarized light---an experimental result supporting a theoretical description of the phenomenon itself only a few years old. Lastly, to explore a space of further-restricted dimensionality, the final chapters describe InP semiconductor nanowires with dimensions small enough to be considered truly one-dimensional. Like the bulk GaAs of the first few chapters, the InP nanowires here crystallize in a wurtzite structure. In the InP nanowire case, though, the experimental techniques explored for characterization are temperature-dependent time-integrated photoluminescence at the single-wire level (including samples with InAsP insertions) and time-resolved photoluminescence at the ensemble level. The carrier dynamics revealed through these time-resolved studies are the first of their kind for wurtzite InP nanowires. The chapters are thus ordered as a progression from three (bulk), to two (quantum well), to one (nanowire), to zero dimensions (axially-structured nanowire), with the uniting theme the emphasis on connecting the semiconductor nanomaterials' crystallinity to its exhibited properties by relevant experimental spectroscopic techniques, whether these are standard methods or effectively invented for the case at hand.

Gate Drain Underlapped-PNIN-GAA-TFET for Comprehensively Upgraded Analog/RF Performance

NASA Astrophysics Data System (ADS)

Madan, Jaya; Chaujar, Rishu

2017-02-01

This work integrates the merits of gate-drain underlapping (GDU) and N+ source pocket on cylindrical gate all around tunnel FET (GAA-TFET) to form GDU-PNIN-GAA-TFET. It is analysed that the source pocket located at the source-channel junction narrows the tunneling barrier width at the tunneling junction and thereby enhances the ON-state current of GAA-TFET. Further, it is obtained that the GDU resists the extension of carrier density (built-up under the gated region) towards the drain side (under the underlapped length), thereby suppressing the ambipolar current and reducing the parasitic capacitances of GAA-TFET. Consequently, the amalgamated merits of both engineering schemes are obtained in GDU-PNIN-GAA-TFET that thus conquers the greatest challenges faced by TFET. Thus, GDU-PNIN-GAA-TFET results in an up-gradation in the overall performance of GAA-TFET. Moreover, it is realised that the RF figure of merits FOMs such as cut-off frequency (fT) and maximum oscillation frequency (fMAX) are also considerably improved with integration of source pocket on GAA-TFET. Thus, the improved analog and RF performance of GDU-PNIN-GAA-TFET makes it ideal for low power and high-speed applications.

Lateral epitaxial overgowth of GaAs by organometallic chemical vapor deposition

NASA Technical Reports Server (NTRS)

Gale, R. P.; Mcclelland, R. W.; Fan, J. C. C.; Bozler, C. O.

1982-01-01

Lateral epitaxial overgrowth of GaAs by organometallic chemical vapor deposition has been demonstrated. Pyrolytic decomposition of trimethylgallium and arsine, without the use of HCl, was used to deposit GaAs on substrates prepared by coating (110) GaAs wafers with SiO2, then using photolithography to open narrow stripes in the oxide. Lateral overgrowth was seeded by epitaxial deposits formed on the GaAs surfaces exposed by the stripe openings. The extent of lateral overgrowth was investigated as a function of stripe orientation and growth temperature. Ratios of lateral to vertical growth rates greater than five have been obtained. The lateral growth is due to surface-kinetic control for the two-dimensional growth geometry studied. A continuous epitaxial GaAs layer 3 microns thick has been grown over a patterned mask on a GaAs substrate and then cleaved from the substrate.

Single shot ultrafast dynamic ellipsometry (UDE) of laser-driven shocks in single crystal explosives

DOE Office of Scientific and Technical Information (OSTI.GOV)

Whitley, Von H; Mcgrane, Shawn D; Moore, David S

2009-01-01

We report on the first experiments to measure states in shocked energetic single crystals with dynamic ellipsometry. We demonstrate that these ellipsometric techniques can produce reasonable Hugoniot values using small amounts of crystalline RDX and PETN. Pressures, particle velocities and shock velocities obtained using shocked ellipsometry are comparable to those found using gas-gun flyer plates and molecular dynamics calculations. The adaptation of the technique from uniform thin films of polymers to thick non-perfect crystalline materials was a significant achievement. Correct sample preparation proved to be a crucial component. Through trial and error, we were able to resolve polishing issues, samplemore » quality problems, birefringence effects and mounting difficulties that were not encountered using thin polymer films.« less

GaAs photoconductive semiconductor switch

DOEpatents

Loubriel, G.M.; Baca, A.G.; Zutavern, F.J.

1998-09-08

A high gain, optically triggered, photoconductive semiconductor switch (PCSS) implemented in GaAs as a reverse-biased pin structure with a passivation layer above the intrinsic GaAs substrate in the gap between the two electrodes of the device is disclosed. The reverse-biased configuration in combination with the addition of the passivation layer greatly reduces surface current leakage that has been a problem for prior PCSS devices and enables employment of the much less expensive and more reliable DC charging systems instead of the pulsed charging systems that needed to be used with prior PCSS devices. 5 figs.

Panel fabrication utilizing GaAs solar cells

NASA Technical Reports Server (NTRS)

Mardesich, N.

1984-01-01

The development of the GaAs solar cells for space applications is described. The activities in the fabrication of GaAs solar panels are outlined. Panels were fabricated while introducing improved quality control, soldering laydown and testing procedures. These panels include LIPS II, San Marco Satellite, and a low concentration panel for Rockwells' evaluation. The panels and their present status are discussed.

Natural organic UV-absorbent coatings based on cellulose and lignin: designed effects on spectroscopic properties.

PubMed

Hambardzumyan, Arayik; Foulon, Laurence; Chabbert, Brigitte; Aguié-Béghin, Véronique

2012-12-10

Novel nanocomposite coatings composed of cellulose nanocrystals (CNCs) and lignin (either synthetic or fractionated from spruce and corn stalks) were prepared without chemical modification or functionalization (via covalent attachment) of one of the two biopolymers. The spectroscopic properties of these coatings were investigated by UV-visible spectrophotometry and spectroscopic ellipsometry. When using the appropriate weight ratio of CNC/lignin (R), these nanocomposite systems exhibited high-performance optical properties, high transmittance in the visible spectrum, and high blocking in the UV spectrum. Atomic force microscopy analysis demonstrated that these coatings were smooth and homogeneous, with visible dispersed lignin nodules in a cellulosic matrix. It was also demonstrated that the introduction of nanoparticles into the medium increases the weight ratio and the CNC-specific surface area, which allows better dispersion of the lignin molecules throughout the solid film. Consequently, the larger molecular expansion of these aromatic polymers on the surface of the cellulosic nanoparticles dislocates the π-π aromatic aggregates, which increases the extinction coefficient and decreases the transmittance in the UV region. These nanocomposite coatings were optically transparent at visible wavelengths.

GaAs Photovoltaics on Polycrystalline Ge Substrates

NASA Technical Reports Server (NTRS)

Wilt, David M.; Pal, AnnaMaria T.; McNatt, Jeremiah S.; Wolford, David S.; Landis, Geoffrey A.; Smith, Mark A.; Scheiman, David; Jenkins, Phillip P.; McElroy Bruce

2007-01-01

High efficiency III-V multijunction solar cells deposited on metal foil or even polymer substrates can provide tremendous advantages in mass and stowage, particularly for planetary missions. As a first step towards that goal, poly-crystalline p/i/n GaAs solar cells are under development on polycrystalline Ge substrates. Organo Metallic Vapor Phase Epitaxy (OMVPE) parameters for pre-growth bake, nucleation and deposition have been examined. Single junction p/i/n GaAs photovoltaic devices, incorporating InGaP front and back window layers, have been grown and processed. Device performance has shown a dependence upon the thickness of a GaAs buffer layer deposited between the Ge substrate and the active device structure. A thick (2 m) GaAs buffer provides for both increased average device performance as well as reduced sensitivity to variations in grain size and orientation. Illumination under IR light (lambda > 1 micron), the cells showed a Voc, demonstrating the presence of an unintended photoactive junction at the GaAs/Ge interface. The presence of this junction limited the efficiency to approx.13% (estimated with an anti-refection coating) due to the current mismatch and lack of tunnel junction interconnect.

Comparisons of single event vulnerability of GaAs SRAMS

NASA Astrophysics Data System (ADS)

Weatherford, T. R.; Hauser, J. R.; Diehl, S. E.

1986-12-01

A GaAs MESFET/JFET model incorporated into SPICE has been used to accurately describe C-EJFET, E/D MESFET and D MESFET/resistor GaAs memory technologies. These cells have been evaluated for critical charges due to gate-to-drain and drain-to-source charge collection. Low gate-to-drain critical charges limit conventional GaAs SRAM soft error rates to approximately 1E-6 errors/bit-day. SEU hardening approaches including decoupling resistors, diodes, and FETs have been investigated. Results predict GaAs RAM cell critical charges can be increased to over 0.1 pC. Soft error rates in such hardened memories may approach 1E-7 errors/bit-day without significantly reducing memory speed. Tradeoffs between hardening level, performance and fabrication complexity are discussed.

Prediction of dislocation generation during Bridgman growth of GaAs crystals

NASA Technical Reports Server (NTRS)

Tsai, C. T.; Yao, M. W.; Chait, Arnon

1992-01-01

Dislocation densities are generated in GaAs single crystals due to the excessive thermal stresses induced by temperature variations during growth. A viscoplastic material model for GaAs, which takes into account the movement and multiplication of dislocations in the plastic deformation, is developed according to Haasen's theory. The dislocation density is expressed as an internal state variable in this dynamic viscoplastic model. The deformation process is a nonlinear function of stress, strain rate, dislocation density and temperature. The dislocation density in the GaAs crystal during vertical Bridgman growth is calculated using a nonlinear finite element model. The dislocation multiplication in GaAs crystals for several temperature fields obtained from thermal modeling of both the GTE GaAs experimental data and artificially designed data are investigated.

Prediction of dislocation generation during Bridgman growth of GaAs crystals

NASA Astrophysics Data System (ADS)

Tsai, C. T.; Yao, M. W.; Chait, Arnon

1992-11-01

Dislocation densities are generated in GaAs single crystals due to the excessive thermal stresses induced by temperature variations during growth. A viscoplastic material model for GaAs, which takes into account the movement and multiplication of dislocations in the plastic deformation, is developed according to Haasen's theory. The dislocation density is expressed as an internal state variable in this dynamic viscoplastic model. The deformation process is a nonlinear function of stress, strain rate, dislocation density and temperature. The dislocation density in the GaAs crystal during vertical Bridgman growth is calculated using a nonlinear finite element model. The dislocation multiplication in GaAs crystals for several temperature fields obtained from thermal modeling of both the GTE GaAs experimental data and artificially designed data are investigated.

Crystal growth of device quality GaAs in space

NASA Technical Reports Server (NTRS)

Gatos, H. C.; Lagowski, J.

1983-01-01

GaAs device technology has recently reached a new phase of rapid advancement, made possible by the improvement of the quality of GaAs bulk crystals. At the same time, the transition to the next generation of GaAs integrated circuits and optoelectronic systems for commercial and government applications hinges on new quantum steps in three interrelated areas: crystal growth, device processing and device-related properties and phenomena. Special emphasis is placed on the establishment of quantitative relationships among crystal growth parameters-material properties-electronic properties and device applications. The overall program combines studies of crystal growth on novel approaches to engineering of semiconductor material (i.e., GaAs and related compounds); investigation and correlation of materials properties and electronic characteristics on a macro- and microscale; and investigation of electronic properties and phenomena controlling device applications and device performance.

Sidewall GaAs tunnel junctions fabricated using molecular layer epitaxy

PubMed Central

Ohno, Takeo; Oyama, Yutaka

2012-01-01

In this article we review the fundamental properties and applications of sidewall GaAs tunnel junctions. Heavily impurity-doped GaAs epitaxial layers were prepared using molecular layer epitaxy (MLE), in which intermittent injections of precursors in ultrahigh vacuum were applied, and sidewall tunnel junctions were fabricated using a combination of device mesa wet etching of the GaAs MLE layer and low-temperature area-selective regrowth. The fabricated tunnel junctions on the GaAs sidewall with normal mesa orientation showed a record peak current density of 35 000 A cm-2. They can potentially be used as terahertz devices such as a tunnel injection transit time effect diode or an ideal static induction transistor. PMID:27877466

Heteroepitaxial growth of GaAs on (100) Ge/Si using migration enhanced epitaxy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tanoto, H.; Loke, W. K.; Yoon, S. F.

In this paper, heteroepitaxial growth of GaAs on nominal (100) Ge/Si substrate was investigated. The root-mean square surface roughness of the sample where the first few monolayers of the GaAs were nucleated by migration enhanced epitaxy (MEE) is four times smaller compared to the sample without such a process, indicating better surface planarity. From the (004) x-ray diffraction rocking curve measurement, the full width at half maximum of the GaAs layer nucleated by MEE is 40% lower compared to that of the GaAs layer without such a process, indicating better crystal quality. Furthermore, it was found that the sample wheremore » the GaAs layer was nucleated by MEE experienced early relaxation. As the MEE process promotes two-dimensional growth, the GaAs layer where nucleation was initiated by such a process has fewer islandlike formations. This leads to a pseudomorphically grown GaAs layer, which experiences higher strain compared to the GaAs layer with more islandlike formations, where most relaxation occurs on the free surface of the islands. Therefore, for the same layer thickness, the GaAs layer on (100) Ge/Si substrate where nucleation was initiated by MEE relaxed first.« less

Formation of pentacene wetting layer on the SiO2 surface and charge trap in the wetting layer.

PubMed

Kim, Chaeho; Jeon, D

2008-09-01

We studied the early-stage growth of vacuum-evaporated pentacene film on a native SiO(2) surface using atomic force microscopy and in-situ spectroscopic ellipsometry. Pentacene deposition prompted an immediate change in the ellipsometry spectra, but atomic force microscopy images of the early stage films did not show a pentacene-related morphology other than the decrease in the surface roughness. This suggested that a thin pentacene wetting layer was formed by pentacene molecules lying on the surface before the crystalline islands nucleated. Growth simulation based on the in situ spectroscopic ellipsometry spectra supported this conclusion. Scanning capacitance microscopy measurement indicated the existence of trapped charges in the SiO(2) and pentacene wetting layer.

Long-term radiation effects on GaAs solar cell characteristics

NASA Technical Reports Server (NTRS)

Heinbockel, J. H.; Doviak, M. J.

1978-01-01

This report investigates preliminary design considerations which should be considered for a space experiment involving Gallium Arsenide (GaAs) solar cells. The electron radiation effects on GaAs solar cells were conducted in a laboratory environment, and a statistical analysis of the data is presented. In order to augment the limited laboratory data, a theoretical investigation of the effect of radiation on GaAs solar cells is also developed. The results of this study are empirical prediction equations which can be used to estimate the actual damage of electrical characteristics in a space environment. The experimental and theoretical studies also indicate how GaAs solar cell parameters should be designed in order to withstand the effects of electron radiation damage.

GaAs thin films and methods of making and using the same

DOEpatents

Boettcher, Shannon; Ritenour, Andrew; Boucher, Jason; Greenaway, Ann

2016-06-14

Disclosed herein are embodiments of methods for making GaAs thin films, such as photovoltaic GaAs thin films. The methods disclosed herein utilize sources, precursors, and reagents that do not produce (or require) toxic gas and that are readily available and relatively low in cost. In some embodiments, the methods are readily scalable for industrial applications and can provide GaAs thin films having properties that are at least comparable to or potentially superior to GaAs films obtained from conventional methods.

High-efficiency thin-film GaAs solar cells, phase2

NASA Technical Reports Server (NTRS)

Yeh, Y. C. M.

1981-01-01

Thin GaAs epi-layers with good crystallographic quality were grown using a (100) Si-substrate on which a thin Ge epi-interlayer was grown by CVD from germane. Both antireflection-coated metal oxide semiconductor (AMOS) and n(+)/p homojunction structures were studied. The AMOS cells were fabricated on undoped-GaAs epi-layers deposited on bulk poly-Ge substrates using organo-metallic CVD film-growth, with the best achieved AM1 conversion efficiency being 9.1%. Both p-type and n(+)-type GaAs growth were optimized using 50 ppm dimethyl zinc and 1% hydrogen sulfide, respectively. A direct GaAs deposition method in fabricating ultra-thin top layer, epitaxial n(+)/p shallow homojunction solar cells on (100) GaAs substrates (without anodic thinning) was developed to produce large area (1 sq/cm) cells, with 19.4% AM1 conversion efficiency achieved. Additionally, an AM1 conversion efficiency of 18.4% (17.5% with 5% grid coverage) was achieved for a single crystal GaAs n(+)/p cell grown by OM-CVD on a Ge wafer.

Immersion transmission ellipsometry (ITE) for the determination of orientation gradients in photoalignment layers

NASA Astrophysics Data System (ADS)

Jung, C. C.; Stumpe, J.

2014-09-01

The capability of the method of immersion transmission ellipsometry (ITE) (Jung et al. Int Patent WO, 2004/109260) to not only determine three-dimensional refractive indices in anisotropic thin films (which was already possible in the past), but even their gradients along the z-direction (perpendicular to the film plane) is investigated in this paper. It is shown that the determination of orientation gradients in deep-sub-μm films becomes possible by applying ITE in combination with reflection ellipsometry. The technique is supplemented by atomic force microscopy for measuring the film thickness. For a photo-oriented thin film, no gradient was found, as expected. For a photo-oriented film, which was subsequently annealed in a nematic liquid crystalline phase, an order was found similar to the one applied in vertically aligned nematic displays, with a tilt angle varying along the z-direction. For fresh films, gradients were only detected for the refractive index perpendicular to the film plane, as expected.

Influence of arsenic flow on the crystal structure of epitaxial GaAs grown at low temperatures on GaAs (100) and (111)A substrates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Galiev, G. B.; Klimov, E. A.; Vasiliev, A. L.

The influence of arsenic flow in a growth chamber on the crystal structure of GaAs grown by molecular-beam epitaxy at a temperature of 240°C on GaAs (100) and (111)A substrates has been investigated. The flow ratio γ of arsenic As4 and gallium was varied in the range from 16 to 50. GaAs films were either undoped, or homogeneously doped with silicon, or contained three equidistantly spaced silicon δ-layers. The structural quality of the annealed samples has been investigated by transmission electron microscopy. It is established for the first time that silicon δ-layers in “low-temperature” GaAs serve as formation centers ofmore » arsenic precipitates. Their average size, concentration, and spatial distribution are estimated. The dependence of the film structural quality on γ is analyzed. Regions 100–150 nm in size have been revealed in some samples and identified (by X-ray microanalysis) as pores. It is found that, in the entire range of γ under consideration, GaAs films on (111)A substrates have a poorer structural quality and become polycrystalline beginning with a thickness of 150–200 nm.« less

Growth and characteristics of p-type doped GaAs nanowire

NASA Astrophysics Data System (ADS)

Li, Bang; Yan, Xin; Zhang, Xia; Ren, Xiaomin

2018-05-01

The growth of p-type GaAs nanowires (NWs) on GaAs (111) B substrates by metal-organic chemical vapor deposition (MOCVD) has been systematically investigated as a function of diethyl zinc (DEZn) flow. The growth rate of GaAs NWs was slightly improved by Zn-doping and kink is observed under high DEZn flow. In addition, the I–V curves of GaAs NWs has been measured and the p-type dope concentration under the II/III ratio of 0.013 and 0.038 approximated to 1019–1020 cm‑3. Project supported by the National Natural Science Foundation of China (Nos. 61376019, 61504010, 61774021) and the Fund of State Key Laboratory of Information Photonics and Optical Communications (Beijing University of Posts and Telecommunications), China (Nos. IPOC2017ZT02, IPOC2017ZZ01).

Sulfur doping of GaAs with (NH4)2Sx solution

NASA Astrophysics Data System (ADS)

Lee, Jong-Lam

1999-01-01

A novel technique for sulfur doping to GaAs was demonstrated. The surface of GaAs was treated with (NH4)2Sx solution, subsequent to annealing using either furnace or rapid thermal processing. Sulfur atoms adsorbed at the surface of GaAs during the (NH4)2Sx treatment diffuse into GaAs during the annealing. The diffusion profiles of sulfur in both types of annealing treatments show a concave shape from the GaAs surface. Diffusion constants of sulfur determined using the Boltzmann-Matano technique increase with the decrease of sulfur concentration via the depth from the surface of GaAs. This suggests that immobile sulfur donor SAs+ forms at the near surface interacts with a Ga divacancy, and results in the production of mobile As interstitials, IAs. The IAs moves fast toward the inside of GaAs and kickout the SAs+ donor, producing a fast diffusing species of interstitial S atoms. The diffusion coefficients of sulfur determined are 2.5×10-14 cm2/s at 840 °C and 5×10-12 cm2/s at 900 °C. The sulfur doping technique is applied to the fabrication of metal-semiconductor field-effect transistors (MESFETs). The MESFETs with 1.0 μm gate length exhibit transconductance of 190 mS/mm, demonstrating the applicability of this technique to the formation of active channel layer of MESFETs.

Surface and Thin Film Analysis during Metal Organic Vapour Phase Epitaxial Growth

NASA Astrophysics Data System (ADS)

Richter, Wolfgang

2007-06-01

In-situ analysis of epitaxial growth is the essential ingredient in order to understand the growth process, to optimize growth and last but not least to monitor or even control the epitaxial growth on a microscopic scale. In MBE (molecular beam epitaxy) in-situ analysis tools existed right from the beginning because this technique developed from Surface Science technology with all its electron based analysis tools (LEED, RHEED, PES etc). Vapour Phase Epitaxy, in contrast, remained for a long time in an empirical stage ("alchemy") because only post growth characterisations like photoluminescence, Hall effect and electrical conductivity were available. Within the last two decades, however, optical techniques were developed which provide similar capabilities as in MBE for Vapour Phase growth. I will discuss in this paper the potential of Reflectance Anisotropy Spectroscopy (RAS) and Spectroscopic Ellipsometry (SE) for the growth of thin epitaxial semiconductor layers with zincblende (GaAs etc) and wurtzite structure (GaN etc). Other techniques and materials will be also mentioned.

Relation between trinucleotide GAA repeat length and sensory neuropathy in Friedreich's ataxia.

PubMed

Santoro, L; De Michele, G; Perretti, A; Crisci, C; Cocozza, S; Cavalcanti, F; Ragno, M; Monticelli, A; Filla, A; Caruso, G

1999-01-01

To verify if GAA expansion size in Friedreich's ataxia could account for the severity of sensory neuropathy. Retrospective study of 56 patients with Friedreich's ataxia selected according to homozygosity for GAA expansion and availability of electrophysiological findings. Orthodromic sensory conduction velocity in the median nerve was available in all patients and that of the tibial nerve in 46 of them. Data of sural nerve biopsy and of a morphometric analysis were available in 12 of the selected patients. The sensory action potential amplitude at the wrist (wSAP) and at the medial malleolus (m mal SAP) and the percentage of myelinated fibres with diameter larger than 7, 9, and 11 microm in the sural nerve were correlated with disease duration and GAA expansion size on the shorter (GAA1) and larger (GAA2) expanded allele in each pair. Pearson's correlation test and stepwise multiple regression were used for statistical analysis. A significant inverse correlation between GAA1 size and wSAP, m mal SAP, and percentage of myelinated fibres was found. Stepwise multiple regression showed that GAA1 size significantly affects electrophysiological and morphometric data, whereas duration of disease has no effect. The data suggest that the severity of the sensory neuropathy is probably genetically determined and that it is not progressive.

Comparison of photoemission characteristics between square and circular wire array GaAs photocathodes.

PubMed

Deng, Wenjuan; Peng, Xincun; Zou, Jijun; Wang, Weilu; Liu, Yun; Zhang, Tao; Zhang, Yijun; Zhang, Daoli

2017-11-10

Two types of negative electron affinity gallium arsenide (GaAs) wire array photocathodes were fabricated by reactive ion etching and inductively coupled plasma etching of bulk GaAs material. High density GaAs wire arrays with high periodicity and good morphology were verified using scanning electron microscopy, and photoluminescence spectra confirmed the wire arrays had good crystalline quality. Reflection spectra showed that circular GaAs wire arrays had superior light trapping compared with square ones. However, after Cs/O activation, the square GaAs wire array photocathodes showed enhanced spectral response. The integral sensitivity of the square wire array photocathodes was approximately 2.8 times that of the circular arrays.

n-Type Doping of Vapor-Liquid-Solid Grown GaAs Nanowires.

PubMed

Gutsche, Christoph; Lysov, Andrey; Regolin, Ingo; Blekker, Kai; Prost, Werner; Tegude, Franz-Josef

2011-12-01

In this letter, n-type doping of GaAs nanowires grown by metal-organic vapor phase epitaxy in the vapor-liquid-solid growth mode on (111)B GaAs substrates is reported. A low growth temperature of 400°C is adjusted in order to exclude shell growth. The impact of doping precursors on the morphology of GaAs nanowires was investigated. Tetraethyl tin as doping precursor enables heavily n-type doped GaAs nanowires in a relatively small process window while no doping effect could be found for ditertiarybutylsilane. Electrical measurements carried out on single nanowires reveal an axially non-uniform doping profile. Within a number of wires from the same run, the donor concentrations ND of GaAs nanowires are found to vary from 7 × 10(17) cm(-3) to 2 × 10(18) cm(-3). The n-type conductivity is proven by the transfer characteristics of fabricated nanowire metal-insulator-semiconductor field-effect transistor devices.

B-spline parameterization of the dielectric function and information criteria: the craft of non-overfitting

NASA Astrophysics Data System (ADS)

Likhachev, Dmitriy V.

2017-06-01

Johs and Hale developed the Kramers-Kronig consistent B-spline formulation for the dielectric function modeling in spectroscopic ellipsometry data analysis. In this article we use popular Akaike, corrected Akaike and Bayesian Information Criteria (AIC, AICc and BIC, respectively) to determine an optimal number of knots for B-spline model. These criteria allow finding a compromise between under- and overfitting of experimental data since they penalize for increasing number of knots and select representation which achieves the best fit with minimal number of knots. Proposed approach provides objective and practical guidance, as opposite to empirically driven or "gut feeling" decisions, for selecting the right number of knots for B-spline models in spectroscopic ellipsometry. AIC, AICc and BIC selection criteria work remarkably well as we demonstrated in several real-data applications. This approach formalizes selection of the optimal knot number and may be useful in practical perspective of spectroscopic ellipsometry data analysis.

Infrared-spectroscopic single-shot laser mapping ellipsometry: Proof of concept for fast investigations of structured surfaces and interactions in organic thin films

NASA Astrophysics Data System (ADS)

Furchner, Andreas; Kratz, Christoph; Gkogkou, Dimitra; Ketelsen, Helge; Hinrichs, Karsten

2017-11-01

We present a novel infrared-spectroscopic laser mapping ellipsometer based on a single-shot measurement concept. The ellipsometric set-up employs multiple analyzers and detectors to simultaneously measure the sample's optical response under different analyzer azimuths. An essential component is a broadly tunable quantum cascade laser (QCL) covering the important marker region of 1800-1540 cm-1. The ellipsometer allows for fast single-wavelength as well as spectroscopic studies with thin-film sensitivity at temporal resolutions of 60 ms per wavelength. We applied the single-shot mapping ellipsometer for the characterization of metal-island enhancement surfaces as well as of molecular interactions in organic thin films. In less than 3 min, a linescan with 1600 steps revealed profile and infrared-enhancement properties of a gradient gold-island film for sensing applications. Spectroscopic measurements were performed to probe the amide I band of thin films of poly(N-isopropylacrylamide) [PNIPAAm], a stimuli-responsive polymer for bioapplications. The QCL spectra agree well with conventional FT-IR ellipsometric results, showing different band components associated with hydrogen-bond interactions between polymer and adsorbed water. Multi-wavelength ellipsometric maps were used to analyze homogeneity and surface contaminations of the polymer films.

Confinement effects on glass transition temperature, transition breadth, and expansivity: comparison of ellipsometry and fluorescence measurements on polystyrene films.

PubMed

Kim, S; Hewlett, S A; Roth, C B; Torkelson, J M

2009-09-01

Using ellipsometry, we characterized the nanoconfinement effect on the glass transition temperature (T (g)of supported polystyrene (PS) films employing two methods: the intersection of fits to the temperature (Tdependences of rubbery- and glassy-state thicknesses, and the transition mid-point between rubbery- and glassy-state expansivities. The results demonstrate a strong effect of thickness: T(g) (bulk) - T(g)(23 nm) = 10 degrees C. The T -range needed for accurate measurement increases significantly with decreasing thickness, an effect that arises from the broadening of the transition with confinement and a region below T (g) where expansivity slowly decreases with decreasing T . As determined from expansivities, the T (g) breadth triples in going from bulk films to a 21-nm-thick film; this broadening of the transition may be a more dramatic effect of confinement than the T (g) reduction itself. In contrast, there is little effect of confinement on the rubbery- and glassy-state expansivities. Compared with ellipsometry, T (g) 's from fluorescence agree well in bulk films but yield lower values in nanoconfined films: T (g)(bulk) - T (g)(23 nm) = 15( degrees ) C via fluorescence. This small difference in the T (g) confinement effect reflects differences in how fluorescence and ellipsometry report "average T (g) " with confinement. With decreasing nanoscale thickness, fluorescence may slightly overweight the contribution of the free-surface layer while ellipsometry may evenly weight or underweight its contribution.

Confinement effects on glass transition temperature, transition breadth, and expansivity: Comparison of ellipsometry and fluorescence measurements on polystyrene films

NASA Astrophysics Data System (ADS)

Kim, S.; Hewlett, S. A.; Roth, C. B.; Torkelson, J. M.

2009-09-01

Using ellipsometry, we characterized the nanoconfinement effect on the glass transition temperature (T gof supported polystyrene (PS) films employing two methods: the intersection of fits to the temperature (Tdependences of rubbery- and glassy-state thicknesses, and the transition mid-point between rubbery- and glassy-state expansivities. The results demonstrate a strong effect of thickness: ensuremath Tg(bulk)-Tg(23{ nm})= 10 circ C. The T -range needed for accurate measurement increases significantly with decreasing thickness, an effect that arises from the broadening of the transition with confinement and a region below T g where expansivity slowly decreases with decreasing T . As determined from expansivities, the T g breadth triples in going from bulk films to a 21-nm-thick film; this broadening of the transition may be a more dramatic effect of confinement than the T g reduction itself. In contrast, there is little effect of confinement on the rubbery- and glassy-state expansivities. Compared with ellipsometry, T g ’s from fluorescence agree well in bulk films but yield lower values in nanoconfined films: T g(bulk) - T g(23 nm) = 15° C via fluorescence. This small difference in the T g confinement effect reflects differences in how fluorescence and ellipsometry report “average T g ” with confinement. With decreasing nanoscale thickness, fluorescence may slightly overweight the contribution of the free-surface layer while ellipsometry may evenly weight or underweight its contribution. in here

Photovoltaic Properties of p-Doped GaAs Nanowire Arrays Grown on n-Type GaAs(111)B Substrate

PubMed Central

2010-01-01

We report on the molecular beam epitaxy growth of Au-assisted GaAs p-type-doped NW arrays on the n-type GaAs(111)B substrate and their photovoltaic properties. The samples are grown at different substrate temperature within the range from 520 to 580 °C. It is shown that the dependence of conversion efficiency on the substrate temperature has a maximum at the substrate temperature of 550 °C. For the best sample, the conversion efficiency of 1.65% and the fill factor of 25% are obtained. PMID:20672038

Two-Photon Pumped Synchronously Mode-Locked Bulk GaAs Laser

NASA Astrophysics Data System (ADS)

Cao, W. L.; Vaucher, A. M.; Ling, J. D.; Lee, C. H.

1982-04-01

Pulses 7 picoseconds or less in duration have been generated from a bulk GaAs crystal by a synchronous mode-locking technique. The GaAs crystal was optically pumped by two-photon absorption of the emission from a mode-locked Nd:glass laser. Two-photon absorption as the means of excitation increases the volume of the gain medium by increasing the pene-tration depth of the pump intensity, enabling generation of intra-cavity pulses with peak power in the megawatt range. Tuning of the wavelength of the GaAs emission is achieved by varying the temperature. A tuning range covering 840 nm to 885 nm has been observed over a temperature range from 97°K to 260°K. The intensity of the GaAs emission has also been observed to decrease as the temperature of the crystal is increased.

Interface demarcation in GaAs by current pulsing

NASA Technical Reports Server (NTRS)

Matthiesen, D. H.; Kafalas, J. A.; Duchene, G. A.; Bellows, A. H.

1990-01-01

GTE Laboratories is currently conducting a program to investigate the effect of convection in the melt on the properties of bulk grown gallium arsenide (GaAs). In addition to extensive ground based experimentation, a Get Away Special growth system has been developed to grow two GaAs crystals aboard the Space Shuttle, each with a one inch diameter. In order to perform a complete segregation analysis of the crystals grown in space, it is necessary to measure the interface shape and growth rate as well as the spatial distribution of the selenium dopant. The techniques for interface demarcation in selenium doped GaAs by current pulsing have been developed at GTE Laboratories and successful interface demarcation has been achieved for current pulses ranging from 20 to 90 amps, in both single crystal and polycrystalline regions.

Microwave GaAs Integrated Circuits On Quartz Substrates

NASA Technical Reports Server (NTRS)

Siegel, Peter H.; Mehdi, Imran; Wilson, Barbara

1994-01-01

Integrated circuits for use in detecting electromagnetic radiation at millimeter and submillimeter wavelengths constructed by bonding GaAs-based integrated circuits onto quartz-substrate-based stripline circuits. Approach offers combined advantages of high-speed semiconductor active devices made only on epitaxially deposited GaAs substrates with low-dielectric-loss, mechanically rugged quartz substrates. Other potential applications include integration of antenna elements with active devices, using carrier substrates other than quartz to meet particular requirements using lifted-off GaAs layer in membrane configuration with quartz substrate supporting edges only, and using lift-off technique to fabricate ultrathin discrete devices diced separately and inserted into predefined larger circuits. In different device concept, quartz substrate utilized as transparent support for GaAs devices excited from back side by optical radiation.

Studies of molecular-beam epitaxy growth of GaAs on porous Si substrates

NASA Technical Reports Server (NTRS)

Mii, Y. J.; Kao, Y. C.; Wu, B. J.; Wang, K. L.; Lin, T. L.; Liu, J. K.

1988-01-01

GaAs has been grown on porous Si directly and on Si buffer layer-porous Si substrates by molecular-beam epitaxy. In the case of GaAs growth on porous Si, transmission electron microscopy (TEM) reveals that the dominant defects in GaAs layers grown on porous Si are microtwins and stacking faults, which originate from the GaAs/porous Si interface. GaAs is found to penetrate into the porous Si layers. By using a thin Si buffer layer (50 nm), GaAs penetration diminishes and the density of microtwins and stacking faults is largely reduced and localized at the GaAs/Si buffer interface. However, there is a high density of threading dislocations remaining. Both Si (100) aligned and four degree tilted substrates have been examined in this study. TEM results show no observable effect of the tilted substrates on the quality of the GaAs epitaxial layer.

Fabrication and characterization of multi-layer InAs/InGaAs quantum dot p-i-n GaAs solar cells grown on silicon substrates

NASA Astrophysics Data System (ADS)

Omri, M.; Sayari, A.; Sfaxi, L.

2018-01-01

This paper reports on InAs/InGaAs quantum dot solar cells (QDSCs) deposited by molecular beam epitaxy (MBE) on (001) n-type silicon ( n-Si) substrates. In-situ RHEED measurements show that InAs/InGaAs QDs SC has a high crystalline structure. The dislocation density in the active layer of the InAs/InGaAs QDSC and the lattice mismatch in the GaAs layer can be reduced by using an Si rough surface buffer layer (RSi). To show the effect of the QD layers, a reference SC with the same p-i-n structure as the InAs/InGaAs QDSC, but without InAs QDs, is also grown. The two SCs were studied by sepectroscopic ellipsometry (SE), in the 1-6 eV photon energy range, photoluminescence and photocurrent measurements. The optical constants of the two devices are determined in the photon energy range 1-6 eV from the SE data. The dominant features in the dielectric function spectra at 3 and 4.5 eV are attributed, respectively, to the E 1 and E 2 critical point structures of GaAs and InAs. The low-temperature photoluminescence spectrum of the InAs/InGaAs QDSC shows ground-state emissions, respectively, from the relatively small QDs near 1081 nm and from the large QDs near 1126 nm. Photocurrent measurements confirm the improved absorption performance (up to 1200 nm) of the InAs QDs SC which is ascribed to the optical absorption from the InAs/InGaAs QDs and the Si substrate as demonstrated by SE and photoluminescence measurements.

Advanced GaAs Process Modeling. Volume 1

DTIC Science & Technology

1989-05-01

COSATI CODES 18 . SUBJECT TERMS (Continue on reverse if necessary and identify by block number) FIELD GROUP SUB-GROUP Gallium Arsenide, MESFET, Process...Background 9 3.2 Model Calculations 10 3.3 Conclusions 17 IV. ION-IMPLANTATION INTO GaAs PROFILE DETERMINATION 18 4.1 Ion Implantation Profile...Determination in GaAs 18 4.1.1. Background 18 4.1.2. Experimental Measurements 20 4.1.3. Results 22 4.1.3.1 Ion-Energy Dependence 22 4.1.3.2. Tilt and Rotation

Generalized Ellipsometry on Complex Nanostructures and Low-Symmetry Materials

NASA Astrophysics Data System (ADS)

Mock, Alyssa Lynn

In this thesis, complex anisotropic materials are investigated and characterized by generalized ellipsometry. In recent years, anisotropic materials have gained considerable interest for novel applications in electronic and optoelectronic devices, mostly due to unique properties that originate from reduced crystal symmetry. Examples include white solid-state lighting devices which have become ubiquitous just recently, and the emergence of high-power, high-voltage electronic transistors and switches in all-electric vehicles. The incorporation of single crystalline material with low crystal symmetry into novel device structures requires reconsideration of existing optical characterization approaches. Here, the generalized ellipsometry concept is extended to include applications for materials with monoclinic and triclinic symmetries. A model eigendielectric displacement vector approach is developed, described and utilized to characterize monoclinic materials. Materials are investigated in spectral regions spanning from the far-infrared to the vacuum ultraviolet. Examples are demonstrated for phonon mode determination in cadmium tungstate and yttrium silicate and for band-to-band transitions in gallia (beta-Ga2O3) single crystals. Furthermore, the anisotropic optical properties of an emerging class of spatially coherent heterostructure materials with nanostructure dimensions are investigated. The so-called anisotropic effective medium approximation for slanted columnar thin films is extended to the concept of slanted columnar heterostructure thin films as well as core-shell heterostructure thin films. Examples include the determination of band-to-band transitions, phonon modes and oxidation properties of cobalt-oxide core shell structures and gas-liquid-solid distribution during controlled adsorption of organic solvents in silicon slanted columnar thin films.

Rare-earth gate oxides for GaAs MOSFET application

NASA Astrophysics Data System (ADS)

Kwon, Kwang-Ho; Yang, Jun-Kyu; Park, Hyung-Ho; Kim, Jongdae; Roh, Tae Moon

2006-08-01

Rare-earth oxide films for gate dielectric on n-GaAs have been investigated. The oxide films were e-beam evaporated on S-passivated GaAs, considering interfacial chemical bonding state and energy band structure. Rare-earth oxides such as Gd 2O 3, (Gd xLa 1- x) 2O 3, and Gd-silicate were employed due to high resistivity and no chemical reaction with GaAs. Structural and bonding properties were characterized by X-ray photoemission, absorption, and diffraction. The electrical characteristics of metal-oxide-semiconductor (MOS) diodes were correlated with material properties and energy band structures to guarantee the feasibility for MOS field effect transistor (FET) application. Gd 2O 3 films were grown epitaxially on S-passivated GaAs (0 0 1) at 400 °C. The passivation induced a lowering of crystallization temperature with an epitaxial relationship of Gd 2O 3 (4 4 0) and GaAs (0 0 1). A better lattice matching relation between Gd 2O 3 and GaAs substrate was accomplished by the substitution of Gd with La, which has larger ionic radius. The in-plane relationship of (Gd xLa 1- x) 2O 3 (4 4 0) with GaAs (0 0 1) was found and the epitaxial films showed an improved crystalline quality. Amorphous Gd-silicate film was synthesized by the incorporation of SiO 2 into Gd 2O 3. These amorphous Gd-silicate films excluded defect traps or current flow path due to grain boundaries and showed a relatively larger energy band gap dependent on the contents of SiO 2. Energy band parameters such as Δ EC, Δ EV, and Eg were effectively controlled by the film composition.

Failure Mechanisms of GaAs Transistors - A Literature Survey

DTIC Science & Technology

1990-03-01

doping profile cannot be as sharp as with epitaxial methods. This is the result of the statistics of the implantation and the general diffusion that...Speed GaAs Logic Gates 5.1 GaAs PLANAR TRANSITOR STRUCTURES USED IN IC’S Some planar transistor structures used in IC’s with examples of the

Tolerance of GaAs as an original substrate for HVPE growth of free standing GaN

NASA Astrophysics Data System (ADS)

Suzuki, Mio; Sato, T.; Suemasu, T.; Hasegawa, F.

2004-09-01

In order to investigate possibility of thick GaN growth on a GaAs substrate by halide vapar phase epitaxy (HVPE), GaN was grown on GaAs(111)/Ti wafer with Ti deposited by E-gun. It was found that surface treatment of the GaAs substrate by HF solution deteriorated greatly the tolerence of GaAs and that Ti can protected GaAs from erosion by NH3. By depositing Ti on GaAs(111)A surface, a millor-like GaN layer could be grown at 1000 °C for 1 hour without serious deterioration of the original GaAs substrate. By increasing the growth rate, a thick free standing GaN will be obtained with GaAs as an original substrate in near future.

Spectroscopic ellipsometric studies of the dielectric function of Cd1-x-yMnxFeyTe single crystals

NASA Astrophysics Data System (ADS)

Hwang, Younghun; Kim, Hyekyeong; Um, Youngho; Park, Hyoyeol

2004-06-01

Cd1-x-yMnxFeyTe single crystals grown by the vertical Bridgman method have been studied by measuring the complex dielectric function using spectroscopic ellipsometry in the 1.5 5.5 eV photon energy range at room temperature. The CP energy parameters of the E0, E1, E1 + 1, and E2 structures were determined by fitting the second-derivative spectra (d2/d2) with a theoretical model, i.e., the standard critical point (SCP) line shapes. The E1, E1 + 1, and E2 energies decreased with increasing Fe composition y, which is due to the hybridization effect of the valence and conduction bands in Cd1-xMnxTe with Fe 3d levels.

Photon counting microstrip X-ray detectors with GaAs sensors

NASA Astrophysics Data System (ADS)

Ruat, M.; Andrä, M.; Bergamaschi, A.; Barten, R.; Brückner, M.; Dinapoli, R.; Fröjdh, E.; Greiffenberg, D.; Lopez-Cuenca, C.; Lozinskaya, A. D.; Mezza, D.; Mozzanica, A.; Novikov, V. A.; Ramilli, M.; Redford, S.; Ruder, C.; Schmitt, B.; Shi, X.; Thattil, D.; Tinti, G.; Tolbanov, O. P.; Tyazhev, A.; Vetter, S.; Zarubin, A. N.; Zhang, J.

2018-01-01

High-Z sensors are increasingly used to overcome the poor efficiency of Si sensors above 15 keV, and further extend the energy range of synchrotron and FEL experiments. Detector-grade GaAs sensors of 500 μm thickness offer 98% absorption efficiency at 30 keV and 50% at 50 keV . In this work we assess the usability of GaAs sensors in combination with the MYTHEN photon-counting microstrip readout chip developed at PSI. Different strip length and pitch are compared, and the detector performance is evaluated in regard of the sensor material properties. Despite increased leakage current and noise, photon-counting strips mounted with GaAs sensors can be used with photons of energy as low as 5 keV, and exhibit excellent linearity with energy. The charge sharing is doubled as compared to silicon strips, due to the high diffusion coefficient of electrons in GaAs.

High temperature GaAs X-ray detectors

NASA Astrophysics Data System (ADS)

Lioliou, G.; Whitaker, M. D. C.; Barnett, A. M.

2017-12-01

Two GaAs p+-i-n+ mesa X-ray photodiodes were characterized for their electrical and photon counting X-ray spectroscopic performance over the temperature range of 100 °C to -20 °C. The devices had 10 μm thick i layers with different diameters: 200 μm (D1) and 400 μm (D2). The electrical characterization included dark current and capacitance measurements at internal electric field strengths of up to 50 kV/cm. The determined properties of the two devices were compared with previously reported results that were made with a view to informing the future development of photon counting X-ray spectrometers for harsh environments, e.g., X-ray fluorescence spectroscopy of planetary surfaces in high temperature environments. The best energy resolution obtained (Full Width at Half Maximum at 5.9 keV) decreased from 2.00 keV at 100 °C to 0.66 keV at -20 °C for the spectrometer with D1, and from 2.71 keV at 100 °C to 0.71 keV at -20 °C for the spectrometer with D2. Dielectric noise was found to be the dominant source of noise in the spectra, apart from at high temperatures and long shaping times, where the main source of photopeak broadening was found to be the white parallel noise.

Laser Induced Electrodeposition on Polyimide and GaAs Substrates

DTIC Science & Technology

1983-10-01

6 3.1 Laser Gold Plating on Undoped Ga As Substrate ........... 6 3.1.1 Deposit Formation...22 iv LIST OF ILLUSTRATIONS Figure Page 1. Experimental Set-Up . . . . . .................. 4 2. Laser Gold Pla’ting Undoped GaAs (100...9 3. Laser Gold Plating Undoped GaAs (100) Deposit Resistance Measurement ......................... .10 4. Laser Gold Plating on Polyimide

Investigation of ZnSe-coated silicon substrates for GaAs solar cells

NASA Technical Reports Server (NTRS)

Huber, Daniel A.; Olsen, Larry C.; Dunham, Glen; Addis, F. William

1993-01-01

Studies are being carried out to determine the feasibility of using ZnSe as a buffer layer for GaAs solar cells grown on silicon. This study was motivated by reports in the literature indicating ZnSe films had been grown by metallorganic chemical vapor deposition (MOCVD) onto silicon with EPD values of 2 x 10(exp 5) cm(sup -2), even though the lattice mismatch between silicon and ZnSe is 4.16 percent. These results combined with the fact that ZnSe and GaAs are lattice matched to within 0.24 percent suggest that the prospects for growing high efficiency GaAs solar cells onto ZnSe-coated silicon are very good. Work to date has emphasized development of procedures for MOCVD growth of (100) ZnSe onto (100) silicon wafers, and subsequent growth of GaAs films on ZnSe/Si substrates. In order to grow high quality single crystal GaAs with a (100) orientation, which is desirable for solar cells, one must grow single crystal (100) ZnSe onto silicon substrates. A process for growth of (100) ZnSe was developed involving a two-step growth procedure at 450 C. Single crystal, (100) GaAs films were grown onto the (100) ZnSe/Si substrates at 610 C that are adherent and specular. Minority carrier diffusion lengths for the GaAs films grown on ZnSe/Si substrates were determined from photoresponse properties of Al/GaAs Schottky barriers. Diffusion lengths for n-type GaAs films are currently on the order of 0.3 microns compared to 2.0 microns for films grown simultaneously by homoepitaxy.

Cathodoluminescence Characterization of Ion Implanted GaAs.

DTIC Science & Technology

1980-03-01

technique that can be used to characterize the semiconductor device "in situ" before further processing can save the Air Force valuable time as well...Patterson Air Force Base,Ohio i! i ill i I ;Wow AFIT/DS/PH/80- I.i1I LEVELOO CATHODOLUMINESCENCE CHARACTERIZATION OF ION IPLANTED GaAs D I SSERUrAT ION...CATODOLUMINESCENCE CHARACTERIZATION .’ a .... OF ION IMPLANTED GaAs’ - .. .. Dtriy’ t’ c:’/ A’: t 1. - Cc;-,P by an i’or Milton L one B.S., M.S. Major USAF Approved

Amplification in Double Heterostructure GaAs Lasers.

DTIC Science & Technology

1981-03-15

done, for example, in the book by Siegman . When the laser signal which is to be amplified is a single mode, it is important to include the possibility...k A’AD-A097 862 AEROSPACE CORP EL SEGUNDO CA ELECTRONICS RESEARCH LAP) P 5 20/5 I AMPLIFICATION IN DOUBLE HETEROSTRUCTURE GAAS LASERS .(U IMAR al E...GARMIRE, M CHANG F04701-80-C-0081I UNCLASSIFIED TR GO81(6930 03)-2 SD-TA8-30 NL Amplification in Double Heterostructure GaAs Lasers E. GARMIRE nd M

GaAs Surface Passivation for Device Applications.

DTIC Science & Technology

1981-12-01

Ga203.’" . QI. a) / b) x 2.5 •• 24 21 18 As3d a) b) x 2. / 0 II 2 46 43 40 BINDING ENERGY (eV) Fig. 3 XPS spectra from a Ga2O3 covered GaAs surface of Ga...wU 24 21 Gas 18 SAs3d As2O3 ) .. 46 43 40 BINDING ENERGY (e) Fig. 4 XPS spectra from a AsJ03- Ga2O3 covered GaAs surface of Ga 3d (upper panel) and As

Inverted thermal conversion - GaAs, a new alternative material for integrated circuits

NASA Technical Reports Server (NTRS)

Lagowski, J.; Gatos, H. C.; Kang, C. H.; Skowronski, M.; Ko, K. Y.

1986-01-01

A new type of GaAs is developed which exhibits inverted thermal conversion (ITC); i.e., it converts from conducting to semiinsulating upon annealing at about 850 C. In device fabrication, its low resistivity prior to high-temperature processing differentiates ITC GaAs from the standard semiinsulating GaAs. The ITC characteristics are obtained through control of the concentration of the midgap donor EL2 based on heat treatment and crystal-growth modification. Thus EL2 does not exist in the conducting state of ITC GaAs. Conversion to the semiinsulating state during 850 C annealing is caused by the formation of EL2.

Dynamics of reflection high-energy electron diffraction intensity oscillations during molecular beam epitaxial growth of GaAs on (111)B GaAs substrates

NASA Astrophysics Data System (ADS)

Yen, M. Y.; Haas, T. W.

1990-06-01

We have observed intensity oscillations in reflection high-energy electron diffraction during molecular beam epitaxial growth of GaAs on (111)B GaAs substrates. These oscillations only exist over a narrow range of growth conditions and their behavior is strongly dependent on the migration kinetics of group III and the molecular dissociative reaction of group V elements.

Temperature-dependent and anisotropic optical response of layered Pr0.5Ca1.5MnO4 probed by spectroscopic ellipsometry

NASA Astrophysics Data System (ADS)

Majidi, M. A.; Thoeng, E.; Gogoi, P. K.; Wendt, F.; Wang, S. H.; Santoso, I.; Asmara, T. C.; Handayani, I. P.; van Loosdrecht, P. H. M.; Nugroho, A. A.; Rübhausen, M.; Rusydi, A.

2013-06-01

We study the temperature dependence as well as anisotropy of optical conductivity (σ1) in the pseudocubic single crystal Pr0.5Ca1.5MnO4 using spectrocopic ellipsometry. Three transition temperatures are observed and can be linked to charge-orbital (TCO/OO˜320 K), two-dimensional-antiferromagnetic (2D-AFM) (˜200 K), and three-dimensional AFM (TN˜125 K) orderings. Below TCO/OO, σ1 shows a charge-ordering peak (˜0.8 eV) with a significant blue shift as the temperature decreases. Calculations based on a model that incorporates a static Jahn-Teller distortion and assumes the existence of a local charge imbalance between two different sublattices support this assignment and explain the blue shift. This view is further supported by the partial spectral weight analysis showing the onset of optical anisotropy at TCO/OO in the charge-ordering region (0.5-2.5 eV). Interestingly, in the charge-transfer region (2.5-4 eV), the spectral weight shows anomalies around the T2D-AFM that we attribute to the role of oxygen-p orbitals in stabilizing the CE-type magnetic ordering. Our result shows the importance of spin, charge, orbital, and lattice degrees of freedom in this layered manganite.

Integration of GaAs vertical-cavity surface emitting laser on Si by substrate removal

NASA Astrophysics Data System (ADS)

Yeh, Hsi-Jen J.; Smith, John S.

1994-03-01

The successful integration of strained quantum well InGaAs vertical-cavity surface-emitting lasers (VCSELs) on both Si and Cu substrates was described using a GaAs substrate removal technique. The GaAs VCSEL structure was metallized and bonded to the Si substrate after growth. The GaAs substrate was then removed by selective chemical wet etching. Finally, the bonded GaAs film metallized on the top (emitting) side and separate lasers were defined. This is the first time a VCSEL had been integrated on a Si substrate with its substrate removed. The performance enhancement of GaAs VCSELs bonded on good thermal conductors are demonstrated.

Lightweight, Light-Trapped, Thin GaAs Solar Cells for Spacecraft Applications.

DTIC Science & Technology

1995-10-05

improve the efficiency of this type of cell. 2 The high efficiency and light weight of the cover glass supported GaAs solar cell can have a significant...is a 3-mil cover glass and 1-mil silicone adhesive on the front surface of the GaAs solar cell. Power Output 3000 400 -{ 2400 { N 300 S18200 W/m2...the ultra-thin, light-trapped GaAs solar ceill 3. Incorporate light trapping. 0 external quantum efficiency at 850 nm increased by 5.2% 4. Develop

The mismatch repair system protects against intergenerational GAA repeat instability in a Friedreich ataxia mouse model.

PubMed

Ezzatizadeh, Vahid; Pinto, Ricardo Mouro; Sandi, Chiranjeevi; Sandi, Madhavi; Al-Mahdawi, Sahar; Te Riele, Hein; Pook, Mark A

2012-04-01

Friedreich ataxia (FRDA) is an autosomal recessive neurodegenerative disorder caused by a dynamic GAA repeat expansion mutation within intron 1 of the FXN gene. Studies of mouse models for other trinucleotide repeat (TNR) disorders have revealed an important role of mismatch repair (MMR) proteins in TNR instability. To explore the potential role of MMR proteins on intergenerational GAA repeat instability in FRDA, we have analyzed the transmission of unstable GAA repeat expansions from FXN transgenic mice which have been crossed with mice that are deficient for Msh2, Msh3, Msh6 or Pms2. We find in all cases that absence of parental MMR protein not only maintains transmission of GAA expansions and contractions, but also increases GAA repeat mutability (expansions and/or contractions) in the offspring. This indicates that Msh2, Msh3, Msh6 and Pms2 proteins are not the cause of intergenerational GAA expansions or contractions, but act in their canonical MMR capacity to protect against GAA repeat instability. We further identified differential modes of action for the four MMR proteins. Thus, Msh2 and Msh3 protect against GAA repeat contractions, while Msh6 protects against both GAA repeat expansions and contractions, and Pms2 protects against GAA repeat expansions and also promotes contractions. Furthermore, we detected enhanced occupancy of Msh2 and Msh3 proteins downstream of the FXN expanded GAA repeat, suggesting a model in which Msh2/3 dimers are recruited to this region to repair mismatches that would otherwise produce intergenerational GAA contractions. These findings reveal substantial differences in the intergenerational dynamics of expanded GAA repeat sequences compared with expanded CAG/CTG repeats, where Msh2 and Msh3 are thought to actively promote repeat expansions. Copyright © 2012 Elsevier Inc. All rights reserved.

The mismatch repair system protects against intergenerational GAA repeat instability in a Friedreich ataxia mouse model

PubMed Central

Ezzatizadeh, Vahid; Pinto, Ricardo Mouro; Sandi, Chiranjeevi; Sandi, Madhavi; Al-Mahdawi, Sahar; te Riele, Hein; Pook, Mark A.

2013-01-01

Friedreich ataxia (FRDA) is an autosomal recessive neurodegenerative disorder caused by a dynamic GAA repeat expansion mutation within intron 1 of the FXN gene. Studies of mouse models for other trinucleotide repeat (TNR) disorders have revealed an important role of mismatch repair (MMR) proteins in TNR instability. To explore the potential role of MMR proteins on intergenerational GAA repeat instability in FRDA, we have analyzed the transmission of unstable GAA repeat expansions from FXN transgenic mice which have been crossed with mice that are deficient for Msh2, Msh3, Msh6 or Pms2. We find in all cases that absence of parental MMR protein not only maintains transmission of GAA expansions and contractions, but also increases GAA repeat mutability (expansions and/or contractions) in the offspring. This indicates that Msh2, Msh3, Msh6 and Pms2 proteins are not the cause of intergenerational GAA expansions or contractions, but act in their canonical MMR capacity to protect against GAA repeat instability. We further identified differential modes of action for the four MMR proteins. Thus, Msh2 and Msh3 protect against GAA repeat contractions, while Msh6 protects against both GAA repeat expansions and contractions, and Pms2 protects against GAA repeat expansions and also promotes contractions. Furthermore, we detected enhanced occupancy of Msh2 and Msh3 proteins downstream of the FXN expanded GAA repeat, suggesting a model in which Msh2/3 dimers are recruited to this region to repair mismatches that would otherwise produce intergenerational GAA contractions. These findings reveal substantial differences in the intergenerational dynamics of expanded GAA repeat sequences compared with expanded CAG/CTG repeats, where Msh2 and Msh3 are thought to actively promote repeat expansions. PMID:22289650

Oxygen in GaAs - Direct and indirect effects

NASA Technical Reports Server (NTRS)

Gatos, H. C.; Skowronski, M.; Pawlowicz, L.; Lagowski, J.

1984-01-01

Oxygen has profound effects on the key electronic properties and point defects of GaAs crystals. Thus, when added in the growth system, it decreases the free electron concentration and enhances the concentration of deep donors in the resulting crystals. Both of these effects are highly beneficial for achieving semi-insulating material and have been utilized for that purpose. They have been attributed to the tendency of oxygen to getter silicon impurities during crystal growth. Only recently, it has been found that oxygen in GaAs introduces also a midgap level, ELO, with essentially the same activation energy as EL2 but with four times greater electron capture cross section. The present report reassesses the electrical and optical properties of the midgap levels in GaAs crystals grown by the horizontal Bridgman (HB) and the Czochralski-LEC techniques. Emphasis is placed on the identification of the specific effects of ELO.

Performance and temperature dependencies of proton irradiated n/p GaAs and n/p silicon cells

NASA Technical Reports Server (NTRS)

Weinberg, I.; Swartz, C. K.; Hart, R. E., Jr.

1985-01-01

The n/p homojunction GaAs cell is found to be more radiation resistant than p/nheteroface GaAs under 10 MeV proton irradiation. Both GaAs cell types outperform conventional silicon n/p cells under the same conditions. An increase temperature dependency of maximum power for the GaAs n/p cells is attributed largely to differences in Voc between the two GaAs cell types. These results and diffusion length considerations are consistent with the conclusion that p-type GaAs is more radiation resistant than n-type and therefore that the n/p configuration is possibly favored for use in the space radiation environment. However, it is concluded that additional work is required in order to choose between the two GaAs cell configurations.

GaAs Spectrometer for Electron Spectroscopy at Europa

NASA Astrophysics Data System (ADS)

Lioliou, G.; Barnett, A. M.

2016-12-01

We propose a GaAs based electron spectrometer for a hypothetical future mission orbiting Europa. Previous observations at Europa's South Pole with the Hubble Space Telescope of hydrogen Lyman-α and oxygen OI 130.4 nm emissions were consistent with water vapor plumes [Roth et al., 2014, Science 343, 171]. Future observations and analysis of plumes on Europa could provide information about its subsurface structure and the distribution of liquid water within its icy shells [Rhoden at al. 2015, Icarus 253, 169]. In situ low energy (1keV - 100keV) electron spectroscopy along with UV imaging either in situ or with the Hubble Space Telescope Wide Field Camera 3 or similar would allow verification of the auroral observations being due to electron impact excitation of water vapor plumes. The proposed spectrometer includes a novel GaAs p+-i-n+ photodiode and a custom-made charge-sensitive preamplifier. The use of an early prototype GaAs detector for direct electron spectroscopy has already been demonstrated in ground based applications [Barnett et al., 2012, J. Instrum. 7, P09012]. Based on previous radiation hardness measurements of GaAs, the expected duration of the mission without degradation of the detector performance is estimated to be 4 months. Simulations and laboratory experiments characterising the detection performance of the proposed system are presented.

Photo-recovery of electron-irradiated GaAs solar cells

NASA Technical Reports Server (NTRS)

Meulenberg, Andrew

1995-01-01

The first long-term (3000 hours) UV testing of unirradiated and 1 MeV electron-irradiated GaAs solar cells, with multilayer-coated coverslides to reduce solar array operating temperature, has produced some unexpected and important results. Two results, independent of the coverslide coatings, are of particular importance in terms of the predictability of GaAs solar-array lifetime in space: ( 1) The GaAs/Ge solar cells used for this series of tests displayed a much higher radiation degradation than that predicted based on JPL Solar Cell Radiation Handbook data. Covered cells degraded more in Isc than did bare cells. Short-term illumination at 60 C did not produce significant recovery (-1%) of the radiation damage. (2) However, electron radiation damage to these GaAs solar celIs anneals at 40 C when exposed to approximately 1 sun AM0 UV light sources for extended periods. The effect appears to be roughly linear with time (-1% of lsc per 1000 UVSH), is large (greater than or equal to 3%), and has not yet saturated (at 3000 hours). This photo-recovery of radiation damage to GaAs solar cells is a new effect and potentially important to the spacecraft community. The figure compares the effects of extended UV on irradiated and unirradiated GaAs solar cells with INTELSAT-6 Si cells. The effect and its generality, the extent of and conditions for photo-recovery, and the implications of such recovery for missions in radiation environments have not yet been determined.

Defect interactions in GaAs single crystals

NASA Technical Reports Server (NTRS)

Gatos, H. C.; Lagowski, J.

1984-01-01

The two-sublattice structural configuration of GaAs and deviations from stoichiometry render the generation and interaction of electrically active point defects (and point defect complexes) critically important for device applications and very complex. Of the defect-induced energy levels, those lying deep into the energy band are very effective lifetime ""killers". The level 0.82 eV below the condition band, commonly referred to as EL2, is a major deep level, particularly in melt-grown GaAs. This level is associated with an antisite defect complex (AsGa - VAS). Possible mechanisms of its formation and its annihilation were further developed.

Heterojunction photovoltaics using GaAs nanowires and conjugated polymers.

PubMed

Ren, Shenqiang; Zhao, Ni; Crawford, Samuel C; Tambe, Michael; Bulović, Vladimir; Gradecak, Silvija

2011-02-09

We demonstrate an organic/inorganic solar cell architecture based on a blend of poly(3-hexylthiophene) (P3HT) and narrow bandgap GaAs nanowires. The measured increase of device photocurrent with increased nanowire loading is correlated with structural ordering within the active layer that enhances charge transport. Coating the GaAs nanowires with TiO(x) shells passivates nanowire surface states and further improves the photovoltaic performance. We find that the P3HT/nanowire cells yield power conversion efficiencies of 2.36% under white LED illumination for devices containing 50 wt % of TiO(x)-coated GaAs nanowires. Our results constitute important progress for the use of nanowires in large area solution processed hybrid photovoltaic cells and provide insight into the role of structural ordering in the device performance.

Transient GaAs plasmonic metasurfaces at terahertz frequencies

DOE PAGES

Yang, Yuanmu; Kamaraju, N.; Campione, Salvatore; ...

2016-12-09

Here we demonstrate the ultrafast formation of terahertz (THz) metasurfaces through all-optical creation of spatially modulated carrier density profiles in a deep-subwavelength GaAs film. The switch-on of the transient plasmon mode, governed by the GaAs effective electron mass and electron–phonon interactions, is revealed by structured-optical pump THz probe spectroscopy, on a time scale of 500 fs. By modulating the carrier density using different pump fluences, we observe a wide tuning of the electric dipole resonance of the transient GaAs metasurface from 0.5 THz to 1.7 THz. Furthermore, we numerically demonstrate that the metasurface presented here can be generalized to moremore » complex architectures for realizing functionalities such as perfect absorption, leading to a 30 dB modulation depth. In conclusion, the platform also provides a pathway to achieve ultrafast manipulation of infrared beams in the linear and, potentially, nonlinear regime.« less

Study on electrical defects level in single layer two-dimensional Ta2O5

NASA Astrophysics Data System (ADS)

Dahai, Li; Xiongfei, Song; Linfeng, Hu; Ziyi, Wang; Rongjun, Zhang; Liangyao, Chen; David, Wei Zhang; Peng, Zhou

2016-04-01

Two-dimensional atomic-layered material is a recent research focus, and single layer Ta2O5 used as gate dielectric in field-effect transistors is obtained via assemblies of Ta2O5 nanosheets. However, the electrical performance is seriously affected by electronic defects existing in Ta2O5. Therefore, spectroscopic ellipsometry is used to calculate the transition energies and corresponding probabilities for two different charged oxygen vacancies, whose existence is revealed by x-ray photoelectron spectroscopy analysis. Spectroscopic ellipsometry fitting also calculates the thickness of single layer Ta2O5, exhibiting good agreement with atomic force microscopy measurement. Nondestructive and noncontact spectroscopic ellipsometry is appropriate for detecting the electrical defects level of single layer Ta2O5. Project supported by the National Natural Science Foundation of China (Grant Nos. 11174058 and 61376093), the Fund from Shanghai Municipal Science and Technology Commission (Grant No. 13QA1400400), the National Science and Technology Major Project, China (Grant No. 2011ZX02707), and the Innovation Program of Shanghai Municipal Education Commission (Grant No. 12ZZ010).

GaAs QWIP Array Containing More Than a Million Pixels

NASA Technical Reports Server (NTRS)

Jhabvala, Murzy; Choi, K. K.; Gunapala, Sarath

2005-01-01

A 1,024 x 1,024-pixel array of quantum-well infrared photodetectors (QWIPs) has been built on a 1.8 x 1.8- cm GaAs chip. In tests, the array was found to perform well in detecting images at wavelengths from 8 to 9 m in operation at temperatures between 60 and 70 K. The largest-format QWIP prior array that performed successfully in tests contained 512 x 640 pixels. There is continuing development effort directed toward satisfying actual and anticipated demands to increase numbers of pixels and pixel sizes in order to increase the imaging resolution of infrared photodetector arrays. A 1,024 x 1,024-pixel and even larger formats have been achieved in the InSb and HgCdTe material systems, but photodetector arrays in these material systems are very expensive and manufactured by fewer than half a dozen large companies. In contrast, GaAs-photodetector-array technology is very mature, and photodetectors in the GaAs material system can be readily manufactured by a wide range of industrial technologists, by universities, and government laboratories. There is much similarity between processing in the GaAs industry and processing in the pervasive silicon industry. With respect to yield and cost, the performance of GaAs technology substantially exceeds that of InSb and HgCdTe technologies. In addition, GaAs detectors can be designed to respond to any portion of the wavelength range from 3 to about 16 micrometers - a feature that is very desirable for infrared imaging. GaAs QWIP arrays, like the present one, have potential for use as imaging sensors in infrared measuring instruments, infrared medical imaging systems, and infrared cameras.

Spin-lattice relaxation of optically polarized nuclei in p -type GaAs

NASA Astrophysics Data System (ADS)

Kotur, M.; Dzhioev, R. I.; Vladimirova, M.; Cherbunin, R. V.; Sokolov, P. S.; Yakovlev, D. R.; Bayer, M.; Suter, D.; Kavokin, K. V.

2018-04-01

Spin-lattice relaxation of the nuclear spin system in p -type GaAs is studied using a three-stage experimental protocol including optical pumping and measuring the difference of the nuclear spin polarization before and after a dark interval of variable length. This method allows us to measure the spin-lattice relaxation time T1 of optically pumped nuclei "in the dark," that is, in the absence of illumination. The measured T1 values fall into the subsecond time range, being three orders of magnitude shorter than in earlier studied n -type GaAs. The drastic difference is further emphasized by magnetic-field and temperature dependencies of T1 in p -GaAs, showing no similarity to those in n -GaAs. This unexpected behavior finds its explanation in the spatial selectivity of the optical pumping in p -GaAs, that is only efficient in the vicinity of shallow donors, together with the quadrupole relaxation of nuclear spins, which is induced by electric fields within closely spaced donor-acceptor pairs. The developed theoretical model explains the whole set of experimental results.

Immersion transmission ellipsometry (ITE): a new method for the precise determination of the 3D indicatrix of thin films

NASA Astrophysics Data System (ADS)

Jung, C. C.; Stumpe, J.

2005-02-01

The new method of immersion transmission ellipsometry (ITE) [1] has been developed. It allows the highly accurate determination of the absolute three-dimensional (3D) refractive indices of anisotropic thin films. The method is combined with conventional ellipsometry in transmission and reflection, and the thickness determination of anisotropic films solely by optical methods also becomes more accurate. The method is applied to the determination of the 3D refractive indices of thin spin-coated films of an azobenzene-containing liquid-crystalline copolymer. The development of the anisotropy in these films by photo-orientation and subsequent annealing is demonstrated. Depending on the annealing temperature, oblate or prolate orders are generated.

Multilayer self-organization of InGaAs quantum wires on GaAs surfaces

NASA Astrophysics Data System (ADS)

Wang, Zhiming M.; Kunets, Vasyl P.; Xie, Yanze Z.; Schmidbauer, Martin; Dorogan, Vitaliy G.; Mazur, Yuriy I.; Salamo, Gregory J.

2010-12-01

Molecular-Beam Epitaxy growth of multiple In 0.4Ga 0.6As layers on GaAs (311)A and GaAs (331)A has been investigated by Atomic Force Microscopy and Photoluminescence. On GaAs (311)A, uniformly distributed In 0.4Ga 0.6As quantum wires (QWRs) with wider lateral separation were achieved, presenting a significant improvement in comparison with the result on single layer [H. Wen, Z.M. Wang, G.J. Salamo, Appl. Phys. Lett. 84 (2004) 1756]. On GaAs (331)A, In 0.4Ga 0.6As QWRs were revealed to be much straighter than in the previous report on multilayer growth [Z. Gong, Z. Niu, Z. Fang, Nanotechnology 17 (2006) 1140]. These observations are discussed in terms of the strain-field interaction among multilayers, enhancement of surface mobility at high temperature, and surface stability of GaAs (311)A and (331)A surfaces.

On the origin of reflectance-anisotropy oscillations during GaAs (0 0 1) homoepitaxy

NASA Astrophysics Data System (ADS)

Ortega-Gallegos, J.; Guevara-Macías, L. E.; Ariza-Flores, A. D.; Castro-García, R.; Lastras-Martínez, L. F.; Balderas-Navarro, R. E.; López-Estopier, R. E.; Lastras-Martínez, A.

2018-05-01

We report on the first spectroscopic study of reflectance-anisotropy (RA) oscillations during molecular beam epitaxy (MBE) GaAs homoepitaxy. Real-time RA spectra measured during epitaxial growth were carried out with a recently developed rapid RA multichannel spectrometer with 100 ms per spectrum acquisition time. An analysis of the time-resolved RA spectra shows that RA oscillations are mostly due to the periodic modulation of the surface orthorhombic strain associated to surface reconstruction. Results reported here demonstrate the power of real-time RA spectroscopy as a probe for the study of epitaxial growth processes. In particular, given its sub monolayer surface-strain sensitivity, RA spectroscopy results a very convenient tool to study epitaxial growth mechanisms in real-time with sub monolayer resolution. This capability allows for real-time RA spectroscopy to be used as a probe for the in situ, real-time control of epitaxial growth, with the additional advantage of operating in higher pressure systems such as CVD, where RHEED monitoring cannot be implemented.

Growth studies of CVD-MBE by in-situ diagnostics

NASA Astrophysics Data System (ADS)

Maracas, George N.; Steimle, Timothy C.

1992-10-01

This is the final technical report for the three year DARPA-URI program 'Growth Studies of CVD-MBE by in-situ Diagnostics'. The goals of the program were to develop non-invasive, real time epitaxial growth monitoring techniques and combine them to gain an understanding of processes that occur during MBE growth from gas sources. We have adapted these techniques to a commercially designed gas source MBE system (Vacuum Generators Inc.) to facilitate technology transfer out of the laboratory into industrial environments. The in-situ measurement techniques of spectroscopic ellipsometry (SE) and laser induced fluorescence (LIF) have been successfully implemented to monitor the optical and chemical properties of the growing epitaxial film and the gas phase reactants. The ellipsometer was jointly developed with the J. Woolam Co. and has become a commercial product. The temperature dependence of group 3 and 5 desorption from GaAs and InP has been measured as well as the incident effusion cell fluxes. The temporal evolution of the growth has also been measured both by SE and LIF to show the smoothing of heterojunction surfaces during growth interruption. Complicated microcavity optical device structures have been monitored by ellipsometry in real time to improve device quality. This data has been coupled with the structural information obtained from reflection high energy electron diffraction (RHEED) to understand the growth processes in binary and ternary bulk 3-5 semiconductors and heterojunctions.

Implementation and Performance of GaAs Digital Signal Processing ASICs

NASA Technical Reports Server (NTRS)

Whitaker, William D.; Buchanan, Jeffrey R.; Burke, Gary R.; Chow, Terrance W.; Graham, J. Scott; Kowalski, James E.; Lam, Barbara; Siavoshi, Fardad; Thompson, Matthew S.; Johnson, Robert A.

1993-01-01

The feasibility of performing high speed digital signal processing in GaAs gate array technology has been demonstrated with the successful implementation of a VLSI communications chip set for NASA's Deep Space Network. This paper describes the techniques developed to solve some of the technology and implementation problems associated with large scale integration of GaAs gate arrays.

Paths to light trapping in thin film GaAs solar cells.

PubMed

Xiao, Jianling; Fang, Hanlin; Su, Rongbin; Li, Kezheng; Song, Jindong; Krauss, Thomas F; Li, Juntao; Martins, Emiliano R

2018-03-19

It is now well established that light trapping is an essential element of thin film solar cell design. Numerous light trapping geometries have already been applied to thin film cells, especially to silicon-based devices. Less attention has been paid to light trapping in GaAs thin film cells, mainly because light trapping is considered less attractive due to the material's direct bandgap and the fact that GaAs suffers from strong surface recombination, which particularly affects etched nanostructures. Here, we study light trapping structures that are implemented in a high-bandgap material on the back of the GaAs active layer, thereby not perturbing the integrity of the GaAs active layer. We study photonic crystal and quasi-random nanostructures both by simulation and by experiment and find that the photonic crystal structures are superior because they exhibit fewer but stronger resonances that are better matched to the narrow wavelength range where GaAs benefits from light trapping. In fact, we show that a 1500 nm thick cell with photonic crystals achieves the same short circuit current as an unpatterned 4000 nm thick cell. These findings are significant because they afford a sizeable reduction in active layer thickness, and therefore a reduction in expensive epitaxial growth time and cost, yet without compromising performance.

Luminescence and Electroluminescence of Nd, Tm and Yb Doped GaAs and some II-Vi Compounds

DTIC Science & Technology

1994-02-28

from the bandgap discontinuity (as was proposed in my publications [1,2]). Also, by using superlattice structure A1GaAs / GaAs: Er / AlGaAs, we could...n ipact ightemiting evic 10 3. The AlGaAs/GaAs: Er/A1GaAs superlattice structure. For the first time we designed the unipolar n’ - superlattice - n...structure as shown in Figure 5. The GaAs: Er/Alo.45Gao.55As superlattice was grown by MBE on an n’ GaAs: Si substrate. It consisted of 60 periods of

Crystal growth of GaAs in space

NASA Technical Reports Server (NTRS)

Gatos, H. C.; Lagowski, J.; Pawlowicz, L. M.; Dabkowski, F.; Li, C. J.

1984-01-01

It is shown that stoichiometry variations in the GaAs melt during growth constitute the most critical parameter regarding defect formations and their interactions; this defect structure determines all relevant characteristics of GaAs. Convection in the melt leads to stoichiometric variations. Growth in axial magnetic fields reduces convection and permits the study of defect structure. In order to control stoichiometry in space and to accommodate expansion during solidification, a partially confined configuration was developed. A triangular prism is employed to contain the growth melt. This configuration permits the presence of the desired vapor phase in contact with the melt for controlling the melt stoichiometry.

A model for proton-irradiated GaAs solar cells

NASA Technical Reports Server (NTRS)

Wilson, J. W.; Walker, G. H.; Outlaw, R. A.; Stock, L. V.

1982-01-01

A simple model for proton radiation damage in GaAs heteroface solar cells is developed. The model includes the effects of spatial nonuniformity of low energy proton damage. Agreement between the model and experimental proton damage data for GaAs heteroface solar cells is satisfactory. An extension of the model to include angular isotropy, as is appropriate for protons in space, is shown to result in significantly less cell damage than for normal proton incidence.

High efficiency thin-film GaAs solar cells

NASA Technical Reports Server (NTRS)

Stirn, R. J.

1977-01-01

Several oxidation techniques are discussed which have been found to increase the open circuit (V sub oc) of metal-GaAs Schottky barrier solar cells, the oxide chemistry, attempts to measure surface state parameters, the evolving characteristics of the solar cell as background contamination (has been decreased, but not eliminated), results of focused Nd/YAG laser beam recrystallization of Ge films evaporated onto tungsten, and studies of AMOS solar cells fabricated on sliced polycrystalline GaAs wafers. Also discussed are projected materials availability and costs for GaAs thin-film solar cells.

Intrinsic evolutions of dielectric function and electronic transition in tungsten doping Ge{sub 2}Sb{sub 2}Te{sub 5} phase change films discovered by ellipsometry at elevated temperatures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Guo, S.; Ding, X. J.; Zhang, J. Z.

2015-02-02

Tungsten (W) doping effects on Ge{sub 2}Sb{sub 2}Te{sub 5} (GSTW) phase change films with different concentrations (3.2, 7.1, and 10.8%) have been investigated by variable-temperature spectroscopic ellipsometry. The dielectric functions from 210 K to 660 K have been evaluated with the aid of Tauc-Lorentz and Drude dispersion models. The analysis of Tauc gap energy (E{sub g}) and partial spectral weight integral reveal the correlation between optical properties and local structural change. The order degree increment and chemical bond change from covalent to resonant should be responsible for band gap narrowing and electronic transition enhancement during the phase change process. It is foundmore » that the elevated crystalline temperature for GSTW can be related to improved disorder degree. Furthermore, the shrinkage of E{sub g} for GSTW should be attributed to the enhanced metallicity compared with undoped GST.« less

Temporal behavior of RHEED intensity oscillations during molecular beam epitaxial growth of GaAs and AlGaAs on (111)B GaAs substrates

NASA Astrophysics Data System (ADS)

Yen, Ming Y.; Haas, T. W.

1990-10-01

We present the temporal behavior of intensity oscillations in reflection high-energy electron diffraction (RHEED) during molecular beam epitaxial (MBE) growth of GaAs and A1GaAs on (1 1 1)B GaAs substrates. The RHEED intensity oscillations were examined as a function of growth parameters in order to provide the insight into the dynamic characteristics and to identify the optimal condition for the two-dimensional layer-by-layer growth. The most intense RHEED oscillation was found to occur within a very narrow temperature range which seems to optimize the surface migration kinetics of the arriving group III elements and the molecular dissodiative reaction of the group V elements. The appearance of an initial transient of the intensity upon commencement of the growth and its implications are described.

DFT algorithms for bit-serial GaAs array processor architectures

NASA Technical Reports Server (NTRS)

Mcmillan, Gary B.

1988-01-01

Systems and Processes Engineering Corporation (SPEC) has developed an innovative array processor architecture for computing Fourier transforms and other commonly used signal processing algorithms. This architecture is designed to extract the highest possible array performance from state-of-the-art GaAs technology. SPEC's architectural design includes a high performance RISC processor implemented in GaAs, along with a Floating Point Coprocessor and a unique Array Communications Coprocessor, also implemented in GaAs technology. Together, these data processors represent the latest in technology, both from an architectural and implementation viewpoint. SPEC has examined numerous algorithms and parallel processing architectures to determine the optimum array processor architecture. SPEC has developed an array processor architecture with integral communications ability to provide maximum node connectivity. The Array Communications Coprocessor embeds communications operations directly in the core of the processor architecture. A Floating Point Coprocessor architecture has been defined that utilizes Bit-Serial arithmetic units, operating at very high frequency, to perform floating point operations. These Bit-Serial devices reduce the device integration level and complexity to a level compatible with state-of-the-art GaAs device technology.

Effects of surface passivation on twin-free GaAs nanosheets.

PubMed

Arab, Shermin; Chi, Chun-Yung; Shi, Teng; Wang, Yuda; Dapkus, Daniel P; Jackson, Howard E; Smith, Leigh M; Cronin, Stephen B

2015-02-24

Unlike nanowires, GaAs nanosheets exhibit no twin defects, stacking faults, or dislocations even when grown on lattice mismatched substrates. As such, they are excellent candidates for optoelectronic applications, including LEDs and solar cells. We report substantial enhancements in the photoluminescence efficiency and the lifetime of passivated GaAs nanosheets produced using the selected area growth (SAG) method with metal organic chemical vapor deposition (MOCVD). Measurements are performed on individual GaAs nanosheets with and without an AlGaAs passivation layer. Both steady-state photoluminescence and time-resolved photoluminescence spectroscopy are performed to study the optoelectronic performance of these nanostructures. Our results show that AlGaAs passivation of GaAs nanosheets leads to a 30- to 40-fold enhancement in the photoluminescence intensity. The photoluminescence lifetime increases from less than 30 to 300 ps with passivation, indicating an order of magnitude improvement in the minority carrier lifetime. We attribute these enhancements to the reduction of nonradiative recombination due to the compensation of surface states after passivation. The surface recombination velocity decreases from an initial value of 2.5 × 10(5) to 2.7 × 10(4) cm/s with passivation.

High-efficiency, radiation-resistant GaAs space cells

NASA Technical Reports Server (NTRS)

Bertness, K. A.; Ristow, M. Ladle; Grounner, M.; Kuryla, M. S.; Werthen, J. G.

1991-01-01

Although many GaAs solar cells are intended for space applicatons, few measurements of cell degradation after radiation are available, particularly for cells with efficiencies exceeding 20 percent (one-sun, AMO). Often the cell performance is optimized for the highest beginning-of-life (BOL) efficiency, despite the unknown effect of such design on end-of-life (EOL) efficiencies. The results of a study of the radiation effects on p-n GaAs cells are presented. The EOL efficiency of GaAs space cell can be increased by adjusting materials growth parameters, resulting in a demonstration of 16 percent EOL efficiency at one-sun, AMO. Reducing base doping levels to below 3 x 10(exp 17)/cu m and decreasing emitter thickness to 0.3 to 0.5 micron for p-n cells led to significant improvements in radiation hardness as measured by EOL/BOL efficiency ratios for irradiation of 10(exp -15)/sq cm electrons at 1 MeV. BOL efficiency was not affected by changes in emitter thickness but did improve with lower base doping.

Influence of GaAs substrate properties on the congruent evaporation temperature

NASA Astrophysics Data System (ADS)

Spirina, A. A.; Nastovjak, A. G.; Shwartz, N. L.

2018-03-01

High-temperature annealing of GaAs(111)A and GaAs(111)B substrates under Langmuir evaporation conditions was studied using Monte Carlo simulation. The maximal value of the congruent evaporation temperature was estimated. The congruent evaporation temperature was demonstrated to be dependent on the surface orientation and concentration of surface defects.

Formation of embedded plasmonic Ga nanoparticle arrays and their influence on GaAs photoluminescence

NASA Astrophysics Data System (ADS)

Kang, M.; Jeon, S.; Jen, T.; Lee, J.-E.; Sih, V.; Goldman, R. S.

2017-07-01

We introduce a novel approach to the seamless integration of plasmonic nanoparticle (NP) arrays into semiconductor layers and demonstrate their enhanced photoluminescence (PL) efficiency. Our approach utilizes focused ion beam-induced self-assembly of close-packed arrays of Ga NPs with tailorable NP diameters, followed by overgrowth of GaAs layers using molecular beam epitaxy. Using a combination of PL spectroscopy and electromagnetic computations, we identify a regime of Ga NP diameter and overgrown GaAs layer thickness where NP-array-enhanced absorption in GaAs leads to enhanced GaAs near-band-edge (NBE) PL efficiency, surpassing that of high-quality epitaxial GaAs layers. As the NP array depth and size are increased, the reduction in spontaneous emission rate overwhelms the NP-array-enhanced absorption, leading to a reduced NBE PL efficiency. This approach provides an opportunity to enhance the PL efficiency of a wide variety of semiconductor heterostructures.

Self-assembled InAs quantum dot formation on GaAs ring-like nanostructure templates

PubMed Central

Strom, NW; Wang, Zh M; AbuWaar, ZY; Mazur, Yu I; Salamo, GJ

2007-01-01

The evolution of InAs quantum dot (QD) formation is studied on GaAs ring-like nanostructures fabricated by droplet homo-epitaxy. This growth mode, exclusively performed by a hybrid approach of droplet homo-epitaxy and Stransky-Krastanor (S-K) based QD self-assembly, enables one to form new QD morphologies that may find use in optoelectronic applications. Increased deposition of InAs on the GaAs ring first produced a QD in the hole followed by QDs around the GaAs ring and on the GaAs (100) surface. This behavior indicates that the QDs prefer to nucleate at locations of high monolayer (ML) step density.

GaAs quantum dots in a GaP nanowire photodetector

NASA Astrophysics Data System (ADS)

Kuyanov, P.; McNamee, S. A.; LaPierre, R. R.

2018-03-01

We report the structural, optical and electrical properties of GaAs quantum dots (QDs) embedded along GaP nanowires. The GaP nanowires contained p-i-n junctions with 15 consecutively grown GaAs QDs within the intrinsic region. The nanowires were grown by molecular beam epitaxy using the self-assisted vapor-liquid-solid process. The crystal structure of the NWs alternated between twinned ZB and WZ as the composition along the NW alternated between the GaP barriers and the GaAs QDs, respectively, leading to a polytypic structure with a periodic modulation of the NW sidewall facets. Photodetector devices containing QDs showed absorption beyond the bandgap of GaP in comparison to nanowires without QDs. Voltage-dependent measurements suggested a field emission process of carriers from the QDs.

GaAs optoelectronic neuron arrays

NASA Technical Reports Server (NTRS)

Lin, Steven; Grot, Annette; Luo, Jiafu; Psaltis, Demetri

1993-01-01

A simple optoelectronic circuit integrated monolithically in GaAs to implement sigmoidal neuron responses is presented. The circuit integrates a light-emitting diode with one or two transistors and one or two photodetectors. The design considerations for building arrays with densities of up to 10,000/sq cm are discussed.

Investigation of high efficiency GaAs solar cells

NASA Technical Reports Server (NTRS)

Olsen, Larry C.; Dunham, Glen; Addis, F. W.; Huber, Dan; Linden, Kurt

1989-01-01

Investigations of basic mechanisms which limit the performance of high efficiency GaAs solar cells are discussed. P/N heteroface structures have been fabricated from MOCVD epiwafers. Typical AM1 efficiencies are in the 21 to 22 percent range, with a SERI measurement for one cell being 21.5 percent. The cells are nominally 1.5 x 1.5 cm in size. Studies have involved photoresponse, T-I-V analyses, and interpretation of data in terms of appropriate models to determine key cell parameters. Results of these studies are utilized to determine future approaches for increasing GaAs solar cell efficiencies.

Plasma-enhanced atomic layer deposition of titanium oxynitrides films: A comparative spectroscopic and electrical study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sowińska, Małgorzata, E-mail: malgorzata.sowinska@b-tu.de; Henkel, Karsten; Schmeißer, Dieter

2016-01-15

The process parameters' impact of the plasma-enhanced atomic layer deposition (PE-ALD) method on the oxygen to nitrogen (O/N) ratio in titanium oxynitride (TiO{sub x}N{sub y}) films was studied. Titanium(IV)isopropoxide in combination with NH{sub 3} plasma and tetrakis(dimethylamino)titanium by applying N{sub 2} plasma processes were investigated. Samples were characterized by the in situ spectroscopic ellipsometry, x-ray photoelectron spectroscopy, and electrical characterization (current–voltage: I-V and capacitance–voltage: C-V) methods. The O/N ratio in the TiO{sub x}N{sub y} films is found to be very sensitive for their electric properties such as conductivity, dielectric breakdown, and permittivity. Our results indicate that these PE-ALD film propertiesmore » can be tuned, via the O/N ratio, by the selection of the process parameters and precursor/coreactant combination.« less

Response of GaAs charge storage devices to transient ionizing radiation

NASA Astrophysics Data System (ADS)

Hetherington, D. L.; Klem, J. F.; Hughes, R. C.; Weaver, H. T.

Charge storage devices in which non-equilibrium depletion regions represent stored charge are sensitive to ionizing radiation. This results since the radiation generates electron-hole pairs that neutralize excess ionized dopant charge. Silicon structures, such as dynamic RAM or CCD cells are particularly sensitive to radiation since carrier diffusion lengths in this material are often much longer than the depletion width, allowing collection of significant quantities of charge from quasi-neutral sections of the device. For GaAs the situation is somewhat different in that minority carrier diffusion lengths are shorter than in silicon, and although mobilities are higher, we expect a reduction of radiation sensitivity as suggested by observations of reduced quantum efficiency in GaAs solar cells. Dynamic memory cells in GaAs have potential increased retention times. In this paper, we report the response of a novel GaAs dynamic memory element to transient ionizing radiation. The charge readout technique is nondestructive over a reasonable applied voltage range and is more sensitive to stored charge than a simple capacitor.

Enhancement of conductance of GaAs sub-microwires under external stimuli

NASA Astrophysics Data System (ADS)

Qu, Xianlin; Deng, Qingsong; Zheng, Kun

2018-03-01

Semiconductors with one dimension on the micro-nanometer scale have many unique physical properties that are remarkably different from those of their bulk counterparts. Moreover, changes in the external field will further modulate the properties of the semiconductor micro-nanomaterials. In this study, we used focused ion beam technology to prepare freestanding ⟨111⟩-oriented GaAs sub-microwires from a GaAs substrate. The effects of laser irradiation and bending or buckling deformation induced by compression on the electrical transport properties of an individual GaAs sub-microwire were studied. The experimental results indicate that both laser irradiation and bending deformation can enhance their electrical transport properties, the laser irradiation resulted in a conductance enhancement of ˜30% compared to the result with no irradiation, and in addition, bending deformation changed the conductance by as much as ˜180% when the average strain was approximately 1%. The corresponding mechanisms are also discussed. This study provides beneficial insight into the fabrication of electronic and optoelectronic devices based on GaAs micro/nano-wires.

Crystal growth of device quality GaAs in space

NASA Technical Reports Server (NTRS)

Gatos, H. C.; Lagowski, J.

1985-01-01

The present program has been aimed at solving the fundamental and technological problems associated with Crystal Growth of Device Quality in Space. The initial stage of the program was devoted strictly to ground-based research. The unsolved problems associated with the growth of bulk GaAs in the presence of gravitational forces were explored. Reliable chemical, structural and electronic characterization methods were developed which would permit the direct relation of the salient materials parameters (particularly those affected by zero gravity conditions) to the electronic characteristics of single crystal GaAs, in turn to device performance. These relationships are essential for the development of optimum approaches and techniques. It was concluded that the findings on elemental semiconductors Ge and Si regarding crystal growth, segregation, chemical composition, defect interactions, and materials properties-electronic properties relationships are not necessarily applicable to GaAs (and to other semiconductor compounds). In many instances totally unexpected relationships were found to prevail.

Blueish green photoluminescence from nitrided GaAs(100) surfaces

NASA Astrophysics Data System (ADS)

Shimaoka, Goro; Udagawa, Takashi

1999-04-01

Optical and structural studies were made on the Si-doped (100)GaAs surfaces nitrided at a temperature between 650° and 750°C for 15 min in the flowing NH 3 gas. The wavelength of photoluminescence (PL) spectra were observed to be shortened from 820 nm of the GaAs nitrided at 650°C with increasing nitridation temperature. Blueish green PL with wavelengths of approx. 490 nm and 470 nm were emitted from the nitrided surfaces at 700° and 750°C, respectively. Results of AES and SIMS indicated that the surfaces are nitrided as GaAs 1- xN x, (0< x≤1) alloy layer, and the nitrided region also tended to increase as the temperature raised. High-resolution transmission electron microscopic (HRTEM), transmission electron diffraction (TED) and energy dispersive X-ray (EDX) results showed that films peeled off from the nitrided surfaces consisted mainly of hexagonal, wurtzite-type gallium nitride (GaN) with stacking faults and microtwins.

GaAs High Breakdown Voltage Front and Back Side Processed Schottky Detectors for X-Ray Detection

DTIC Science & Technology

2007-11-01

front and back side processed, unintentionally doped bulk gallium -arsenic (GaAs) Schottky detectors and determined that GaAs detectors with a large...a few materials that fulfill these requirements are gallium -arsenic (GaAs) and cadmium-zinc-tellurium (CdZnTe or CZT). They are viable alternative...Whitehill, C.; Pospíšil, S.; Wilhem, I.; Doležal, Z.; Juergensen, H.; Heuken, M. Development of low-pressure vapour -phase epitaxial GaAs for medical imaging

Room temperature lasing of GaAs quantum wire vertical-cavity surface-emitting lasers grown on (7 7 5) B GaAs substrates by molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Higuchi, Y.; Osaki, S.; Kitada, T.; Shimomura, S.; Takasuka, Y.; Ogura, M.; Hiyamizu, S.

2006-06-01

Self-organized GaAs/(GaAs) 4(AlAs) 2 quantum wires (QWRs) grown on (7 7 5) B-oriented GaAs substrates by molecular beam epitaxy have been applied to an active region of vertical-cavity surface-emitting lasers (VCSELs). The (7 7 5) B GaAs QWR-VCSEL with an aperture diameter of 3 μm lased at a wavelength of 765 nm with a threshold current of 0.38 mA at room temperature. This is the first demonstration of laser operation of the QWR-VCSEL by current injection. The light output was linearly polarized in the direction parallel to the QWRs due to the optical anisotropy of the self-organized (7 7 5) B GaAs QWRs.

Growth and characterization of molecular beam epitaxial GaAs layers on porous silicon

NASA Technical Reports Server (NTRS)

Lin, T. L.; Liu, J. K.; Sadwick, L.; Wang, K. L.; Kao, Y. C.

1987-01-01

GaAs layers have been grown on porous silicon (PS) substrates with good crystallinity by molecular beam epitaxy. In spite of the surface irregularity of PS substrates, no surface morphology deterioration was observed on epitaxial GaAs overlayers. A 10-percent Rutherford backscattering spectroscopy minimum channeling yield for GaAs-on-PS layers as compared to 16 percent for GaAs-on-Si layers grown under the same condition indicates a possible improvement of crystallinity when GaAs is grown on PS. Transmission electron microscopy reveals that the dominant defects in the GaAs-on-PS layers are microtwins and stacking faults, which originate from the GaAs/PS interface. GaAs is found to penetrate into the PS layers. n-type GaAs/p-type PS heterojunction diodes were fabricated with good rectifying characteristics.

ZnSe Window Layers for GaAs and GaInP2 Solar Cells

NASA Technical Reports Server (NTRS)

Olsen, Larry C.

1997-01-01

This report concerns studies of the use of n-type ZnSe as a window layer for n/p GaAs and GaInP2 solar cells. Emphasis was placed in this phase of the project on characterizing the interface between n-type ZnSe films grown on epi-GaAs films grown onto single crystal GaAs. Epi-GaAs and heteroepitaxial ZnSe films were grown by MOCVD with a Spire 50OXT Reactor. After growing epitaxial GaAs films on single crystal GaAs wafers, well-oriented crystalline ZnSe films were grown by MOCVD. ZnSe films were grown with substrate temperatures ranging from 250 C to 450 C. Photoluminescence studies carried out by researchers at NASA Lewis determined that the surface recombination velocity at a GaAs surface was significantly reduced after the deposition of a heteroepitaxial layer of ZnSe. The optimum temperature for ZnSe deposition appears to be on the order of 350 C.

Quantification of Ligand Binding to G-Protein Coupled Receptors on Cell Membranes by Ellipsometry

PubMed Central

Kriechbaumer, Verena; Nabok, Alexei; Widdowson, Robert; Smith, David P.; Abell, Ben M.

2012-01-01

G-protein-coupled receptors (GPCRs) are prime drug targets and targeted by approximately 60% of current therapeutic drugs such as β-blockers, antipsychotics and analgesics. However, no biophysical methods are available to quantify their interactions with ligand binding in a native environment. Here, we use ellipsometry to quantify specific interactions of receptors within native cell membranes. As a model system, the GPCR-ligand CXCL12α and its receptor CXCR4 are used. Human-derived Ishikawa cells were deposited onto gold coated slides via Langmuir-Schaefer film deposition and interactions between the receptor CXCR4 on these cells and its ligand CXCL12α were detected via total internal reflection ellipsometry (TIRE). This interaction could be inhibited by application of the CXCR4-binding drug AMD3100. Advantages of this approach are that it allows measurement of interactions in a lipid environment without the need for labelling, protein purification or reconstitution of membrane proteins. This technique is potentially applicable to a wide variety of cell types and their membrane receptors, providing a novel method to determine ligand or drug interactions targeting GPCRs and other membrane proteins. PMID:23049983

Low-temperature photoluminescence study of thin epitaxial GaAs films on Ge substrates

NASA Astrophysics Data System (ADS)

Brammertz, Guy; Mols, Yves; Degroote, Stefan; Motsnyi, Vasyl; Leys, Maarten; Borghs, Gustaaf; Caymax, Matty

2006-05-01

Thin epitaxial GaAs films, with thickness varying from 140 to 1000 nm and different Si doping levels, were grown at 650 °C by organometallic vapor phase epitaxy on Ge substrates and analyzed by low-temperature photoluminescence (PL) spectroscopy. All spectra of thin GaAs on Ge show two different structures, one narrow band-to-band (B2B) structure at an energy of ~1.5 eV and a broad inner-band-gap (IB) structure at an energy of ~1.1 eV. Small strain in the thin GaAs films causes the B2B structure to be separated into a light-hole and a heavy-hole peak. At 2.5 K the good structural quality of the thin GaAs films on Ge can be observed from the narrow excitonic peaks. Peak widths of less than 1 meV are measured. GaAs films with thickness smaller than 200 nm show B2B PL spectra with characteristics of an n-type doping level of approximately 1018 at./cm3. This is caused by heavy Ge diffusion from the substrate into the GaAs at the heterointerface between the two materials. The IB structure observed in all films consists of two Gaussian peaks with energies of 1.04 and 1.17 eV. These deep trapping states arise from Ge-based complexes formed within the GaAs at the Ge-GaAs heterointerface, due to strong diffusion of Ge atoms into the GaAs. Because of similarities with Si-based complexes, the peak at 1.04 eV was identified to be due to a GeGa-GeAs complex, whereas the peak at 1.17 eV was attributed to the GeGa-VGa complex. The intensity of the IB structure decreases strongly as the GaAs film thickness is increased. PL intensity of undoped GaAs films containing antiphase domains (APDs) is four orders of magnitude lower than for similar films without APDs. This reduction in intensity is due to the electrically active Ga-Ga and As-As bonds at the boundaries between the different APDs. When the Si doping level is increased, the PL intensity of the APD-containing films is increased again as well. A film containing APDs with a Si doping level of ~1018 at./cm3 has only a factor 10

Maskless micro/nanofabrication on GaAs surface by friction-induced selective etching

PubMed Central

2014-01-01

In the present study, a friction-induced selective etching method was developed to produce nanostructures on GaAs surface. Without any resist mask, the nanofabrication can be achieved by scratching and post-etching in sulfuric acid solution. The effects of the applied normal load and etching period on the formation of the nanostructure were studied. Results showed that the height of the nanostructure increased with the normal load or the etching period. XPS and Raman detection demonstrated that residual compressive stress and lattice densification were probably the main reason for selective etching, which eventually led to the protrusive nanostructures from the scratched area on the GaAs surface. Through a homemade multi-probe instrument, the capability of this fabrication method was demonstrated by producing various nanostructures on the GaAs surface, such as linear array, intersecting parallel, surface mesas, and special letters. In summary, the proposed method provided a straightforward and more maneuverable micro/nanofabrication method on the GaAs surface. PMID:24495647

The ZnSe(110) puzzle - Comparison with GaAs(110)

NASA Technical Reports Server (NTRS)

Duke, C. B.; Paton, A.; Kahn, A.; Tu, D.-W.

1984-01-01

The surface structure of monocrystalline ZnSe(110) and of 4-5-nm-thick ZnSe(110) layers epitaxially grown on GaAs(110) is investigated by means of elastic LEED and AES; the results are analyzed using the computer programs and R-factor methods of Duke et al. (1981 and 1983), presented in graphs and tables, and compared to those for GaAs(110). Significant differences are attributed to bond-length-conserving outward rotation of Se and inward rotation of Zn in the top layer, with an angle of 4 deg between the actual plane of the cation-anion chain and the truncated bulk surface. The R intensities measured for ZnSe(110) and GaAs(110) are given as Rx = 0.22 and RI = 0.21 and Rx = 0.24 and RI = 0.16, respectively.

First tests of Timepix detectors based on semi-insulating GaAs matrix of different pixel size

NASA Astrophysics Data System (ADS)

Zaťko, B.; Kubanda, D.; Žemlička, J.; Šagátová, A.; Zápražný, Z.; Boháček, P.; Nečas, V.; Mora, Y.; Pichotka, M.; Dudák, J.

2018-02-01

In this work, we have focused on Timepix detectors coupled with the semi-insulating GaAs material sensor. We used undoped bulk GaAs material with the thickness of 350 μm. We prepared and tested four pixelated detectors with 165 μm and 220 μm pixel size with two versions of technology preparation, without and with wet chemically etched trenches around each pixel. We have carried out adjustment of GaAs Timepix detectors to optimize their performance. The energy calibration of one GaAs Timepix detector in Time-over-threshold mode was performed with the use of 241Am and 133Ba radioisotopes. We were able to detect γ-photons with the energy up to 160 keV. The X-ray imaging quality of GaAs Timepix detector was tested with X-ray source using various samples. After flat field we obtained very promising imaging performance of tested GaAs Timepix detectors.

Performance and temperature dependencies of proton irradiated n/p and p/n GaAs and n/p silicon cells

NASA Technical Reports Server (NTRS)

Weinberg, I.; Swartz, C. K.; Hart, R. E., Jr.

1985-01-01

n/p homojunction GaAs cells are found to be more radiation resistant than p/n heteroface GaAs under 10 MeV proton irradiation. Both GaAs cell types outperform conventional silicon n/p cells under the same conditions. An increased temperature dependency of maximum power for the GaAs n/p cells is attributed to differences in Voc between the two GaAs cell types. These results and diffusion length considerations are consistent with the conclusion that p-type GaAs is more radiation resistant than n-type and therefore that the n/p configuration is possibly favored for use in the space radiation environment. However, it is concluded that additional work is required in order to choose between the two GaAs cell configurations.

GaAs laser diode pumped Nd:YAG laser

NASA Technical Reports Server (NTRS)

Conant, L. C.; Reno, C. W.

1974-01-01

A 1.5-mm by 3-cm neodymium-ion doped YAG laser rod has been side pumped using a GaAs laser diode array tuned to the 8680-A absorption line, achieving a multimode average output power of 120 mW for a total input power of 20 W to the final-stage laser diode drivers. The pumped arrangement was designed to take advantage of the high brightness of a conventional GaAs array as a linear source by introducing the pump light through a slit into a close-wrapped gold coated pump cavity. This cavity forms an integrating chamber for the pump light.

Effects of ultrathin oxides in conducting MIS structures on GaAs

NASA Technical Reports Server (NTRS)

Childs, R. B.; Ruths, J. M.; Sullivan, T. E.; Fonash, S. J.

1978-01-01

Schottky barrier-type GaAs baseline devices (semiconductor surface etched and then immediately metalized) and GaAs conducting metal oxide-semiconductor devices are fabricated and characterized. The baseline surfaces (no purposeful oxide) are prepared by a basic or an acidic etch, while the surface for the MIS devices are prepared by oxidizing after the etch step. The metallizations used are thin-film Au, Ag, Pd, and Al. It is shown that the introduction of purposeful oxide into these Schottky barrier-type structures examined on n-type GaAs modifies the barrier formation, and that thin interfacial layers can modify barrier formation through trapping and perhaps chemical reactions. For Au- and Pd-devices, enhanced photovoltaic performance of the MIS configuration is due to increased barrier height.

Probability of twin formation on self-catalyzed GaAs nanowires on Si substrate

PubMed Central

2012-01-01

We attempted to control the incorporation of twin boundaries in self-catalyzed GaAs nanowires (NWs). Self-catalyzed GaAs NWs were grown on a Si substrate under various arsenic pressures using molecular beam epitaxy and the vapor-liquid-solid method. When the arsenic flux is low, wurtzite structures are dominant in the GaAs NWs. On the other hand, zinc blende structures become dominant as the arsenic flux rises. We discussed this phenomenon on the basis of thermodynamics and examined the probability of twin-boundary formation in detail. PMID:23043754

Modified energetics and growth kinetics on H-terminated GaAs (110)

NASA Astrophysics Data System (ADS)

Galiana, B.; Benedicto, M.; Díez-Merino, L.; Lorbek, S.; Hlawacek, G.; Teichert, C.; Tejedor, P.

2013-10-01

Atomic hydrogen modification of the surface energy of GaAs (110) epilayers, grown at high temperatures from molecular beams of Ga and As4, has been investigated by friction force microscopy (FFM). The reduction of the friction force observed with longer exposures to the H beam has been correlated with the lowering of the surface energy originated by the progressive de-relaxation of the GaAs (110) surface occurring upon H chemisorption. Our results indicate that the H-terminated GaAs (110) epilayers are more stable than the As-stabilized ones, with the minimum surface energy value of 31 meV/Å2 measured for the fully hydrogenated surface. A significant reduction of the Ga diffusion length on the H-terminated surface irrespective of H coverage has been calculated from the FFM data, consistent with the layer-by-layer growth mode and the greater As incorporation coefficient determined from real-time reflection high-energy electron diffraction studies. Arsenic incorporation through direct dissociative chemisorption of single As4 molecules mediated by H on the GaAs (110) surface has been proposed as the most likely explanation for the changes in surface kinetics observed.

Surface segregation and the Al problem in GaAs quantum wells

NASA Astrophysics Data System (ADS)

Chung, Yoon Jang; Baldwin, K. W.; West, K. W.; Shayegan, M.; Pfeiffer, L. N.

2018-03-01

Low-defect two-dimensional electron systems (2DESs) are essential for studies of fragile many-body interactions that only emerge in nearly-ideal systems. As a result, numerous efforts have been made to improve the quality of modulation-doped AlxGa1 -xAs /GaAs quantum wells (QWs), with an emphasis on purifying the source material of the QW itself or achieving better vacuum in the deposition chamber. However, this approach overlooks another crucial component that comprises such QWs, the AlxGa1 -xAs barrier. Here we show that having a clean Al source and hence a clean barrier is instrumental to obtain a high-quality GaAs 2DES in a QW. We observe that the mobility of the 2DES in GaAs QWs declines as the thickness or Al content of the AlxGa1 -xAs barrier beneath the QW is increased, which we attribute to the surface segregation of oxygen atoms that originate from the Al source. This conjecture is supported by the improved mobility in the GaAs QWs as the Al cell is cleaned out by baking.

Large Signal Modeling and Analysis of the GaAs MESFET.

DTIC Science & Technology

1986-07-09

various dimensions and physical parameters. A powerful computer aided design system can be developed by automating the circuit element and parameter...circuit model of the GaAs MESFET to aid in the designs of microwave MESFET circuits. The circuit elements of this model are obtained either directly...34. -. ’ Abstract The purpose of this work is to develop a large signal signal lumped circuit model of the GaAs MESFET to aid In the designs of microwave MESFET

Structural and electronic properties of isovalent boron atoms in GaAs

NASA Astrophysics Data System (ADS)

Krammel, C. M.; Nattermann, L.; Sterzer, E.; Volz, K.; Koenraad, P. M.

2018-04-01

Boron containing GaAs, which is grown by metal organic vapour phase epitaxy, is studied at the atomic level by cross-sectional scanning tunneling microscopy (X-STM) and spectroscopy (STS). In topographic X-STM images, three classes of B related features are identified, which are attributed to individual B atoms on substitutional Ga sites down to the second layer below the natural {110} cleavage planes. The X-STM contrast of B atoms below the surface reflects primarily the structural modification of the GaAs matrix by the small B atoms. However, B atoms in the cleavage plane have in contrast to conventional isovalent impurities, such as Al and In, a strong influence on the local electronic structure similar to donors or acceptors. STS measurements show that B in the GaAs {110} surfaces gives rise to a localized state short below the conduction band (CB) edge while in bulk GaAs, the B impurity state is resonant with the CB. The analysis of BxGa1-xAs/GaAs quantum wells reveals a good crystal quality and shows that the incorporation of B atoms in GaAs can be controlled along the [001] growth direction at the atomic level. Surprisingly, the formation of the first and fourth nearest neighbor B pairs, which are oriented along the <110 > directions, is strongly suppressed at a B concentration of 1% while the third nearest neighbor B pairs are found more than twice as often than expected for a completely spatially random pattern.

Giant and reversible enhancement of the electrical resistance of GaAs1-xNx by hydrogen irradiation

NASA Astrophysics Data System (ADS)

Alvarez, J.; Kleider, J.-P.; Trotta, R.; Polimeni, A.; Capizzi, M.; Martelli, F.; Mariucci, L.; Rubini, S.

2011-08-01

The electrical properties of untreated and hydrogen-irradiated GaAs1-xNx are investigated by conductive-probe atomic force microscopy (CP-AFM). After hydrogen irradiation, the resistance R of GaAs1-xNx increases by more than three orders of magnitude while that of a N-free GaAs reference slightly decreases. Thermal annealing at 550 °C of H-irradiated GaAs1-xNx restores the pristine electrical properties of the as-grown sample thus demonstrating that this phenomenon is fully reversible. These effects are attributed to the nitrogen-hydrogen complexes that passivate N in GaAs1-xNx (thus restoring the energy gap of N-free GaAs) and, moreover, reduce the carrier scattering time by more than one order of magnitude. This opens up a route to the fabrication of planar conductive/resistive/conductive heterostructures with submicrometer spatial resolution, which is also reported here.

Electrical and band structural analyses of Ti1-x Al x O y films grown by atomic layer deposition on p-type GaAs

NASA Astrophysics Data System (ADS)

An, Youngseo; Mahata, Chandreswar; Lee, Changmin; Choi, Sungho; Byun, Young-Chul; Kang, Yu-Seon; Lee, Taeyoon; Kim, Jiyoung; Cho, Mann-Ho; Kim, Hyoungsub

2015-10-01

Amorphous Ti1-x Al x O y films in the Ti-oxide-rich regime (x  <  0.5) were deposited on p-type GaAs via atomic layer deposition with titanium isopropoxide, trimethylaluminum, and H2O precursor chemistry. The electrical properties and energy band alignments were examined for the resulting materials with their underlying substrates, and significant frequency dispersion was observed in the accumulation region of the Ti-oxide-rich Ti1-x Al x O y films. Although a further reduction in the frequency dispersion and leakage current (under gate electron injection) could be somewhat achieved through a greater addition of Al-oxide in the Ti1-x Al x O y film, the simultaneous decrease in the dielectric constant proved problematic in finding an optimal composition for application as a gate dielectric on GaAs. The spectroscopic band alignment measurements of the Ti-oxide-rich Ti1-x Al x O y films indicated that the band gaps had a rather slow increase with the addition of Al-oxide, which was primarily compensated for by an increase in the valance band offset, while a nearly-constant conduction band offset with a negative electron barrier height was maintained.

Testing a GaAs cathode in SRF gun

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, E.; Kewisch, J.; Ben-Zvi, I.

RF electron guns with a strained superlattice GaAs cathode are expected to generate polarized electron beams of higher brightness and lower emittance than do DC guns, due to their higher field gradient at the cathode's surface and lower cathode temperature. We plan to install a bulk GaAs:Cs in a SRF gun to evaluate the performance of both the gun and the cathode in this environment. The status of this project is: In our 1.3 GHz 1/2 cell SRF gun, the vacuum can be maintained at nearly 10{sup -12} Torr because of cryo-pumping at 2K. With conventional activation of bulk GaAs,more » we obtained a QE of 10% at 532 nm, with lifetime of more than 3 days in the preparation chamber and have shown that it can survive in transport from the preparation chamber to the gun. The beam line has been assembled and we are exploring the best conditions for baking the cathode under vacuum. We report here the progress of our test of the GaAs cathode in the SRF gun. Future particle accelerators, such as eRHIC and the ILC require high-brightness, high-current polarized electrons. Strained superlattice GaAs:Cs has been shown to be an efficient cathode for producing polarized electrons. Activation of GaAs with Cs,O(F) lowers the electron affinity and makes it energetically possible for all the electrons, excited into the conduction band that drift or diffuse to the emission surface, to escape into the vacuum. Presently, all operating polarized electron sources, such as the CEBAF, are DC guns. In these devices, the excellent ultra-high vacuum extends the lifetime of the cathode. However, the low field gradient on the photocathode's emission surface of the DC guns limits the beam quality. The higher accelerating gradients, possible in the RF guns, generate a far better beam. Until recently, most RF guns operated at room temperature, limiting the vacuum to {approx}10{sup -9} Torr. This destroys the GaAs's NEA surface. The SRF guns combine the excellent vacuum conditions of DC guns and the

Design of quantum efficiency measurement system for variable doping GaAs photocathode

NASA Astrophysics Data System (ADS)

Chen, Liang; Yang, Kai; Liu, HongLin; Chang, Benkang

2008-03-01

To achieve high quantum efficiency and good stability has been a main direction to develop GaAs photocathode recently. Through early research, we proved that variable doping structure is executable and practical, and has great potential. In order to optimize variable doping GaAs photocathode preparation techniques and study the variable doping theory deeply, a real-time quantum efficiency measurement system for GaAs Photocathode has been designed. The system uses FPGA (Field-programmable gate array) device, and high speed A/D converter to design a high signal noise ratio and high speed data acquisition card. ARM (Advanced RISC Machines) core processor s3c2410 and real-time embedded system are used to obtain and show measurement results. The measurement precision of photocurrent could reach 1nA, and measurement range of spectral response curve is within 400~1000nm. GaAs photocathode preparation process can be real-time monitored by using this system. This system could easily be added other functions to show the physic variation of photocathode during the preparation process more roundly in the future.

Epitaxial lateral overgrowth of GaAs: effect of doping on LPE growth behaviour

NASA Astrophysics Data System (ADS)

Zytkiewicz, Z. R.; Dobosz, D.; Pawlowska, M.

1999-05-01

Results of epitaxial lateral overgrowth (ELO) of GaAs on (001) GaAs substrates by liquid phase epitaxy are reported. We show that by introducing Si, Sn or Te impurities to the Ga-As solution the vertical growth rate is reduced while the lateral growth rate is significantly enhanced, which leads to a growth habit modification. Furthermore, the impurity incorporation into the growing layer is different on the upper and side surfaces of the ELO, reflecting the fundamental differences between the lateral and vertical growth modes. This phenomenon can be applied for studying the temporal development of ELO layers.

Electric field effects on the optical properties of buckled GaAs monolayer

NASA Astrophysics Data System (ADS)

Bahuguna, Bhagwati Prasad; Saini, L. K.; Sharma, Rajesh O.

2018-04-01

Buckled GaAs monolayer has a direct band gap semiconductor with energy gap of 1.31 eV in the absence of electric field. When we applied transverse electric field, the value of band gap decreases with increasing of electric field strength. In our previous work [1], it is observed that the buckled GaAs monolayer becomes metallic at 1.3 V/Å. In the present work, we investigate the optical properties such as photon energy-dependent dielectric functions, extinction coefficient, refractive index, absorption spectrum and reflectivity of buckled GaAs monolayer in the semiconducting phase i.e. absence of external electric field and metallic phase i.e. presence of external electric field using density functional theory.

Nuclear spin warm up in bulk n -GaAs

NASA Astrophysics Data System (ADS)

Kotur, M.; Dzhioev, R. I.; Vladimirova, M.; Jouault, B.; Korenev, V. L.; Kavokin, K. V.

2016-08-01

We show that the spin-lattice relaxation in n -type insulating GaAs is dramatically accelerated at low magnetic fields. The origin of this effect, which cannot be explained in terms of well-known diffusion-limited hyperfine relaxation, is found in the quadrupole relaxation, induced by fluctuating donor charges. Therefore, quadrupole relaxation, which governs low field nuclear spin relaxation in semiconductor quantum dots, but was so far supposed to be harmless to bulk nuclei spins in the absence of optical pumping, can be studied and harnessed in the much simpler model environment of n -GaAs bulk crystal.

46 CFR Sec. 7 - Operation under current GAA/MSTS Southeast Asia Program.

Code of Federal Regulations, 2013 CFR

2013-10-01

... provisions of NSA Order 35 (OPR-2) to the particular circumstances of the present GAA/MSTS Southeast Asia... General Agency operations not related to the current GAA/MSTS Southeast Asia Program, NSA Order 35 (OPR-2... lieu of those appearing in sections 3 and 4 of NSA Order 35 (OPR-2). Continental United States ports do...

46 CFR Sec. 7 - Operation under current GAA/MSTS Southeast Asia Program.

Code of Federal Regulations, 2012 CFR

2012-10-01

... provisions of NSA Order 35 (OPR-2) to the particular circumstances of the present GAA/MSTS Southeast Asia... General Agency operations not related to the current GAA/MSTS Southeast Asia Program, NSA Order 35 (OPR-2... lieu of those appearing in sections 3 and 4 of NSA Order 35 (OPR-2). Continental United States ports do...

46 CFR Sec. 7 - Operation under current GAA/MSTS Southeast Asia Program.

Code of Federal Regulations, 2010 CFR

2010-10-01

... provisions of NSA Order 35 (OPR-2) to the particular circumstances of the present GAA/MSTS Southeast Asia... General Agency operations not related to the current GAA/MSTS Southeast Asia Program, NSA Order 35 (OPR-2... lieu of those appearing in sections 3 and 4 of NSA Order 35 (OPR-2). Continental United States ports do...

46 CFR Sec. 7 - Operation under current GAA/MSTS Southeast Asia Program.

Code of Federal Regulations, 2014 CFR

2014-10-01

... provisions of NSA Order 35 (OPR-2) to the particular circumstances of the present GAA/MSTS Southeast Asia... General Agency operations not related to the current GAA/MSTS Southeast Asia Program, NSA Order 35 (OPR-2... lieu of those appearing in sections 3 and 4 of NSA Order 35 (OPR-2). Continental United States ports do...

46 CFR Sec. 7 - Operation under current GAA/MSTS Southeast Asia Program.

Code of Federal Regulations, 2011 CFR

2011-10-01

... provisions of NSA Order 35 (OPR-2) to the particular circumstances of the present GAA/MSTS Southeast Asia... General Agency operations not related to the current GAA/MSTS Southeast Asia Program, NSA Order 35 (OPR-2... lieu of those appearing in sections 3 and 4 of NSA Order 35 (OPR-2). Continental United States ports do...

GaAs Solar Cell Radiation Handbook

NASA Technical Reports Server (NTRS)

Anspaugh, B. E.

1996-01-01

History of GaAs solar cell development is provided. Photovoltaic equations are described along with instrumentation techniques for measuring solar cells. Radiation effects in solar cells, electrical performance, and spacecraft flight data for solar cells are discussed. The space radiation environment and solar array degradation calculations are addressed.

Influence of annealing temperature and Sn doping on the optical properties of hematite thin films determined by spectroscopic ellipsometry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Souza, Lígia P. de; Chaves, Rodrigo O. G.; Malachias, Angelo

2016-06-28

Hematite (α-Fe{sub 2}O{sub 3}) thin films were prepared by sol-gel route and investigated for application in H{sub 2} generation by photo-assisted water splitting. The photoelectrochemical (PEC) performance was shown to increase significantly for films deposited on SnO{sub 2}:F/glass subjected to high temperature (T) annealing (>750 °C). Strong correlation was found between photogenerated current, donor concentration, and Sn concentration as determined by Mott-Schottky analysis and X-ray photoelectron spectroscopy. The effects of thermal annealing and Sn addition in the resulting microstructure and optical properties of hematite films deposited on fused silica substrates were determined by a combination of structural characterization techniques and spectroscopicmore » ellipsometry. Thermal annealing (>600 °C) induces a higher optical absorption that is associated directly to film densification and grain growth; however, it promotes no changes in the energy positions of the main Fe{sub 2}O{sub 3} electronic transitions. The band gap energy was found to be 2.21 eV and independent of microstructure and of Sn concentration for all studied films. On the other hand, Sn can be incorporated in the Fe{sub 2}O{sub 3} lattice for concentration up to Sn/Fe ∼2%, leading to an increase in energy split of the main absorption peak, attributed to a distortion of the Fe{sub 2}O{sub 3} lattice. For higher concentrations, Sn incorporation leads to a reduction in absorption, associated with higher porosity and the formation of a secondary Sn-rich phase. In summary, the variation in the optical properties induced by thermal annealing and Sn addition cannot account for the order of magnitude increase of the current density generated by photoanodes annealed at high T (>750 °C); thus, it is concluded that the major contribution for the enhanced PEC performance comes from improved electronic properties induced by the n-type doping caused by Sn diffusion from the SnO{sub 2}:F

Interface dynamics and crystal phase switching in GaAs nanowires

NASA Astrophysics Data System (ADS)

Jacobsson, Daniel; Panciera, Federico; Tersoff, Jerry; Reuter, Mark C.; Lehmann, Sebastian; Hofmann, Stephan; Dick, Kimberly A.; Ross, Frances M.

2016-03-01

Controlled formation of non-equilibrium crystal structures is one of the most important challenges in crystal growth. Catalytically grown nanowires are ideal systems for studying the fundamental physics of phase selection, and could lead to new electronic applications based on the engineering of crystal phases. Here we image gallium arsenide (GaAs) nanowires during growth as they switch between phases as a result of varying growth conditions. We find clear differences between the growth dynamics of the phases, including differences in interface morphology, step flow and catalyst geometry. We explain these differences, and the phase selection, using a model that relates the catalyst volume, the contact angle at the trijunction (the point at which solid, liquid and vapour meet) and the nucleation site of each new layer of GaAs. This model allows us to predict the conditions under which each phase should be observed, and use these predictions to design GaAs heterostructures. These results could apply to phase selection in other nanowire systems.

Periodic annealing of radiation damage in GaAs solar cells

NASA Technical Reports Server (NTRS)

Loo, R. Y.; Knechtli, R. C.; Kamath, G. S.

1980-01-01

Continuous annealing of GaAs solar cells is compared with periodic annealing to determine their relative effectiveness in minimizing proton radiation damage. It is concluded that continuous annealing of the cells in space at 150 C can effectively reduce the proton radiation damage to the GaAs solar cells. Periodic annealing is most effective if it can be initiated at relatively low fluences (approximating continuous annealing), especially if low temperatures of less than 200 C are to be used. If annealing is started only after the fluence of the damaging protons has accumulated to a high value 10 to the 11th power sq/pcm), effective annealing is still possible at relatively high temperatures. Finally, since electron radiation damage anneals even more easily than proton radiation damage, substantial improvements in GaAs solar cell life can be achieved by incorporating the proper annealing capabilities in solar panels for practical space missions where both electron and proton radiation damage have to be minimized.

Interface dynamics and crystal phase switching in GaAs nanowires.

PubMed

Jacobsson, Daniel; Panciera, Federico; Tersoff, Jerry; Reuter, Mark C; Lehmann, Sebastian; Hofmann, Stephan; Dick, Kimberly A; Ross, Frances M

2016-03-17

Controlled formation of non-equilibrium crystal structures is one of the most important challenges in crystal growth. Catalytically grown nanowires are ideal systems for studying the fundamental physics of phase selection, and could lead to new electronic applications based on the engineering of crystal phases. Here we image gallium arsenide (GaAs) nanowires during growth as they switch between phases as a result of varying growth conditions. We find clear differences between the growth dynamics of the phases, including differences in interface morphology, step flow and catalyst geometry. We explain these differences, and the phase selection, using a model that relates the catalyst volume, the contact angle at the trijunction (the point at which solid, liquid and vapour meet) and the nucleation site of each new layer of GaAs. This model allows us to predict the conditions under which each phase should be observed, and use these predictions to design GaAs heterostructures. These results could apply to phase selection in other nanowire systems.

GaSb thermophotovoltaic cells grown on GaAs by molecular beam epitaxy using interfacial misfit arrays

DOE Office of Scientific and Technical Information (OSTI.GOV)

Juang, Bor-Chau, E-mail: bcjuang@ucla.edu; Laghumavarapu, Ramesh B.; Foggo, Brandon J.

There exists a long-term need for foreign substrates on which to grow GaSb-based optoelectronic devices. We address this need by using interfacial misfit arrays to grow GaSb-based thermophotovoltaic cells directly on GaAs (001) substrates and demonstrate promising performance. We compare these cells to control devices grown on GaSb substrates to assess device properties and material quality. The room temperature dark current densities show similar characteristics for both cells on GaAs and on GaSb. Under solar simulation the cells on GaAs exhibit an open-circuit voltage of 0.121 V and a short-circuit current density of 15.5 mA/cm{sup 2}. In addition, the cells on GaAsmore » substrates maintain 10% difference in spectral response to those of the control cells over a large range of wavelengths. While the cells on GaSb substrates in general offer better performance than the cells on GaAs substrates, the cost-savings and scalability offered by GaAs substrates could potentially outweigh the reduction in performance. By further optimizing GaSb buffer growth on GaAs substrates, Sb-based compound semiconductors grown on GaAs substrates with similar performance to devices grown directly on GaSb substrates could be realized.« less

Disruption of Higher Order DNA Structures in Friedreich’s Ataxia (GAA)n Repeats by PNA or LNA Targeting

PubMed Central

Bergquist, Helen; Rocha, Cristina S. J.; Álvarez-Asencio, Rubén; Nguyen, Chi-Hung; Rutland, Mark. W.; Smith, C. I. Edvard; Good, Liam; Nielsen, Peter E.; Zain, Rula

2016-01-01

Expansion of (GAA)n repeats in the first intron of the Frataxin gene is associated with reduced mRNA and protein levels and the development of Friedreich’s ataxia. (GAA)n expansions form non-canonical structures, including intramolecular triplex (H-DNA), and R-loops and are associated with epigenetic modifications. With the aim of interfering with higher order H-DNA (like) DNA structures within pathological (GAA)n expansions, we examined sequence-specific interaction of peptide nucleic acid (PNA) with (GAA)n repeats of different lengths (short: n=9, medium: n=75 or long: n=115) by chemical probing of triple helical and single stranded regions. We found that a triplex structure (H-DNA) forms at GAA repeats of different lengths; however, single stranded regions were not detected within the medium size pathological repeat, suggesting the presence of a more complex structure. Furthermore, (GAA)4-PNA binding of the repeat abolished all detectable triplex DNA structures, whereas (CTT)5-PNA did not. We present evidence that (GAA)4-PNA can invade the DNA at the repeat region by binding the DNA CTT strand, thereby preventing non-canonical-DNA formation, and that triplex invasion complexes by (CTT)5-PNA form at the GAA repeats. Locked nucleic acid (LNA) oligonucleotides also inhibited triplex formation at GAA repeat expansions, and atomic force microscopy analysis showed significant relaxation of plasmid morphology in the presence of GAA-LNA. Thus, by inhibiting disease related higher order DNA structures in the Frataxin gene, such PNA and LNA oligomers may have potential for discovery of drugs aiming at recovering Frataxin expression. PMID:27846236

A comparison of GaAs and Si hybrid solar power systems

NASA Technical Reports Server (NTRS)

Heinbockel, J. H.; Roberts, A. S., Jr.

1977-01-01

Five different hybrid solar power systems using silicon solar cells to produce thermal and electric power are modeled and compared with a hybrid system using a GaAs cell. Among the indices determined are capital cost per unit electric power plus mechanical power, annual cost per unit electric energy, and annual cost per unit electric plus mechanical work. Current costs are taken to be $35,000/sq m for GaAs cells with an efficiency of 15% and $1000/sq m for Si cells with an efficiency of 10%. It is shown that hybrid systems can be competitive with existing methods of practical energy conversion. Limiting values for annual costs of Si and GaAs cells are calculated to be 10.3 cents/kWh and 6.8 cents/kWh, respectively. Results for both systems indicate that for a given flow rate there is an optimal operating condition for minimum cost photovoltaic output. For Si cell costs of $50/sq m optimal performance can be achieved at concentrations of about 10; for GaAs cells costing 1000/sq m, optimal performance can be obtained at concentrations of around 100. High concentration hybrid systems offer a distinct cost advantage over flat systems.

Basic mechanisms study for MIS solar cell structures on GaAs

NASA Technical Reports Server (NTRS)

Fonash, S. J.

1978-01-01

The solar cell structure examined is the MIS configuration on (n) GaAs. The metal room temperature oxide/(n) GaAs materials system was studied. Metals with electronegativities varying from 2.4 (Au) to 1.5 (Al) were used as the upper electrode. The thinnest metallization that did not interfere with the measurement techniques (by introducing essentially transmission line series resistance problems across a device) was used. Photovoltaic response was not optimized.

Chemical beam epitaxy of GaAs1-xNx using MMHy and DMHy precursors, modeled by ab initio study of GaAs(100) surfaces stability over As2, H2 and N2

NASA Astrophysics Data System (ADS)

Valencia, Hubert; Kangawa, Yoshihiro; Kakimoto, Koichi

2017-06-01

Using ab initio calculations, a simple model for GaAs1-xNx vapor-phase epitaxy on (100) surface of GaAs was created. By studying As2 and H2 molecules adsorptions and As/N atom substitutions on (100) GaAs surfaces, we obtain a relative stability diagram of all stable surfaces under varying As2, H2, and N2 conditions. We previously proved that this model could describe the vapor-phase epitaxy of GaAs1-x Nx with simple, fully decomposed, precursors. In this paper, we show that in more complex reaction conditions using monomethylhydrazine (MMHy), and dimethylhydrazine (DMHy), it is still possible to use our model to obtain an accurate description of the temperature and pressure stability domains for each surfaces, linked to chemical beam epitaxy (CBE) growth conditions. Moreover, the different N-incorporation regimes observed experimentally at different temperature can be explain and predict by our model. The use of MMHy and DMHy precursors can also be rationalized. Our model should then help to better understand the conditions needed to obtain an high quality GaAs1-xNx using vapor-phase epitaxy.

Photoelectrochemical Water Oxidation by GaAs Nanowire Arrays Protected with Atomic Layer Deposited NiO x Electrocatalysts

NASA Astrophysics Data System (ADS)

Zeng, Joy; Xu, Xiaoqing; Parameshwaran, Vijay; Baker, Jon; Bent, Stacey; Wong, H.-S. Philip; Clemens, Bruce

2018-02-01

Photoelectrochemical (PEC) hydrogen production makes possible the direct conversion of solar energy into chemical fuel. In this work, PEC photoanodes consisting of GaAs nanowire (NW) arrays were fabricated, characterized, and then demonstrated for the oxygen evolution reaction (OER). Uniform and periodic GaAs nanowire arrays were grown on a heavily n-doped GaAs substrates by metal-organic chemical vapor deposition selective area growth. The nanowire arrays were characterized using cyclic voltammetry and impedance spectroscopy in a non-aqueous electrochemical system using ferrocene/ferrocenium (Fc/Fc+) as a redox couple, and a maximum oxidation photocurrent of 11.1 mA/cm2 was measured. GaAs NW arrays with a 36 nm layer of nickel oxide (NiO x ) synthesized by atomic layer deposition were then used as photoanodes to drive the OER. In addition to acting as an electrocatalyst, the NiO x layer served to protect the GaAs NWs from oxidative corrosion. Using this strategy, GaAs NW photoanodes were successfully used for the oxygen evolution reaction. This is the first demonstration of GaAs NW arrays for effective OER, and the fabrication and protection strategy developed in this work can be extended to study any other nanostructured semiconductor materials systems for electrochemical solar energy conversion.

Monolithic optical integrated control circuitry for GaAs MMIC-based phased arrays

NASA Technical Reports Server (NTRS)

Bhasin, K. B.; Ponchak, G. E.; Kascak, T. J.

1985-01-01

Gallium arsenide (GaAs) monolithic microwave integrated circuits (MMIC's) show promise in phased-array antenna applications for future space communications systems. Their efficient usage will depend on the control of amplitude and phase signals for each MMIC element in the phased array and in the low-loss radiofrequency feed. For a phased array contining several MMIC elements a complex system is required to control and feed each element. The characteristics of GaAs MMIC's for 20/30-GHz phased-array systems are discussed. The optical/MMIC interface and the desired characteristics of optical integrated circuits (OIC's) for such an interface are described. Anticipated fabrication considerations for eventual full monolithic integration of optical integrated circuits with MMIC's on a GaAs substrate are presented.

Nitride surface passivation of GaAs nanowires: impact on surface state density.

PubMed

Alekseev, Prokhor A; Dunaevskiy, Mikhail S; Ulin, Vladimir P; Lvova, Tatiana V; Filatov, Dmitriy O; Nezhdanov, Alexey V; Mashin, Aleksander I; Berkovits, Vladimir L

2015-01-14

Surface nitridation by hydrazine-sulfide solution, which is known to produce surface passivation of GaAs crystals, was applied to GaAs nanowires (NWs). We studied the effect of nitridation on conductivity and microphotoluminescence (μ-PL) of individual GaAs NWs using conductive atomic force microscopy (CAFM) and confocal luminescent microscopy (CLM), respectively. Nitridation is found to produce an essential increase in the NW conductivity and the μ-PL intensity as well evidence of surface passivation. Estimations show that the nitride passivation reduces the surface state density by a factor of 6, which is of the same order as that found for GaAs/AlGaAs nanowires. The effects of the nitride passivation are also stable under atmospheric ambient conditions for six months.

Spectroscopic ellipsometric characterization of Si/Si(1-x)Ge(x) strained-layer superlattices

NASA Technical Reports Server (NTRS)

Yao, H.; Woollam, J. A.; Wang, P. J.; Tejwani, M. J.; Alterovitz, S. A.

1993-01-01

Spectroscopic ellipsometry (SE) was employed to characterize Si/Si(1-x)Ge(x) strained-layer superlattices. An algorithm was developed, using the available optical constants measured at a number of fixed x values of Ge composition, to compute the dielectric function spectrum of Si(1-x)Ge(x) at an arbitrary x value in the spectral range 17 to 5.6 eV. The ellipsometrically determined superlattice thicknesses and alloy compositional fractions were in excellent agreement with results from high-resolution x ray diffraction studies. The silicon surfaces of the superlattices were subjected to a 9:1 HF cleaning prior to the SE measurements. The HF solution removed silicon oxides on the semiconductor surface, and terminated the Si surface with hydrogen-silicon bonds, which were monitored over a period of several weeks, after the HF cleaning, by SE measurements. An equivalent dielectric layer model was established to describe the hydrogen-terminated Si surface layer. The passivated Si surface remained unchanged for greater than 2 h, and very little surface oxidation took place even over 3 to 4 days.

High purity low dislocation GaAs single crystals

NASA Technical Reports Server (NTRS)

Chen, R. T.; Holmes, D. E.; Kirkpatrick, C. G.

1982-01-01

Recent advances in GaAs bulk crystal growth using the LEC (liquid encapsulated Czochralski) technique are described. The dependence of the background impurity concentration and the dislocation density distribution on the materials synthesis and growth conditions were investigated. Background impurity concentrations as low as 4 x 10 to the 15th power were observed in undoped LEC GaAs. The dislocation density in selected regions of individual ingots was very low, below the 3000 cm .3000/sq cm threshold. The average dislocation density over a large annular ring on the wafers fell below the 10000/sq cm level for 3 inch diameter ingots. The diameter control during the program advanced to a diameter variation along a 3 inch ingot less than 2 mm.

Insertion of GaAs MMICs into EW systems

NASA Astrophysics Data System (ADS)

Schineller, E. R.; Pospishil, A.; Grzyb, J.

1989-09-01

Development activities on a microwave/mm-wave monolithic IC (MIMIC) program are described, as well as the methodology for inserting these GaAs IC chips into several EW systems. The generic EW chip set developed on the MIMIC program consists of 23 broadband chip types, including amplifiers, oscillators, mixers, switches, variable attenuators, power dividers, and power combiners. These chips are being designed for fabrication using the multifunction self-aligned gate process. The benefits from GaAs IC insertion are quantified by a comparison of hardware units fabricated with existing MIC and digital ECL technology and the same units manufactured with monolithic technology. It is found that major improvements in cost, reliability, size, weight, and performance can be realized. Examples illustrating the methodology for technology insertion are presented.

Total internal reflection ellipsometry and SPR detection of low molecular weight environmental toxins

NASA Astrophysics Data System (ADS)

Nabok, A. V.; Tsargorodskaya, A.; Hassan, A. K.; Starodub, N. F.

2005-06-01

The environmental toxins, such as herbicides simazine and atrazine, and T2 mycotoxin were registered with the optical methods of surface plasmon resonance (SPR) and recently developed total internal reflection ellipsometry (TIRE). The immune assay approach was exploited for in situ registration of the above low molecular weight toxins with specific antibodies immobilised onto the gold surface via (poly)allylamine hydrochloride layer using electrostatic self-assembly (ESA) technique. The comparison of two methods of SPR and TIRE shows a higher sensitivity of the latter.

Highly efficient single-junction GaAs thin-film solar cell on flexible substrate.

PubMed

Moon, Sunghyun; Kim, Kangho; Kim, Youngjo; Heo, Junseok; Lee, Jaejin

2016-07-20

There has been much interest in developing a thin-film solar cell because it is lightweight and flexible. The GaAs thin-film solar cell is a top contender in the thin-film solar cell market in that it has a high power conversion efficiency (PCE) compared to that of other thin-film solar cells. There are two common structures for the GaAs solar cell: n (emitter)-on-p (base) and p-on-n. The former performs better due to its high collection efficiency because the electron diffusion length of the p-type base region is much longer than the hole diffusion length of the n-type base region. However, it has been limited to fabricate highly efficient n-on-p single-junction GaAs thin film solar cell on a flexible substrate due to technical obstacles. We investigated a simple and fast epitaxial lift-off (ELO) method that uses a stress originating from a Cr/Au bilayer on a 125-μm-thick flexible substrate. A metal combination of AuBe/Pt/Au is employed as a new p-type ohmic contact with which an n-on-p single-junction GaAs thin-film solar cell on flexible substrate was successfully fabricated. The PCE of the fabricated single-junction GaAs thin-film solar cells reached 22.08% under air mass 1.5 global illumination.

SEMICONDUCTOR TECHNOLOGY: GaAs surface wet cleaning by a novel treatment in revolving ultrasonic atomization solution

NASA Astrophysics Data System (ADS)

Zaijin, Li; Liming, Hu; Ye, Wang; Ye, Yang; Hangyu, Peng; Jinlong, Zhang; Li, Qin; Yun, Liu; Lijun, Wang

2010-03-01

A novel process for the wet cleaning of GaAs surface is presented. It is designed for technological simplicity and minimum damage generated within the GaAs surface. It combines GaAs cleaning with three conditions consisting of (1) removal of thermodynamically unstable species and (2) surface oxide layers must be completely removed after thermal cleaning, and (3) a smooth surface must be provided. Revolving ultrasonic atomization technology is adopted in the cleaning process. At first impurity removal is achieved by organic solvents; second NH4OH:H2O2:H2O = 1:1:10 solution and HCl: H2O2:H2O = 1:1:20 solution in succession to etch a very thin GaAs layer, the goal of the step is removing metallic contaminants and forming a very thin oxidation layer on the GaAs wafer surface; NH4OH:H2O = 1:5 solution is used as the removed oxide layers in the end. The effectiveness of the process is demonstrated by the operation of the GaAs wafer. Characterization of the oxide composition was carried out by X-ray photoelectron spectroscopy. Metal-contamination and surface morphology was observed by a total reflection X-ray fluorescence spectroscopy and atomic force microscope. The research results show that the cleaned surface is without contamination or metal contamination. Also, the GaAs substrates surface is very smooth for epitaxial growth using the rotary ultrasonic atomization technology.

Radiation testing of GaAs on CRRES and LIPS experiment

NASA Technical Reports Server (NTRS)

Trumble, T. M.; Masloski, K.

1984-01-01

The radiation damage of solar cells has become a prime concern to the U.S. Air Force due to longer satellite lifetime requirements. Flight experiments were undertaken on the Navy Living Plume Shield (LPS) satellite and the NASA/Air Force Combined Release and Radiation Effects Satellite (CRRES) to complement existing radiation testing. Each experiment, the rationale behind it, and its approach and status are presented. The effect of space radiation on gallium arsenide (GaAs) solar cells was the central parameter investigated. Specifications of the GaAs solar cells are given.

Core-level photoemission investigation of atomic-fluorine adsorption on GaAs(110)

NASA Astrophysics Data System (ADS)

McLean, A. B.; Terminello, L. J.; McFeely, F. R.

1989-12-01

The adsorption of atomic F on the cleaved GaAs(110) surface has been studied with use of high-resolution core-level photoelectron spectroscopy by exposing the GaAs(110) surfaces to XeF2, which adsorbs dissociatively, leaving atomic F behind. This surface reaction produces two chemically shifted components in the Ga 3d core-level emission which are attributed to an interfacial monofluoride and a stable trifluoride reaction product, respectively. The As 3d core level develops only one chemically shifted component and from its exposure-dependent behavior it is attributed to an interfacial monofluoride. Least-squares analysis of the core-level line shapes revealed that (i) the F bonds to both the anion and the cation , (ii) the GaF3 component (characteristic of strong interfacial reaction) and the surface core-level shifted component (characteristic of a well ordered, atomically clean surface) are present together over a relatively large range of XeF2 exposures, and (iii) it is the initial disruption of the GaAs(110) surface that is the rate-limiting step in this surface reaction. These results are compared with similar studies of Cl and O adsorption on GaAs(110).

Self-catalyzed GaAs nanowires on silicon by hydride vapor phase epitaxy.

PubMed

Dong, Zhenning; André, Yamina; Dubrovskii, Vladimir G; Bougerol, Catherine; Leroux, Christine; Ramdani, Mohammed R; Monier, Guillaume; Trassoudaine, Agnès; Castelluci, Dominique; Gil, Evelyne

2017-03-24

Gold-free GaAs nanowires on silicon substrates can pave the way for monolithic integration of photonic nanodevices with silicon electronic platforms. It is extensively documented that the self-catalyzed approach works well in molecular beam epitaxy but is much more difficult to implement in vapor phase epitaxies. Here, we report the first gallium-catalyzed hydride vapor phase epitaxy growth of long (more than 10 μm) GaAs nanowires on Si(111) substrates with a high integrated growth rate up to 60 μm h -1 and pure zincblende crystal structure. The growth is achieved by combining a low temperature of 600 °C with high gaseous GaCl/As flow ratios to enable dechlorination and formation of gallium droplets. GaAs nanowires exhibit an interesting bottle-like shape with strongly tapered bases, followed by straight tops with radii as small as 5 nm. We present a model that explains the peculiar growth mechanism in which the gallium droplets nucleate and rapidly swell on the silicon surface but then are gradually consumed to reach a stationary size. Our results unravel the necessary conditions for obtaining gallium-catalyzed GaAs nanowires by vapor phase epitaxy techniques.

Enhanced second-harmonic generation from resonant GaAs gratings.

PubMed

de Ceglia, D; D'Aguanno, G; Mattiucci, N; Vincenti, M A; Scalora, M

2011-03-01

We theoretically study second harmonic generation in nonlinear, GaAs gratings. We find large enhancement of conversion efficiency when the pump field excites the guided mode resonances of the grating. Under these circumstances the spectrum near the pump wavelength displays sharp resonances characterized by dramatic enhancements of local fields and favorable conditions for second-harmonic generation, even in regimes of strong linear absorption at the harmonic wavelength. In particular, in a GaAs grating pumped at 1064 nm, we predict second-harmonic conversion efficiencies approximately 5 orders of magnitude larger than conversion rates achievable in either bulk or etalon structures of the same material.

Scanning microwave microscopy applied to semiconducting GaAs structures

NASA Astrophysics Data System (ADS)

Buchter, Arne; Hoffmann, Johannes; Delvallée, Alexandra; Brinciotti, Enrico; Hapiuk, Dimitri; Licitra, Christophe; Louarn, Kevin; Arnoult, Alexandre; Almuneau, Guilhem; Piquemal, François; Zeier, Markus; Kienberger, Ferry

2018-02-01

A calibration algorithm based on one-port vector network analyzer (VNA) calibration for scanning microwave microscopes (SMMs) is presented and used to extract quantitative carrier densities from a semiconducting n-doped GaAs multilayer sample. This robust and versatile algorithm is instrument and frequency independent, as we demonstrate by analyzing experimental data from two different, cantilever- and tuning fork-based, microscope setups operating in a wide frequency range up to 27.5 GHz. To benchmark the SMM results, comparison with secondary ion mass spectrometry is undertaken. Furthermore, we show SMM data on a GaAs p-n junction distinguishing p- and n-doped layers.

Theoretical and experimental study of highly textured GaAs on silicon using a graphene buffer layer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alaskar, Yazeed; Arafin, Shamsul; Lin, Qiyin

2015-09-01

A novel heteroepitaxial growth technique, quasi-van der Waals epitaxy, promises the ability to deposit three-dimensional GaAs materials on silicon using two-dimensional graphene as a buffer layer by overcoming the lattice and thermal expansion mismatch. In this study, density functional theory (DFT) simulations were performed to understand the interactions at the GaAs/graphene hetero-interface as well as the growth orientations of GaAs on graphene. To develop a better understanding of the molecular beam epitaxy-grown GaAs films on graphene, samples were characterized by x-ray diffraction (..theta..-2..theta.. scan, ..omega..-scan, grazing incidence XRD and pole figure measurement) and transmission electron microscopy. The realizations of smoothmore » GaAs films with a strong (111) oriented fiber-texture on graphene/silicon using this deposition technique are a milestone towards an eventual demonstration of the epitaxial growth of GaAs on silicon, which is necessary for integrated photonics application.« less

Reflection high energy electron diffraction study of nitrogen plasma interactions with a GaAs (100) surface

NASA Astrophysics Data System (ADS)

Hauenstein, R. J.; Collins, D. A.; Cai, X. P.; O'Steen, M. L.; McGill, T. C.

1995-05-01

Effect of a nitrogen electron-cyclotron-resonance (ECR) microwave plasma on near-surface composition, crystal structure, and morphology of the As-stabilized GaAs (100) surface is investigated with the use of digitally image-processed in situ reflection high energy electron diffraction. Nitridation is performed on molecular beam epitaxially (MBE) grown GaAs surfaces near 600 °C under typical conditions for ECR microwave plasma-assisted MBE growth of GaN films on GaAs. Brief plasma exposures (≊3-5 s) are shown to result in a specular, coherently strained, relatively stable, GaN film approximately one monolayer in thickness, which can be commensurately overgrown with GaAs while longer exposures (up to 1 min) result in incommensurate zincblende epitaxial GaN island structures. Specular and nonspecular film formations are explained in terms of N-for-As surface and subsurface anion exchange reactions, respectively. Commensurate growth of ultrathin buried GaN layers in GaAs is achieved.

Development of a spectroscopic Mueller matrix imaging ellipsometer for nanostructure metrology

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Xiuguo; Du, Weichao; Yuan, Kui

2016-05-15

In this paper, we describe the development of a spectroscopic Mueller matrix imaging ellipsometer (MMIE), which combines the great power of Mueller matrix ellipsometry with the high spatial resolution of optical microscopy. A dual rotating-compensator configuration is adopted to collect the full 4 × 4 imaging Mueller matrix in a single measurement. The light wavelengths are scanned in the range of 400–700 nm by a monochromator. The instrument has measurement accuracy and precision better than 0.01 for all the Mueller matrix elements in both the whole image and the whole spectral range. The instrument was then applied for the measurementmore » of nanostructures combined with an inverse diffraction problem solving technique. The experiment performed on a photoresist grating sample has demonstrated the great potential of MMIE for accurate grating reconstruction from spectral data collected by a single pixel of the camera and for efficient quantification of geometrical profile of the grating structure over a large area with pixel resolution. It is expected that MMIE will be a powerful tool for nanostructure metrology in future high-volume nanomanufacturing.« less

Recent advances in characterization of CaCu3Ti4O12 thin films by spectroscopic ellipsometric metrology.

PubMed

Lo Nigro, Raffaella; Malandrino, Graziella; Toro, Roberta G; Losurdo, Maria; Bruno, Giovanni; Fragalà, Ignazio L

2005-10-12

CaCu3Ti4O12 (CCTO) thin films were successfully grown on LaAlO3(100) and Pt/TiO2/SiO2/Si(100) substrates by a novel MOCVD approach. Epitaxial CCTO(001) thin films have been obtained on LaAlO3(100) substrates, while polycrystalline CCTO films have been grown on Pt/TiO2/SiO2/Si(100) substrates. Surface morphology and grain size of the different nanostructured deposited films were examined by AFM, and spectroscopic ellipsometry has been used to investigate the electronic part of the dielectric constant (epsilon2). Looking at the epsilon2 curves, it can be seen that by increasing the film structural order, a greater dielectric response has been obtained. The measured dielectric properties accounted for the ratio between grain volumes and grain boundary areas, which is very different in the different structured films.

Fermi level pinning at epitaxial Si on GaAs(100) interfaces

NASA Astrophysics Data System (ADS)

Silberman, J. A.; de Lyon, T. J.; Woodall, J. M.

1991-12-01

GaAs Schottky barrier contacts and metal-insulator-semiconductor structures that include thin epitaxial Si interfacial layers operate in a manner consistent with an unpinned Fermi level at the GaAs interface. These findings raise the question of whether this effect is an intrinsic property of the epitaxial GaAs(100)-Si interface. We have used x-ray photoemission spectroscopy to monitor the Fermi level position during in situ growth of thin epitaxial Si layers. In particular, films formed on heavily doped n- and p-type substrates were compared so as to use the large depletion layer fields available with high impurity concentration as a field-effect probe of the interface state density. The results demonstrate that epitaxial bonding at the interface alone is insufficient to eliminate Fermi level pinning, indicating that other mechanisms affect the interfacial charge balance in the devices that utilize Si interlayers.

GaAs VLSI for aerospace electronics

NASA Technical Reports Server (NTRS)

Larue, G.; Chan, P.

1990-01-01

Advanced aerospace electronics systems require high-speed, low-power, radiation-hard, digital components for signal processing, control, and communication applications. GaAs VLSI devices provide a number of advantages over silicon devices including higher carrier velocities, ability to integrate with high performance optical devices, and high-resistivity substrates that provide very short gate delays, good isolation, and tolerance to many forms of radiation. However, III-V technologies also have disadvantages, such as lower yield compared to silicon MOS technology. Achieving very large scale integration (VLSI) is particularly important for fast complex systems. At very short gate delays (less than 100 ps), chip-to-chip interconnects severely degrade circuit clock rates. Complex systems, therefore, benefit greatly when as many gates as possible are placed on a single chip. To fully exploit the advantages of GaAs circuits, attention must be focused on achieving high integration levels by reducing power dissipation, reducing the number of devices per logic function, and providing circuit designs that are more tolerant to process and environmental variations. In addition, adequate noise margin must be maintained to ensure a practical yield.

A new structure for comparing surface passivation materials of GaAs solar cells

NASA Technical Reports Server (NTRS)

Desalvo, Gregory C.; Barnett, Allen M.

1989-01-01

The surface recombination velocity (S sub rec) for bare GaAs is typically as high as 10 to the 6th power to 10 to the 7th power cm/sec, which dramatically lowers the efficiency of GaAs solar cells. Early attempts to circumvent this problem by making an ultra thin junction (xj less than .1 micron) proved unsuccessful when compared to lowering S sub rec by surface passivation. Present day GaAs solar cells use an GaAlAs window layer to passivate the top surface. The advantages of GaAlAs in surface passivation are its high bandgap energy and lattice matching to GaAs. Although GaAlAs is successful in reducing the surface recombination velocity, it has other inherent problems of chemical instability (Al readily oxidizes) and ohmic contact formation. The search for new, more stable window layer materials requires a means to compare their surface passivation ability. Therefore, a device structure is needed to easily test the performance of different passivating candidates. Such a test device is described.

Covalent attachment of TAT peptides and thiolated alkyl molecules on GaAs surfaces.

PubMed

Cho, Youngnam; Ivanisevic, Albena

2005-07-07

Four TAT peptide fragments were used to functionalize GaAs surfaces by adsorption from solution. In addition, two well-studied alkylthiols, mercaptohexadecanoic acid (MHA) and 1-octadecanethiol (ODT) were utilized as references to understand the structure of the TAT peptide monolayer on GaAs. The different sequences of TAT peptides were employed in recognition experiments where a synthetic RNA sequence was tested to verify the specific interaction with the TAT peptide. The modified GaAs surfaces were characterized by atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared reflection absorption spectroscopy (FT-IRRAS). AFM studies were used to compare the surface roughness before and after functionalization. XPS allowed us to characterize the chemical composition of the GaAs surface and conclude that the monolayers composed of different sequences of peptides have similar surface chemistries. Finally, FT-IRRAS experiments enabled us to deduce that the TAT peptide monolayers have a fairly ordered and densely packed alkyl chain structure. The recognition experiments showed preferred interaction of the RNA sequence toward peptides with high arginine content.

Structures, Properties and Defects of SrTiO3/GaAs Hetero-interfaces

NASA Astrophysics Data System (ADS)

Hong, Liang; Bhatnagar, Kunal; Droopad, Ravi; Öğüt, Serdar; Klie, Robert

SrTiO3 thin film can be epitaxially grown on GaAs substrate and used as a platform for growing other oxides to create functional metal-oxide-semiconductor devices, where a high-quality SrTiO3/GaAs interface is essential. We studied the structural and electronic properties of SrTiO3/GaAs hetero-interfaces at atomic level using scanning transmission electron microscopy and first-principles calculations. Our results suggest the preferred termination of GaAs (001) is significantly dependent on the oxygen concentration in the first oxide layer. The favorable interface structure is characterized as oxygen-deficient SrO in contact with arsenic and is observed in both experiment and simulation. The electronic properties are calculated and found to be tunable by interfacial defects such as oxygen, gallium and arsenic vacancies. This work was supported by the National Science Foundation (Grant No. DMR-1408427). This work made use of instruments in the Electron Microscopy Service and the High Performance Computing Clusters at University of Illinois at Chicago.

Accelerated GaAs growth through MOVPE for low-cost PV applications

NASA Astrophysics Data System (ADS)

Ubukata, Akinori; Sodabanlu, Hassanet; Watanabe, Kentaroh; Koseki, Shuichi; Yano, Yoshiki; Tabuchi, Toshiya; Sugaya, Takeyoshi; Matsumoto, Koh; Nakano, Yoshiaki; Sugiyama, Masakazu

2018-05-01

The high growth rate of epitaxial GaAs was investigated using a novel horizontal metalorganic vapor phase epitaxy (MOVPE) reactor, from the point of view of realizing low-cost photovoltaic (PV) solar cells. The GaAs growth rate exhibited an approximately linear relationship with the amount of trimethylgalium (TMGa) supplied, up to a rate of 90 μm/h. The distribution of growth rate was observed for a two-inch wafer, along the flow direction, and the normalized profile of the distribution was found to be independent of the precursor input, from 20 to 70 μm/h. These tendencies indicated that significant parasitic prereaction did not occur in the gaseous phase, for this range of growth rate. GaAs p-n single-junction solar cells were successfully fabricated at growth rates of 20, 60, and 80 μm/h. The conversion efficiency of the cell grown at 80 μm/h was comparable to that of the 20 μm/h cell, indicating the good quality and properties of GaAs. The epitaxial growth exhibited good uniformity, as evidenced by the uniformity of the cell performance across the wafer, from the center to the edge. The result indicated the potential of high-throughput MOVPE for low-cost production, not only for PV devices but also for other semiconductor applications.

Divacancy complexes induced by Cu diffusion in Zn-doped GaAs

NASA Astrophysics Data System (ADS)

Elsayed, M.; Krause-Rehberg, R.; Korff, B.; Ratschinski, I.; Leipner, H. S.

2013-08-01

Positron annihilation spectroscopy was applied to investigate the nature and thermal behavior of defects induced by Cu diffusion in Zn-doped p-type GaAs crystals. Cu atoms were intentionally introduced in the GaAs lattice through thermally activated diffusion from a thin Cu capping layer at 1100 °C under defined arsenic vapor pressure. During isochronal annealing of the obtained Cu-diffused GaAs in the temperature range of 450-850 K, vacancy clusters were found to form, grow and finally disappear. We found that annealing at 650 K triggers the formation of divacancies, whereas further increasing in the annealing temperature up to 750 K leads to the formation of divacancy-copper complexes. The observations suggest that the formation of these vacancy-like defects in GaAs is related to the out-diffusion of Cu. Two kinds of acceptors are detected with a concentration of about 1016 - 1017 cm-3, negative ions and arsenic vacancy copper complexes. Transmission electron microscopy showed the presence of voids and Cu precipitates which are not observed by positron measurements. The positron binding energy to shallow traps is estimated using the positron trapping model. Coincidence Doppler broadening spectroscopy showed the presence of Cu in the immediate vicinity of the detected vacancies. Theoretical calculations suggested that the detected defect is VGaVAs-2CuGa.

Aging behavior of Au-based ohmic contacts to GaAs

NASA Technical Reports Server (NTRS)

Fatemi, Navid S.

1989-01-01

Gold based alloys, commonly used as ohmic contacts for solar cells, are known to react readily with GaAs. It is shown that the contact interaction with the underlying GaAs can continue even at room temperature upon aging, altering both the electrical characteristics of the contacts and the nearby pn junction. Au-Ge-Ni as-deposited (no heat-treatment) contacts made to thin emitter (0.15 microns) GaAs diodes have shown severe shunting of the pn junction upon aging for several months at room temperature. The heat-treated contacts, despite showing degradation in contact resistance, did not affect the underlying pn junction. Au-Zn-Au contacts to p-GaAs emitter (0.2 microns) diodes, however, showed slight improvement in contact resistance upon 200 C isothermal annealing for several months, without degrading the pn junction. The effect of aging on electrical characteristics of the as-deposited and heat-treated contacts and the nearby pn junction, as well as on the surface morphology of the contacts are presented.

Aging behavior of Au-based ohmic contacts to GaAs

NASA Technical Reports Server (NTRS)

Fatemi, Navid S.

1988-01-01

Gold based alloys, commonly used as ohmic contacts for solar cells, are known to react readily with GaAs. It is shown that the contact interaction with the underlying GaAs can continue even at room temperature upon aging, altering both the electrical characteristics of the contacts and the nearby pn junction. Au-Ge-Ni as-deposited (no heat treatment) contacts made to thin emitter (0.15 micrometer) GaAs diodes have shown severe shunting of the pn junction upon aging for several months at room temperature. The heat-treated contacts, despite showing degradation in contact resistance did not affect the underlying pn junction. Au-Zn-Au contacts to p-GaAs emitter (0.2 micrometer) diodes, however, showed slight improvement in contact resistance upon 200 C isothermal annealing for several months, without degrading the pn junction. The effect of aging on electrical characteristics of the as-deposited and heat-treated contacts and the nearby pn junction, as well as on the surface morphology of the contacts are presented.

Study of strain boundary conditions and GaAs buffer sizes in InGaAs quantum dots

NASA Technical Reports Server (NTRS)

Oyafuso, F.; Klimeck, G.; Boykin, T. B.; Bowen, R. C.; Allmen, P. von

2003-01-01

NEMO 3-D has been developed for the simulation of electronic structure in self-assembled InGaAs quantum dots on GaAs substrates. Typical self-assembled quantum dots in that material system contain about 0.5 to 1 million atoms. Effects of strain by the surrounding GaAs buffer modify the electronic structure inside the quantum dot significantly and a large GaAs buffer must be included in the strain and electronic structure.

Alternatives to Arsine: The Atmospheric Pressure Organometallic Chemical Vapor Deposition Growth of GaAs Using Triethylarsenic.

DTIC Science & Technology

1987-08-15

SUPPLEMENTARY NOTATION 17. COSATI CODES 18 SUBJECT TERMS (Corinue on reverse if necessary and identify by block number) FIELD GROUP SUB-GROUP Epitaxy GaAs 9...Zr leiK m I141’ FIGURES 1 . Effect of Growth Parameters on Residual Doping Type ................... 7 2. Photoluminescence Spectrum of a GaAs Epilayer... 1 3 Successful homoepitaxial growth of high purity, unintentionally doped GaAs epilayers by organometallic chemical vapor deposition (OMCVD) has

Study on the high-power semi-insulating GaAs PCSS with quantum well structure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Luan, Chongbiao; Wang, Bo; Huang, Yupeng

A high-power semi-insulating GaAs photoconductive semiconductor switch (PCSS) with quantum well structure was fabricated. The AlGaAs layer was deposited on the surface of the GaAs material, and the reflecting film and the antireflection film have been made on the surface of the GaAs and AlGaAs, respectively. When the prepared PCSS worked at a bias voltage of 9.8 kV and triggered by a laser pulse with an incident optical energy of 5.4 mJ, a wavelength of 1064 nm and an optical pulse width of 25 ns, the on-state resistance of the AlGaAs/GaAs PCSS was only 0.45 Ω, and the longevity ofmore » the AlGaAs/GaAs PCSS was larger than 10{sup 6} shots. The results show that this structure reduces the on-state resistance and extends the longevity of the GaAs PCSS.« less

Origin and enhancement of the 1.3 μm luminescence from GaAs treated by ion-implantation and flash lamp annealing

NASA Astrophysics Data System (ADS)

Gao, Kun; Prucnal, S.; Skorupa, W.; Helm, M.; Zhou, Shengqiang

2013-09-01

GaAs and GaAs based materials have outstanding optoelectronic properties and are widely used as light emitting media in devices. Many approaches have been applied to GaAs to generate luminescence at 0.88, 1.30, and 1.55 μm which are transmission windows of optical fibers. In this paper, we present the photoluminescence at 1.30 μm from deep level defects in GaAs treated by ion-implantation and flash lamp annealing (FLA). Such emission, which exhibits superior temperature stability, can be obtained from FLA treated virgin GaAs as well as doped GaAs. Indium-doping in GaAs can greatly enhance the luminescence. By photoluminescence, Raman measurements, and positron annihilation spectroscopy, we conclude that the origin of the 1.30 μm emission is from transitions between the VAs-donor and X-acceptor pairs.

Novel anti-reflection technology for GaAs single-junction solar cells using surface patterning and Au nanoparticles.

PubMed

Kim, Youngjo; Lam, Nguyen Dinh; Kim, Kangho; Kim, Sangin; Rotermund, Fabian; Lim, Hanjo; Lee, Jaejin

2012-07-01

Single-junction GaAs solar cell structures were grown by low-pressure MOCVD on GaAs (100) substrates. Micro-rod arrays with diameters of 2 microm, 5 microm, and 10 microm were fabricated on the surfaces of the GaAs solar cells via photolithography and wet chemical etching. The patterned surfaces were coated with Au nanoparticles using an Au colloidal solution. Characteristics of the GaAs solar cells with and without the micro-rod arrays and Au nanoparticles were investigated. The short-circuit current density of the GaAs solar cell with 2 microm rod arrays and Au nanoparticles increased up to 34.9% compared to that of the reference cell without micro-rod arrays and Au nanoparticles. The conversion efficiency of the GaAs solar cell that was coated with Au nanoparticles on the patterned surface with micro-rod arrays can be improved from 14.1% to 19.9% under 1 sun AM 1.5G illumination. These results show that micro-rod arrays and Au nanoparticle coating can be applied together in surface patterning to achieve a novel cost-effective anti-reflection technology.

Measurement of electron beam polarization produced by photoemission from bulk GaAs using twisted light

NASA Astrophysics Data System (ADS)

Clayburn, Nathan; Dreiling, Joan; McCarter, James; Ryan, Dominic; Poelker, Matt; Gay, Timothy

2012-06-01

GaAs photocathodes produce spin polarized electron beams when illuminated with circularly polarized light with photon energy approximately equal to the bandgap energy [1, 2]. A typical polarization value obtained with bulk GaAs and conventional circularly polarized light is 35%. This study investigated the spin polarization of electron beams emitted from GaAs illuminated with ``twisted light,'' an expression that describes a beam of light having orbital angular momentum (OAM). In the experiment, 790nm laser light was focused to a near diffraction-limited spot size on the surface of the GaAs photocathode to determine if OAM might couple to valence band electron spin mediated by the GaAs lattice. Our polarization measurements using a compact retarding-field micro-Mott polarimeter [3] have established an upper bound on the polarization of the emitted electron beam of 2.5%. [4pt] [1] D.T. Pierce, F. Meier, P. Zurcher, Appl. Phys. Lett. 26 670 (1975).[0pt] [2] C.K. Sinclair, et al., PRSTAB 10 023501 (2007).[0pt] [3] J.L. McCarter, M.L. Stutzman, K.W. Trantham, T.G. Anderson, A.M. Cook, and T.J. Gay Nucl. Instrum. and Meth. A (2010).

Wafer-scale layer transfer of GaAs and Ge onto Si wafers using patterned epitaxial lift-off

NASA Astrophysics Data System (ADS)

Mieda, Eiko; Maeda, Tatsuro; Miyata, Noriyuki; Yasuda, Tetsuji; Kurashima, Yuichi; Maeda, Atsuhiko; Takagi, Hideki; Aoki, Takeshi; Yamamoto, Taketsugu; Ichikawa, Osamu; Osada, Takenori; Hata, Masahiko; Ogawa, Arito; Kikuchi, Toshiyuki; Kunii, Yasuo

2015-03-01

We have developed a wafer-scale layer-transfer technique for transferring GaAs and Ge onto Si wafers of up to 300 mm in diameter. Lattice-matched GaAs or Ge layers were epitaxially grown on GaAs wafers using an AlAs release layer, which can subsequently be transferred onto a Si handle wafer via direct wafer bonding and patterned epitaxial lift-off (ELO). The crystal properties of the transferred GaAs layers were characterized by X-ray diffraction (XRD), photoluminescence, and the quality of the transferred Ge layers was characterized using Raman spectroscopy. We find that, after bonding and the wet ELO processes, the quality of the transferred GaAs and Ge layers remained the same compared to that of the as-grown epitaxial layers. Furthermore, we realized Ge-on-insulator and GaAs-on-insulator wafers by wafer-scale pattern ELO technique.

Nanoscale Footprints of Self-Running Gallium Droplets on GaAs Surface

PubMed Central

Wu, Jiang; Wang, Zhiming M.; Li, Alvason Z.; Benamara, Mourad; Li, Shibin; Salamo, Gregory J.

2011-01-01

In this work, the nanoscale footprints of self-driven liquid gallium droplet movement on a GaAs (001) surface will be presented and analyzed. The nanoscale footprints of a primary droplet trail and ordered secondary droplets along primary droplet trails are observed on the GaAs surface. A well ordered nanoterrace from the trail is left behind by a running droplet. In addition, collision events between two running droplets are investigated. The exposed fresh surface after a collision demonstrates a superior evaporation property. Based on the observation of droplet evolution at different stages as well as nanoscale footprints, a schematic diagram of droplet evolution is outlined in an attempt to understand the phenomenon of stick-slip droplet motion on the GaAs surface. The present study adds another piece of work to obtain the physical picture of a stick-slip self-driven mechanism in nanoscale, bridging nano and micro systems. PMID:21673965

Negative differential velocity in ultradilute GaAs1-xNx alloys

NASA Astrophysics Data System (ADS)

Vogiatzis, N.; Rorison, J. M.

2011-04-01

We present theoretical results on steady state characteristics in bulk GaAs1-xNx alloys (x ≤ 0.2) using the single electron Monte-Carlo method. Two approaches have been used; the first assumes a GaAs band with a strong nitrogen scattering resonance and the second uses the band anti-crossing model, in which the localized N level interacts with the GaAs band strongly perturbing the conduction band. In the first model we observe two negative differential velocity peaks, the lower one associated with nitrogen scattering while the higher one with polar optical phonon emission accounting for the nonparabolicity effect. In the second model one negative differential velocity peak is observed associated with polar optical phonon emission. Good agreement with experimental low field mobility is obtained from the first model. We also comment on the results from both Models when the intervalley Г → L transfer is accounted for.

Intrinsic Spin-Hall Effect in n-Doped Bulk GaAs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bernevig, B.Andrei; Zhang, Shou-Cheng; /Stanford U., Phys. Dept.

2010-01-15

We show that the bulk Dresselhauss (k{sup 3}) spin-orbit coupling term leads to an intrinsic spin-Hall effect in n-doped bulk GaAs, but without the appearance of uniform magnetization. The spin-Hall effect in strained and unstrained bulk GaAs has been recently observed experimentally by Kato et. al. [1]. We show that the experimental result is quantitatively consistent with the intrinsic spin-Hall effect due to the Dresselhauss term, when lifetime broadening is taken into account. On the other hand, extrinsic contribution to the spin-Hall effect is several orders of magnitude smaller than the observed effect.

Ab initio study of GaAs(100) surface stability over As2, H2 and N2 as a model for vapor-phase epitaxy of GaAs1-xNx

NASA Astrophysics Data System (ADS)

Valencia, Hubert; Kangawa, Yoshihiro; Kakimoto, Koichi

2015-12-01

GaAs(100) c(4×4) surfaces were examined by ab initio calculations, under As2, H2 and N2 gas mixed conditions as a model for GaAs1-xNx vapor-phase epitaxy (VPE) on GaAs(100). Using a simple model consisting of As2 and H2 molecules adsorptions and As/N atom substitutions, it was shown to be possible to examine the crystal growth behavior considering the relative stability of the resulting surfaces against the chemical potential of As2, H2 and N2 gases. Such simple model allows us to draw a picture of the temperature and pressure stability domains for each surfaces that can be linked to specific growth conditions, directly. We found that, using this simple model, it is possible to explain the different N-incorporation regimes observed experimentally at different temperatures, and to predict the transition temperature between these regimes. Additionally, a rational explanation of N-incorporation ratio for each of these regimes is provided. Our model should then lead to a better comprehension and control of the experimental conditions needed to realize a high quality VPE of GaAs1-xNx.

Terahertz pulse induced intervalley scattering in photoexcited GaAs.

PubMed

Su, F H; Blanchard, F; Sharma, G; Razzari, L; Ayesheshim, A; Cocker, T L; Titova, L V; Ozaki, T; Kieffer, J-C; Morandotti, R; Reid, M; Hegmann, F A

2009-06-08

Nonlinear transient absorption bleaching of intense few-cycle terahertz (THz) pulses is observed in photoexcited GaAs using opticalpump--THz-probe techniques. A simple model of the electron transport dynamics shows that the observed nonlinear response is due to THz-electric- field-induced intervalley scattering over sub-picosecond time scales as well as an increase in the intravalley scattering rate attributed to carrier heating. Furthermore, the nonlinear nature of the THz pulse transmission at high peak fields leads to a measured terahertz conductivity in the photoexcited GaAs that deviates significantly from the Drude behavior observed at low THz fields, emphasizing the need to explore nonlinear THz pulse interactions with materials in the time domain.

Crystal growth of device quality GaAs in space

NASA Technical Reports Server (NTRS)

Gatos, Harry C.; Lagowski, Jacek

1989-01-01

The program on Crystal Growth of Device Quality GaAs in Space was initiated in 1977. The initial stage covering 1977 to 1984 was devoted strictly to ground-based research. By 1985 the program had evolved into its next logical stage aimed at space growth experiments; however, since the Challenger disaster, the program has been maintained as a ground-based program awaiting activation of experimentation in space. The overall prgram has produced some 80 original scientific publications on GaAs crystal growth, crystal characterization, and new approaches to space processing. Publication completed in the last three years are listed. Their key results are outlined and discussed in the twelve publications included as part of the report.

High-Performance GaAs Nanowire Solar Cells for Flexible and Transparent Photovoltaics.

PubMed

Han, Ning; Yang, Zai-xing; Wang, Fengyun; Dong, Guofa; Yip, SenPo; Liang, Xiaoguang; Hung, Tak Fu; Chen, Yunfa; Ho, Johnny C

2015-09-16

Among many available photovoltaic technologies at present, gallium arsenide (GaAs) is one of the recognized leaders for performance and reliability; however, it is still a great challenge to achieve cost-effective GaAs solar cells for smart systems such as transparent and flexible photovoltaics. In this study, highly crystalline long GaAs nanowires (NWs) with minimal crystal defects are synthesized economically by chemical vapor deposition and configured into novel Schottky photovoltaic structures by simply using asymmetric Au-Al contacts. Without any doping profiles such as p-n junction and complicated coaxial junction structures, the single NW Schottky device shows a record high apparent energy conversion efficiency of 16% under air mass 1.5 global illumination by normalizing to the projection area of the NW. The corresponding photovoltaic output can be further enhanced by connecting individual cells in series and in parallel as well as by fabricating NW array solar cells via contact printing showing an overall efficiency of 1.6%. Importantly, these Schottky cells can be easily integrated on the glass and plastic substrates for transparent and flexible photovoltaics, which explicitly demonstrate the outstanding versatility and promising perspective of these GaAs NW Schottky photovoltaics for next-generation smart solar energy harvesting devices.

Growth of High-Quality GaAs on Ge by Controlling the Thickness and Growth Temperature of Buffer Layer

NASA Astrophysics Data System (ADS)

Zhou, Xu-Liang; Pan, Jiao-Qing; Yu, Hong-Yan; Li, Shi-Yan; Wang, Bao-Jun; Bian, Jing; Wang, Wei

2014-12-01

High-quality GaAs thin films grown on miscut Ge substrates are crucial for GaAs-based devices on silicon. We investigate the effect of different thicknesses and temperatures of GaAs buffer layers on the crystal quality and surface morphology of GaAs on Ge by metal-organic chemical vapor deposition. Through high resolution x-ray diffraction measurements, it is demonstrated that the full width at half maximum for the GaAs epilayer (Ge substrate) peak could achieve 19.3 (11.0) arcsec. The value of etch pit density could be 4×104 cm-2. At the same time, GaAs surfaces with no pyramid-shaped pits are obtained when the buffer layer growth temperature is lower than 360°C, due to effective inhibition of initial nucleation at terraces of the Ge surface. In addition, it is shown that large island formation at the initial stage of epitaxial growth is a significant factor for the final rough surface and that this initial stage should be carefully controlled when a device quality GaAs surface is desired.

Frequency-tunable continuous-wave terahertz sources based on GaAs plasmonic photomixers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Shang-Hua; Jarrahi, Mona; Electrical Engineering Department, University of California Los Angeles, Los Angeles, California 90095

2015-09-28

We present frequency-tunable, continuous-wave terahertz sources based on GaAs plasmonic photomixers, which offer high terahertz radiation power levels at 50% radiation duty cycle. The use of plasmonic contact electrodes enhances photomixer quantum efficiency while maintaining its ultrafast operation by concentrating a large number of photocarriers in close proximity to the device contact electrodes. Additionally, the relatively high thermal conductivity and high resistivity of GaAs allow operation under high optical pump power levels and long duty cycles without reaching the thermal breakdown limit of the photomixer. We experimentally demonstrate continuous-wave terahertz radiation with a radiation frequency tuning range of more thanmore » 2 THz and a record-high radiation power of 17 μW at 1 THz through plasmonic photomixers fabricated on a low temperature grown GaAs substrate at 50% radiation duty cycle.« less

Experimental investigation of millimeter-wave GaAs TED oscillators cooled to cryogenic temperatures

NASA Astrophysics Data System (ADS)

Rydberg, Anders; Kollberg, Erik

1988-03-01

The output power and operating (bias) point for 80-100-GHz GaAs TED oscillators have been investigated for temperatures between 300 and 40 K. It is shown experimentally that the power can be increased by as much as nearly four times by cooling the oscillator. The thermal design of the oscillator was studied for GaAs and InP TED oscillators.

Single crystal and polycrystalline GaAs solar cells using AMOS technology

NASA Technical Reports Server (NTRS)

Stirn, R. J.; Yeh, Y. C. M.

1976-01-01

A description is given of current technology for fabricating single AMOS (antireflection-coated metal oxide semiconductor) solar cells, with attention given to thermal, plasma, and anodic oxidation, native oxide stripping, and X-ray photoelectron spectroscopy results. Some preliminary results are presented on the chemistry and electrical characterization of such cells, and the characteristics of cells fabricated on sliced polycrystalline GaAs wafers are examined. Consideration is also given to the recrystallization of evaporated Ge films for use as low-cost substrates for polycrystalline GaAs solar cells.

Formation and photoluminescence of GaAs1-xNx dilute nitride achieved by N-implantation and flash lamp annealing

NASA Astrophysics Data System (ADS)

Gao, Kun; Prucnal, S.; Skorupa, W.; Helm, M.; Zhou, Shengqiang

2014-07-01

In this paper, we present the fabrication of dilute nitride semiconductor GaAs1-xNx by nitrogen-ion-implantation and flash lamp annealing (FLA). N was implanted into the GaAs wafers with atomic concentration of about ximp1 = 0.38% and ximp2 = 0.76%. The GaAs1-xNx layer is regrown on GaAs during FLA treatment in a solid phase epitaxy process. Room temperature near band-edge photoluminescence (PL) has been observed from the FLA treated GaAs1-xNx samples. According to the redshift of the near band-edge PL peak, up to 80% and 44% of the implanted N atoms have been incorporated into the lattice by FLA for ximp1 = 0.38% and ximp2 = 0.76%, respectively. Our investigation shows that ion implantation followed by ultrashort flash lamp treatment, which allows for large scale production, exhibits a promising prospect on bandgap engineering of GaAs based semiconductors.

Wafer-Fused Orientation-Patterned GaAs

DTIC Science & Technology

2008-02-13

frequencies utilizing existing industrial foundries. 15. SUBJECT TERMS Orientation-patterned Gallium Arsenide, hydride vapor phase epitaxy, quasi-phase... Gallium Arsenide, hydride vapor phase epitaxy, quasi-phase-matching, nonlinear frequency conversion 1. INTRODUCTION Quasi-phase-matching (QPM)1...and E. Lallier, “Second harmonic generation of CO2 laser using thick quasi-phase-matched GaAs layer grown by hydride vapour phase epitaxy

Dielectric constant extraction of graphene nanostructured on SiC substrates from spectroscopy ellipsometry measurement using Gauss–Newton inversion method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Maulina, Hervin; Santoso, Iman, E-mail: iman.santoso@ugm.ac.id; Subama, Emmistasega

2016-04-19

The extraction of the dielectric constant of nanostructured graphene on SiC substrates from spectroscopy ellipsometry measurement using the Gauss-Newton inversion (GNI) method has been done. This study aims to calculate the dielectric constant and refractive index of graphene by extracting the value of ψ and Δ from the spectroscopy ellipsometry measurement using GNI method and comparing them with previous result which was extracted using Drude-Lorentz (DL) model. The results show that GNI method can be used to calculate the dielectric constant and refractive index of nanostructured graphene on SiC substratesmore faster as compared to DL model. Moreover, the imaginary partmore » of the dielectric constant values and coefficient of extinction drastically increases at 4.5 eV similar to that of extracted using known DL fitting. The increase is known due to the process of interband transition and the interaction between the electrons and electron-hole at M-points in the Brillouin zone of graphene.« less

Role of surface energy on the morphology and optical properties of GaP micro & nano structures grown on polar and non-polar substrates

NASA Astrophysics Data System (ADS)

Roychowdhury, R.; Kumar, Shailendra; Wadikar, A.; Mukherjee, C.; Rajiv, K.; Sharma, T. K.; Dixit, V. K.

2017-10-01

Role of surface energy on the morphology, crystalline quality, electronic structure and optical properties of GaP layer grown on Si (001), Si (111), Ge (111) and GaAs (001) is investigated. GaP layers are grown on four different substrates under identical growth kinetics by metal organic vapour phase epitaxy. The atomic force microscopy images show that GaP layer completely covers the surface of GaAs substrate. On the other hand, the surfaces of Si (001), Si (111), Ge (111) substrates are partially covered with crystallographically morphed GaP island type micro and nano-structures. Origin of these crystallographically morphed GaP island is explained by the theoretical calculation of surface energy of the layer and corresponding substrates respectively. The nature of GaP island type micro and nano-structures and layers are single crystalline with existence of rotational twins on Si and Ge (111) substrates which is confirmed by the phi, omega and omega/2theta scans of high resolution x-ray diffraction. The electronic valence band offsets between the GaP and substrates have been determined from the valence band spectra of ultraviolet photoelectron spectroscopy. The valence electron plasmon of GaP are investigated by studying the energy values of Ga (3d) core level along with loss peaks in the energy dependent photoelectron spectra. The peak observed within the range of 3-6 eV from the Ga (3d) core level in the photoelectron spectra are associated to inter band transitions as their energy values are estimated from the pseudo dielectric function by the spectroscopic ellipsometry.

High power cascaded mid-infrared InAs/GaSb light emitting diodes on mismatched GaAs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Provence, S. R., E-mail: sydney-provence@uiowa.edu; Ricker, R.; Aytac, Y.

2015-09-28

InAs/GaSb mid-wave, cascaded superlattice light emitting diodes are found to give higher radiance when epitaxially grown on mismatched GaAs substrates compared to lattice-matched GaSb substrates. Peak radiances of 0.69 W/cm{sup 2}-sr and 1.06 W/cm{sup 2}-sr for the 100 × 100 μm{sup 2} GaSb and GaAs-based devices, respectively, were measured at 77 K. Measurement of the recombination coefficients shows the shorter Shockley-Read-Hall recombination lifetime as misfit dislocations for growth on GaAs degrade the quantum efficiency only at low current injection. The improved performance on GaAs was found to be due to the higher transparency and improved thermal properties of the GaAs substrate.

Analysis of GAA/TTC DNA triplexes using nuclear magnetic resonance and electrospray ionization mass spectrometry.

PubMed

Mariappan, S V Santhana; Cheng, Xun; van Breemen, Richard B; Silks, Louis A; Gupta, Goutam

2004-11-15

The formation of a GAA/TTC DNA triplex has been implicated in Friedreich's ataxia. The destabilization of GAA/TTC DNA triplexes either by pH or by binding to appropriate ligands was analyzed by nuclear magnetic resonance (NMR) and positive-ion electrospray mass spectrometry. The triplexes and duplexes were identified by changes in the NMR chemical shifts of H8, H1, H4, 15N7, and 15N4. The lowest pH at which the duplex is detectable depends upon the overall stability and the relative number of Hoogsteen C composite function G to T composite function A basepairs. A melting pH (pHm) of 7.6 was observed for the destabilization of the (GAA)2T4(TTC)2T4(CTT)2 triplex to the corresponding Watson-Crick duplex and the T4(CTT)2 overhang. The mass spectrometric analyses of (TTC)6.(GAA)6 composite function(TTC)6 triplex detected ions due to both triplex and single-stranded oligonucleotides under acidic conditions. The triplex ions disappeared completely at alkaline pH. Duplex and single strands were detectable only at neutral and alkaline pH values. Mass spectrometric analyses also showed that minor groove-binding ligands berenil, netropsin, and distamycin and the intercalating ligand acridine orange destabilize the (TTC)6.(GAA)6 composite function (TTC)6 triplex. These NMR and mass spectrometric methods may function as screening assays for the discovery of agents that destabilize GAA/TTC triplexes and as general methods for the characterization of structure, dynamics, and stability of DNA and DNA-ligand complexes.

High-efficiency thin-film GaAs solar cells

NASA Technical Reports Server (NTRS)

Stirn, R. J.

1979-01-01

GaAs chemical vapor deposition (CVD) growth on single-crystal GaAs substrates was investigated over a temperature range of 600 to 750 C, As/GA mole-ratio range of 3 to 11, and gas molefraction range 5 x 10 to the minus 9th power to 7x 10 to the minus 7th power for H2S doping. GasAs CVD growth on recrystallized Ge films was investigated for a temperature range of 550 to 700 C, an As/GA mole ratio of 5, and for various H2S mole fraction. The highest efficiency cell observed on these films with 2 mm dots was 4.8% (8% when AR-coated). Improvements in fill factor and opencircuit voltage by about 40% each are required in order to obtain efficiencies of 15% or greater.

Arsenic ambient conditions preventing surface degradation of GaAs during capless annealing at high temperatures

NASA Technical Reports Server (NTRS)

Kang, C. H.; Kondo, K.; Lagowski, J.; Gatos, H. C.

1987-01-01

Changes in surface morphology and composition caused by capless annealing of GaAs were studied as a function of annealing temperature, T(GaAs), and the ambient arsenic pressure controlled by the temperature, T(As), of an arsenic source in the annealing ampul. It was established that any degradation of the GaAs surface morphology could be completely prevented, providing that T(As) was more than about 0.315T(GaAs) + 227 C. This empirical relationship is valid up to the melting point temperature of GaAs (1238 C), and it may be useful in some device-processing steps.

Image quality of a pixellated GaAs X-ray detector

NASA Astrophysics Data System (ADS)

Sun, G. C.; Makham, S.; Bourgoin, J. C.; Mauger, A.

2007-02-01

X-ray detection requires materials with large atomic numbers Z in order to absorb the radiation efficiently. In case of X-ray imaging, fluorescence is a limiting factor for the spatial resolution and contrast at energies above the kα threshold. Since both the energy and yield of the fluorescence of a given material increase with the atomic number, there is an optimum value of Z. GaAs, which can now be epitaxially grown as self-supported thick layers to fulfil the requirements for imaging (good homogeneity of the electronic properties) corresponds to this optimum. Image performances obtained with this material are evaluated in terms of line spread function and modulation transfer function, and a comparison with CsI is made. We evaluate the image contrast obtained for a given object contrast with GaAs and CsI detectors, in the photon energy range of medical applications. Finally, we discuss the minimum object size, which can be detected by these detectors in of mammography conditions. This demonstrates that an object of a given size can be detected using a GaAs detector with a dose at least 100 times lower than using a CsI detector.

Surface science analysis of GaAs photocathodes following sustained electron beam delivery

DOE Office of Scientific and Technical Information (OSTI.GOV)

Carlos Hernandez-Garcia, Fay Hannon, Marcy Stutzman, V. Shutthanandan, Z. Zhu, M. Nandasri, S. V. Kuchibhatla, S. Thevuthasan, W. P. Hess

2012-06-01

Degradation of the photocathode materials employed in photoinjectors represents a challenge for sustained operation of nuclear physics accelerators and high power Free Electron Lasers (FEL). Photocathode quantum efficiency (QE) degradation is due to residual gasses in the electron source vacuum system being ionized and accelerated back to the photocathode. These investigations are a first attempt to characterize the nature of the photocathode degradation, and employ multiple surface and bulk analysis techniques to investigate damage mechanisms including sputtering of the Cs-oxidant surface monolayer, other surface chemistry effects, and ion implantation. Surface and bulk analysis studies were conducted on two GaAs photocathodes,more » which were removed from the JLab FEL DC photoemission gun after delivering electron beam, and two control samples. The analysis techniques include Helium Ion Microscopy (HIM), Rutherford Backscattering Spectrometry (RBS), Atomic Force Microscopy (AFM) and Secondary Ion Mass Spectrometry (SIMS). In addition, two high-polarization strained superlattice GaAs photocathode samples, one removed from the Continuous Electron Beam Accelerator Facility (CEBAF) photoinjector and one unused, were also analyzed using Transmission Electron Microscopy (TEM) and SIMS. It was found that heat cleaning the FEL GaAs wafer introduces surface roughness, which seems to be reduced by prolonged use. The bulk GaAs samples retained a fairly well organized crystalline structure after delivering beam but shows evidence of Cs depletion on the surface. Within the precision of the SIMS and RBS measurements the data showed no indication of hydrogen implantation or lattice damage from ion back bombardment in the bulk GaAs wafers. In contrast, SIMS and TEM measurements of the strained superlattice photocathode show clear crystal damage in the wafer from ion back bombardment.« less

Optical detectors for GaAs MMIC integration: Technology assessment

NASA Technical Reports Server (NTRS)

Claspy, P. C.; Bhasin, K. B.

1989-01-01

Fiber optic links are being considered to transmit digital and analog signals in phased array antenna feed networks in space communications systems. The radiating elements in these arrays will be GaAs monolithic microwave integrated circuits (MMIC's) in numbers ranging from a few hundred to several thousand. If such optical interconnects are to be practical it appears essential that the associated components, including detectors, be monolithically integrated on the same chip as the microwave circuitry. The general issue of monolithic integration of microwave and optoelectronic components is addressed from the point of view of fabrication technology and compatibility. Particular attention is given to the fabrication technology of various types of GaAs optical detectors that are designed to operate at a wavelength of 830 nm.

Dopant diffusion and segregation in semiconductor heterostructures: Part III, diffusion of Si into GaAs

NASA Astrophysics Data System (ADS)

Chen, C.-H.; Gösele, U. M.; Tan, T. Y.

We have mentioned previously that in the third part of the present series of papers, a variety of n-doping associated phenomena will be treated. Instead, we have decided that this paper, in which the subject treated is diffusion of Si into GaAs, shall be the third paper of the series. This choice is arrived at because this subject is a most relevent heterostructure problem, and also because of space and timing considerations. The main n-type dopant Si in GaAs is amphoteric which may be incorporated as shallow donor species SiGa+ and as shallow acceptor species SiAs-. The solubility of SiAs- is much lower than that of SiGa+ except at very high Si concentration levels. Hence, a severe electrical self-compensation occurs at very high Si concentrations. In this study we have modeled the Si distribution process in GaAs by assuming that the diffusing species is SiGa+ which will convert into SiAs- in accordance with their solubilities and that the point defect species governing the diffusion of SiGa+ are triply-negatively-charged Ga vacancies VGa3-. The outstanding features of the Si indiffusion profiles near the Si/GaAs interface have been quantitatively explained for the first time. Deposited on the GaAs crystal surface, the Si source material is a polycrystalline Si layer which may be undoped or n+-doped using As or P. Without the use of an As vapor phase in the ambient, the As- and P-doped source materials effectively render the GaAs crystals into an As-rich composition, which leads to a much more efficient Si indiffusion process than for the case of using undoped source materials which maintains the GaAs crystals in a relatively As-poor condition. The source material and the GaAs crystal together form a heterostructure with its junction influencing the electron distribution in the region, which, in turn, affects the Si indiffusion process prominently.

Growth and characterization of amorphous selenium: An exploration into the glass transition temperature

NASA Astrophysics Data System (ADS)

Schaefers, Justin Kyle

The glass transition temperature (Tg) of alpha-Se films and its correlation to percent As inclusion was explored using such characterization tools as Raman spectroscopy, spectroscopic ellipsometry, atomic force microscopy, and microphotography. The films were deposited under ultra high vacuum conditions in a dedicated molecular beam epitaxy chamber onto semi-insulating GaAs (100) substrates. After deposition, the samples were thermally annealed in 5°C increments until they began to crystallize, as evident in the characterizations performed. It was discovered that not only is Tg directly related to percent As, but that the film thickness is as well. Higher than previously reported values, Tg was found to be 80°C for 0% As, 110°C for 2% As, and 125°C for 5% As. In addition, instead of producing polycrystalline films containing all the allotropes of Se as a result of the annealing process, films of the trigonal allotrope of crystalline selenium (t-Se) were produced through the annealing process. The transition from the amorphous phase to the trigonal phase has never been reported prior to this dissertation. Finally, it was also discovered that the MBE deposition of the films is truly epitaxial in nature.

Calculation of optical band gaps of a-Si:H thin films by ellipsometry and UV-Vis spectrophotometry

NASA Astrophysics Data System (ADS)

Qiu, Yijiao; Li, Wei; Wu, Maoyang; Fu, Junwei; Jiang, Yadong

2010-10-01

Hydrogenated amorphous silicon (a-Si:H) thin films doped with Phosphorus (P) and Nitrogen (N) were deposited by radio frequency plasma enhanced chemical vapor deposition (RF-PECVD). The optical band gaps of the thin films obtained through either changing the gas pressure (P-doped only) or adulterating nitrogen concentration (with fixed P content) were investigated by means of Ellipsometric and Ultraviolet-Visible (UV-Vis) spectroscopy, respectively. Tauc formula was used in calculating the optical band gaps of the thin films in both methods. The results show that Ellipsometry and UV-Vis spectrophotometry can be applied in the research of the optical properties of a-Si:H thin films experimentally. Both methods reflect the variation law of the optical band gaps caused by CVD process parameters, i.e., the optical band gap of the a-Si:H thin films is increased with the rise of the gas pressure or the nitrogen concentration respectively. The difference in optical band gaps of the doped a-Si:H thin films calculated by Ellipsometry or UV-Vis spectrophotometry are not so great that they both can be used to measure the optical band gaps of the thin films in practical applications.

The 20 GHz power GaAs FET development

NASA Technical Reports Server (NTRS)

Crandell, M.

1986-01-01

The development of power Field Effect Transistors (FET) operating in the 20 GHz frequency band is described. The major efforts include GaAs FET device development (both 1 W and 2 W devices), and the development of an amplifier module using these devices.

Cryogenic measurements of aerojet GaAs n-JFETs

NASA Technical Reports Server (NTRS)

Goebel, John H.; Weber, Theodore T.

1993-01-01

The spectral noise characteristics of Aerojet gallium arsenide (GaAs) junction field effect transistors (JFET's) have been investigated down to liquid-helium temperatures. Noise characterization was performed with the field effect transistor (FET) in the floating-gate mode, in the grounded-gate mode to determine the lowest noise readings possible, and with an extrinsic silicon photodetector at various detector bias voltages to determine optimum operating conditions. The measurements indicate that the Aerojet GaAs JFET is a quiet and stable device at liquid helium temperatures. Hence, it can be considered a readout line driver or infrared detector preamplifier as well as a host of other cryogenic applications. Its noise performance is superior to silicon (Si) metal oxide semiconductor field effect transistor (MOSFET's) operating at liquid helium temperatures, and is equal to the best Si n channel junction field effect transistor (n-JFET's) operating at 300 K.

GaAs nanowire array solar cells with axial p-i-n junctions.

PubMed

Yao, Maoqing; Huang, Ningfeng; Cong, Sen; Chi, Chun-Yung; Seyedi, M Ashkan; Lin, Yen-Ting; Cao, Yu; Povinelli, Michelle L; Dapkus, P Daniel; Zhou, Chongwu

2014-06-11

Because of unique structural, optical, and electrical properties, solar cells based on semiconductor nanowires are a rapidly evolving scientific enterprise. Various approaches employing III-V nanowires have emerged, among which GaAs, especially, is under intense research and development. Most reported GaAs nanowire solar cells form p-n junctions in the radial direction; however, nanowires using axial junction may enable the attainment of high open circuit voltage (Voc) and integration into multijunction solar cells. Here, we report GaAs nanowire solar cells with axial p-i-n junctions that achieve 7.58% efficiency. Simulations show that axial junctions are more tolerant to doping variation than radial junctions and lead to higher Voc under certain conditions. We further study the effect of wire diameter and junction depth using electrical characterization and cathodoluminescence. The results show that large diameter and shallow junctions are essential for a high extraction efficiency. Our approach opens up great opportunity for future low-cost, high-efficiency photovoltaics.

Elastomeric nanoparticle composites covalently bound to Al2O3/GaAs surfaces.

PubMed

Song, Hyon Min; Ye, Peide D; Ivanisevic, Albena

2007-08-28

This article reports the modification of Al2O3/GaAs surfaces with multifunctional soft materials. Siloxane elastomers were covalently bound to dopamine-modified Al2O3/GaAs semiconductor surfaces using MPt (M = Fe, Ni) nanoparticles. The sizes of the monodisperse FePt and NiPt nanoparticles were less than 5 nm. The surfaces of the nanoparticles as well as the Al2O3/GaAs substrates were modified with allyl-functionalized dopamine that utilized a dihydroxy group as a strong ligand. The immobilization of the elastomers was performed via a hydrosilation reaction of the allyl-functionalized dopamines with the siloxane backbones. X-ray photoelectron spectroscopy (XPS) experiments confirmed the covalent bonding of the siloxane elastomers to the oxide layer on the semiconductor surface. Fourier transform-infrared reflection absorption spectroscopy (FT-IRRAS) measurements revealed that the allyl functional groups are bonded to the siloxane backbones. The FT-IRRAS data also showed that the density of the allyl groups on the surface was lower than that of the siloxane backbones. The mechanical properties of the surface-bound nanocomposites were tested using nanoindentation experiments. The nanoindentation data showed that the soft matrix composed of the elastomeric coating on the surfaces behaves differently from the inner, hard Al2O3/GaAs substrate.

Growth of GaAs crystals from the melt in a partially confined configuration

NASA Technical Reports Server (NTRS)

Gatos, Harry C.; Lagowski, Jacek

1988-01-01

The experimental approach was directed along two main goals: (1) the implementation of an approach to melt growth in a partially confined configuration; and (2) the investigation of point defect interaction and electronic characteristics as related to thermal treatment following solidification and stoichiometry. Significant progress was made along both fronts. Crystal growth of GaAs in triangular ampuls was already carried out successfully and consistent with the model. In fact, pronounced surface tension phenomena which cannot be observed in ordinary confinement system were identified and should premit the assessment of Maragoni effects prior to space processing. Regarding thermal treatment, it was discovered that the rate of cooling from elevated temperatures is primarily responsible for a whole class of defect interactions affecting the electronic characteristics of GaAs and that stoichiometry plays a critical role in the quality of GaAs.

Quantum-confinement effects on conduction band structure of rectangular cross-sectional GaAs nanowires

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tanaka, H., E-mail: tanaka@semicon.kuee.kyoto-u.ac.jp; Morioka, N.; Mori, S.

2014-02-07

The conduction band structure and electron effective mass of GaAs nanowires with various cross-sectional shapes and orientations were calculated by two methods, a tight-binding method and an effective mass equation taking the bulk full-band structure into account. The effective mass of nanowires increases as the cross-sectional size decreases, and this increase in effective mass depends on the orientations and substrate faces of nanowires. Among [001], [110], and [111]-oriented rectangular cross-sectional GaAs nanowires, [110]-oriented nanowires with wider width along the [001] direction showed the lightest effective mass. This dependence originates from the anisotropy of the Γ valley of bulk GaAs. Themore » relationship between effective mass and bulk band structure is discussed.« less

Interface states and internal photoemission in p-type GaAs metal-oxide-semiconductor surfaces

NASA Technical Reports Server (NTRS)

Kashkarov, P. K.; Kazior, T. E.; Lagowski, J.; Gatos, H. C.

1983-01-01

An interface photodischarge study of p-type GaAs metal-oxide-semiconductor (MOS) structures revealed the presence of deep interface states and shallow donors and acceptors which were previously observed in n-type GaAs MOS through sub-band-gap photoionization transitions. For higher photon energies, internal photoemission was observed, i.e., injection of electrons to the conduction band of the oxide from either the metal (Au) or from the GaAs valence band; the threshold energies were found to be 3.25 and 3.7 + or - 0.1 eV, respectively. The measured photoemission current exhibited a thermal activation energy of about 0.06 eV, which is consistent with a hopping mechanism of electron transport in the oxide.

Development of a 1K x 1K GaAs QWIP Far IR Imaging Array

NASA Technical Reports Server (NTRS)

Jhabvala, M.; Choi, K.; Goldberg, A.; La, A.; Gunapala, S.

2003-01-01

In the on-going evolution of GaAs Quantum Well Infrared Photodetectors (QWIPs) we have developed a 1,024 x 1,024 (1K x1K), 8.4-9 microns infrared focal plane array (FPA). This 1 megapixel detector array is a hybrid using the Rockwell TCM 8050 silicon readout integrated circuit (ROIC) bump bonded to a GaAs QWIP array fabricated jointly by engineers at the Goddard Space Flight Center (GSFC) and the Army Research Laboratory (ARL). The finished hybrid is thinned at the Jet Propulsion Lab. Prior to this development the largest format array was a 512 x 640 FPA. We have integrated the 1K x 1K array into an imaging camera system and performed tests over the 40K-90K temperature range achieving BLIP performance at an operating temperature of 76K (f/2 camera system). The GaAs array is relatively easy to fabricate once the superlattice structure of the quantum wells has been defined and grown. The overall arrays costs are currently dominated by the costs associated with the silicon readout since the GaAs array fabrication is based on high yield, well-established GaAs processing capabilities. In this paper we will present the first results of our 1K x 1K QWIP array development including fabrication methodology, test data and our imaging results.

New dynamic FET logic and serial memory circuits for VLSI GaAs technology

NASA Technical Reports Server (NTRS)

Eldin, A. G.

1991-01-01

The complexity of GaAs field effect transistor (FET) very large scale integration (VLSI) circuits is limited by the maximum power dissipation while the uniformity of the device parameters determines the functional yield. In this work, digital GaAs FET circuits are presented that eliminate the DC power dissipation and reduce the area to 50% of that of the conventional static circuits. Its larger tolerance to device parameter variations results in higher functional yield.

Photoreflectance from GaAs and GaAs/GaAs interfaces

NASA Astrophysics Data System (ADS)

Sydor, Michael; Angelo, James; Wilson, Jerome J.; Mitchel, W. C.; Yen, M. Y.

1989-10-01

Photoreflectance from semi-insulating GaAs, and GaAs/GaAs interfaces, is discussed in terms of its behavior with temperature, doping, epilayer thickness, and laser intensity. Semi-insulating substrates show an exciton-related band-edge signal below 200 K and an impurity-related photoreflectance above 400 K. At intermediate temperatures the band-edge signal from thin GaAs epilayers contains a contribution from the epilayer-substrate interface. The interface effect depends on the epilayer's thickness, doping, and carrier mobility. The effect broadens the band-edge photoreflectance by 5-10 meV, and artifically lowers the estimates for the critical-point energy, ECP, obtained through the customary third-derivative functional fit to the data.

Effect of low and staggered gap quantum wells inserted in GaAs tunnel junctions

NASA Astrophysics Data System (ADS)

Louarn, K.; Claveau, Y.; Marigo-Lombart, L.; Fontaine, C.; Arnoult, A.; Piquemal, F.; Bounouh, A.; Cavassilas, N.; Almuneau, G.

2018-04-01

In this article, we investigate the impact of the insertion of either a type I InGaAs or a type II InGaAs/GaAsSb quantum well on the performances of MBE-grown GaAs tunnel junctions (TJs). The devices are designed and simulated using a quantum transport model based on the non-equilibrium Green’s function formalism and a 6-band k.p Hamiltonian. We experimentally observe significant improvements of the peak tunneling current density on both heterostructures with a 460-fold increase for a moderately doped GaAs TJ when the InGaAs QW is inserted at the junction interface, and a 3-fold improvement on a highly doped GaAs TJ integrating a type II InGaAs/GaAsSb QW. Thus, the simple insertion of staggered band lineup heterostructures enables us to reach a tunneling current well above the kA cm‑2 range, equivalent to the best achieved results for Si-doped GaAs TJs, implying very interesting potential for TJ-based components, such as multi-junction solar cells, vertical cavity surface emitting lasers and tunnel-field effect transistors.

Gallium arsenide (GaAs) power conversion concept

NASA Technical Reports Server (NTRS)

Nussberger, A. A.

1980-01-01

A summary design analysis of a GaAs power conversion system for the solar power satellite (SPS) is presented. Eight different satellite configuration options for the solar arrays are compared. Solar cell annealing effects after proton irradiation are considered. Mass estimates for the SPS and the effect of solar cell parameters on SPS array design are discussed.

GaAs photovoltaics and optoelectronics using releasable multilayer epitaxial assemblies.

PubMed

Yoon, Jongseung; Jo, Sungjin; Chun, Ik Su; Jung, Inhwa; Kim, Hoon-Sik; Meitl, Matthew; Menard, Etienne; Li, Xiuling; Coleman, James J; Paik, Ungyu; Rogers, John A

2010-05-20

Compound semiconductors like gallium arsenide (GaAs) provide advantages over silicon for many applications, owing to their direct bandgaps and high electron mobilities. Examples range from efficient photovoltaic devices to radio-frequency electronics and most forms of optoelectronics. However, growing large, high quality wafers of these materials, and intimately integrating them on silicon or amorphous substrates (such as glass or plastic) is expensive, which restricts their use. Here we describe materials and fabrication concepts that address many of these challenges, through the use of films of GaAs or AlGaAs grown in thick, multilayer epitaxial assemblies, then separated from each other and distributed on foreign substrates by printing. This method yields large quantities of high quality semiconductor material capable of device integration in large area formats, in a manner that also allows the wafer to be reused for additional growths. We demonstrate some capabilities of this approach with three different applications: GaAs-based metal semiconductor field effect transistors and logic gates on plates of glass, near-infrared imaging devices on wafers of silicon, and photovoltaic modules on sheets of plastic. These results illustrate the implementation of compound semiconductors such as GaAs in applications whose cost structures, formats, area coverages or modes of use are incompatible with conventional growth or integration strategies.

Imaging performance of a Timepix detector based on semi-insulating GaAs

NASA Astrophysics Data System (ADS)

Zaťko, B.; Zápražný, Z.; Jakůbek, J.; Šagátová, A.; Boháček, P.; Sekáčová, M.; Korytár, D.; Nečas, V.; Žemlička, J.; Mora, Y.; Pichotka, M.

2018-01-01

This work focused on a Timepix chip [1] coupled with a bulk semi-insulating GaAs sensor. The sensor consisted of a matrix of 256 × 256 pixels with a pitch of 55 μm bump-bonded to a Timepix ASIC. The sensor was processed on a 350 μm-thick SI GaAs wafer. We carried out detector adjustment to optimize its performance. This included threshold equalization with setting up parameters of the Timepix chip, such as Ikrum, Pream, Vfbk, and so on. The energy calibration of the GaAs Timepix detector was realized using a 241Am radioisotope in two Timepix detector modes: time-over-threshold and threshold scan. An energy resolution of 4.4 keV in FWHM (Full Width at Half Maximum) was observed for 59.5 keV γ-photons using threshold scan mode. The X-ray imaging quality of the GaAs Timepix detector was tested using various samples irradiated by an X-ray source with a focal spot size smaller than 8 μm and accelerating voltage up to 80 kV. A 700 μm × 700 μm gold testing object (X-500-200-16Au with Siemens star) fabricated with high precision was used for the spatial resolution testing at different values of X-ray image magnification (up to 45). The measured spatial resolution of our X-ray imaging system was about 4 μm.

Hb Beograd [beta121(GH4)Glu-->Val, GAA-->GTA] in the Turkish population.

PubMed

Atalay, Ayfer; Koyuncu, Hasan; Köseler, Aylin; Ozkan, Anzel; Atalay, Erol O

2007-01-01

Hb Beograd [beta121(GH4)Glu-->Val, GAA-->GTA] is a rare variant first reported in Yugoslavia and then in Turkey, Australia and New Zealand. We report two further unrelated cases from Turkey. The importance of identifying Hb Beograd at the molecular level, especially in regions where Hb D-Los Angeles [beta121(GH4)Glu-->Gln, GAA-->CAA] is prevalent, is emphasized.

Electrophilic surface sites as precondition for the chemisorption of pyrrole on GaAs(001) surfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bruhn, Thomas; Leibniz-Institut für Analytische Wissenschaften - ISAS - e.V., Albert-Einstein-Str.9, 12489 Berlin; Fimland, Bjørn-Ove

We report how the presence of electrophilic surface sites influences the adsorption mechanism of pyrrole on GaAs(001) surfaces. For this purpose, we have investigated the adsorption behavior of pyrrole on different GaAs(001) reconstructions with different stoichiometries and thus different surface chemistries. The interfaces were characterized by x-ray photoelectron spectroscopy, scanning tunneling microscopy, and by reflectance anisotropy spectroscopy in a spectral range between 1.5 and 5 eV. On the As-rich c(4 × 4) reconstruction that exhibits only nucleophilic surface sites, pyrrole was found to physisorb on the surface without any significant modification of the structural and electronic properties of the surface. Onmore » the Ga-rich GaAs(001)-(4 × 2)/(6 × 6) reconstructions which exhibit nucleophilic as well as electrophilic surface sites, pyrrole was found to form stable covalent bonds mainly to the electrophilic (charge deficient) Ga atoms of the surface. These results clearly demonstrate that the existence of electrophilic surface sites is a crucial precondition for the chemisorption of pyrrole on GaAs(001) surfaces.« less

Thermal stress cycling of GaAs solar cells

NASA Technical Reports Server (NTRS)

Janousek, B. K.; Francis, R. W.; Wendt, J. P.

1985-01-01

A thermal cycling experiment was performed on GaAs solar cells to establish the electrical and structural integrity of these cells under the temperature conditions of a simulated low-Earth orbit of 3-year duration. Thirty single junction GaAs cells were obtained and tests were performed to establish the beginning-of-life characteristics of these cells. The tests consisted of cell I-V power output curves, from which were obtained short-circuit current, open circuit voltage, fill factor, and cell efficiency, and optical micrographs, spectral response, and ion microprobe mass analysis (IMMA) depth profiles on both the front surfaces and the front metallic contacts of the cells. Following 5,000 thermal cycles, the performance of the cells was reexamined in addition to any factors which might contribute to performance degradation. It is established that, after 5,000 thermal cycles, the cells retain their power output with no loss of structural integrity or change in physical appearance.

Sn nanothreads in GaAs: experiment and simulation

NASA Astrophysics Data System (ADS)

Semenikhin, I.; Vyurkov, V.; Bugaev, A.; Khabibullin, R.; Ponomarev, D.; Yachmenev, A.; Maltsev, P.; Ryzhii, M.; Otsuji, T.; Ryzhii, V.

2016-12-01

The gated GaAs structures like the field-effect transistor with the array of the Sn nanothreads was fabricated via delta-doping of vicinal GaAs surface by Sn atoms with a subsequent regrowth. That results in the formation of the chains of Sn atoms at the terrace edges. Two device models were developed. The quantum model accounts for the quantization of the electron energy spectrum in the self-consistent two-dimensional electric potential, herewith the electron density distribution in nanothread arrays for different gate voltages is calculated. The classical model ignores the quantization and electrons are distributed in space according to 3D density of states and Fermi-Dirac statistics. It turned out that qualitatively both models demonstrate similar behavior, nevertheless, the classical one is in better quantitative agreement with experimental data. Plausibly, the quantization could be ignored because Sn atoms are randomly placed along the thread axis. The terahertz hot-electron bolometers (HEBs) could be based on the structure under consideration.

Monolithic GaAs dual-gate FET phase shifter

NASA Astrophysics Data System (ADS)

Kumar, M.; Subbarao, S. N.; Menna, R.

1981-09-01

The objective of this program is to develop a monolithic GaAs dual-gate FET phase shifter, operating over the 4- to 8-GHz frequency band and capable of a continuously programmable phase shift from 0 deg through N times 360 deg where N is an integer. The phase shift is to be controllable to within +3 deg. This phase shifter will be capable of delivering an output power up to 0 dBm with an input and output VSWR of less than 1.5:1. Progress 1: The photomask of a 0 to 90 deg monolithic GaAs dual-gate FET phase shifter has been procured, and we are in the process of fabricating the phase shifter. 2: We have designed and fabricated a 50 ohm, 4-line interdigitated coupler. Also, we have designed and fabricated a 25-ohm, 6-line interdigitated coupler. The performance of both couplers agrees quite well with the theoretical results. Technical Problems: there was no major problem during this period.

28 percent efficient GaAs concentrator solar cells

NASA Technical Reports Server (NTRS)

Macmillan, H. F.; Hamaker, H. C.; Kaminar, N. R.; Kuryla, M. S.; Ladle Ristow, M.

1988-01-01

AlGaAs/GaAs heteroface solar concentrator cells which exhibit efficiencies in excess of 27 percent at high solar concentrations (over 400 suns, AM1.5D, 100 mW/sq cm) have been fabricated with both n/p and p/n configurations. The best n/p cell achieved an efficiency of 28.1 percent around 400 suns, and the best p/n cell achieved an efficiency of 27.5 percent around 1000 suns. The high performance of these GaAs concentrator cells compared to earlier high-efficiency cells was due to improved control of the metal-organic chemical vapor deposition growth conditions and improved cell fabrication procedures (gridline definition and edge passivation). The design parameters of the solar cell structures and optimized grid pattern were determined with a realistic computer modeling program. An evaluation of the device characteristics and a discussion of future GaAs concentrator cell development are presented.

Use of a corrugated surface to enhance radiation tolerance in a GaAs solar cell

NASA Technical Reports Server (NTRS)

Leon, Rosa P.; Piszczor, Michael F., Jr.

1985-01-01

The use of a corrugated surface on a GaAs solar cell and its effects on radiation resistance were studied. A compute code was developed to determine the performance of the cell for various geometric parameters. The large optical absorption coefficient of GaAs allows grooves to be only 4-5 micrometers deep. Using accepted material parameters for GaAs solar cells the theoretical performances were compared for various corrugated cells before and after minority carrier diffusion length degradation. The total power output was maximized for both n(+)/p and p(+)/n cells. Optimum values of 1.0-1.5 and 5.0 micrometers for groove and ridge widths respectively were determined.

Interpolative modeling of GaAs FET S-parameter data bases for use in Monte Carlo simulations

NASA Technical Reports Server (NTRS)

Campbell, L.; Purviance, J.

1992-01-01

A statistical interpolation technique is presented for modeling GaAs FET S-parameter measurements for use in the statistical analysis and design of circuits. This is accomplished by interpolating among the measurements in a GaAs FET S-parameter data base in a statistically valid manner.

GaAs monolithic RF modules for SARSAT distress beacons

NASA Technical Reports Server (NTRS)

Cauley, Michael A.

1991-01-01

Monolithic GaAs UHF components for use in SARSAT Emergency Distress beacons are under development by Microwave Monolithics, Inc., Simi Valley, CA. The components include a bi-phase modulator, driver amplifier, and a 5 watt power amplifier.

Low temperature growth and electrical characterization of insulators for GaAs MISFETS

NASA Technical Reports Server (NTRS)

Borrego, J. M.; Ghandhi, S. K.

1981-01-01

Progress in the low temperature growth of oxides and layers on GaAs and the detailed electrical characterization of these oxides is reported. A plasma anodization system was designed, assembled, and put into operation. A measurement system was assembled for determining capacitance and conductance as a function of gate voltage for frequencies in the range from 1 Hz to 1 MHz. Initial measurements were carried out in Si-SiO2 capacitors in order to test the system and in GaAs MIS capacitors abricated using liquid anodization.

Photoluminescence Study of N-Type Thermal Conversion in Semi-Insulating GaAs.

DTIC Science & Technology

1982-12-01

free electron to the crystal. For example, in GaAs, a tellurium atom on an arsenic site (TeAs) or a silicon atom on a gallium site (SiGa) are donor atoms...Photoconductivity Photoluminescenc Silicon, SiGa 5.81 6.80 Germanium, GeGa 6.08 Sulfur, SAs 6.10 Selenium, SeAs 5.89 6.10 Tellurium , TeAs When an electron...34 to the neutral donor or acceptor (Ref 16:15). The following excitonic com- plexes have been observed in GaAs: (i) exciton bound to a neutron donor at

Ferromagnetic GaAs structures with single Mn delta-layer fabricated using laser deposition.

PubMed

Danilov, Yuri A; Vikhrova, Olga V; Kudrin, Alexey V; Zvonkov, Boris N

2012-06-01

The new technique combining metal-organic chemical vapor epitaxy with laser ablation of solid targets was used for fabrication of ferromagnetic GaAs structures with single Mn delta-doped layer. The structures demonstrated anomalous Hall effect, planar Hall effect, negative and anisotropic magnetoresistance in temperature range of 10-35 K. In GaAs structures with only single Mn delta-layer (without additional 2D hole gas channel or quantum well) ferromagnetism was observed for the first time.

Structural and optical characterization of GaAs nano-crystals selectively grown on Si nano-tips by MOVPE.

PubMed

Skibitzki, Oliver; Prieto, Ivan; Kozak, Roksolana; Capellini, Giovanni; Zaumseil, Peter; Arroyo Rojas Dasilva, Yadira; Rossell, Marta D; Erni, Rolf; von Känel, Hans; Schroeder, Thomas

2017-03-01

We present the nanoheteroepitaxial growth of gallium arsenide (GaAs) on nano-patterned silicon (Si) (001) substrates fabricated using a CMOS technology compatible process. The selective growth of GaAs nano-crystals (NCs) was achieved at 570 °C by MOVPE. A detailed structure and defect characterization study of the grown nano-heterostructures was performed using scanning transmission electron microscopy, x-ray diffraction, micro-Raman, and micro-photoluminescence (μ-PL) spectroscopy. The results show single-crystalline, nearly relaxed GaAs NCs on top of slightly, by the SiO 2 -mask compressively strained Si nano-tips (NTs). Given the limited contact area, GaAs/Si nanostructures benefit from limited intermixing in contrast to planar GaAs films on Si. Even though a few growth defects (e.g. stacking faults, micro/nano-twins, etc) especially located at the GaAs/Si interface region were detected, the nanoheterostructures show intensive light emission, as investigated by μ-PL spectroscopy. Achieving well-ordered high quality GaAs NCs on Si NTs may provide opportunities for superior electronic, photonic, or photovoltaic device performances integrated on the silicon technology platform.

GaAs monolayer: Excellent SHG responses and semi metallic to metallic transition modulated by vacancy effect

NASA Astrophysics Data System (ADS)

Rozahun, Ilmira; Bahti, Tohtiaji; He, Guijie; Ghupur, Yasenjan; Ablat, Abduleziz; Mamat, Mamatrishat

2018-05-01

Monolayer materials are considered as a promising candidate for novel applications due to their attractive magnetic, electronic and optical properties. Investigation on nonlinear optical (NLO) properties and effect of vacancy on monolayer materials are vital to property modulations of monolayers and extending their applications. In this work, with the aid of first-principles calculations, the crystal structure, electronic, magnetic, and optical properties of GaAs monolayers with the vacancy were investigated. The result shows gallium arsenic (GaAs) monolayer produces a strong second harmonic generation (SHG) response. Meanwhile, the vacancy strongly affects structural, electronic, magnetic and optical properties of GaAs monolayers. Furthermore, arsenic vacancy (VAs) brings semi metallic to metallic transition, while gallium vacancy (VGa) causes nonmagnetic to magnetic conversion. Our result reveals that GaAs monolayer possesses application potentials in Nano-amplifying modulator and Nano-optoelectronic devices, and may provide useful guidance in designing new generation of Nano-electronic devices.

Formation of a pn junction on an anisotropically etched GaAs surface using metalorganic chemical vapor deposition

NASA Technical Reports Server (NTRS)

Leon, R. P.; Bailey, S. G.; Mazaris, G. A.; Williams, W. D.

1986-01-01

A continuous p-type GaAs epilayer has been deposited on an n-type sawtooth GaAs surface using MOCVD. A wet chemical etching process was used to expose the intersecting (111)Ga and (-1 -1 1)Ga planes with 6-micron periodicity. Charge-collection microscopy was used to verify the presence of the pn junction thus formed and to measure its depth. The ultimate goal of this work is to fabricate a V-groove GaAs cell with improved absorptivity, high short-circuit current, and tolerance to particle radiation.

Comparative research on activation technique for GaAs photocathodes

NASA Astrophysics Data System (ADS)

Chen, Liang; Qian, Yunsheng; Chang, Benkang; Chen, Xinlong; Yang, Rui

2012-03-01

The properties of GaAs photocathodes mainly depend on the material design and activation technique. In early researches, high-low temperature two-step activation has been proved to get more quantum efficiency than high-temperature single-step activation. But the variations of surface barriers for two activation techniques have not been well studied, thus the best activation temperature, best Cs-O ratio and best activation time for two-step activation technique have not been well found. Because the surface photovoltage spectroscopy (SPS) before activation is only in connection with the body parameters for GaAs photocathode such as electron diffusion length and the spectral response current (SRC) after activation is in connection with not only body parameters but also surface barriers, thus the surface escape probability (SEP) can be well fitted through the comparative research between SPS before activation and SEP after activation. Through deduction for the tunneling process of surface barriers by Schrödinger equation, the width and height for surface barrier I and II can be well fitted through the curves of SEP. The fitting results were well proved and analyzed by quantitative analysis of angle-dependent X-ray photoelectron spectroscopy (ADXPS) which can also study the surface chemical compositions, atomic concentration percentage and layer thickness for GaAs photocathodes. This comparative research method for fitting parameters of surface barriers through SPS before activation and SRC after activation shows a better real-time in system method for the researches of activation techniques.

Displacement damage and predicted non-ionizing energy loss in GaAs

NASA Astrophysics Data System (ADS)

Gao, Fei; Chen, Nanjun; Hernandez-Rivera, Efrain; Huang, Danhong; LeVan, Paul D.

2017-03-01

Large-scale molecular dynamics (MD) simulations, along with bond-order interatomic potentials, have been applied to study the defect production for lattice atom recoil energies from 500 eV to 20 keV in gallium arsenide (GaAs). At low energies, the most surviving defects are single interstitials and vacancies, and only 20% of the interstitial population is contained in clusters. However, a direct-impact amorphization in GaAs occurs with a high degree of probability during the cascade lifetime for Ga PKAs (primary knock-on atoms) with energies larger than 2 keV. The results reveal a non-linear defect production that increases with the PKA energy. The damage density within a cascade core is evaluated, and used to develop a model that describes a new energy partition function. Based on the MD results, we have developed a model to determine the non-ionizing energy loss (NIEL) in GaAs, which can be used to predict the displacement damage degradation induced by space radiation on electronic components. The calculated NIEL predictions are compared with the available data, thus validating the NIEL model developed in this study.

GaAs Optoelectronic Integrated-Circuit Neurons

NASA Technical Reports Server (NTRS)

Lin, Steven H.; Kim, Jae H.; Psaltis, Demetri

1992-01-01

Monolithic GaAs optoelectronic integrated circuits developed for use as artificial neurons. Neural-network computer contains planar arrays of optoelectronic neurons, and variable synaptic connections between neurons effected by diffraction of light from volume hologram in photorefractive material. Basic principles of neural-network computers explained more fully in "Optoelectronic Integrated Circuits For Neural Networks" (NPO-17652). In present circuits, devices replaced by metal/semiconductor field effect transistors (MESFET's), which consume less power.

First results from GaAs double-sided detectors

NASA Astrophysics Data System (ADS)

Beaumont, S. P.; Bertin, R.; Booth, C. N.; Buttar, C.; Carraresi, L.; Cindolo, F.; Colocci, M.; Combley, F. H.; D'Auria, S.; del Papa, C.; Dogru, M.; Edwards, M.; Foster, F.; Francescato, A.; Gowdy, S.; Gray, R.; Hill, G.; Hou, Y.; Houston, P.; Hughes, G.; Jones, B. K.; Lynch, J. G.; Lisowski, B.; Matheson, J.; Nava, F.; Nuti, M.; O'Shea, V.; Pelfer, P. G.; Raine, C.; Santana, J.; Saunders, I. J.; Seller, P. H.; Shankar, K.; Sharp, P. H.; Skillicorn, I. O.; Sloan, T.; Smith, K. M.; ten Have, I.; Turnbull, R. M.; Vanni, U.; Zichichi, A.

1994-09-01

Preliminary results are presented on the performance of double-sided microstrip detectors using Schottky contacts on both sides of a semi-insulating (SI) GaAs substrate wafer, after exposure to 10 14 neutrons cm -2 at the ISIS facility. A qualitative explanation of the device behaviour is given.

Expanded GAA repeats impair FXN gene expression and reposition the FXN locus to the nuclear lamina in single cells.

PubMed

Silva, Ana M; Brown, Jill M; Buckle, Veronica J; Wade-Martins, Richard; Lufino, Michele M P

2015-06-15

Abnormally expanded DNA repeats are associated with several neurodegenerative diseases. In Friedreich's ataxia (FRDA), expanded GAA repeats in intron 1 of the frataxin gene (FXN) reduce FXN mRNA levels in averaged cell samples through a poorly understood mechanism. By visualizing FXN expression and nuclear localization in single cells, we show that GAA-expanded repeats decrease the number of FXN mRNA molecules, slow transcription, and increase FXN localization at the nuclear lamina (NL). Restoring histone acetylation reverses NL positioning. Expanded GAA-FXN loci in FRDA patient cells show increased NL localization with increased silencing of alleles and reduced transcription from alleles positioned peripherally. We also demonstrate inefficiencies in transcription initiation and elongation from the expanded GAA-FXN locus at single-cell resolution. We suggest that repressive epigenetic modifications at the expanded GAA-FXN locus may lead to NL relocation, where further repression may occur. © The Author 2015. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Room Temperature Sensing Achieved by GaAs Nanowires and oCVD Polymer Coating.

PubMed

Wang, Xiaoxue; Ermez, Sema; Goktas, Hilal; Gradečak, Silvija; Gleason, Karen

2017-06-01

Novel structures comprised of GaAs nanowire arrays conformally coated with conducting polymers (poly(3,4-ethylenedioxythiophene) (PEDOT) or poly(3,4-ethylenedioxythiophene-co-3-thiophene acetic acid) display both sensitivity and selectivity to a variety of volatile organic chemicals. A key feature is room temperature operation, so that neither a heater nor the power it would consume, is required. It is a distinct difference from traditional metal oxide sensors, which typically require elevated operational temperature. The GaAs nanowires are prepared directly via self-seeded metal-organic chemical deposition, and conducting polymers are deposited on GaAs nanowires using oxidative chemical vapor deposition (oCVD). The range of thickness for the oCVD layer is between 100 and 200 nm, which is controlled by changing the deposition time. X-ray diffraction analysis indicates an edge-on alignment of the crystalline structure of the PEDOT coating layer on GaAs nanowires. In addition, the positive correlation between the improvement of sensitivity and the increasing nanowire density is demonstrated. Furthermore, the effect of different oCVD coating materials is studied. The sensing mechanism is also discussed with studies considering both nanowire density and polymer types. Overall, the novel structure exhibits good sensitivity and selectivity in gas sensing, and provides a promising platform for future sensor design. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Temperature dependent GaAs MMIC radiation effects

DOE Office of Scientific and Technical Information (OSTI.GOV)

Anderson, W.T.; Roussos, J.A.; Gerdes, J.

1993-12-01

The temperature dependence of pulsed neutron and flash x-ray radiation effects was studied in GaAs MMICs. Above room temperature the long term current transients are dominated by electron trapping in previously existing defects. At low temperature in the range 126 to 259 K neutron induced lattice damage appears to play an increasingly important role in producing long term current transients.

Design and implementation of GaAs HBT circuits with ACME

NASA Technical Reports Server (NTRS)

Hutchings, Brad L.; Carter, Tony M.

1993-01-01

GaAs HBT circuits offer high performance (5-20 GHz) and radiation hardness (500 Mrad) that is attractive for space applications. ACME is a CAD tool specifically developed for HBT circuits. ACME implements a novel physical schematic-capture design technique where designers simultaneously view the structure and physical organization of a circuit. ACME's design interface is similar to schematic capture; however, unlike conventional schematic capture, designers can directly control the physical placement of both function and interconnect at the schematic level. In addition, ACME provides design-time parasitic extraction, complex wire models, and extensions to Multi-Chip Modules (MCM's). A GaAs HBT gate-array and semi-custom circuits have been developed with ACME; several circuits have been fabricated and found to be fully functional .

Structural investigations of human hairs by spectrally resolved ellipsometry

NASA Astrophysics Data System (ADS)

Chan, Danny; Schulz, Benjamin; Rübhausen, Michael; Wessel, Sonya; Wepf, Roger

2006-01-01

Human hair is a biological layered system composed of two major layers, the cortex and the cuticle. We show spectrally resolved ellipsometry measurements of the ellipsometric parameters Ψ and Δ of single human hairs. The spectra reflect the layered nature of hair and the optical anisotropy of the hair's structure. In addition, measurements on strands of human hair show a high reproducibility of the ellipsometric parameters for different hair fiber bundles from the same person. Based on the measurements, we describe a dielectric model of hair that explains the spectra in terms of the dielectric properties of the major parts of hair and their associated layer thicknesses. In addition, surface roughness effects modeled by a roughness layer with a complex refractive index given by an effective medium approach can be seen to have a significant effect on the measurements. We derive values for the parameters of the cuticle surface roughness layer of the thickness dACu=273 to 360 nm and the air inclusion fA=0.6 to 5.7%.

Structural investigations of human hairs by spectrally resolved ellipsometry

NASA Astrophysics Data System (ADS)

Schulz, Benjamin; Chan, D.; Ruebhausen, M.; Wessel, S.; Wepf, R.

2006-03-01

Human hair is a biological layered system composed of two major layers, the cortex and the cuticle. We show spectrally resolved ellipsometry measurements of the ellipsometric parameters ψ and δ of single human hairs. The spectra reflect the layered nature of hair and the optical anisotropy of the hair’s structure. In addition, measurements on strands of human hair show a high reproducibility of the ellipsometric parameters for different hair fiber bundles from the same person. Based on the measurements, we develop a model of the dielectric function of hair that explains the spectra. This model includes the dielectric properties of the cuticle and cortex as well as their associated layer thicknesses. In addition, surface roughness effects modelled by a roughness layer with an complex refractive index given by an effective medium approach can have a significant effect on the measurements. We derive values for the parameters of the cuticle surface roughness layer of the thickness dACu= 273-360 nm and the air inclusion fA= 0.6 -5.7%. [1] accepted for publication in J. Biomed Opt., 2005

E+ Transition in GaAs1-xNx and GaAs1-xBix Due to Isoelectronic-Impurity-Induced Perturbation of the Conduction Band

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fluegel, B.; Mascarenhas, A.; Ptak, A. J.

2007-01-01

An above-band-gap transition E{sub +} is experimentally observed in the dilute GaAs{sub 1-x}Bi{sub x} alloy. Precise measurements at very low dilutions are made of the above-band-gap transition E{sub +} that is observed in GaAs{sub 1-x}N{sub x}, making it possible to compare the behavior of the different isoelectronic traps Bi and N in the common host GaAs with respect to their perturbation to the host electronic structure. We suggest that the origin of the E{sub +} level observed in GaAs is not the isolated isoelectronic impurity level N{sub x}, as is presumed in the band-anticrossing model, but rather the isoelectronic-impurity-induced perturbationmore » of the conduction band L{sub 6}{sup c}.« less

All-optical switching in GaAs microdisk resonators by a femtosecond pump-probe technique through tapered-fiber coupling.

PubMed

Lin, Yen-Chih; Mao, Ming-Hua; Lin, You-Ru; Lin, Hao-Hsiung; Lin, Che-An; Wang, Lon A

2014-09-01

We demonstrate ultrafast all-optical switching in GaAs microdisk resonators using a femtosecond pump-probe technique through tapered-fiber coupling. The temporal tuning of the resonant modes resulted from the refractive index change due to photoexcited carrier density variation inside the GaAs microdisk resonator. Transmission through the GaAs microdisk resonator can be modulated by more than 10 dB with a switching time window of 8 ps in the switch-off operation using pumping pulses with energies as low as 17.5 pJ. The carrier lifetime was fitted to be 42 ps, much shorter than that of the bulk GaAs, typically of the order of nanoseconds. The above observation indicates that the surface recombination plays an important role in increasing the switching speed.

GaAs CLEFT solar cells for space applications. [CVD thin film growth technology

NASA Technical Reports Server (NTRS)

Fan, J. C. C.; Mcclelland, R. W.; King, B. D.

1984-01-01

Although GaAs solar cells are radiation-resistant and have high conversion efficiencies, there are two major obstacles that such cells must overcome before they can be widely adopted for space applications: GaAs wafers are too expensive and cells made from these wafers are too heavy. The CLEFT process permits the growth of thin single-crystal films on reusable substrates, resulting in a drastic reduction in both cell cost and cell weight. Recent advances in CLEFT technology have made it possible to achieve efficiencies of about 14 percent AM0 for 0.51-sq cm GaAs solar cells 5 microns thick with a 41-mil-thick coverglass. In preliminary experiments efficiencies close to 19 percent AM1 have been obtained for 10-micron-thick cells. It is suggested that the CLEFT technology should yield inexpensive, highly efficient modules with a beginning-of-life specific power close to 1 kW/kg (for a coverglass thickness of 4 mils).

Dual-gate GaAs FET switches

NASA Astrophysics Data System (ADS)

Vorhaus, J. L.; Fabian, W.; Ng, P. B.; Tajima, Y.

1981-02-01

A set of multi-pole, multi-throw switch devices consisting of dual-gate GaAs FET's is described. Included are single-pole, single-throw (SPST), double-pole, double-throw (DPDT), and single-pole four-throw (SP4T) switches. Device fabrication and measurement techniques are discussed. The device models for these switches were based on an equivalent circuit of a dual-gate FET. The devices were found to have substantial gain in X-band and low Ku-band.

Manipulation of morphology and structure of the top of GaAs nanowires grown by molecular-beam epitaxy

NASA Astrophysics Data System (ADS)

Li, Lixia; Pan, Dong; Yu, Xuezhe; So, Hyok; Zhao, Jianhua

2017-10-01

Self-catalyzed GaAs nanowires (NWs) are grown on Si (111) substrates by molecular-beam epitaxy. The effect of different closing sequences of the Ga and As cell shutters on the morphology and structural phase of GaAs NWs is investigated. For the sequences of closing the Ga and As cell shutters simultaneously or closing the As cell shutter 1 min after closing the Ga cell shutter, the NWs grow vertically to the substrate surface. In contrast, when the As cell shutter is closed first, maintaining the Ga flux is found to be critical for the following growth of GaAs NWs, which can change the growth direction from [111] to < 11\\bar{1}> . The evolution of the morphology and structural phase transition at the tips of these GaAs NWs confirm that the triple-phase-line shift mode is at work even for the growth with different cell shutter closing sequences. Our work will provide new insights for better understanding of the growth mechanism and realizing of the morphology and structure control of the GaAs NWs. Project supported partly by the MOST of China (No. 2015CB921503), the National Natural Science Foundation of China (Nos. 61504133, 61334006, 61404127), and Youth Innovation Promotion Association, CAS (No. 2017156).

Second harmonic generation in photonic crystal cavities in (111)-oriented GaAs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Buckley, Sonia, E-mail: bucklesm@stanford.edu; Radulaski, Marina; Vučković, Jelena

2013-11-18

We demonstrate second harmonic generation at telecommunications wavelengths in photonic crystal cavities in (111)-oriented GaAs. We fabricate 30 photonic crystal structures in both (111)- and (100)-oriented GaAs and observe an increase in generated second harmonic power in the (111) orientation, with the mean power increased by a factor of 3, although there is a large scatter in the measured values. We discuss possible reasons for this increase, in particular, the reduced two photon absorption for transverse electric modes in (111) orientation, as well as a potential increase due to improved mode overlap.

Fabrication of p(+)-n junction GaAs solar cells by a novel method

NASA Technical Reports Server (NTRS)

Ghandhi, S. K.; Mathur, G.; Rode, H.; Borrego, J. M.

1984-01-01

A novel method for making p(+)-n diffused junction GaAs solar cells, with the formation of a diffusion source, an anti-reflective coating, and a protective cover glass in a single chemical-vapor deposition operation is discussed. Consideration is given to device fabrication and to solar-cell characteristics. The advantages of the technique are that the number of process steps is kept to an absolute minimum, the fabrication procedure is low-cost, and the GaAs surface is protected during the entire operation.

Fabrication, testing and reliability modeling of copper/titanium-metallized GaAs MESFETs and HEMTs for low-noise applications

NASA Astrophysics Data System (ADS)

Feng, Ting

Today, GaAs based field effect transistors (FETs) have been used in a broad range of high-speed electronic military and commercial applications. However, their reliability still needs to be improved. Particularly the hydrogen induced degradation is a large remaining issue in the reliability of GaAs FETs, because hydrogen can easily be incorporated into devices during the crystal growth and virtually every device processing step. The main objective of this research work is to develop a new gate metallization system in order to reduce the hydrogen induced degradation from the gate region for GaAs based MESFETs and HEMTs. Cu/Ti gate metallization has been introduced into the GaAs MESFETs and HEMTs in our work in order to solve the hydrogen problem. The purpose of the use of copper is to tie up the hydrogen atoms and prevent hydrogen penetration into the device active region as well as to keep a low gate resistance for low noise applications. In this work, the fabrication technology of GaAs MESFETs and AlGaAs/GaAs HEMTs with Cu/Ti metallized gates have been successfully developed and the fabricated Cu/Ti FETs have shown comparable DC performance with similar Au-based GaAs FETs. The Cu/Ti FETs were subjected to temperature accelerated testing at NOT under 5% hydrogen forming gas and the experimental results show the hydrogen induced degradation has been reduced for the Cu/Ti FETs compared to commonly used AuPtTi based GaAs FETs. A long-term reliability testing for Cu/Ti FETs has also been carried out at 200°C and up to 1000hours and testing results show Cu/Ti FETs performed with adequate reliability. The failure modes were found to consist of a decrease in drain saturation current and pinch-off voltage and an increase in source ohmic contact resistance. Material characterization tools including Rutherford backscattering spectroscopy and a back etching technique were used in Cu/Ti GaAs FETs, and pronounced gate metal copper in-diffusion and intermixing compounds at the

High Quality GaAs Growth by MBE on Si Using GeSi Buffers and Prospects for Space Photovoltaics

NASA Technical Reports Server (NTRS)

Carlin, J. A.; Ringel, S. A.; Fitzgerald, E. A.; Bulsara, M.

2005-01-01

III-V solar cells on Si substrates are of interest for space photovoltaics since this would combine high performance space cells with a strong, lightweight and inexpensive substrate. However, the primary obstacles blocking III-V/Si cells from achieving high performance to date have been fundamental materials incompatabilities, namely the 4% lattice mismatch between GaAs and Si, and the large mismatch in thermal expansion coefficient. In this paper, we report on the molecular beam epitaxial (MBE) growth and properties of GaAs layers and single junction GaAs cells on Si wafers which utilize compositionally graded GeSi Intermediate buffers grown by ultra-high vacuum chemical vapor deposition (UHVCVD) to mitigate the large lattice mismatch between GaAs and Si. Ga As cell structures were found to incorporate a threading dislocation density of 0.9-1.5 x 10 (exp 6) per square centimeter, identical to the underlying relaxed Ge cap of the graded buffer, via a combination of transmission electron microscopy, electron beam induced current, and etch pit density measurements. AlGaAs/GaAs double heterostructures wre grown on the GeSi/Si substrates for time-resolved photoluminescence measurements, which revealed a bulk GaAs minority carrier lifetime in excess of 10 ns, the highest lifetime ever reported for GaAs on Si. A series of growth were performed to ass3ss the impact of a GaAs buffer to a thickness of only 0.1 micrometer. Secondary ion mass spectroscopy studies revealed that there is negligible cross diffusion of Ga, As and Ge at he III-V/Ge interface, identical to our earlier findings for GaAs grown on Ge wafers using MBE. This indicates that there is no need for a buffer to "bury" regions of high autodopjing,a nd that either pn or np configuration cells are easily accomodated by these substrates. Preliminary diodes and single junction Al Ga As heteroface cells were grown and fabricated on the Ge/GeSi/Si substrates for the first time. Diodes fabricated on GaAs, Ge and Ge

Crystal growth of device quality GaAs in space

NASA Technical Reports Server (NTRS)

Gatos, H. C.; Lagowski, J.

1986-01-01

It was established that the findings on elemental semiconductors Ge and Si regarding crystal growth, segregation, chemical composition, defect interactions, and materials properties-electronic properties relationships are not necessarily applicable to GaAs (and to other semiconductor compounds). In many instances totally unexpected relationships were found to prevail. It was further established that in compound semiconductors with a volatile constituent, control of stoichiometry is far more critical than any other crystal growth parameter. It was also shown that, due to suppression of nonstoichiometric fluctuations, the advantages of space for growth of semiconductor compounds extend far beyond those observed in elemental semiconductors. A novel configuration was discovered for partial confinement of GaAs melt in space which overcomes the two major problems associated with growth of semiconductors in total confinement. They are volume expansion during solidification and control of pressure of the volatile constituent. These problems are discussed in detail.

Investigation of the fabrication mechanism of self-assembled GaAs quantum rings grown by droplet epitaxy.

PubMed

Tong, C Z; Yoon, S F

2008-09-10

We have directly imaged the formation of a GaAs quantum ring (QR) using droplet epitaxy followed by annealing in arsenic ambient. Based on the atomic force micrograph measurement and the analysis of surface energy, we determine that the formation of self-assembled GaAs QRs is due to the gallium atom's diffusion and crystallization driven by the gradient of surface energy. The phenomenon that GaAs is etched by the gallium droplets is reported and analyzed. It has been demonstrated that the epitaxy layers, such as AlAs and InGaP, can be used as the etching stop layer and hence can be used to control the shape and height of the QRs.

Burst annealing of high temperature GaAs solar cells

NASA Technical Reports Server (NTRS)

Brothers, P. R.; Horne, W. E.

1991-01-01

One of the major limitations of solar cells in space power systems is their vulnerability to radiation damage. One solution to this problem is to periodically heat the cells to anneal the radiation damage. Annealing was demonstrated with silicon cells. The obstacle to annealing of GaAs cells was their susceptibility to thermal damage at the temperatures required to completely anneal the radiation damage. GaAs cells with high temperature contacts and encapsulation were developed. The cells tested are designed for concentrator use at 30 suns AMO. The circular active area is 2.5 mm in diameter for an area of 0.05 sq cm. Typical one sun AMO efficiency of these cells is over 18 percent. The cells were demonstrated to be resistant to damage after thermal excursions in excess of 600 C. This high temperature tolerance should allow these cells to survive the annealing of radiation damage. A limited set of experiments were devised to investigate the feasibility of annealing these high temperature cells. The effect of repeated cycles of electron and proton irradiation was tested. The damage mechanisms were analyzed. Limitations in annealing recovery suggested improvements in cell design for more complete recovery. These preliminary experiments also indicate the need for further study to isolate damage mechanisms. The primary objective of the experiments was to demonstrate and quantify the annealing behavior of high temperature GaAs cells. Secondary objectives were to measure the radiation degradation and to determine the effect of repeated irradiation and anneal cycles.

Surface Analysis Cluster Tool | Materials Science | NREL

Science.gov Websites

spectroscopic ellipsometry during film deposition. The cluster tool can be used to study the effect of various prior to analysis. Here we illustrate the surface cleaning effect of an aqueous ammonia treatment on a

Formation of two-dimensionally confined superparamagnetic (Mn, Ga)As nanocrystals in high-temperature annealed (Ga, Mn)As/GaAs superlattices.

PubMed

Sadowski, Janusz; Domagala, Jaroslaw Z; Mathieu, Roland; Kovacs, Andras; Dłużewski, Piotr

2013-05-15

The annealing-induced formation of (Mn, Ga)As nanocrystals in (Ga, Mn)As/GaAs superlattices was studied by x-ray diffraction, transmission electron microscopy and magnetometry. The superlattice structures with 50 Å thick (Ga, Mn)As layers separated by 25, 50 and 100 Å thick GaAs spacers were grown by molecular beam epitaxy at low temperature (250 °C), and then annealed at high temperatures of 400, 560 and 630 °C. The high-temperature annealing causes decomposition to a (Ga, Mn)As ternary alloy and the formation of (Mn, Ga)As nanocrystals inside the GaAs matrix. The nanocrystals are confined in the planes that were formerly occupied by (Ga, Mn)As layers for the up to 560 °C annealing and diffuse throughout the GaAs spacer layers at 630 °C annealing. The two-dimensionally confined nanocrystals exhibit a superparamagnetic behavior which becomes high-temperature ferromagnetism (~350 K) upon diffusion.

High purity, low dislocation GaAs single crystals

NASA Technical Reports Server (NTRS)

Chen, R. T.; Holmes, D. E.; Kirkpatrick, C. G.

1983-01-01

Liquid encapsulated Czochralski crystal growth techniques for producing undoped, high resistivity, low dislocation material suitable for device applications is described. Technique development resulted in reduction of dislocation densities in 3 inch GaAs crystals. Control over the melt stoichiometry was determined to be of critical importance for the reduction of twinning and polycrystallinity during growth.

Femtosecond coherent emission from GaAs bulk microcavities

NASA Astrophysics Data System (ADS)

Gurioli, Massimo; Bogani, Franco; Ceccherini, Simone; Colocci, Marcello; Beltram, Fabio; Sorba, Lucia

1999-02-01

The emission from a λ/2 GaAs bulk microcavity resonantly excited by femtosecond pulses has been characterized by using an interferometric correlation technique. It is found that the emission is dominated by the coherent signal due to light elastically scattered by disorder, and that scattering is predominantly originated from the lower polariton branch.

Tunneling effect on double potential barriers GaAs and PbS

NASA Astrophysics Data System (ADS)

Prastowo, S. H. B.; Supriadi, B.; Ridlo, Z. R.; Prihandono, T.

2018-04-01

A simple model of transport phenomenon tunnelling effect through double barrier structure was developed. In this research we concentrate on the variation of electron energy which entering double potential barriers to transmission coefficient. The barriers using semiconductor materials GaAs (Galium Arsenide) with band-gap energy 1.424 eV, distance of lattice 0.565 nm, and PbS (Lead Sulphide) with band gap energy 0.41 eV distance of lattice is 18 nm. The Analysisof tunnelling effect on double potentials GaAs and PbS using Schrodinger’s equation, continuity, and matrix propagation to get transmission coefficient. The maximum energy of electron that we use is 1.0 eV, and observable from 0.0025 eV- 1.0 eV. The shows the highest transmission coefficient is0.9982 from electron energy 0.5123eV means electron can pass the barriers with probability 99.82%. Semiconductor from materials GaAs and PbS is one of selected material to design semiconductor device because of transmission coefficient directly proportional to bias the voltage of semiconductor device. Application of the theoretical analysis of resonant tunnelling effect on double barriers was used to design and develop new structure and combination of materials for semiconductor device (diode, transistor, and integrated circuit).

Engineering Controlled Spalling in (100)-Oriented GaAs for Wafer Reuse

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sweet, Cassi A.; McNeely, Joshua E.; Gorman, Brian

Controlled spalling offers a way to cleave thin, single-crystal films or devices from wafers, particularly if the fracture planes in the material are oriented parallel to the wafer surface. Unfortunately, misalignment between the favored fracture planes and the wafer surface preferred for photovoltaic growth in (100)-oriented GaAs produces a highly faceted surface when subject to controlled spalling. This highly faceted cleavage surface is problematic in several ways: (1) it can result in large variations of spall depth due to unstable crack propagation; (2) it may introduce defects into the device zone or underlying substrate; and (3) it consumes many micronsmore » of material outside of the device zone. We present the ways in which we have engineered controlled spalling for (100)-oriented GaAs to minimize these effects. We expand the operational window for controlled spalling to avoid spontaneous spalling, find no evidence of dislocation activity in the spalled film or the parent wafer, and reduce facet height and facet height irregularity. Resolving these issues provides a viable path forward for reducing III-V device cost through the controlled spalling of (100)-oriented GaAs devices and subsequent wafer reuse when these processes are combined with a high-throughput growth method such as Hydride Vapor Phase Epitaxy.« less

Molecular beam epitaxial growth and structural characterization of ZnS on (001) GaAs

NASA Technical Reports Server (NTRS)

Benz, R. G., II; Huang, P. C.; Stock, S. R.; Summers, C. J.

1988-01-01

The effect of surface nucleation processes on the quality of ZnS layers grown on (001) GaAs substrates by molecular beam epitaxy is reported. Reflection high energy electron diffraction indicated that nucleation at high temperatures produced more planar surfaces than nucleation at low temperatures, but the crystalline quality as assessed by X-ray double crystal diffractometry is relatively independent of nucleation temperature. A critical factor in layer quality was the initial roughness of the GaAs surfaces.

Resonant electronic Raman scattering of below-gap states in molecular-beam epitaxy grown and liquid-encapsulated Czochralski grown GaAs

NASA Astrophysics Data System (ADS)

Fluegel, B.; Rice, A. D.; Mascarenhas, A.

2018-05-01

Resonant electronic Raman (ER) scattering is used to compare the below-gap excitations in molecular-beam epitaxially grown GaAs and in undoped semi-insulating GaAs substrates. The measurement geometry was designed to eliminate common measurement artifacts caused by the high optical transmission below the fundamental absorption edge. In epitaxial GaAs, ER is a clear Raman signal from the two-electron transitions of donors, eliminating an ambiguity encountered in previous results. In semi-insulating GaAs, ER occurs in a much broader dispersive band well below the bound exciton energies. The difference in the two materials may be due to the occupation of the substrate acceptor states in the presence of the midgap state EL2.

Diffraction studies of the high pressure phases of GaAs and GaP

NASA Technical Reports Server (NTRS)

Baublitz, M., Jr.; Ruoff, A. L.

1982-01-01

High pressure structural phase transitions of GaAs and GaP have been studied by energy dispersive X-ray diffraction with the radiation from the Cornell High Energy Synchrotron Source. GaAs began to transform at 172 + or - 7 kbar to an orthorhombic structure possibly belonging to space group Fmmm. GaP transformed to a tetragonal beta-Sn type phase at 215 + or - 8 kbar. Although pressure transmitting media were used to minimize shear stresses in the specimens, the high pressure diffraction results were interpreted as showing evidence for planar defects in the specimens.

Velocity surface measurements for ZnO films over /001/-cut GaAs

NASA Technical Reports Server (NTRS)

Kim, Yoonkee; Hunt, William D.; Liu, Yongsheng; Jen, Cheng-Kuei

1994-01-01

A potential application for a piezoelectic film deposited on a GaAs substrate is the monolithic integration of surface acoustic wave (SAW) devices with GaAs electronics. Knowledge of the SAW properties of the filmed structure is critical for the optimum design of such devices. In this article, the measurements of the velocity surface, which directly affects the SAW diffraction, on the bare and metallized ZnO/SiO2 or Si3N4/GaAs /001/-cut samples are reported using two different techniques: (1) knife-edge laser probe, (2) line-focus-beam scanning acoustic microscope. Comparisons, such as measurement accuracy and tradeoffs, between the former (dry) and the latter (wet) method are given. It is found that near the group of zone axes (110) propagation direction the autocollimating SAW property of the bare GaAs changes into a noncollimating one for the layered structure, but a reversed phenomenon exists near the group of zone axes (100) direction. The passivation layer of SiO2 or Si3N4 (less than 0.2 micrometer thick) and the metallization layer change the relative velocity but do not significantly affect the velocity surface. On the other hand, the passivation layer reduces the propagation loss by 0.5-1.3 dB/microseconds at 240 MHz depending upon the ZnO film thickness. Our SAW propagation measurements agree well with theorectical calculations. We have also obtained the anisotropy factors for samples with ZnO films of 1.6, 2.8, and 4.0 micrometer thickness. Comparisons concerning the piezoelectric coupling and acoustic loss between dc triode and rf magnetron sputtered ZnO films are provided.

Scaling behavior of GaAs and GaMnAs quantum rings grown by droplet epitaxy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Placidi, E.; Dipartimento di Fisica, Universita di Roma 'Tor Vergata,' via della Ricerca Scientifica 1, 00133 Roma Italy; Arciprete, F.

2012-10-01

The transition from the liquid phase of Ga droplets to the formation of GaAs and GaMnAs quantum rings has been studied as a function of temperature. We show that different aggregation processes involve the GaAs (GaMnAs) island and the droplet formation. Furthermore, the aspect ratio of the islands exhibits an anomalous scaling law related to a tendency to aggregate in the vertical direction.

Capless Annealing of Ion Implanted GaA.

DTIC Science & Technology

1980-12-01

1967). 10. " Thermophysical Properties of Matter," edited by Y. S. Touloukian (Plenum, New York, 1977), v. 13. 11. J. F. Gibbons, W. S. Johnson and S. W...temperatures of 850 C. Using rf spark-source mass spectrometry, an As con- centration in excess of the equilibrium value of As over GaAs at the annealing...38 4.0 SUMMARY AND RECOMMENDATIONS ................... *.* ...... ..... 46 5.0 REFERENCES ..................... *.. o

LEO Flight Testing of GaAs on Si Solar Cells Aboard MISSES

NASA Technical Reports Server (NTRS)

Wilt, David M.; Clark, Eric B.; Ringel, Steven A.; Andre, Carrie L.; Smith, Mark A.; Scheiman, David A.; Jenkins, Phillip P.; Maurer, William F.; Fitzgerald, Eugene A.; Walters, R. J.

2004-01-01

Previous research efforts have demonstrated small area (0.04 cm) GaAs on Si (GaAs/Si) solar cells with AM0 efficiencies in excess of 17%. These results were achieved on Si substrates coated with a step graded buffer of Si(x),Ge(1-x) alloys graded to 100% Ge. Recently, a 100-fold increase in device area was accomplished for these devices in preparation for on-orbit testing of this technology aboard Materials International Space Station Experiment number 5 (MISSE5). The GaAs/Si MISSE5 experiment contains five (5) GaAs/Si test devices with areas of lcm(exp 2) and 4cm(exp 4) as well as two (2) GaAs on GaAs control devices. Electrical performance data, measured on-orbit for three (3) of the test devices and one (1) of the control devices, will be telemetered to ground stations daily. After approximately one year on orbit, the MISSE5 payload will be returned to Earth for post flight evaluation. This paper will discuss the development of the GaAs/Si devices for the MISSE5 flight experiment and will present recent ground and on-orbit performance data.

Nanoepitaxy of GaAs on a Si(001) substrate using a round-hole nanopatterned SiO2 mask.

PubMed

Hsu, Chao-Wei; Chen, Yung-Feng; Su, Yan-Kuin

2012-12-14

GaAs is grown by metal-organic vapor-phase epitaxy on a 55 nm round-hole patterned Si substrate with SiO(2) as a mask. The threading dislocations, which are stacked on the lowest energy facet plane, move along the SiO(2) walls, reducing the number of dislocations. The etching pit density of GaAs on the 55 nm round-hole patterned Si substrate is about 3.3 × 10(5) cm(-2). Compared with the full width at half maximum measurement from x-ray diffraction and photoluminescence spectra of GaAs on a planar Si(001) substrate, those of GaAs on the 55 nm round-hole patterned Si substrate are reduced by 39.6 and 31.4%, respectively. The improvement in material quality is verified by transmission electron microscopy, field-emission scanning electron microscopy, Hall measurements, Raman spectroscopy, photoluminescence, and x-ray diffraction studies.

GaAs monolithic R.F. modules for SARSAT distress beacons

NASA Technical Reports Server (NTRS)

Cauley, Michael A.

1991-01-01

Monolithic GaAs UHF components for use in SARSAT Emergency Distress beacons are under development by Microwave Monolithics, Inc., Simi Valley, CA. The components include a bi-phase modulator, driver amplifier, and a 5 watt power amplifier.

Photoelectron and Auger electron diffraction studies of a sulfur-terminated GaAs(001)-(2×6) surface

NASA Astrophysics Data System (ADS)

Shimoda, M.; Tsukamoto, S.; Koguchi, N.

1998-01-01

Core-level X-ray photoelectron diffraction (XPD) and Auger electron diffraction (AED) have been applied to investigate the sulfur-terminated GaAs(001)-(2×6) surface. No forward scattering peaks were found in the XPD pattern of S 2s emission, indicating that adsorbed S atoms form a single layer on the GaAs substrate. In accordance with the zincblende structure of GaAs, the AED patterns of Ga L 3M 45M 45 and As L 3M 45M 45 emission almost coincide with each other, if one of the emissions is rotated by 90° around the [001] direction. This fact suggests that the diffraction patterns mainly reflect the structure of the bulk GaAs crystal. In order to investigate the surface structure, AED patterns in large polar angles were analyzed with single scattering cluster (SSC) calculations. The best result was obtained with a model cluster where the S-S bond length was set at 0.28 nm, 30% shorter than the corresponding length of the ideal (1×1) structure, and the adsorption height was set at 0.12-0.13 nm, 10% shorter than the ideal interlayer distance of GaAs(001) planes. These values are in good agreement with the results of STM measurements. A modulation of the inter-dimer distance was also found, suggesting the existence of missing dimers.

Optimization of conditions for thermal smoothing GaAs surfaces

NASA Astrophysics Data System (ADS)

Akhundov, I. O.; Kazantsev, D. M.; Kozhuhov, A. S.; Alperovich, V. L.

2018-03-01

GaAs thermal smoothing by annealing in conditions which are close to equilibrium between the surface and vapors of As and Ga was earlier proved to be effective for the step-terraced surface formation on epi-ready substrates with a small root-mean-square roughness (Rq ≤ 0.15 nm). In the present study, this technique is further developed in order to reduce the annealing duration and to smooth GaAs samples with a larger initial roughness. To this end, we proposed a two-stage anneal with the first high-temperature stage aimed at smoothing "coarse" relief features and the second stage focused on "fine" smoothing at a lower temperature. The optimal temperatures and durations of two-stage annealing are found by Monte Carlo simulations and adjusted after experimentation. It is proved that the temperature and duration of the first high-temperature stage are restricted by the surface roughening, which occurs due to deviations from equilibrium conditions.

Gettering of donor impurities by V in GaAs and the growth of semi-insulating crystals

NASA Technical Reports Server (NTRS)

Ko, K. Y.; Lagowski, J.; Gatos, H. C.

1989-01-01

Vanadium added to the GaAs melt getters shallow donor impurities (Si and S) and decreases their concentration in the grown crystals. This gettering is driven by chemical reactions in the melt rather than in the solid. Employing V gettering, reproducibly semi-insulating GaAs were grown by horizontal Bridgman and liquid-encapsulated Czochralski techniques, although V did not introduce any midgap energy levels. The compensation mechanism in these crystals was controlled by the balance between the native midgap donor EL2 and residual shallow acceptors. Vanadium gettering contributed to the reduction of the concentration of shallow donors below the concentration of acceptors. The present findings clarify the long-standing controversy on the role of V in achieving semi-insulating GaAs.

Growth of GaAs “nano ice cream cones” by dual wavelength pulsed laser ablation

NASA Astrophysics Data System (ADS)

Schamp, C. T.; Jesser, W. A.; Shivaram, B. S.

2007-05-01

Harmonic generation crystals inherently offer the possibility of using multiple wavelengths of light in a single laser pulse. In the present experiment, the fundamental (1064 nm) and second harmonic (532 nm) wavelengths from an Nd:YAG laser are focused together on GaAs and GaSb targets for ablation. Incident energy densities up to about 45 J/cm 2 at 10 Hz with substrate temperatures between 25 and 600 °C for durations of about 60 s have been used in an ambient gas pressure of about 10 -6 Torr. The ablated material was collected on electron-transparent amorphous carbon films for TEM analysis. Apart from a high density of isolated nanocrystals, the most common morphology observed consists of a crystalline GaAs cone-like structure in contact with a sphere of liquid Ga, resembling an "ice cream cone", typically 50-100 nm in length. For all of the heterostuctures of this type, the liquid/solid/vacuum triple junction is found to correspond to the widest point on the cone. These heterostructures likely form by preferential evaporation of As from molten GaAs drops ablated from the target. The resulting morphology minimizes the interfacial and surface energies of the liquid Ga and solid GaAs.

Resonant electronic Raman scattering of below-gap states in molecular-beam epitaxy grown and liquid-encapsulated Czochralski grown GaAs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fluegel, B.; Rice, A. D.; Mascarenhas, A.

Resonant electronic Raman (ER) scattering is used to compare the below-gap excitations in molecular-beam epitaxially grown GaAs and in undoped semi-insulating GaAs substrates. The measurement geometry was designed to eliminate common measurement artifacts caused by the high optical transmission below the fundamental absorption edge. In epitaxial GaAs, ER is a clear Raman signal from the two-electron transitions of donors, eliminating an ambiguity encountered in previous results. In semi-insulating GaAs, ER occurs in a much broader dispersive band well below the bound exciton energies. Furthermore, the difference in the two materials may be due to the occupation of the substrate acceptormore » states in the presence of the midgap state EL2.« less

GaAs and 3-5 compound solar cells status and prospects for use in space

NASA Technical Reports Server (NTRS)

Flood, D. J.; Brinker, D. J.

1984-01-01

Gallium arsenide solar cells equal or supass the best silicon solar cells in efficiency, radiation resistance, annealability, and in the capability to produce usable power output at elevated temperatures. NASA has been involved in a long range research and development program to capitalize on these manifold advantages, and to explore alternative III-V compounds for additional potential improvements. The current status and future prospects for research and development in this area are reviewed and the progress being made toward development of GaAs cells suitable for variety of space missions is discussed. Cell types under various stages of development include n(+)/p shallow homojunction thin film GaAs cells, x100 concentration ratio p/n and n/p GaAs small area concentrator cells, mechanically-stacked, two-junction tandem cells, and three-junction monolithic cascade cells, among various other cell types.

GaAs shallow-homojunction solar cells

NASA Technical Reports Server (NTRS)

Fan, J. C.

1980-01-01

With the objective of demonstrating the feasibility of fabricating 2 x 2 cm efficient, shallow homojunction GaAs solar cells for space applications, this program addresses the basic problems of material preparation and device fabrication. Significant progress was made and conversion efficiencies close to 16 percent at AM0 were obtained on 2 x 2 cm cells. Measurements and computer analyses on the n(+)/p/p(+) shallow homojunction cells indicate that such cell configuration should be very resistant to 1 MeV electron irradiation.

Photoluminescence upconversion at GaAs /InGa P2 interfaces driven by a sequential two-photon absorption mechanism

NASA Astrophysics Data System (ADS)

Hylton, N. P.; Hinrichsen, T. F.; Vaquero-Stainer, A. R.; Yoshida, M.; Pusch, A.; Hopkinson, M.; Hess, O.; Phillips, C. C.; Ekins-Daukes, N. J.

2016-06-01

This paper reports on the results of an investigation into the nature of photoluminescence upconversion at GaAs /InGa P2 interfaces. Using a dual-beam excitation experiment, we demonstrate that the upconversion in our sample proceeds via a sequential two-photon optical absorption mechanism. Measurements of photoluminescence and upconversion photoluminescence revealed evidence of the spatial localization of carriers in the InGa P2 material, arising from partial ordering of the InGa P2 . We also observed the excitation of a two-dimensional electron gas at the GaAs /InGa P2 heterojunction that manifests as a high-energy shoulder in the GaAs photoluminescence spectrum. Furthermore, the results of upconversion photoluminescence excitation spectroscopy demonstrate that the photon energy onset of upconversion luminescence coincides with the energy of the two-dimensional electron gas at the GaAs /InGa P2 interface, suggesting that charge accumulation at the interface can play a crucial role in the upconversion process.

Ellipsometry analysis of the in vitro adsorption of tea polyphenols onto salivary pellicles.

PubMed

Joiner, Andrew; Muller, Dries; Elofsson, Ulla M; Arnebrant, Thomas

2004-12-01

The adsorption of components from black tea and of purified tea polyphenols onto a whole unstimulated salivary pellicle-like protein layer, formed in vitro on hydroxyapatite discs, was studied by in situ ellipsometry. It was found that components from black tea and the purified polyphenols epicatechin-3-gallate (ECG), epigallocatechin-3-gallate (EGCG) and theaflavin readily adsorbed onto the pellicle. Further investigations showed that under the experimental conditions of this study, no black tea- or purified polyphenol-modified pellicles were eluted by either phosphate buffer or sodium dodecyl sulphate rinses. Therefore, black tea and its polyphenol components are indicated to have a profound effect on in vitro pellicle modification. Similar effects were observed for tannic acid. Copyright Eur J Oral Sci, 2004.

Study of subband electronic structure of Si δ-doped GaAs using magnetotransport measurements in tilted magnetic fields

NASA Astrophysics Data System (ADS)

Li, G.; Hauser, N.; Jagadish, C.; Antoszewski, J.; Xu, W.

1996-06-01

Si δ-doped GaAs grown by metal organic vapor phase epitaxy (MOVPE) is characterized using magnetotransport measurements in tilted magnetic fields. Angular dependence of the longitudinal magnetoresistance (Rxx) vs the magnetic field (B) traces in tilted magnetic fields is used to examine the existence of a quasi-two-dimensional electron gas. The subband electron densities (ni) are obtained applying fast Fourier transform (FFT) analysis to the Rxx vs B trace and using mobility spectrum (MS) analysis of the magnetic field dependent Hall data. Our results show that (1) the subband electron densities remain roughly constant when the tilted magnetic field with an angle <30° measured from the Si δ-doped plane normal is ramped up to 13 T; (2) FFT analysis of the Rxx vs B trace and MS analysis of the magnetic field dependent Hall data both give the comparable results on subband electron densities of Si δ-doped GaAs with low δ-doping concentration, however, for Si δ-doped GaAs with very high δ-doping concentration, the occupation of the lowest subbands cannot be well resolved in the MS analysis; (3) the highest subband electron mobility reported to date of 45 282 cm2/s V is observed in Si δ-doped GaAs at 77 K in the dark; and (4) the subband electron densities of Si δ-doped GaAs grown by MOVPE at 700 °C are comparable to those grown by MBE at temperatures below 600 °C. A detailed study of magnetotransport properties of Si δ-doped GaAs in the parallel magnetic fields is then carried out to further confirm the subband electronic structures revealed by FFT and MS analysis. Our results are compared to theoretical calculation previously reported in literature. In addition, influence of different cap layer structures on subband electronic structures of Si δ-doped GaAs is observed and also discussed.

The transcriptional activator GaaR of Aspergillus niger is required for release and utilization of d- galacturonic acid from pectin

DOE PAGES

Alazi, Ebru; Niu, Jing; Kowalczyk, Joanna E.; ...

2016-05-13

We identified the d-galacturonic acid (GA)-responsive transcriptional activator GaaR of the saprotrophic fungus, Aspergillus niger, which was found to be essential for growth on GA and polygalacturonic acid (PGA). Growth of the ΔgaaR strain was reduced on complex pectins. Genome-wide expression analysis showed that GaaR is required for the expression of genes necessary to release GA from PGA and more complex pectins, to transport GA into the cell, and to induce the GA catabolic pathway. Residual growth of ΔgaaR on complex pectins is likely due to the expression of pectinases acting on rhamnogalacturonan and subsequent metabolism of the monosaccharides othermore » than GA.« less

Designing optical metamaterial with hyperbolic dispersion based on Al:ZnO/ZnO nano-layered structure using Atomic Layer Deposition technique

DOE PAGES

Kelly, Priscilla; Liu, Mingzhao; Kuznetsova, Lyuba

2016-04-07

In this study, nano-layered Al:ZnO/ZnO hyperbolic dispersion metamaterial with a large number of layers was fabricated using the atomic layer deposition (ALD) technique. Experimental dielectric functions for Al:ZnO/ZnO structures are obtained by an ellipsometry technique in the visible and near-infrared spectral ranges. The theoretical modeling of the Al:ZnO/ZnO dielectric permittivity is done using effective medium approximation. A method for analysis of spectroscopic ellipsometry data is demonstrated to extract the optical permittivity for this highly anisotropic nano-layered metamaterial. The results of the ellipsometry analysis show that Al:ZnO/ZnO structures with a 1:9 ALD cycle ratio exhibit hyperbolic dispersion transition change near 1.8more » μm wavelength.« less

Dual demodulation interferometer with two-wave mixing in GaAs photorefractive crystal

NASA Astrophysics Data System (ADS)

Zhenzhen, Zhang; Zhongqing, Jia; Guangrong, Ji; Qiwu, Wang

2018-07-01

A dual demodulation interferometer with two-wave mixing (TWM) in the GaAs photorefractive crystal (PRC) is proposed and experimentally demonstrated. The GaAs PRC has tiny temperature change under high voltage thus not requiring thermoelectric cooler (TEC) to stabilize the temperature, and adaptive to low frequency fluctuation below 200 Hz. The system is an unbalanced TWM interferometer, which could demodulate the phase change both space variation and wavelength shift induced by strain. Two demodulation modes' formulas are provided in theory respectively. Experimental results have been tested and compared with theoretical analysis, demonstrating that it is a practical and flexible system for detection of mechanical vibration or structure health monitoring (SHM) in engineering by selecting different demodulation mode.

Optical pumping and negative luminescence polarization in charged GaAs quantum dots

NASA Astrophysics Data System (ADS)

Shabaev, Andrew; Stinaff, Eric A.; Bracker, Allan S.; Gammon, Daniel; Efros, Alexander L.; Korenev, Vladimir L.; Merkulov, Igor

2009-01-01

Optical pumping of electron spins and negative photoluminescence polarization are observed when interface quantum dots in a GaAs quantum well are excited nonresonantly by circularly polarized light. Both observations can be explained by the formation of long-lived dark excitons through hole spin relaxation in the GaAs quantum well prior to exciton capture. In this model, optical pumping of resident electron spins is caused by capture of dark excitons and recombination in charged quantum dots. Negative polarization results from accumulation of dark excitons in the quantum well and is enhanced by optical pumping. The dark exciton model describes the experimental results very well, including intensity and bias dependence of the photoluminescence polarization and the Hanle effect.

Image processing using Gallium Arsenide (GaAs) technology

NASA Technical Reports Server (NTRS)

Miller, Warner H.

1989-01-01

The need to increase the information return from space-borne imaging systems has increased in the past decade. The use of multi-spectral data has resulted in the need for finer spatial resolution and greater spectral coverage. Onboard signal processing will be necessary in order to utilize the available Tracking and Data Relay Satellite System (TDRSS) communication channel at high efficiency. A generally recognized approach to the increased efficiency of channel usage is through data compression techniques. The compression technique implemented is a differential pulse code modulation (DPCM) scheme with a non-uniform quantizer. The need to advance the state-of-the-art of onboard processing was recognized and a GaAs integrated circuit technology was chosen. An Adaptive Programmable Processor (APP) chip set was developed which is based on an 8-bit slice general processor. The reason for choosing the compression technique for the Multi-spectral Linear Array (MLA) instrument is described. Also a description is given of the GaAs integrated circuit chip set which will demonstrate that data compression can be performed onboard in real time at data rate in the order of 500 Mb/s.

A GaAs vector processor based on parallel RISC microprocessors

NASA Astrophysics Data System (ADS)

Misko, Tim A.; Rasset, Terry L.

A vector processor architecture based on the development of a 32-bit microprocessor using gallium arsenide (GaAs) technology has been developed. The McDonnell Douglas vector processor (MVP) will be fabricated completely from GaAs digital integrated circuits. The MVP architecture includes a vector memory of 1 megabyte, a parallel bus architecture with eight processing elements connected in parallel, and a control processor. The processing elements consist of a reduced instruction set CPU (RISC) with four floating-point coprocessor units and necessary memory interface functions. This architecture has been simulated for several benchmark programs including complex fast Fourier transform (FFT), complex inner product, trigonometric functions, and sort-merge routine. The results of this study indicate that the MVP can process a 1024-point complex FFT at a speed of 112 microsec (389 megaflops) while consuming approximately 618 W of power in a volume of approximately 0.1 ft-cubed.

Biexciton emission from single isoelectronic traps formed by nitrogen-nitrogen pairs in GaAs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Takamiya, Kengo; Fukushima, Toshiyuki; Yagi, Shuhei

2013-12-04

We have studied photoluminescence (PL) from individual isoelectronic traps formed by nitrogen-nitrogen (NN) pairs in GaAs. Sharp emission lines due to exciton and biexciton were observed from individual isoelectronic traps in nitrogen atomic-layer doped (ALD) GaAs. The binding energy of biexciton bound to individual isoelectronic traps was approximately 8 meV. Both the exciton and biexciton luminescence lines show completely random polarization and no fine-structure splitting. These results are desirable to the application to the quantum cryptography used in the field of quantum information technology.

Growth of semimetallic ErAs films epitaxially embedded in GaAs

NASA Astrophysics Data System (ADS)

Crook, Adam M.; Nair, Hari P.; Lee, Jong H.; Ferrer, Domingo A.; Akinwande, Deji; Bank, Seth R.

2011-10-01

We present models for the growth and electrical conductivity of ErAs films grown with the nanoparticle-seeded film growth technique. This growth mode overcomes the mismatch in rotational symmetry between the rocksalt ErAs crystal structure and the zincblende GaAs crystal structure. This results in films of ErAs grown through a thin film of GaAs that preserves the symmetry of the substrate. The conductivity of the films, as a function of film thickness, are investigated and a surface roughness model is used to explain observed trends. Transmission electron micrographs confirm the suppression of anti-phase domains. A simple diffusion model is developed to describe the diffusion and incorporation of surface erbium into subsurface ErAs layers and predict potential failure mechanisms of the growth method.

Optical and structural properties of 100 MeV Fe{sup 9+} ion irradiated InP

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dubey, R. L., E-mail: radhekrishna.dubey@xaviers.edu; Department of Physics, University of Mumbai, Mumbai-400 032; Dubey, S. K.

2016-05-06

Single crystal InP samples were irradiated with 100 MeV Fe{sup 9+} ions for ion fluences 1x10{sup 12} and 1x10{sup 13} cm{sup −2}. Optical properties of irradiated InP was investigated by Spectroscopic Ellipsometry and UV-VIS-NIR spectroscopy. The optical parameters like, refractive index, extinction coefficient, absorption coefficient is found to be fluence dependent near the surface as well as near the projected range. Small change in the optical parameters near the surface region as investigated by Spectroscopic Ellipsometry indicatesthat the surfaces of irradiated InP are similar to non-irradiated InP. This is also supported by RBS/C measurements. The UV-VIS-NIR study revealed the decrease inmore » the band gap and increase in the defect concentration in the irradiated sample as a result of nuclear energy loss.« less

Experimental evidence of exciton-plasmon coupling in densely packed dye doped core-shell nanoparticles obtained via microfluidic technique

NASA Astrophysics Data System (ADS)

De Luca, A.; Iazzolino, A.; Salmon, J.-B.; Leng, J.; Ravaine, S.; Grigorenko, A. N.; Strangi, G.

2014-09-01

The interplay between plasmons and excitons in bulk metamaterials are investigated by performing spectroscopic studies, including variable angle pump-probe ellipsometry. Gain functionalized gold nanoparticles have been densely packed through a microfluidic chip, representing a scalable process towards bulk metamaterials based on self-assembly approach. Chromophores placed at the hearth of plasmonic subunits ensure exciton-plasmon coupling to convey excitation energy to the quasi-static electric field of the plasmon states. The overall complex polarizability of the system, probed by variable angle spectroscopic ellipsometry, shows a significant modification under optical excitation, as demonstrated by the behavior of the ellipsometric angles Ψ and Δ as a function of suitable excitation fields. The plasmon resonances observed in densely packed gain functionalized core-shell gold nanoparticles represent a promising step to enable a wide range of electromagnetic properties and fascinating applications of plasmonic bulk systems for advanced optical materials.

HfO2 Gate Dielectric on (NH4)2S Passivated (100) GaAs Grown by Atomic Layer Deposition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, P.T.; /Stanford U., Materials Sci. Dept.; Sun, Y.

2007-09-28

The interface between hafnium oxide grown by atomic layer deposition and (100) GaAs treated with HCl cleaning and (NH{sub 4}){sub 2}S passivation has been characterized. Synchrotron radiation photoemission core level spectra indicated successful removal of the native oxides and formation of passivating sulfides on the GaAs surface. Layer-by-layer removal of the hafnia film revealed a small amount of As{sub 2}O{sub 3} formed at the interface during the dielectric deposition. Traces of arsenic and sulfur out-diffusion into the hafnia film were observed after a 450 C post-deposition anneal, and may be the origins for the electrically active defects. Transmission electron microscopymore » cross section images showed thicker HfO{sub 2} films for a given precursor exposure on S-treated GaAs versus the non-treated sample. In addition, the valence-band and the conduction-band offsets at the HfO{sub 2}/GaAs interface were deduced to be 3.18 eV and a range of 0.87-0.97 eV, respectively. It appears that HCl+(NH{sub 4})2{sub S} treatments provide a superior chemical passivation for GaAs and initial surface for ALD deposition.« less

A high-speed GaAs MESFET optical controller

NASA Technical Reports Server (NTRS)

Claspy, P. C.; Bhasin, K. B.; Richard, M.; Bendett, M.; Gustafson, G.

1989-01-01

Optical interconnects are being considered for control signal distribution in phased array antennas. A packaged hybrid GaAs optical controller with a 1:16 demultiplexed output that is suitable for this application is described. The controller, which was fabricated using enhancement/depletion mode MESFET technology, operates at demultiplexer-limited input data rates up to 305 Mb/s and requires less than 200 microW optical input power.

Impact of dislocation densities on n+/p and p+/n junction GaAs diodes and solar cells on SiGe virtual substrates

NASA Astrophysics Data System (ADS)

Andre, C. L.; Wilt, D. M.; Pitera, A. J.; Lee, M. L.; Fitzgerald, E. A.; Ringel, S. A.

2005-07-01

Recent experimental measurements have shown that in GaAs with elevated threading dislocation densities (TDDs) the electron lifetime is much lower than the hole lifetime [C. L. Andre, J. J. Boeckl, D. M. Wilt, A. J. Pitera, M. L. Lee, E. A. Fitzgerald, B. M. Keyes, and S. A. Ringel, Appl. Phys. Lett. 84, 3884 (2004)]. This lower electron lifetime suggests an increase in depletion region recombination and thus in the reverse saturation current (J0 for an n+/p diode compared with a p+/n diode at a given TDD. To confirm this, GaAs diodes of both polarities were grown on compositionally graded Ge /Si1-xGex/Si (SiGe) substrates with a TDD of 1×106cm-2. It is shown that the ratio of measured J0 values is consistent with the inverse ratio of the expected lifetimes. Using a TDD-dependent lifetime in solar cell current-voltage models we found that the Voc, for a given short-circuit current, also exhibits a poorer TDD tolerance for GaAs n+/p solar cells compared with GaAs p+/n solar cells. Experimentally, the open-circuit voltage (Voc) for the n+/p GaAs solar cell grown on a SiGe substrate with a TDD of ˜1×106cm-2 was ˜880mV which was significantly lower than the ˜980mV measured for a p+/n GaAs solar cell grown on SiGe at the same TDD and was consistent with the solar cell modeling results reported in this paper. We conclude that p+/n polarity GaAs junctions demonstrate superior dislocation tolerance than n+/p configured GaAs junctions, which is important for optimization of lattice-mismatched III-V devices.

Hydrogenation of GaAs covered by GaAlAs and subgrain boundary passivation

NASA Astrophysics Data System (ADS)

Djemel, A.; Castaing, J.; Chevallier, J.; Henoc, P.

1992-12-01

Cathodoluminescence (CL) has been performed to study the influence of hydrogen on electronic properties of GaAs with and without a GaAlAs layer. Recombination at sub-boundaries has been examined. These extended defects have been introduced by high temperature plastic deformation. The results show that they are passivated by hydrogen. The penetration of hydrogen is slowed down by the GaAlAs layer. La cathodoluminescence (CL) a été utilisée pour étudier l'influence de l'hydrogène sur les propriétés électroniques de GaAs nu et recouvert d'une couche de GaAlAs. Le caractère recombinant des sous-joints de grains a été examiné. Ces défauts étendus ont été introduits par déformation plastique à chaud. Les résultats montrent que l'hydrogène passive ces défauts. La pénétration de l'hydrogène à l'intérieur de GaAs est retardée par la présence de la couche de GaAlAs.

Vertically aligned GaAs nanowires on graphite and few-layer graphene: generic model and epitaxial growth.

PubMed

Munshi, A Mazid; Dheeraj, Dasa L; Fauske, Vidar T; Kim, Dong-Chul; van Helvoort, Antonius T J; Fimland, Bjørn-Ove; Weman, Helge

2012-09-12

By utilizing the reduced contact area of nanowires, we show that epitaxial growth of a broad range of semiconductors on graphene can in principle be achieved. A generic atomic model is presented which describes the epitaxial growth configurations applicable to all conventional semiconductor materials. The model is experimentally verified by demonstrating the growth of vertically aligned GaAs nanowires on graphite and few-layer graphene by the self-catalyzed vapor-liquid-solid technique using molecular beam epitaxy. A two-temperature growth strategy was used to increase the nanowire density. Due to the self-catalyzed growth technique used, the nanowires were found to have a regular hexagonal cross-sectional shape, and are uniform in length and diameter. Electron microscopy studies reveal an epitaxial relationship of the grown nanowires with the underlying graphitic substrates. Two relative orientations of the nanowire side-facets were observed, which is well explained by the proposed atomic model. A prototype of a single GaAs nanowire photodetector demonstrates a high-quality material. With GaAs being a model system, as well as a very useful material for various optoelectronic applications, we anticipate this particular GaAs nanowire/graphene hybrid to be promising for flexible and low-cost solar cells.

Fabrication of GaAs symmetric pyramidal mesas prepared by wet-chemical etching using AlAs interlayer

NASA Astrophysics Data System (ADS)

Kicin, S.; Cambel, V.; Kuliffayová, M.; Gregušová, D.; Kováčová, E.; Novák, J.; Kostič, I.; Förster, A.

2002-01-01

We present a wet-chemical-etching method developed for the preparation of GaAs four-sided pyramid-shaped mesas. The method uses a fast lateral etching of AlAs interlayer that influences the cross-sectional profiles of etched structures. We have tested the method using H3PO4:H2O2:H2O etchant for the (100) GaAs patterning. The sidewalls of the prepared pyramidal structures together with the (100) bottom facet formed the cross-sectional angles 25° and 42° for mask edges parallel, resp. perpendicular to {011} cleavage planes. For mask edges turned in 45° according to the cleavage planes, 42° cross-sectional angles were obtained. Using the method, symmetric and more than 10-μm-high GaAs "Egyptian" pyramids with smooth tilted facets were prepared.

Structural and optical properties of GaAs(100) with a thin surface layer doped with chromium

DOE Office of Scientific and Technical Information (OSTI.GOV)

Seredin, P. V., E-mail: paul@phys.vsu.ru; Fedyukin, A. V.; Arsentyev, I. N.

The aim of this study is to explore the structural and optical properties of single-crystal GaAs(100) doped with Cr atoms by burning them into the substrate at high temperatures. The diffusion of chromium into single-crystal GaAs(100) substrates brings about the formation of a thin (~20–40 μm) GaAs:Cr transition layer. In this case, chromium atoms are incorporated into the gallium-arsenide crystal lattice and occupy the regular atomic sites of the metal sublattice. As the chromium diffusion time is increased, such behavior of the dopant impurity yields changes in the energy structure of GaAs, a decrease in the absorption at free chargemore » carriers, and a lowering of the surface recombination rate. As a result, the photoluminescence signal from the sample is significantly enhanced.« less

The 25 percent-efficient GaAs Cassegrainian concentrator cell

NASA Technical Reports Server (NTRS)

Hamaker, H. C.; Grounner, M.; Kaminar, N. R.; Kuryla, M. S.; Ladle, M. J.; Liu, D. D.; Macmillan, H. F.; Partain, L. D.; Virshup, G. F.; Werthen, J. G.

1989-01-01

Very high-efficiency GaAs Cassegrainian solar cells have been fabricated in both the n-p and p-n configurations. The n-p configuration exhibits the highest efficiency at concentration, the best cells having an efficiency eta of 24.5 percent (100X, AM0, temperature T = 28 C). Although the cells are designed for operation at this concentration, peak efficiency is observed near 300 suns (eta = 25.1 percent). To our knowledge, this is the highest reported solar cell efficiency for space applications. The improvement in efficiency over that reported at the previous SPRAT conference is attributed primarily to lower series resistance and improved grid-line plating procedures. Using previously measured temperature coefficients, researchers estimate that the n-p GaAs cells should deliver approximately 22.5 percent efficiency at the operating conditions of 100 suns and T = 80 C. This performance exceeds the NASA program goal of 22 percent for the Cassegrainian cell. One hundred Cassegrainian cells have been sent to NASA as deliverables, sixty-eight in the n-p configuration and thirty-two in the p-n configuration.

Structural and optical characteristics of GaAs films grown on Si/Ge substrates

NASA Astrophysics Data System (ADS)

Rykov, A. V.; Dorokhin, M. V.; Vergeles, P. S.; Baidus, N. V.; Kovalskiy, V. A.; Yakimov, E. B.; Soltanovich, O. A.

2018-03-01

A GaAs/AlAs heterostructure and a GaAs film grown on Si/Ge substrates have been fabricated and studied. A Ge buffer on a silicon substrate was fabricated using the MBE process. A3B5 films were grown by MOCVD at low pressures. Photoluminescence spectroscopy was used to define the optical quality of A3B5 films. Structural properties were investigated using the electron beam induced current method. It was established that despite a rather high density of dislocations on the epitaxial layers, the detected photoluminescence radiation of layers indicates the acceptable crystalline quality of the top GaAs layer.

Physical mechanism of coherent acoustic phonons generation and detection in GaAs semiconductor

NASA Astrophysics Data System (ADS)

Babilotte, P.; Morozov, E.; Ruello, P.; Mounier, D.; Edely, M.; Breteau, J.-M.; Bulou, A.; Gusev, V.

2007-12-01

We first describe the picosecond acoustic interferometry study of GaAs with two-colors pump-probe laser pulses. The dependence of the generation process on the pump wavelength and the detection process on the probe wavelength both can cause the shift in the phase of the Brillouin signal. Secondly, in order to distinguish the short high frequency wideband acoustic pulse from low frequency Brillouin contribution, we accomplished experiments with (100)GaAs semiconductor coated by a transparent and photoelastically inactive thin film, serving a delay line for the acoustic pulse. Even with highly penetrating pump light (approx 680nm), short acoustic disturbances of approx 7ps of duration have been registered.

GaAs Solar Cells on V-Grooved Silicon via Selective Area Growth: Preprint

DOE Office of Scientific and Technical Information (OSTI.GOV)

Warren, Emily L; Jain, Nikhil; Tamboli, Adele C

Interest in integrating III-Vs onto Si has recently resurged as a promising pathway towards high-efficiency, low-cost tandem photovoltaics. Here, we present a single junction GaAs solar cell grown monolithically on polished Si (001) substrates using V-grooves, selective area growth, and aspect ratio trapping to mitigate defect formation without the use of expensive, thick graded buffers. The GaAs is free of antiphase domains and maintains a relatively low TDD of 4x107 cm-2, despite the lack of a graded buffer. This 6.25 percent-efficient demonstration solar cell shows promise for further improvements to III-V/Si tandems to enable cost-competitive photovoltaics.

Temperature effect on the coupling between coherent longitudinal phonons and plasmons in n -type and p -type GaAs

NASA Astrophysics Data System (ADS)

Hu, Jianbo; Zhang, Hang; Sun, Yi; Misochko, Oleg V.; Nakamura, Kazutaka G.

2018-04-01

The coupling between longitudinal optical (LO) phonons and plasmons plays a fundamental role in determining the performance of doped semiconductor devices. In this work, we report a comparative investigation into the dependence of the coupling on temperature and doping in n - and p -type GaAs by using ultrafast coherent phonon spectroscopy. A suppression of coherent oscillations has been observed in p -type GaAs at lower temperature, strikingly different from n -type GaAs and other materials in which coherent oscillations are strongly enhanced by cooling. We attribute this unexpected observation to a cooling-induced elongation of the depth of the depletion layer which effectively increases the screening time of the surface field due to a slow diffusion of photoexcited carriers in p -type GaAs. Such an increase breaks the requirement for the generation of coherent LO phonons and, in turn, LO phonon-plasmon coupled modes because of their delayed formation in time.

InGaAs quantum dots grown on B-type high index GaAs substrates: surface morphologies and optical properties

NASA Astrophysics Data System (ADS)

Liang, B. L.; Wang, Zh M.; Mazur, Yu I.; Strelchuck, V. V.; Holmes, K.; Lee, J. H.; Salamo, G. J.

2006-06-01

We systematically investigated the correlation between morphological and optical properties of InGaAs self-assembled quantum dots (QDs) grown by solid-source molecular beam epitaxy on GaAs (n 11)B (n = 9, 8, 7, 5, 3, 2) substrates. Remarkably, all InGaAs QDs on GaAs(n 11)B under investigation show optical properties superior to those for ones on GaAs(100) as regards the photoluminescence (PL) linewidth and intensity. The morphology for growth of InGaAs QDs on GaAs (n 11)B, where n = 9, 8, 7, 5, is observed to have a rounded shape with a higher degree of lateral ordering than that on GaAs(100). The optical property and the lateral ordering are best for QDs grown on a (511)B substrate surface, giving a strong correlation between lateral ordering and PL optical quality. Our results demonstrate the potential for high quality InGaAs QDs on GaAs(n 11)B for optoelectronic applications.

Isolating GaSb membranes grown metamorphically on GaAs substrates using highly selective substrate removal etch processes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lavrova, Olga; Balakrishnan, Ganesh

2017-02-24

The etch rates of NH 4OH:H 2O 2 and C 6H 8O 7:H 2O 2 for GaAs and GaSb have been investigated to develop a selective etch for GaAs substrates and to isolate GaSb epilayers grown on GaAs. The NH 4OH:H 2O 2 solution has a greater etch rate differential for the GaSb/GaAs material system than C 6H 8O 7:H 2O 2 solution. The selectivity of NH 4OH:H 2O 2 for GaAs/GaSb under optimized etch conditions has been observed to be as high as 11471 ± 1691 whereas that of C 6H 8O 7:H 2O 2 has been measured upmore » to 143 ± 2. The etch contrast has been verified by isolating 2 μm thick GaSb epi-layers that were grown on GaAs substrates. GaSb membranes were tested and characterized with high-resolution X-Ray diffraction (HR-XRD) and atomic force microscopy (AFM).« less

Optical techniques to feed and control GaAs MMIC modules for phased array antenna applications

NASA Astrophysics Data System (ADS)

Bhasin, K. B.; Anzic, G.; Kunath, R. R.; Connolly, D. J.

A complex signal distribution system is required to feed and control GaAs monolithic microwave integrated circuits (MMICs) for phased array antenna applications above 20 GHz. Each MMIC module will require one or more RF lines, one or more bias voltage lines, and digital lines to provide a minimum of 10 bits of combined phase and gain control information. In a closely spaced array, the routing of these multiple lines presents difficult topology problems as well as a high probability of signal interference. To overcome GaAs MMIC phased array signal distribution problems optical fibers interconnected to monolithically integrated optical components with GaAs MMIC array elements are proposed as a solution. System architecture considerations using optical fibers are described. The analog and digital optical links to respectively feed and control MMIC elements are analyzed. It is concluded that a fiber optic network will reduce weight and complexity, and increase reliability and performance, but higher power will be required.

Optical techniques to feed and control GaAs MMIC modules for phased array antenna applications

NASA Technical Reports Server (NTRS)

Bhasin, K. B.; Anzic, G.; Kunath, R. R.; Connolly, D. J.

1986-01-01

A complex signal distribution system is required to feed and control GaAs monolithic microwave integrated circuits (MMICs) for phased array antenna applications above 20 GHz. Each MMIC module will require one or more RF lines, one or more bias voltage lines, and digital lines to provide a minimum of 10 bits of combined phase and gain control information. In a closely spaced array, the routing of these multiple lines presents difficult topology problems as well as a high probability of signal interference. To overcome GaAs MMIC phased array signal distribution problems optical fibers interconnected to monolithically integrated optical components with GaAs MMIC array elements are proposed as a solution. System architecture considerations using optical fibers are described. The analog and digital optical links to respectively feed and control MMIC elements are analyzed. It is concluded that a fiber optic network will reduce weight and complexity, and increase reliability and performance, but higher power will be required.

Effect of a low-temperature-grown GaAs layer on InAs quantum-dot photoluminescence

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kosarev, A. N.; Chaldyshev, V. V., E-mail: chald.gvg@mail.ioffe.ru; Preobrazhenskii, V. V.

2016-11-15

The photoluminescence of InAs semiconductor quantum dots overgrown by GaAs in the low-temperature mode (LT-GaAs) using various spacer layers or without them is studied. Spacer layers are thin GaAs or AlAs layers grown at temperatures normal for molecular-beam epitaxy (MBE). Direct overgrowth leads to photoluminescence disappearance. When using a thin GaAs spacer layer, the photoluminescence from InAs quantum dots is partially recovered; however, its intensity appears lower by two orders of magnitude than in the reference sample in which the quantum-dot array is overgrown at normal temperature. The use of wider-gap AlAs as a spacer-layer material leads to the enhancementmore » of photoluminescence from InAs quantum dots, but it is still more than ten times lower than that of reference-sample emission. A model taking into account carrier generation by light, diffusion and tunneling from quantum dots to the LT-GaAs layer is constructed.« less

Growth of GaAs from a free surface melt under controlled arsenic pressure in a partially confined configuration

NASA Technical Reports Server (NTRS)

Gatos, H. C.; Lagowski, J.; Wu, Y.

1988-01-01

A partially confined configuration for the growth of GaAs from melt in space was developed, consisting of a triangular prism containing the seed crystal and source material in the form of a rod. It is suggested that the configuration overcomes two obstacles in the growth of GaAs in space: total confinement in a quartz crucible and lack of arsenic pressure control. Ground tests of the configuration show that it is capable of crystal growth in space and is useful for studying the growth of GaAs from a free-surface melt on earth. The resulting chemical composition, electrical property variations, and phenomenological models to account for the results are presented.

Structural Study of GaAs(001):In 4×2 Surface

NASA Astrophysics Data System (ADS)

Lee, T.-L.; Zegenhagen, J.; Lyman, P. F.; Bedzyk, M. J.

1997-03-01

In a STM and LEED investigation (U. Resch-Esser et al., JVST B 13, 1672 (1995)), the indium-terminated GaAs(001) surface exhibited a (4×2) reconstruction. Based on this study, a dimer model, similar to that proposed by Biegelsen et al. (PRB 41, 5701(1990)) for the (4×2) clean surface, was proposed. However, the detailed local structure of the In ad-atoms was not resolvable from the STM image. In this work, we applied in situ x-ray standing wave (XSW) measurements to determine the surface structure of the GaAs(001) upon the adsorption of In at low coverages. The (4×2)/c(8×2) In-terminated GaAs(001) surface (Θ_In = 0.2 ML) was prepared by MBE. The (004) XSW measurement showed that the In ad-atoms were located 1.61 Åabove the (004) diffraction planes. At higher In coverages (up to 0.6 ML) the In (004) coherent fraction was small. This is consistent with the ladder-type pattern observed by STM at Θ_In > 0.5 ML, which indicated that there were two coexisting surface structures. For Θ_In = 0.2 ML, we found that our off-normal XSW measurements did not agree with the model proposed by Resch-Esser et al.. This work is sponsored by DOE-BES No. W-31-109-ENG-38 and by NSF No. DMR-9632472.

Tunneling Spectroscopy of Chemically Treated Surfaces of GaAs(001)

NASA Astrophysics Data System (ADS)

Fan, Jia-Fa; Tokumoto, Hiroshi

1996-03-01

Effect of surface chemical treatment on the surface electronic properties of GaAs(001) was studied by tunneling spectroscopy. Samples of highly-Si-doped GaAs were first cleaned and etched using conventional processes, then soaked in aqueous solutions of (NH_4)_2Sx and/or NH_4F for few hours, and finally rinsed in ethanol. The constant separation spectroscopy was done under pure N2 ambient at room temperature (295K) with our scanning tunneling microscope (STM). As a result, the sulfide treament lead to electron tunnelings starting typically at the sample voltages of -0.50 V and 0.90 V at initial settings of 1.50 V and 0.20 nA. For etched-only surface, however, the starting voltages were -0.70 V and 0.70 V. Effects of heating, laser-irradiation, and the fluoride treatment will be presented. Also, the mechanism of the shift of the surface Fermi level will be discussed.

A graphene/single GaAs nanowire Schottky junction photovoltaic device.

PubMed

Luo, Yanbin; Yan, Xin; Zhang, Jinnan; Li, Bang; Wu, Yao; Lu, Qichao; Jin, Chenxiaoshuai; Zhang, Xia; Ren, Xiaomin

2018-05-17

A graphene/nanowire Schottky junction is a promising structure for low-cost high-performance optoelectronic devices. Here we demonstrate a graphene/single GaAs nanowire Schottky junction photovoltaic device. The Schottky junction is fabricated by covering a single layer graphene onto an n-doped GaAs nanowire. Under 532 nm laser excitation, the device exhibits a high responsivity of 231 mA W-1 and a short response/recover time of 85/118 μs at zero bias. Under AM 1.5 G solar illumination, the device has an open-circuit voltage of 75.0 mV and a short-circuit current density of 425 mA cm-2, yielding a remarkable conversion efficiency of 8.8%. The excellent photovoltaic performance of the device is attributed to the strong built-in electric field in the Schottky junction as well as the transparent property of graphene. The device is promising for self-powered high-speed photodetectors and low-cost high-efficiency solar cells.

High-reliability GaAs image intensifier with unfilmed microchannel plate

NASA Astrophysics Data System (ADS)

Bender, Edward J.; Estrera, Joseph P.; Ford, C. E.; Giordana, A.; Glesener, John W.; Lin, P. P.; Nico, A. J.; Sinor, Timothy W.; Smithson, R. H.

1999-07-01

Current GaAs image intensifier technology requires that the microchannel plate (MCP) have a thin dielectric film on the side facing the photocathode. This protective coating substantially reduces the amount of outgassing of ions and neutral species from the microchannels. The prevention of MCP outgassing is necessary in order to prevent the `poisoning' of the Cs:O surface on the GaAs photocathode. Many authors have experimented with omitting the MCP coating. The results of such experiments invariably lead to an intensifier with a reported useful life of less than 100 hours, due to contamination of the Cs:O layer on the photocathode. Unfortunately, the MCP film is also a barrier to electron transport within the intensifier. Substantial enhancement of the image intensifier operating parameters is the motivation for the removal of the MCP film. This paper presents results showing for the first time that it is possible to fabricate a long lifetime image intensifier with a single uncoated MCP.

The presence of isolated hydrogen donors in heavily carbon-doped GaAs

NASA Astrophysics Data System (ADS)

Fushimi, Hiroshi; Wada, Kazumi

1994-12-01

The deactivation mechanism of carbon acceptors in GaAs has systematically been studied by measuring the annealing behavior and depth profiles of the carrier concentration. It is found that hydrogen impurities dominate carbon deactivation. Their deactivation undergoes two different ways: Hydrogen donors isolated from carbon acceptors compensate carbon and hydrogen impurities neutralize the carbon by forming neutral carbon-hydrogen complexes. The compensating hydrogen donors diffuse out extremely fast at relatively low temperatures. This is, to the best of our knowledge, the first report on the presence of isolated hydrogen donors in heavily carbon-doped GaAs. The dissociation of carbon-hydrogen complexes is much slower than reported. The mechanism is discussed in terms of a hydrogen retrapping effect by carbon.

Effects of gold diffusion on n-type doping of GaAs nanowires.

PubMed

Tambe, Michael J; Ren, Shenqiang; Gradecak, Silvija

2010-11-10

The deposition of n-GaAs shells is explored as a method of n-type doping in GaAs nanowires grown by the Au-mediated metal-organic chemical vapor deposition. Core-shell GaAs/n-GaAs nanowires exhibit an unintended rectifying behavior that is attributed to the Au diffusion during the shell deposition based on studies using energy dispersive X-ray spectroscopy, current-voltage, capacitance-voltage, and Kelvin probe force measurements. Removing the gold prior to n-type shell deposition results in the realization of n-type GaAs nanowires without rectification. We directly correlate the presence of gold impurities to nanowire electrical properties and provide an insight into the role of seed particles on the properties of nanowires and nanowire heterostructures.

Real-time observation of rotational twin formation during molecular-beam epitaxial growth of GaAs on Si (111) by x-ray diffraction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Suzuki, Hidetoshi, E-mail: hsuzuki@cc.miyazaki-u.ac.jp; Nakata, Yuka; Takahasi, Masamitu

2016-03-15

The formation and evolution of rotational twin (TW) domains introduced by a stacking fault during molecular-beam epitaxial growth of GaAs on Si (111) substrates were studied by in situ x-ray diffraction. To modify the volume ratio of TW to total GaAs domains, GaAs was deposited under high and low group V/group III (V/III) flux ratios. For low V/III, there was less nucleation of TW than normal growth (NG) domains, although the NG and TW growth rates were similar. For high V/III, the NG and TW growth rates varied until a few GaAs monolayers were deposited; the mean TW domain sizemore » was smaller for all film thicknesses.« less

Germanium- and tellurium-doped GaAs for non-alloyed p-type and n-type ohmic contacts

NASA Astrophysics Data System (ADS)

Park, Joongseo; Barnes, Peter A.; Lovejoy, Michael L.

1995-08-01

Epitaxial ohmic contacts to GaAs were grown by liquid phase epitaxy. Heavily Ge-doped GaAs was grown to prepare ohmic contacts to p-GaAs while Te was used for the n-type contacts. Hall measurements were carried out for the samples grown from melts in which the mole fraction of Ge was varied between 1.55 atomic % and 52.2 atomic %, while the Te mole fractions varied between 0.03% and 0.5%. Specific contact resistance, rc, as low as rcp=2.9×10-6 ohm-cm 2 for Ge doping of p=(Na-Nd)=6.0×1019 holes/cm3 was measured for p-contacts and rcn=9.6×10-5 ohm-cm2 was measured for Te doping of n=(Nd-Na)=8.9×1018 electrons/cm3 for GaAs metallized with non-alloyed contacts of Ti/Al.

Reflection high energy electron diffraction and reflectance difference studies of surface anisotropy in InGaAs chemical beam epitaxy on flat and vicinal (001) GaAs

NASA Astrophysics Data System (ADS)

Junno, B.; Paulsson, G.; Miller, M.; Samuelson, L.

1994-03-01

InGaAs quantum wells (QWs) were grown in a chemical beam epitaxy (CBE) machine with trimethylindium (TMI), triethylgallium (TEG) and tertiarybutylarsine (TBA) as precursors. Growth was monitored in-situ by reflectance difference (RD) and reflection high energy electron diffraction (RHEED), on both flat and vicinal (2° off in the <111> A direction) (001)GaAs substrates. The RD was monitored at 632.8 nm. At this wavelength the RD signal from a GaAs surface is primarily related to the absorption by Ga dimers. When InGaAs had been grown, both the average RD signal and the amplitude of the RD oscillations for the subsequent growth of GaAs increased significantly, compared to GaAs growth on GaAs. This In influence was found to persist even after the growth of 20-30 ML of pure GaAs. As a result we were able to monitor growth oscillations with RD and RHEED simultaneously during growth of quantum wells of InGaAs in GaAs. As a conclusion to these observations we suggest that the group III dimer bond concentration, detected in the RD signal, increases.

Effective electron mass and phonon modes in n-type hexagonal InN

NASA Astrophysics Data System (ADS)

Kasic, A.; Schubert, M.; Saito, Y.; Nanishi, Y.; Wagner, G.

2002-03-01

Infrared spectroscopic ellipsometry and micro-Raman scattering are used to study vibrational and electronic properties of high-quality hexagonal InN. The 0.22-μm-thick highly n-conductive InN film was grown on c-plane sapphire by radio-frequency molecular-beam epitaxy. Combining our results from the ellipsometry data analysis with Hall-effect measurements, the isotropically averaged effective electron mass in InN is determined as 0.14m0. The resonantly excited zone center E1 (TO) phonon mode is observed at 477 cm-1 in the ellipsometry spectra. Despite the high electron concentration in the film, a strong Raman mode occurs in the spectral range of the unscreened A1(LO) phonon. Because an extended carrier-depleted region at the sample surface can be excluded from the ellipsometry-model analysis, we assign this mode to the lower branch of the large-wave-vector LO-phonon-plasmon coupled modes arising from nonconserving wave-vector scattering processes. The spectral position of this mode at 590 cm-1 constitutes a lower limit for the unscreened A1(LO) phonon frequency.

Registration of T-2 mycotoxin with total internal reflection ellipsometry and QCM impedance methods.

PubMed

Nabok, A V; Tsargorodskaya, A; Holloway, A; Starodub, N F; Gojster, O

2007-01-15

A sensitive optical method of total internal reflection ellipsometry (TIRE) in conjunction with immune assay approach was exploited for the registration of T-2 mycotoxin in a wide range of concentrations from 100 microg/ml down to 0.15 ng/ml. Association constants of 1.4x10(6) and 1.9x10(7)mol(-1)s for poly- and monoclonal T-2 antibodies, respectively, were evaluated from TIRE kinetic measurements. According to TIRE data fitting, binding of T-2 molecules to antibodies (at saturation) has resulted in the increase in adsorbed layer thickness of 4-5 nm. The QCM impedance measurements data showed anomalously large mass increase and film softening, most likely, due to the binding of large T-2 aggregates to antibodies.

Electrical properties of spin coated ultrathin titanium oxide films on GaAs

NASA Astrophysics Data System (ADS)

Dutta, Shankar; Pal, Ramjay; Chatterjee, Ratnamala

2015-04-01

In recent years, ultrathin (<50 nm) metal oxide films have been being extensively studied as high-k dielectrics for future metal oxide semiconductor (MOS) technology. This paper discusses deposition of ultrathin TiO2 films (˜10 nm) on GaAs substrates (one sulfur-passivated, another unpassivated) by spin coating technique. The sulfur passivation is done to reduce the surface states of GaAs substrate. After annealing at 400 °C in a nitrogen environment, the TiO2 films are found to be polycrystalline in nature with rutile phase. The TiO2 films exhibit consistent grain size of 10-20 nm with thickness around 10-12 nm. Dielectric constants of the films are found to be 65.4 and 47.1 corresponding to S-passivated and unpassivated substrates, respectively. Corresponding threshold voltages of the MOS structures are measured to be -0.1 V to -0.3 V for the S-passivated and unpassivated samples, respectively. The S-passivated TiO2 film showed improved (lower) leakage current density (5.3 × 10-4 A cm-2 at 3 V) compared to the unpassivated film (1.8 × 10-3 A/cm2 at 3 V). Dielectric breakdown-field of the TiO2 films on S-passivated and unpassivated GaAs samples are found to be 8.4 MV cm-1 and 7.2 MV cm-1 respectively.

InGaN working electrodes with assisted bias generated from GaAs solar cells for efficient water splitting.

PubMed

Liu, Shu-Yen; Sheu, J K; Lin, Yu-Chuan; Chen, Yu-Tong; Tu, S J; Lee, M L; Lai, W C

2013-11-04

Hydrogen generation through water splitting by n-InGaN working electrodes with bias generated from GaAs solar cell was studied. Instead of using an external bias provided by power supply, a GaAs-based solar cell was used as the driving force to increase the rate of hydrogen production. The water-splitting system was tuned using different approaches to set the operating points to the maximum power point of the GaAs solar cell. The approaches included changing the electrolytes, varying the light intensity, and introducing the immersed ITO ohmic contacts on the working electrodes. As a result, the hybrid system comprising both InGaN-based working electrodes and GaAs solar cells operating under concentrated illumination could possibly facilitate efficient water splitting.

High-temperature degradation-free rapid thermal annealing of GaAs and InP

NASA Astrophysics Data System (ADS)

Pearton, Stephen J.; Katz, Avishay; Geva, Michael

1991-04-01

Rapid thermal annealing of GaAs and InP within enclosed SiC-coated graphite susceptors is shown to eliminate slip formation during implant activation treatments and to provide much better protection against surface degradation at the edges of wafers compared to the more conventional proximity method. Two different types of susceptor were investigated-the first type must be charged with As or P prior to the annealing cycles while the second type incorporates small reservoirs into the susceptor which provide a continuous overpressure of the group V species. Degradation-free annealing of patterned metallized wafers is possible using the latter type of susceptor. The activation of Si and Be implants in GaAs by RTA is also discussed.

Dielectric function of InGaAs in the visible

NASA Technical Reports Server (NTRS)

Alterovitz, S. A.; Sieg, R. E.; Yao, H. D.; Snyder, P. G.; Woollam, J. A.; Pamulapati, J.; Bhattacharya, P. K.; Sekula-Moise, P. A.

1990-01-01

Measurements are reported of the dielectric function of thermodynamically stable In(x)Ga(1-x)As in the composition range 0.3 equal to or less than X = to or less than 0.7. The optically thick samples of InGaAs were made by molecular beam epitaxy (MBE) in the range 0.4 = to or less than X = to or less than 0.7 and by metal-organic chemical vapor deposition (MOCVD) for X = 0.3. The MBE made samples, usually 1 micron thick, were grown on semi-insulating InP and included a strain release structure. The MOCVD sample was grown on GaAs and was 2 microns thick. The dielectric functions were measured by variable angle spectroscopic ellipsometry in the range 1.55 to 4.4 eV. The data was analyzed assuming an optically thick InGaAs material with an oxide layer on top. The thickness of this layer was estimated by comparing the results for the InP lattice matched material, i.e., X = 0.53, with results published in the literature. The top oxide layer mathematically for X = 0.3 and X = 0.53 was removed to get the dielectric function of the bare InGaAs. In addition, the dielectric function of GaAs in vacuum, after a protective arsenic layer was removed. The dielectric functions for X = 0, 0.3, and 0.53 together with the X = 1 result from the literature to evaluate an algorithm for calculating the dielectric function of InGaAs for an arbitrary value of X(0 = to or less than X = to or less than 1) were used. Results of the dielectric function calculated using the algorithm were compared with experimental data.

Dielectric function of InGaAs in the visible

NASA Technical Reports Server (NTRS)

Alterovitz, S. A.; Yao, H. D.; Snyder, P. G.; Woolam, J. A.; Pamulapati, J.; Bhattacharya, P. K.; Sekula-Moise, P. A.; Sieg, R. E.

1990-01-01

Measurements are reported of the dielectric function of thermodynamically stable In(x)Ga(1-x)As in the composition range 0.3 equal to or less than X = to or less than 0.7. The optically thick samples of InGaAs were made by molecular beam epitaxy (MBE) in the range 0.4 = to or less than X = to or less than 0.7 and by metal-organic chemical vapor deposition (MOCVD) for X = 0.3. The MBE made samples, usually 1 micron thick, were grown on semi-insulating InP and included a strain release structure. The MOCVD sample was grown on GaAs and was 2 microns thick. The dielectric functions were measured by variable angle spectroscopic ellipsometry in the range 1.55 to 4.4 eV. The data was analyzed assuming an optically thick InGaAs material with an oxide layer on top. The thickness of this layer was estimated by comparing the results for the InP lattice matched material, i.e., X = 0.53, with results published in the literature. The top oxide layer mathematically for X = 0.3 and X = 0.53 was removed to get the dielectric function of the bare InGaAs. In addition, the dielectric function of GaAs in vacuum, after a protective arsenic layer was removed. The dielectric functions for X = 0, 0.3, and 0.53 together with the X = 1 result from the literature to evaluate an algorithm for calculating the dielectric function of InGaAs for an arbitrary value of X (0 = to or less than X = to or less than 1) were used. Results of the dielectric function calculated using the algorithm were compared with experimental data.

GAA repeat expansion mutation mouse models of Friedreich ataxia exhibit oxidative stress leading to progressive neuronal and cardiac pathology.

PubMed

Al-Mahdawi, Sahar; Pinto, Ricardo Mouro; Varshney, Dhaval; Lawrence, Lorraine; Lowrie, Margaret B; Hughes, Sian; Webster, Zoe; Blake, Julian; Cooper, J Mark; King, Rosalind; Pook, Mark A

2006-11-01

Friedreich ataxia (FRDA) is a neurodegenerative disorder caused by an unstable GAA repeat expansion mutation within intron 1 of the FXN gene. However, the origins of the GAA repeat expansion, its unstable dynamics within different cells and tissues, and its effects on frataxin expression are not yet completely understood. Therefore, we have chosen to generate representative FRDA mouse models by using the human FXN GAA repeat expansion itself as the genetically modified mutation. We have previously reported the establishment of two lines of human FXN YAC transgenic mice that contain unstable GAA repeat expansions within the appropriate genomic context. We now describe the generation of FRDA mouse models by crossbreeding of both lines of human FXN YAC transgenic mice with heterozygous Fxn knockout mice. The resultant FRDA mice that express only human-derived frataxin show comparatively reduced levels of frataxin mRNA and protein expression, decreased aconitase activity, and oxidative stress, leading to progressive neurodegenerative and cardiac pathological phenotypes. Coordination deficits are present, as measured by accelerating rotarod analysis, together with a progressive decrease in locomotor activity and increase in weight. Large vacuoles are detected within neurons of the dorsal root ganglia (DRG), predominantly within the lumbar regions in 6-month-old mice, but spreading to the cervical regions after 1 year of age. Secondary demyelination of large axons is also detected within the lumbar roots of older mice. Lipofuscin deposition is increased in both DRG neurons and cardiomyocytes, and iron deposition is detected in cardiomyocytes after 1 year of age. These mice represent the first GAA repeat expansion-based FRDA mouse models that exhibit progressive FRDA-like pathology and thus will be of use in testing potential therapeutic strategies, particularly GAA repeat-based strategies.

Analysis of twin defects in GaAs(111)B molecular beam epitaxy growth

DOE Office of Scientific and Technical Information (OSTI.GOV)

Park, Yeonjoon; Cich, Michael J.; Zhao, Rian

2000-05-01

The formation of twin is common during GaAs(111) and GaN(0001) molecular beam epitaxy (MBE) metalorganic chemical vapor deposition growth. A stacking fault in the zinc-blende (ZB)(111) direction can be described as an insertion of one monolayer of wurtzite structure, sandwiched between two ZB structures that have been rotated 60 degree sign along the growth direction. GaAs(111)A/B MBE growth within typical growth temperature regimes is complicated by the formation of pyramidal structures and 60 degree sign rotated twins, which are caused by faceting and stacking fault formation. Although previous studies have revealed much about the structure of these twins, a well-establishedmore » simple nondestructive characterization method which allows the measurement of total aerial density of the twins does not exist at present. In this article, the twin density of AlGaAs layers grown on 1 degree sign miscut GaAs(111)B substrates has been measured using high resolution x-ray diffraction, and characterized with a combination of Nomarski microscopy, atomic force microscopy, and transmission electron microscopy. These comparisons permit the relationship between the aerial twin density and the growth condition to be determined quantitatively. (c) 2000 American Vacuum Society.« less

Optical characterizations of silver nanoprisms embedded in polymer thin film layers

NASA Astrophysics Data System (ADS)

Carlberg, Miriam; Pourcin, Florent; Margeat, Olivier; Le Rouzo, Judikael; Berginc, Gerard; Sauvage, Rose-Marie; Ackermann, Jorg; Escoubas, Ludovic

2017-10-01

The precise control of light-matter interaction has a wide range of applications and is currently driven by the use of nanoparticles (NPs) by the recent advances in nanotechnology. Taking advantage of the material, size, shape, and surrounding media dependence of the optical properties of plasmonic NPs, thin film layers with tunable optical properties are achieved. The NPs are synthesized by wet chemistry and embedded in a polyvinylpyrrolidone (PVP) polymer thin film layer. Spectrophotometer and spectroscopic ellipsometry measurements are coupled to finite-difference time domain numerical modeling to optically characterize the heterogeneous thin film layers. Silver nanoprisms of 10 to 50 nm edge size exhibit high absorption through the visible wavelength range. A simple optical model composed of a Cauchy law and a Lorentz law, accounting for the optical properties of the nonabsorbing polymer and the absorbing property of the nanoprisms, fits the spectroscopic ellipsometry measurements. Knowing the complex optical indices of heterogeneous thin film layers let us design layers of any optical properties.

Characteristic of Nano-Cu Film Prepared by Energy Filtrating Magnetron Sputtering Technique and Its Optical Property

NASA Astrophysics Data System (ADS)

Wang, Zhaoyong; Hu, Xing; Yao, Ning

2015-03-01

At the optimized deposition parameters, Cu film was deposited by the direct current magnetron sputtering (DMS) technique and the energy filtrating magnetron sputtering (EFMS) technique. The nano-structure was charactered by x-ray diffraction. The surface morphology of the film was observed by atomic force microscopy. The optical properties of the film were measured by spectroscopic ellipsometry. The refractive index, extinction coefficient and the thickness of the film were obtained by the fitted spectroscopic ellipsometry data using the Drude-Lorentz oscillator optical model. Results suggested that a Cu film with different properties was fabricated by the EFMS technique. The film containing smaller particles is denser and the surface is smoother. The average transmission coefficient, the refractive index and the extinction coefficients are higher than those of the Cu film deposited by the DMS technique. The average transmission coefficient (400-800 nm) is more than three times higher. The refractive index and extinction coefficient (at 550 nm) are more than 36% and 14% higher, respectively.

Thermally-induced first-order phase transition in the (FC6H4C2H4NH3)2[PbI4] photoluminescent organic-inorganic material

NASA Astrophysics Data System (ADS)

Koubaa, M.; Dammak, T.; Garrot, D.; Castro, M.; Codjovi, E.; Mlayah, A.; Abid, Y.; Boukheddaden, K.

2012-03-01

The thermal properties of the perovskite slab alkylammonium lead iodide (FC6H4C2H4NH3)2[PbI4] are investigated using spectroscopic ellipsometry, differential scanning calorimetry, photoluminescence, and Raman spectroscopy. The spectroscopic ellipsometry, performed in the heating mode, clearly evidenced the presence of a singularity at 375 K. This is corroborated by the temperature dependence of the photoluminescence, which pointed out a first-order order-disorder phase transition at ˜375 K, with a hysteresis loop of 40 K width. Raman spectroscopy data suggest that this transition arises from a dynamic rotational disordering of the ammonium headgroups of the alkylammonium chain. In contrast, differential scanning calorimetry measurements on a pellet sample led to an entropy change value ΔS ≈0.39 J/K/mol at the transition, suggesting the existence of a residual short-range order of the NH3+ on cooling from the high temperature phase.

Infrared metamaterial by RF magnetron sputtered ZnO/Al:ZnO multilayers

NASA Astrophysics Data System (ADS)

Santiago, Kevin C.; Mundle, Rajeh; White, Curtis; Bahoura, Messaoud; Pradhan, Aswini K.

2018-03-01

Hyperbolic metamaterials create artificial anisotropy using metallic wires suspended in dielectric media or alternating layers of a metal and dielectric (Type I or Type II). In this study we fabricated ZnO/Al:ZnO (AZO) multilayers by the RF magnetron sputtering deposition technique. Our fabricated multilayers satisfy the requirements for a type II hyperbolic metamaterial. The optical response of individual AZO and ZnO films, as well as the multilayered film were investigated via UV-vis-IR transmittance and spectroscopic ellipsometry. The optical response of the multilayered system is calculated using the nonlocal-corrected Effective Medium Approximation (EMA). The spectroscopic ellipsometry data of the multilayered system was modeled using a uniaxial material model and EMA model. Both theoretical and experimental studies validate the fabricated multilayers undergo a hyperbolic transition at a wavelength of 2.2 μm. To our knowledge this is the first AZO/ZnO type II hyperbolic metamaterial system fabricated by magnetron sputtering deposition method.

Gallium arsenide (GaAs) solar cell modeling studies

NASA Technical Reports Server (NTRS)

Heinbockel, J. H.

1980-01-01

Various models were constructed which will allow for the variation of system components. Computer studies were then performed using the models constructed in order to study the effects of various system changes. In particular, GaAs and Si flat plate solar power arrays were studied and compared. Series and shunt resistance models were constructed. Models for the chemical kinetics of the annealing process were prepared. For all models constructed, various parametric studies were performed.

Solar heating of GaAs nanowire solar cells.

PubMed

Wu, Shao-Hua; Povinelli, Michelle L

2015-11-30

We use a coupled thermal-optical approach to model the operating temperature rise in GaAs nanowire solar cells. We find that despite more highly concentrated light absorption and lower thermal conductivity, the overall temperature rise in a nanowire structure is no higher than in a planar structure. Moreover, coating the nanowires with a transparent polymer can increase the radiative cooling power by 2.2 times, lowering the operating temperature by nearly 7 K.

Solar heating of GaAs nanowire solar cells

DOE PAGES

Wu, Shao-Hua; Povinelli, Michelle L.

2015-09-25

We use a coupled thermal-optical approach to model the operating temperature rise in GaAs nanowire solar cells. Our findings show that despite more highly concentrated light absorption and lower thermal conductivity, the overall temperature rise in a nanowire structure is no higher than in a planar structure. Moreover, coating the nanowires with a transparent polymer can increase the radiative cooling power by 2.2 times, lowering the operating temperature by nearly 7 K.

Type I band alignment in GaAs{sub 81}Sb{sub 19}/GaAs core-shell nanowires

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, T.; Key Laboratory of Advanced Display and System Application, Shanghai University, 149 Yanchang Road, Shanghai 200072; Wei, M. J.

2015-09-14

The composition and band gap of the shell that formed during the growth of axial GaAs/GaAs{sub 81}Sb{sub 19}/ GaAs heterostructure nanowires have been investigated by transmission electron microscopy combined with energy dispersion spectroscopy, scanning tunneling spectroscopy, and density functional theory calculations. On the GaAs{sub 81}Sb{sub 19} intermediate segment, the shell is found to be free of Sb (pure GaAs shell) and transparent to the tunneling electrons, despite the (110) biaxial strain that affects its band gap. As a result, a direct measurement of the core band gap allows the quantitative determination of the band offset between the GaAs{sub 81}Sb{sub 19}more » core and the GaAs shell and identifies it as a type I band alignment.« less

Raman scattering studies of strain effects in (100) and (311)B GaAs1-xBix epitaxial layers

NASA Astrophysics Data System (ADS)

Steele, J. A.; Lewis, R. A.; Henini, M.; Lemine, O. M.; Alkaoud, A.

2013-11-01

We report room-temperature Raman studies of strained (100) and (311)B GaAs1-xBix epitaxial layers for x ≤ 0.039. The Raman spectra exhibit a two-mode behavior, as well as disorder-activated GaAs-like phonons. The experimental results show that the GaAs-like LO(Γ) mode experiences a strong composition-dependent redshift as a result of alloying. The peak frequency decreases linearly from the value for pure GaAs (˜293 cm-1) with the alloyed Bi fraction x and the introduced in-plane lattice strain ɛ∥, by ΔωLO=Δωalloy-Δωstrain. X-ray diffraction measurements are used to determine x and ɛ∥ allowing Δωalloy to be decoupled and is estimated to be -12(±4) cm-1/x for (100) GaAs1-xBix. ΔωLO is measured to be roughly double for samples grown on (311)B-oriented substrates to that of (100) GaAs. This large difference in redshift is accounted for by examining the Bi induced strain, effects from alloying, and defects formed during high-index (311)B crystal growth.

Optimization of GaAs Nanowire Pin Junction Array Solar Cells by Using AlGaAs/GaAs Heterojunctions

NASA Astrophysics Data System (ADS)

Wu, Yao; Yan, Xin; Wei, Wei; Zhang, Jinnan; Zhang, Xia; Ren, Xiaomin

2018-04-01

We optimized the performance of GaAs nanowire pin junction array solar cells by introducing AlGaAs/GaAs heterejunctions. AlGaAs is used for the p type top segment for axial junctions and the p type outer shell for radial junctions. The AlGaAs not only serves as passivation layers for GaAs nanowires but also confines the optical generation in the active regions, reducing the recombination loss in heavily doped regions and the minority carrier recombination at the top contact. The results show that the conversion efficiency of GaAs nanowires can be greatly enhanced by using AlGaAs for the p segment instead of GaAs. A maximum efficiency enhancement of 8.42% has been achieved in this study. And for axial nanowire, by using AlGaAs for the top p segment, a relatively long top segment can be employed without degenerating device performance, which could facilitate the fabrication and contacting of nanowire array solar cells. While for radial nanowires, AlGaAs/GaAs nanowires show better tolerance to p-shell thickness and surface condition.

Optimization of GaAs Nanowire Pin Junction Array Solar Cells by Using AlGaAs/GaAs Heterojunctions.

PubMed

Wu, Yao; Yan, Xin; Wei, Wei; Zhang, Jinnan; Zhang, Xia; Ren, Xiaomin

2018-04-25

We optimized the performance of GaAs nanowire pin junction array solar cells by introducing AlGaAs/GaAs heterejunctions. AlGaAs is used for the p type top segment for axial junctions and the p type outer shell for radial junctions. The AlGaAs not only serves as passivation layers for GaAs nanowires but also confines the optical generation in the active regions, reducing the recombination loss in heavily doped regions and the minority carrier recombination at the top contact. The results show that the conversion efficiency of GaAs nanowires can be greatly enhanced by using AlGaAs for the p segment instead of GaAs. A maximum efficiency enhancement of 8.42% has been achieved in this study. And for axial nanowire, by using AlGaAs for the top p segment, a relatively long top segment can be employed without degenerating device performance, which could facilitate the fabrication and contacting of nanowire array solar cells. While for radial nanowires, AlGaAs/GaAs nanowires show better tolerance to p-shell thickness and surface condition.

Nanopatterning as a Probe of Unstable Growth on GaAs(001)

NASA Astrophysics Data System (ADS)

Cosert, Krista; Lin, Chuan-Fu; Hammouda, Ajmi; Kan, Hung-Chih; Subrumaniam, Kanakaraju; Richardson, Chris; Phaneuf, Ray

2009-03-01

We report on observations of unstable growth on nanopatterned GaAs(001) surfaces. For growth at 500^oC, 1 ML/sec and an As2/Ga beam equivalent pressure ratio of 10:1, we find that grooves oriented at right angles to [110] produce a build up of ridges of GaAs at the upper edges, while for grooves oriented at right angles to [110] no ridges form; instead cusps evolve at the bottoms of such grooves [1]. The cusp-forming grooves show a pronounced initial amplification of depth during growth which changes with length/width ratio, and become more narrow. The ridge-forming grooves instead broaden during growth. We compare these experimental observations with kinetic Monte Carlo simulations in which a small anisotropic Ehrlich-Schwoebel barrier is included. [1] T. Tadayyon-Eslami, H.-C. Kan, L. C. Calhoun and R. J. Phaneuf, Phys. Rev. Lett. 97, 126101 (2006)

Spectral ellipsometry as a method for characterization of nanosized films with ferromagnetic layers

NASA Astrophysics Data System (ADS)

Hashim, H.; Singkh, S. P.; Panina, L. V.; Pudonin, F. A.; Sherstnev, I. A.; Podgornaya, S. V.; Shpetnyi, I. A.; Beklemisheva, A. V.

2017-11-01

Nanosized films with ferromagnetic layers are widely used in nanoelectronics, sensor systems and telecommunications. Their properties may strongly differ from those of bulk materials that is on account of interfaces, intermediate layers and diffusion. In the present work, spectral ellipsometry and magnetooptical methods are adapted for characterization of the optical parameters and magnetization processes in two- and three-layer Cr/NiFe, Al/NiFe and Cr(Al)/Ge/NiFe films onto a sitall substrate for various thicknesses of Cr and Al layers. At a layer thickness below 20 nm, the complex refractive coefficients depend pronouncedly on the thickness. In two-layer films, remagnetization changes weakly over a thickness of the top layer, but the coercive force in three-layer films increases by more than twice upon remagnetization, while increasing the top layer thickness from 4 to 20 nm.

Rugged spin-polarized electron sources based on negative electron affinity GaAs photocathode with robust Cs2Te coating

NASA Astrophysics Data System (ADS)

Bae, Jai Kwan; Cultrera, Luca; DiGiacomo, Philip; Bazarov, Ivan

2018-04-01

Photocathodes capable of providing high intensity and highly spin-polarized electron beams with long operational lifetimes are of great interest for the next generation nuclear physics facilities like Electron Ion Colliders. We report on GaAs photocathodes activated by Cs2Te, a material well known for its robustness. GaAs activated by Cs2Te forms Negative Electron Affinity, and the lifetime for extracted charge is improved by a factor of 5 compared to that of GaAs activated by Cs and O2. The spin polarization of photoelectrons was measured using a Mott polarimeter and found to be independent from the activation method, thereby shifting the paradigm on spin-polarized electron sources employing photocathodes with robust coatings.

Photoluminescence emission from GaAs nanodisks in GaAs/AlGaAs nanopillar arrays fabricated by neutral beam etching

NASA Astrophysics Data System (ADS)

Ohori, Daisuke; Fukuyama, Atsuhiko; Sakai, Kentaro; Higo, Akio; Thomas, Cedric; Samukawa, Seiji; Ikari, Tetsuo

2017-05-01

GaAs quantum nanodisks (QNDs) in nanopillar (NP) arrays are considered to be an attractive candidate for photonic device applications. We report a damageless fabrication technique that can be used to produce large-area lattice-matched GaAs/AlGaAs heterostructure NP arrays through the use of a bio-template and neutral beam etching. We have successfully realized GaAs QNDs in NPs owing to nanoscale iron oxide masks included in poly(ethylene glycol)-decorated ferritin protein shells. We observed for first time the photoluminescence emission from as-etched GaAs QNDs and confirmed quantum confinement by quantum mechanical calculation. Our methodology is vital for high-efficiency pillar-based optoelectronic devices such as NP laser diodes.

Measurements with Si and GaAs pixel detectors bonded to photon counting readout chips

NASA Astrophysics Data System (ADS)

Schwarz, C.; Campbell, M.; Goeppert, R.; Ludwig, J.; Mikulec, B.; Runge, K.; Smith, K. M.; Snoeys, W.

2001-06-01

Detectors fabricated with SI-GaAs and Si bulk material were bonded to Photon Counting Chips (PCC), developed in the framework of the MEDIPIX Collaboration. The PCC consists of a matrix of 64×64 identical square pixels (170 μm×170 μm) with a 15-bit counter in each cell. We investigated the imaging properties of these detector systems under exposure of a dental X-ray tube at room temperature. The image homogeneity and the mean count rate were determined via flood exposure images and compared. Exposures for GaAs detectors exhibit a 3 times larger spread in count rate per image in comparison to Si detectors. This also results in a 3 times worse signal to noise ratio. IV-characteristics and X-ray images at different values of the detectors bias voltage were also taken and show a 30 times higher leakage current for GaAs. The Si detector is fully active beginning from 70 V, whereas the GaAs detector does not reach full charge collection. The presampling modulation transfer function of both assembly types was measured via slit images and gives a spatial resolution of 4.3 lp/mm for both detector systems.

Phase diagrams for understanding gold-seeded growth of GaAs and InAs nanowires

NASA Astrophysics Data System (ADS)

Ghasemi, Masoomeh; Johansson, Jonas

2017-04-01

Phase diagrams are useful tools to study the phase equilibria of nanowire materials systems because the growth of nanowires is accompanied by phase formation and phase transition. We have modeled the phase equilibria of the As-Au-Ga ternary system by means of the CALPHAD method. This method is a well-established semi-empirical technique for thermodynamic modeling in which Gibbs energy functions with free parameters are defined for all phases in a system followed by adjusting these parameters to the experimental data. Using the resulting As-Au-Ga thermodynamic database, four vertical cuts of this ternary system are calculated and all show good agreement with experiments. This ternary system is particularly useful for predicting the state of the Au seed alloys when growing GaAs nanowires and we discuss such predictions. Similar calculations are performed for Au-seeded InAs nanowires. We show that the vapor-liquid-solid (VLS) growth fails for InAs nanowires, while GaAs nanowires can grow from a liquid particle. Our calculations are in agreement with experimental data on the growth of Au-seeded GaAs and InAs nanowires.

Multilayer-Grown Ultrathin Nanostructured GaAs Solar Cells as a Cost-Competitive Materials Platform for III-V Photovoltaics.

PubMed

Gai, Boju; Sun, Yukun; Lim, Haneol; Chen, Huandong; Faucher, Joseph; Lee, Minjoo L; Yoon, Jongseung

2017-01-24

Large-scale deployment of GaAs solar cells in terrestrial photovoltaics demands significant cost reduction for preparing device-quality epitaxial materials. Although multilayer epitaxial growth in conjunction with printing-based materials assemblies has been proposed as a promising route to achieve this goal, their practical implementation remains challenging owing to the degradation of materials properties and resulting nonuniform device performance between solar cells grown in different sequences. Here we report an alternative approach to circumvent these limitations and enable multilayer-grown GaAs solar cells with uniform photovoltaic performance. Ultrathin single-junction GaAs solar cells having a 300-nm-thick absorber (i.e., emitter and base) are epitaxially grown in triple-stack releasable multilayer assemblies by molecular beam epitaxy using beryllium as a p-type impurity. Microscale (∼500 × 500 μm 2 ) GaAs solar cells fabricated from respective device layers exhibit excellent uniformity (<3% relative) of photovoltaic performance and contact properties owing to the suppressed diffusion of p-type dopant as well as substantially reduced time of epitaxial growth associated with ultrathin device configuration. Bifacial photon management employing hexagonally periodic TiO 2 nanoposts and a vertical p-type metal contact serving as a metallic back-surface reflector together with specialized epitaxial design to minimize parasitic optical losses for efficient light trapping synergistically enable significantly enhanced photovoltaic performance of such ultrathin absorbers, where ∼17.2% solar-to-electric power conversion efficiency under simulated AM1.5G illumination is demonstrated from 420-nm-thick single-junction GaAs solar cells grown in triple-stack epitaxial assemblies.

Characteristic measurement for femtosecond laser pulses using a GaAs PIN photodiode as a two-photon photovoltaic receiver

NASA Astrophysics Data System (ADS)

Chen, Junbao; Xia, Wei; Wang, Ming

2017-06-01

Photodiodes that exhibit a two-photon absorption effect within the spectral communication band region can be useful for building an ultra-compact autocorrelator for the characteristic inspection of optical pulses. In this work, we develop an autocorrelator for measuring the temporal profile of pulses at 1550 nm from an erbium-doped fiber laser based on the two-photon photovoltaic (TPP) effect in a GaAs PIN photodiode. The temporal envelope of the autocorrelation function contains two symmetrical temporal side lobes due to the third order dispersion of the laser pulses. Moreover, the joint time-frequency distribution of the dispersive pulses and the dissimilar two-photon response spectrum of GaAs and Si result in different delays for the appearance of the temporal side lobes. Compared with Si, GaAs displays a greater sensitivity for pulse shape reconstruction at 1550 nm, benefiting from the higher signal-to-noise ratio of the side lobes and the more centralized waveform of the autocorrelation trace. We also measure the pulse width using the GaAs PIN photodiode, and the resolution of the measured full width at half maximum of the TPP autocorrelation trace is 0.89 fs, which is consistent with a conventional second-harmonic generation crystal autocorrelator. The GaAs PIN photodiode is shown to be highly suitable for real-time second-order autocorrelation measurements of femtosecond optical pulses. It is used both for the generation and detection of the autocorrelation signal, allowing the construction of a compact and inexpensive intensity autocorrelator.

Spectroscopic micro-tomography of metallic-organic composites by means of photon-counting detectors

NASA Astrophysics Data System (ADS)

Pichotka, M.; Jakubek, J.; Vavrik, D.

2015-12-01

The presumed capabilities of photon counting detectors have aroused major expectations in several fields of research. In the field of nuclear imaging ample benefits over standard detectors are to be expected from photon counting devices. First of all a very high contrast, as has by now been verified in numerous experiments. The spectroscopic capabilities of photon counting detectors further allow material decomposition in computed tomography and therefore inherently adequate beam hardening correction. For these reasons measurement setups featuring standard X-ray tubes combined with photon counting detectors constitute a possible replacement of the much more cost intensive tomographic setups at synchrotron light-sources. The actual application of photon counting detectors in radiographic setups in recent years has been impeded by a number of practical issues, above all by restrictions in the detectors size. Currently two tomographic setups in Czech Republic feature photon counting large-area detectors (LAD) fabricated in Prague. The employed large area hybrid pixel-detector assemblies [1] consisting of 10×10/10×5 Timepix devices have a surface area of 143×143 mm2 / 143×71,5 mm2 respectively, suitable for micro-tomographic applications. In the near future LAD devices featuring the Medipix3 readout chip as well as heavy sensors (CdTe, GaAs) will become available. Data analysis is obtained by a number of in house software tools including iterative multi-energy volume reconstruction.In this paper tomographic analysis of of metallic-organic composites is employed to illustrate the capabilities of our technology. Other than successful material decomposition by spectroscopic tomography we present a method to suppress metal artefacts under certain conditions.

A Novel Growth Method To Improve the Quality of GaAs Nanowires Grown by Ga-Assisted Chemical Beam Epitaxy.

PubMed

García Núñez, Carlos; Braña, Alejandro F; López, Nair; García, Basilio J

2018-06-13

The successful synthesis of high crystalline quality and high aspect ratio GaAs nanowires (NWs) with a uniform diameter is needed to develop advanced applications beyond the limits established by thin film and bulk material properties. Vertically aligned GaAs NWs have been extensively grown by Ga-assisted vapor-liquid-solid (VLS) mechanism on Si(111) substrates, and they have been used as building blocks in photovoltaics, optoelectronics, electronics, and so forth. However, the nucleation of parasitic species such as traces and nanocrystals on the Si substrate surface during the NW growth could affect significantly the controlled nucleation of those NWs, and therefore the resulting performance of NW-based devices. Preventing the nucleation of parasitic species on the Si substrate is a matter of interest, because they could act as traps for gaseous precursors and/or chemical elements during VLS growth, drastically reducing the maximum length of grown NWs, affecting their morphology and structure, and reducing the NW density along the Si substrate surface. This work presents a novel and easy to develop growth method (i.e., without using advanced nanolithography techniques) to prevent the nucleation of parasitic species, while preserving the quality of GaAs NWs even for long duration growths. GaAs NWs are grown by Ga-assisted chemical beam epitaxy on oxidized Si(111) substrates using triethylgallium and tertiarybutylarsine precursors by a two-step-based growth method presented here; this method includes a growth interruption for an oxidation on air between both steps of growth, reducing the nucleation of parasitic crystals on the thicker SiO x capping layer during the second and longer growth step. VLS conditions are preserved overtime, resulting in a stable NW growth rate of around 6 μm/h for growth times up to 1 h. Resulting GaAs NWs have a high aspect ratio of 85 and average radius of 35 nm. We also report on the existence of characteristic reflection high

Segment density profiles of polyelectrolyte brushes determined by Fourier transform ellipsometry

NASA Astrophysics Data System (ADS)

Biesalski, Markus; Rühe, Jürgen; Johannsmann, Diethelm

1999-10-01

We describe a method for the explicit determination of the segment density profile φ(z) of surface-attached polymer brushes with multiple angle of incidence null-ellipsometry. Because the refractive index contrast between the brush layer and the solvent is weak, multiple reflections are of minor influence and the ellipsometric spectrum is closely related to the Fourier transform of the refractive index profile, thereby allowing for explicit inversion of the ellipsometric data. We chose surface-attached monolayers of polymethacrylic acid (PMAA), a weak polyelectrolyte, as a model system and determined the segment density profile of this system as a function of the pH value of the surrounding medium by the Fourier method. Complementary to the Fourier analysis, fits with error functions are given as well. The brushes were prepared on the bases of high refractive index prisms with the "grafting-from" technique. In water, the brushes swell by more than a factor of 30. The swelling increases with increasing pH because of a growing fraction of dissociated acidic groups leading to a larger electrostatic repulsion.

A thermochemical model of radiation damage and annealing applied to GaAs solar cells

NASA Technical Reports Server (NTRS)

Conway, E. J.; Walker, G. H.; Heinbockel, J. H.

1981-01-01

Calculations of the equilibrium conditions for continuous radiation damage and thermal annealing are reported. The calculations are based on a thermochemical model developed to analyze the incorporation of point imperfections in GaAs, and modified by introducing the radiation to produce native lattice defects rather than high-temperature and arsenic atmospheric pressure. The concentration of a set of defects, including vacancies, divacancies, and impurity vacancy complexes, are calculated as a function of temperature. Minority carrier lifetimes, short circuit current, and efficiency are deduced for a range of equilibrium temperatures. The results indicate that GaAs solar cells could have a mission life which is not greatly limited by radiation damage.

Surface ordering of (In,Ga)As quantum dots controlled by GaAs substrate indexes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Zh.M.; Seydmohamadi, Sh.; Lee, J.H.

Self-organized surface ordering of (In,Ga)As quantum dots in a GaAs matrix was investigated using stacked multiple quantum dot layers prepared by molecular-beam epitaxy. While one-dimensional chain-like ordering is formed on singular and slightly misorientated GaAs(100) surfaces, we report on two-dimensional square-like ordering that appears on GaAs(n11)B, where n is 7, 5, 4, and 3. Using a technique to control surface diffusion, the different ordering patterns are found to result from the competition between anisotropic surface diffusion and anisotropic elastic matrix, a similar mechanism suggested before by Solomon [Appl. Phys. Lett. 84, 2073 (2004)].