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Sample records for ge hf sn

  1. Study on the Ge{sub 1−x}Sn{sub x}/HfO{sub 2} interface and its impacts on Ge{sub 1−x}Sn{sub x} tunneling transistor

    SciTech Connect

    Qiu, Yingxin; Wang, Runsheng E-mail: r.wang@pku.edu.cn; Huang, Qianqian; Huang, Ru E-mail: r.wang@pku.edu.cn

    2014-06-21

    In this paper, we employ first-principle calculation to investigate the Ge{sub 1−x}Sn{sub x}/HfO{sub 2} interface, and then evaluate its impacts on Ge{sub 1−x}Sn{sub x} tunneling field-effect transistor (TFET). First-principle calculations of Ge{sub 1−x}Sn{sub x}/HfO{sub 2} interfaces in the oxygen-rich process atmosphere indicate that the interface states originate from the Ge and Sn dangling bond, rather than Hf-bond. The total density of state shows that there are more interface states in the semiconductor bandgap with increasing Sn fraction. By further incorporating the material and interface parameters from density functional theory calculation into advanced device simulation, the electrical characteristics of Ge{sub 1−x}Sn{sub x} TFET are investigated. Removing the Sn atom from the first atom layer of Ge{sub 1−x}Sn{sub x} in device processes is found to be beneficial to reduce the degradations. For the degradation mechanisms, the trap-assisted-tunneling is the dominant mechanism at the low Sn fraction, and enhanced Shockley-Read-Hall recombination induced by traps becomes the dominant mechanism with increasing Sn fraction. The results are helpful for the interface optimization of Ge{sub 1−x}Sn{sub x} TFET.

  2. Pseudomorphic GeSn/Ge (001) heterostructures

    SciTech Connect

    Tonkikh, A. A.; Talalaev, V. G.; Werner, P.

    2013-11-15

    The synthesis of pseudomorphic GeSn heterostructures on a Ge (001) substrate by molecular-beam epitaxy is described. Investigations by transmission electron microscopy show that the GeSn layers are defect free and possess cubic diamondlike structure. Photoluminescence spectroscopy reveals interband radiative recombination in the GeSn quantum wells, which is identified as indirect transitions between the subbands of heavy electrons and heavy holes. On the basis of experimental data and modeling of the band structure of pseudomorphic GeSn compounds, the lower boundary of the bowing parameter for the indirect band gap is estimated as b{sub L} {>=} 1.47 eV.

  3. (29)Si, (47)Ti, (49)Ti and (195)Pt solid state MAS NMR spectroscopic investigations of ternary silicides TPtSi, germanides TPtGe (T = Ti, Zr, Hf) and stannide TiPtSn.

    PubMed

    Benndorf, Christopher; Eckert, Hellmut; Pöttgen, Rainer

    2016-05-10

    Eight ternary tetrelides TPtX (T = Ti, Zr, Hf; X = Si, Ge, Sn) were synthesized from the elements by arc-melting and subsequent annealing. TiPtSi, ZrPtSi, ZrPtGe, HfPtSi and HfPtGe crystallize with the orthorhombic TiNiSi type structure, in the space group Pnma. The structures of HfPtSi (a = 654.44(9), b = 387.97(6), c = 750.0(1) pm, wR2 = 0.0592, 411 F(2) values, 20 variables) and HfPtGe (a = 660.36(7), b = 395.18(4), c = 763.05(8) pm, wR2 = 0.0495, 430 F(2) values, 20 variables) were refined from single crystal X-ray diffractometer data. TiPtSn adopts the cubic MgAgAs type. TiPtGe is dimorphic with a TiNiSi type high-temperature modification which transforms to cubic LT-TiPtGe (MgAgAs type). All phases were investigated by high resolution (29)Si, (47)Ti, (49)Ti and (195)Pt solid state MAS NMR spectroscopy. In the cubic compounds, the (47/49)Ti NMR signals are easily detected owing to the absence of quadrupolar broadening effects. The (195)Pt resonances of the orthorhombic compounds are characterized by strongly negative isotropic Knight shifts and large Knight shift anisotropies, whereas positive isotropic Knight shifts and no anisotropies are observed for the cubic compounds. These results indicate that the phase transition in TiPtGe is associated with dramatic changes in the electronic properties. Within each group of isotypic compounds the isotropic (29)Si, (47/49)Ti and (195)Pt Knight shifts show systematic dependences on the transition metal or tetrel atomic number, suggesting that the numerical values are influenced by the electronegativities of the metallic (or metalloid) neighbours. PMID:27097719

  4. Characteristics of Sn segregation in Ge/GeSn heterostructures

    NASA Astrophysics Data System (ADS)

    Li, H.; Chang, C.; Chen, T. P.; Cheng, H. H.; Shi, Z. W.; Chen, H.

    2014-10-01

    We report an investigation of Sn segregation in Ge/GeSn heterostructures occurred during the growth by molecular beam epitaxy. The measured Sn profile in the Ge layer shows that: (a) the Sn concentration decreases rapidly near the Ge/GeSn interface, and (b) when moving away from the interface, the Sn concentration reduced with a much slower rate. The 1/e decay lengths of the present system are much longer than those of the conventional group IV system of Ge segregation in the Si overlayer because of the smaller kinetic potential as modeled by a self-limited two-state exchange scheme. The demonstration of the Sn segregation shows the material characteristics of the heterostructure, which are needed for the investigation of its optical properties.

  5. Li mobility in Nasicon-type materials LiM2(PO4)3, M = Ge, Ti, Sn, Zr and Hf, followed by 7Li NMR spectroscopy.

    PubMed

    Arbi, K; París, M A; Sanz, J

    2011-10-21

    Lithium mobility in LiM(2)(PO(4))(3) compounds, M = Ge and Sn, has been investigated by (7)Li Nuclear Magnetic Resonance (NMR) spectroscopy, and deduced information compared with that reported previously in Ti, Zr and Hf members of the series in the temperature range 100-500 K. From the analysis of (7)Li NMR quadrupole interactions (C(Q) and η parameters), spin-spin T(2)(-1) and spin-lattice T(1)(-1) relaxation rates, structural sites occupancy and mobility of lithium have been deduced. Below 250 K, Li ions are preferentially located at M(1) sites in rhombohedral phases, but occupy intermediate M(12) sites between M(1) and M(2) sites in triclinic ones. In high-temperature rhombohedral phases, a superionic state is achieved when residence times at M(1) and M(12) sites become similar and correlation effects on Li motion decrease. This state can be obtained by large order-disorder transformations in rhombohedral phases or by sharp first order transitions in triclinic ones. The presence of two relaxation mechanisms in T(1)(-1) plots of rhombohedral phases has been associated with departures of conductivity from the Arrhenius behavior. Long term mobility of lithium is discussed in terms of the cation vacancy distribution along conduction paths. PMID:21897945

  6. Low Temperature Deposition of High-k/Metal Gate Stacks on High-Sn Content (Si)GeSn-Alloys.

    PubMed

    Schulte-Braucks, C; von den Driesch, N; Glass, S; Tiedemann, A T; Breuer, U; Besmehn, A; Hartmann, J-M; Ikonic, Z; Zhao, Q T; Mantl, S; Buca, D

    2016-05-25

    (Si)GeSn is an emerging group IV alloy system offering new exciting properties, with great potential for low power electronics due to the fundamental direct band gap and prospects as high mobility material. In this Article, we present a systematic study of HfO2/TaN high-k/metal gate stacks on (Si)GeSn ternary alloys and low temperature processes for large scale integration of Sn based alloys. Our investigations indicate that SiGeSn ternaries show enhanced thermal stability compared to GeSn binaries, allowing the use of the existing Si technology. Despite the multielemental interface and large Sn content of up to 14 atom %, the HfO2/(Si)GeSn capacitors show small frequency dispersion and stretch-out. The formed TaN/HfO2/(Si)GeSn capacitors present a low leakage current of 2 × 10(-8) A/cm(2) at -1 V and a high breakdown field of ∼8 MV/cm. For large Sn content SiGeSn/GeSn direct band gap heterostructures, process temperatures below 350 °C are required for integration. We developed an atomic vapor deposition process for TaN metal gate on HfO2 high-k dielectric and validated it by resistivity as well as temperature and frequency dependent capacitance-voltage measurements of capacitors on SiGeSn and GeSn. The densities of interface traps are deduced to be in the low 10(12) cm(-2) eV(-1) range and do not depend on the Sn-concentration. The new processes developed here are compatible with (Si)GeSn integration in large scale applications. PMID:27149260

  7. Synthesis of Epitaxial Films Based on Ge-Si-Sn Materials with Ge/GeSn, Ge/GeSiSn, and GeSn/GeSiSn Heterojunctions

    NASA Astrophysics Data System (ADS)

    Timofeev, V. A.; Kokhanenko, A. P.; Nikiforov, A. I.; Mashanov, V. I.; Tuktamyshev, A. R.; Loshkarev, I. D.

    2015-11-01

    Results of investigations into the synthesis of heterostructures based on Ge-Si-Sn materials by the method of low-temperature molecular beam epitaxy are presented. The formation of epitaxial films during structure growth has been controlled by the reflection high-energy electron diffraction method. Films with Ge/GeSn, Ge/GeSiSn, and GeSn/GeSiSn heterojunctions are grown with Sn content changing from 2 to 10 % at temperatures in the interval 150-350°C. The stressed state, the composition, and the lattice parameter are studied by the x-ray diffraction method using Omega-scan curves and reciprocal space maps. A tensile strain in the Ge film during Ge/Ge0.9Sn0.1/Si structure growth has reached 0.86%.

  8. Pseudopotential calculations of strained-GeSn/SiGeSn hetero-structures

    NASA Astrophysics Data System (ADS)

    Sant, Saurabh; Schenk, Andreas

    2014-10-01

    We have obtained empirical pseudopotential parameters for α-Sn and employed the pseudopotential method along with the virtual crystal approximation to model GeSn and SiGeSn alloys. The calculated direct and indirect band gaps of GeSn and SiGeSn show good agreement with experimental data at 300 K available till date. The derived pseudopotential parameter set was used to extract various band structure quantities required to model band-to-band tunneling in simulating GeSn/SiGeSn hetero-junction Tunnel Field Effect Transistors (TFET). All the required band structure quantities have been extracted as a function of biaxial strain, Si content, and Sn content and have been fitted to a quadratic expression. An attempt to simulate Si0.5Ge0.5/Si hetero-junction TFETs based on the extracted band structure quantities yields ID - VG plots that are in good agreement with the experimental ones—an indication for the reliability of the extracted band structure quantities. Thus, the calculated pseudopotential and extracted band structure parameters provide a complete data base for the modeling of GeSn/SiGeSn hetero-junction TFETs.

  9. Study on the Ge1-xSnx/HfO2 interface and its impacts on Ge1-xSnx tunneling transistor

    NASA Astrophysics Data System (ADS)

    Qiu, Yingxin; Wang, Runsheng; Huang, Qianqian; Huang, Ru

    2014-06-01

    In this paper, we employ first-principle calculation to investigate the Ge1-xSnx/HfO2 interface, and then evaluate its impacts on Ge1-xSnx tunneling field-effect transistor (TFET). First-principle calculations of Ge1-xSnx/HfO2 interfaces in the oxygen-rich process atmosphere indicate that the interface states originate from the Ge and Sn dangling bond, rather than Hf-bond. The total density of state shows that there are more interface states in the semiconductor bandgap with increasing Sn fraction. By further incorporating the material and interface parameters from density functional theory calculation into advanced device simulation, the electrical characteristics of Ge1-xSnx TFET are investigated. Removing the Sn atom from the first atom layer of Ge1-xSnx in device processes is found to be beneficial to reduce the degradations. For the degradation mechanisms, the trap-assisted-tunneling is the dominant mechanism at the low Sn fraction, and enhanced Shockley-Read-Hall recombination induced by traps becomes the dominant mechanism with increasing Sn fraction. The results are helpful for the interface optimization of Ge1-xSnx TFET.

  10. High-k gate stacks on low bandgap tensile strained Ge and GeSn alloys for field-effect transistors.

    PubMed

    Wirths, Stephan; Stange, Daniela; Pampillón, Maria-Angela; Tiedemann, Andreas T; Mussler, Gregor; Fox, Alfred; Breuer, Uwe; Baert, Bruno; San Andrés, Enrique; Nguyen, Ngoc D; Hartmann, Jean-Michel; Ikonic, Zoran; Mantl, Siegfried; Buca, Dan

    2015-01-14

    We present the epitaxial growth of Ge and Ge0.94Sn0.06 layers with 1.4% and 0.4% tensile strain, respectively, by reduced pressure chemical vapor deposition on relaxed GeSn buffers and the formation of high-k/metal gate stacks thereon. Annealing experiments reveal that process temperatures are limited to 350 °C to avoid Sn diffusion. Particular emphasis is placed on the electrical characterization of various high-k dielectrics, as 5 nm Al2O3, 5 nm HfO2, or 1 nmAl2O3/4 nm HfO2, on strained Ge and strained Ge0.94Sn0.06. Experimental capacitance-voltage characteristics are presented and the effect of the small bandgap, like strong response of minority carriers at applied field, are discussed via simulations. PMID:25531887

  11. Hf3Fe4Sn4 and Hf9Fe4-xSn10+x: Two stannide intermetallics with low-dimensional iron sublattices

    NASA Astrophysics Data System (ADS)

    Calta, Nicholas P.; Kanatzidis, Mercouri G.

    2016-04-01

    This article reports two new Hf-rich intermetallics synthesized using Sn flux: Hf3Fe4Sn4 and Hf9Fe4-xSn10+x. Hf3Fe4Sn4 adopts an ordered variant the Hf3Cu8 structure type in orthorhombic space group Pnma with unit cell edges of a=8.1143(5) Å, b=8.8466(5) Å, and c=10.6069(6) Å. Hf9Fe4-xSn10+x, on the other hand, adopts a new structure type in Cmc21 with unit cell edges of a=5.6458(3) Å, b=35.796(2) Å, and c=8.88725(9) Å for x=0. It exhibits a small amount of phase width in which Sn substitutes on one of the Fe sites. Both structures are fully three-dimensional and are characterized by pseudo one- and two-dimensional networks of Fe-Fe homoatomic bonding. Hf9Fe4-xSn10+x exhibits antiferromagnetic order at TN=46(2) K and its electrical transport behavior indicates that it is a normal metal with phonon-dictated resistivity. Hf3Fe4Sn4 is also an antiferromagnet with a rather high ordering temperature of TN=373(5) K. Single crystal resistivity measurements indicate that Hf3Fe4Sn4 behaves as a Fermi liquid at low temperatures, indicating strong electron correlation.

  12. Epi-cleaning of Ge/GeSn heterostructures

    NASA Astrophysics Data System (ADS)

    Di Gaspare, L.; Sabbagh, D.; De Seta, M.; Sodo, A.; Wirths, S.; Buca, D.; Zaumseil, P.; Schroeder, T.; Capellini, G.

    2015-01-01

    We demonstrate a very-low temperature cleaning technique based on atomic hydrogen irradiation for highly (1%) tensile strained Ge epilayers grown on metastable, partially strain relaxed GeSn buffer layers. Atomic hydrogen is obtained by catalytic cracking of hydrogen gas on a hot tungsten filament in an ultra-high vacuum chamber. X-ray photoemission spectroscopy, reflection high energy electron spectroscopy, atomic force microscopy, secondary ion mass spectroscopy, and micro-Raman showed that an O- and C-free Ge surface was achieved, while maintaining the same roughness and strain condition of the as-deposited sample and without any Sn segregation, at a process temperature in the 100-300 °C range.

  13. Epi-cleaning of Ge/GeSn heterostructures

    SciTech Connect

    Di Gaspare, L.; Sabbagh, D.; De Seta, M.; Sodo, A.; Wirths, S.; Buca, D.; Zaumseil, P.; Schroeder, T.; Capellini, G.

    2015-01-28

    We demonstrate a very-low temperature cleaning technique based on atomic hydrogen irradiation for highly (1%) tensile strained Ge epilayers grown on metastable, partially strain relaxed GeSn buffer layers. Atomic hydrogen is obtained by catalytic cracking of hydrogen gas on a hot tungsten filament in an ultra-high vacuum chamber. X-ray photoemission spectroscopy, reflection high energy electron spectroscopy, atomic force microscopy, secondary ion mass spectroscopy, and micro-Raman showed that an O- and C-free Ge surface was achieved, while maintaining the same roughness and strain condition of the as-deposited sample and without any Sn segregation, at a process temperature in the 100–300 °C range.

  14. Tensely strained GeSn alloys as optical gain media

    NASA Astrophysics Data System (ADS)

    Wirths, S.; Ikonic, Z.; Tiedemann, A. T.; Holländer, B.; Stoica, T.; Mussler, G.; Breuer, U.; Hartmann, J. M.; Benedetti, A.; Chiussi, S.; Grützmacher, D.; Mantl, S.; Buca, D.

    2013-11-01

    This letter presents the epitaxial growth and characterization of a heterostructure for an electrically injected laser, based on a strained GeSn active well. The elastic strain within the GeSn well can be tuned from compressive to tensile by high quality large Sn content (Si)GeSn buffers. The optimum combination of tensile strain and Sn alloying softens the requirements upon indirect to direct bandgap transition. We theoretically discuss the strain-doping relation for maximum net gain in the GeSn active layer. Employing tensile strain of 0.5% enables reasonable high optical gain values for Ge0.94Sn0.06 and even without any n-type doping for Ge0.92Sn0.08.

  15. Parametrized dielectric functions of amorphous GeSn alloys

    NASA Astrophysics Data System (ADS)

    D'Costa, Vijay Richard; Wang, Wei; Schmidt, Daniel; Yeo, Yee-Chia

    2015-09-01

    We obtained the complex dielectric function of amorphous Ge1-xSnx (0 ≤ x ≤ 0.07) alloys using spectroscopic ellipsometry from 0.4 to 4.5 eV. Amorphous GeSn films were formed by room-temperature implantation of phosphorus into crystalline GeSn alloys grown by molecular beam epitaxy. The optical response of amorphous GeSn alloys is similar to amorphous Ge and can be parametrized using a Kramers-Kronig consistent Cody-Lorentz dispersion model. The parametric model was extended to account for the dielectric functions of amorphous Ge0.75Sn0.25 and Ge0.50Sn0.50 alloys from literature. The compositional dependence of band gap energy Eg and parameters associated with the Lorentzian oscillator have been determined. The behavior of these parameters with varying x can be understood in terms of the alloying effect of Sn on Ge.

  16. Germanium–tin interdiffusion in strained Ge/GeSn multiple-quantum-well structure

    NASA Astrophysics Data System (ADS)

    Wang, Wei; Dong, Yuan; Zhou, Qian; Tok, Eng Soon; Yeo, Yee-Chia

    2016-06-01

    The thermal stability and germanium–tin (Ge–Sn) interdiffusion properties were studied in epitaxial Ge/GeSn multiple-quantum-well (MQW) structure. No obvious interdiffusion was observed for annealing temperatures of 300 °C or below, while observable interdiffusion occurred for annealing temperatures of 380 °C and above. High-resolution x-ray diffraction was used to obtain the interdiffusion coefficient by analyzing the decrease rate of Ge/GeSn periodic satellite peaks. The interdiffusion coefficient is much higher, and the activation enthalpy of 1.21 eV is substantially lower in Ge/GeSn MQW structure than that previously reported in silicon–germanium (Si–Ge) systems. When the annealing temperature is increased to above 500 °C, Ge–Sn interdiffusion becomes severe. Some small pits appear on the surface, which should be related to Sn out-diffusion to the Ge cap layer, followed by Sn desorption from the top surface. This work provides insights into the Ge–Sn interdiffusion and Sn segregation behaviors in Ge/GeSn MQW structure, and the thermal budget that may be used for fabrication of devices comprising Ge/GeSn heterostructures.

  17. Crystal structure refinements of the κ phases in the Hf-Mo-Se and Hf-Mo-Ge systems

    NASA Astrophysics Data System (ADS)

    Ha˚rsta, Anders

    1985-05-01

    The crystal structures of κ-(Hf-Mo-Se) and κ-(Hf-Mo-Ge) were determined using X-ray single-crystal diffractometry. Both structures crystallize in the space group P6 3/mmc (No. 194) with the unit-cell dimensions a = 8.6995(4)A˚, c = 8.6234(7)A˚ for κ-(Hf-Mo-Se) and a = 8.6394(4)A˚, c = 8.6827(5)A˚ for κ-(Hf-Mo-Ge). The structures have been refined on F 2 to R(F 2) values of 0.0784 and 0.0661, respectively. κ-(Hf-Mo-Se) and κ-(Hf-Mo-Ge) are isostructural with κ-(Hf-Mo-P) with a variable degree of hafnium substitution on the molybdenum sites of the structure. In κ-(Hf-Mo-Ge) germanium vacancies were found to occur on the trigonal prismatic 2 c site and the phase was also found to contain oxygen on the octahedral 6g site. According to the final refinements the compositions are Hf 9+xMo 4-xSe with x = 0.40(2) and Hf 9+xMo 4- xGe yO 2 with x = 0.25(2), y = 0.88(1), and z = 1.47(12).

  18. Ge/GeSn heterostructures grown on Si (100) by molecular-beam epitaxy

    SciTech Connect

    Sadofyev, Yu. G. Martovitsky, V. P.; Bazalevsky, M. A.; Klekovkin, A. V.; Averyanov, D. V.; Vasil’evskii, I. S.

    2015-01-15

    The growth of GeSn layers by molecular-beam epitaxy on Si (100) wafers coated with a germanium buffer layer is investigated. The properties of the fabricated structures are controlled by reflection high-energy electron diffraction, atomic-force microscopy, X-ray diffractometry, Rutherford backscattering, and Raman scattering. It is shown that GeSn layers with thicknesses up to 0.5 μm and Sn molar fractions up to 0.073 manifest no sign of plastic relaxation upon epitaxy. The lattice constant of the GeSn layers within the growth plane is precisely the same as that of Ge. The effect of rapid thermal annealing on the conversion of metastable elastically strained GeSn layers into a plastically relaxed state is examined. Ge/GeSn quantum wells with Sn molar fraction up to 0.11 are obtained.

  19. Simulation of GeSn/Ge tunneling field-effect transistors for complementary logic applications

    NASA Astrophysics Data System (ADS)

    Liu, Lei; Liang, Renrong; Wang, Jing; Xiao, Lei; Xu, Jun

    2016-09-01

    GeSn/Ge tunneling field-effect transistors (TFETs) with different device configurations are comprehensively investigated by numerical simulation. The lateral PIN- and PNPN-type point-tunneling and vertical line-tunneling device structures are analyzed and compared. Both n- and p-type TFETs are optimized to construct GeSn complementary logic applications. Simulation results indicate that GeSn/Ge heterochannel and heterosource structures significantly improve the device characteristics of point- and line-TFETs, respectively. Device performance and subthreshold swing can be further improved by increasing the Sn composition. GeSn/Ge heterosource line-TFETs exhibit excellent device performance and superior inverter voltage-transfer characteristic, which make them promising candidates for GeSn complementary TFET applications.

  20. Robustness of Sn precipitation during thermal oxidation of Ge1-xSnx on Ge(001)

    NASA Astrophysics Data System (ADS)

    Kato, Kimihiko; Asano, Takanori; Taoka, Noriyuki; Sakashita, Mitsuo; Takeuchi, Wakana; Nakatsuka, Osamu; Zaima, Shigeaki

    2014-08-01

    The thermal robustness of Sn segregation and precipitation in epitaxial Ge1-xSnx layers on Ge(001) substrates with a Sn content greater than the equilibrium solubility limit has been investigated for applications of Ge1-xSnx in high-performance metal-oxide-semiconductor field-effect transistors (MOSFETs). Sn segregation and precipitation occur on the Ge1-xSnx surface after epitaxial growth of the Ge1-xSnx layer at 150 °C. After the thermal oxidation of the Ge1-xSnx layer below 500 °C, there are no significant decreases in the average Sn content in the Ge1-xSnx layer and no additional Sn segregation on the Ge1-xSnx surface. However, Sn precipitation occurs at the Ge1-xSnx surface during the thermal oxidation of the Ge1-xSnx layer with an average Sn content as high as 8.7% at 600 °C, causing a decrease in the Sn content in the Ge1-xSnx layer. The Sn content in the Ge1-xSnx oxide is 1.5 times greater than that observed near the Ge1-xSnx surface for the sample with a Sn content of 8.7% after the thermal oxidation at 400 to 500 °C. The capacitance-voltage characteristics of the Al/Al2O3/Ge1-xSnx/Ge MOS capacitors treated with thermal oxidation at 400 °C indicate that the slow state density increases with the Sn content. Meanwhile, the small interface state density could be achieved via thermal oxidation of the Ge1-xSnx layer, even with a high Sn content.

  1. Charge storage characteristics and tunneling mechanism of amorphous Ge-doped HfOx films

    NASA Astrophysics Data System (ADS)

    Qiu, X. Y.; Zhang, S. Y.; Zhang, T.; Wang, R. X.; Li, L. T.; Zhang, Y.; Dai, J. Y.

    2016-09-01

    Amorphous Ge-doped HfOx films have been deposited on p-Si(100) substrates by means of RF magnetron sputtering. Microstructural investigations reveal the partial oxidation of doped Ge atoms in the amorphous HfOx matrix and the existence of HfSiOx interfacial layer. Capacitance-voltage hysteresis of the Ag-/Ge-doped HfOx/Si/Ag memory capacitor exhibits a memory window of 3.15 V which can maintain for >5 × 104 cycles. Current-voltage characteristics reveal that Poole-Frenkel tunneling is responsible for electron transport in the Ge-doped HfOx film.

  2. Thermal Stability of Ge/GeSn Nanostructures Grown by MBE on (001) Si/Ge Virtual Wafers

    NASA Astrophysics Data System (ADS)

    Sadofyev, Yu. G.; Martovitsky, V. P.; Klekovkin, A. V.; Saraikin, V. V.; Vasil'evskii, I. S.

    A stack of five metastable 200-nm-thick elastically strained GeSn epitaxial layers separated by 20-nm-thick Ge spacers was grown on (001) Si/Ge virtual substrate by MBE. The molar fraction of Sn in different layers varied from 0.005 to 0.10, increasing with the layer distance from the Ge buffer. The phase separation of the GeSn alloy during postgrowth annealing takes place along with plastic relaxation. The phase separation begins well before the completion of the plastic relaxation process. The degree of phase separation at a given annealing temperature depends strongly on the Sn content in the GeSn alloy. The Sn released from the decomposed GeSn alloy predominantly accumulates as an amorphous layer on the surface of the sample.

  3. Pseudomorphic GeSn/Ge(001) quantum wells: Examining indirect band gap bowing

    NASA Astrophysics Data System (ADS)

    Tonkikh, Alexander A.; Eisenschmidt, Christian; Talalaev, Vadim G.; Zakharov, Nikolay D.; Schilling, Joerg; Schmidt, Georg; Werner, Peter

    2013-07-01

    A study of the bandgap character of compressively strained GeSn0.060-0.091/Ge(001) quantum wells grown by molecular beam epitaxy is reported. The built-in strain in GeSn wells leads to an increased separation between L and Γ conduction band minima. The prevalent indirect interband transitions in GeSn were probed by photoluminescence spectroscopy. As a result we could simulate the L-valley bowing parameter in GeSn alloys, bL = 0.80 ± 0.06 eV at 10 K. From this we conclude that even compressively strained GeSn/Ge(001) alloys could become direct band gap semiconductors at the Sn-fraction higher than 17.0 at. %.

  4. Pseudomorphic GeSn/Ge(001) quantum wells: Examining indirect band gap bowing

    SciTech Connect

    Tonkikh, Alexander A.; Eisenschmidt, Christian; Schmidt, Georg; Talalaev, Vadim G.; Zakharov, Nikolay D.; Werner, Peter; Schilling, Joerg

    2013-07-15

    A study of the bandgap character of compressively strained GeSn{sub 0.060-0.091}/Ge(001) quantum wells grown by molecular beam epitaxy is reported. The built-in strain in GeSn wells leads to an increased separation between L and {Gamma} conduction band minima. The prevalent indirect interband transitions in GeSn were probed by photoluminescence spectroscopy. As a result we could simulate the L-valley bowing parameter in GeSn alloys, b{sub L} = 0.80 {+-} 0.06 eV at 10 K. From this we conclude that even compressively strained GeSn/Ge(001) alloys could become direct band gap semiconductors at the Sn-fraction higher than 17.0 at. %.

  5. Epitaxial growth of highly compressively strained GeSn alloys up to 12.5% Sn

    NASA Astrophysics Data System (ADS)

    Oehme, M.; Buca, D.; Kostecki, K.; Wirths, S.; Holländer, B.; Kasper, E.; Schulze, J.

    2013-12-01

    This paper reports on the growth and characterization of highly compressive strained GeSn layers on thin strain relaxed Ge virtual substrates on Si wafers. Sn concentration up to 12.5%, which is about more than 10 times the thermal equilibrium predicted for GeSn binaries, are successfully epitaxially grown by ultra-low temperature (160 °C) molecular beam epitaxy. A minimum channeling yield of 9% evidence the high crystalline quality of the GeSn alloys while angular channeling scan demonstrate that all GeSn layers are fully pseudomorphic on the relaxed Ge virtual substrate. The strain analysis shows a deviation from the Vegard's law for Sn contents above 8%. The analysis is completed by the Raman mode dependence on the alloys composition.

  6. Growth of ultrahigh-Sn-content Ge1- x Sn x epitaxial layer and its impact on controlling Schottky barrier height of metal/Ge contact

    NASA Astrophysics Data System (ADS)

    Suzuki, Akihiro; Nakatsuka, Osamu; Shibayama, Shigehisa; Sakashita, Mitsuo; Takeuchi, Wakana; Kurosawa, Masashi; Zaima, Shigeaki

    2016-04-01

    We examined the epitaxial growth of an ultrahigh-Sn-content Ge1- x Sn x layer on a Ge substrate and investigated the impact of a Ge1- x Sn x interlayer on the Schottky barrier height (SBH) of the metal/Ge contact. In this study, we considered guidelines of the strain energy and growth temperature to realize a high-Sn-content Ge1- x Sn x layer while keeping the epitaxial growth and suppressing the Sn precipitation. By reducing the film thickness and keeping a low growth temperature, we formed an atomically flat and uniform Ge1- x Sn x epitaxial layer with a Sn content up to 46% on a Ge(001) substrate. We also performed the current density-voltage measurement for Al/Ge1- x Sn x /n-Ge Schottky diodes to estimate the SBH. We found that the SBH of Al/Ge1- x Sn x /n-Ge contact decreases with increasing Sn content in the Ge1- x Sn x interlayer. The shift of the pinning position towards the conduction band edge of Ge is one of the reasons for the SBH reduction of Al/Ge1- x Sn x /n-Ge contact because the valence band edge of Ge1- x Sn x would rise as the Sn content increases.

  7. Franz-Keldysh effect in GeSn pin photodetectors

    NASA Astrophysics Data System (ADS)

    Oehme, M.; Kostecki, K.; Schmid, M.; Kaschel, M.; Gollhofer, M.; Ye, K.; Widmann, D.; Koerner, R.; Bechler, S.; Kasper, E.; Schulze, J.

    2014-04-01

    The optical properties and the Franz-Keldysh effect at the direct band gap of GeSn alloys with Sn concentrations up to 4.2% at room temperature were investigated. The GeSn material was embedded in the intrinsic region of a Ge heterojunction photodetector on Si substrates. The layer structure was grown by means of ultra-low temperature molecular beam epitaxy. The absorption coefficient as function of photon energy and the direct bandgap energies were determined. In all investigated samples, the Franz-Keldysh effect can be observed. A maximum absorption ratio of 1.5 was determined for 2% Sn for a voltage swing of 3 V.

  8. 70 °C synthesis of high-Sn content (25%) GeSn on insulator by Sn-induced crystallization of amorphous Ge

    NASA Astrophysics Data System (ADS)

    Toko, K.; Oya, N.; Saitoh, N.; Yoshizawa, N.; Suemasu, T.

    2015-02-01

    Polycrystalline GeSn thin films are fabricated on insulating substrates at low temperatures by using Sn-induced crystallization of amorphous Ge (a-Ge). The Sn layer stacked on the a-Ge layer (100-nm thickness each) had two roles: lowering the crystallization temperature of a-Ge and composing GeSn. Slow annealing at an extremely low temperature of 70 °C allowed for a large-grained (350 nm) GeSn layer with a lattice constant of 0.590 nm, corresponding to a Sn composition exceeding 25%. The present investigation paves the way for advanced electronic optical devices integrated on a flexible plastic substrate as well as on a Si platform.

  9. Parametrized dielectric functions of amorphous GeSn alloys

    SciTech Connect

    D'Costa, Vijay Richard Wang, Wei; Yeo, Yee-Chia; Schmidt, Daniel

    2015-09-28

    We obtained the complex dielectric function of amorphous Ge{sub 1−x}Sn{sub x} (0 ≤ x ≤ 0.07) alloys using spectroscopic ellipsometry from 0.4 to 4.5 eV. Amorphous GeSn films were formed by room-temperature implantation of phosphorus into crystalline GeSn alloys grown by molecular beam epitaxy. The optical response of amorphous GeSn alloys is similar to amorphous Ge and can be parametrized using a Kramers-Kronig consistent Cody-Lorentz dispersion model. The parametric model was extended to account for the dielectric functions of amorphous Ge{sub 0.75}Sn{sub 0.25} and Ge{sub 0.50}Sn{sub 0.50} alloys from literature. The compositional dependence of band gap energy E{sub g} and parameters associated with the Lorentzian oscillator have been determined. The behavior of these parameters with varying x can be understood in terms of the alloying effect of Sn on Ge.

  10. GeSn p-i-n photodetectors with GeSn layer grown by magnetron sputtering epitaxy

    NASA Astrophysics Data System (ADS)

    Zheng, Jun; Wang, Suyuan; Liu, Zhi; Cong, Hui; Xue, Chunlai; Li, Chuanbo; Zuo, Yuhua; Cheng, Buwen; Wang, Qiming

    2016-01-01

    We report an investigation of normal-incidence GeSn-based p-i-n photodetectors (PDs) with a Ge0.94Sn0.06 active layer grown using sputter epitaxy on a Ge(100) substrate. A low dark current density of 0.24 A/cm2 was obtained at a reverse bias of 1 V. A high optical responsivity of the Ge0.94Sn0.06/Ge p-i-n PDs at zero bias was achieved, with an optical response wavelength extending to 1985 nm. The temperature-dependent optical-response measurement was performed, and a clear redshift absorption edge was observed. This work presents an approach for developing efficient and cost-effective GeSn-based infrared devices.

  11. Fabrication of GeSn-multiple quantum wells by overgrowth of Sn on Ge by using molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Oliveira, F.; Fischer, I. A.; Benedetti, A.; Zaumseil, P.; Cerqueira, M. F.; Vasilevskiy, M. I.; Stefanov, S.; Chiussi, S.; Schulze, J.

    2015-12-01

    We report on the fabrication and structural characterization of epitaxially grown ultra-thin layers of Sn on Ge virtual substrates (Si buffer layer overgrown by a 50 nm thick Ge epilayer followed by an annealing step). Samples with 1 to 5 monolayers of Sn on Ge virtual substrates were grown using solid source molecular beam epitaxy and characterized by atomic force microscopy. We determined the critical thickness at which the transition from two-dimensional to three-dimensional growth occurs. This transition is due to the large lattice mismatch between Ge and Sn (≈14.7%). By depositing Ge on top of Sn layers, which have thicknesses at or just below the critical thickness, we were able to fabricate ultra-narrow GeSn multi-quantum-well structures that are fully embedded in Ge. We report results on samples with one and ten GeSn wells separated by 5 and 10 nm thick Ge spacer layers that were characterized by high resolution transmission electron microscopy and X-ray diffraction. We discuss the structure and material intermixing observed in the samples.

  12. Fabrication of GeSn-multiple quantum wells by overgrowth of Sn on Ge by using molecular beam epitaxy

    SciTech Connect

    Oliveira, F.; Fischer, I. A.; Schulze, J.; Benedetti, A.; Zaumseil, P.; Cerqueira, M. F.; Vasilevskiy, M. I.; Stefanov, S.; Chiussi, S.

    2015-12-28

    We report on the fabrication and structural characterization of epitaxially grown ultra-thin layers of Sn on Ge virtual substrates (Si buffer layer overgrown by a 50 nm thick Ge epilayer followed by an annealing step). Samples with 1 to 5 monolayers of Sn on Ge virtual substrates were grown using solid source molecular beam epitaxy and characterized by atomic force microscopy. We determined the critical thickness at which the transition from two-dimensional to three-dimensional growth occurs. This transition is due to the large lattice mismatch between Ge and Sn (≈14.7%). By depositing Ge on top of Sn layers, which have thicknesses at or just below the critical thickness, we were able to fabricate ultra-narrow GeSn multi-quantum-well structures that are fully embedded in Ge. We report results on samples with one and ten GeSn wells separated by 5 and 10 nm thick Ge spacer layers that were characterized by high resolution transmission electron microscopy and X-ray diffraction. We discuss the structure and material intermixing observed in the samples.

  13. Comparison of EL emitted by LEDs on Si substrates containing Ge and Ge/GeSn MQW as active layers

    NASA Astrophysics Data System (ADS)

    Schwartz, B.; Arguirov, T.; Kittler, M.; Oehme, M.; Kostecki, K.; Kasper, E.; Schulze, J.

    2015-02-01

    We analyzed Ge- and GeSn/Ge multiple quantum well (MQW) light emitting diodes (LEDs). The structures were grown by molecular beam epitaxy (MBE) on Si. In the Ge LEDs the active layer was 300 nm thick. Sb doping was ranging from 1×1018 to 1×1020 cm-3. An unintentionally doped Ge-layer served as reference. The LEDs with the MQWs consist of ten alternating GeSn/Ge-layers. The Ge-layers were 10 nm thick and the GeSn-layers were grown with 6 % Sn and thicknesses between 6 and 12 nm. The top contact of all LEDs was identical. Accordingly, the light extraction is comparable. The electroluminescence (EL) analysis was performed under forward bias at different currents. Sample temperatures between <300 K and 80 K were studied. For the reference LED the direct transition at 0.8 eV dominates. With increasing current the peak is slightly redshifted due to Joule heating. Sb doping of the active Ge-layer affects the intensity and at 3×1019 cm-3 the strongest emission appears. It is ~4 times higher as compared to the reference. Moreover a redshift of the peak position is caused by bandgap narrowing. The LEDs with undoped GeSn/Ge-MQWs as active layer show a very broad luminescence band with a peak around 0.65 eV, pointing to a dominance of the GeSn-layers. The light emission intensity is at least 17 times stronger as compared to the reference Ge-LED. Due to incorporation of Sn in the MQWs the active layer should approach to a direct semiconductor. In indirect Si and Ge we observed an increase of intensity with increasing temperature, whereas the intensity of GeSn/Ge-MQWs was much less affected. But a deconvolution of the spectra revealed that the energy of indirect transition in the wells is still below the one of the direct transition.

  14. Performance Investigation of Nanoscale Strained Ge pMOSFETs with a GeSn Alloy Stressor.

    PubMed

    Lee, Chang-Chun; Chang, Shu-Tong; Cheng, Sen-Wen; Chian, Bow-Tsin

    2015-11-01

    A germanium (Ge)-based substrate combined with germanium-tin (GeSn) alloy embedded in source/drain (S/D) regions has attracted significant attention because of its ability to satisfy the requirements of a high-mobility channel. Devices are shrunk in their geometries to meet the target of superior density in layout arrangement. Thus, determining the influences of devices on mobility gain is important. Accordingly, several designed factors, including gate width, S/D length, and Sn concentration of the GeSn stressor, are systematically analyzed in this study. A second-order formula composed of piezoresistance coefficients is derived and adopted to achieve a precise mobility gain estimation. A peak of the carrier mobility gain appears when a nanoscale geometry combination of 20 nm gate length and -200 nm gate width is used in the Ge channel, and 10% of the Sn mole proportion of the GeSn alloy is applied. PMID:26726661

  15. Defect states in HfO 2 on deposited on Ge(1 1 1) and Ge(1 0 0) substrates

    NASA Astrophysics Data System (ADS)

    Lucovsky, G.; Seo, H.; Long, J. P.; Chung, K.-B.; Vasic, R.; Ulrich, M.

    2009-04-01

    There is considerable interest in the direct bonding between Si and Ge substrates and high-K nano-crystalline transition metal elemental and complex oxides. Implicit in this is the elimination of lower-K interfacial transition regions (ITRs) in gate stacks which limit device down-scaling of advanced devices to meet roadmap targets. A novel approach is presented in this article for (i) deposition of HfO 2 onto N-passivated Ge(1 1 1) and Ge(1 0 0) substrates, a process that also prevents subcutaneous oxidation of the Ge substrate during the deposition of nano-crystalline HfO 2 and non-crystalline Hf Si oxynitride dielectrics as well, and (ii) the effective removal of Ge-N, during an 800 °C rapid thermal annealing. Removal of Ge-N bonding has been confirmed by X-ray absorption N K 1 spectra (XAS). However, even though X-ray photoelectron spectroscopy (XPS) studies has indicated no detectable Ge-O bonding at the Ge-dielectric interfaces as-deposited, a significant amount of Ge-O bonding throughout the entire HfO 2 film is detected by XPS and XAS after the 800 °C anneal. Current-voltage measurements indicate significantly higher leakage for HfO 2 films on Ge(1 1 1) compared with Ge(1 0 0). These correlate with differences in band edge defect state densities obtained from spectroscopic measurements, and are consistent with a more columnar, bonding morphology for direct bonding of HfO 2 on Ge(1 1 1) than for Ge(1 0 0).

  16. Chemical states and electronic structure of a HfO(-2) / Ge(001) interface

    SciTech Connect

    Seo, Kang-ill; McIntyre, Paul C.; Sun, Shiyu; Lee, Dong-Ick; Pianetta, Piero; Saraswat, Krishna C.; /Stanford U., Elect. Eng. Dept.

    2005-05-04

    We report the chemical bonding structure and valence band alignment at the HfO{sub 2}/Ge (001) interface by systematically probing various core level spectra as well as valence band spectra using soft x-rays at the Stanford Synchrotron Radiation Laboratory. We investigated the chemical bonding changes as a function of depth through the dielectric stack by taking a series of synchrotron photoemission spectra as we etched through the HfO{sub 2} film using a dilute HF-solution. We found that a very non-stoichiometric GeO{sub x} layer exists at the HfO{sub 2}/Ge interface. The valence band spectra near the Fermi level in each different film structure were carefully analyzed, and as a result, the valence band offset between Ge and GeO{sub x} was determined to be {Delta}E{sub v} (Ge-GeO{sub x}) = 2.2 {+-} 0.15 eV, and that between Ge and HfO{sub 2}, {Delta}E{sub v} (Ge-HfO{sub 2}) = 2.7 {+-} 0.15 eV.

  17. Lattice Thermal Conductivity of the Binary and Ternary Group-IV Alloys Si-Sn, Ge-Sn, and Si-Ge-Sn

    NASA Astrophysics Data System (ADS)

    Khatami, S. N.; Aksamija, Z.

    2016-07-01

    Efficient thermoelectric (TE) energy conversion requires materials with low thermal conductivity and good electronic properties. Si-Ge alloys, and their nanostructures such as thin films and nanowires, have been extensively studied for TE applications; other group-IV alloys, including those containing Sn, have not been given as much attention as TEs, despite their increasing applications in other areas including optoelectronics. We study the lattice thermal conductivity of binary (Si-Sn and Ge-Sn) and ternary (Si-Ge-Sn) alloys and their thin films in the Boltzmann transport formalisms, including a full phonon dispersion and momentum-dependent boundary-roughness scattering. We show that Si-Sn alloys have the lowest conductivity (3 W /mK ) of all the bulk alloys, more than 2 times lower than Si-Ge, attributed to the larger difference in mass between the two constituents. In addition, we demonstrate that thin films offer an additional reduction in thermal conductivity, reaching around 1 W /mK in 20-nm-thick Si-Sn, Ge-Sn, and ternary Si-Ge-Sn films, which is near the conductivity of amorphous SiO2 . We conclude that group-IV alloys containing Sn have the potential for high-efficiency TE energy conversion.

  18. Interface properties of Ge on cubic SrHfO3 (001)

    NASA Astrophysics Data System (ADS)

    Wang, Jianli; Wang, Chenxiang; Tang, Gang; Zhang, Junting; Guo, Sandong; Han, Yujia

    2016-06-01

    High quality Ge-on-high-k oxide interface is essential to facilitate the high performance metal-oxide semiconductor field-effect transistors and monolithically integrated optoelectronics device performance. The atomic structure and electronic properties of Ge on perfect and defective (001) SrHfO3 are investigated by first-principle calculations. The amplitude of the surface rumpling for the SrO-terminated surface is much larger than that for HfO2-terminated surface, although both SrO- and HfO2-terminated surfaces are stable for a comparable range of the HfO2 chemical potential. The distance between the first and second planes compresses while that of the second and third planes expands due to the relaxation of the slab. We investigated systematically the specific adsorption sites and the atomic structure at the initial growth stage of Ge on the SrHfO3 (001) substrate. The top sites of the oxygen atoms are favorable for 1/2 (1/3) monolayer Ge adsorbate at SrO (HfO2)-terminated surface. We calculated the surface grand potential and presented the complete surface phase diagram. We also pointed out the energetically favorable interfaces among the atomic arrangements of the Ge/SrHfO3 (001) interfaces. The atomic structure and electronic properties of the intrinsic point defects were calculated and analyzed for the Ge/SrHfO3 (001) interfaces.

  19. Franz-Keldysh effect in GeSn pin photodetectors

    SciTech Connect

    Oehme, M. Kostecki, K.; Schmid, M.; Kaschel, M.; Gollhofer, M.; Ye, K.; Widmann, D.; Koerner, R.; Bechler, S.; Kasper, E.; Schulze, J.

    2014-04-21

    The optical properties and the Franz-Keldysh effect at the direct band gap of GeSn alloys with Sn concentrations up to 4.2% at room temperature were investigated. The GeSn material was embedded in the intrinsic region of a Ge heterojunction photodetector on Si substrates. The layer structure was grown by means of ultra-low temperature molecular beam epitaxy. The absorption coefficient as function of photon energy and the direct bandgap energies were determined. In all investigated samples, the Franz-Keldysh effect can be observed. A maximum absorption ratio of 1.5 was determined for 2% Sn for a voltage swing of 3 V.

  20. Density and Capture Cross-Section of Interface Traps in GeSnO2 and GeO2 Grown on Heteroepitaxial GeSn.

    PubMed

    Gupta, Somya; Simoen, Eddy; Loo, Roger; Madia, Oreste; Lin, Dennis; Merckling, Clement; Shimura, Yosuke; Conard, Thierry; Lauwaert, Johan; Vrielinck, Henk; Heyns, Marc

    2016-06-01

    An imperative factor in adapting GeSn as the channel material in CMOS technology, is the gate-oxide stack. The performance of GeSn transistors is degraded due to the high density of traps at the oxide-semiconductor interface. Several oxide-gate stacks have been pursued, and a midgap Dit obtained using the ac conductance method, is found in literature. However, a detailed signature of oxide traps like capture cross-section, donor/acceptor behavior and profile in the bandgap, is not yet available. We investigate the transition region between stoichiometric insulators and strained GeSn epitaxially grown on virtual Ge substrates. Al2O3 is used as high-κ oxide and either Ge1-xSnxO2 or GeO2 as interfacial layer oxide. The interface trap density (Dit) profile in the lower half of the bandgap is measured using deep level transient spectroscopy, and the importance of this technique for small bandgap materials like GeSn, is explained. Our results provide evidence for two conclusions. First, an interface traps density of 1.7 × 10(13) cm(-2)eV(-1) close to the valence band edge (Ev + 0.024 eV) and a capture cross-section (σp) of 1.7 × 10(-18) cm(2) is revealed for GeSnO2. These traps are associated with donor states. Second, it is shown that interfacial layer passivation of GeSn using GeO2 reduces the Dit by 1 order of magnitude (2.6 × 10(12) cm(-2)eV(-1)), in comparison to GeSnO2. The results are cross-verified using conductance method and saturation photovoltage technique. The Dit difference is associated with the presence of oxidized (Sn(4+)) and elemental Sn in the interfacial layer oxide. PMID:27172051

  1. GeSn pin diodes: from pure Ge to direct-gap materials

    NASA Astrophysics Data System (ADS)

    Gallagher, James; Senaratne, Charutha; Xu, Chi; Aoki, Toshihiro; Kouvetakis, John; Menendez, Jose

    2015-03-01

    Complete n - i - p Ge1-ySny diode structures (y =0-0.09) were fabricated on Si substrates with Sn concentrations covering the entire range between pure Ge and direct-gap materials. The structures typically consist of a thick (>1 μm) n + + Ge buffer layer grown by Gas Source Molecular Epitaxy using Ge4H10 and either P(SiH3)3 or P(GeH3)3 , followed by a GeSn intrinsic layer (~ 500 nm), grown by Chemical Vapor Deposition (CVD) using Ge3H8 and SnD4, and a GeSn p-type top layer (~ 200 nm) grown by CVD using Ge3H8,SnD4andB2H6. Temperature-dependence of the I - V characteristics of these diodes as well as the forward-bias dependence of their electroluminescence (EL) signal were investigated, making it possible for the first time to extract the compositional dependence of parameters such as band gaps, activation energies, and dark currents. The EL spectra are dominated by direct-gap emission, which shifts from 1590 nm to 2300 nm, in agreement with photoluminescence results. DOD AFOSR FA9550-12-1-0208 and DOD AFOSR FA9550-13-1-0022.

  2. Influence of hydrogen surface passivation on Sn segregation, aggregation, and distribution in GeSn/Ge(001) materials

    NASA Astrophysics Data System (ADS)

    Johll, Harman; Samuel, Milla; Koo, Ruey Yi; Kang, Hway Chuan; Yeo, Yee-Chia; Tok, Eng Soon

    2015-05-01

    Plane-wave density functional theory is used to investigate the impact of hydrogen passivation of the p(2×2) reconstructed Ge1-xSnx surface on Sn segregation, aggregation, and distribution. On a clean surface, Sn preferentially segregates to the surface layer, with surface coverages of 25%, 50%, and 100% for total Sn concentrations of 2.5%, 5.0%, and 10.0%, respectively. In contrast, a hydrogen passivated surface increases interlayer migration of Sn to subsurface layers, in particular, to the third layer from the surface, and results in surface coverages of 0%, 0%, and 50% corresponding to Sn concentrations of 2.5%, 5.0%, and 10.0%, respectively. Hydrogen transfer from a Ge-capped surface to the one enriched with increasing Sn surface coverage is also an unfavorable process. The presence of hydrogen therefore reduces the surface energy by passivating the reactive dangling bonds and enhancing Sn interlayer migration to the subsurface layers. For both clean and hydrogenated surfaces, aggregation of Sn at the surface layer is also not favored. We explain these results by considering bond enthalpies and the enthalpies of hydrogenation for various surface reactions. Our results thus point to reduced Sn segregation to the surface in a Ge1-xSnx epitaxial thin film if CVD growth, using hydride precursors in the hydrogen limited growth regime, is used. This would lead to a more abrupt interface and is consistent with recent experimental observation. Hydrogenation is therefore a promising method for controlling and manipulating elemental population of Sn in a Ge1-xSnx epitaxial thin film.

  3. Linear magnetoresistance and zero-field anomalies in HfNiSn single crystals

    NASA Astrophysics Data System (ADS)

    Steinke, Lucia; Kistner-Morris, Jedediah J.; Deng, Haiming; Geschwind, Gayle; Aronson, Meigan C.

    The Half-Heusler compound HfNiSn is probably best known as a candidate material for thermoelectric applications, and studies of its properties have mainly focused on polycrystalline samples and thin films. However, magnetotransport studies of HfNiSn show unusual transport properties like linear magnetoresistance (LMR), where single-crystalline samples of HfNiSn exhibit unexpected LMR at very low fields. In this work, we optimized the solution growth of HfNiSn to obtain high-quality single crystals, where electrical transport measurements show that it is a compensated semimetal below ~ 200 K, where the Hall voltage is zero. At higher temperatures, we see a finite Hall contribution from activated excess carriers. In the semimetallic regime, we observe transport anomalies like resistive signals that strongly depend on contact configuration, and LMR below 5 K. Both low-field DC and low frequency AC magntization measurements show pronounced diamagnetic behavior and the onset of paramagnetism below 4 K. High-frequency diamagnetic screening may be attributed to a decreased skin depth with decreased resistance, but this scenario seems unlikely in HfNiSn since the measured resistance increases steeply at the lowest temperatures This research was supported by the Army Research Office.

  4. An improvement of HfO2/Ge interface by in situ remote N2 plasma pretreatment for Ge MOS devices

    NASA Astrophysics Data System (ADS)

    Chi, Xiaowei; Lan, Xiaoling; Lu, Chao; Hong, Haiyang; Li, Cheng; Chen, Songyan; Lai, Hongkai; Huang, Wei; Xu, Jianfang

    2016-03-01

    In situ remote N2 plasma pretreatment of Ge substrate before deposition of HfO2 is proved effective to reduce GeOx interlayer at the HfO2/Ge interface, resulting in a smaller capacitance equivalent oxide thickness, lower interface trap density and leakage current density for the metal/HfO2/n-Ge capacitors. However, it has no obvious impact on the metal/HfO2/p-Ge capacitors, showing a much higher interface trap density than that on n-Ge. The high equivalent permittivity of the HfO2 gate stacks (∼24.2) confirmed the removal of GeOx interlayer by N2 plasma pretreatment. In situ remote N2 plasma pretreatment is demonstrated perspective to make metal/HfO2/n-Ge MOSFET with scaling capacitance equivalent oxide thickness.

  5. Energy band alignment of atomic layer deposited HfO{sub 2} oxide film on epitaxial (100)Ge, (110)Ge, and (111)Ge layers

    SciTech Connect

    Hudait, Mantu K.; Zhu Yan

    2013-03-21

    Crystallographically oriented epitaxial Ge layers were grown on (100), (110), and (111)A GaAs substrates by in situ growth process using two separate molecular beam epitaxy chambers. The band alignment properties of atomic layer hafnium oxide (HfO{sub 2}) film deposited on crystallographically oriented epitaxial Ge were investigated using x-ray photoelectron spectroscopy (XPS). Valence band offset, {Delta}E{sub v} values of HfO{sub 2} relative to (100)Ge, (110)Ge, and (111)Ge orientations were 2.8 eV, 2.28 eV, and 2.5 eV, respectively. Using XPS data, variation in valence band offset, {Delta}E{sub V}(100)Ge>{Delta}E{sub V}(111)Ge>{Delta}E{sub V}(110)Ge, was obtained related to Ge orientation. Also, the conduction band offset, {Delta}E{sub c} relation, {Delta}E{sub c}(110)Ge>{Delta}E{sub c}(111)Ge>{Delta}E{sub c}(100)Ge related to Ge orientations was obtained using the measured bandgap of HfO{sub 2} on each orientation and with the Ge bandgap of 0.67 eV. These band offset parameters for carrier confinement would offer an important guidance to design Ge-based p- and n-channel metal-oxide field-effect transistor for low-power application.

  6. Si based GeSn light emitter: mid-infrared devices in Si photonics

    NASA Astrophysics Data System (ADS)

    Yu, S. Q.; Ghetmiri, S. A.; Du, W.; Margetis, J.; Zhou, Y.; Mosleh, A.; Al-Kabi, S.; Nazzal, A.; Sun, G.; Soref, R. A.; Tolle, J.; Li, B.; Naseem, H. A.

    2015-02-01

    Ge1-xSnx/Ge thin films and Ge/Ge1-xSnx/Ge n-i-p double heterostructure (DHS) have been grown using commercially available reduced pressure chemical vapor deposition (RPCVD) reactor. The Sn compositional material and optical characteristics have been investigated. A direct bandgap GeSn material has been identified with Sn composition of 10%. The GeSn DHS samples were fabricated into LED devices. Room temperature electroluminescence spectra were studied. A maximum emission power of 28mW was obtained with 10% Sn LED under the injection current density of 800 A/cm2.

  7. HfO2 nanocrystal memory on SiGe channel

    NASA Astrophysics Data System (ADS)

    Lin, Yu-Hsien; Chien, Chao-Hsin

    2013-02-01

    This study proposes a novel HfO2 nanocrystal memory on epi-SiGe (Ge: 15%) channel. Because SiGe has a smaller bandgap than that of silicon, it increases electron/hole injection and the enhances program/erase speeds. This study compares the characteristics of HfO2 nanocrystal memories with different oxynitride tunnel oxide thicknesses on Si and epi-SiGe substrate. Results show that the proposed nonvolatile memory possesses superior characteristics in terms of considerably large memory window for two-bits operation, high speed program/erase for low power applications, long retention time, excellent endurance, and strong immunity to disturbance.

  8. Effects of constant voltage stressing on HfTaOx/SiGe gate stack

    NASA Astrophysics Data System (ADS)

    Mallik, S.; Mahata, C.; Hota, M. K.; Sarkar, C. K.; Maiti, C. K.

    2012-10-01

    Ultrathin HfTaOx gate dielectric has been deposited on Si0.81Ge0.19 by RF co-sputtering of HfO2 and Ta2O5 targets. X-ray photoelectron spectroscopic (XPS) analyses indicate an interfacial layer containing GeOx, Hf silicate, SiOx (layer of Hf- Si-Ge-O) formation during deposition of HfTaOx. No evidence of Ta-silicate or Ta incorporation was found at the interface. X-ray diffraction (GIXRD) measurements show that as-deposited HfTaOx films are amorphous; however, the crystallization temperature of HfTaOx film is found to increase significantly after annealing beyond 500 °C (for 5 min) along with the incorporation of Ta (with 18% Ta). It has been found that HfTaOx gate dielectric on Si0.81Ge0.19 exhibit excellent electrical properties with low interface state density (~6.0×1011 cm-2eV-1) and hysteresis voltage (<70 mV). Charge trapping/detrapping behavior of the gate stacks has been studied under constant voltage stressing and the degradation mechanism of the dielectrics has been studied in detail.

  9. Polycrystalline GeSn thin films on Si formed by alloy evaporation

    NASA Astrophysics Data System (ADS)

    Kim, Munho; Fan, Wenjuan; Seo, Jung-Hun; Cho, Namki; Liu, Shih-Chia; Geng, Dalong; Liu, Yonghao; Gong, Shaoqin; Wang, Xudong; Zhou, Weidong; Ma, Zhenqiang

    2015-06-01

    Polycrystalline GeSn thin films on Si substrates with a Sn composition up to 4.5% have been fabricated and characterized. The crystalline structure, surface morphology, and infrared (IR) absorption coefficient of the annealed GeSn thin films were carefully investigated. It was found that the GeSn thin films with a Sn composition of 4.5% annealed at 450 °C possessed a desirable polycrystalline structure according to X-ray diffraction (XRD) analyses and Raman spectroscopy analyses. In addition, the absorption coefficient of the polycrystalline GeSn thin films in the IR region was significantly better than that of the single crystalline bulk Ge.

  10. Vertical Ge and GeSn heterojunction gate-all-around tunneling field effect transistors

    NASA Astrophysics Data System (ADS)

    Schulze, Jörg; Blech, Andreas; Datta, Arnab; Fischer, Inga A.; Hähnel, Daniel; Naasz, Sandra; Rolseth, Erlend; Tropper, Eva-Maria

    2015-08-01

    We present experimental results on the fabrication and characterization of vertical Ge and GeSn heterojunction Tunneling Field Effect Transistors (TFETs). A gate-all-around process with mesa diameters down to 70 nm is used to reduce leakage currents and improve electrostatic control of the gate over the transistor channel. An ION = 88.4 μA/μm at VDS = VG = -2 V is obtained for a TFET with a 10 nm Ge0.92Sn0.08 layer at the source/channel junction. We discuss further possibilities for device improvements.

  11. Ab initio molecular orbital study on the Ge-, Sn-, Zr- and Si/Ge-mixed silsesquioxanes.

    PubMed

    Kudo, Takako; Akasaka, Mitsutoshi; Gordon, Mark S

    2008-05-29

    For the purpose of designing new functional silsesquioxanes (POSS), the structure and stability of the analogous compounds of the heavier group 14 and 4 elements such as germanium (Ge-POSS), tin (Sn-POSS) and zirconium (Zr-POSS) analogues of POSS were investigated and compared with those of the parent POSS and the titanium analogue (Ti-POSS) with electronic structure theory calculations, including electron correlation effects. In order to obtain information about the metalloxane (-X-O-X-) linkage, the structures and properties of the building blocks of metallasilsesquioxanes, such as dimetalloxanes, H(OH)2XOX(OH)2H, X = Ge, Sn and Zr, and cyclometalloxanes, [H(OH)XO]n , n = 3-6, X = Ge, Sn and Zr, were examined. The stability of the Si/Ge-mixed POSS were also studied in comparison with POSS and the completely germanium-substituted POSS. PMID:18444638

  12. Investigation of Ge1-xSnx/Ge with high Sn composition grown at low-temperature

    NASA Astrophysics Data System (ADS)

    Yu, I. S.; Wu, T. H.; Wu, K. Y.; Cheng, H. H.; Mashanov, V. I.; Nikiforov, A. I.; Pchelyakov, O. P.; Wu, X. S.

    2011-12-01

    We report on experimental investigations of the growth of Ge1-xSnx film with thickness above the critical thickness using Molecular Beam Epitaxy. A series of Ge1-xSnx films with various Sn compositions up to 14% are deposited on a Ge buffer layer for growth at low temperatures close to the melting point of Sn. Analysis of various measurements shows that the Ge1-xSnx film is defect free in the XTEM image and that Sn is distributed almost uniformly in the film for Sn compositions up to 9.3%. The Sn composition of the films is higher than the Sn composition that is theoretically predicted to cause the energy band of Ge to change from an indirect to a direct bandgap; thus, the present investigation provides a method for growing direct bandgap GeSn film, which is desired for use in applications involving optoelectronic devices.

  13. Site segregation in model clusters of small bimetallic RuGe and RuSn aggregates

    SciTech Connect

    Goursot, A.; Pedocchi, L.; Coq, B.

    1994-09-01

    RuGe and RuSn model clusters in both fixed bulk and relaxed structures are studied for stability during relaxation. Distortion causes a reduction in coordination of the Sn or Ge atom. Relaxation causes the Ge to have a small preference for the corner site (low coordination), but the Sn has a large corner site preference. 45 refs., 1 fig., 4 tabs.

  14. Sn-enriched Ge/GeSn nanostructures grown by MBE on (001) GaAs and Si wafers

    SciTech Connect

    Sadofyev, Yu. G. Martovitsky, V. P.; Klekovkin, A. V.; Saraykin, V. V.; Vasil’evskii, I. S.

    2015-12-15

    Elastically stressed metastable GeSn layers with a tin molar fraction as large as 0.185 are grown on (001) Si and GaAs wafers covered with a germanium buffer layer. A set of wafers with a deviation angle in the range 0°–10° is used. It is established that the GeSn crystal undergoes monoclinic deformation with the angle β to 88° in addition to tetragonal deformation. Misorientation of the wafers surface results in increasing efficiency of the incorporation of tin adatoms into the GeSn crystal lattice. Phase separation in the solid solution upon postgrowth annealing of the structures begins long before the termination of plastic relaxation of elastic heteroepitaxial stresses. Tin released as a result of GeSn decomposition predominantly tends to be found on the surface of the sample. Manifestations of the brittle–plastic mechanism of the relaxation of stresses resulting in the occurrence of microcracks in the subsurface region of the structures under investigation are found.

  15. Strain relaxation and Sn segregation in GeSn epilayers under thermal treatment

    NASA Astrophysics Data System (ADS)

    Li, H.; Cui, Y. X.; Wu, K. Y.; Tseng, W. K.; Cheng, H. H.; Chen, H.

    2013-06-01

    We report the effects of thermal annealing on the characteristics of GeSn epilayers grown on Ge-buffered Si wafers with a high Sn content near a threshold value that affords a direct bandgap. On annealing at temperatures below 400 °C, the characteristics of the epilayer remain unchanged, compared to those of the as-grown samples. On annealing the samples at a temperature in the range of 440-540 °C, strain relaxation in the epilayer is observed, accompanied by generation of misfit dislocations at the GeSn/Ge interface. A further increase in annealing temperature beyond 580 °C causes not only a relaxation in strain but also a change in the microstructure of the epilayer. In addition, Sn forms clusters and segregates to the surface, resulting in a reduction in the Sn content of the epilayer. The present investigation shows changes in the characteristics of the film under thermal treatment, providing an insight into the physical properties of such devices.

  16. Temperature dependent band gaps of GeSiSn alloys grown on Ge buffered Si substrates

    NASA Astrophysics Data System (ADS)

    Fernando, Nalin; Nunley, T. N.; Zollner, S.; Xu, C.; Menendez, J.; Kouvetakis, J.

    2015-03-01

    Band gap engineering of Ge by controlling tensile strain and alloying with Si and Sn has attracted great interest. Ge1 - x - ySixSny ternary alloy with two compositional degrees of freedom allows decoupling lattice constant and electronic structures. Hence it is important to determine the temperature and compositional dependence of optical properties of these materials. The complex pseudodielectric functions of Ge films grown on Si(100) and GeSiSn grown on buffered Ge were measured using spectroscopic ellipsometry in the 0.76-6.6 eV energy range between 77-800 K to investigate the E1 and E1 +Δ1 critical point (CP) energies. CP energies and related parameters were obtained by analyzing the second-derivative d2 ɛ /d2 ω of the dielectric function. Our experimental results are in good agreement with the theoretically predicted E1CP energy shift of Ge on Si due to strain generated by thermal expansivity mismatch. We will discuss the compositional dependence of the E1 and E1 +Δ1 CP energies of GeSiSn alloys and effects of temperature on shifting CP energies.

  17. Electrical characterization of p-GeSn/n-Ge diodes with interface traps under dc and ac regimes

    NASA Astrophysics Data System (ADS)

    Baert, B.; Gupta, S.; Gencarelli, F.; Loo, R.; Simoen, E.; Nguyen, N. D.

    2015-08-01

    In this work, the electrical properties of p-GeSn/n-Ge diodes are investigated in order to assess the impact of defects at the interface between Ge and GeSn using temperature-dependent current-voltage and capacitance-voltage measurements. These structures are made from GeSn epitaxial layers grown by CVD on Ge with in situ doping by Boron. As results, an average ideality factor of 1.2 has been determined and an activation energy comprised between 0.28 eV and 0.30 eV has been extracted from the temperature dependence of the reverse-bias current. Based on the comparison with numerical results obtained from device simulations, we explain this activation energy by the presence of traps located near the GeSn/Ge interface.

  18. Doping and strain dependence of the electronic band structure in Ge and GeSn alloys

    NASA Astrophysics Data System (ADS)

    Xu, Chi; Gallagher, James; Senaratne, Charutha; Brown, Christopher; Fernando, Nalin; Zollner, Stefan; Kouvetakis, John; Menendez, Jose

    2015-03-01

    A systematic study of the effect of dopants and strain on the electronic structure of Ge and GeSn alloys is presented. Samples were grown by UHV-CVD on Ge-buffered Si using Ge3H8 and SnD4 as the sources of Ge and Sn, and B2H6/P(GeH3)3 as dopants. High-energy critical points in the joint-density of electronic states were studied using spectroscopic ellipsometry, which yields detailed information on the strain and doping dependence of the so-called E1, E1 +Δ1 , E0' and E2 transitions. The corresponding dependencies of the lowest direct band gap E0 and the fundamental indirect band gap Eindwere studied via room-T photoluminescence spectroscopy. Of particular interest for this work were the determination of deformation potentials, band gap renormalization effects, Burstein-Moss shifts due to the presence of carriers at band minima, and the dependence of other critical point parameters, such as amplitudes and phase angles, on the doping concentration. The selective blocking of transitions due to high doping makes it possible to investigate the precise k-space location of critical points. These studies are complemented with detailed band-structure calculations within a full-zone k-dot- p approach. Supported by AFOSR under DOD AFOSR FA9550-12-1-0208 and DOD AFOSR FA9550-13-1-0022.

  19. Buffer-Free GeSn and SiGeSn Growth on Si Substrate Using In Situ SnD4 Gas Mixing

    NASA Astrophysics Data System (ADS)

    Mosleh, Aboozar; Alher, Murtadha; Cousar, Larry C.; Du, Wei; Ghetmiri, Seyed Amir; Al-Kabi, Sattar; Dou, Wei; Grant, Perry C.; Sun, Greg; Soref, Richard A.; Li, Baohua; Naseem, Hameed A.; Yu, Shui-Qing

    2016-04-01

    Buffer-free GeSn and SiGeSn films have been deposited on Si via a cold-wall, ultra-high vacuum chemical vapor deposition reactor using in situ gas mixing of deuterated stannane, silane and germane. Material characterization of the films using x-ray diffraction and transmission electron microscopy shows crystalline growth with an array of misfit dislocation formed at the Si substrate interface. Energy dispersive x-ray maps attained from the samples show uniform incorporation of the elements. The Z-contrast map of the high-angle annular dark-field of the film cross section shows uniform incorporation along the growth as well. Optical characterization of the GeSn films through photoluminescence technique shows reduction in the bandgap edge of the materials.

  20. Giant Seebeck effect in Ge-doped SnSe

    PubMed Central

    Gharsallah, M.; Serrano-Sánchez, F.; Nemes, N. M.; Mompeán, F. J.; Martínez, J. L.; Fernández-Díaz, M. T.; Elhalouani, F.; Alonso, J. A.

    2016-01-01

    Thermoelectric materials may contribute in the near future as new alternative sources of sustainable energy. Unprecedented thermoelectric properties in p-type SnSe single crystals have been recently reported, accompanied by extremely low thermal conductivity in polycrystalline samples. In order to enhance thermoelectric efficiency through proper tuning of this material we report a full structural characterization and evaluation of the thermoelectric properties of novel Ge-doped SnSe prepared by a straightforward arc-melting method, which yields nanostructured polycrystalline samples. Ge does not dope the system in the sense of donating carriers, yet the electrical properties show a semiconductor behavior with resistivity values higher than that of the parent compound, as a consequence of nanostructuration, whereas the Seebeck coefficient is higher and thermal conductivity lower, favorable to a better ZT figure of merit. PMID:27251233

  1. Giant Seebeck effect in Ge-doped SnSe.

    PubMed

    Gharsallah, M; Serrano-Sánchez, F; Nemes, N M; Mompeán, F J; Martínez, J L; Fernández-Díaz, M T; Elhalouani, F; Alonso, J A

    2016-01-01

    Thermoelectric materials may contribute in the near future as new alternative sources of sustainable energy. Unprecedented thermoelectric properties in p-type SnSe single crystals have been recently reported, accompanied by extremely low thermal conductivity in polycrystalline samples. In order to enhance thermoelectric efficiency through proper tuning of this material we report a full structural characterization and evaluation of the thermoelectric properties of novel Ge-doped SnSe prepared by a straightforward arc-melting method, which yields nanostructured polycrystalline samples. Ge does not dope the system in the sense of donating carriers, yet the electrical properties show a semiconductor behavior with resistivity values higher than that of the parent compound, as a consequence of nanostructuration, whereas the Seebeck coefficient is higher and thermal conductivity lower, favorable to a better ZT figure of merit. PMID:27251233

  2. Giant Seebeck effect in Ge-doped SnSe

    NASA Astrophysics Data System (ADS)

    Gharsallah, M.; Serrano-Sánchez, F.; Nemes, N. M.; Mompeán, F. J.; Martínez, J. L.; Fernández-Díaz, M. T.; Elhalouani, F.; Alonso, J. A.

    2016-06-01

    Thermoelectric materials may contribute in the near future as new alternative sources of sustainable energy. Unprecedented thermoelectric properties in p-type SnSe single crystals have been recently reported, accompanied by extremely low thermal conductivity in polycrystalline samples. In order to enhance thermoelectric efficiency through proper tuning of this material we report a full structural characterization and evaluation of the thermoelectric properties of novel Ge-doped SnSe prepared by a straightforward arc-melting method, which yields nanostructured polycrystalline samples. Ge does not dope the system in the sense of donating carriers, yet the electrical properties show a semiconductor behavior with resistivity values higher than that of the parent compound, as a consequence of nanostructuration, whereas the Seebeck coefficient is higher and thermal conductivity lower, favorable to a better ZT figure of merit.

  3. GeSn waveguide structures for efficient light detection and emission

    NASA Astrophysics Data System (ADS)

    Lin, You-Long; Huang, Yu-Hui; Chen, Shao-Wei; Chang, Guo-En

    2015-02-01

    We report the fabrication and characterization of GeSn waveguide structures on Si substrates grown by molecular beam epitaxy for efficient light-detection and emission. For photodetectors, GeSn waveguide structures exhibit a higher optical response compared to a reference Ge device as revealed by the photocurrent experiments. For light-emission, room-temperature photoluminescence experiments show a redshifted emission wavelength for the GeSn samples compared to the Ge reference sample due to the Sn incorporation. Besides, we observe ripple characteristics in the amplified spontaneous emission spectrum of the GeSn waveguide structure, which are attributed to the waveguide modes. Those results suggest that GeSn waveguide structures are promising for high-performance Si-based lightdetectors and emitters integrable with Si electronics.

  4. Formation of GeSn alloy on Si(100) by low-temperature molecular beam epitaxy

    SciTech Connect

    Talochkin, A. B.; Mashanov, V. I.

    2014-12-29

    GeSn alloys grown on Si(100) by the low-temperature (100 °C) molecular beam epitaxy are studied using scanning tunneling microscopy and Raman spectroscopy. It is found that the effect of Sn as a surfactant modifies substantially the low-temperature growth mechanism of Ge on Si. Instead of the formation of small Ge islands surrounded by amorphous Ge, in the presence of Sn, the growth of pure Ge islands appears via the Stranski-Krastanov growth mode, and a partially relaxed Ge{sub 1−x}Sn{sub x} alloy layer with the high Sn-fraction up to 40 at. % is formed in the area between them. It is shown that the observed growth mode induced by high surface mobility of Sn and the large strain of the pseudomorphic state of Ge to Si ensures the minimum elastic-strain energy of the structure.

  5. Giant piezoelectricity of monolayer group IV monochalcogenides: SnSe, SnS, GeSe, and GeS

    NASA Astrophysics Data System (ADS)

    Fei, Ruixiang; Li, Wenbin; Li, Ju; Yang, Li

    2015-10-01

    We predict enormous, anisotropic piezoelectric effects in intrinsic monolayer group IV monochalcogenides (MX, M=Sn or Ge, X=Se or S), including SnSe, SnS, GeSe, and GeS. Using first-principle simulations based on the modern theory of polarization, we find that their piezoelectric coefficients are about one to two orders of magnitude larger than those of other 2D materials, such as MoS2 and GaSe, and bulk quartz and AlN which are widely used in industry. This enhancement is a result of the unique "puckered" C2v symmetry and electronic structure of monolayer group IV monochalcogenides. Given the achieved experimental advances in the fabrication of monolayers, their flexible character, and ability to withstand enormous strain, these 2D structures with giant piezoelectric effects may be promising for a broad range of applications such as nano-sized sensors, piezotronics, and energy harvesting in portable electronic devices.

  6. Giant piezoelectricity of monolayer group IV monochalcogenides: SnSe, SnS, GeSe, and GeS

    SciTech Connect

    Fei, Ruixiang; Yang, Li; Li, Wenbin; Li, Ju

    2015-10-26

    We predict enormous, anisotropic piezoelectric effects in intrinsic monolayer group IV monochalcogenides (MX, M=Sn or Ge, X=Se or S), including SnSe, SnS, GeSe, and GeS. Using first-principle simulations based on the modern theory of polarization, we find that their piezoelectric coefficients are about one to two orders of magnitude larger than those of other 2D materials, such as MoS{sub 2} and GaSe, and bulk quartz and AlN which are widely used in industry. This enhancement is a result of the unique “puckered” C{sub 2v} symmetry and electronic structure of monolayer group IV monochalcogenides. Given the achieved experimental advances in the fabrication of monolayers, their flexible character, and ability to withstand enormous strain, these 2D structures with giant piezoelectric effects may be promising for a broad range of applications such as nano-sized sensors, piezotronics, and energy harvesting in portable electronic devices.

  7. Formation of GeSn alloy on Si(100) by low-temperature molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Talochkin, A. B.; Mashanov, V. I.

    2014-12-01

    GeSn alloys grown on Si(100) by the low-temperature (100 °C) molecular beam epitaxy are studied using scanning tunneling microscopy and Raman spectroscopy. It is found that the effect of Sn as a surfactant modifies substantially the low-temperature growth mechanism of Ge on Si. Instead of the formation of small Ge islands surrounded by amorphous Ge, in the presence of Sn, the growth of pure Ge islands appears via the Stranski-Krastanov growth mode, and a partially relaxed Ge1-xSnx alloy layer with the high Sn-fraction up to 40 at. % is formed in the area between them. It is shown that the observed growth mode induced by high surface mobility of Sn and the large strain of the pseudomorphic state of Ge to Si ensures the minimum elastic-strain energy of the structure.

  8. Liquid-Sn-driven lateral growth of poly-GeSn on insulator assisted by surface oxide layer

    NASA Astrophysics Data System (ADS)

    Kurosawa, Masashi; Taoka, Noriyuki; Sakashita, Mitsuo; Nakatsuka, Osamu; Miyao, Masanobu; Zaima, Shigeaki

    2013-09-01

    Effects of surface oxide layers on liquid-Sn-driven GeSn crystallization on insulators at various temperatures (<475 °C) are investigated. An amorphous Ge in neighborhood of patterned-Sn (<3.5 μm) becomes to polycrystalline Ge1-xSnx (x ≈ 0.025 - 0.14) after annealing at 150-475 °C, which is independent of the surface oxide thickness. Interestingly, a 50-μm-length lateral growth of polycrystalline Ge0.99Sn0.01 layers achieved by combination of thickening of the surface-oxide treated by NH4OH and annealing above melting temperature of Sn (231.9 °C). The growth length is 15 times longer than without the treatment. The advanced process promises to achieve group-IV-based optic and electronic devices on flexible substrates and Si platforms.

  9. GeSn p-i-n waveguide photodetectors on silicon substrates

    NASA Astrophysics Data System (ADS)

    Peng, Yu-Hsiang; Cheng, H. H.; Mashanov, Vladimir I.; Chang, Guo-En

    2014-12-01

    We report an investigation on GeSn p-i-n waveguide photodetectors grown on a Ge-buffered Si wafer. In comparison with a reference Ge detector, the GeSn detector shows an enhanced responsivity in the measured energy range, mainly attributed to the smaller bandgap caused by Sn-alloying. Analysis of the quantum efficiency indicates that increasing the Sn content in the active layers can significantly shorten the required device length to achieve the maximum efficiency. The present investigation demonstrates the planar photodetectors desired for monolithic integration with electronic devices.

  10. GeSn p-i-n waveguide photodetectors on silicon substrates

    SciTech Connect

    Peng, Yu-Hsiang; Chang, Guo-En; Cheng, H. H.; Mashanov, Vladimir I.

    2014-12-08

    We report an investigation on GeSn p-i-n waveguide photodetectors grown on a Ge-buffered Si wafer. In comparison with a reference Ge detector, the GeSn detector shows an enhanced responsivity in the measured energy range, mainly attributed to the smaller bandgap caused by Sn-alloying. Analysis of the quantum efficiency indicates that increasing the Sn content in the active layers can significantly shorten the required device length to achieve the maximum efficiency. The present investigation demonstrates the planar photodetectors desired for monolithic integration with electronic devices.

  11. Sn-based Ge/Ge0.975Sn0.025/Ge p-i-n photodetector operated with back-side illumination

    NASA Astrophysics Data System (ADS)

    Chang, C.; Li, H.; Huang, S. H.; Cheng, H. H.; Sun, G.; Soref, R. A.

    2016-04-01

    We report an investigation of a GeSn-based p-i-n photodetector grown on a Ge wafer that collects light signal from the back of the wafer. Temperature dependent absorption measurements performed over a wide temperature range (300 K down to 25 K) show that (a) absorption starts at the indirect bandgap of the active GeSn layer and continues up to the direct bandgap of the Ge wafer, and (b) the peak responsivity increases rapidly at first with decreasing temperature, then increases more slowly, followed by a decrease at the lower temperatures. The maximum responsivity happens at 125 K, which can easily be achieved with the use of liquid nitrogen. The temperature dependence of the photocurrent is analyzed by taking into consideration of the temperature dependence of the electron and hole mobility in the active layer, and the analysis result is in reasonable agreement with the data in the temperature regime where the rapid increase occurs. This investigation demonstrates the feasibility of a GeSn-based photodiode that can be operated with back-side illumination for applications in image sensing systems.

  12. GeOx interfacial layer scavenging remotely induced by metal electrode in metal/HfO2/GeOx/Ge capacitors

    NASA Astrophysics Data System (ADS)

    Lee, Taehoon; Jung, Yong Chan; Seong, Sejong; Lee, Sung Bo; Park, In-Sung; Ahn, Jinho

    2016-07-01

    The metal gate electrodes of Ni, W, and Pt have been investigated for their scavenging effect: a reduction of the GeOx interfacial layer (IL) between HfO2 dielectric and Ge substrate in metal/HfO2/GeOx/Ge capacitors. All the capacitors were fabricated using the same process except for the material used in the metal electrodes. Capacitance-voltage measurements, scanning transmission electron microscopy, and electron energy loss spectroscopy were conducted to confirm the scavenging of GeOx IL. Interestingly, these metals are observed to remotely scavenge the interfacial layer, reducing its thickness in the order of Ni, W, and then Pt. The capacitance equivalent thickness of these capacitors with Ni, W, and Pt electrodes are evaluated to be 2.7 nm, 3.0 nm, and 3.5 nm, and each final remnant physical thickness of GeOx IL layer is 1.1 nm 1.4 nm, and 1.9 nm, respectively. It is suggested that the scavenging effect induced by the metal electrodes is related to the concentration of oxygen vacancies generated by oxidation reaction at the metal/HfO2 interface.

  13. Sn diffusion during Ni germanide growth on Ge1-xSnx

    NASA Astrophysics Data System (ADS)

    Demeulemeester, J.; Schrauwen, A.; Nakatsuka, O.; Zaima, S.; Adachi, M.; Shimura, Y.; Comrie, C. M.; Fleischmann, C.; Detavernier, C.; Temst, K.; Vantomme, A.

    2011-11-01

    We report on the redistribution of Sn during Ni germanide formation on Ge1-xSnx/<Ge(100)> and its influence on the thin film growth and properties. These results show that the reaction involves the formation of Ni5Ge3 and NiGe. Sn redistributes homogenously in both phases, in which the Sn/Ge ratio retains the ratio of the as-deposited Ge1-xSnx film. Sn continues to diffuse after full NiGe formation and segregates in two regions: (1) at the interface between the germanide and Ge1-xSnx and (2) at the surface, which has major implications for the thin film and contact properties.

  14. Sn migration control at high temperature due to high deposition speed for forming high-quality GeSn layer

    NASA Astrophysics Data System (ADS)

    Taoka, Noriyuki; Capellini, Giovanni; von den Driesch, Nils; Buca, Dan; Zaumseil, Peter; Schubert, Markus Andreas; Klesse, Wolfgang Matthias; Montanari, Michele; Schroeder, Thomas

    2016-03-01

    A key factor for controlling Sn migration during GeSn deposition at a high temperature of 400 °C was investigated. Calculated results with a simple model for the Sn migration and experimental results clarified that low-deposition-speed (vd) deposition with vd’s of 0.68 and 2.8 nm/min induces significant Sn precipitation, whereas high-deposition-speed (vd = 13 nm/min) deposition leads to high crystallinity and good photoluminescence spectrum of the GeSn layer. These results indicate that vd is a key parameter, and that control of Sn migration at a high temperature is possible. These results are of great relevance for the application of high-quality Sn-based alloys in future optoelectronics devices.

  15. Comparative studies of clustering effect, electronic and optical properties for GePb and GeSn alloys with low Pb and Sn concentration

    NASA Astrophysics Data System (ADS)

    Huang, Wenqi; Cheng, Buwen; Xue, Chunlai; Li, Chuanbo

    2014-06-01

    The first principle calculations are performed to study the impurity clustering effect, electronic and optical properties of GePb and GeSn alloys. The calculated results show that for a given concentration, the maximum impurity (Sn or Pb) clustered configuration is the most stable equilibrium structure (corresponding to the lowest total energy) which has the highest band gap. The calculated lattice constants and bulk modulus agree well with experimental and others' theoretical values. The calculated band structures of virtual crystal structure and super-cell structure both indicate that GePb alloys undergo a transition from indirect to direct band gap as Pb concentration increases, and the transitional concentration is much lower than that of GeSn alloy. This conclusion indicates that GePb alloy can be a very prospective material for fabricating group-IV laser. The density of states and charge density maps of GeSn and GePb alloys are analyzed comparatively. For optical properties, the dielectric function, absorption spectrum, reflectivity, refractive index and loss function of Ge22Sn2 and Ge22Pb2 are investigated in detail.

  16. Intermixing between HfO2 and GeO2 films deposited on Ge(001) and Si(001): Role of the substrate

    NASA Astrophysics Data System (ADS)

    Soares, G. V.; Krug, C.; Miotti, L.; Bastos, K. P.; Lucovsky, G.; Baumvol, I. J. R.; Radtke, C.

    2011-03-01

    Thermally driven atomic transport in HfO2/GeO2/substrate structures on Ge(001) and Si(001) was investigated in N2 ambient as function of annealing temperature and time. As-deposited stacks showed no detectable intermixing and no instabilities were observed on Si. On Ge, loss of O and Ge was detected in all annealed samples, presumably due to evolution of GeO from the GeO2/Ge interface. In addition, hafnium germanate is formed at 600 °C. Our data indicate that at 500 °C and above HfO2/GeO2 stacks are stable only if isolated from the Ge substrate.

  17. Pulse number controlled laser annealing for GeSn on insulator structure with high substitutional Sn concentration

    NASA Astrophysics Data System (ADS)

    Moto, Kenta; Matsumura, Ryo; Sadoh, Taizoh; Ikenoue, Hiroshi; Miyao, Masanobu

    2016-06-01

    Crystalline GeSn-on-insulator structures with high Sn concentration (>8%), which exceeds thermal equilibrium solid-solubility (˜2%) of Sn in Ge, are essential to achieve high-speed thin film transistors and high-efficiency optical devices. We investigate non-thermal equilibrium growth of Ge1-xSnx (0 ≤ x ≤ 0.2) on quartz substrates by using pulsed laser annealing (PLA). The window of laser fluence enabling complete crystallization without film ablation is drastically expanded (˜5 times) by Sn doping above 5% into Ge. Substitutional Sn concentration in grown layers is found to be increased with decreasing irradiation pulse number. This phenomenon can be explained on the basis of significant thermal non-equilibrium growth achieved by higher cooling rate after PLA with a lower pulse number. As a result, GeSn crystals with substitutional Sn concentration of ˜12% are realized at pulse irradiation of single shot for the samples with the initial Sn concentration of 15%. Raman spectroscopy and electron microscopy measurements reveal the high quality of the grown layer. This technique will be useful to fabricate high-speed thin film transistors and high-efficiency optical devices on insulating substrates.

  18. Investigation of Sn surface segregation during GeSn epitaxial growth by Auger electron spectroscopy and energy dispersive x-ray spectroscopy

    NASA Astrophysics Data System (ADS)

    Tsukamoto, Takahiro; Hirose, Nobumitsu; Kasamatsu, Akifumi; Mimura, Takashi; Matsui, Toshiaki; Suda, Yoshiyuki

    2015-02-01

    The mechanism of Sn surface segregation during the epitaxial growth of GeSn on Si (001) substrates was investigated by Auger electron spectroscopy and energy dispersive X-ray spectroscopy. Sn surface segregation depends on the growth temperature and Sn content of GeSn layers. During Sn surface segregation, Sn-rich nanoparticles form and move on the surface during the deposition, which results in a rough surface owing to facet formation. The Sn-rich nanoparticles moving on the surface during the deposition absorb Sn from the periphery and yield a lower Sn content, not on the surface but within the layer, because the Sn surface segregation and the GeSn deposition occur simultaneously. Sn surface segregation can occur at a lower temperature during the deposition compared with that during postannealing. This suggests that the Sn surface segregation during the deposition is strongly promoted by the migration of deposited Ge and Sn adatoms on the surface originating from the thermal effect of substrate temperature, which also suggests that limiting the migration of deposited Ge and Sn adatoms can reduce the Sn surface segregation and improve the crystallinity of GeSn layers.

  19. Towards simultaneous achievement of carrier activation and crystallinity in Ge and GeSn with heated phosphorus ion implantation: An optical study

    NASA Astrophysics Data System (ADS)

    D'Costa, Vijay Richard; Wang, Lanxiang; Wang, Wei; Lim, Sin Leng; Chan, Taw Kuei; Chua, Lye Hing; Henry, Todd; Zou, Wei; Hatem, Christopher; Osipowicz, Thomas; Tok, Eng Soon; Yeo, Yee-Chia

    2014-09-01

    We have investigated the optical properties of Ge and GeSn alloys implanted with phosphorus ions at 400 °C by spectroscopic ellipsometry from far-infrared to ultraviolet. The dielectric response of heated GeSn implants displays structural and transport properties similar to those of heated Ge implants. The far-infrared dielectric function of as-implanted Ge and GeSn shows the typical free carrier response which can be described by a single Drude oscillator. Bulk Ge-like critical points E1, E1 + Δ1, E0', and E2 are observed in the visible-UV dielectric function of heated Ge and GeSn indicating single crystalline quality of the as-implanted layers. Although the implantation at 400 °C recovers crystallinity in both Ge and GeSn, an annealing step is necessary to enhance the carrier activation.

  20. Carrier and heat transport properties of polycrystalline GeSn films on SiO2

    NASA Astrophysics Data System (ADS)

    Uchida, Noriyuki; Maeda, Tatsuro; Lieten, Ruben R.; Okajima, Shingo; Ohishi, Yuji; Takase, Ryohei; Ishimaru, Manabu; Locquet, Jean-Pierre

    2015-12-01

    We evaluated the potential of polycrystalline (poly-) GeSn as channel material for the fabrication of thin film transistors (TFTs) at a low thermal budget (<600 °C). Poly-GeSn films with a grain size of ˜50 nm showed a carrier mobility of ˜30 cm2 V-1 s-1 after low-temperature annealing at 475-500 °C. Not only carrier mobility but also thermal conductivity of the films is important in assessing the self-heating effect of the poly-GeSn channel TFT. The thermal conductivity of the poly-GeSn films is 5-9 W m-1 K-1, which is significantly lower compared with 30-60 W m-1 K-1 of bulk Ge; this difference results from phonon scattering at grain boundaries and Sn interstitials. The poly-GeSn films have higher carrier mobility and thermal conductivity than poly-Ge films annealed at 600 °C, because of the improved crystal quality and coarsened grain size resulting from Sn-induced crystallization. Therefore, the poly-GeSn film is well-suited as channel material for TFTs, fabricated with a low thermal budget.

  1. Electron dominated thermoelectric response in MNiSn (M: Ti, Zr, Hf) half-Heusler alloys.

    PubMed

    Gandi, Appala Naidu; Schwingenschlögl, Udo

    2016-05-18

    We solve the transport equations of the electrons and phonons to understand the thermoelectric behaviour of the technologically important half-Heusler alloys MNiSn (M: Ti, Zr, Hf). Doping is simulated within the rigid band approximation. We clarify the origin of the electron dominated thermoelectric response and determine the carrier concentrations with maximal figures of merit. The phonon mean free path is studied to calculate the grain size below which grain refinement methods can enforce ballistic heat conduction to enhance the figure of merit. PMID:27156360

  2. Compositional dependence of optical interband transition energies in GeSn and GeSiSn alloys

    NASA Astrophysics Data System (ADS)

    Xu, Chi; Senaratne, Charutha L.; Kouvetakis, John; Menéndez, José

    2015-08-01

    The dielectric functions of GeSn and GeSiSn alloys were measured in the 1-6 eV energy range using spectroscopic ellipsometry. The contributions from the E1, E1 + Δ1, E0‧, E2, and E1‧ critical points in the joint density of electronic states were enhanced by computing numerical second derivatives of the measured dielectric function, and the resulting lineshapes were fitted with model expressions from which the critical point energies, amplitudes, broadenings, and phases were determined. A detailed analysis of the compositional dependence of the different transition energies is presented. By describing this dependence in terms of quadratic polynomials, the bowing parameter (quadratic coefficient) for each transition is determined. It is shown that the bowing parameters in the ternary alloy follow a distinct chemical trend, in which the ternary is well described in terms of bowing parameters for the underlying binary alloys, and these bowing parameters increase as a function of the size and electronegativity mismatch of the alloy constituents.

  3. Biaxial stress evaluation in GeSn film epitaxially grown on Ge substrate by oil-immersion Raman spectroscopy

    NASA Astrophysics Data System (ADS)

    Takeuchi, Kazuma; Suda, Kohei; Yokogawa, Ryo; Usuda, Koji; Sawamoto, Naomi; Ogura, Atsushi

    2016-09-01

    GeSn is being paid much attention as a next-generation channel material. In this work, we performed the excitation of forbidden transverse optical (TO) phonons from strained GeSn, as well as longitudinal optical (LO) phonons, under the backscattering geometry from the (001) surface by oil-immersion Raman spectroscopy. Using the obtained LO/TO phonons, we derived the phonon deformation potentials (PDPs), which play an important role in the stress evaluation, of the strained Ge1‑ x Sn x for the first time. The results suggest that PDPs are almost constant for the Ge1‑ x Sn x (x < 0.032). Biaxial stress calculated using the derived PDPs reasonably indicated the isotropic states.

  4. High hole mobility GeSn on insulator formed by self-organized seeding lateral growth

    NASA Astrophysics Data System (ADS)

    Liu, Zhi; Wen, Juanjuan; Zhang, Xu; Li, Chuanbo; Xue, Chunlai; Zuo, Yuhua; Cheng, Buwen; Wang, Qiming

    2014-11-01

    Tensile strained single-crystal GeSn on insulator (GSOI) was obtained using self-organized seeding lateral growth. Segregation of Sn atoms and Sn distribution occurred during the lateral growth of the GeSn stripe. At both edges of the GSOI, Sn concentration distribution was found in good agreement with calculation based on the Scheil equation. P-channel metal-oxide-semiconductor field effect transistors were fabricated using the GSOI materials. Good transistor performance with the low field peak hole mobility of 383 cm2 V-1 s-1 was obtained, which indicated the high quality of this GSOI structure.

  5. Temperature varying photoconductivity of GeSn alloys grown by chemical vapor deposition with Sn concentrations from 4% to 11%

    NASA Astrophysics Data System (ADS)

    Hart, John; Adam, Thomas; Kim, Yihwan; Huang, Yi-Chiau; Reznicek, Alexander; Hazbun, Ramsey; Gupta, Jay; Kolodzey, James

    2016-03-01

    Pseudomorphic GeSn layers with Sn atomic percentages between 4.5% and 11.3% were grown by chemical vapor deposition using digermane and SnCl4 precursors on Ge virtual substrates grown on Si. The layers were characterized by x-ray diffraction rocking curves and reciprocal space maps. Photoconductive devices were fabricated, and the dark current was found to increase with Sn concentration. The responsivity of the photoconductors was measured at a wavelength of 1.55 μm using calibrated laser illumination at room temperature and a maximum value of 2.7 mA/W was measured for a 4.5% Sn device. Moreover, the responsivity for higher Sn concentration was found to increase with decreasing temperature. Spectral photoconductivity was measured using Fourier transform infrared spectroscopy. The photoconductive absorption edge continually increased in wavelength with increasing tin percentage, out to approximately 2.4 μm for an 11.3% Sn device. The direct band gap was extracted using Tauc plots and was fit to a bandgap model accounting for layer strain and Sn concentration. This direct bandgap was attributed to absorption from the heavy-hole band to the conduction band. Higher energy absorption was also observed, which was thought to be likely from absorption in the light-hole band. The band gaps for these alloys were plotted as a function of temperature. These experiments show the promise of GeSn alloys for CMOS compatible short wave infrared detectors.

  6. Superconductivity in HfCuGe2: A non-magnetic analog of the 1111 iron pnictides

    NASA Astrophysics Data System (ADS)

    Schoop, Leslie; Hirai, Daigorou; Felser, Claudia; Cava, R. J.

    2013-03-01

    Bulk superconductivity with a transition temperature Tc = 0.6 K is reported for the intermetallic compound HfCuGe2. HfCuGe2 is structurally related to the “1111” iron pnictide structure, which hosts a large number of Fe-based superconductors. It can therefore be viewed as a non-magnetic analog to the “1111”-type Fe-based superconductors.

  7. Photoconductivity of ultra-thin Ge(GeSn) layers grown in Si by low-temperature molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Talochkin, A. B.; Chistokhin, I. B.; Mashanov, V. I.

    2016-04-01

    Photoconductivity (PC) spectra of Si/Ge(GeSn)/Si structures with the ultra-thin (1.0-2.3 nm) Ge and GeSn alloy layers grown by the low-temperature (T = 100 °C) molecular beam epitaxy are studied. Photoresponse in the range of 1.2-0.4 eV related to light absorption in the buried Ge(GeSn) layer is observed. It is shown that in case of lateral PC, a simple diffusion model can be used to determine the absorption coefficient of this layer α ˜ 105 cm-1. This value is 100 times larger than that of a single Ge quantum dot layer and is reached significantly above the band gap of most bulk semiconductors. The observed absorption is caused by optical transitions between electron and hole states localized at the interfaces. The anomalous high value of α can be explained by the unusual state of Ge(GeSn) layer with high concentration of dangling bonds, the optical properties of which have been predicted theoretically by Knief and von Niessen (Phys. Rev. B 59, 12940 (1999)).

  8. Kesterite Cu2Zn(Sn,Ge)(S,Se)4 thin film with controlled Ge-doping for photovoltaic application.

    PubMed

    Zhao, Wangen; Pan, Daocheng; Liu, Shengzhong Frank

    2016-05-21

    Cu2ZnSn(S,Se)4 (CZTSSe) semiconductors have been a focus of extensive research effort owing to low-toxicity, high abundance and low material cost. Yet, the CZTSSe thin film solar cell has a low open-circuit voltage value that presents challenges. Herein, using GeSe2 as a new Ge source material, we have achieved a wider band gap CZTSSe-based semiconductor absorber layer with its band-gap controlled by adjusting the ratio of SnS2 : GeSe2 used. In addition, the Cu2Zn(Sn,Ge)(S,Se)4 thin films were prepared with optimal Ge doping (30%) and solar cells were fabricated to attain a respectable power conversion efficiency of 4.8% under 1.5 AM with an active area of 0.19 cm(2) without an anti-reflection layer. PMID:27121893

  9. Ultrathin GeSn p-channel MOSFETs grown directly on Si(111) substrate using solid phase epitaxy

    NASA Astrophysics Data System (ADS)

    Maeda, Tatsuro; Jevasuwan, Wipakorn; Hattori, Hiroyuki; Uchida, Noriyuki; Miura, Shu; Tanaka, Masatoshi; Santos, Nuno D. M.; Vantomme, André; Locquet, Jean-Pierre; Lieten, Ruben R.

    2015-04-01

    Ultrathin GeSn layers with a thickness of 5.5 nm are fabricated on a Si(111) substrate by solid phase epitaxy (SPE) of amorphous GeSn layers with Sn concentrations up to 6.7%. We demonstrate well-behaved depletion-mode operation of GeSn p-channel metal-oxide-semiconductor field-effect transistors (pMOSFETs) with an on/off ratio of more than 1000 owing to the ultrathin GeSn channel layer (5.5 nm). It is found that the on current increases significantly with increasing Sn concentration at the same gate overdrive, attributed to an increasing substitutional Sn incorporation in Ge. The GeSn (6.7%) layer sample shows approximately 90% enhancement in hole mobility in comparison with a pure Ge channel on Si.

  10. GeSn-on-insulator substrate formed by direct wafer bonding

    NASA Astrophysics Data System (ADS)

    Lei, Dian; Lee, Kwang Hong; Bao, Shuyu; Wang, Wei; Wang, Bing; Gong, Xiao; Tan, Chuan Seng; Yeo, Yee-Chia

    2016-07-01

    GeSn-on-insulator (GeSnOI) on Silicon (Si) substrate was realized using direct wafer bonding technique. This process involves the growth of Ge1-xSnx layer on a first Si (001) substrate (donor wafer) followed by the deposition of SiO2 on Ge1-xSnx, the bonding of the donor wafer to a second Si (001) substrate (handle wafer), and removal of the Si donor wafer. The GeSnOI material quality is investigated using high-resolution transmission electron microscopy, high-resolution X-ray diffraction (HRXRD), atomic-force microscopy, Raman spectroscopy, and spectroscopic ellipsometry. The Ge1-xSnx layer on GeSnOI substrate has a surface roughness of 1.90 nm, which is higher than that of the original Ge1-xSnx epilayer before transfer (surface roughness is 0.528 nm). The compressive strain of the Ge1-xSnx film in the GeSnOI is as low as 0.10% as confirmed using HRXRD and Raman spectroscopy.

  11. GeSn-based p-i-n photodiodes with strained active layer on a Si wafer

    NASA Astrophysics Data System (ADS)

    Tseng, H. H.; Li, H.; Mashanov, V.; Yang, Y. J.; Cheng, H. H.; Chang, G. E.; Soref, R. A.; Sun, G.

    2013-12-01

    We report an investigation of GeSn-based p-i-n photodiodes with an active GeSn layer that is almost fully strained. The results show that (a) the response of the Ge/GeSn/Ge heterojunction photodiodes is stronger than that of the reference Ge-based photodiodes at photon energies above the 0.8 eV direct bandgap of bulk Ge (<1.55 μm), and (b) the optical response extends to lower energy regions (1.55-1.80 μm wavelengths) as characterized by the strained GeSn bandgap. A cusp-like spectral characteristic is observed for samples with high Sn contents, which is attributed to the significant strain-induced energy splitting of heavy and light hole bands. This work represents a step forward in developing GeSn-based infrared photodetectors.

  12. Infrared electroluminescence from GeSn heterojunction diodes grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Gupta, Jay Prakash; Bhargava, Nupur; Kim, Sangcheol; Adam, Thomas; Kolodzey, James

    2013-06-01

    Infrared electroluminescence was observed from GeSn/Ge p-n heterojunction diodes with 8% Sn, grown by molecular beam epitaxy. The GeSn layers were boron doped, compressively strained, and pseudomorphic on Ge substrates. Spectral measurements indicated an emission peak at 0.57 eV, about 50 meV wide, increasing in intensity with applied pulsed current, and with reducing device temperatures. The total integrated emitted power from a single edge facet was 54 μW at an applied peak current of 100 mA at 100 K. These results suggest that GeSn-based materials maybe useful for practical light emitting diodes operating in the infrared wavelength range near 2 μm.

  13. Unusual Yb magnetic properties in YbMn6Ge1.8-xSn4.2Gax and YbMn6Ge1.8Sn4.2-yGay

    NASA Astrophysics Data System (ADS)

    Eichenberger, L.; Malaman, B.; Mazet, T.

    2016-05-01

    We investigate the magnetic properties of the new HfFe6Ge6-type (P6/mmm) YbMn6Ge1.8-xSn4.2Gax (x=0.05, 0.4 and 0.9) and YbMn6Ge1.8Sn4.2-yGay (y=0.05, 0.5 and 1.0) alloys from DC magnetization and powder neutron diffraction experiments. The electronic structure modifications induced by the Ga substitution are found to promote the ferromagnetic order of the Mn sublattice, to enhance the Yb ordering temperature (up to TYb∼170 K) and to strongly increase the low-temperature coercive field (up to μ0Hc∼1 T). By contrast, the changes in the Yb magnetic moment magnitude upon Ga substitution are analyzed to be mainly driven by chemical pressure effects. The reduced Yb magnetic moment (1.0 μB

  14. Absorption coefficients of GeSn extracted from PIN photodetector response

    NASA Astrophysics Data System (ADS)

    Ye, Kaiheng; Zhang, Wogong; Oehme, Michael; Schmid, Marc; Gollhofer, Martin; Kostecki, Konrad; Widmann, Daniel; Körner, Roman; Kasper, Erich; Schulze, Jörg

    2015-08-01

    In this paper the optical absorption of the GeSn PIN photodetector was investigated. The vertical GeSn PIN photodetectors were fabricated by molecular beam epitaxy (MBE) and dry etching. By means of current density-voltage (J-V) and capacity-voltage (C-V) measurements the photodetector device was characterized. The absorption coefficients of GeSn material were finally extracted from the optical response of PIN structure. With further direct bandgap analysis the influences of device structure was proved negligible.

  15. Theoretical calculation of performance enhancement in lattice-matched SiGeSn/GeSn p-channel tunneling field-effect transistor with type-II staggered tunneling junction

    NASA Astrophysics Data System (ADS)

    Wang, Hongjuan; Han, Genquan; Wang, Yibo; Peng, Yue; Liu, Yan; Zhang, Chunfu; Zhang, Jincheng; Hu, Shengdong; Hao, Yue

    2016-04-01

    In this work, a lattice-matched SiGeSn/GeSn heterostructure p-channel tunneling field-effect transistor (hetero-PTFET) with a type-II staggered tunneling junction (TJ) is investigated theoretically. Lattice matching and type-II band alignment at the Γ-point is obtained at the SiGeSn/GeSn interface by tuning Sn and Si compositions. A steeper subthreshold swing (SS) and a higher on state current (I ON) are demonstrated in SiGeSn/GeSn hetero-PTFET than in GeSn homo-PTFET. Si0.31Ge0.49Sn0.20/Ge0.88Sn0.12 hetero-PTFET achieves a 2.3-fold higher I ON than Ge0.88Sn0.12 homo-PTFET at V DD of 0.3 V. Hetero-PTFET achieves a more abrupt hole profile and a higher carrier density near TJ than the homo-PTFET, which contributes to the significantly enhanced band-to-band tunneling (BTBT) rate and tunneling current in hetero-PTFET.

  16. Density functional theory study of adsorption and dissociation of HfCl4 and H2O on Ge /Si(100)-(2×1): Initial stage of atomic layer deposition of HfO2 on SiGe surface

    NASA Astrophysics Data System (ADS)

    Chen, Wei; Lu, Hong-Liang; Zhang, David Wei; Xu, Min; Ren, Jie; Zhang, Jian-Yun; Wang, Ji-Tao; Wang, Li-Kang

    2005-04-01

    We have investigated adsorption and dissociation of water and HfCl4 on Ge /Si(100)-(2×1) surface with density functional theory. The Si-Ge heterodimer and Ge-Ge homodimer are employed to represent the Si1-xGex surface. The activation energy for adsorption of water on Ge-Ge homodimer is much higher than that on Si-Ge heterodimer. No net activation barrier exists during the adsorption of HfCl4 on both SiGe surface dimers. The differences in the potential energy surface between reactions on Si-Ge and Ge-Ge dimers are due to different bond strengths. It should also be noticed that the activation energy for HfCl4 is quite flat, thus HfCl4 adsorbs and dissociates on Ge /Si(100)-(2×1) easily.

  17. Metal-HfO{sub 2}-Ge capacitor: Its enhanced charge trapping properties with S-treated substrate and atomic-layer-deposited HfO{sub 2} layer

    SciTech Connect

    Park, In-Sung; Jung, Yong Chan; Seong, Sejong; Ahn, Jinho; Lee, Sung Bo

    2015-01-15

    The charge trapping properties of metal-HfO{sub 2}-Ge capacitor as a nonvolatile memory have been investigated with (NH{sub 4}){sub 2}S-treated Ge substrate and atomic-layer-deposited HfO{sub 2} layer. The interfacial layer generated by (NH{sub 4}){sub 2}S-treated Ge substrate reveals a trace of -S- bonding, very sharp interface edges, and smooth surface morphology. The Ru-HfO{sub 2}-Ge capacitor with (NH{sub 4}){sub 2}S-treated Ge substrate shows an enhanced interface state with little frequency dispersion, a lower leakage current, and very reliable properties with the enhanced endurance and retention than Ru-HfO{sub 2}-Ge capacitor with cyclic-cleaned Ge substrate.

  18. Direct-bandgap GeSn grown on silicon with 2230 nm photoluminescence

    NASA Astrophysics Data System (ADS)

    Ghetmiri, Seyed Amir; Du, Wei; Margetis, Joe; Mosleh, Aboozar; Cousar, Larry; Conley, Benjamin R.; Domulevicz, Lucas; Nazzal, Amjad; Sun, Greg; Soref, Richard A.; Tolle, John; Li, Baohua; Naseem, Hameed A.; Yu, Shui-Qing

    2014-10-01

    Material and optical characterizations have been conducted for epitaxially grown Ge1-xSnx thin films on Si with Sn composition up to 10%. A direct bandgap Ge0.9Sn0.1 alloy has been identified by temperature-dependent photoluminescence (PL) study based on the single peak spectrum and the narrow line-width. Room temperature PL emission as long as 2230 nm has also been observed from the same sample.

  19. Interaction of Sn atoms with defects introduced by ion implantation in Ge substrate

    SciTech Connect

    Taoka, Noriyuki Fukudome, Motoshi; Takeuchi, Wakana; Arahira, Takamitsu; Sakashita, Mitsuo; Nakatsuka, Osamu; Zaima, Shigeaki

    2014-05-07

    The interaction of Sn atoms with defects induced by Sn implantation of Ge substrates with antimony (Sb) as an n-type dopant and the impact of H{sub 2} annealing on these defects were investigated by comparison with defects induced by Ge self-implantation. In the Ge samples implanted with either Sn or Ge, and annealed at temperatures of less than 200 °C, divacancies, Sb-vacancy complexes with single or double acceptor-like states, and defects related to Sb and interstitial Ge atoms were present. On the other hand, after annealing at 500 °C in an N{sub 2} or H{sub 2} atmosphere, defects with different structures were observed in the Sn-implanted samples by deep level transition spectroscopy. The energy levels of the defects were 0.33 eV from the conduction band minimum and 0.55 eV from the valence band maximum. From the capacitance-voltage (C-V) characteristics, interaction between Sn atoms and defects after annealing at 500 °C was observed. The effect of H{sub 2} annealing at around 200 °C was observed in the C-V characteristics, which can be attributed to hydrogen passivation, and this effect was observed in both the Ge- and Sn-implanted samples. These results suggest the presence of defects that interact with Sn or hydrogen atoms. This indicates the possibility of defect control in Ge substrates by Sn or hydrogen incorporation. Such defect control could yield high-performance Ge-based devices.

  20. Compositional dependence of optical critical point parameters in pseudomorphic GeSn alloys

    NASA Astrophysics Data System (ADS)

    D'Costa, Vijay Richard; Wang, Wei; Zhou, Qian; Chan, Taw Kuei; Osipowicz, Thomas; Tok, Eng Soon; Yeo, Yee-Chia

    2014-08-01

    Spectroscopic ellipsometry was used to investigate the optical response of pseudomorphic Ge1-xSnx (0 ≤ x ≤ 0.17) alloys grown directly on Ge (100) by molecular beam epitaxy. A detailed compositional study of amplitudes, broadenings, energies, and phase angles associated with critical points E1, E1 + Δ1, E 0 ', and E2 of GeSn alloys was carried out using a derivative analysis. The results can be understood in terms of the electronic bandstructure of Ge or relaxed GeSn alloys with the following differences. First, broadening parameters in pseudomorphic alloys are found to have lower values compared to relaxed alloys indicating lower dislocation density in our pseudomorphic alloys relative to relaxed alloys. Second, the amplitudes of E1 and E1 + Δ1 are enhanced and reduced, respectively, with respect to relaxed GeSn alloys, and the trends are captured using the k.p method as a biaxial stress induced effect. Third, phase angles are lower than Ge for all the critical points suggesting reduction of excitonic effects in GeSn with respect to Ge.

  1. Dispersion of nonresonant third-order nonlinearities in GeSiSn ternary alloys.

    PubMed

    De Leonardis, Francesco; Troia, Benedetto; Soref, Richard A; Passaro, Vittorio M N

    2016-01-01

    Silicon (Si), tin (Sn), and germanium (Ge) alloys have attracted research attention as direct band gap semiconductors with applications in electronics and optoelectronics. In particular, GeSn field effect transistors can exhibit very high performance in terms of power reduction and operating speed because of the high electron drift mobility, while the SiGeSn system can be constructed using CMOS-compatible techniques to realize lasers, LED, and photodetectors. The wide Si, Ge and Sn transparencies allow the use of binary and ternary alloys extended to mid-IR wavelengths, where nonlinearities can also be employed. However, neither theoretical or experimental predictions of nonlinear features in SiGeSn alloys are reported in the literature. For the first time, a rigorous and detailed physical investigation is presented to estimate the two photon absorption (TPA) coefficient and the Kerr refractive index for the SiGeSn alloy up to 12 μm. The TPA spectrum, the effective TPA wavelength cut-off, and the Kerr nonlinear refractive index have been determined as a function of alloy compositions. The promising results achieved can pave the way to the demonstration of on-chip nonlinear-based applications, including mid-IR spectrometer-on-a-chip, all-optical wavelength down/up-conversion, frequency comb generation, quantum-correlated photon-pair source generation and supercontinuum source creation, as well as Raman lasing. PMID:27622979

  2. Contact resistivities of antimony-doped n-type Ge1‑x Sn x

    NASA Astrophysics Data System (ADS)

    Senthil Srinivasan, V. S.; Fischer, Inga A.; Augel, Lion; Hornung, Anja; Koerner, Roman; Kostecki, Konrad; Oehme, Michael; Rolseth, Erlend; Schulze, Joerg

    2016-08-01

    As Ge1‑x Sn x is being investigated for CMOS applications, obtaining contacts to n-type Ge1‑x Sn x with low specific contact resistivity (ρ c) is a major concern. Here, we present results on specific contact resistivities of Sb doped n-type Ge1‑x Sn x with 0 ≤ x ≤ 0.08 also with varying doping concentrations using Ni, Ag and Mn as contact metals. Our results show that Ni offers the lowest ρ c for all x values of Ge1‑x Sn x . The lowest ρ c measured for Ni contacts on highly n-doped Ge0.92Sn0.08 is 2.29 × 10‑6 Ω cm2. We find a strong dependence of the specific contact resistivity on doping, which we attribute to the fact that strong Fermi level pinning is present in metal/n-Ge1‑x Sn x contacts.

  3. Kesterite Cu2Zn(Sn,Ge)(S,Se)4 thin film with controlled Ge-doping for photovoltaic application

    NASA Astrophysics Data System (ADS)

    Zhao, Wangen; Pan, Daocheng; Liu, Shengzhong (Frank)

    2016-05-01

    Cu2ZnSn(S,Se)4 (CZTSSe) semiconductors have been a focus of extensive research effort owing to low-toxicity, high abundance and low material cost. Yet, the CZTSSe thin film solar cell has a low open-circuit voltage value that presents challenges. Herein, using GeSe2 as a new Ge source material, we have achieved a wider band gap CZTSSe-based semiconductor absorber layer with its band-gap controlled by adjusting the ratio of SnS2 : GeSe2 used. In addition, the Cu2Zn(Sn,Ge)(S,Se)4 thin films were prepared with optimal Ge doping (30%) and solar cells were fabricated to attain a respectable power conversion efficiency of 4.8% under 1.5 AM with an active area of 0.19 cm2 without an anti-reflection layer.Cu2ZnSn(S,Se)4 (CZTSSe) semiconductors have been a focus of extensive research effort owing to low-toxicity, high abundance and low material cost. Yet, the CZTSSe thin film solar cell has a low open-circuit voltage value that presents challenges. Herein, using GeSe2 as a new Ge source material, we have achieved a wider band gap CZTSSe-based semiconductor absorber layer with its band-gap controlled by adjusting the ratio of SnS2 : GeSe2 used. In addition, the Cu2Zn(Sn,Ge)(S,Se)4 thin films were prepared with optimal Ge doping (30%) and solar cells were fabricated to attain a respectable power conversion efficiency of 4.8% under 1.5 AM with an active area of 0.19 cm2 without an anti-reflection layer. Electronic supplementary information (ESI) available: The XRD patterns, chemical component analysis, top-view and cross-sectional images, and XPS of CZTGSSe thin films with different Ge content are exhibited. See DOI: 10.1039/c6nr00959j

  4. Rapid solidification and dendrite growth of ternary Fe-Sn-Ge and Cu-Pb-Ge monotectic alloys

    NASA Astrophysics Data System (ADS)

    Zhang, Xuehua; Ruan, Ying; Wang, Weili; Wei, Bingbo

    2007-08-01

    The phase separation and dendrite growth characteristics of ternary Fe-43.9%Sn-10%Ge and Cu-35.5%Pb-5%Ge monotectic alloys were studied systematically by the glass fluxing method under substantial undercooling conditions. The maximum undercoolings obtained in this work are 245 and 257 K, respectively, for these two alloys. All of the solidified samples exhibit serious macrosegregation, indicating that the homogenous alloy melt is separated into two liquid phases prior to rapid solidification. The solidification structures consist of four phases including α-Fe, (Sn), FeSn and FeSn2 in Fe-43.9%Sn-10%Ge ternary alloy, whereas only (Cu) and (Pb) solid solution phases in Cu-35.5%Pb-5%Ge alloy under different undercoolings. In the process of rapid monotectic solidification, α-Fe and (Cu) phases grow in a dendritic mode, and the transition “dendrite→monotectic cell” happens when alloy undercoolings become sufficiently large. The dendrite growth velocities of α-Fe and (Cu) phases are found to increase with undercooling according to an exponential relation.

  5. Reduction of Schottky barrier height at metal/n-Ge interface by introducing an ultra-high Sn content Ge1-xSnx interlayer

    NASA Astrophysics Data System (ADS)

    Suzuki, Akihiro; Nakatsuka, Osamu; Shibayama, Shigehisa; Sakashita, Mitsuo; Takeuchi, Wakana; Kurosawa, Masashi; Zaima, Shigeaki

    2015-11-01

    We investigated the impact of introducing an ultra-high Sn content Ge1-xSnx interlayer on the electrical properties at the metal/Ge interface. We achieved epitaxial growth of a Ge1-xSnx thin layer with an ultra-high substitutional Sn content of up to 46% on a Ge(001) substrate by considering the misfit strain between Ge1-xSnx and Ge. From the current-voltage characteristics of Al/Ge1-xSnx/n-Ge Schottky diodes, we found an increase in the forward current density of the thermionic emission current with increasing Sn content in the Ge1-xSnx interlayer. The Schottky barrier height estimated in Al/Ge1-xSnx/n-Ge diodes decreases to 0.49 eV with an increase in the Sn content up to 46% of the Ge1-xSnx interlayer. The reduction of the barrier height may be due to the shift of the Fermi level pinning position at the metal/Ge interface with a Ge1-xSnx interlayer whose valence band edge is higher than that of Ge. This result enables the effective reduction of the contact resistivity by introducing a group-IV semiconductor alloy interlayer of Ge1-xSnx into the metal/n-Ge interface.

  6. Theoretical investigation of Sn-doped Ge2Sb2Te5 alloy in crystalline phase

    NASA Astrophysics Data System (ADS)

    Singh, Janpreet; Singh, Gurinder; Kaura, Aman; Tripathi, S. K.

    2015-06-01

    Ge2Sb2Te5 (GST) is technologically important for phase-change random access memory applications. It has been shown that the 2.2 atomic % doping of Sn weakens the Ge-Te bond strength while maintaining the symmetry of stable phase of GST. The influence of Sn doping upon the phase change characteristics of the crystalline GST alloy has been investigated by ab initio calculations. The lattice parameter, average interface distances between two adjacent (111) layers, equilibrium volume, metallic character and electrical resistance has been calculated for the stable phase of GST and Sn-doped GST.

  7. SnGa2GeS6: synthesis, structure, linear and nonlinear optical properties.

    PubMed

    Lin, Zuohong; Li, Chao; Kang, Lei; Lin, Zheshuai; Yao, Jiyong; Wu, Yicheng

    2015-04-28

    A new sulfide, SnGa2GeS6, has been synthesized, which represents the first member in the quaternary Sn/M/M'/Q (M = Ga, In; M' = Si, Ge; Q = S, Se, Te) system. It adopts a new structure type in the non-centrosymmetric space group Fdd2. In the structure, Sn(2+) is coordinated to a distorted square-pyramid of five S atoms, demonstrating the stereochemical activity of the lone electron pair, while the Ge atom and Ga atom are both tetrahedrally coordinated to four S atoms. The SnS5 square-pyramids and the MS4 (M = Ga, Ge) tetrahedra are connected to each other via corner and edge-sharing to generate a three-dimensional framework. The compound exhibits a powder second harmonic generation signal at 2 μm whose strength is about one-fourth that of the benchmark material AgGaS2, which may be explained in view of the macroscopic arrangement of the SnS5 square-pyramids and the MS4 tetrahedra. Moreover, based on UV-vis-NIR spectroscopy measurements and the electronic structure calculations, SnGa2GeS6 has two optical transitions at about 1.12 eV and 2.04 eV respectively. PMID:25801715

  8. GeSn-on-Si normal incidence photodetectors with bandwidths more than 40 GHz.

    PubMed

    Oehme, Michael; Kostecki, Konrad; Ye, Kaiheng; Bechler, Stefan; Ulbricht, Kai; Schmid, Marc; Kaschel, Mathias; Gollhofer, Martin; Körner, Roman; Zhang, Wogong; Kasper, Erich; Schulze, Jörg

    2014-01-13

    GeSn (Sn content up to 4.2%) photodiodes with vertical pin structures were grown on thin Ge virtual substrates on Si by a low temperature (160 °C) molecular beam epitaxy. Vertical detectors were fabricated by a double mesa process with mesa radii between 5 µm and 80 µm. The nominal intrinsic absorber contains carrier densities from below 1 · 10(16) cm(-3) to 1 · 10(17) cm(-3) for Ge reference detectors and GeSn detectors with 4.2% Sn, respectively. The photodetectors were investigated with electrical and optoelectrical methods from direct current up to high frequencies (40 GHz). For a laser wavelength of 1550 nm an increasing of the optical responsivities (84 mA/W -218 mA/W) for vertical incidence detectors with thin (300 nm) absorbers as function of the Sn content were found. Most important from an application perspective all detectors had bandwidth above 40 GHz at enough reverse voltage which increased from zero to -5 V within the given Sn range. Increasing carrier densities (up to 1 · 10(17) cm(-3)) with Sn contents caused the depletion of the nominal intrinsic absorber at increasing reverse voltages. PMID:24515043

  9. Negative differential resistance in direct bandgap GeSn p-i-n structures

    NASA Astrophysics Data System (ADS)

    Schulte-Braucks, C.; Stange, D.; von den Driesch, N.; Blaeser, S.; Ikonic, Z.; Hartmann, J. M.; Mantl, S.; Buca, D.

    2015-07-01

    Certain GeSn alloys are group IV direct bandgap semiconductors with prospects for electrical and optoelectronical applications. In this letter, we report on the temperature dependence of the electrical characteristics of high Sn-content Ge 0.89 Sn 0.11 p-i-n diodes. NiGeSn contacts were used to minimize the access resistance and ensure compatibility with silicon technology. The major emphasis is placed on the negative differential resistance in which peak to valley current ratios up to 2.3 were obtained. TCAD simulations were performed to identify the origin of the various current contributions, providing evidence for direct band to band tunneling and trap assisted tunneling.

  10. Charge density waves or dynamical fluctuations at the Pb/Ge(111) and Sn/Ge(111) interfaces?

    NASA Astrophysics Data System (ADS)

    Asensio, M. C.

    2001-03-01

    Critical phenomena are a fascinating area of current research in solid state physics. The complex phenomenology associated to the phase transitions can be analyzed in a simple playground of low-dimensional systems. In particular, Carpinelli et al. (Nature 381(1996)398) have initially reported a temperature-driven phase transition for a Pb or Sn layer deposited on Ge(111). The low temperature 3x3 phase was described as the stabilization of a charge density wave (CDW) in the Pb layer, driven by electron-phonon coupling in the two dimensional Fermi surface. A similar phenomenology has been observed for Sn/Ge(111). This picture, however, was seriously questioned in several aspects by further investigations. First, the experimental Fermi surface exhibits no significant nesting, a crucial point for the proposed CDW model. Second, valence-band photoemission results do not support that electron correlation plays a major role and the surface valence bands in both phases are split, in disagreement with CDW theoretical calculations. Third, Core-level photoemission for Sn/Ge(111) at room and low temperature indicates the existence of two kinds of Sn atoms. All these experimental facts could be rationalized assuming a corrugated Sn or Pb layer, which we have recently confirmed using surface X-R Diffraction and theoretical calculations (Phys. Rev. Lett 82 (1999) 2524 and Phys. Rev. Lett. 82 (1999) 442 ) .We conclude that the origin of this reversible temperature transition is not a CDW. Both phases have a strong rippling of the Sn (Pb) layer ( ~ 0.49 Åwith two well distinctive Sn (or Pb) sites. Hence, the room temperature phase is the result of a vertical flipping of the Sn (or Pb) adatoms, which is frozen at low temperature.

  11. High-mobility BaSnO3 thin-film transistor with HfO2 gate insulator

    NASA Astrophysics Data System (ADS)

    Kim, Young Mo; Park, Chulkwon; Kim, Useong; Ju, Chanjong; Char, Kookrin

    2016-01-01

    Thin-film transistors have been fabricated using La-doped BaSnO3 as n-type channels and (In,Sn)2O3 as source, drain, and gate electrodes. HfO2 was grown as gate insulators by atomic layer deposition. The field-effect mobility, Ion/Ioff ratio, and subthreshold swing of the device are 24.9 cm2 V-1 s-1, 6.0 × 106, and 0.42 V dec-1, respectively. The interface trap density, evaluated to be higher than 1013 cm-2 eV-1, was found to be slightly lower than that of the thin-film transistor with an Al2O3 gate insulator. We attribute the much smaller subthreshold swing values to the higher dielectric constant of HfO2.

  12. Features of the band structure and conduction mechanisms in the n-HfNiSn semiconductor heavily doped with Ru

    SciTech Connect

    Romaka, V. A.; Rogl, P.; Romaka, V. V.; Stadnyk, Yu. V.; Korzh, R. O.; Krayovskyy, V. Ya.; Horyn, A. M.

    2014-12-15

    The crystal and electronic structure and energy and kinetic properties of the n-HfNiSn semiconductor heavily doped with a Ru acceptor impurity are investigated in the temperature and Ru concentration ranges T = 80–400 K and N{sub A}{sup Ru} ≈ 9.5 × 10{sup 19}−5.7 × 10{sup 20} cm{sup −3} (x = 0–0.03), respectively. The mechanism of structural-defect generation is established, which changes the band gap and degree of compensation of the semiconductor and consists in the simultaneous concentration reduction and elimination of donor structural defects by means of the displacement of ∼1% of Ni atoms from the Hf (4a) positions, the generation of acceptor structural defects upon the substitution of Ru atoms for Ni atoms in the 4c positions, and the generation of donor defects in the form of vacancies in the Sn (4b) positions. The calculated electronic structure of HfNi{sub 1−x}Ru{sub x}Sn is consistent with the experiment. The results obtained are discussed within the Shklovsky-Efros model for a heavily doped and compensated semiconductor.

  13. Features of the band structure and conduction mechanisms of n-HfNiSn semiconductor heavily Lu-doped

    SciTech Connect

    Romaka, V. A.; Rogl, P.; Romaka, V. V.; Kaczorowski, D.; Stadnyk, Yu. V.; Korzh, R. O.; Krayovskyy, V. Ya.; Kovbasyuk, T. M.

    2015-03-15

    The crystal and electronic structures, energy, kinetic, and magnetic characteristics of n-HfNiSn semiconductor heavily doped with a Lu acceptor impurity in the ranges T = 80–400 K and N{sub A}{sup Lu} ≈ 1.9 × 10{sup 20}−1.9 × 10{sup 21} cm{sup −3} (x = 0.01–0.10) at H ≤ 10 kG is studied. The nature of the structural-defect generation mechanism leading to changes in the band gap and the degree of semiconductor compensation is determined. Its essence is the simultaneous reduction and elimination of donor-type structural defects due to the displacement of ∼1% of Ni atoms from the Hf (4a) site, the generation of acceptor-type structural defects by substituting Ni atoms with Lu atoms at the 4c site, and the generation of donor-type defects such as vacancies at the Sn (4b) site. The results of calculations of the electronic structure of Hf{sub 1−x}Lu{sub x}NiSn are in agreement with experimental data. The results are discussed within the model of a heavily doped and compensated Shklovskii-Efros semiconductor.

  14. Formation of non-substitutional β-Sn defects in Ge1-xSnx alloys

    NASA Astrophysics Data System (ADS)

    Fuhr, J. D.; Ventura, C. I.; Barrio, R. A.

    2013-11-01

    Although group IV semiconductor alloys are expected to form substitutionally, in Ge1-xSnx this is true only for low concentrations (x < 0.13). The use of these alloys as a narrow gap semiconductor depends on the ability to produce samples with the high quality required for optoelectronic device applications. In a previous paper, we proposed the existence of a non-substitutional complex defect (β-Sn), consisting of a single Sn atom in the center of a Ge divacancy, which may account for the segregation of Sn at large x. Afterwards, the existence of this defect was confirmed experimentally. In this paper we study the local environment and the interactions of the substitutional defect (α-Sn), the vacancy in Ge, and the β-Sn defect by performing extensive numerical ab initio calculations. Our results confirm that a β-Sn defect can be formed by natural diffusion of a vacancy around the substitutional α-Sn defect, since the energy barrier for the process is very small.

  15. Thermally-driven H interaction with HfO{sub 2} films deposited on Ge(100) and Si(100)

    SciTech Connect

    Soares, G. V. Feijó, T. O.; Baumvol, I. J. R.; Aguzzoli, C.; Krug, C.; Radtke, C.

    2014-01-27

    In the present work, we investigated the thermally-driven H incorporation in HfO{sub 2} films deposited on Si and Ge substrates. Two regimes for deuterium (D) uptake were identified, attributed to D bonded near the HfO{sub 2}/substrate interface region (at 300 °C) and through the whole HfO{sub 2} layer (400–600 °C). Films deposited on Si presented higher D amounts for all investigated temperatures, as well as, a higher resistance for D desorption. Moreover, HfO{sub 2} films underwent structural changes during annealings, influencing D incorporation. The semiconductor substrate plays a key role in this process.

  16. Enhanced performance of GeSn source-pocket tunnel field-effect transistors for low-power applications

    NASA Astrophysics Data System (ADS)

    Liu, Lei; Liang, Renrong; Wang, Jing; Xu, Jun

    2016-07-01

    Germanium–tin (GeSn) source-pocket tunnel field-effect transistors (TFETs) are comprehensively investigated by numerical device simulations at low supply voltages. Device configurations with homo- and hetero-tunneling junctions (TJ) are analyzed and compared. It is shown that direct-gap GeSn alloys are favorable for increasing the source-pocket tunneling rate. Increasing the source Sn composition of the device may aid the on-state current increase, but the subthreshold swing (SS) is degraded because of the reduced band gap. At ultrascaled supply voltages, the GeSn hetero-TJ TFET with higher pocket Sn composition exhibits the best performance and SS, and the device performance can be further improved by increasing the Sn composition in the pocket region. These simulation results could be used to understand and optimize the performance of GeSn source-pocket TFETs, which are very promising electronic devices for low-power applications.

  17. Tensile-Strained GeSn Metal-Oxide-Semiconductor Field-Effect Transistor Devices on Si(111) Using Solid Phase Epitaxy

    NASA Astrophysics Data System (ADS)

    Lieten, Ruben R.; Maeda, Tatsuro; Jevasuwan, Wipakorn; Hattori, Hiroyuki; Uchida, Noriyuki; Miura, Shu; Tanaka, Masatoshi; Locquet, Jean-Pierre

    2013-10-01

    We demonstrate tensile-strained GeSn metal-oxide-semiconductor field-effect transistor (MOSFET) devices on Si(111) substrates using solid phase epitaxy of amorphous GeSn layers. Amorphous GeSn layers are obtained by limiting the adatom surface mobility during deposition. Subsequent annealing transforms the amorphous layer into single-crystalline GeSn by solid phase epitaxy. Single-crystalline GeSn layers with 4.5% Sn and 0.33% tensile strain are fabricated on Si(111) substrates. To verify the structural quality of thin-film GeSn as a channel material, we fabricate ultrathin GeSn p-channel MOSFETs (pMOSFETs) on Si(111). We demonstrate junctionless depletion-mode operation of tensile-strained GeSn(111) pMOSFETs on Si substrates.

  18. Pressure and temperature induced elastic properties of Si, Ge, Sn, and Pt carbides

    NASA Astrophysics Data System (ADS)

    Shriya, S.; Jain, S.; Khenata, R.; Varshney, M.; Varshney, Dinesh

    2015-06-01

    The pressure and temperature dependent mechanical properties as melting temperature, hardness and brittle nature of XC (X=Si, Ge, Sn, and Pt) are studied. The model Hamiltonian in ab initio theory include long-range Coulomb, charge transfer, covalency, van der Waals interaction and the short-range repulsive interaction upto second-neighbor ions within the Hafemeister and Flygare approach. Estimated values of volume discontinuity in pressure-volume phase diagram indicate the structural phase transition from ZnS to NaCl structure. From the investigations of elastic constants the pressure (temperature) dependent (Tm) and Vickers Hardness (HV) of XC (X=Si, Ge, Sn, and Pt) and Poisson's and Pugh ratio are calculated. It is noticed that XC (X=Si, Ge, Sn, and Pt) is brittle on applied pressure and temperature.

  19. Multi-stacks of epitaxial GeSn self-assembled dots in Si: Structural analysis

    NASA Astrophysics Data System (ADS)

    Oliveira, F.; Fischer, I. A.; Benedetti, A.; Cerqueira, M. F.; Vasilevskiy, M. I.; Stefanov, S.; Chiussi, S.; Schulze, J.

    2015-03-01

    We report on the growth and structural and morphologic characterization of stacked layers of self-assembled GeSn dots grown on Si (100) substrates by molecular beam epitaxy at low substrate temperature T = 350 °C. Samples consist of layers (from 1 up to 10) of Ge0.96Sn0.04 self-assembled dots separated by Si spacer layers, 10 nm thick. Their structural analysis was performed based on transmission electron microscopy, atomic force microscopy, and Raman scattering. We found that up to 4 stacks of dots could be grown with good dot layer homogeneity, making the GeSn dots interesting candidates for optoelectronic device applications.

  20. Formation and characterization of Ni/Al Ohmic contact on n+-type GeSn

    NASA Astrophysics Data System (ADS)

    Zhang, Xu; Zhang, Dongliang; Zheng, Jun; Liu, Zhi; He, Chao; Xue, Chunlai; Zhang, Guangze; Li, Chuanbo; Cheng, Buwen; Wang, Qiming

    2015-12-01

    In this study, a Ni/Al Ohmic contact on a highly doped n-type GeSn has been investigated. A specific contact resistivity as low as (2.26 ± 0.11) × 10-4 Ω cm2 was obtained with the GeSn sample annealed at a temperature of 450 °C for 30 s. The linear Ohmic behavior was attributed to the low resistance of the Ni(GeSn) phase; this behavior was determined using glancing-angle X-ray diffraction, and the quantum tunneling current through the Schottky barrier narrowed because of high doping; this phenomenon was confirmed from the contact resistance characteristics at different temperatures from 45 to 205 K.

  1. Multi-stacks of epitaxial GeSn self-assembled dots in Si: Structural analysis

    SciTech Connect

    Oliveira, F.; Fischer, I. A.; Schulze, J.; Benedetti, A.; Cerqueira, M. F.; Vasilevskiy, M. I.; Stefanov, S.; Chiussi, S.

    2015-03-28

    We report on the growth and structural and morphologic characterization of stacked layers of self-assembled GeSn dots grown on Si (100) substrates by molecular beam epitaxy at low substrate temperature T = 350 °C. Samples consist of layers (from 1 up to 10) of Ge{sub 0.96}Sn{sub 0.04} self-assembled dots separated by Si spacer layers, 10 nm thick. Their structural analysis was performed based on transmission electron microscopy, atomic force microscopy, and Raman scattering. We found that up to 4 stacks of dots could be grown with good dot layer homogeneity, making the GeSn dots interesting candidates for optoelectronic device applications.

  2. Intrinsic carrier effects in HfO2-Ge metal-insulator-semiconductor capacitors

    NASA Astrophysics Data System (ADS)

    Dimoulas, A.; Vellianitis, G.; Mavrou, G.; Evangelou, E. K.; Sotiropoulos, A.

    2005-05-01

    Germanium metal-insulator-semiconductor capacitors with HfO2 or other high-κ gate dielectrics show unusual low frequency behavior of the high frequency (1 kHz or higher) capacitance-voltage characteristics when biased in inversion. Here, we provide evidence that this effect is partly due to the high intrinsic carrier concentration ni in Ge. We show in particular that the ac conductance in inversion is thermally activated and it is governed either by generation-recombination processes in depletion, varying proportional to ni or by diffusion-limited processes varying as ni2, depending on whether the temperature is below or above 45 °C, respectively. From these measurements, we also show that the minority carrier response time in Ge is very short, in the microsecond range (much shorter than in Si), depending inversely proportional to ni at room temperature. This means that due to high ni, the inversion charge is built fast in response to high frequency signals at the gate, inducing the observed low frequency behavior.

  3. Investigation of Ge nanocrytals in a metal-insulator-semiconductor structure with a HfO2/SiO2 stack as the tunnel dielectric

    NASA Astrophysics Data System (ADS)

    Wang, Shiye; Liu, Weili; Wan, Qing; Dai, J. Y.; Lee, P. F.; Suhua, Luo; Shen, Qinwo; Zhang, Miao; Song, Zhitang; Lin, Chenglu

    2005-03-01

    A metal-insulator-semiconductor (MIS) structure containing a HfO2 control gate, a Ge nanocrystal-embedded HfO2 dielectric and a HfO2/SiO2 stack layer as tunnel oxide, was fabricated by an electron-beam evaporation method. High-resolution transmission electron microscopy study revealed that the HfO2/SiO2 stack layer minimized Ge penetration, leading to the formation of Ge nanocrystals that are self-aligned between the tunnel oxide and the capping HfO2 layer. Influence of different annealing conditions on the formation and distribution of Ge nanocrystals was studied. Current-voltage (I -V) and capacitance-voltage (C-V) measurements revealed promising electrical characteristics of the MIS structure, and relatively high stored charge density of 1012cm-2 was achieved.

  4. Electrical characteristics of Ni Ohmic contact on n-type GeSn

    NASA Astrophysics Data System (ADS)

    Li, H.; Cheng, H. H.; Lee, L. C.; Lee, C. P.; Su, L. H.; Suen, Y. W.

    2014-06-01

    We report an investigation of the electrical and material characteristics of Ni on an n-type GeSn film under thermal annealing. The current-voltage traces measured with the transmission line method are linear for a wide range of annealing temperatures. The specific contact resistivity was found to decrease with increasing annealing temperature, followed by an increase as the annealing temperature further increased, with a minimum value at an annealing temperature of 350 °C. The material characteristics at the interface layer were measured by energy-dispersive spectrometer, showing that an atomic ratio of (Ni)/(GeSn) = 1:1 yields the lowest specific contact resistivity.

  5. Syntheses, structural variants and characterization of AInM‧S4 (A=alkali metals, Tl; M‧ = Ge, Sn) compounds; facile ion-exchange reactions of layered NaInSnS4 and KInSnS4 compounds

    NASA Astrophysics Data System (ADS)

    Yohannan, Jinu P.; Vidyasagar, Kanamaluru

    2016-06-01

    Ten AInM‧S4 (A=alkali metals, Tl; M‧= Ge, Sn) compounds with diverse structure types have been synthesized and characterized by single crystal and powder X-ray diffraction and a variety of spectroscopic methods. They are wide band gap semiconductors. KInGeS4(1-β), RbInGeS4(2), CsInGeS4(3-β), TlInGeS4(4-β), RbInSnS4(8-β) and CsInSnS4(9) compounds with three-dimensional BaGa2S4 structure and CsInGeS4(3-α) and TlInGeS4(4-α) compounds with a layered TlInSiS4 structure have tetrahedral [InM‧S4]- frameworks. On the other hand, LiInSnS4(5) with spinel structure and NaInSnS4(6), KInSnS4(7), RbInSnS4(8-α) and TlInSnS4(10) compounds with layered structure have octahedral [InM‧S4]- frameworks. NaInSnS4(6) and KInSnS4(7) compounds undergo facile topotactic ion-exchange, at room temperature, with various mono-, di- and tri-valent cations in aqueous medium to give rise to metastable layered phases.

  6. Lattice constant and substitutional composition of GeSn alloys grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Bhargava, Nupur; Coppinger, Matthew; Prakash Gupta, Jay; Wielunski, Leszek; Kolodzey, James

    2013-07-01

    Single crystal epitaxial Ge1-xSnx alloys with atomic fractions of tin up to x = 0.145 were grown by solid source molecular beam epitaxy on Ge (001) substrates. The Ge1-xSnx alloys formed high quality, coherent, strained layers at growth temperatures below 250 °C, as shown by high resolution X-ray diffraction. The amount of Sn that was on lattice sites, as determined by Rutherford backscattering spectrometry channeling, was found to be above 90% substitutional in all alloys. The degree of strain and the dependence of the effective unstrained bulk lattice constant of Ge1-xSnx alloys versus the composition of Sn have been determined.

  7. Direct bandgap GeSn light emitting diodes for short-wave infrared applications grown on Si

    NASA Astrophysics Data System (ADS)

    von den Driesch, Nils; Stange, Daniela; Wirths, Stephan; Rainko, Denis; Mussler, Gregor; Stoica, Toma; Ikonic, Zoran; Hartmann, Jean-Michel; Grützmacher, Detlev; Mantl, Siegfried; Buca, Dan

    2016-03-01

    The experimental demonstration of fundamental direct bandgap, group IV GeSn alloys has constituted an important step towards realization of the last missing ingredient for electronic-photonic integrated circuits, i.e. the efficient group IV laser source. In this contribution, we present electroluminescence studies of reduced-pressure CVD grown, direct bandgap GeSn light emitting diodes (LEDs) with Sn contents up to 11 at.%. Besides homojunction GeSn LEDs, complex heterojunction structures, such as GeSn/Ge multi quantum wells (MQWs) have been studied. Structural and compositional investigations confirm high crystalline quality, abrupt interfaces and tailored strain of the grown structures. While also being suitable for light absorption applications, all devices show light emission in a narrow short-wave infrared (SWIR) range. Temperature dependent electroluminescence (EL) clearly indicates a fundamentally direct bandgap in the 11 at.% Sn sample, with room temperature emission at around 0.55 eV (2.25 µm). We have, however, identified some limitations of the GeSn/Ge MQW approach regarding emission efficiency, which can be overcome by introducing SiGeSn ternary alloys as quantum confinement barriers.

  8. Emission of direct-gap band in germanium with Ge-GeSn layers on one-dimensional structure

    NASA Astrophysics Data System (ADS)

    Huang, Zhong-Mei; Huang, Wei-Qi; Liu, Shi-Rong; Dong, Tai-Ge; Wang, Gang; Wu, Xue-Ke; Qin, Cao-Jian

    2016-04-01

    In our experiment, it was observed that the emission of direct-gap band in germanium with Ge-GeSn layers on one-dimensional (1D) structure. The results of experiment and calculation demonstrate that the uniaxial tensile strain in the (111) and (110) direction can efficiently transform Ge to a direct bandgap material with the bandgap energy useful for technological application. It is interested that under the tensile strain from Ge-GeSn layers on 1D structure in which the uniaxial strain could be obtained by curved layer (CL) effect, the two bandgaps EΓg and ELg in the (111) direction become nearly equal at 0.83 eV related to the emission of direct-gap band near 1500 nm in the experiments. It is discovered that the red-shift of the peaks from 1500 nm to 1600 nm occurs with change of the uniaxial tensile strain, which proves that the peaks come from the emission of direct-gap band.

  9. Emission of direct-gap band in germanium with Ge-GeSn layers on one-dimensional structure.

    PubMed

    Huang, Zhong-Mei; Huang, Wei-Qi; Liu, Shi-Rong; Dong, Tai-Ge; Wang, Gang; Wu, Xue-Ke; Qin, Cao-Jian

    2016-01-01

    In our experiment, it was observed that the emission of direct-gap band in germanium with Ge-GeSn layers on one-dimensional (1D) structure. The results of experiment and calculation demonstrate that the uniaxial tensile strain in the (111) and (110) direction can efficiently transform Ge to a direct bandgap material with the bandgap energy useful for technological application. It is interested that under the tensile strain from Ge-GeSn layers on 1D structure in which the uniaxial strain could be obtained by curved layer (CL) effect, the two bandgaps EΓg and ELg in the (111) direction become nearly equal at 0.83 eV related to the emission of direct-gap band near 1500 nm in the experiments. It is discovered that the red-shift of the peaks from 1500 nm to 1600 nm occurs with change of the uniaxial tensile strain, which proves that the peaks come from the emission of direct-gap band. PMID:27097990

  10. Emission of direct-gap band in germanium with Ge-GeSn layers on one-dimensional structure

    PubMed Central

    Huang, Zhong-Mei; Huang, Wei-Qi; Liu, Shi-Rong; Dong, Tai-Ge; Wang, Gang; Wu, Xue-Ke; Qin, Cao-Jian

    2016-01-01

    In our experiment, it was observed that the emission of direct-gap band in germanium with Ge-GeSn layers on one-dimensional (1D) structure. The results of experiment and calculation demonstrate that the uniaxial tensile strain in the (111) and (110) direction can efficiently transform Ge to a direct bandgap material with the bandgap energy useful for technological application. It is interested that under the tensile strain from Ge-GeSn layers on 1D structure in which the uniaxial strain could be obtained by curved layer (CL) effect, the two bandgaps EΓg and ELg in the (111) direction become nearly equal at 0.83 eV related to the emission of direct-gap band near 1500 nm in the experiments. It is discovered that the red-shift of the peaks from 1500 nm to 1600 nm occurs with change of the uniaxial tensile strain, which proves that the peaks come from the emission of direct-gap band. PMID:27097990

  11. Orthorhombic-tetragonal phase coexistence and enhanced piezo-response at room temperature in Zr, Sn, and Hf modified BaTiO{sub 3}

    SciTech Connect

    Kalyani, Ajay Kumar; Brajesh, Kumar; Ranjan, Rajeev; Senyshyn, Anatoliy

    2014-06-23

    The effect of Zr, Hf, and Sn in BaTiO{sub 3} has been investigated at close composition intervals in the dilute concentration limit. Detailed structural analysis by x-ray and neutron powder diffraction revealed that merely 2 mol. % of Zr, Sn, and Hf stabilizes a coexistence of orthorhombic (Amm2) and tetragonal (P4mm) phases at room temperature. As a consequence, all the three systems show substantial enhancement in the longitudinal piezoelectric coefficient (d{sub 33}), with Sn modification exhibiting the highest value ∼425 pC/N.

  12. Formation of high-quality oxide/Ge1-xSnx interface with high surface Sn content by controlling Sn migration

    NASA Astrophysics Data System (ADS)

    Kato, Kimihiko; Taoka, Noriyuki; Asano, Takanori; Yoshida, Teppei; Sakashita, Mitsuo; Nakatsuka, Osamu; Zaima, Shigeaki

    2014-09-01

    In this paper, we investigated how Sn migrated during annealing for Ge1-xSnx at its surface and in its interior, as well as the Ge oxide formation on Ge1-xSnx with controlling surface oxidation. After oxidation at 400 °C, X-ray photoelectron spectroscopy and X-ray diffraction measurements revealed Sn migration from inside the epitaxial Ge1-xSnx layer to its surface. Annealing was not the primary cause of significant Sn migration; rather, it was caused mostly by oxidation near the Ge1-xSnx surface. This process formed a Ge1-xSnx oxide with a very high Sn content of 30%, inducing a wide hysteresis loop in the capacitance-voltage characteristics of its corresponding MOS device. We also found that forming a thin GeO2 layer by using a deposition method that controls Ge surface oxidation produced low densities of interface states and slow states. From these results, we conclude that controlling Sn migration is critical to forming a high-quality Ge1-xSnx gate stack.

  13. Indium (In)- and tin (Sn)-based metal induced crystallization (MIC) on amorphous germanium (α-Ge)

    SciTech Connect

    Kang, Dong-Ho; Park, Jin-Hong

    2014-12-15

    Highlights: • In- and Sn-based MIC phenomenon on amorphous (α)-Ge is newly reported. • The In- and Sn-MIC phenomenon respectively started at 250 °C and 400 °C. • The Sn-MIC process presents higher sheet resistance and bigger crystal grains. - Abstract: In this paper, metal-induced crystallization (MIC) phenomenon on α-Ge by indium (In) and tin (Sn) are thoroughly investigated. In- and Sn-MIC process respectively started at 250 °C and 400 °C. Compared to the previously reported MIC samples including In-MIC, Sn-MIC process presented higher sheet resistance (similar to that of SPC) and bigger crystal grains above 50 nm (slightly smaller than that of SPC). According to SIMS analysis, Sn atoms diffused more slowly into Ge than In at 400 °C, providing lower density of heterogeneous nuclei induced by metals and consequently larger crystal grains.

  14. Ultra-high-speed lateral solid phase crystallization of GeSn on insulator combined with Sn-melting-induced seeding

    NASA Astrophysics Data System (ADS)

    Chikita, H.; Matsumura, R.; Kai, Y.; Sadoh, T.; Miyao, M.

    2014-11-01

    To produce high-performance devices on flexible plastic substrates, it is essential to form Ge-based group IV semiconductors on insulating substrates at low temperatures (≤250 °C). We have developed a technique for solid phase crystallization of amorphous GeSn (≤220 °C) enhanced by Sn doping, and combined with a seeding technique induced by Sn melting (˜250 °C). This combination produces lateral crystallization of amorphous GeSn from seed arrays with no incubation time. As a result, extremely high growth velocities at 220 °C, depending on Sn concentration, e.g., 0.13 μm/h (14% Sn) and 1100 μm/h (23% Sn), are achieved. These velocities are 104-108 times higher than that of pure Ge. This technique enables growth of crystalline GeSn island arrays (diameters: 50-150 μm) at low temperatures (≤250 °C) at controlled positions on insulating substrates.

  15. Influence of Sn-substitution on the thermoelectric properties of the clathrate type-I, Ba8Zn(x)Ge(46-x-y)Sn(y).

    PubMed

    Falmbigl, Matthias; Grytsiv, Andriy; Rogl, Peter; Yan, Xinlin; Royanian, Esmaeil; Bauer, Ernst

    2013-02-28

    A systematic investigation is presented on the influence of Sn-substitution in the clathrate-I compound Ba(8)Zn(x)Ge(46-x-y)Sn(y), particularly for the crystal structure and thermoelectric properties including electrical resistivity, Seebeck coefficient, and thermal conductivity. Two series of samples were prepared to explore the changes for different Sn-contents, (y), and to define the optimum Zn-content, (x), for Ba(8)Zn(x)Ge(46-x-y)Sn(y). Sn-incorporation leads to a linear expansion of the unit cell parameters. Sn-atoms occupy the 6d and 24k positions of the clathrate type-I structure (SG Pm3n, standardized setting). Whereas the electrical resistivity and the Seebeck coefficient modify only slightly compared to Ba(8)Zn(x)Ge(46-x), the thermal conductivity is significantly decreased by the Sn-atoms incorporated into the clathrate-I framework. Furthermore the charge carrier mobility is larger and the effective mass (m* = 1.7 m(e)) is much smaller than those of the ternary compound Ba(8)Zn(x)Ge(46-x). The maximum thermoelectric figure of merit is improved by 80% and reaches ZT = 0.82 at 850 K for Ba(8)Zn(7.66)Ge(36.55)Sn(1.79). PMID:23243666

  16. Electroluminescence from GeSn heterostructure pin diodes at the indirect to direct transition

    SciTech Connect

    Gallagher, J. D.; Menéndez, J.; Senaratne, C. L.; Sims, P.; Kouvetakis, J.; Aoki, T.

    2015-03-02

    The emission properties of GeSn heterostructure pin diodes have been investigated. The devices contain thick (400–600 nm) Ge{sub 1−y}Sn{sub y} i-layers spanning a broad compositional range below and above the crossover Sn concentration y{sub c} where the Ge{sub 1−y}Sn{sub y} alloy becomes a direct-gap material. These results are made possible by an optimized device architecture containing a single defected interface thereby mitigating the deleterious effects of mismatch-induced defects. The observed emission intensities as a function of composition show the contributions from two separate trends: an increase in direct gap emission as the Sn concentration is increased, as expected from the reduction and eventual reversal of the separation between the direct and indirect edges, and a parallel increase in non-radiative recombination when the mismatch strains between the structure components is partially relaxed by the generation of misfit dislocations. An estimation of recombination times based on the observed electroluminescence intensities is found to be strongly correlated with the reverse-bias dark current measured in the same devices.

  17. Temperature-dependent electroluminescence from GeSn heterojunction light-emitting diode on Si substrate

    NASA Astrophysics Data System (ADS)

    Chang, Chiao; Li, Hui; Huang, Ssu-Hsuan; Lin, Li-Chien; Cheng, Hung-Hsiang

    2016-04-01

    The electroluminescence from a Ge/GeSn/Ge p-i-n light-emitting diode on Si was investigated under different temperatures ranging from 25 to 150 K. The diode was operated at a low injection current density of 13 A/cm2. We obtained no-phonon- and phonon-assisted replicas in emission spectra. Also, the relationship between indirect bandgap energy and temperature was investigated. The temperature-dependent bandgap energy followed Varshni’s empirical expression with α = 4.884 × 10-4 eV/K and β = 130 K.

  18. Improved n-channel Ge gate stack performance using HfAlO high-k dielectric for various Al concentrations

    NASA Astrophysics Data System (ADS)

    Kothari, Shraddha; Joishi, Chandan; Ghosh, Sayantan; Biswas, Dipankar; Vaidya, Dhirendra; Ganguly, Swaroop; Lodha, Saurabh

    2016-07-01

    We demonstrate improved Ge n-channel gate stack performance versus HfO2 using HfAlO high-k dielectric for a wide (1.5–33%) range of Al% and post-high-k-deposition annealing (PDA) at 400 °C. Addition of Al to HfO2 is shown to mitigate degradation of the GeO2/Ge interface during PDA. HfAlO stacks with an equivalent oxide thickness (EOT) of 8 nm and large Al% exhibit improved transistor mobility (1.8 times higher) and midgap D it (2 times lower), whereas thin (1.9 nm) EOT HfAlO stacks show reduced gate leakage J g (by 10 times) and D it (by 1.5 times) and 1.6 times higher mobility for Al% as low as 1.5% at matched EOT.

  19. Increased electrical conductivity in fine-grained (Zr,Hf)NiSn based thermoelectric materials with nanoscale precipitates

    NASA Astrophysics Data System (ADS)

    Xie, Han-Hui; Yu, Cui; Zhu, Tie-Jun; Fu, Chen-Guang; Jeffrey Snyder, G.; Zhao, Xin-Bing

    2012-06-01

    Grain refinement has been conducted to reduce the thermal conductivity and improve the thermoelectric performance of the (Zr,Hf)NiSn based half-Heusler alloys. Nanoscale in situ precipitates were found embedded in the matrix with submicron grains. The lattice thermal conductivity was decreased due to the enhanced boundary scattering of phonons. The increased carrier concentration and electrical conductivity were observed compared to the coarse-grained alloys, which is discussed in relation to the existence of nanoscale precipitates, the effect of antisite defects, and composition change. It is suggested that the nanoscale precipitates play a significant role in the observed electrical conductivity increase.

  20. Thermoelectric performance enhancement of Mg2Sn based solid solutions by band convergence and phonon scattering via Pb and Si/Ge substitution for Sn.

    PubMed

    Mao, Jun; Wang, Yumei; Ge, Binghui; Jie, Qing; Liu, Zihang; Saparamadu, Udara; Liu, Weishu; Ren, Zhifeng

    2016-07-27

    In this study, the thermoelectric properties of Mg2Sn0.98-xPbxSb0.02 were first studied, and then Mg2Sn0.93-xSixPb0.05Sb0.02 and Mg2Sn0.93-xGexPb0.05Sb0.02 were accordingly investigated. The results showed that the formation of Mg2Sn0.98-xPbxSb0.02 solid solutions effectively reduced the lattice thermal conductivity of Mg2Sn. The room temperature lattice thermal conductivity of Mg2Sn0.98Sb0.02 is ∼5.2 W m(-1) K(-1) but only ∼2.5 W m(-1) K(-1) for Mg2Sn0.73Pb0.25Sb0.02, a reduction of ∼52%. Further alloying Mg2Sn0.98-xPbxSb0.02 with Mg2Si or Mg2Ge to form Mg2Sn0.93-xSixPb0.05Sb0.02 or Mg2Sn0.93-xGexPb0.05Sb0.02 reduced the lattice thermal conductivity significantly due to enhanced phonon scattering by point defects as well as nanoparticles. Moreover, bipolar thermal conductivities were suppressed due to the larger bandgap of Mg2Si and Mg2Ge than Mg2Sn. Furthermore, similar to the pseudo-binary Mg2Sn-Mg2Si and Mg2Sn-Mg2Ge systems, band convergence was also observed in pseudo-ternary Mg2Sn0.93-xSixPb0.05Sb0.02 and Mg2Sn0.93-xGexPb0.05Sb0.02 materials. The convergence of conduction bands led to higher PFs at lower temperatures for Mg2Sn0.93-xSixPb0.05Sb0.02 and Mg2Sn0.93-xGexPb0.05Sb0.02 materials. As a result, higher peak ZTs of ∼1.3 for Mg2Sn0.63Si0.3Pb0.05Sb0.02 and ∼1.2 for Mg2Sn0.68Ge0.25Pb0.05Sb0.02 were achieved. PMID:27412367

  1. Si-Ge-Sn alloys with 1.0 eV gap for CPV multijunction solar cells

    SciTech Connect

    Roucka, Radek Clark, Andrew; Landini, Barbara

    2015-09-28

    Si-Ge-Sn ternary group IV alloys offer an alternative to currently used 1.0 eV gap materials utilized in multijunction solar cells. The advantage of Si-Ge-Sn is the ability to vary both the bandgap and lattice parameter independently. We present current development in fabrication of Si-Ge-Sn alloys with gaps in the 1.0 eV range. Produced material exhibits excellent structural properties, which allow for integration with existing III-V photovoltaic cell concepts. Time dependent room temperature photoluminescence data demonstrate that these materials have long carrier lifetimes. Absorption tunable by compositional changes is observed. As a prototype device set utilizing the 1 eV Si-Ge-Sn junction, single junction Si-Ge-Sn device and triple junction device with Si-Ge-Sn subcell have been fabricated. The resulting I-V and external quantum efficiency data show that the Si-Ge-Sn junction is fully functional and the performance is comparable to other 1.0 eV gap materials currently used.

  2. Above-bandgap optical properties of biaxially strained GeSn alloys grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Richard D'Costa, Vijay; Wang, Wei; Zhou, Qian; Soon Tok, Eng; Yeo, Yee-Chia

    2014-01-01

    The complex dielectric function of biaxially strained Ge1-xSnx (0 ≤ x ≤ 0.17) alloys grown on Ge (100) has been determined by spectroscopic ellipsometry from 1.2 to 4.7 eV. The effect of substitutional Sn incorporation and the epitaxial strain on the energy transitions E1, E1 + Δ1, E0', and E2 of GeSn alloys is investigated. Our results indicate that the strained GeSn alloys show Ge-like electronic bandstructure with all the transitions shifted downward due to the alloying of Sn. The strain dependence of E1 and E1 + Δ1 transitions is explained using the deformation potential theory, and values of -5.4 ± 0.4 eV and 3.8 ± 0.5 eV are obtained for the hydrostatic and shear deformation potentials, respectively.

  3. Growth of highly strain-relaxed Ge1-xSnx/virtual Ge by a Sn precipitation controlled compositionally step-graded method

    NASA Astrophysics Data System (ADS)

    Takeuchi, Shotaro; Shimura, Yosuke; Nakatsuka, Osamu; Zaima, Shigeaki; Ogawa, Masaki; Sakai, Akira

    2008-06-01

    We have investigated Sn precipitation and strain relaxation behaviors in the growth of Ge1-xSnx layers on virtual Ge substrates (v-Ge) for strain engineering of Ge. By varying misfit strain at Ge1-xSnx/v-Ge and Ge1-ySny/Ge1-xSnx interfaces, we found that a critical misfit strain controls the onset of Sn precipitation at a given thickness of the Ge1-xSnx layer. A compositionally step-graded method, in which the critical misfit strain is taken into account, was applied to the growth of strain-relaxed Ge1-xSnx layers on v-Ge. Postdeposition annealing at each growth step led to lateral propagation of threading dislocations preexisting in the layer and originating from v-Ge, which resulted in high degree of strain relaxation. An epitaxial Ge layer was grown on the strain-relaxed Ge1-xSnx layer and an in-plane tensile strain of 0.68% was achieved.

  4. Ge{sub 1-y}Sn{sub y} (y = 0.01-0.10) alloys on Ge-buffered Si: Synthesis, microstructure, and optical properties

    SciTech Connect

    Senaratne, C. L.; Kouvetakis, J.; Gallagher, J. D.; Jiang, Liying; Smith, D. J.; Menéndez, J.; Aoki, Toshihiro

    2014-10-07

    Novel hydride chemistries are employed to deposit light-emitting Ge{sub 1-y}Sn{sub y} alloys with y ≤ 0.1 by Ultra-High Vacuum Chemical Vapor Deposition (UHV-CVD) on Ge-buffered Si wafers. The properties of the resultant materials are systematically compared with similar alloys grown directly on Si wafers. The fundamental difference between the two systems is a fivefold (and higher) decrease in lattice mismatch between film and virtual substrate, allowing direct integration of bulk-like crystals with planar surfaces and relatively low dislocation densities. For y ≤ 0.06, the CVD precursors used were digermane Ge₂H₆ and deuterated stannane SnD₄. For y ≥ 0.06, the Ge precursor was changed to trigermane Ge₃H₈, whose higher reactivity enabled the fabrication of supersaturated samples with the target film parameters. In all cases, the Ge wafers were produced using tetragermane Ge₄H₁₀ as the Ge source. The photoluminescence intensity from Ge{sub 1–y}Sn{sub y}/Ge films is expected to increase relative to Ge{sub 1–y}Sn{sub y}/Si due to the less defected interface with the virtual substrate. However, while Ge{sub 1–y}Sn{sub y}/Si films are largely relaxed, a significant amount of compressive strain may be present in the Ge{sub 1–y}Sn{sub y}/Ge case. This compressive strain can reduce the emission intensity by increasing the separation between the direct and indirect edges. In this context, it is shown here that the proposed CVD approach to Ge{sub 1–y}Sn{sub y}/Ge makes it possible to approach film thicknesses of about 1 μm, for which the strain is mostly relaxed and the photoluminescence intensity increases by one order of magnitude relative to Ge{sub 1–y}Sn{sub y}/Si films. The observed strain relaxation is shown to be consistent with predictions from strain-relaxation models first developed for the Si{sub 1–x}Ge{sub x}/Si system. The defect structure and atomic distributions in the films are studied in detail using advanced electron

  5. Room temperature lasing in GeSn alloys: A path to CMOS-compatible infrared lasers

    NASA Astrophysics Data System (ADS)

    Li, Zairui; Zhao, Yun; Gallagher, James; Menéndez, José; Kouvetakis, John; Agha, Imad; Mathews, Jay

    The semiconductor industry has been pushing silicon photonics development for many years, resulting in the realization of many CMOS-compatible optoelectronic devices. However, one challenge that has not been overcome is the development of Si-based lasers. Recently, GeSn alloys grown on Si have shown much promise in the field of infrared optoelectronics. These alloy films are compatible with CMOS processing, have band gaps in the infrared, and the band structure of GeSn can be tuned via Sn concentration to induce direct band gap emission. In this work, we report on room temperature lasing in optically-pumped waveguides fabricated from GeSn films grown epitaxially on Si(100) substrates. The waveguides were defined using standard UV photolithography and dry-etched in a Cl plasma. The end facets were mirror polished, and Al was deposited on one facet to enhance cavity quality. The waveguides were optically-pumped using a 976nm wavelength solid-state laser, and the corresponding emission was measured. The dependence of the emission power on the pump power shows a clear transition between spontaneous and stimulated emission, thereby demonstrating room temperature lasing.

  6. Comparative studies of band structures for biaxial (100)-, (110)-, and (111)-strained GeSn: A first-principles calculation with GGA+U approach

    NASA Astrophysics Data System (ADS)

    Huang, Wenqi; Cheng, Buwen; Xue, Chunlai; Liu, Zhi

    2015-10-01

    Experiments and calculations performed in previous studies indicate that compressive strain will increase (100)-strained GeSn's need for Sn to realize a direct bandgap when it is pseudomorphically grown on Ge buffers. To eliminate this negative effect, we systematically investigate the band structures of biaxial (100)-, (110)-, and (111)-strained GeSn using a first-principle calculation combined with supercell models and the GGA+U approach. This method has proven to be efficient and accurate for calculating the properties of GeSn. The calculated lattice constants and elastic constants of Ge and Sn are in good agreement with the experimental results. The crossover value of Sn concentration which is required to change the bandgap of unstrained GeSn from indirect to direct is found to be 8.5%, which is very close to the recent experimental result of 9%. The calculated bandgaps of strained GeSn show that the moving rate of the Γ valley is higher than those of the L and X valleys in (100)- and (110)-strained GeSn. However, the moving rate of the L valley is higher than those of Γ and X valleys in (111)-strained GeSn. Tensile strain has a positive effect on the transition of (100)- and (110)-strained GeSn, changing the bandgap from indirect to direct, whereas compressive strain has a positive effect for (111)-strained GeSn. The use of the (111) orientation can reduce GeSn's need for Sn and greatly increase the energy difference between the L valley and Γ valley. Thus, for strained GeSn grown on Ge buffers, the (111) orientation is a good choice to take advantage of compressive strain.

  7. Cu2Sn1‑ x Ge x S3 solar cells fabricated with a graded bandgap structure

    NASA Astrophysics Data System (ADS)

    Umehara, Mitsutaro; Tajima, Shin; Aoki, Yuko; Takeda, Yasuhiko; Motohiro, Tomoyoshi

    2016-07-01

    We fabricated Cu2Sn1‑ x Ge x S3 (CTGS) solar cells with a graded bandgap structure in order to improve their photovoltaic performance. Bandgap gradation was formed by changing the Ge/Sn ratio in the depth direction of the CTGS layers. The composition profile of each sample was measured by secondary ion mass spectrometry, and we confirmed that the Ge/Sn ratio near the buffer layer was lower than that near the back electrode. This means that the bandgap increases with depth from the surface. The performance of the cells was improved to over 6.7% in conversion efficiency.

  8. Sn(78)Ge(22)@carbon core-shell nanowires as fast and high-capacity lithium storage media.

    PubMed

    Lee, Hyojin; Cho, Jaephil

    2007-09-01

    Branched Sn78Ge22@carbon core-shell nanowires were prepared by thermal annealing of butyl-capped Sn78Ge22 clusters at 600 degrees C in a vacuum. The first discharge and charge capacities are 1250 and 1107 mA h/g, showing a Coulombic efficiency of 88%. Such a one-dimensional core-shell design exploits the benefits of the Sn78Ge22 nanowire to produce an exceptional high rate lithium reactivity (93% Coulombic efficiency at 8C (=6400 mA/g) rate) as well as excellent capacity retention after extended cycles (capacity retention of 94%). PMID:17661523

  9. Features of conduction mechanisms in n-HfNiSn semiconductor heavily doped with a Rh acceptor impurity

    SciTech Connect

    Romaka, V. A.; Rogl, P.; Stadnyk, Yu. V.; Romaka, V. V.; Hlil, E. K.; Krajovskii, V. Ya.; Horyn, A. M.

    2013-09-15

    The crystal structure and electron-density distribution, as well as the energy, kinetic, and magnetic characteristics of n-HfNiSn intermetallic semiconductor heavily doped with a Rh acceptor impurity in the temperature range T = 80-400 K, in the acceptor-concentration range N{sub A}{sup Rh} Almost-Equal-To 9.5 Multiplication-Sign 10{sup 19}-1.9 Multiplication-Sign 10{sup 21} cm{sup -3} (x = 0.005-0.10), and in magnetic fields H {<=} 10 kG are investigated. It is established that doping is accompanied by a simultaneous decrease in concentration, the elimination of donor-type structural defects (to x Almost-Equal-To 0.02), and an increase in the concentration of acceptor-type structural defects (0 < x {<=} 0.10). The dependence of the degree of semiconductor compensation on temperature is revealed. A model of the spatial arrangement of atoms in HfNi{sub 1-x}Rh{sub x}Sn is proposed, and the results of calculating the electron structure based on this model agree with the results of investigations of the kinetic and magnetic characteristics of the semiconductor. The results are discussed within the context of the Shklovskii-Efros model for a heavily doped and compensated semiconductor.

  10. Epitaxial GeSn film formed by solid phase epitaxy and its application to Yb{sub 2}O{sub 3}-gated GeSn metal-oxide-semiconductor capacitors with sub-nm equivalent oxide thickness

    SciTech Connect

    Lee, Ching-Wei; Wu, Yung-Hsien; Hsieh, Ching-Heng; Lin, Chia-Chun

    2014-11-17

    Through the technique of solid phase epitaxy (SPE), an epitaxial Ge{sub 0.955}Sn{sub 0.045} film was formed on a Ge substrate by depositing an amorphous GeSn film followed by a rapid thermal annealing at 550 °C. A process that uses a SiO{sub 2} capping layer on the amorphous GeSn film during SPE was proposed and it prevents Sn precipitation from occurring while maintaining a smooth surface due to the reduced surface mobility of Sn atoms. The high-quality epitaxial GeSn film was observed to have single crystal structure, uniform thickness and composition, and tiny surface roughness with root mean square of 0.56 nm. With a SnO{sub x}-free surface, Yb{sub 2}O{sub 3}-gated GeSn metal-oxide-semiconductor (MOS) capacitors with equivalent oxide thickness (EOT) of 0.55 nm were developed. A small amount of traps inside the Yb{sub 2}O{sub 3} was verified by negligible hysteresis in capacitance measurement. Low leakage current of 0.4 A/cm{sup 2} at gate bias of flatband voltage (V{sub FB})-1 V suggests the high quality of the gate dielectric. In addition, the feasibility of using Yb{sub 2}O{sub 3} to well passivate GeSn surface was also evidenced by the small interface trap density (D{sub it}) of 4.02 × 10{sup 11} eV{sup −1} cm{sup −2}, which can be attributed to smooth GeSn surface and Yb{sub 2}O{sub 3} valency passivation. Both leakage current and D{sub it} performance outperform other passivation techniques at sub-nm EOT regime. The proposed epitaxial GeSn film along with Yb{sub 2}O{sub 3} dielectric paves an alternative way to enable high-performance GeSn MOS devices.

  11. Ge2Sb2Te5/SnSe2 nanocomposite multilayer thin films for phase change memory application

    NASA Astrophysics Data System (ADS)

    Feng, Xiaoyi; Wen, Ting; Zhai, Jiwei; Lai, Tianshu; Wang, Changzhou; Song, Sannian; Song, Zhitang

    2014-10-01

    By nanocompositing Ge2Sb2Te5 and SnSe2, the electrical and thermal proprieties of Ge2Sb2Te5/SnSe2 multilayer films for phase change random access memory (PCRAM) are better than those of Ge2Sb2Te5 films. The crystallization temperature rises and can be controlled. The resistance gap can reach approximately five orders of magnitude to ensure high data reliability. The activity energy (Ea) is more than 2.60 eV and the temperature for 10 year data retention reach 110 °C. The analysis of both XRD patterns and TEM images confirmed the reversible phase change transition between amorphous and crystalline state in Ge2Sb2Te5/SnSe2 nanocomposite multilayer films. According to transient photoreflectance traces, the speed of crystallization process was about 33 ns. Among different Ge2Sb2Te5/SnSe2 multilayer films, the film constitute of [Ge2Sb2Te5 (4 nm)/SnSe2(10 nm)]7 showed better properties and was manufactured by CMOS technology to phase change memory (PCM) cells. This result revealed that the Ge2Sb2Te5/SnSe2 nanocomposite multilayer film is a promising phase change material.

  12. Formation of non-substitutional β-Sn defects in Ge{sub 1−x}Sn{sub x} alloys

    SciTech Connect

    Fuhr, J. D.; Ventura, C. I.; Barrio, R. A.

    2013-11-21

    Although group IV semiconductor alloys are expected to form substitutionally, in Ge{sub 1−x}Sn{sub x} this is true only for low concentrations (x < 0.13). The use of these alloys as a narrow gap semiconductor depends on the ability to produce samples with the high quality required for optoelectronic device applications. In a previous paper, we proposed the existence of a non-substitutional complex defect (β-Sn), consisting of a single Sn atom in the center of a Ge divacancy, which may account for the segregation of Sn at large x. Afterwards, the existence of this defect was confirmed experimentally. In this paper we study the local environment and the interactions of the substitutional defect (α-Sn), the vacancy in Ge, and the β-Sn defect by performing extensive numerical ab initio calculations. Our results confirm that a β-Sn defect can be formed by natural diffusion of a vacancy around the substitutional α-Sn defect, since the energy barrier for the process is very small.

  13. An investigation of new infrared nonlinear optical material: BaCdSnSe4, and three new related centrosymmetric compounds: Ba2SnSe4, Mg2GeSe4, and Ba2Ge2S6.

    PubMed

    Wu, Kui; Su, Xin; Yang, Zhihua; Pan, Shilie

    2015-12-14

    A series of new metal chalcongenides, BaCdSnSe4 (1), Ba2SnSe4 (2), Mg2GeSe4 (3), and Ba2Ge2S6 (4), were successfully synthesized for the first time. Among them, compounds 2 and 4 were prepared by a molten flux method with Zn as the flux. In their structures, all of them have MQ4 (M = Sn, Ge; Q = S, Se) units. For compound 1, the CdSe4 and SnSe4 groups are connected to form CdSnSe6 layers and these layers are linked together by the Ba atoms. Compounds 2 and 3 are composed of isolated MSe4 (M = Sn, Ge) units and charge-balanced by the Ba or Mg atoms, respectively, while compound 4 has infinite ∞(GeS3)n chains, which is different from the structures of the other three compounds that only have isolated MSe4 (M = Sn, Ge) units. The measured IR and Raman data of the title compounds show wide infrared transmission ranges. The experimental band gaps of compounds 1, 2, 3 and were determined to be 1.79, 1.90, and 2.02 eV, respectively. Band structures were also calculated and indicate that their tetrahedral units, such as [SnSe4], [GeS4] and [GeSe4], determine the energy band gaps of the title compounds, respectively. As for compound 1, based on fundamental light at 2.09 μm, the experimental second harmonic generation (SHG) response is about 1.6 times that of the benchmark AgGaS2, which is also consistent with the calculated value. Based on the above results, compound 1 has promising applications in the IR field as a NLO material. PMID:26509847

  14. Chemical synthesis of porous hierarchical Ge-Sn binary composites using metathesis reaction for rechargeable Li-ion batteries.

    PubMed

    Lin, Ning; Zhou, Jie; Han, Ying; Zhang, Kailong; Zhu, Yongchun; Qian, Yitai

    2015-12-14

    Direct metathesis reaction between Mg2Ge and SnCl4 is introduced to prepare porous hierarchical Ge-Sn binary composites, in which the Ge and Sn components are distributed uniformly, with a tap density of 2.3 g cm(-3). As an anode for LIBs, the Ge-Sn composite displays a specific capacity of 980 mA h g(-1) at 0.5 A g(-1) after 250 cycles, and 890 mA h g(-1) at 3 A g(-1) over 1700 cycles. When paired with a commercial LiCoO2 cathode, a 3.6 V full battery with a capacity of 830 mA h g(-1) is obtained. PMID:26455516

  15. Electrical characteristics of Ni Ohmic contact on n-type GeSn

    SciTech Connect

    Li, H.; Cheng, H. H.; Lee, L. C.; Lee, C. P.; Su, L. H.; Suen, Y. W.

    2014-06-16

    We report an investigation of the electrical and material characteristics of Ni on an n-type GeSn film under thermal annealing. The current-voltage traces measured with the transmission line method are linear for a wide range of annealing temperatures. The specific contact resistivity was found to decrease with increasing annealing temperature, followed by an increase as the annealing temperature further increased, with a minimum value at an annealing temperature of 350 °C. The material characteristics at the interface layer were measured by energy-dispersive spectrometer, showing that an atomic ratio of (Ni)/(GeSn) = 1:1 yields the lowest specific contact resistivity.

  16. Thermal expansivity of Ge{sub 1-y}Sn{sub y} alloys

    SciTech Connect

    Roucka, R.; Fang, Y.-Y.; Kouvetakis, J.; Chizmeshya, A. V. G.; Menendez, J.

    2010-06-15

    The temperature dependence of the lattice parameter of Ge{sub 1-y}Sn{sub y} alloys deposited on Si substrates has been determined from an analysis of their x-ray reciprocal-space maps. It is found that over the range 0Ge and {alpha}-Sn are nearly the same. Alternative interpolation formulas based on a Debye model and a mixed Debye-Einstein model of the phonon structure are tested and it is found that they also fail to explain the observed increase in thermal expansivity.

  17. Temperature-dependent study of Si-based GeSn photoconductors

    NASA Astrophysics Data System (ADS)

    Pham, Thach; Du, Wei; Margetis, Joe; Ghetmiri, Seyed A.; Mosleh, Aboozar; Sun, Greg; Soref, Richard A.; Tolle, John; Naseem, Hameed A.; Li, Baohua; Yu, Shui-Qing

    2015-02-01

    Si based Ge1-xSnx photoconductors, with Sn incorporation of 0.9, 3.2, and 7%, were fabricated using a CMOS-compatible process. Temperature dependent study was conducted from 300 to 77 K. The first generation device (standard photoconductor, PD) shows long wavelength cut-off beyond 2.1 μm for 7%-Sn devices at room temperature. The peak responsivity and D* of the 7% Sn device at 1.55 μm were obtained at 77K as 0.08 A/W and 1×109 cm*Hz1/2*W-1, respectively. Improved responsivity and specific detectivity (D*) were observed on second generation devices by a newly designed electrode structure (photoconductor with interdigitated electrodes, IEPD). The enhancement factor of responsivity was up to 15 at 77 K.

  18. The interaction between divacancies and shallow dopants in irradiated Ge:Sn

    SciTech Connect

    Khirunenko, L. I.; Pomozov, Yu. V.; Sosnin, M. G.; Abrosimov, N. V.; Riemann, H.

    2014-02-21

    It has been found that upon annealing of irradiated Ge doped with gallium and Sn simultaneously with disappearance of divacancies V{sub 2}{sup 0} the appearance of the new absorption spectrum consisting of sharp lines was observed. The spectrum is identical to the absorption spectrum of gallium. It is shown that the defect, to which the new spectrum corresponds, has hydrogen-like properties. The distances between the lines in the spectrum are in good agreement with those predicted by effective-mass theory. The appearance of Fano resonance in the continuum region in addition to intracenter transitions of the defect was detected. The defect found is identified as SnV{sub 2}{sup 0}Ga. The binding energy for the ground state of the SnV{sub 2}{sup 0}Ga centers has been estimated.

  19. Electroluminescence from GeSn heterostructure pin diodes at the indirect to direct transition

    NASA Astrophysics Data System (ADS)

    Gallagher, J. D.; Senaratne, C. L.; Sims, P.; Aoki, T.; Menéndez, J.; Kouvetakis, J.

    2015-03-01

    The emission properties of GeSn heterostructure pin diodes have been investigated. The devices contain thick (400-600 nm) Ge1-ySny i-layers spanning a broad compositional range below and above the crossover Sn concentration yc where the Ge1-ySny alloy becomes a direct-gap material. These results are made possible by an optimized device architecture containing a single defected interface thereby mitigating the deleterious effects of mismatch-induced defects. The observed emission intensities as a function of composition show the contributions from two separate trends: an increase in direct gap emission as the Sn concentration is increased, as expected from the reduction and eventual reversal of the separation between the direct and indirect edges, and a parallel increase in non-radiative recombination when the mismatch strains between the structure components is partially relaxed by the generation of misfit dislocations. An estimation of recombination times based on the observed electroluminescence intensities is found to be strongly correlated with the reverse-bias dark current measured in the same devices.

  20. The Double-peaked SN 2013ge: A Type Ib/c SN with an Asymmetric Mass Ejection or an Extended Progenitor Envelope

    NASA Astrophysics Data System (ADS)

    Drout, M. R.; Milisavljevic, D.; Parrent, J.; Margutti, R.; Kamble, A.; Soderberg, A. M.; Challis, P.; Chornock, R.; Fong, W.; Frank, S.; Gehrels, N.; Graham, M. L.; Hsiao, E.; Itagaki, K.; Kasliwal, M.; Kirshner, R. P.; Macomb, D.; Marion, G. H.; Norris, J.; Phillips, M. M.

    2016-04-01

    We present extensive multiwavelength (radio to X-ray) observations of the Type Ib/c supernova (SN Ib/c) SN 2013ge from ‑13 to +457 days relative to maximum light, including a series of optical spectra and Swift UV–optical photometry beginning 2–4 days post-explosion. This data set makes SN 2013ge one of the best-observed normal SNe Ib/c at early times—when the light curve is particularly sensitive to the progenitor configuration and mixing of radioactive elements—and reveals two distinct light curve components in the UV bands. The first component rises over 4–5 days and is visible for the first week post-explosion. Spectra of the first component have blue continua and show a plethora of moderately high velocity (∼15,000 km s‑1) but narrow (∼3500 km s‑1) spectroscopic features, indicating that the line-forming region is restricted. The explosion parameters estimated for the bulk explosion ({M}{{ej}} ∼ 2–3 {M}ȯ ; {E}{{K}} ∼ (1–2) × 1051 erg) are standard for SNe Ib/c, and there is evidence for weak He features at early times—in an object that would have otherwise been classified as Type Ic. In addition, SN 2013ge exploded in a low-metallicity environment (∼0.5 {Z}ȯ ), and we have obtained some of the deepest radio and X-ray limits for an SN Ib/c to date, which constrain the progenitor mass-loss rate to be \\dot{M} < 4 × 10‑6 {M}ȯ yr‑1. We are left with two distinct progenitor scenarios for SN 2013ge, depending on our interpretation of the early emission. If the first component is cooling envelope emission, then the progenitor of SN 2013ge either possessed an extended (≳30 {R}ȯ ) envelope or ejected a portion of its envelope in the final ≲ 1 yr before core collapse. Alternatively, if the first component is due to outwardly mixed 56Ni, then our observations are consistent with the asymmetric ejection of a distinct clump of nickel-rich material at high velocities. Current models for the collision of an SN shock with a binary

  1. Material Characterization of Ge1- x Sn x Alloys Grown by a Commercial CVD System for Optoelectronic Device Applications

    NASA Astrophysics Data System (ADS)

    Mosleh, Aboozar; Ghetmiri, Seyed Amir; Conley, Benjamin R.; Hawkridge, Michael; Benamara, Mourad; Nazzal, Amjad; Tolle, John; Yu, Shui-Qing; Naseem, Hameed A.

    2014-04-01

    High-quality compressive-strained Ge1- x Sn x /Ge films have been deposited on Si(001) substrate using a mainstream commercial chemical vapor deposition reactor. The growth temperature was kept below 450°C to be compatible with Si complementary metal-oxide-semiconductor processes. Germanium tin (Ge1- x Sn x ) layers were grown with different Sn composition ranging from 0.9% to 7%. Material characterizations, such as secondary-ion mass spectrometry, Rutherford backscattering spectrometry, and x-ray diffraction analysis, show stable Sn incorporation in the Ge lattice. Comparison of the Sn mole fractions obtained using these methods shows that the bowing factor of 0.166 nm (in Vegard's law) is in close agreement with other experimental data. High-resolution transmission electron microscopy and atomic force microscopy results show that the films have started to relax through the formation of misfit and threading dislocations. Raman spectroscopy, ellipsometry, and photoluminescence (PL) techniques are used to study the structural and optical properties of the films. Room-temperature PL of the films shows that 7% Sn incorporation in the Ge lattice results in a decrease in the direct bandgap of Ge from 0.8 eV to 0.56 eV.

  2. Ultra-low temperature (≤300 °C) growth of Ge-rich SiGe by solid-liquid-coexisting annealing of a-GeSn/c-Si structures

    NASA Astrophysics Data System (ADS)

    Sadoh, Taizoh; Chikita, Hironori; Matsumura, Ryo; Miyao, Masanobu

    2015-09-01

    Ultra-low temperature (≤300 °C) growth of Ge-rich SiGe on Si substrates is strongly desired to realize advanced electronic and optical devices, which can be merged onto Si large-scale integrated circuits (LSI). To achieve this, annealing characteristics of a-GeSn/c-Si structures are investigated under wide ranges of the initial Sn concentrations (0%-26%) and annealing conditions (300-1000 °C, 1 s-48 h). Epitaxial growth triggered by SiGe mixing is observed after annealing, where the annealing temperatures necessary for epitaxial growth significantly decrease with increasing initial Sn concentration and/or annealing time. As a result, Ge-rich (˜80%) SiGe layers with Sn concentrations of ˜2% are realized by ultra-low temperature annealing (300 °C, 48 h) for a sample with the initial Sn concentration of 26%. The annealing temperature (300 °C) is in the solid-liquid coexisting temperature region of the phase diagram for Ge-Sn system. From detailed analysis of crystallization characteristics and composition profiles in grown layers, it is suggested that SiGe mixing is generated by a liquid-phase reaction even at ultra-low temperatures far below the melting temperature of a-GeSn. This ultra-low-temperature growth technique of Ge-rich SiGe on Si substrates is expected to be useful to realize next-generation LSI, where various multi-functional devices are integrated on Si substrates.

  3. Ultra-low temperature (≤300 °C) growth of Ge-rich SiGe by solid-liquid-coexisting annealing of a-GeSn/c-Si structures

    SciTech Connect

    Sadoh, Taizoh Chikita, Hironori; Miyao, Masanobu; Matsumura, Ryo

    2015-09-07

    Ultra-low temperature (≤300 °C) growth of Ge-rich SiGe on Si substrates is strongly desired to realize advanced electronic and optical devices, which can be merged onto Si large-scale integrated circuits (LSI). To achieve this, annealing characteristics of a-GeSn/c-Si structures are investigated under wide ranges of the initial Sn concentrations (0%–26%) and annealing conditions (300–1000 °C, 1 s–48 h). Epitaxial growth triggered by SiGe mixing is observed after annealing, where the annealing temperatures necessary for epitaxial growth significantly decrease with increasing initial Sn concentration and/or annealing time. As a result, Ge-rich (∼80%) SiGe layers with Sn concentrations of ∼2% are realized by ultra-low temperature annealing (300 °C, 48 h) for a sample with the initial Sn concentration of 26%. The annealing temperature (300 °C) is in the solid-liquid coexisting temperature region of the phase diagram for Ge-Sn system. From detailed analysis of crystallization characteristics and composition profiles in grown layers, it is suggested that SiGe mixing is generated by a liquid-phase reaction even at ultra-low temperatures far below the melting temperature of a-GeSn. This ultra-low-temperature growth technique of Ge-rich SiGe on Si substrates is expected to be useful to realize next-generation LSI, where various multi-functional devices are integrated on Si substrates.

  4. Electronic band structure trends of perovskite halides: Beyond Pb and Sn to Ge and Si

    NASA Astrophysics Data System (ADS)

    Huang, Ling-yi; Lambrecht, Walter R. L.

    2016-05-01

    The trends in electronic band structure are studied in the cubic A B X3 halide perovskites for A =Cs ; B =Pb , Sn, Ge, Si; and X =I , Br, Cl. The gaps are found to decrease from Pb to Sn and from Ge to Si, but increase from Sn to Ge. The trend is explained in terms of the atom s levels of the group-IV element and the atomic sizes which changes the amount of hybridization with X -p and hence the valence bandwidth. Along the same series spin-orbit coupling also decreases and this tends to increase the gap because of the smaller splitting of the conduction band minimum. Both effects compensate each other to a certain degree. The trend with halogens is to reduce the gap from Cl to I, i.e., with decreasing electronegativity. The role of the tolerance factor in avoiding octahedron rotations and octahedron edge sharing is discussed. The Ge containing compounds have tolerance factor t >1 and hence do not show the series of octahedral rotation distortions and the existence of edge-sharing octahedral phases known for Pb and Sn-based compounds, but rather a rhombohedral distortion. CsGeI3 is found to have a suitable gap for photovoltaics both in its cubic (high-temperature) and rhombohedral (low-temperature) phases. The structural stability of the materials in the different phases is also discussed. We find the rhombohedral phase to have lower total energy and slightly larger gaps but to present a less significant distortion of the band structure than the edge-sharing octahedral phases, such as the yellow phase in CsSnI3. The corresponding silicon based compounds have not yet been synthesized and therefore our estimates are less certain but indicate a small gap for cubic CsSiI3 and CsSiBr3 of about 0.2 ±0.2 eV and 0.8 ±0.6 eV for CsSiCl3. The intrinsic stability of the Si compounds is discussed.

  5. Theoretical investigation of tensile strained GeSn waveguide with Si₃N₄ liner stressor for mid-infrared detector and modulator applications.

    PubMed

    Zhang, Qingfang; Liu, Yan; Yan, Jing; Zhang, Chunfu; Hao, Yue; Han, Genquan

    2015-03-23

    We theoretically investigate a tensile strained GeSn waveguide integrated with Si₃N₄ liner stressor for the applications in mid-infrared (MIR) detector and modulator. A substantial tensile strain is induced in a 1 × 1 μm² GeSn waveguide by the expansion of 500 nm Si₃N₄ liner stressor and the contour plots of strain are simulated by the finite element simulation. Under the tensile strain, the direct bandgap E(G,Γ) of GeSn is significantly reduced by lowering the Γ conduction valley in energy and lifting of degeneracy of valence bands. Absorption coefficients of tensile strained GeSn waveguides with different Sn compositions are calculated. As the Si₃N₄ liner stressor expands by 1%, the cut-off wavelengths of tensile strained Ge(0.97)Sn(0.03), Ge(0.95)Sn(0.05), and Ge(0.90)Sn(0.10) waveguide photodetectors are extended to 2.32, 2.69, and 4.06 μm, respectively. Tensile strained Ge(0.90)Sn(0.10) waveguide electro-absorption modulator based on Franz-Keldysh (FK) effect is demonstrated in theory. External electric field dependence of cut-off wavelength and propagation loss of tensile strained Ge(0.90)Sn(0.10) waveguide is observed, due to the FK effect. PMID:25837129

  6. Electric Field Gradient at Nb Site in the Intermetallic Compounds Nb3X (X = AI, In, Si, Ge, Sn) Measured by PAC

    NASA Astrophysics Data System (ADS)

    Junqueira, A. C.; Carbonari, A. W.; Filho, J. Mestnik; Saxena, R. N.

    2000-02-01

    The electric field gradient (efg) at the Nb site in the intermetallic compounds Nb3X (X = Al, In, Si, Ge, Sn) was measured by the Perturbed Angular Correlation (PAC) method using the well-known gamma-gamma cascade of 133 -482 keV in 181Ta from the β- decay of 181Hf, substituting approximately 0.1 atom percent of Nb. The PAC results show that Vzz drops by nearly 40% when X changes from Al to In, and by about 25% when X changes from Si to Ge and Sn. This behavior is most probably related to the change in the degree of sp hybridization in these compounds. The Vzz values of the studied compounds do not follow the well known universal correlation for the efg's in non-cubic metals but the observed trend is well reproduced by results of ab-initio electronic structure calculations. In the case of Nb3 Al a linear temperature dependence of the quadrupole frequencies was observed in the temperature range of 6.5 to 1210 K.

  7. Electrical and structural properties of group-4 transition-metal nitride (TiN, ZrN, and HfN) contacts on Ge

    SciTech Connect

    Yamamoto, Keisuke; Nakashima, Hiroshi; Noguchi, Ryutaro; Wang, Dong; Mitsuhara, Masatoshi; Nishida, Minoru; Hara, Toru

    2015-09-21

    Electrical and structural properties were investigated for group-4 transition-metal nitride contacts on Ge (TiN/Ge, ZrN/Ge, and HfN/Ge), which were prepared by direct sputter depositions using nitride targets. These contacts could alleviate the intrinsic Fermi-level pinning (FLP) position toward the conduction band edge. It was revealed that this phenomenon is induced by an amorphous interlayer (a-IL) containing nitrogen atoms at the nitride/Ge interfaces. The strength of FLP alleviation positively depended on the thickness of a-IL. TiN/Ge and ZrN/Ge contacts with ∼2 nm-thick a-ILs showed strong FLP alleviations with hole barrier heights (Φ{sub BP}) in the range of 0.52–56 eV, and a HfN/Ge contact with an ∼1 nm-thick a-IL showed a weaker one with a Φ{sub BP} of 0.39 eV. However, TaN/Ge contact without a-IL did not show such FLP alleviation. Based on the results of depth distributions for respective elements, we discussed the formation kinetics of a-ILs at TiN/Ge and ZrN/Ge interfaces. Finally, we proposed an interfacial dipole model to explain the FLP alleviation.

  8. Large grain growth of Ge-rich Ge{sub 1−x}Sn{sub x} (x ≈ 0.02) on insulating surfaces using pulsed laser annealing in flowing water

    SciTech Connect

    Kurosawa, Masashi; Taoka, Noriyuki; Nakatsuka, Osamu; Zaima, Shigeaki; Ikenoue, Hiroshi

    2014-02-10

    We investigate Sn incorporation effects on the growth characteristics of Ge-rich Ge{sub 1−x}Sn{sub x} (x < 0.02) on SiO{sub 2} crystallized by pulsed laser annealing (PLA) in air and water. Despite the very low Sn content of 2%, Sn atoms within the GeSn layers play a role in preventing ablation and aggregation of the layers during these PLA. Raman and electron backscatter diffraction measurements demonstrate achievement of large-grain (∼800 nmϕ) growth of Ge{sub 0.98}Sn{sub 0.02} polycrystals by using PLA in water. These polycrystals also show a tensile-strain of ∼0.68%. This result opens up the possibility for developing GeSn-based devices fabricated on flexible substrates as well as Si platforms.

  9. Crystal structure and magnetic properties of novel Hf3Ni2Si3-type R3Co2Ge3 compounds (R=Y, Sm, Tb-Tm)

    NASA Astrophysics Data System (ADS)

    Morozkin, A. V.; Nirmala, R.; Yao, Jinlei; Mozharivskyj, Y.; Isnard, O.

    2012-12-01

    The novel R3Co2Ge3 compounds with R=Y, Sm, Tb-Tm adopt the Hf3Ni2Si3-type structure (ordered variant of the Ca3Ga5-type one, space group Cmcm). Sm3Co2Ge3, Tb3Co2Ge3, Ho3Co2Ge3 and Er3Co2Ge3 undergo an antiferromagnetic-type ordering and Tb3Co2Ge3 demonstrates a field-sensitive magnetic behavior. Tm3Co2Ge3 is a pure paramagnet down to 5 K, whereas Y3Co2Ge3 demonstrates Pauli paramagnetism down to ∼120 K. In zero applied field and between ∼50 and ∼15 K Tb3Co2Ge3 shows a non-collinear antiferromagnetic ordering with wave vectors K0=[0, 0, 0] and K1=[±1/3, 0, 0] and a magnetic unit cell 3aTb3Co2Ge2×bTb3Co2Ge3×cTb3Co2Ge3 , whereas below ∼15 K it exhibits a complex antiferromagnetic ordering with K0=[0, 0, 0], K1=[±1/3, 0, 0] and K2=[1/2, 0, 0] wave vectors and magnetic unit cell 6aTb3Co2Ge2×bTb3Co2Ge2×cTb3Co2Ge2.

  10. Distribution of free carriers near heavily-doped epitaxial surfaces of n-type Ge(100) upon HF and HCl treatments

    SciTech Connect

    Park, S. J.; Bolotov, L.; Uchida, N.; Tada, T.

    2015-10-15

    Carrier distributions near n-type epitaxially-grown Ge(100) surfaces with high impurity concentrations (1 × 10{sup 20} cm{sup −3}) were studied using high resolution electron energy loss spectroscopy (HREELS) upon surface treatments in aqueous solutions of HF and HCl. After surface treatments with HCl and HF, the molecular vibration modes distinctly showed either chloride or hydride terminations of Ge surfaces with negligible oxidation. The free-carrier concentration profile was inferred from the conduction band plasmon measurements as a function of the incident electron energies employing a dielectric theory simulation with a 4-layer structure and an effective electron mass of 0.02m{sub 0}. A carrier-free layer of 40 and 24 Å were derived for HCl- and HF-treated Ge(100), respectively. The surface band bending was estimated to be 0.32 eV for HF-treated Ge. HCl-treated Ge surfaces showed a band bending of 0.91 eV attributed to the strong effect of the surface Cl-Ge dipole.

  11. Systematic study of GeSn heterostructure-based light-emitting diodes towards mid-infrared applications

    NASA Astrophysics Data System (ADS)

    Zhou, Yiyin; Dou, Wei; Du, Wei; Pham, Thach; Ghetmiri, Seyed Amir; Al-Kabi, Sattar; Mosleh, Aboozar; Alher, Murtadha; Margetis, Joe; Tolle, John; Sun, Greg; Soref, Richard; Li, Baohua; Mortazavi, Mansour; Naseem, Hameed; Yu, Shui-Qing

    2016-07-01

    Temperature-dependent characteristics of GeSn light-emitting diodes with Sn composition up to 9.2% have been systematically studied. Such diodes were based on Ge/GeSn/Ge double heterostructures (DHS) that were grown directly on a Si substrate via a chemical vapor deposition system. Both photoluminescence and electroluminescence spectra have been characterized at temperatures from 300 to 77 K. Based on our theoretical calculation, all GeSn alloys in this study are indirect bandgap materials. However, due to the small energy separation between direct and indirect bandgap, and the fact that radiative recombination rate greater than non-radiative, the emissions are mainly from the direct Γ-valley to valence band transitions. The electroluminescence emissions under current injection levels from 102 to 357 A/cm2 were investigated at 300 K. The monotonic increase of the integrated electroluminescence intensity was observed for each sample. Moreover, the electronic band structures of the DHS were discussed. Despite the indirect GeSn bandgap owing to the compressive strain, type-I band alignment was achieved with the barrier heights ranging from 11 to 47 meV.

  12. Electronic Transport Properties of New 2-D Materials GeH and NaSn2As2

    NASA Astrophysics Data System (ADS)

    He, Bin; Cultrara, Nicholas; Arguilla, Maxx; Goldberger, Joshua; Heremans, Joseph

    2-D materials potentially have superior thermoelectric properties compared to traditional 3-D materials due to their layered structure. Here we present electrical and thermoelectric transport properties of 2 types of 2-D materials, GeH and NaSn2As2. GeH is a graphane analog which is prepared using chemical exfoliation of CaGe2 crystals. Intrinsic GeH is proven to be a highly resistive material at room temperature. Resistance and Seebeck coefficient of Ga doped GeH are measured in a cryostat with a gating voltage varying from -100V to 100V. NaSn2As2 is another 2-D system, with Na atom embedded between nearly-2D Sn-As layers. Unlike GeH, NaSn2As2 is a metal based of Hall measurements, with p-type behavior, and with van der Pauw resistances on the order of 5m Ω/square. Thermoelectric transport properties of NaSn2As2 will be reported. This work is support by the NSF EFRI-2DARE project EFRI-1433467.

  13. First-principle studies of Ca-X (X=Si,Ge,Sn,Pb) intermetallic compounds

    SciTech Connect

    Yang Zhiwen; Shi Dongmin; Wen Bin; Melnik, Roderick; Yao Shan; Li Tingju

    2010-01-15

    The structural properties, elastic properties, heats of formation, electronic structures, and densities of states of 20 intermetallic compounds in the Ca-X (X=Si, Ge, Sn, Pb) systems have been systematically investigated by using first-principle calculations. Our computational results indicated that with increasing atomic weight of X, the bulk modulus of Ca-X intermetallic compounds decreases gradually. It was also found that Ca{sub 36}Sn{sub 23} and CaPb are mechanically unstable phases. Results on the electronic energy band and densities of states also indicated that Ca{sub 3}Si{sub 4} is an indirect band gap semiconductor with a band gap of 0.598 eV, and Ca{sub 2}Si, Ca{sub 2}Ge, Ca{sub 2}Sn, and Ca{sub 2}Pb are direct band gap semiconductors with band gaps of 0.324, 0.265, 0.06, and 0.07 eV, respectively. In addition, it is found that the absolute values of heats of formation for all Ca-X intermetallics are larger than 30 kJ/mol atom. - Graphical abstract: Calculated (a) bulk moduli and (b) shear moduli of Ca-X system intermetallic compounds.

  14. Control of Sn Precipitation and Strain Relaxation in Compositionally Step-Graded Ge1-xSnx Buffer Layers for Tensile-Strained Ge Layers

    NASA Astrophysics Data System (ADS)

    Shimura, Yosuke; Tsutsui, Norimasa; Nakatsuka, Osamu; Sakai, Akira; Zaima, Shigeaki

    2009-04-01

    We investigated the relationship between Sn precipitation and strain relaxation in Ge1-xSnx buffer layers grown by the compositionally step-graded (CSG) method on a virtual Ge substrate. We found that the strain in the upper Ge1-xSnx layers is reduced by Sn precipitation rather than the lateral propagation of misfit dislocations at the interfaces of upper Ge1-xSnx layers in the CSG method. The critical misfit strain was increased to 5.8 ×10-3 compared with that in our previous work by lowering the temperature of the postdeposition annealing, and a Sn content of 6.3% in the Ge1-xSnx buffer layer was achieved with a large degree of strain relaxation using only two stacked layers of the CSG structure. An in-plane tensile strain of 0.62% in a 30-nm-thick Ge layer fabricated on these Ge1-xSnx buffer layers was achieved.

  15. Insights into thermal diffusion of germanium and oxygen atoms in HfO2/GeO2/Ge gate stacks and their suppressed reaction with atomically thin AlOx interlayers

    NASA Astrophysics Data System (ADS)

    Ogawa, Shingo; Asahara, Ryohei; Minoura, Yuya; Sako, Hideki; Kawasaki, Naohiko; Yamada, Ichiko; Miyamoto, Takashi; Hosoi, Takuji; Shimura, Takayoshi; Watanabe, Heiji

    2015-12-01

    The thermal diffusion of germanium and oxygen atoms in HfO2/GeO2/Ge gate stacks was comprehensively evaluated by x-ray photoelectron spectroscopy and secondary ion mass spectrometry combined with an isotopic labeling technique. It was found that 18O-tracers composing the GeO2 underlayers diffuse within the HfO2 overlayers based on Fick's law with the low activation energy of about 0.5 eV. Although out-diffusion of the germanium atoms through HfO2 also proceeded at the low temperatures of around 200 °C, the diffusing germanium atoms preferentially segregated on the HfO2 surfaces, and the reaction was further enhanced at high temperatures with the assistance of GeO desorption. A technique to insert atomically thin AlOx interlayers between the HfO2 and GeO2 layers was proven to effectively suppress both of these independent germanium and oxygen intermixing reactions in the gate stacks.

  16. Insights into thermal diffusion of germanium and oxygen atoms in HfO{sub 2}/GeO{sub 2}/Ge gate stacks and their suppressed reaction with atomically thin AlO{sub x} interlayers

    SciTech Connect

    Ogawa, Shingo; Asahara, Ryohei; Minoura, Yuya; Hosoi, Takuji Shimura, Takayoshi; Watanabe, Heiji; Sako, Hideki; Kawasaki, Naohiko; Yamada, Ichiko; Miyamoto, Takashi

    2015-12-21

    The thermal diffusion of germanium and oxygen atoms in HfO{sub 2}/GeO{sub 2}/Ge gate stacks was comprehensively evaluated by x-ray photoelectron spectroscopy and secondary ion mass spectrometry combined with an isotopic labeling technique. It was found that {sup 18}O-tracers composing the GeO{sub 2} underlayers diffuse within the HfO{sub 2} overlayers based on Fick's law with the low activation energy of about 0.5 eV. Although out-diffusion of the germanium atoms through HfO{sub 2} also proceeded at the low temperatures of around 200 °C, the diffusing germanium atoms preferentially segregated on the HfO{sub 2} surfaces, and the reaction was further enhanced at high temperatures with the assistance of GeO desorption. A technique to insert atomically thin AlO{sub x} interlayers between the HfO{sub 2} and GeO{sub 2} layers was proven to effectively suppress both of these independent germanium and oxygen intermixing reactions in the gate stacks.

  17. Extended X-ray absorption fine structure investigation of Sn local environment in strained and relaxed epitaxial Ge1-xSnx films

    NASA Astrophysics Data System (ADS)

    Gencarelli, F.; Grandjean, D.; Shimura, Y.; Vincent, B.; Banerjee, D.; Vantomme, A.; Vandervorst, W.; Loo, R.; Heyns, M.; Temst, K.

    2015-03-01

    We present an extended X-ray absorption fine structure investigation of the local environment of Sn atoms in strained and relaxed Ge1-xSnx layers with different compositions. We show that the preferred configuration for the incorporation of Sn atoms in these Ge1-xSnx layers is that of a α-Sn defect, with each Sn atom covalently bonded to four Ge atoms in a classic tetrahedral configuration. Sn interstitials, Sn-split vacancy complexes, or Sn dimers, if present at all, are not expected to involve more than 2.5% of the total Sn atoms. This finding, along with a relative increase of Sn atoms in the second atomic shell around a central Sn atom in Ge1-xSnx layers with increasing Sn concentrations, suggests that the investigated materials are homogeneous random substitutional alloys. Within the accuracy of the measurements, the degree of strain relaxation of the Ge1-xSnx layers does not have a significant impact on the local atomic surrounding of the Sn atoms. Finally, the calculated topological rigidity parameter a** = 0.69 ± 0.29 indicates that the strain due to alloying in Ge1-xSnx is accommodated via bond stretching and bond bending, with a slight predominance of the latter, in agreement with ab initio calculations reported in literature.

  18. Elastic, vibrational and thermodynamic properties of α-Sn based group IV semiconductors and GeC under pressure

    NASA Astrophysics Data System (ADS)

    Souadkia, M.; Bennecer, B.; Kalarasse, F.

    2013-11-01

    We present first-principles calculations of the structural, elastic, vibrational and thermodynamic properties of SnSi, SnGe, SnC and GeC. We employ the density-functional perturbation theory (DFPT) within the local density approximation in conjunction with the quasi-harmonic approximation. The calculated lattice parameters, which are obtained by minimizing the total energy, are in the range of those reported in the literature for the binary compounds and in good agreement with the measured ones for the elemental components. Our results for the elastic properties show that c44 softens as pressure increases for SnSi and SnGe. The phonon spectra, the density of states and the Born effective charge at zero pressure are calculated and the phonon frequencies are positive. A pressure induced soft transverse acoustic phonon mode is identified at the zone boundary X point of the Brillouin zone at pressure of 12.95 and 12.45 GPa for SnSi and SnGe respectively. The linear expansion coefficient for the elemental components is calculated and compared to experiment. The temperature and pressure dependence of the thermal expansion, the overall Grüneisen parameter, the bulk modulus and the heat capacity is predicted. The thermal expansion coefficient decreases with increasing pressure and does not show any negative behavior for GeC and this is due to the positive transverse acoustic mode Grüneisen parameters. Our results for SnxGe alloys using the supercell method indicate that the variation of the Grüneisen parameter and the thermal expansion with concentration has the same trend and the bulk modulus softens.

  19. Above-bandgap optical properties of biaxially strained GeSn alloys grown by molecular beam epitaxy

    SciTech Connect

    Richard D’Costa, Vijay Wang, Wei; Zhou, Qian; Yeo, Yee-Chia; Soon Tok, Eng

    2014-01-13

    The complex dielectric function of biaxially strained Ge{sub 1−x}Sn{sub x} (0 ≤ x ≤ 0.17) alloys grown on Ge (100) has been determined by spectroscopic ellipsometry from 1.2 to 4.7 eV. The effect of substitutional Sn incorporation and the epitaxial strain on the energy transitions E{sub 1}, E{sub 1} + Δ{sub 1}, E{sub 0}′, and E{sub 2} of GeSn alloys is investigated. Our results indicate that the strained GeSn alloys show Ge-like electronic bandstructure with all the transitions shifted downward due to the alloying of Sn. The strain dependence of E{sub 1} and E{sub 1} + Δ{sub 1} transitions is explained using the deformation potential theory, and values of −5.4 ± 0.4 eV and 3.8 ± 0.5 eV are obtained for the hydrostatic and shear deformation potentials, respectively.

  20. First-principles calculations of Mg2X (X = Si, Ge, Sn) semiconductors with the calcium fluorite structure

    NASA Astrophysics Data System (ADS)

    Sandong, Guo

    2015-05-01

    The electronic structures of Mg2X (X = Si, Ge, Sn) have been calculated by using generalized gradient approximation, various screened hybrid functionals, as well as Tran and Blaha's modified Becke and Johnson exchange potential. It was found that the Tran and Blaha's modified Becke and Johnson exchange potential provides a more realistic description of the electronic structures and the optical properties of Mg2X (X = Si, Ge, Sn) than else exchange-correlation potential, and the theoretical gaps and dielectric functions of Mg2X (X = Si, Ge, Sn) are quite compatible with the experimental data. The elastic properties of Mg2X (X = Si, Ge, Sn) have also been studied in detail with the generalized gradient approximation, including bulk modulus, shear modulus, Young's modulus, Poisson's ratio, sound velocities, and Debye temperature. The phonon dispersions of Mg2X (X = Si, Ge, Sn) have been calculated within the generalized gradient approximation, suggesting no structural instability, and the measurable phonon heat capacity as a function of the temperature has been also calculated. Project supported by the Fundamental Research Funds for the Central Universities (No. 2013QNA32) and the National Natural Science Foundation of China (No. 11404391).

  1. Si based mid-infrared GeSn photo detectors and light emitters

    NASA Astrophysics Data System (ADS)

    Du, Wei; Pham, Thach; Margetis, Joe; Tran, Huong; Ghetmiri, Seyed A.; Mosleh, Aboozar; Sun, Greg; Soref, Richard A.; Tolle, John; Naseem, Hameed A.; Li, Baohua; Yu, Shui-Qing

    2015-08-01

    In this work, high performance GeSn photoconductor and light emitting diodes (LED) have been demonstrated. For the photoconductor, the high responsivity was achieved due to high photoconductive gain, which is attributed to the novel optical and electrical design. The longwave cutoff at 2.4 μm was also observed at room temperature. For LED, temperature-dependent study was conducted. The electroluminescence (EL) spectra at different temperatures were obtained and EL peak shift was observed. Moreover, the emission power at different temperatures was measured. High power emission at 2.1 μm was achieved.

  2. Dielectric behavior of a-Sn-Se-Pb-Ge chalcogenide glass

    SciTech Connect

    Kumar, Prashant Modgil, Vivek; Choudhary, Shobhana; Nidhi, A. V.; Rangra, V. S.

    2015-05-15

    The bulk material Sn{sub 8}Se{sub 74}Pb{sub 18-x}Ge{sub x}(7≤x≤11) has been prepared by melt quenching technique. The viterous and glassy nature have been confirmed by X-Ray Diffraction (XRD) and Differential Scanning Calorimetery (DSC) techniques respectively. The material exhibits the good thermal stability and high value of glass transition temperature. The dielectric behavior has been studied in frequency range 50Hz-1MHz, using pallet method. The universal dielectric behaviour of amorphous semiconductors has been observed for the glass system. The compositional dependence of dielectric behavior has also been observed.

  3. Order-disorder transition of the (3 x 3) Sn/Ge(111) phase

    SciTech Connect

    Floreano, L.; Cvetko, D.; Bavdek, G.; Benes, M.; Morgante, A.

    2001-08-15

    We have measured the long-range order of the {alpha} phase of Sn on the Ge(111) surface throughout the (3 x 3){yields}(3 x 3)R30{sup o} phase transition. The transition has been found of the order-disorder type with a critical temperature T{sub c}{approx}220 K. The expected three-state Potts critical exponents are shown to be consistent with the observed power-law dependence of the (3 x 3) order parameter and its correlation length close to T{sub c}, thus excluding a charge-density wave driven phase transition.

  4. Density-functional theory molecular dynamics simulations of a-HfO2/Ge(100)(2 × 1) and a-ZrO2/Ge(100)(2 × 1) interface passivation.

    PubMed

    Chagarov, E A; Porter, L; Kummel, A C

    2016-02-28

    The structural properties of a-HfO2/Ge(2 × 1)-(001) and a-ZrO2/Ge(2 × 1)-(001) interfaces were investigated with and without a GeOx interface interlayer using density-functional theory (DFT) molecular dynamics (MD) simulations. Realistic a-HfO2 and a-ZrO2 samples were generated using a hybrid classical-DFT MD "melt-and-quench" approach and tested against experimental properties. The oxide/Ge stacks were annealed at 700 K, cooled to 0 K, and relaxed providing the system with enough freedom to form realistic interfaces. For each high-K/Ge stack type, two systems with single and double interfaces were investigated. All stacks were free of midgap states; however, stacks with a GeO(x) interlayer had band-edge states which decreased the band gaps by 0%-30%. These band-edge states were mainly produced by under-coordinated Ge atoms in GeO(x) layer or its vicinity due to deformation, intermixing, and bond-breaking. The DFT-MD simulations show that electronically passive interfaces can be formed either directly between high-K dielectrics and Ge or with a monolayer of GeO2 if the processing does not create or properly passivate under-coordinated Ge atoms and Ge's with significantly distorted bonding angles. Comparison to the charge states of the interfacial atoms from DFT to experimental x-ray photoelectron spectroscopy results shows that while most studies of gate oxide on Ge(001) have a GeO(x) interfacial layer, it is possible to form an oxide/Ge interface without a GeO(x) interfacial layer. Comparison to experiments is consistent with the dangling bonds in the suboxide being responsible for midgap state formation. PMID:26931715

  5. Density-functional theory molecular dynamics simulations of a-HfO2/Ge(100)(2 × 1) and a-ZrO2/Ge(100)(2 × 1) interface passivation

    NASA Astrophysics Data System (ADS)

    Chagarov, E. A.; Porter, L.; Kummel, A. C.

    2016-02-01

    The structural properties of a-HfO2/Ge(2 × 1)-(001) and a-ZrO2/Ge(2 × 1)-(001) interfaces were investigated with and without a GeOx interface interlayer using density-functional theory (DFT) molecular dynamics (MD) simulations. Realistic a-HfO2 and a-ZrO2 samples were generated using a hybrid classical-DFT MD "melt-and-quench" approach and tested against experimental properties. The oxide/Ge stacks were annealed at 700 K, cooled to 0 K, and relaxed providing the system with enough freedom to form realistic interfaces. For each high-K/Ge stack type, two systems with single and double interfaces were investigated. All stacks were free of midgap states; however, stacks with a GeOx interlayer had band-edge states which decreased the band gaps by 0%-30%. These band-edge states were mainly produced by under-coordinated Ge atoms in GeOx layer or its vicinity due to deformation, intermixing, and bond-breaking. The DFT-MD simulations show that electronically passive interfaces can be formed either directly between high-K dielectrics and Ge or with a monolayer of GeO2 if the processing does not create or properly passivate under-coordinated Ge atoms and Ge's with significantly distorted bonding angles. Comparison to the charge states of the interfacial atoms from DFT to experimental x-ray photoelectron spectroscopy results shows that while most studies of gate oxide on Ge(001) have a GeOx interfacial layer, it is possible to form an oxide/Ge interface without a GeOx interfacial layer. Comparison to experiments is consistent with the dangling bonds in the suboxide being responsible for midgap state formation.

  6. C-H activation of cycloalkenes by dimetallynes (M = Ge, Sn) under ambient conditions.

    PubMed

    Summerscales, Owen T; Fettinger, James C; Power, Philip P

    2011-08-10

    Treatment of the dimetallynes Ar'EEAr' [E = Ge, Sn; Ar' = C(6)H(3)-2,6-(C(6)H(3)-2,6-iPr(2))(2)] with a cyclic olefin-cyclopentadiene (CpH), cyclopentene, 1,4-cyclohexadiene (CHD), or cyclohexene-showed that, with the exception of cyclohexene, they react readily, affording C-H activation at room temperature. Reaction of the digermyne and distannyne with CpH gave the cyclopentadienyl anion, which is bound in a π-fashion to a mononuclear group 14 element center, along with evolution of hydrogen gas. Unusually, the digermyne also reacted with cyclopentene to give the same dehydroaromatization product, formed from triple C-H activation/dehydrogenation. It also was found to react with CHD to give a mixture of (Ar'GeH)(2), benzene, and a new 7-germanorbornadiene species bound to a cyclohex-2-enyl fragment. PMID:21749107

  7. Strained germanium-tin (GeSn) p-channel metal-oxide-semiconductor field-effect-transistors (p-MOSFETs) with ammonium sulfide passivation

    NASA Astrophysics Data System (ADS)

    Wang, Lanxiang; Su, Shaojian; Wang, Wei; Gong, Xiao; Yang, Yue; Guo, Pengfei; Zhang, Guangze; Xue, Chunlai; Cheng, Buwen; Han, Genquan; Yeo, Yee-Chia

    2013-05-01

    High-mobility strained Ge0.958Sn0.042 p-channel metal-oxide-semiconductor field-effect-transistors (p-MOSFETs) with ammonium sulfide [(NH4)2S] surface passivation were demonstrated. A ˜10 nm thick fully-strained single crystalline GeSn layer was epitaxially grown on Ge (1 0 0) substrate as the channel layer. (NH4)2S surface passivation was performed for the GeSn surface, followed by gate stack formation. Ge0.958Sn0.042 p-MOSFETs with (NH4)2S passivation show decent electrical characteristics and a peak effective mobility of 509 cm2/V s, which is the highest reported peak mobility obtained for GeSn channel p-MOSFETs so far.

  8. Chemical bonding in RFe6Ge4 (R = Li, Sc, Zr) and LuTi6Sn4 with rhombohedral LiFe6Ge4 type structure

    NASA Astrophysics Data System (ADS)

    Matar, Samir F.; Fickenscher, Thomas; Gerke, Birgit; Niehaus, Oliver; Rodewald, Ute Ch; Al Alam, Adel F.; Ouaini, Naïm; Pöttgen, Rainer

    2015-01-01

    The germanide ScFe6Ge4 was synthesized from the elements by arc-melting. Its crystal structure was refined from single crystal X-ray diffractometer data: LiFe6Ge4 type, R 3 bar m, a = 507.9(3), c = 2000.9(1) pm, wR2 = 0.0737, 242 F2 values, 16 variables. The structure has two main building units. The iron atoms form double-layers of Kagomé networks (248-297 pm Fe-Fe) which are separated by layers of edge-sharing Sc@Ge8 hexagonal bipyramids (265-293 pm Sc-Ge). Chemical bonding has been studied based on DFT calculations for the AFe6Ge4 (A = Li, Sc, Zr) series and isotypic LuTi6Sn4. Existence of MgFe6Ge4 is proposed on the basis of full geometry optimization. Major differences are observed between the electronic structures and the magnetic properties and bonding of LuTi6Sn4 on the one hand and the AFe6Ge4 family on the other hand whereby the iron Kagomé substructure develops magnetization in all AFe6Ge4 compounds, in contrast to LuTi6Sn4. The Ti-Ti Kagomé substructure is found with bonding character throughout the valence band whereas Fe-Fe interactions are both bonding and antibonding with characteristic spin-dependent bonding. Spin-polarized calculations hint for magnetic ordering in the iron containing representatives. This was proven experimentally for ScFe6Ge4. Temperature-dependent susceptibility measurements show a Curie temperature of TC = 491(3) K. 57Fe Mössbauer spectroscopic measurements at ambient temperature show a single resonance at an isomer shift of 0.22(1) mm s-1 with a magnetic hyperfine field of 19.1(1) T.

  9. N-MOSFETs Formed on Solid Phase Epitaxially Grown GeSn Film with Passivation by Oxygen Plasma Featuring High Mobility.

    PubMed

    Fang, Yung-Chin; Chen, Kuen-Yi; Hsieh, Ching-Heng; Su, Chang-Chia; Wu, Yung-Hsien

    2015-12-01

    Solid phase epitaxially grown GeSn was employed as the platform to assess the eligibility of direct O2 plasma treatment on GeSn surface for passivation of GeSn N-MOSFETs. It has been confirmed that O2 plasma treatment forms a GeSnO(x) film on the surface and the GeSnO(x) topped by in situ Al2O3 constitutes the gate stack of GeSn MOS devices. The capability of the surface passivation was evidenced by the low interface trap density (D(it)) of 1.62 × 10(11) cm(-2) eV(-1), which is primarily due to the formation of Ge-O and Sn-O bonds at the surface by high density/reactivity oxygen radicals that effectively suppress dangling bonds and decrease gap states. The good D(it) not only makes tiny frequency dispersion in the characterization of GeSn MOS capacitors, but results in GeSn N-MOSFETs with outstanding peak electron mobility as high as 518 cm(2)/(V s) which outperforms other devices reported in the literature due to reduced undesirable carrier scattering. In addition, the GeSn N-MOSFETs also exhibit promising characteristics in terms of acceptable subthreshold swing of 156 mV/dec and relatively large I(ON)/I(OFF) ratio more than 4 orders. Moreover, the robust reliability in terms small V(t) variation against high field stress attests the feasibility of using the O2 plasma-treated passivation to advanced GeSn technology. PMID:26579560

  10. Ab initio phonon properties of half-Heusler NiTiSn, NiZrSn and NiHfSn

    NASA Astrophysics Data System (ADS)

    Andrea, Luc; Hug, Gilles; Chaput, Laurent

    2015-10-01

    A theoretical investigation of phonon properties from first-principles calculations is carried out for the half-Heusler compounds NiXSn, X=\\text{Ti} , Zr and Hf. The crystal structures are optimised via ab initio calculations within the framework of density functional theory. The phonon properties are retrieved from harmonic and anharmonic interatomic force constants calculations using the finite size displacements method and many-body perturbation theory. A solution to the linearized phonon Boltzmann transport equation is then used to compute the ab initio thermal conductivities. For X   =   Ti, Zr and Hf, we found 15.4, 13.3 and 15.8 W m-1 K-1 at 300 K, respectively. Thanks to a spectral analysis of the velocities and lifetimes we were able appreciate the differences in the thermal conductivities between the three compounds under study. Our results provide insights to understand the behaviour of the thermal conductivity and therefore to improve the thermoelectric figure of merit for such materials.

  11. Ab initio phonon properties of half-Heusler NiTiSn, NiZrSn and NiHfSn.

    PubMed

    Andrea, Luc; Hug, Gilles; Chaput, Laurent

    2015-10-28

    A theoretical investigation of phonon properties from first-principles calculations is carried out for the half-Heusler compounds NiXSn, [Formula: see text], Zr and Hf. The crystal structures are optimised via ab initio calculations within the framework of density functional theory. The phonon properties are retrieved from harmonic and anharmonic interatomic force constants calculations using the finite size displacements method and many-body perturbation theory. A solution to the linearized phonon Boltzmann transport equation is then used to compute the ab initio thermal conductivities. For X   =   Ti, Zr and Hf, we found 15.4, 13.3 and 15.8 W m(-1) K(-1) at 300 K, respectively. Thanks to a spectral analysis of the velocities and lifetimes we were able appreciate the differences in the thermal conductivities between the three compounds under study. Our results provide insights to understand the behaviour of the thermal conductivity and therefore to improve the thermoelectric figure of merit for such materials. PMID:26441218

  12. Effect of hafnium doping on density of states in dual-target magnetron co-sputtering HfZnSnO thin film transistors

    SciTech Connect

    Huang, Chuan-Xin; Li, Jun Fu, Yi-Zhou; Jiang, Xue-Yin; Zhang, Jian-Hua; Zhang, Zhi-Lin

    2015-11-23

    This study investigates the effect of hafnium doping on the density of states (DOSs) in HfZnSnO thin film transistors fabricated by dual-target magnetron co-sputtering system. The DOSs is extracted by temperature-dependent field-effect measurements, and they decrease from 1.1 × 10{sup 17} to 4.6 × 10{sup 16 }eV/cm{sup 3} with increasing the hafnium concentrations. The behavior of DOSs for the increasing hafnium concentration HfZnSnO thin film transistors can be confirmed by both the reduction of ΔV{sub T} under bias stress and the trapping charges calculated by capacitance voltage measurements. It suggests that the reduction in DOSs due to the hafnium doping is closely related with the bias stability and thermal stability.

  13. Systematic study on the anisotropic elastic properties of tetragonal XYSb (X = Ti, Zr, Hf; Y = Si, Ge) compounds

    NASA Astrophysics Data System (ADS)

    Ozyar, U. F.; Deligoz, E.; Colakoglu, K.

    2015-02-01

    The anisotropic elastic properties of XYSb (X = Ti, Zr, Hf; Y = Si, Ge) compounds have been investigated by using first-principles calculations based on density functional theory. The calculated lattice parameters are in excellent agreement with the available experimental data. The computed elastic constants indicate that all compounds are mechanically stable according to the elastic stability criteria under pressure. We have calculated the bulk modulus, shear modulus, Young's modulus, Poisson's ratio, Debye temperature, and anisotropy value from the obtained elastic constants according to the Voigt-Reuss-Hill approximation. Additionally, the ductility and brittleness are characterized with the estimation from Pugh's rule (B/G) and Poisson's ratio. Furthermore, the elastic anisotropy have been visualized in detail by plotting the directional dependence of compressibility, Young's and shear moduli.

  14. Distribution of impurity states and charge transport in Zr0.25Hf0.75Ni1+xSn1-ySby nanocomposites

    NASA Astrophysics Data System (ADS)

    Liu, Yuanfeng; Makongo, Julien P. A.; Page, Alexander; Sahoo, Pranati; Uher, Ctirad; Stokes, Kevin; Poudeu, Pierre F. P.

    2016-02-01

    Energy filtering of charge carriers in a semiconducting matrix using atomically coherent nanostructures can lead to a significant improvement of the thermoelectric figure of merit of the resulting composite. In this work, several half-Heusler/full-Heusler (HH/FH) nanocomposites with general compositions Zr0.25Hf0.75Ni1+xSn1-ySby (0≤x≤0.15 and y=0.005, 0.01 and 0.025) were synthesized in order to investigate the behavior of extrinsic carriers at the HH/FH interfaces. Electronic transport data showed that energy filtering of carriers at the HH/FH interfaces in Zr0.25Hf0.75Ni1+xSn1-ySby samples strongly depends on the doping level (y value) as well as the energy levels occupied by impurity states in the samples. For example, it was found that carrier filtering at HH/FH interfaces is negligible in Zr0.25Hf0.75Ni1+xSn1-ySby (y=0.01 and 0.025) composites where donor states originating from Sb dopant dominate electronic conduction. However, we observed a drastic decrease in the effective carrier density upon introduction of HH/FH interfaces for the mechanically alloyed Zr0.25Hf0.75Ni1+xSn0.995Sb0.005 samples where donor states from unintentional Fe impurities contribute the largest fraction of conduction electrons. This work demonstrates the ability to synergistically integrate the concepts of doping and energy filtering through nanostructuring for the optimization of electronic transport in semiconductors.

  15. On the interplay between relaxation, defect formation, and atomic Sn distribution in Ge{sub (1−x)}Sn{sub (x)} unraveled with atom probe tomography

    SciTech Connect

    Kumar, A. Bran, J. Melkonyan, D. Shimura, Y. Vandervorst, W.; Demeulemeester, J. Bogdanowicz, J. Fleischmann, C. Loo, R.; Gencarelli, F. Wang, W.

    2015-07-14

    Ge{sub (1−x)}Sn{sub (x)} has received a lot of interest for opto-electronic applications and for strain engineering in advanced complementary-metal-oxide-semiconductor technology, because it enables engineering of the band gap and inducing strain in the alloy. To target a reliable technology for mass application in microelectronic devices, the physical problem to be addressed is to unravel the complex relationship between strain relaxation (as induced by the growth of large layer thicknesses or a thermal anneal) and defect formation, and/or stable Sn-cluster formation. In this paper, we study the onset of Sn-cluster formation and its link to strain relaxation using Atom Probe Tomography (APT). To this end, we also propose a modification of the core-linkage [Stephenson et al., Microsc. Microanal. 13, 448 (2007)] cluster analysis method, to overcome the challenges of limited detection efficiency and lateral resolution of APT, and the quantitative assessment for very small clusters (<40 atoms) embedded in a random distribution of Sn-atoms. We concluded that the main relaxation mechanism for these layers is defect generation (misfit dislocations, threading dislocations, etc.), irrespective of the cause (thickness of layer or thermal anneal) of relaxation and is independent of the cluster formation. The low thermodynamic solubility limit of Sn in Ge seems to be the driving force for Sn-cluster formation. Finally, we also discuss the spatial distribution of Sn in clusters and relate them to the theoretically predicted stable Sn clusters [Ventura et al., Phys. Rev. B 79, 155202 (2009)].

  16. Simulation investigation of tensile strained GeSn fin photodetector with Si(3)N(4) liner stressor for extension of absorption wavelength.

    PubMed

    Zhang, Qingfang; Liu, Yan; Yan, Jing; Zhang, Chunfu; Hao, Yue; Han, Genquan

    2015-01-26

    In this paper, we design a biaxial tensile strained GeSn photodetector with fin structure wrapped in Si(3)N(4) liner stressor. A large biaxial tensile strain is induced in GeSn fins by the expansion of Si(3)N(4) liner stressor. The distribution of tensile strain in GeSn fins was calculated by a finite element simulation. It is observed that magnitude of the strain increases with the reduction of fin thickness T(fin). Under the biaxial tensile strain, the direct band gap E(G,Γ) of GeSn fin photodetector is significantly reduced by lowering Γ conduction valley in energy and lifting of degeneracy of valence bands. As the 30 nm Si(3)N(4) liner stressor expanses by 1%, a E(G,Γ) reduction of ~0.14 eV is achieved in Ge(0.92)Sn(0.08) fins with a T(fin) of 100 nm. The cut-off wavelengths of strained Ge(0.96)Sn(0.04), Ge(0.92)Sn(0.08) and Ge(0.90)Sn(0.10) fin photodetectors with a T(fin) of 100 nm are extended to 2.4, 3.3, and 4 μm, respectively. GeSn fin photodetector integrated with Si(3)N(4) liner stressor provides an effective technique for extending the absorption edge of GeSn with Sn composition less than 10% to mid-infrared wavelength. PMID:25835833

  17. Epitaxial growth of ultrahigh density Ge1-xSnx quantum dots on Si (111) substrates by codeposition of Ge and Sn on ultrathin SiO2 films

    NASA Astrophysics Data System (ADS)

    Nakamura, Yoshiaki; Masada, Akiko; Cho, Sung-Pyo; Tanaka, Nobuo; Ichikawa, Masakazu

    2007-12-01

    A method to form epitaxial Ge1-xSnx quantum dots (QDs) on Si (111) substrates has been developed by codeposition of Ge and Sn on ultrathin SiO2 films with predeposited Ge nuclei. Hemispherical Ge1-xSnx QDs with an ultrahigh density (˜1012 cm-2) were epitaxially grown in the nanometer-size range. The QD size was controlled by changing the GeSn deposition amount. High-resolution transmission electron microscopy observations revealed that the main formed Ge1-xSnx QDs had less strain and no misfit dislocations.

  18. Structural defect generation and band-structure features in the HfNi{sub 1−x}Co{sub x}Sn semiconductor

    SciTech Connect

    Romaka, V. A.; Rogl, P.; Romaka, V. V.; Stadnyk, Yu. V.; Krayovskyy, V. Ya.; Kaczorowski, D.; Nakonechnyy, I. N.; Goryn, A. M.

    2015-08-15

    The crystal and electronic structure and magnetic, energy, and kinetic properties of the n-HfNiSn semiconductor heavily doped with the Co acceptor impurity (HfNi{sub 1−x}Co{sub x}Sn) are investigated in the temperature and Co concentration ranges T = 80–400 K and N{sub A}{sup Co} ≈ 9.5 × 10{sup 19}-5.7 × 10{sup 21} cm{sup −3} (x = 0.005–0.30), respectively, and under magnetic field H ≤ 10 kOe. It is established that the degree of compensation of the semiconductor changes due to transformation of the crystal structure upon doping, which leads to the generation of acceptor and donor structural defects. The calculated electronic structure is consistent with the experiment; the HfNi{sub 1−x}Co{sub x}Sn semiconductor is shown to be a promising thermoelectric material. The results obtained are discussed within the Shklovsky-Efros model for a heavily doped and compensated semiconductor.

  19. Enhancement of photoluminescence from n-type tensile-strained GeSn wires on an insulator fabricated by lateral liquid-phase epitaxy

    NASA Astrophysics Data System (ADS)

    Shimura, Takayoshi; Matsue, Masahiro; Tominaga, Kohei; Kajimura, Keiko; Amamoto, Takashi; Hosoi, Takuji; Watanabe, Heiji

    2015-11-01

    We investigated the optical properties of undoped and n-type GeSn wires fabricated by a lateral liquid-phase epitaxial method. The Sn concentration was approximately 0.5% in the region from the seed to near the wire end. Moreover, the Sn concentration increased to 6% at the wire end, whereas Si diffusion from the seed was enhanced and extended to 200 μm from the seed. Tensile strain gradually decreased from 0.5% close the seed to 0.25% at the wire end. The photoluminescence (PL) peak was red-shifted by Sn incorporation into the Ge wires, and a PL peak at 0.66 eV was observed from the wire end. Upon n-type doping, the PL intensity of the GeSn layers was significantly enhanced to approximately 10 times higher than that of the undoped GeSn wires.

  20. Atomic layer deposition of Al2O3 on germanium-tin (GeSn) and impact of wet chemical surface pre-treatment

    NASA Astrophysics Data System (ADS)

    Gupta, Suyog; Chen, Robert; Harris, James S.; Saraswat, Krishna C.

    2013-12-01

    GeSn is quickly emerging as a potential candidate for high performance Si-compatible transistor technology. Fabrication of high-ĸ gate stacks on GeSn with good interface properties is essential for realizing high performance field effect transistors based on this material system. We demonstrate an effective surface passivation scheme for n-Ge0.97Sn0.03 alloy using atomic layer deposition (ALD) of Al2O3. The effect of pre-ALD wet chemical surface treatment is analyzed and shown to be critical in obtaining a good quality interface between GeSn and Al2O3. Using proper surface pre-treatment, mid-gap trap density for the Al2O3/GeSn interface of the order of 1012 cm-2 has been achieved.

  1. 125Te NMR chemical-shift trends in PbTe–GeTe and PbTe–SnTe alloys

    SciTech Connect

    Njegic, Bosiljka; Levin, Evgenii M.; Schmidt-Rohr, Klaus

    2013-10-08

    Complex tellurides, such as doped PbTe, GeTe, and their alloys, are among the best thermoelectric materials. Knowledge of the change in 125Te NMR chemical shift due to bonding to dopant or “solute” atoms is useful for determination of phase composition, peak assignment, and analysis of local bonding. We have measured the 125Te NMR chemical shifts in PbTe-based alloys, Pb1-xGexTe and Pb1-xSnxTe, which have a rocksalt-like structure, and analyzed their trends. For low x, several peaks are resolved in the 22-kHz MAS 125Te NMR spectra. A simple linear trend in chemical shifts with the number of Pb neighbors is observed. No evidence of a proposed ferroelectric displacement of Ge atoms in a cubic PbTe matrix is detected at low Ge concentrations. The observed chemical shift trends are compared with the results of DFT calculations, which confirm the linear dependence on the composition of the first-neighbor shell. The data enable determination of the composition of various phases in multiphase telluride materials. They also provide estimates of the 125Te chemical shifts of GeTe and SnTe (+970 and +400±150 ppm, respectively, from PbTe), which are otherwise difficult to access due to Knight shifts of many hundreds of ppm in neat GeTe and SnTe.

  2. Temperature dependent spectral response and detectivity of GeSn photoconductors on silicon for short wave infrared detection.

    PubMed

    Conley, Benjamin R; Mosleh, Aboozar; Ghetmiri, Seyed Amir; Du, Wei; Soref, Richard A; Sun, Greg; Margetis, Joe; Tolle, John; Naseem, Hameed A; Yu, Shui-Qing

    2014-06-30

    The GeSn direct gap material system, with Si complementary-metal-oxide semiconductor (CMOS) compatibility, presents a promising solution for direct incorporation of focal plane arrays with short wave infrared detection on Si. A temperature dependence study of GeSn photoconductors with 0.9, 3.2, and 7.0% Sn was conducted using both electrical and optical characterizations from 300 to 77 K. The GeSn layers were grown on Si substrates using a commercially available chemical vapor deposition reactor in a Si CMOS compatible process. Carrier activation energies due to ionization and trap states are extracted from the temperature dependent dark I-V characteristics. The temperature dependent spectral response of each photoconductor was measured, and a maximum long wavelength response to 2.1 μm was observed for the 7.0% Sn sample. The DC responsivity measured at 1.55 μm showed around two orders of magnitude improvement at reduced temperatures for all samples compared to room temperature measurements. The noise current and temperature dependent specific detectivity (D*) were also measured for each sample at 1.55 μm, and a maximum D* value of 1 × 10(9) cm·√Hz/W was observed at 77 K. PMID:24977823

  3. Hyperfine magnetic field on Cd-111 in Heusler alloys Co2MnZ (Z = Si, Ga, Ge, Sn)

    NASA Technical Reports Server (NTRS)

    Jha, S.; Mitros, C.; Lahamer, Amer; Yehia, Sherif; Julian, Glenn M.

    1989-01-01

    The time differential perturbed angular correlation method has been used to measure, as a function of temperature, the hyperfine magnetic field at Cd sites in the Heusler alloys Co2MnZ (Z = Si, Ga, Ge, Sn). The hyperfine fields, normalized to the total magnetic moment per formula unit, show an approximately linear trend toward more positive values with increasing lattice parameter.

  4. Vibrational properties of the gallium monohydrides SrGaGeH, BaGaSiH, BaGaGeH, and BaGaSnH

    SciTech Connect

    Evans, Michael J.; Lee, Myeong H.; Holland, Gregory P.; Daemen, Luke L.; Sankey, Otto F.; Haeussermann, Ulrich

    2009-08-15

    Vibrational properties of the gallium monohydrides SrGaGeH, BaGaSiH, BaGaGeH, and BaGaSnH (AeGaTtH) have been investigated by means of inelastic neutron scattering (INS) and first principles calculations. The compounds contain separated Ga-H units being part of a two dimensional polyanionic layer, [TtGaH]{sup 2-} (Tt=Si, Ge, Sn). The INS spectra show internal Ga-H bending and stretching modes at frequencies around 900 and 1200 cm{sup -1}, respectively. While the stretching mode is virtually invariant with respect to the variable chemical environment of the Ga-H unit, the bending mode frequency varies and is highest for BaGaSiH and lowest for BaGaSnH. The stretching mode is a direct measure of the Ga-H bond strength, whereas the bending mode reflects indirectly the strength of alkaline earth metal-hydrogen interaction. Accordingly, the terminal Ga-H bond in solid state AeGaTtH is distinct, but-compared to molecular gallium hydrides-very weak. - Graphical abstract: Vibrational properties of the gallium monohydrides SrGaGeH, BaGaSiH, BaGaGeH, and BaGaSnH have been investigated and revealed Ga-H stretching mode frequencies around 1200 cm{sup -1}. This implies that the terminal Ga-H bond in solid state polyanionic gallium hydrides is very weak compared to molecular gallium hydride species.

  5. Effect of Sn atoms on incorporation of vacancies in epitaxial Ge1-xSnx film grown at low temperature

    NASA Astrophysics Data System (ADS)

    Kamiyama, Eiji; Nakagawa, Satoko; Sueoka, Koji; Ohmura, Takuma; Asano, Takanori; Nakatsuka, Osamu; Taoka, Noriyuki; Zaima, Shigeaki; Izunome, Koji; Kashima, Kazuhiko

    2014-02-01

    The anomalous increase and decrease in the S-parameters of Doppler broadening spectroscopy in positron annihilation spectroscopy in a narrow range of Sn atom content were detected in a Ge1-xSnx thin film grown by MBE at low temperatures. The increase can be explained in terms of vacancies when the target content of 1.7% Sn atoms is incorporated in a Ge matrix, owing to the binding nature between them. However, the S-parameters were markedly decreased when the target content of Sn atoms in the film grown at the same temperature was 0.1%. These changes in the S-parameters correspond to the carrier concentrations obtained by Hall measurements.

  6. Disorder-induced enhancement of indirect absorption in a GeSn photodetector grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Li, H.; Chang, C.; Cheng, H. H.; Sun, G.; Soref, R. A.

    2016-05-01

    We report an investigation on the absorption mechanism of a GeSn photodetector with 2.4% Sn composition in the active region. Responsivity is measured and absorption coefficient is calculated. Square root of absorption coefficient linearly depends on photon energy indicating an indirect transition. However, the absorption coefficient is found to be at least one order of magnitude higher than that of most other indirect materials, suggesting that the indirect optical absorption transition cannot be assisted only by phonon. Our analysis of absorption measurements by other groups on the same material system showed the values of absorption coefficient on the same order of magnitude. Our study reveals that the strong enhancement of absorption for the indirect optical transition is the result of alloy disorder from the incorporation of the much larger Sn atoms into the Ge lattice that are randomly distributed.

  7. Infrared Polarizer Fabrication by Imprinting on Sb-Ge-Sn-S Chalcogenide Glass

    NASA Astrophysics Data System (ADS)

    Yamada, Itsunari; Yamashita, Naoto; Tani, Kunihiko; Einishi, Toshihiko; Saito, Mitsunori; Fukumi, Kouhei; Nishii, Junji

    2012-01-01

    We fabricated infrared wire-grid polarizers consisting of a 500-nm pitch Al grating on a low toxic chalcogenide glass (Sb-Ge-Sn-S system) using the direct imprinting of subwavelength grating followed by a deposition of Al metal by thermal evaporation. To fabricate the subwavelength grating on a chalcogenide glass more easily, the sharp grating was formed on the mold surface. The fabricated polarizer with Al thickness of 130 nm exhibited a polarization function with a transverse magnetic transmittance greater than 60% in the 5-9 µm wavelength range, and an extinction ratio greater than 20 dB in 3.5-11 µm wavelength range. The extinction ratio of the element with Al wires of 180-nm thickness reached 27 dB at 5.4-µm wavelength. The polarizer can be fabricated at lower costs and simpler fabrication processes compared to conventional infrared polarizers.

  8. Effect of atomic deuterium irradiation on initial growth of Sn and Ge1-xSnx on Ge(0 0 1) substrates

    NASA Astrophysics Data System (ADS)

    Shinoda, Tatsuya; Nakatsuka, Osamu; Shimura, Yosuke; Takeuchi, Shotaro; Zaima, Shigeaki

    2012-10-01

    We have investigated the effect of the irradiation of atomic deuterium (D) on the initial growth of Sn and Ge1-xSnx on Ge(0 0 1) substrates by using scanning tunneling microscopy (STM) comparing to the effect of the irradiation of atomic hydrogen (H). We found that the surfactant effect appears and the surface roughness is reduced when the surface coverage of D or H is higher than 69%. The efficiency for reducing the surface roughness increased with the coverage of D and H. Moreover, we found that D atoms effectively work as a surfactant on the Ge surface compared to H atoms under the same irradiation condition. Utilizing D as a surfactant is expected to improve the termination process of Ge surface.

  9. Lasing in direct-bandgap GeSn alloy grown on Si

    NASA Astrophysics Data System (ADS)

    Wirths, S.; Geiger, R.; von den Driesch, N.; Mussler, G.; Stoica, T.; Mantl, S.; Ikonic, Z.; Luysberg, M.; Chiussi, S.; Hartmann, J. M.; Sigg, H.; Faist, J.; Buca, D.; Grützmacher, D.

    2015-02-01

    Large-scale optoelectronics integration is limited by the inability of Si to emit light efficiently, because Si and the chemically well-matched Ge are indirect-bandgap semiconductors. To overcome this drawback, several routes have been pursued, such as the all-optical Si Raman laser and the heterogeneous integration of direct-bandgap III-V lasers on Si. Here, we report lasing in a direct-bandgap group IV system created by alloying Ge with Sn without mechanically introducing strain. Strong enhancement of photoluminescence emerging from the direct transition with decreasing temperature is the signature of a fundamental direct-bandgap semiconductor. For T ≤ 90 K, the observation of a threshold in emitted intensity with increasing incident optical power, together with strong linewidth narrowing and a consistent longitudinal cavity mode pattern, highlight unambiguous laser action. Direct-bandgap group IV materials may thus represent a pathway towards the monolithic integration of Si-photonic circuitry and complementary metal-oxide-semiconductor (CMOS) technology.

  10. Critical thickness for strain relaxation of Ge{sub 1−x}Sn{sub x} (x ≤ 0.17) grown by molecular beam epitaxy on Ge(001)

    SciTech Connect

    Wang, Wei; Zhou, Qian; Dong, Yuan; Yeo, Yee-Chia; Tok, Eng Soon

    2015-06-08

    We investigated the critical thickness (h{sub c}) for plastic relaxation of Ge{sub 1−x}Sn{sub x} grown by molecular beam epitaxy. Ge{sub 1−x}Sn{sub x} films with various Sn mole fraction x (x ≤ 0.17) and different thicknesses were grown on Ge(001). The strain relaxation of Ge{sub 1−x}Sn{sub x} films and the h{sub c} were investigated by high-resolution x-ray diffraction and reciprocal space mapping. It demonstrates that the measured h{sub c} values of Ge{sub 1−x}Sn{sub x} layers are as much as an order of magnitude larger than that predicted by the Matthews and Blakeslee (M-B) model. The People and Bean (P-B) model was also used to predict the h{sub c} values in Ge{sub 1−x}Sn{sub x}/Ge system. The measured h{sub c} values for various Sn content follow the trend, but slightly larger than that predicted by the P-B model.

  11. Effect of in situ Sb doping on crystalline and electrical characteristics of n-type Ge1- x Sn x epitaxial layer

    NASA Astrophysics Data System (ADS)

    Jeon, Jihee; Asano, Takanori; Shimura, Yosuke; Takeuchi, Wakana; Kurosawa, Masashi; Sakashita, Mitsuo; Nakatsuka, Osamu; Zaima, Shigeaki

    2016-04-01

    We examined the molecular beam epitaxy of Ge1- x Sn x with in situ Sb doping on Ge substrates. The effects of Sb doping on the crystalline and electrical characteristics of Ge1- x Sn x epitaxial layer were investigated in detail. We found that Sb doping with a concentration of 1020 cm-3 remarkably improves the crystallinity, and surface uniformity of the Ge1- x Sn x epitaxial layer by changing the growth mode by the surfactant effect of Sb atoms. Low-temperature Ge1- x Sn x growth with in situ Sb doping realizes a very high electron concentration of 1020 cm-3, which is above the thermal equilibrium solid solubility, as a result of suppressing Sb segregation and precipitation.

  12. Temperature dependence of energy gap of Ge1‑x Sn x alloys with x  <  0.11 studied by photoreflectance

    NASA Astrophysics Data System (ADS)

    Zelazna, K.; Wełna, M.; Misiewicz, J.; Dekoster, J.; Kudrawiec, R.

    2016-06-01

    Compressively strained Ge1‑x Sn x layers of various Sn content grown on Ge/Si templates have been studied by photoreflectance in 15–295 K temperature range. It has been confirmed that the direct optical transition between heavy-hole band and conduction band shifts to lower energy upon incorporation of Sn atoms. The shift of the transition energy in that temperature range has been found to be 68–91 meV which is slightly higher than the energy shift of direct transitions in Ge over the same temperature range. Varshni and Bose–Einstein coefficients for compressively strained Ge1‑x Sn x have been extracted from the analysis of the direct transitions and compared with parameters from literature. In addition the heavy- and light-hole related direct optical transitions in tensile strained Ge buffer layers have been measured and analyzed.

  13. Ge{sub 1−x−y}Si{sub x}Sn{sub y} light emitting diodes on silicon for mid-infrared photonic applications

    SciTech Connect

    Gallagher, J. D.; Xu, C.; Menéndez, J.; Senaratne, C. L.; Wallace, P. M.; Kouvetakis, J.; Aoki, T.

    2015-10-07

    This paper reports initial the demonstration of prototype Ge{sub 1−x−y}Si{sub x}Sn{sub y} light emitting diodes with distinct direct and indirect edges and high quality I-V characteristics. The devices are fabricated on Si (100) wafers in heterostructure pin geometry [n-Ge/i-Ge{sub 1−x−y}Si{sub x}Sn{sub y}/p-Ge(Sn/Si)] using ultra low-temperature (T < 300 °C) depositions of the highly reactive chemical sources Si{sub 4}H{sub 10}, Ge{sub 4}H{sub 10}, Ge{sub 3}H{sub 8}, and SnD{sub 4}. The Sn content in the i-Ge{sub 1−x−y}Si{sub x}Sn{sub y} layer was varied from ∼3.5% to 11%, while the Si content was kept constant near 3%. The Si/Sn amounts in the p-layer were selected to mitigate the lattice mismatch so that the top interface grows defect-free, thereby reducing the deleterious effects of mismatch-induced dislocations on the optical/electrical properties. The spectral responsivity plots of the devices reveal sharp and well-defined absorption edges that systematically red-shift in the mid-IR from 1750 to 2100 nm with increasing Sn content from 3.5% to 11%. The electroluminescence spectra reveal strong direct-gap emission peaks and weak lower energy shoulders attributed to indirect gaps. Both peaks in a given spectrum red-shift with increasing Sn content and their separation decreases as the material approaches direct gap conditions in analogy with binary Ge{sub 1−y}Sn{sub y} counterparts. These findings-combined with the enhanced thermal stability of Ge{sub 1−x−y}Si{sub x}Sn{sub y} relative to Ge{sub 1−y}Sn{sub y} and the observation that ternary alloy disorder does not adversely affect the emission properties—indicate that Ge{sub 1−x−y}Si{sub x}Sn{sub y} may represent a practical target system for future generations of group-IV light sources on Si.

  14. Germylenes and stannylenes stabilized within N2PE rings (E = Ge or Sn): combined experimental and theoretical study.

    PubMed

    Vrána, Jan; Ketkov, Sergey; Jambor, Roman; Růžička, Aleš; Lyčka, Antonín; Dostál, Libor

    2016-06-21

    The deprotonation of aminophosphanes PhP(NHR)2 (R = t-Bu or Dip; Dip = 2,6-i-Pr2C6H3) and t-BuP(NHDip)2 using n-BuLi gave, depending on the stoichiometry, both the dilithium compounds {[PhP(Nt-Bu)2]Li2}2 (), [PhP(Nt-Bu)(NDip)]Li2·(Et2O) (), [t-BuP(NDip)2]Li2·(Et2O)2 () and [t-BuP(NDip)2]Li2·(tmeda)2 (), and the monolithium compounds [PhP(NHt-Bu)(NR)]Li·(tmeda) (R = t-Bu , Dip ) and [t-BuP(NHDip)(NDip)]Li·(tmeda) (). Treatment of , and with GeCl2·dioxane or SnCl2 in a 1 : 1 stoichiometric ratio gave the corresponding tetrylenes [PhP(Nt-Bu)2]E (E = Ge , Sn ), [PhP(Nt-Bu)(NDip)]Ge () and [t-BuP(NDip)2]E (E = Ge , Sn ). The heteroleptic germylene [Ph(H)P(Nt-Bu)2]GeCl () was obtained by the reaction of the monolithium compound [PhP(NHt-Bu)(Nt-Bu)]Li·(tmeda) () with GeCl2·dioxane in a 1 : 1 stoichiometric ratio, as a result of a spontaneous NH → PH tautomeric shift in the ligand backbone. In contrast, an analogous reaction with SnCl2 produced only stannylene along with the PhP(NHt-Bu)2 starting material, suggesting scrambling of the ligands rather than a NH → PH tautomeric shift. Finally, heating in solution led to P-C bond cleavage and formation of the bis(imino)phosphide [DipNPNDip]Li·(tmeda) (). The reaction of with GeCl2·dioxane, SnCl2 or PbCl2 in a 2 : 1 stoichiometric ratio yielded the unprecedented tetrylenes [DipNPNDip]2E (E = Ge , Sn and Pb ), in which the tetrylene center is incorporated within two N2PE rings. Treatment of the monolithium compound with n-BuLi and K (or KC8) gave [t-BuNPNt-Bu]Li·(tmeda) () and{[t-BuNPNt-Bu]K(tmeda)}2 (), respectively. In contrast to the reaction with , similar reactions of with GeCl2·dioxane and SnCl2 resulted in the known compounds cis-[P(μ-Nt-Bu)2P(t-BuN)2]E (E = Ge, Sn); evidently the t-Bu groups do not provide sufficient steric shielding to protect the bis(imino)phosphide backbone as in the case of . The bonding situation in a set of selected compounds (, ) has been subjected to a theoretical

  15. Electron energy-loss spectroscopy analysis of HfO2 dielectric films on strained and relaxed SiGe /Si substrates

    NASA Astrophysics Data System (ADS)

    Jang, Jiyoung; Park, Tae Joo; Kwon, Ji-Hwan; Jang, Jae Hyuck; Hwang, Cheol Seong; Kim, Miyoung

    2008-06-01

    In this investigation, HfO2 thin films were deposited on strained and strain-relaxed epitaxial-SiGe /Si substrates, and subsequently subjected to annealing. Electron energy-loss spectroscopy analysis was used to investigate the electronic structure and composition of the film as well as the interfacial layer (IL). While the energy-loss function of the dielectric films revealed predominant Si diffusion in the strained substrates, post deposition annealing (PDA) significantly influenced the diffusion and altered the local composition of the IL in strain-relaxed substrates. Analysis of electronic structures revealed the origin of significant loss of Ge atoms at the IL during PDA.

  16. A theoretical study of stability, electronic, and optical properties of GeC and SnC

    NASA Astrophysics Data System (ADS)

    Pandey, Ravindra; Rérat, Michel; Darrigan, Clovis; Causà, Mauro

    2000-12-01

    We present the results of a first principles study on the ordered Ge0.50C0.50 and Sn0.50C0.50 cubic alloys. A linear combination of atomic orbitals approach in the framework of density functional theory is employed for total energy calculations in the zincblende phase. A fitting of the energy surface to the equation of state yields the lattice constant of 4.61 and 5.17 Å and the bulk modulus of 181 and 119 GPa for GeC and SnC, respectively. Analysis of band structure suggests a crossover of the nature of the band gap from indirect to direct in going from SiC to GeC to SnC. Although both alloys predicted to be unstable with respect to their elemental components at zero pressure and temperature, GeC appears to become stable at higher pressure. It appears that both the lattice constant and bulk modulus of the ordered alloys do not follow Végard's linear rule, though the calculated dielectric constant of the cubic alloys is approximately the average of the dielectric constant of their elemental components.

  17. Band alignment at interfaces of amorphous Al{sub 2}O{sub 3} with Ge{sub 1−x}Sn{sub x}- and strained Ge-based channels

    SciTech Connect

    Chou, H.-Y.; Afanas'ev, V. V. Houssa, M.; Stesmans, A.; Vincent, B.; Gencarelli, F.; Shimura, Y.; Merckling, C.; Loo, R.; Nakatsuka, O.; Zaima, S.

    2014-05-19

    Spectroscopy of internal photoemission of electrons from Ge and Ge{sub 1−x}Sn{sub x} (x ≤ 0.08) alloys into amorphous Al{sub 2}O{sub 3} is used to evaluate the energy of the semiconductor valence band top. It is found that in Ge and Ge{sub 1−x}Sn{sub x} the valence bands are aligned within the measurement accuracy (±0.05 eV) irrespective of the strain imposed on the semiconductor or by the kind of passivating inter-layer applied between the semiconductor and alumina. This indicates that the Ge{sub 1−x}Sn{sub x}-stressor approach may be useful for strain engineering in p-channel Ge metal-oxide-semiconductor transistors.

  18. Observation of heavy- and light-hole split direct bandgap photoluminescence from tensile-strained GeSn (0.03% Sn)

    NASA Astrophysics Data System (ADS)

    Harris, Thomas R.; Yeo, Yung Kee; Ryu, Mee-Yi; Beeler, Richard T.; Kouvetakis, John

    2014-09-01

    Temperature- (T-) and laser power-dependent photoluminescence (PL) measurements have been made for the tensile-strained, undoped GeSn (0.03% Sn) film grown on Si substrate. The PL results show not only clear strain-split direct bandgap transitions to the light-hole (LH) and heavy-hole (HH) bands at energies of 0.827 and 0.851 eV at 10 K, respectively, but also clearly show both strong direct and indirect bandgap related PL emissions at almost all temperatures, which are rarely observed. This split of PL emissions can be directly observed only at low T and moderate laser power, and the two PL peaks merge into one broad PL peak at room temperature, which is mainly due to the HH PL emission rather than LH transition. The evolution of T-dependent PL results also clearly show the competitive nature between the direct and indirect bandgap related PL transitions as T changes. The PL analysis also indicates that the energy gap reduction in Γ valley could be larger, whereas the bandgap reduction in L valley could be smaller than the theory predicted. As a result, the separation energy between Γ and L valleys (˜86 meV at 300 K) is smaller than theory predicted (125 meV) for this Ge-like sample, which is mainly due to the tensile strain. This finding strongly suggests that the indirect-to-direct bandgap transition of Ge1-ySny could be achieved at much lower Sn concentration than originally anticipated if one utilizes the tensile strain properly. Thus, Ge1-ySny alloys could be attractive materials for the fabrication of direct bandgap Si-based light emitting devices.

  19. Preparation and thermoelectric properties of sintered iodine-containing clathrate compounds Ge38Sb8I8 and Sn38Sb8I8

    NASA Astrophysics Data System (ADS)

    Kishimoto, Kengo; Arimura, Shuntaro; Koyanagi, Tsuyoshi

    2006-05-01

    The iodine-containing cationic type-I clathrates Ge38Sb8I8 and Sn38Sb8I8 were prepared and their thermodynamic properties as well as their thermoelectric properties were investigated. Their atomic displacement parameters were as large as those of anionic clathrates such as Ba8Ga16Ge30 and Cs8Cd4Sn42. The room temperature thermal conductivities of Ge38Sb8I8 and Sn38Sb8I8 were 7 and 12mWcm-1K-1, respectively; these values were as low as that of the above anionic clathrates. Both cationic clathrates had negative Seebeck coefficients; the band gap energies of Ge38Sb8I8 and Sn38Sb8I8 were 1.16 and 0.80eV, respectively.

  20. Theoretical investigations on the structural, lattice dynamical and thermodynamic properties of XC (X=Si, Ge, Sn)

    NASA Astrophysics Data System (ADS)

    Zhang, Xudong; Quan, Shanyu; Ying, Caihong; Li, Zhijie

    2011-11-01

    First-principles calculations, which is based on the plane-wave pseudopotential approach to the density functional perturbation theory within the local density approximation, have been performed to investigate the structural, lattice dynamical, and thermodynamic properties of SiC, GeC, and SnC. The results of ground state parameters, phase transition pressure and phonon dispersion are compared and agree well with the experimental and theoretical data in the previous literature. The obtained phonon frequencies at the zone-center are analyzed. We also used the phonon density of states and quasiharmonic approximation to calculate and predict some thermodynamic properties such as entropy, heat capacity, internal energy, and phonon free energy of SiC, GeC, and SnC in B3 phase.

  1. Photovoltaic effect in Cd/sub 2/ SnO/sub 4/-CdGeP/sub 2/ heterojunctions

    SciTech Connect

    Lunev, A.V.; Rud, Yu.V.; Tairov, M.A.; Undalov, Yu.K.

    1989-01-01

    It is shown experimentally to be possible to form rectifying photosensitive heterojunctions by using the method of reactive cathodic sputtering to deposit layers of Cd/sub 2/SnO/sub 4/ on the surface of n- and p-type CdGeP/sub 2/ single crystals. It is demonstrated that photosensitivity is seen in the range between widths of the forbidden bands of CdGeP/sub 2/ and Cd/sub 2/SnO/sub 4/; photosensitivity is 3-4 orders of magnitude greater for n-n junctions than for n-p junctions. The parameters of polarizational photosensitivity were established and analyzed, providing evidence that the investigated system, with an n-n contact, can be used to make polarimetric photodetectors.

  2. Use of nonpolar BaHfO3 gate oxide for field effect on the high mobility BaSnO3

    NASA Astrophysics Data System (ADS)

    Park, Chulkwon; Kim, Useong; Kim, Young Mo; Ju, Chanjong; Char, Kookrin

    2015-03-01

    Recently, BaSnO3 (BSO) has attracted attentions as a transparent conducting oxide and/or a transparent oxide semiconductor due to its novel properties: the excellent oxygen stability even at high temperature and the high electrical mobility at room temperature. We fabricated field effect transistors using La-doped BSO as the semiconducting channel on undoped BSO buffer layers on SrTiO3 substrates. A non-polar perovskite BaHfO3 was used as the gate insulator, and 4% La-doped BSO as the source, the drain, and the gate electrodes grown by pulsed laser deposition. We have measured the optical and the dielectric properties of the epitaxial BaHfO3 gate oxide layer, namely the optical band gap, the dielectric constant, and the breakdown field. Using such BaHfO3 gate oxide, we observed carrier modulation in the active layer by field effect. In this presentation, we will report on the performance of such field effect transistors: the output and the transfer characteristics, the field effect mobility, the Ion/Ioff ratio, and the subthreshold swing.

  3. In Situ Synchrotron Based X-ray Fluorescence and Scattering Measurements During Atomic Layer Deposition: Initial Growth of HfO2 on Si and Ge Substrates

    SciTech Connect

    K Devloo-Casier; J Dendooven; K Ludwig; G Lekens; J DHaen; C Detavernier

    2011-12-31

    The initial growth of HfO{sub 2} was studied by means of synchrotron based in situ x-ray fluorescence (XRF) and grazing incidence small angle x-ray scattering (GISAXS). HfO{sub 2} was deposited by atomic layer deposition (ALD) using tetrakis(ethylmethylamino)hafnium and H{sub 2}O on both oxidized and H-terminated Si and Ge surfaces. XRF quantifies the amount of deposited material during each ALD cycle and shows an inhibition period on H-terminated substrates. No inhibition period is observed on oxidized substrates. The evolution of film roughness was monitored using GISAXS. A correlation is found between the inhibition period and the onset of surface roughness.

  4. Effect of the Sn dopant on the crystallization of amorphous Ge2Sb2Te5 films induced by an excimer laser

    NASA Astrophysics Data System (ADS)

    Bai, N.; Liu, F. R.; Han, X. X.; Zhu, Z.; Liu, F.; Lin, X.; Sun, N. X.

    2015-11-01

    In this paper, the influence of Sn doping (0%, 8%, and 14%) on the crystallization of Ge2Sb2Te5 (GST) was studied with the aid of an ultraviolet laser. It was found that the addition of Sn element not only expanded the lattice parameter but also decreased the crystallization temperature and activation energy as compared to the GST. As compared to the Ge2Sb2Te5, a more complete crystallization of the Sn doping Ge2Sb2Te5 is mainly due to the lower binding energy of Sn-Te (359.8 kJ/mol), which could be more easily taken part in the bond breakage and formation than Ge-Te (456 kJ/mol) in such a short time as 30 ns. The equiaxial grains were obtained for the Sn8Ge15Sb23Te54 films when crystallization was induced by the laser fluence of 20 mJ/cm2 but the grains elongated when the laser fluence was increased to 60 mJ/cm2. The reason may be the incorporation of Sn elements changed the crystal nucleation mode.

  5. A study on the crystallization behavior of Sn-doped amorphous Ge2Sb2Te5 by ultraviolet laser radiation

    NASA Astrophysics Data System (ADS)

    Bai, N.; Liu, F. R.; Han, X. X.; Zhu, Z.; Liu, F.; Lin, X.; Sun, N. X.

    2014-10-01

    In this paper, the influence of Sn doping (0%, 8% and 14%) on the crystallization of Ge2Sb2Te5 was studied with the aid of an ultraviolet laser. The XRD analyses revealed that the addition of Sn maintained the NaCl-type structure of Ge2Sb2Te5 after crystallization but expanded the lattice parameter due to the smaller atomic radii of Ge replaced by Sn. Raman peaks (123, 150 and 110 cm-1) moved towards lower wavenumbers (118, 137 and 104 cm-1), which can be explained by the remarkable decrease of the binding energy from Ge-Te to Sn-Te. A remarkable increase in optical contrast from 15% to 40% was observed in the Sn-doped Ge2Sb2Te5 film after crystallization with both the isothermal annealing and laser radiance. While the optical contrast changed little for a fixed volume fraction of Sn-doped sample with the variation of laser fluence which is attributed to the crystallization mechanism induced by laser under different fluences is the same.

  6. Low-temperature (˜180 °C) position-controlled lateral solid-phase crystallization of GeSn with laser-anneal seeding

    NASA Astrophysics Data System (ADS)

    Matsumura, Ryo; Chikita, Hironori; Kai, Yuki; Sadoh, Taizoh; Ikenoue, Hiroshi; Miyao, Masanobu

    2015-12-01

    To realize next-generation flexible thin-film devices, solid-phase crystallization (SPC) of amorphous germanium tin (GeSn) films on insulating substrates combined with seeds formed by laser annealing (LA) has been investigated. This technique enables the crystallization of GeSn at controlled positions at low temperature (˜180 °C) due to the determination of the starting points of crystallization by LA seeding and Sn-induced SPC enhancement. The GeSn crystals grown by SPC from LA seeds showed abnormal lateral profiles of substitutional Sn concentration. These lateral profiles are caused by the annealing time after crystallization being a function of distance from the LA seeds. This observation of a post-annealing effect also indicates that GeSn with a substitutional Sn concentration of up to ˜10% possesses high thermal stability. These results will facilitate the fabrication of next-generation thin-film devices on flexible plastic substrates with low softening temperatures (˜250 °C).

  7. A systematic study of the optical and electrical properties of Ge1-ySny and Ge1-x-ySixSn y semiconductor alloys

    NASA Astrophysics Data System (ADS)

    Harris, Thomas R.

    In order to fully utilize newly developed Ge1-ySny and Ge1-x-ySixSny materials for new novel optoelectronic devices, the optical and electrical properties of these alloys were investigated using photoluminescence (PL) and Hall-effect measurements. Direct bandgap PL emission was observed from almost all the samples, making them very promising candidates for Si-based light emitting devices. T-dependent PL studies also indicate that the indirect-to-direct bandgap transition of Ge1-ySny alloys might take place at a much lower Sn content than the theory predicts. T-dependent Hall-effect measurements showed both degenerate parallel conducting layers as well as a conductivity type change from p to n at around 370-435 K, which could affect the operation of devices made from these materials. Etch studies were performed to determine the properties of the epilayers alone. Reasonable results for the average volume carrier density in the film were obtained. It was also found that there exists high level of surface states at the surface of almost all the samples. These studies should be very useful for the development of practical devices based on Ge1-ySny alloys.

  8. Strained Germanium-Tin (GeSn) P-Channel Metal-Oxide-Semiconductor Field-Effect Transistors Featuring High Effective Hole Mobility

    NASA Astrophysics Data System (ADS)

    Liu, Yan; Yan, Jing; Wang, Hongjuan; Cheng, Buwen; Han, Genquan

    2015-06-01

    Compressively strained and p-channel metal-oxide-semiconductor field-effect transistors (MOSFETs) are fabricated with low-temperature surface passivation. High crystallinity GeSn films epitaxially grown on a Ge(001) substrate are used for the device fabrication. The impacts of the Sn composition on the subthreshold swing , threshold voltage , on-state current , and effective hole mobility of the devices are investigated. GeSn pMOSFETs with different Sn compositions show a similar , indicating almost the same midgap density of interface states . A positive shift of with an increase of the Sn composition is observed. A pMOSFET exhibits a significant improvement in as compared to a device with a lower Sn composition, which is due to the superior hole mobility in a device with a higher Sn composition. pMOSFETs achieve a peak effective hole mobility of , which is much higher than that of devices. The enhancement of the compressive strain and chemical effect in the channel region with increased Sn composition leads to an improvement of.

  9. Semiconducting ZnSn{sub x}Ge{sub 1−x}N{sub 2} alloys prepared by reactive radio-frequency sputtering

    SciTech Connect

    Shing, Amanda M.; Coronel, Naomi C.; Lewis, Nathan S.; Atwater, Harry A.

    2015-07-01

    We report on the fabrication and structural and optoelectronic characterization of II-IV-nitride ZnSn{sub x}Ge{sub 1−x}N{sub 2} thin-films. Three-target reactive radio-frequency sputtering was used to synthesize non-degenerately doped semiconducting alloys having <10% atomic composition (x = 0.025) of tin. These low-Sn alloys followed the structural and optoelectronic trends of the alloy series. Samples exhibited semiconducting properties, including optical band gaps and increasing in resistivities with temperature. Resistivity vs. temperature measurements indicated that low-Sn alloys were non-degenerately doped, whereas alloys with higher Sn content were degenerately doped. These films show potential for ZnSn{sub x}Ge{sub 1−x}N{sub 2} as tunable semiconductor absorbers for possible use in photovoltaics, light-emitting diodes, or optical sensors.

  10. Enhanced carrier mobility and direct tunneling probability of biaxially strained Ge{sub 1−x}Sn{sub x} alloys for field-effect transistors applications

    SciTech Connect

    Liu, Lei; Liang, Renrong E-mail: junxu@tsinghua.edu.cn; Wang, Jing; Xu, Jun E-mail: junxu@tsinghua.edu.cn

    2015-05-14

    The carrier transport and tunneling capabilities of biaxially strained Ge{sub 1−x}Sn{sub x} alloys with (001), (110), and (111) orientations were comprehensively investigated and compared. The electron band structures of biaxially strained Ge{sub 1−x}Sn{sub x} alloys were calculated by the nonlocal empirical pseudopotential method and the modified virtual crystal approximation was adopted in the calculation. The electron and hole effective masses at the band edges were extracted using a parabolic line fit. It is shown that the applied biaxial strain and the high Sn composition are both helpful for the reduction of carrier effective masses, which leads to the enhanced carrier mobility and the boosted direct band-to-band-tunneling probability. Furthermore, the strain induced valance band splitting reduces the hole interband scattering, and the splitting also results in the significantly enhanced direct tunneling rate along the out-of-plane direction compared with that along the in-plane direction. The biaxially strained (111) Ge{sub 1−x}Sn{sub x} alloys exhibit the smallest band gaps compared with (001) and (110) orientations, leading to the highest in-plane and out-of-plane direct tunneling probabilities. The small effective masses on (110) and (111) planes in some strained conditions also contribute to the enhanced carrier mobility and tunneling probability. Therefore, the biaxially strained (110) and (111) Ge{sub 1−x}Sn{sub x} alloys have the potential to outperform the corresponding (001) Ge{sub 1−x}Sn{sub x} devices. It is important to optimize the applied biaxial strain, the Sn composition, and the substrate orientation for the design of high performance Ge{sub 1−x}Sn{sub x} field-effect transistors.

  11. Electronic structure and optical properties of Cs 2 AX2 ' X 4 (A=Ge,Sn,Pb; X',X=Cl,Br,I)

    NASA Astrophysics Data System (ADS)

    Wang, Guangtao; Wang, Dongyang; Shi, Xianbiao

    2015-12-01

    We studied the crystal structures, electronic structures and optical properties of Cs 2 AX2 ' X 4 (A=Ge,Sn,Pb; X', X=Cl, Br, I) compounds using the first-principles calculation. Our optimized structures agree well with experimental and theoretical results. Band structure calculations, using the modified Becke-Johnson (mBJ) potential method, indicate that these compounds (with the exception of Cs 2 PbX2 ' I 4 ) are semiconductors with the direct band gap ranging from 0.36 to 4.09 eV. We found the compounds Cs2GeBr2I4, Cs2GeCl2I4, Cs2GeI2Br4, Cs2SnI6, and Cs2SnBr2I4 may be good candidates for lead-free solar energy absorber materials.

  12. n-type thermoelectric material Mg2Sn0.75Ge0.25 for high power generation

    PubMed Central

    Liu, Weishu; Kim, Hee Seok; Chen, Shuo; Jie, Qing; Lv, Bing; Yao, Mengliang; Ren, Zhensong; Opeil, Cyril P.; Wilson, Stephen; Chu, Ching-Wu; Ren, Zhifeng

    2015-01-01

    Thermoelectric power generation is one of the most promising techniques to use the huge amount of waste heat and solar energy. Traditionally, high thermoelectric figure-of-merit, ZT, has been the only parameter pursued for high conversion efficiency. Here, we emphasize that a high power factor (PF) is equivalently important for high power generation, in addition to high efficiency. A new n-type Mg2Sn-based material, Mg2Sn0.75Ge0.25, is a good example to meet the dual requirements in efficiency and output power. It was found that Mg2Sn0.75Ge0.25 has an average ZT of 0.9 and PF of 52 μW⋅cm−1⋅K−2 over the temperature range of 25–450 °C, a peak ZT of 1.4 at 450 °C, and peak PF of 55 μW⋅cm−1⋅K−2 at 350 °C. By using the energy balance of one-dimensional heat flow equation, leg efficiency and output power were calculated with Th = 400 °C and Tc = 50 °C to be of 10.5% and 6.6 W⋅cm−2 under a temperature gradient of 150 °C⋅mm−1, respectively. PMID:25733845

  13. Non-radiative recombination in Ge{sub 1−y}Sn{sub y} light emitting diodes: The role of strain relaxation in tuned heterostructure designs

    SciTech Connect

    Gallagher, J. D.; Xu, C.; Smith, D. J.; Menéndez, J.; Senaratne, C. L.; Sims, P.; Kouvetakis, J.; Aoki, T.

    2015-06-28

    This paper describes the properties of Ge{sub 1−y}Sn{sub y} light emitting diodes with a broad range of Sn concentrations (y = 0.0–0.11). The devices are grown upon Si(100) platforms using ultra-low temperature deposition of highly reactive Ge and Sn hydrides. The device fabrication adopts two new photodiode designs which lead to optimized performance and enables a systematic study of the effects of strain relaxation on emission efficiency. In contrast with n-Ge/i-Ge{sub 1−y}Sn{sub y}/p-Ge analogs, which in most cases contain two defected interfaces, our designs include a p-layer with composition Ge{sub 1−z}Sn{sub z} chosen to be z < y to facilitate light extraction, but with z close enough to y to guarantee no strain relaxation at the i/p interface. In addition, a Ge{sub 1−x}Sn{sub x} alloy is also used for the n layer, with compositions in the 0 ≤ x ≤ y range, so that defected and non-defected n/i interfaces can be studied. The electroluminescence spectra vs the Sn content y in the intrinsic layer of the diodes exhibit a monotonic shift in the emission wavelength from 1550 nm to 2500 nm. On the other hand, the emission intensities show a complex dependence that cannot be explained solely on the basis of Sn concentrations. Detailed theoretical modeling of these intensities makes it possible to extract recombination lifetimes that are found to be more than three times longer in samples in which strain relaxation has not occurred at the n-i interface, demonstrating the existence of a large non-radiative contribution from the relaxation defects. This finding is particularly significant for direct gap diodes with y > 0.09, for which it is practically impossible to avoid strain relaxation in n-Ge/i-Ge{sub 1−y}Sn{sub y}/p-Ge analogs. The new designs introduced here open the door to the fabrication of highly efficient electrically pumped systems for applications in future generations of integrated photonics.

  14. New members of the A2 M ‧ M2″ structure family (A=Ca, Sr, Yb, La; M ‧ = In , Sn , Pb; M ″ = Si , Ge)

    NASA Astrophysics Data System (ADS)

    Jehle, Michael; Dürr, Ines; Fink, Saskia; Lang, Britta; Langenmaier, Michael; Steckhan, Julia; Röhr, Caroline

    2015-01-01

    The new mixed tetrelides Sr2PbGe2 and Yb2SnGe2, several mixed Ca/Sr (AII) germanides A2II (Sn , Pb)Ge2 and two polymorphs of La2 InSi2 represent new members of the general structure family of ternary alkaline-earth/lanthanoid main group silicides/germanides A2 M ‧ M2″ (M ‧ = In , Sn , Pb ; M ″ = Si , Ge). All compounds were synthesized from melts of the elements and their crystal structures have been determined by means of single crystal X-ray diffraction. Sr2PbGe2 (Cmmm, a=402.36(11), b=1542.3(4), c=463.27(10) pm) crystallizes with the Mn2AlB2 -type structure. In exhibiting infinite planar Ge zig-zag chains, it represents one border of the compound series. The other borderline case, where only [Ge2 ] dumbbells are left as Ge building units, is represented by the Ca/Yb tin germanides Ca2SnGe2 and Yb2SnGe2 (Mo2FeB2 -type; P4/mbm, a=748.58(13)/740.27(7), c=445.59(8)/435.26(5) pm). In between these two border structures compounds with variable Si/Ge chain lengths could be obtained by varying the averaged size of the AII cations: Ca0.45Sr1.55PbGe2 (new structure type; Pbam, a=791.64(5), b=2311.2(2), c=458.53(3) pm) contains planar six-membered chain segments [Ge6 ]. Tetrameric pieces [Ge4 ] are the conspicuous structure elements in Ca1.16Sr0.84SnGe2 and La2 InSi2 (La2 InNi2 -type; Pbam, a=781.01(2)/762.01(13), b=1477.95(3)/1494.38(6), c=457.004(9)/442.1(3) pm). The tetragonal form of 'La2 In Si2‧ (exact composition: La2In1.07Si1.93, P4/mbm, a=1309.11(12), c=443.32(4) pm) also crystallizes in a new structure type, containing only [Si3 ] trimers as cutouts of the planar chains. In all structures the Si/Ge zig-zag chains/chain segments are connected by In/Sn/Pb atoms to form planar M layers, which are separated by pure A layers. Band structure calculations within the FP-LAPW DFT approach together with the Zintl formalism, extended by the presence of hypervalent bonding of the heavier M ‧ elements, give insight into the chemical bonding of this series of p

  15. Observation of a metallic ground state of Sn/Ge(111)-3×3 at 4 K

    NASA Astrophysics Data System (ADS)

    Morikawa, Harumo; Jeong, Sukmin; Yeom, Han Woong

    2008-12-01

    The Sn/Ge(111)-3×3 surface was investigated by scanning tunneling microscopy/spectroscopy (STM/STS) at low temperature, for which a triangular Mott-Hubbard ground state was suggested recently. Our detailed STM/STS observation at 77 K combined with ab initio calculations unambiguously determines its atomic structure as the one-up two-down model with one third of Sn adatoms lifted upward from the flat 3×3 layer. The surface is metallic due to the partially filled dangling bonds on the down adatoms. On cooling down to 4 K, another 3×3 phase with a distinct but still metallic electronic structure was observed. The Mott-Hubbard ground state with an undistorted 3×3 structure is denied.

  16. High Pressure in situ Micro-Raman Spectroscopy of Ge-Sn System Synthesized in a Laser Heated Diamond Anvil Cell

    NASA Astrophysics Data System (ADS)

    Sorb, Y. A.; Subramanian, N.; Ravindran, T. R.; Sahu, P. Ch.

    2011-07-01

    GexSn1-x has been predicted to be a direct band-gap semiconductor, but attempts to synthesize this in bulk form by conventional synthesis methods have not been successful on account of the poor solubility of Sn in Ge. In this work, laser heated diamond anvil cell (LHDAC) technique has been employed to explore formation of bulk GexSn1-x (x = 0.7) at varying pressures and temperatures. At ˜8 GPa, in situ micro-Raman spectroscopy done on several regions of temperature quenched samples laser heated up to ˜2000 K reveals vanishing of the intense Ge TO(Γ) phonon at ˜326 cm-1 and appearance of a softer mode, concurrent with appearance of a new high intensity Raman mode at ˜660 cm-1. These indicate dilation of the Ge-Ge bond by virtue of significant miscibility of βSn at these high P-T conditions and hints at formation of new stiff Ge-Sn bonds.

  17. Planar versus puckered nets in the polar intermetallic series EuGaTt (Tt = Si, Ge, Sn).

    PubMed

    You, Tae-Soo; Grin, Yuri; Miller, Gordon J

    2007-10-15

    The ternary polar intermetallic compounds EuGaTt (Tt = Si, Ge, Sn) have been synthesized and characterized experimentally, as well as theoretically. EuGaSi crystallizes in the hexagonal AlB(2)-type structure (space group P6/mmm, Z = 1, Pearson symbol hP3) with randomly distributed Ga and Si atoms on the graphite-type planes: a = 4.1687(6) A, c = 4.5543(9) A. On the other hand, EuGaGe and EuGaSn adopt the hexagonal YPtAs-type structure (space group P6(3)/mmc, Z = 4, Pearson symbol hP12): a = 4.2646(6) A and c = 18.041(5) A for EuGaGe; a = 4.5243(5) A and c = 18.067(3) A for EuGaSn. The three crystal structures contain formally [GaTt](2-) polyanionic 3-bonded, hexagonal networks, which change from planar to puckered and exhibit a significant decrease in interlayer Ga-Ga distances as the size of Tt increases. Magnetic susceptibility measurements of this series of compounds show Curie-Weiss behavior above 86(5), 95(5), and 116(5) K with magnetic moments of 7.93, 7.97, and 7.99 mu(B) for EuGaSi, EuGaGe, and EuGaSn, respectively, indicating a 4f(7) electronic configuration (Eu(2+)) for Eu atoms. X-ray absorption spectra (XAS) are also consistent with these magnetic properties. Electronic structure calculations supplemented by a crystal orbital Hamilton population (COHP) analysis identifies the synergy between atomic sizes, from both Eu and Tt atoms, and the orbital contributions from Eu toward influencing the structural features of EuGaTt. A multicentered interaction between planes of Eu atoms and the [GaTt](2-) layers rather than through-space Ga-Ga bonding is seen in ELF distributions. PMID:17880208

  18. Growth and applications of GeSn-related group-IV semiconductor materials

    NASA Astrophysics Data System (ADS)

    Zaima, Shigeaki; Nakatsuka, Osamu; Taoka, Noriyuki; Kurosawa, Masashi; Takeuchi, Wakana; Sakashita, Mitsuo

    2015-08-01

    We review the technology of Ge1-xSnx-related group-IV semiconductor materials for developing Si-based nanoelectronics. Ge1-xSnx-related materials provide novel engineering of the crystal growth, strain structure, and energy band alignment for realising various applications not only in electronics, but also in optoelectronics. We introduce our recent achievements in the crystal growth of Ge1-xSnx-related material thin films and the studies of the electronic properties of thin films, metals/Ge1-xSnx, and insulators/Ge1-xSnx interfaces. We also review recent studies related to the crystal growth, energy band engineering, and device applications of Ge1-xSnx-related materials, as well as the reported performances of electronic devices using Ge1-xSnx related materials.

  19. Atomic layer deposition of crystalline SrHfO{sub 3} directly on Ge (001) for high-k dielectric applications

    SciTech Connect

    McDaniel, Martin D.; Ngo, Thong Q.; Ekerdt, John G.; Hu, Chengqing; Jiang, Aiting; Yu, Edward T.; Lu, Sirong; Smith, David J.; Posadas, Agham; Demkov, Alexander A.

    2015-02-07

    The current work explores the crystalline perovskite oxide, strontium hafnate, as a potential high-k gate dielectric for Ge-based transistors. SrHfO{sub 3} (SHO) is grown directly on Ge by atomic layer deposition and becomes crystalline with epitaxial registry after post-deposition vacuum annealing at ∼700 °C for 5 min. The 2 × 1 reconstructed, clean Ge (001) surface is a necessary template to achieve crystalline films upon annealing. The SHO films exhibit excellent crystallinity, as shown by x-ray diffraction and transmission electron microscopy. The SHO films have favorable electronic properties for consideration as a high-k gate dielectric on Ge, with satisfactory band offsets (>2 eV), low leakage current (<10{sup −5} A/cm{sup 2} at an applied field of 1 MV/cm) at an equivalent oxide thickness of 1 nm, and a reasonable dielectric constant (k ∼ 18). The interface trap density (D{sub it}) is estimated to be as low as ∼2 × 10{sup 12 }cm{sup −2 }eV{sup −1} under the current growth and anneal conditions. Some interfacial reaction is observed between SHO and Ge at temperatures above ∼650 °C, which may contribute to increased D{sub it} value. This study confirms the potential for crystalline oxides grown directly on Ge by atomic layer deposition for advanced electronic applications.

  20. K2Sn2ZnSe6, Na2Ge2ZnSe6, and Na2In2GeSe6: a new series of quaternary selenides with intriguing structural diversity and nonlinear optical properties.

    PubMed

    Zhou, Molin; Li, Chao; Li, Xiaoshuang; Yao, Jiyong; Wu, Yicheng

    2016-05-01

    Three new compounds (i.e., K2Sn2ZnSe6, Na2Ge2ZnSe6, and Na2In2GeSe6) with intriguing structural diversity and nonlinear optical properties were discovered for the first time. They crystallize in space groups P4/ncc, I4/mcm and Cc, respectively. In K2Sn2ZnSe6 and Na2Ge2ZnSe6, the [Sn(Ge)Se4] tetrahedra and [ZnSe4] tetrahedra are linked via edge-sharing to build up a 1D [Sn2ZnSe6] infinite chain separated by K(+)(Na(+)) cations along the c direction, while the structure of Na2In2GeSe6 is an interesting three-dimensional framework composed of [InSe4] and [GeSe4] tetrahedra via corner-sharing with Na(+) cations in the cavities. The experimental optical band gaps of these compounds were determined as 1.71(2) eV, 2.36(4) eV and 2.47(2) eV, respectively, according to UV-vis-NIR diffuse reflectance spectroscopy. Interestingly, in addition to the large band gap (1.80 eV for AgGaSe2, as a comparison), Na2In2GeSe6 exhibits phase-matchable nonlinear optical (NLO) properties with a powder second harmonic generation signal about 0.8 times that of AgGaS2. Moreover, Na2In2GeSe6 melts congruently at a rather low temperature of 671 °C, which suggests that bulk crystals can be easily obtained by the Bridgman-Stockbarger method. Our preliminary results indicate that Na2In2GeSe6 has promising applications in IR nonlinear optics. PMID:27049006

  1. Syntheses and structural characterization of non-centrosymmetric Na2M2M'S6 (M, M‧=Ga, In, Si, Ge, Sn, Zn, Cd) sulfides

    NASA Astrophysics Data System (ADS)

    Yohannan, Jinu P.; Vidyasagar, Kanamaluru

    2016-06-01

    Seven new non-centrosymmetric Na2M2M'S6 sulfides, namely, Na2Sn2ZnS6(1), Na2Ga2GeS6(2), Na2Ga2SnS6(3-α), Na2Ga2SnS6(3-β), Na2Ge2ZnS6(4), Na2Ge2CdS6(5), Na2In2SiS6(6) and Na2In2GeS6(7), were synthesized by high temperature solid state reactions and structurally characterized by single crystal X-ray diffraction. They crystallize in non-centrosymmetric Fdd2 and Cc space groups and their three-dimensional [M2M‧S6]2-framework structures consist of MS4 and M‧S4 tetrahedra corner-connected to one another in either orderly or disordered fashion. Sodium ions reside in the tunnels of the anionic framework. Compounds 1, 2 and 3-α have the structure of known Li2Ga2GeS6, whereas compounds 6 and 7 are isostructural with known Li2In2GeS6 compound. Isostructural compounds 4 and 5 represent a new structural variant. Compounds 3-α and its new monoclinic structural variant 3-β have disordered structural framework. All of them are wide band gap semiconductors. Na2Ga2GeS6(2), Na2Ga2SnS6(3), Na2Ge2ZnS6(4) and Na2In2GeS6(7) compounds are found to be second-harmonic generation (SHG) active. Compounds 1, 2 and 3-α melt congruently.

  2. Theoretical investigation of the dipole polarisability and second hyperpolarisability of cyclopentadiene homologues C 4H 4XH 2 (X=C, Si, Ge, Sn)

    NASA Astrophysics Data System (ADS)

    Alparone, A.; Millefiori, A.; Millefiori, S.

    2004-03-01

    Static and frequency-dependent electronic dipole polarisability, α, and second hyperpolarisability, γ, of the cyclopentadiene homologues C 4H 4XH 2 (X=C, Si, Ge, Sn) were calculated by ab initio HF, MP2 and DFT-B3LYP methods using Sadlej POL basis sets, including vibrational and relativistic effects. The latter calculations were extended also to the furan homologues for comparison. The results show that both α and γ values increase monotonically as the heteroatom size increases. The energy values of the electronic transitions to the two lowest singlet 1 1B2 and 2 1A1 excited states decrease not uniformly as the heteroatom becomes heavier and the two-state model approximation is not adequate to explain the evolution of the (hyper)polarisability along the series, which indeed is essentially determined by the heteroatom property. Frequency dispersion correction on α increases down the group, by contrast γ dispersion is highest in cyclopentadiene and almost constant, at a lower value, in the heavier homologues. Electron correlation correction on the calculated properties is positive and rather large on γ. HF relativistic effects on < α> and < γ> are of little importance for both stannole and tellurophene and cannot account for the observed large discrepancy between the experimental and theoretical < γe>(- ω; ω, ω,- ω) value in the latter compound. Vibrational contributions are calculated for the optically-heterodyned optical Kerr process (OHD-OKE). They are non negligible and show a clear heavy atom dependence. In the cyclopentadiene series they amount to 4-10% of < αe> and to 8-16% of < γe>(- ω; ω, ω,- ω), while they are somewhat lower in the furan series. The transversal γxxxx value is higher in the cyclopentadiene than in the furan series by ca. 30-40%, suggesting that α- α'-linked cyclopentadiene homologues can be considered as valid alternatives to the corresponding furan homologues in projecting π-conjugated oligomers and polymers for NLO

  3. Electronic and Optical Properties of Ca3MN (M = Ge, Sn, Pb, P, As, Sb and Bi) Antiperovskite Compounds

    NASA Astrophysics Data System (ADS)

    Iqbal, Samad; Murtaza, G.; Khenata, R.; Mahmood, Asif; Yar, Abdullah; Muzammil, M.; Khan, Matiullah

    2016-08-01

    The electronic and optical properties of cubic antiperovskites Ca3MN (M = Ge, Sn, Pb, P, As, Sb and Bi) were investigated by applying the full potential linearized augmented plane wave plus local orbitals (FP-LAPW + lo) scheme based on density functional theory. Different exchange correlation potentials were adopted for the calculations. The results of band structure and density of states show that, by changing the central anion of Ca3MN, the nature of the materials change from metallic (Ca3GeN, Ca3SnN, Ca3PbN) to semiconducting with small band gaps (Ca3SbN and Ca3BiN) to insulating (Ca3PN and Ca3AsN). The optical properties such as dielectric function, absorption coefficient, optical conductivity, reflectivity and refractive indices have also been calculated. The results reveal that all the studied compounds are optically active in the visible and ultraviolet energy regions, and therefore can be effectively utilized for optoelectronic devices.

  4. Electronic and Optical Properties of Ca3MN (M = Ge, Sn, Pb, P, As, Sb and Bi) Antiperovskite Compounds

    NASA Astrophysics Data System (ADS)

    Iqbal, Samad; Murtaza, G.; Khenata, R.; Mahmood, Asif; Yar, Abdullah; Muzammil, M.; Khan, Matiullah

    2016-05-01

    The electronic and optical properties of cubic antiperovskites Ca3MN (M = Ge, Sn, Pb, P, As, Sb and Bi) were investigated by applying the full potential linearized augmented plane wave plus local orbitals (FP-LAPW + lo) scheme based on density functional theory. Different exchange correlation potentials were adopted for the calculations. The results of band structure and density of states show that, by changing the central anion of Ca3MN, the nature of the materials change from metallic (Ca3GeN, Ca3SnN, Ca3PbN) to semiconducting with small band gaps (Ca3SbN and Ca3BiN) to insulating (Ca3PN and Ca3AsN). The optical properties such as dielectric function, absorption coefficient, optical conductivity, reflectivity and refractive indices have also been calculated. The results reveal that all the studied compounds are optically active in the visible and ultraviolet energy regions, and therefore can be effectively utilized for optoelectronic devices.

  5. Electronic structure and thermoelectric properties of (Mg2X)2 / (Mg2Y)2 (X, Y = Si, Ge, Sn) superlattices from first-principle calculations

    NASA Astrophysics Data System (ADS)

    Guo, San-Dong

    2016-05-01

    To identify thermoelectric materials containing abundant, low-cost and non-toxic elements, we have studied the electronic structures and thermoelectric properties of (Mg2X)2/ (Mg2Y)2 (X, Y = Si, Ge, Sn) superlattices with state-of-the-art first-principles calculations using a modified Becke and Johnson (mBJ) exchange potential. Our results show that (Mg2Ge)2/ (Mg2Sn)2 and (Mg2Si)2/ (Mg2Sn)2 are semi-metals using mBJ plus spin-orbit coupling (mBJ + SOC), while (Mg2Si)2/ (Mg2Ge)2 is predicted to be a direct-gap semiconductor with a mBJ gap value of 0.46 eV and mBJ + SOC gap value of 0.44 eV. Thermoelectric properties are predicted by through solving the Boltzmann transport equations within the constant scattering time approximation. It is found that (Mg2Si)2/ (Mg2Ge)2 has a larger Seebeck coefficient and power factor than (Mg2Ge)2/ (Mg2Sn)2 and (Mg2Si)2/ (Mg2Sn)2 for both p-type and n-type doping. The detrimental influence of SOC on the power factor of p-type (Mg2X)2/ (Mg2Y)2 (X, Y = Si, Ge, Sn) is analyzed as a function of the carrier concentration, but there is a negligible SOC effect for n-type. These results can be explained by the influence of SOC on their valence and conduction bands near the Fermi level.

  6. Strained Germanium-Tin pMOSFET Fabricated on a Silicon-on-Insulator Substrate with Relaxed Ge Buffer

    NASA Astrophysics Data System (ADS)

    Su, Shao-Jian; Han, Gen-Quan; Zhang, Dong-Liang; Zhang, Guang-Ze; Xue, Chun-Lai; Wang, Qi-Ming; Cheng, Bu-Wen

    2013-11-01

    Germanium-tin (Ge1-xSnx) p-type metal-oxide-semiconductor field effect transistors (pMOSFETs) were fabricated using a strained Ge0.985Sn0.015 thin film that was epitaxially grown on a silicon-on-insulator substrate with a relaxed Ge buffer layer. The Ge buffer was deposited using a two-step chemical vapor deposition growth technique. The high quality Ge0.985Sn0.015 layer was grown by solid source molecular beam epitaxy. Ge0.985Sn0.015 pMOSFETs with Si surface passivation, TaN/HfO2 gate stack, and nickel stanogermanide [Ni(Ge1-xSnx)] source/drain were fabricated on the grown substrate. The device achieves an effective hole mobility of 182 cm2/V·s at an inversion carrier density of 1 × 1013 cm-2.

  7. Theoretical investigation of Sn-doped Ge{sub 2}Sb{sub 2}Te{sub 5} alloy in crystalline phase

    SciTech Connect

    Singh, Janpreet; Tripathi, S. K.; Singh, Gurinder; Kaura, Aman

    2015-06-24

    Ge{sub 2}Sb{sub 2}Te{sub 5} (GST) is technologically important for phase-change random access memory applications. It has been shown that the 2.2 atomic % doping of Sn weakens the Ge–Te bond strength while maintaining the symmetry of stable phase of GST. The influence of Sn doping upon the phase change characteristics of the crystalline GST alloy has been investigated by ab initio calculations. The lattice parameter, average interface distances between two adjacent (111) layers, equilibrium volume, metallic character and electrical resistance has been calculated for the stable phase of GST and Sn-doped GST.

  8. HfO2 gate dielectric on Ge (1 1 1) with ultrathin nitride interfacial layer formed by rapid thermal NH3 treatment

    NASA Astrophysics Data System (ADS)

    Agrawal, Khushabu S.; Patil, Vilas S.; Khairnar, Anil G.; Mahajan, Ashok M.

    2016-02-01

    Interfacial properties of the ALD deposited HfO2 over the surface nitrided germanium substrate have been studied. The formation of GeON (∼1.7 nm) was confirmed by X-ray photoelectron spectroscopy (XPS) and high resolution transmission electron spectroscopy (HRTEM) over the germanium surface. The effect of post deposition annealing temperature was investigated to study the interfacial and electrical properties of hafnium oxide/germanium oxynitride gate stacks. The high-k MOS devices with ultrathin GeON layer shows the good electrical characteristics including higher k value ∼18, smaller equivalent oxide thickness (EOT) around 1.5 nm and smaller hysteresis value less than 170 mV. The Qeff and Dit values are somewhat greater due to the (1 1 1) orientation of the germanium and may be due to the presence of nitrogen at the interface. The Fowler-Northeim (FN) tunneling of Ge MOS devices has been studied. The barrier height ΦB extracted from the plot is ∼1 eV.

  9. GeP and (Ge{sub 1−x}Sn{sub x})(P{sub 1−y}Ge{sub y}) (x≈0.12, y≈0.05): Synthesis, structure, and properties of two-dimensional layered tetrel phosphides

    SciTech Connect

    Lee, Kathleen; Synnestvedt, Sarah; Bellard, Maverick; Kovnir, Kirill

    2015-04-15

    GeP and Sn-doped GeP were synthesized from elements in bismuth and tin flux, respectively. The layered crystal structures of these compounds were characterized by single crystal X-ray diffraction. Both phosphides crystallize in a GaTe structure type in the monoclinic space group C2/m (No. 12) with GeP: a=15.1948(7) Å, b=3.6337(2) Å, c=9.1941(4) Å, β=101.239(2)°; Ge{sub 0.93(3)}P{sub 0.95(1)}Sn{sub 0.12(3)}: a=15.284(9) Å, b=3.622(2) Å, c=9.207(5) Å, β=101.79(1)°. The crystal structure of GeP consists of 2-dimensional GeP layers held together by weak electron lone pair interactions between the phosphorus atoms that confine the layer. Each layer is built of Ge–Ge dumbbells surrounded by a distorted antiprism of phosphorus atoms. Sn-doped GeP has a similar structural motif, but with a significant degree of disorder emphasized by the splitting of all atomic positions. Resistivity measurements together with quantum-chemical calculations reveal semiconducting behavior for the investigated phosphides. - Graphical abstract: Layered phosphides GeP and Sn-doped GeP were synthesized from elements in bismuth and tin flux, respectively. The crystal structure of GeP consists of 2-dimensional GeP layers held together by weak electron lone pair interactions between the phosphorus atoms that confine the layer. Sn-doped GeP has a similar structural motif with a significant degree of disorder emphasized by the splitting of all atomic positions. Resistivity measurements together with quantum-chemical calculations reveal semiconducting behavior for the investigated phosphides. - Highlights: • GeP crystallizes in a layered crystal structure. • Doping of Sn into GeP causes large structural distortions. • GeP is narrow bandgap semiconductor. • Sn-doped GeP exhibits an order of magnitude higher resistivity due to disorder.

  10. Pseudo single crystal, direct-band-gap Ge{sub 0.89}Sn{sub 0.11} on amorphous dielectric layers towards monolithic 3D photonic integration

    SciTech Connect

    Li, Haofeng; Brouillet, Jeremy; Wang, Xiaoxin; Liu, Jifeng

    2014-11-17

    We demonstrate pseudo single crystal, direct-band-gap Ge{sub 0.89}Sn{sub 0.11} crystallized on amorphous layers at <450 °C towards 3D Si photonic integration. We developed two approaches to seed the lateral single crystal growth: (1) utilize the Gibbs-Thomson eutectic temperature depression at the tip of an amorphous GeSn nanotaper for selective nucleation; (2) laser-induced nucleation at one end of a GeSn strip. Either way, the crystallized Ge{sub 0.89}Sn{sub 0.11} is dominated by a single grain >18 μm long that forms optoelectronically benign twin boundaries with others grains. These pseudo single crystal, direct-band-gap Ge{sub 0.89}Sn{sub 0.11} patterns are suitable for monolithic 3D integration of active photonic devices on Si.

  11. Oxide microstructural evolution of Zr-0.7Sn-0.35Nb-0.3Fe alloys containing Ge corroded in lithiated water

    NASA Astrophysics Data System (ADS)

    Xie, Xingfei; Zhang, Jinlong; Yao, Meiyi; Zhou, Bangxin; Peng, Jianchao; Liang, Xue

    2014-08-01

    The results of corrosion tests conducted in lithiated water with 0.01 M LiOH at 360 °C/18.6 MPa revealed that the corrosion resistance of the Zr-0.7Sn-0.35Nb-0.3Fe alloy in wt% was considerably improved by Ge addition of 0.05-0.2 wt%. To further understand the mechanism on the effect of Ge addition on the corrosion resistance of the Zr-0.7Sn-0.35Nb-0.3Fe alloy in wt%, the microstructures of alloys and oxides were investigated by transmission electron microscopy and scanning electron microscopy. For the Zr-0.7Sn-0.35Nb-0.3Fe-0.2Ge alloy, the outer layer of oxide mainly consisted of equiaxed grains, while the middle layer of oxide mainly consisted of many columnar grains in a direction perpendicular to the oxide/metal interface. The suitable amount of Ge can retard the evolution from the columnar grains to the equiaxed grains and delay the developing process of the defects to form the micro-cracks in oxide. The amorphous phase produced around the [Zr(Fe,Cr,Nb,Ge)2]O SPPs could relax the compressive stress, which could improve the corrosion resistance of zirconium alloy. The corrosion resistance could be degraded by the formation of cracks from the coarse [Zr3Ge]O SPPs towards the outer surface of oxide layers.

  12. Improvement in the Positive Bias Temperature Stability of SnOx-Based Thin Film Transistors by Hf and Zn Doping.

    PubMed

    Han, Dongsuk; Park, Jaehyung; Kang, Minsoo; Jeon, Hyeongtag; Park, Jongwan

    2015-10-01

    We investigated the performance of tin oxide thin film transistors (TFTs) using DC magnetron sputtering. A remarkable improvement in the transfer characteristics was obtained for the Hf-doped tin oxide (HTO) TFT. We also developed amorphous hafnium-zinc-tin oxide (HZTO) thin film transistors and investigated the effects of hafnium doping on the electrical characteristics of the HTO TFTs. Doping with hafnium resulted in a reduced defect density in the tin oxide channel layer related to oxygen vacancies, which may result from increased field effect mobility. Zinc atoms have relatively higher oxidation potential compared to tin atoms, so more oxygen molecules can be absorbed and more electrons are trapped in the HZTO films. The HZTO TFTs exhibited good electrical characteristics with a field effect mobility of 10.98 cm2/Vs, and a high ION/IOFF ratio over 10(8). PMID:26726382

  13. Molecular approaches to p- and n-nanoscale doping of Ge 1-ySn y semiconductors: Structural, electrical and transport properties

    NASA Astrophysics Data System (ADS)

    Xie, Junqi; Tolle, J.; D'Costa, V. R.; Weng, C.; Chizmeshya, A. V. G.; Menendez, J.; Kouvetakis, J.

    2009-08-01

    We report the development of practical doping protocols via designer molecular sources to create n- and p-type doped Ge 1-ySn y layers grown directly upon Si(1 0 0). These materials will have applications in the fabrication of advanced PIN devices that are intended to extend the infrared optical response beyond that of Ge by utilizing the Sn composition as an additional design parameter. Highly controlled and efficient n-doping of single-layer structures is achieved using custom built P(GeH 3) 3 and As(GeH 3) 3, precursors containing preformed Ge-As and Ge-P near-tetrahedral bonding arrangements compatible with the structure of the host Ge-Sn lattice. Facile substitution and complete activation of the P and As atoms at levels ˜10 17-10 19 cm -3 is obtained via in situ depositions at low temperatures (350 °C). Acceptor doping is readily achieved using conventional diborane yielding carrier concentrations between 10 17-10 19 cm -3 under similar growth conditions. Full activation of the as-grown dopant concentrations is demonstrated by combined SIMS and Hall experiments, and corroborated using a contactless spectroscopic ellipsometry approach. RTA processing of the samples leads to a significant increase in carrier mobility comparable to that of bulk Ge containing similar doping levels. The alloy scattering contribution appears to be negligible for electron carrier concentrations beyond 10 19 cm -3 in n-type samples and hole concentrations beyond 10 18 cm -3 in p-type samples. A comparative study using the classical lower-order hydrides PH 3 and AsH 3 produced n-doped films with carrier densities (up to 9 × 10 19 cm -3) similar to those afforded by P(GeH 3) 3 and As(GeH 3) 3. However, early results indicate that the simpler PH 3 and AsH 3 sources yield materials with inferior morphology and microstructure. Calculations of surface energetics using bond enthalpies suggest that the latter massive compounds bind to the surface via strong Ge-Ge bonds and likely act as

  14. Theoretical investigations on vibrational properties and thermal conductivities of ternary antimonides TiXSb, ZrXSb and HfXSb (X = Si, Ge)

    NASA Astrophysics Data System (ADS)

    Deligoz, E.; Ozyar, U. F.; Ozisik, H. B.

    2016-06-01

    We have performed density functional calculations of the vibrational and thermodynamic properties of the ternary antimonides TiXSb, ZrXSb and HfXSb (X = Si, Ge). The direct method is used to calculate the phonon dispersion relation and phonon density of states for these compounds as well as their infrared and Raman active mode frequencies for the first time. Their dynamical stability is confirmed by phonon spectra. The lattice thermal conductivities of these compounds have been calculated from third-order force constants and plotted as a function of temperature. We have also evaluated the high temperature thermal conductivity by means of the Clarke's model and Cahill's model. Some selected thermodynamical properties, e.g. Gibbs free energy, entropy and heat capacity at constant volume are predicted theoretically and discussed. We have showed the relationships between thermodynamical properties and temperature. The numerical calculations reported in this paper were partially performed at Aksaray University, Science and Technology Application and Research Center.

  15. Wave-function engineering and absorption spectra in Si{sub 0.16}Ge{sub 0.84}/Ge{sub 0.94}Sn{sub 0.06}/Si{sub 0.16}Ge{sub 0.84} strained on relaxed Si{sub 0.10}Ge{sub 0.90} type I quantum well

    SciTech Connect

    Yahyaoui, N. E-mail: moncef-said@yahoo.fr; Sfina, N.; Said, M. E-mail: moncef-said@yahoo.fr; Lazzari, J.-L.; Bournel, A.

    2014-01-21

    We theoretically investigate germanium-tin alloy as a semiconductor for the design of near infrared optical modulators in which the Ge{sub 1−x}Sn{sub x} alloy is the active region. We have calculated the electronic band parameters for heterointerfaces between strained Ge{sub 1−x}Sn{sub x} and relaxed Si{sub 1−y}Ge{sub y}. Then, a type-I strain-compensated Si{sub 0.10}Ge{sub 0.90}/Si{sub 0.16}Ge{sub 0.84}/Ge{sub 0.94}Sn{sub 0.06} quantum well heterostructure optimized in terms of compositions and thicknesses is studied by solving Schrödinger equation without and under applied bias voltage. The strong absorption coefficient (>1.5 × 10{sup 4} cm{sup −1}) and the shift of the direct transition under large Stark effect at 3 V are useful characteristics for the design of optoelectronic devices based on compressively strained IV-IV heterostructures at near infrared wavelengths.

  16. Ab Initio Study of Binary and Ternary Nb3(X,Y) A15 Intermetallic Phases (X,Y = Al, Ge, Si, Sn)

    NASA Astrophysics Data System (ADS)

    Papadimitriou, Ioannis; Utton, Claire; Scott, Andrew; Tsakiropoulos, Panos

    2015-02-01

    Elastic and thermodynamic properties of binary and ternary A15 phases containing Al, Ge, Si, and Sn were studied using the first-principles pseudopotential plane-wave method based on density functional theory. The temperature dependence of the enthalpy of formation for the A15 intermetallics is reported using the quasiharmonic approximation. Elastic properties of the studied compounds were calculated at T = 0 K and were in agreement with the measured values reported in the literature. The elastic properties and thermodynamic data for the metastable A15-Nb3Si are reported for the first time. The Nb3Si has the highest bulk, shear, and Young's modulus values and is predicted to be less ductile than the other three binary A15 intermetallics. The calculations suggest (i) that Al and Sn have a positive effect on the ductility of the A15 compounds of this study, (ii) that Ge as a ternary addition has a ductilizing effect only in the A15-Nb3Si, and (iii) that Si as a ternary addition has a negative effect on the ductility of all the A15 compounds of the present study. The linear thermal expansion coefficients of the Nb, Al, the A15 Nb3Al, Nb3Ge, Nb3Sn, and Nb3Si (A15) phases are reported. The Sn and Al additions in the Nb3Si stabilize the A15 structure, while the Ge addition has the opposite effect, stabilizing the tP32 Nb3Si.

  17. Ground and excited states of group IVA diatomics from local-spin-density calculations: Model potentials for Si, Ge, and Sn

    NASA Astrophysics Data System (ADS)

    Andzelm, Jan; Russo, Nino; Salahub, Dennis R.

    1987-12-01

    LCGTO-MP-LSD results are reported for the spectroscopic constants and electronic structure of the diatomic molecules Si2, Ge2, Sn2, SiGe, SiSn, and GeSn in their low-lying electronic states. For the homonuclear molecules we found that the ground state is 3Σ-g with the most important lower-lying excited states being 3Πu, 1Πu, and 1Σ+g, respectively. Our results are in good agreement with the available experimental data and also in qualitative agreement with other theoretical studies. We present here the first theoretical study on the heteronuclear molecules, for which experimental data are not available. We found the 3Σ- state to be the lowest, followed by 3Π and 1Σ+ states. Model potentials (MP) are reported for the Si, Ge, and Sn atoms. The reliable results for molecules complement those for the atoms and show that the LSD model potentials presented here allow for an accurate description of chemical bonding and spectroscopic properties in the title molecules.

  18. First-principles investigations of stability, electronic and thermodynamic properties of Ti2FeGe and Ti2FeSn

    NASA Astrophysics Data System (ADS)

    Wei, Xiao-Ping; Mao, Ge-Yong; Chu, Shi-Bin; Deng, Hong; Deng, Jian-Bo; Hu, Xian-Ru

    2013-09-01

    We present a study of the thermodynamic and physical properties of Ti2FeGe and Ti2FeSn based on the density-functional theory first-principles calculations. Both compounds are found to be half-metallic ferromagnets with a total spin magnetic moment per formula unit of 2.00 μB. The stability is evaluated from the physical, chemical and mechanical points of view. The Curie temperature is estimated to be 354 K for Ti2FeGe and 475 K for Ti2FeSn, respectively, which is well-above the room temperature. In addition, the half-metallicity of Ti2FeGe and Ti2FeSn is retained when the lattice constants are changed by -2.6% to 9.7% and -7.1% to 6.9%, respectively. Finally, by using a quasiharmonic Debye model, the Debye temperature, the heat capacity, the coefficient of thermal expansion, and the Grüneisen parameter have also been obtained in the present work. The present calculations show that Ti2FeGe and Ti2FeSn have a great application potential in the spin valve and magnetic tunnel junction.

  19. Composition-driven phase boundary and electrical properties in (Ba0.94Ca0.06)(Ti1-xMx)O3 (M = Sn, Hf, Zr) lead-free ceramics.

    PubMed

    Zhao, Chunlin; Wang, Hui; Xiong, Jie; Wu, Jiagang

    2016-04-12

    In this study, we systematically investigated the composition dependence of the phase structure, microstructure, and electrical properties of (Ba0.94Ca0.06)(Ti1-xMx)O3 (M = Sn, Hf, Zr) ceramics synthesised by the conventional solid-state reaction method. The phase boundary type strongly depends on the composition, and then different electrical properties were exhibited. The addition of Hf and Zr can more quickly shift phase transition temperatures (TR-O and TO-T) to a higher temperature with respect to Sn, leading to the formation of different phase boundaries. In addition, different phase boundaries can also be affected by their doped contents. The R-O and O-T phase boundaries can be shown in the Sn-doped ceramics with x = 0.10, and the R-O phase boundary can exist in the Hf (x = 0.07) or Zr (x = 0.075)-doped ceramics. A high piezoelectric property of d33 = 600 pC N(-1) can be achieved in the Sn-doped ceramics due to the involvement of converging R-O/O-T phase boundaries, an enhanced ferroelectric performance with Pr = 14.54 μC cm(-2) and Ec = 1.82 kV cm(-1) can be attained in the Zr-doped ceramics, and Hf would benefit from obtaining a large strain behaviour (∼0.20%). We believe that the electrical properties and the related physical mechanisms of BaTiO3-based ceramics can be well unveiled by studying their chemical modification behavior. PMID:26952807

  20. Study on Momentum Density in Semiconductor Alloys GeC and SnC by Positron Annihilation

    NASA Astrophysics Data System (ADS)

    Amrane, N.

    The independent particle model (IPM) coupled with empirical pseudopotential method (EPM) was used to compute the thermalized positron charge densities in specific family of binary tetrahedrally coordinated crystals of formula ANB8-N. Initial results show a clear asymmetrical positron charge distribution relative to the bond center. It is observed that the positron density is maximum in the open interstices and is excluded not only from the ion cores but also to a considerable degree from the valence bonds. Electron-positron momentum densities are calculated for the (001, 110) planes. The results are used to analyze the positron effects in GeC and SnC. Our computational technique provides the theoretical means of interpreting the k-space densities obtained experimentally using the two-dimensional angular correlation of annihilation radiation (2D-ACAR).

  1. VizieR Online Data Catalog: Photometry of the Type Ib/c SN2013ge (Drout+, 2016)

    NASA Astrophysics Data System (ADS)

    Drout, M. R.; Milisavljevic, D.; Parrent, J.; Margutti, R.; Kamble, A.; Soderberg, A. M.; Challis, P.; Chornock, R.; Fong, W.; Frank, S.; Gehrels, N.; Graham, M. L.; Hsiao, E.; Itagaki, K.; Kasliwal, M.; Kirshner, R. P.; Macomb, D.; Marion, G. H.; Norris, J.; Phillips, M. M.

    2016-06-01

    We obtained UV and optical photometry of the Type Ib/c SN2013ge spanning 466 days. Data were obtained with the UV Optical Telescope (UVOT) on board Swift (w2, m2 , w1, u, b, and v bands; table1.dat), the 0.4 m telescope at the Challis Astronomical Observatory (CAO; B, V, R, and I bands; table2.dat), the 1.2m telescope plus KeplerCam CCD at the Fred Lawrence Whipple Observatory (FLWO; B, V, r, and i bands; table3.dat), the MMTCam instrument mounted on the 6.5 m MMT telescope, the Large Binocular Camera (LBC) mounted on the Large Binocular Telescope (LBT), and the Inamori-Magellan Areal Camera and Spectrograph (IMACS) on Magellan-Baade (r, i, and z bands; table4.dat). (4 data files).

  2. Phase equilibria in systems Ce-M-Sb (M=Si, Ge, Sn) and superstructure Ce{sub 12}Ge{sub 9-x}Sb{sub 23+x} (x=3.8+-0.1)

    SciTech Connect

    Nasir, Navida; Grytsiv, Andriy; Rogl, Peter; Saccone, Adriana; Giester, Gerald

    2009-04-15

    Phase relations in the ternary systems Ce-M-Sb (M=Si, Ge, Sn) in composition regions CeSb{sub 2}-Sb-M were studied by optical and electron microscopy, X-ray diffraction, and electron probe microanalysis on arc-melted alloys and specimens annealed in the temperature region from 850 to 200 deg. C. The results, in combination with an assessment of all literature data available, were used to construct solidus surfaces and a series of isothermal sections. No ternary compounds were found to form in the Ce-Si-Sb system whilst Ce{sub 12}Ge{sub 9-x}Sb{sub 23+x} (3.3Sn{sub x}Sb{sub 2} (0.1Ge{sub 9-x}Sb{sub 23+x} (x=3.8+-0.1) were determined from X-ray single crystal and powder diffraction. For the binary system Ge-Sb a eutectic was defined Lreversible(Ge)+(Sb) at 591.6 deg. C and 22.5 at%. Ge EPMA revealed a maximal solubility of 6.3 at% Ge in (Sb) at the eutectic temperature. - Graphical abstract: Phase relations in the ternary systems Ce-M-Sb (M=Si, Ge, Sn) in composition regions CeSb{sub 2}-Sb-M have been studied by optical and electron microscopy, XRD and EPMA on as cast alloys and specimens annealed in the temperature region 200-850 deg. C.

  3. Revealing the origin of the strong second harmonic generation of Li2CdXS4 and Li2CdXS4 (X = Ge or Sn)

    NASA Astrophysics Data System (ADS)

    Reshak, A. H.

    2016-03-01

    Second harmonic generation (SHG) and the first hyperpolarizability ( βij k ) of two novel quaternary diamond-like semiconductors, Li2CdGeS4 and Li2CdSnS4, are investigated based on the band structure calculations. Calculations show that these materials possess wide and direct energy gaps of about 3.10 eV (Li2CdGeS4) and 3.23 eV (Li2CdSnS4) in close agreement with the measured gaps (3.15 eV and 3.26 eV). The energy gap values confirm that these materials exhibit exceptional laser damage thresholds. The presence of polarizable M-S bonds tunes these compounds to exhibit strong SHG. The calculated linear optical properties exhibit considerable anisotropy, which favors the enhanced phase matching conditions necessary for observation of SHG and optical parametric oscillation. It has been found that Li2CdGeS4 and Li2CdSnS4 exhibit negative uniaxial anisotropy and positive birefringence. The calculated SHG of the dominant component is about 18.64 pm/V for Li2CdGeS4, which is larger than that obtained from Li2CdSnS4 (12.75 pm/V). These results are in concordance with the experimental value of the well known nonlinear crystal KTiOPO4. The calculated first hyperpolarizability ( β333 ) at λ = 1064 nm is about 13.015 × 10-30 esu for Li2CdGeS4 and 9.704 × 10-30 esu for Li2CdSnS4.

  4. Ternary arsenides ATt3As3 (A=K, Rb; Tt=Ge, Sn) with layered structures

    NASA Astrophysics Data System (ADS)

    Khatun, Mansura; Stoyko, Stanislav S.; Mar, Arthur

    2016-06-01

    The four ternary arsenides ATt3As3 (A=K, Rb; Tt=Ge, Sn) were obtained by reaction of the elements at 600-650 °C. They adopt an orthorhombic structure (space group Pnma, Z=4, with cell parameters ranging from a=9.9931(11) Å, b=3.7664(4) Å, c=18.607(2) Å for KGe3As3 to a=10.3211(11) Å, b=4.0917(4) Å, c=19.570(2) Å for RbSn3As3) containing corrugated [Tt3As3] layers built from Tt-centred trigonal pyramids and tetrahedra forming five-membered rings decorated with As handles. They can be considered to be Zintl phases with Tt atoms in +4, +3, and +1 oxidation states. Band structure calculations predict that these compounds are semiconductors with narrow band gaps (0.71 eV in KGe3As3, 0.50 eV in KSn3As3).

  5. Increased photoluminescence of strain-reduced, high-Sn composition Ge1-xSnx alloys grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Chen, Robert; Lin, Hai; Huo, Yijie; Hitzman, Charles; Kamins, Theodore I.; Harris, James S.

    2011-10-01

    We synthesized up to Ge0.914Sn0.086 alloys on (100) GaAs/InyGa1-yAs buffer layers using molecular beam epitaxy. The buffer layers enable engineered control of strain in the Ge1-xSnx layers to reduce strain-related defects and precipitation. Samples grown under similar conditions show a monotonic increase in the integrated photoluminescence (PL) intensity as the Sn composition is increased, indicating changes in the bandstructure favorable for optoelectronics. We account for bandgap changes from strain and composition to determine a direct bandgap bowing parameter of b = 2.1 ± 0.1. According to our models, these are the first Ge1-xSnx samples that are both direct-bandgap and exhibit PL.

  6. Chemical pressure effects on magnetism in the quantum spin liquid candidates Yb2X2O7 (X =Sn, Ti, Ge)

    NASA Astrophysics Data System (ADS)

    Dun, Z. L.; Lee, M.; Choi, E. S.; Hallas, A. M.; Wiebe, C. R.; Gardner, J. S.; Arrighi, E.; Freitas, R. S.; Arevalo-Lopez, A. M.; Attfield, J. P.; Zhou, H. D.; Cheng, J. G.

    2014-02-01

    The linear and nonlinear ac susceptibility measurements of Yb-pyrochlores, Yb2X2O7 (X =Sn, Ti, and Ge), show transitions with a ferromagnetic nature at 0.13 and 0.25 K for Yb2Sn2O7 and Yb2Ti2O7, respectively, and an antiferromagnetic ordering at 0.62 K for Yb2Ge2O7. These systematical results (i) provided information about the nature of the unconventional magnetic ground state in Yb2Ti2O7; (ii) realized a distinct antiferromagnetic ordering state in Yb2Ge2O7; and (iii) demonstrated that the application of chemical pressure through the series of Yb-pyrochlores can efficiently perturb the fragile quantum spin fluctuations of the Yb3+ ions and lead to very different magnetic ground states.

  7. Near-bandgap optical properties of pseudomorphic GeSn alloys grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    D'Costa, Vijay Richard; Wang, Wei; Yeo, Yee-Chia

    2016-08-01

    We investigated the compositional dependence of the near-bandgap dielectric function and the E0 critical point in pseudomorphic Ge1-xSnx alloys grown on Ge (100) substrate by molecular beam epitaxy. The complex dielectric functions were obtained using spectroscopic ellipsometry from 0.5 to 4.5 eV at room temperature. Analogous to the E1 and E1+Δ1 transitions, a model consisting of the compositional dependence of relaxed alloys along with the strain contribution predicted by the deformation potential theory fully accounts for the observed compositional dependence in pseudomorphic alloys.

  8. Panoscopically optimized thermoelectric performance of a half-Heusler/full-Heusler based in situ bulk composite Zr(0.7)Hf(0.3)Ni(1+x)Sn: an energy and time efficient way.

    PubMed

    Bhardwaj, A; Chauhan, N S; Sancheti, Bhagyashree; Pandey, G N; Senguttuvan, T D; Misra, D K

    2015-11-28

    All scale hierarchical architecturing, matrix/inclusion band alignment and intra-matrix electronic structure engineering, the so called panoscopic approach for thermoelectric materials has been demonstrated to be an effective paradigm for optimizing high ZT. To achieve such hierarchically organized microstructures, composition engineering has been considered to be an efficient strategy. In this work, such a panoscopic concept has been extended to demonstrate for the first time in the case of half-Heusler based thermoelectric materials via a composition engineering route. A series of new off-stoichiometric n-type Zr0.7Hf0.3Ni1+xSn (0 ≤x≤ 0.10) HH compositions have been modified to derive HH(1 -x)/full-Heusler (FH)(x) composite with an all scale hierarchically modified microstructure with FH inclusions within the matrix to study the temperature dependent thermoelectric properties. The structural analysis employing XRD, FE-SEM and HR-TEM of these materials reveal a composite of HH and FH, with hierarchically organized microstructures. In such a submicron/nano-composite, the electronic properties are observed to be well optimized yielding a large power factor; α(2)σ (∼30.7 × 10(-4) W m(-1) K(-2) for Zr0.7Hf0.3Ni1.03Sn) and reduced thermal conductivity (∼2.4 W m(-1) K(-1) for Zr0.7Hf0.3Ni1.03Sn) yielding a high ZT∼ 0.96 at 773 K for composition Zr0.7Hf0.3Ni1.03Sn which is ∼250% larger than the normal HH Zr0.7Hf0.3NiSn (ZT∼ 0.27 at 773 K). The enhancement in ZT of these composites has been discussed in terms of primary electron filtering, electron injection and several phonon scattering mechanisms such as alloy scattering, point defect scattering, and grain boundary scattering. The Bergman and Fel model is used to calculate effective thermoelectric parameters of these composites for comparing the experimental results. PMID:26499748

  9. Structure and stability of noble gas bound EX3+ compounds (E = C, Ge, Sn, Pb; X = H, F, Cl, Br).

    PubMed

    Pan, Sudip; Moreno, Diego; Ghosh, Sreyan; Chattaraj, Pratim K; Merino, Gabriel

    2016-01-15

    It has been analyzed at the MP2/def2-QZVPPD level whether EX3+ (E = C-Pb; X = H, F-Br) can bind noble gas atoms. Geometrical and electronic structures, dissociation energy values, thermochemical parameters, natural bond order, electron density, and energy decomposition analyses highlight the possibility of such noble gas bound EX3+ compounds. Except He and Ne, the other heavier congeners of this family make quite strong bonds with E. In fact, the dissociations of Ar-Rn bound analogues turn out to be endergonic in nature at 298 K, except in the cases of ArGe Cl3+, Ar/KrGeBr3+, and ArSnBr3+. GeH3+ and EF3+ (E = Ge-Pb) can even bind two Ng atoms with reasonably high dissociation energy. As the pz orbital of the E center in EX3+ plays a crucial role in its binding with the noble gas atoms, the effect of the π back-bonding causing X → E electron transfer ought to be properly understood. Due to the larger back-donation, the Ng binding ability of EX3+ gradually decreases along F to Br. EH2+ and the global minimum HE(+…) H2 (E = Sn, Pb) complexes are also able to bind Ar-Rn atoms quite effectively. The NgE bonds in Ar-Rn bound CH3+, GeH3+, and EF3+ (E = Ge-Pb) and Xe/RnE bonds in NgECl3+ and NgEBr3+ (E = Ge, Sn) are mainly of covalent type. PMID:26132752

  10. Dielectric behavior of a-Sn-Se-Pb-Ge chalcogenide glass

    NASA Astrophysics Data System (ADS)

    Kumar, Prashant; Modgil, Vivek; Choudhary, Shobhana; Nidhi, A. V.; Rangra, V. S.

    2015-05-01

    The bulk material Sn8Se74Pb18-xGex(7≤x≤11) has been prepared by melt quenching technique. The viterous and glassy nature have been confirmed by X-Ray Diffraction (XRD) and Differential Scanning Calorimetery (DSC) techniques respectively. The material exhibits the good thermal stability and high value of glass transition temperature. The dielectric behavior has been studied in frequency range 50Hz-1MHz, using pallet method. The universal dielectric behaviour of amorphous semiconductors has been observed for the glass system. The compositional dependence of dielectric behavior has also been observed.

  11. Magnetic and half-metallic properties of the full-Heusler alloys Co2TiX(X=Al,Ga;Si,Ge,Sn;Sb)

    NASA Astrophysics Data System (ADS)

    Lee, S. C.; Lee, T. D.; Blaha, P.; Schwarz, K.

    2005-05-01

    The electronic structure and magnetic properties of the full-Heusler alloys Co2TiX (X element from groups III, IV and V) were studied by first principle calculations. Previous calculations found Co2TiAl and Co2TiSn not to be half metallic. In this paper, however, it will be shown that the alloys with X =Al,Si,Ge,Sn are half metallic and ferromagnetic. The effect of atomic disorder in the Ti-Al sublattices reduces the half metallicity of the Co2TiAl Heusler alloy.

  12. Electronic and Thermoelectric Properties of Layered Sn- and Pb-Doped Ge2Sb2Te5 Alloys Using First Principle Calculations

    NASA Astrophysics Data System (ADS)

    Singh, Janpreet; Singh, Gurinder; Kaura, Aman; Tripathi, S. K.

    2016-06-01

    A computational study on stable hexagonal phase of undoped, and Sn- and Pb-doped Ge2Sb2Te5 (GST) phase change materials has been carried out. The electronic structure, lattice dynamics and thermoelectric properties of doped GST have been extensively investigated using ab initio methods with virtual crystal approximation. The hexagonal symmetry of the GST is maintained with the addition of Sn and Pb dopants. The lattice parameters and atomic volume of the Sn-doped GST structure is larger than that of the undoped GST. Electronic band structure calculations show that there is an increase in band gap with the increase in the concentration of Sn (≤4.4 at.%). However, with the addition of a very small amount of Pb, there is a continuous decrease in lattice parameters and band gap values. The calculated energy band structure is then used in combination with the Boltzmann transport equation to calculate the thermoelectric parameters of GST and Sn- and Pb-doped materials. Seebeck coefficient ( S), electronic thermal conductivity ( κ e) and the thermoelectric figure-of-merit ( ZT) have been calculated with the help of BoltzTraP code. It was found that the thermoelectric properties of GST are enhanced with the addition of Sn.

  13. Electronic structure, magnetic and thermal properties of Rh2MnZ (Z=Ge, Sn, Pb) compounds under pressure from ab-initio quasi-harmonic method

    NASA Astrophysics Data System (ADS)

    Benkhelifa, F. Z.; Lekhal, A.; Méçabih, S.; Abbar, B.; Bouhafs, B.

    2014-12-01

    We have investigated the electronic structure, magnetic and thermal properties of the ternary full-Heusler alloys Rh2MnZ (Z=Ge, Sn, Pb) under pressure employing the full potential linearized augmented plane wave (FP-LAPW) plus local orbitals method based on the density functional theory (DFT), For the exchange-correlation effects we have adopted the generalized gradient approximation (GGA).Through the quasi-harmonic Debye model, we also study the thermodynamic properties of Rh2MnZ (Z=Ge, Sn and Pb). The thermal expansion versus temperature and pressure, the thermodynamic parameters (Debye temperature and specific heat) with pressure P, and the heat capacity at various pressures and temperatures in the ranges of 0 GPa to 0.6 GPa and 0 K to 400 K have been obtained.

  14. The ground state and the bonding properties of the hypothetical cubic zinc-blende-like GeC and SnC compounds

    NASA Astrophysics Data System (ADS)

    Benzair, A.; Bouhafs, B.; Khelifa, B.; Mathieu, C.; Aourag, H.

    2001-04-01

    We present a first-principles all-electron total-energy calculations of the structural and electronic properties for group IV zinc-blende-like compounds GeC, SnC using the full-potential linearized augmented plane wave (FP-LAPW) approach within the density functional theory (DFT) in the local spin density approximation (LSDA) including the generalized gradient approximation (GGA). We have calculated the ground-state energy, the lattice constant, the bulk modulus, and its pressure derivative. The distribution of the valence charge density suggests that the bonding in GeC and SnC is more ionic than in SiC. The results are compared with the few existing measurements and with calculations done by other authors.

  15. Heat capacity and heat content measurements on binary compounds in the Ru-Si, Ru-Ge, and Ru-Sn systems

    SciTech Connect

    Kuntz, J.J.; Gachon, J.C.; Feschotte, P.; Perring, L. |

    1997-11-01

    Molar heat capacities of Ru{sub 0.5}Si{sub 0.5} Ru{sub 0.4}Si{sub 0.6}, Ru{sub 0.5}Ge{sub 0.5}, Ru{sub 0.4}Ge{sub 0.6}, Ru{sub 0.4}Sn{sub 0.6}, and Ru{sub 0.3}Sn{sub 0.7} were determined every 10 K by differential scanning calorimetry in the temperature range from 310 to 1080 K. The present results have been fitted by a polynomial function of temperature: C{sub p} = a+bT-cT{sup -2}. Heat contents of the six phases have been verified by drop calorimetry. Standard enthalpies of formation are given for the studied compounds.

  16. Si based GeSn photoconductors with a 1.63 A/W peak responsivity and a 2.4 μm long-wavelength cutoff

    NASA Astrophysics Data System (ADS)

    Conley, Benjamin R.; Margetis, Joe; Du, Wei; Tran, Huong; Mosleh, Aboozar; Ghetmiri, Seyed Amir; Tolle, John; Sun, Greg; Soref, Richard; Li, Baohua; Naseem, Hameed A.; Yu, Shui-Qing

    2014-12-01

    Thin-film Ge0.9Sn0.1 structures were grown by reduced-pressure chemical vapor deposition and were fabricated into photoconductors on Si substrates using a CMOS-compatible process. The temperature-dependent responsivity and specific detectivity (D*) were measured from 300 K down to 77 K. The peak responsivity of 1.63 A/W measured at 1.55 μm and 77 K indicates an enhanced responsivity due to photoconductive gain. The measured spectral response of these devices extends to 2.4 μm at 300 K, and to 2.2 μm at 77 K. From analysis of the carrier drift and photoconductive gain measurements, we have estimated the carrier lifetime of this Ge0.9Sn0.1 thin film. The longest measured effective carrier lifetime of 1.0 × 10-6 s was observed at 77 K.

  17. Crystal structure and magnetic properties of novel Hf{sub 3}Ni{sub 2}Si{sub 3}-type R{sub 3}Co{sub 2}Ge{sub 3} compounds (R=Y, Sm, Tb-Tm)

    SciTech Connect

    Morozkin, A.V.; Nirmala, R.; Yao, Jinlei; Mozharivskyj, Y.; Isnard, O.

    2012-12-15

    The novel R{sub 3}Co{sub 2}Ge{sub 3} compounds with R=Y, Sm, Tb-Tm adopt the Hf{sub 3}Ni{sub 2}Si{sub 3}-type structure (ordered variant of the Ca{sub 3}Ga{sub 5}-type one, space group Cmcm). Sm{sub 3}Co{sub 2}Ge{sub 3}, Tb{sub 3}Co{sub 2}Ge{sub 3}, Ho{sub 3}Co{sub 2}Ge{sub 3} and Er{sub 3}Co{sub 2}Ge{sub 3} undergo an antiferromagnetic-type ordering and Tb{sub 3}Co{sub 2}Ge{sub 3} demonstrates a field-sensitive magnetic behavior. Tm{sub 3}Co{sub 2}Ge{sub 3} is a pure paramagnet down to 5 K, whereas Y{sub 3}Co{sub 2}Ge{sub 3} demonstrates Pauli paramagnetism down to {approx}120 K. In zero applied field and between {approx}50 and {approx}15 K Tb{sub 3}Co{sub 2}Ge{sub 3} shows a non-collinear antiferromagnetic ordering with wave vectors K{sub 0}=[0, 0, 0] and K{sub 1}=[{+-}1/3, 0, 0] and a magnetic unit cell 3a{sub Tb{sub 3Co{sub 2Ge{sub 2}}}} Multiplication-Sign b{sub Tb{sub 3Co{sub 2Ge{sub 3}}}} Multiplication-Sign c{sub Tb{sub 3Co{sub 2Ge{sub 3}}}} , whereas below {approx}15 K it exhibits a complex antiferromagnetic ordering with K{sub 0}=[0, 0, 0], K{sub 1}=[{+-}1/3, 0, 0] and K{sub 2}=[1/2, 0, 0] wave vectors and magnetic unit cell 6a{sub Tb{sub 3Co{sub 2Ge{sub 2}}}} Multiplication-Sign b{sub Tb{sub 3Co{sub 2Ge{sub 2}}}} Multiplication-Sign c{sub Tb{sub 3Co{sub 2Ge{sub 2}}}}. - Graphical abstract: The Hf{sub 3}Ni{sub 2}Si{sub 3}-type {l_brace}Y, Sm, Gd-Tm{r_brace}{sub 3}Co{sub 2}Ge{sub 3} (space group Cmcm) demonstrate complex field sensitive antiferromagnetic ordering. The rare earth sublattice of 4d site plays crucial role in the magnetisation of R{sub 3}Co{sub 2}Ge{sub 3} compounds. Highlights: Black-Right-Pointing-Pointer The {l_brace}Y, Sm, Gd-Tm{r_brace}{sub 3}Co{sub 2}Ge{sub 3} adopts the Hf{sub 3}Ni{sub 2}Si{sub 3}-type structure (space group Cmcm). Black-Right-Pointing-Pointer They demonstrate complex field sensitive antiferromagnetic ordering. Black-Right-Pointing-Pointer The 4d site rare earth sublattice plays crucial role in the magnetism of R{sub 3

  18. Indirect-to-direct band gap transition in relaxed and strained Ge{sub 1−x−y}Si{sub x}Sn{sub y} ternary alloys

    SciTech Connect

    Attiaoui, Anis; Moutanabbir, Oussama

    2014-08-14

    Sn-containing group IV semiconductors create the possibility to independently control strain and band gap thus providing a wealth of opportunities to develop an entirely new class of low dimensional systems, heterostructures, and silicon-compatible electronic and optoelectronic devices. With this perspective, this work presents a detailed investigation of the band structure of strained and relaxed Ge{sub 1−x−y}Si{sub x}Sn{sub y} ternary alloys using a semi-empirical second nearest neighbors tight binding method. This method is based on an accurate evaluation of the deformation potential constants of Ge, Si, and α-Sn using a stochastic Monte-Carlo approach as well as a gradient based optimization method. Moreover, a new and efficient differential evolution approach is also developed to accurately reproduce the experimental effective masses and band gaps. Based on this, we elucidated the influence of lattice disorder, strain, and composition on Ge{sub 1−x−y}Si{sub x}Sn{sub y} band gap energy and directness. For 0 ≤ x ≤ 0.4 and 0 ≤ y ≤ 0.2, we found that tensile strain lowers the critical content of Sn needed to achieve a direct band gap semiconductor with the corresponding band gap energies below 0.76 eV. This upper limit decreases to 0.43 eV for direct gap, fully relaxed ternary alloys. The obtained transition to direct band gap is given by y > 0.605 × x + 0.077 and y > 1.364 × x + 0.107 for epitaxially strained and fully relaxed alloys, respectively. The effects of strain, at a fixed composition, on band gap directness were also investigated and discussed.

  19. Theoretical investigation of the electronic and optical properties of pseudocubic Si3P4, Ge3P4 and Sn3P4

    NASA Astrophysics Data System (ADS)

    Xu, Ming; Wang, Songyou; Yin, Gang; Chen, Liangyao; Jia, Yu

    2006-01-01

    Group-IV phosphides are relatively unknown materials as compared to the Group-IV carbide. In this work, we detailed the first principles calculations of the electronic and optical properties of the pseudocubic M3 P4 (M=Si, Ge, Sn) using the density function theory (DFT). Results are in good agreement with those previous works. Furthermore, the optical constants, such as the dielectric function, energy loss function and effective number of valence electrons are calculated and presented in the study.

  20. Study of the energy distribution of the interface trap density in a GeSn MOS structure by numerical simulation of the electrical characteristics

    NASA Astrophysics Data System (ADS)

    Baert, B.; Schmeits, M.; Nguyen, N. D.

    2014-02-01

    Using a custom-made numerical simulation tool, we performed a systematic study of the energy distribution of the interface trap density in a GeSn MOS structure and of their effect on the electrical characteristics such as C-V and impedance spectra. Interface traps with various densities of states and energies in the bandgap have been investigated and the application of the conductance method was assessed.

  1. Thermal and Optical Characterization of a Sn-Se-Pb-Ge Glassy Alloy

    NASA Astrophysics Data System (ADS)

    Kumar, Prashant; Modgil, Vivek; Rangra, V. S.

    2016-01-01

    Thermal behavior of bulk material analyzed through differential scanning calorimetry and optical properties of thin films have been studied. The material exhibits a high glass transition temperature ( T g) and wide thermal stability region (Δ T), which make the glass of potential use in temperature sensitive technological applications. We see the enhanced cross-linking and stronger bonding network in the glassy matrix by substituting Pb with Ge, which plays a significant role in tuning the properties of the material. Addition of heavier Pb in base glass matrix causes a red shift in the absorption edge and reduces optical losses in chalcogenide glass. The material possesses a tunable band gap around 1.75 eV and high refractive index around 2.8. Effect of compositional variation and thickness on optical constants has also taken into account.

  2. Analytical potential energy functions and theoretical spectroscopic constants for MX/MX- (M dbond Ge, Sn, Pb; X dbond O, S, Se, Te, Po) and LuA (A dbond H, F) systems: Density functional theory calculations

    NASA Astrophysics Data System (ADS)

    Jalbout, Abraham F.; Li, Xin-Hua; Abou-Rachid, Hakima

    The molecular spectroscopic constants for the chalcogenide complexes MX (M dbond Ge, Sn, Pb; X dbond O, S, Se, Te, Po) and their corresponding MX- anions are presented with the LSDA/SDD, B1LYP/SDD, and B3LYP/SDD methods. Although many methods were attempted, only the most promising results are reported. We show that the best results are obtained by LSDA/SDD calculations, and thus this method is emphasized as an illustrative example of our methodology. The potential energy curves and physical property characterizations for X1 ?+ state of LuH and LuF are presented with a variety of density functional theory (DFT) methods. Comparisons with wave function-based treatments (HF, MP2, CCSD, QCISD) are made in addition to experimental correlations. We show that the best results are obtained by the B3LYP/SDD method for LuH, and the MPW1PW91/SDD method for LuF.

  3. Hydrogenated caged clusters of Si, Ge, and Sn and their endohedral doping with atoms: Ab initio calculations

    NASA Astrophysics Data System (ADS)

    Kumar, Vijay; Kawazoe, Yoshiyuki

    2007-04-01

    We report results of an ab initio study on the stability of hydrogenated empty cages XnHn with X=Si , Ge, and Sn, and n=8 , 10, 12, 14, 16, 18, 20, 24, and 28. All these cages have large highest-occupied-lowest-unoccupied molecular orbital (HOMO-LUMO) gaps. The HOMO-LUMO gap for Ge cages is found to be even larger than the values for Si cages, though in bulk Ge has a smaller band gap than Si. Cages with n=16 and 20 are found to be particularly stable in the form of fullerene structures. The bonding in the dodecahedral X20H20 cage is very close to sp3 type and it leads to the highest stability of this cage with perfect icosahedral symmetry. Endohedral doping of the empty cages such as SinHn (n=10-28) , with different guest atoms shows that doping can be used to manipulate the HOMO-LUMO gap with the possibility of varying their optical properties as well as to prepare species with large magnetic moments. Depending upon the guest atom, the character of the HOMO and the LUMO states and their origins either from the cage or the guest atom changes. This could lead to their applications in sensors. In contrast to the metal-encapsulated silicon-caged clusters, the embedding energy of the guest atom in the hydrogenated silicon fullerenes is small in most cases due to the weak interactions with the cage and therefore these slaved guest atoms can keep their atomic properties to a large extent. We find that atoms with closed electronic shell configurations such as Ca, Ba,… generally occupy the center of the cage. However, Be and other open electronic shell atoms tend to drift towards the wall of the cage. Doping of halogens such as iodine and alkalis such as Na can be used to produce, respectively hole and electron doping while transition-metal atoms such as V, Cr, Mn, and Fe are shown to produce atomiclike magnetic moments in many cases. In most of these cases the HOMO-LUMO gap becomes small because the guest atom orbital(s) are only partially occupied. However, for Ni and

  4. Chemical bonding and elastic properties of Ti 3AC 2 phases ( A = Si, Ge, and Sn): A first-principle study

    NASA Astrophysics Data System (ADS)

    Bai, Yuelei; He, Xiaodong; Sun, Yue; Zhu, Chuncheng; Li, Mingwei; Shi, Liping

    2010-07-01

    The chemical bonding and elastic properties as well as the effect of atomic radii for A element in the Ti 3AC 2 phases ( A = Si, Ge, and Sn) were studied by ab initio total energy calculations using plane-wave pseudopotential method based on DFT. The atomic radii of A element has a weak effect on the electronic structure. However, the bond stiffness was quantitatively examined, which shows that the bond stiffness is affected by the atomic radii of A element. The calculated results including lattice constants, internal coordinate, elastic modulus, sound velocity, and Debye temperature agree with experimental values very well. With the increase of atomic radii of A element from Si, Ge to Sn, the cohesive energy and elastic moduli as well as Debye temperature decrease, but the elastic anisotropy increases. This is related to the change of bond stiffness. It can be predicted that the fracture toughness of Ti 3SnC 2 would be comparable with that of Ti 3SiC 2 and Ti 3GeC 2.

  5. Na2 BaMQ4 (M=Ge, Sn; Q=S, Se): Infrared Nonlinear Optical Materials with Excellent Performances and that Undergo Structural Transformations.

    PubMed

    Wu, Kui; Yang, Zhihua; Pan, Shilie

    2016-06-01

    Infrared nonlinear optical (IR NLO) materials with excellent performances are particularly important in laser technology. However, to design and synthesize an efficient IR NLO material with a balance between the optical band gap and the NLO coefficient is still a huge challenge. With this in mind, four new IR NLO materials Na2 BaSnS4 , Na2 BaSnSe4 , Na2 BaGeS4 , and Na2 BaGeSe4 were successfully designed and synthesized. The compounds exhibit excellent properties with a suitable balance of band gap and NLO coefficient measured for Na2 BaSnS4 (3.27 eV and about 17×KDP, that is, about 17 times that of KH2 PO4 (KDP)) and Na2 BaGeS4 (3.7 eV and about 10×KDP), demonstrating that the systems satisfy the key requirements as promising IR NLO candidates. Remarkably, the new compounds also undergo a novel structural transformation from tetragonal to trigonal systems, the first time that this has been reported for quaternary metal chalcogenides. PMID:27100773

  6. Linear and nonlinear optical properties of α-K2Hg3Ge2S8 and α-K2Hg3Sn2S8 compounds

    NASA Astrophysics Data System (ADS)

    Reshak, A. H.; Azam, Sikander

    2014-11-01

    The linear and nonlinear optical properties of α-K2Hg3Ge2S8 and α-K2Hg3Sn2S8 compounds are performed using the first-principles calculations. Particularly, we appraised the optical dielectric function and the second-harmonic generation (SHG) response. We have analyzed the linear optical properties, i.e. the real and imaginary part of the dielectric tensor, the reflectivity, refractive index, extension coefficient and energy loss function. The linear optical properties show a considerable anisotropy which is important for SHG as it is defined by the phase-matching condition. The scrutiny of the roles of diverse transitions to the SHG coefficients demonstrates that the virtual electron process is foremost. The features in the spectra of χ322(2)(ω) are successfully interrelated with the character of the linear dielectric function ε(ω) in terms of single-photon and two-photon resonances. In additional, we have calculated the first hyperpolarizability, βijk, for the dominant component at the static limit for the for α-K2Hg3Ge2S8 and α-K2Hg3Sn2S8 compounds. The calculated values of β322(ω) are 2.28 × 10-30 esu for α-K2Hg3Ge2S8 and 3.69 × 10-30 esu for α-K2Hg3Sn2S8.

  7. Solvothermal synthesis, structure and physical properties of Cs[Cr(en)2MSe4] (M = Ge, Sn) with [MSe4](4-) tetrahedra as chelating ligand.

    PubMed

    Wang, Yingqi; Wang, Ruiqi; Liu, Qinglong; Lai, Xiaofang; Zhang, Xian; Chen, Haijie; Zheng, Chong; Lin, Jianhua; Huang, Fuqiang

    2016-05-31

    Two chromium chalcogenide Cs[Cr(en)2GeSe4] () and Cs[Cr(en)2SnSe4] () have been synthesized by a solvothermal method. Both compounds crystallize in the monoclinic space group P21/n. The structures of the two compounds are characterized by isolated [Cr(en)2MSe4](-) clusters separated by Cs(+) ions. The optical properties of the two compounds were measured which indicate a similar band gap of 1.58 eV. DFT calculations demonstrated that the valance band maximum (VBM) consist of Cr 3d orbitals and Se 4p orbitals while the conductive band minimum (CBM) are composed of Cr 3d orbitals for both compounds, which explains their similar optical band gap energies. Both compounds possess paramagnetic behaviors with the effective magnetic moment of 3.97μB for Cs[Cr(en)2GeSe4] and 3.91μB for Cs[Cr(en)2SnSe4], respectively. Field-dependent magnetization measurements demonstrated their potential as magnetocaloric materials, with the magnetic entropy change of 11.6 J (kg K)(-1) for Cs[Cr(en)2GeSe4], and 14.2 J (kg K)(-1) for Cs[Cr(en)2SnSe4]. PMID:27164409

  8. Anharmonic properties in M g2X (X =C ,Si ,Ge ,Sn ,Pb ) from first-principles calculations

    NASA Astrophysics Data System (ADS)

    Chernatynskiy, Aleksandr; Phillpot, Simon R.

    2015-08-01

    Thermal conductivity reduction is one of the potential routes to improve the performance of thermoelectric materials. However, detailed understanding of the thermal transport of many promising materials is still missing. In this paper, we employ electronic-structure calculations at the level of density functional theory to elucidate thermal transport properties of the M g2X (X =C , Si, Ge, Sn, and Pb) family of compounds, which includes M g2Si , a material already identified as a potential thermoelectric. All these materials crystallize into the same antifluorite structure. Systematic trends in the anharmonic properties of these materials are presented and examined. Our calculations indicate that the reduction in the group velocity is the main driver of the thermal conductivity trend in these materials, as the phonon lifetimes in these compounds are very similar. We also examine the limits of the applicability of perturbation theory to study the effect of point defects on thermal transport and find that it is in good agreement with experiment in a wide range of scattering parameter values. The thermal conductivity of the recently synthesized M g2C is computed and predicted to be 34 W/mK at 300 °C.

  9. Large band gap quantum spin hall insulators of fluorinated Pb-X (X = C, Si, Ge, Sn)

    NASA Astrophysics Data System (ADS)

    Padilha, Jose Eduardo; Pontes, Renato Borges; Schmidt, Tome Mauro; Miwa, Roberto Hiroki; Fazzio, Adalberto

    The Quantum Spin Hall Insulating (QSHI) phase was first observed in the HgTe/CdTe quantum well structure. However, the observed band gap of 5 meV is too small for practical applications. Other materials have also been proposed for the observation of the QSHI phase, such as silicene, germanene, stanene, and its halogenated phases. The spin-orbit interaction is a key feature in topological insulators, raising the interest in heavy elements, such as Bismuth. In fact, Bi is responsible for the high spin-orbit coupling that drives the band inversion in Bi2 Se 3 andBi 2Te3. Another element that also has a large spin-orbit interaction is Lead (Pb). Here we present a set of 2D QSH insulators with a very large band gap based on fluorinated Pb-X (X= C, Si, Ge, Sn). First-principles phonon dispersion calculations indicate that these systems are structurally and mechanically stable. By performing DFT-based electronic structure calculations we show that 2D Pb-X functionalized with fluorine are topological insulators with very large band gaps (over 0.7 eV). Addtional calculations, for nanoribbons structures, show the presence of a Dirac cone at the center of the Brillouin zone. These results can establish a new route to the observation of QSHI phase at room temperature.

  10. Thermal and electronic charge transport in bulk nanostructured Zr{sub 0.25}Hf{sub 0.75}NiSn composites with full-Heusler inclusions

    SciTech Connect

    Makongo, Julien P.A.; Misra, Dinesh K.; Salvador, James R.; Takas, Nathan J.; Wang, Guoyu; Shabetai, Michael R.; Pant, Aditya; Paudel, Pravin; Uher, Ctirad; Stokes, Kevin L.; Poudeu, Pierre F.P.

    2011-11-15

    Bulk Zr{sub 0.25}Hf{sub 075}NiSn half-Heusler (HH) nanocomposites containing various mole fractions of full-Heusler (FH) inclusions were prepared by solid state reaction of pre-synthesized HH alloy with elemental Ni at 1073 K. The microstructures of spark plasma sintered specimens of the HH/FH nanocomposites were investigated using transmission electron microscopy and their thermoelectric properties were measured from 300 K to 775 K. The formation of coherent FH inclusions into the HH matrix arises from solid-state Ni diffusion into vacant sites of the HH structure. HH(1-y)/FH(y) composites with mole fraction of FH inclusions below the percolation threshold, y{approx}0.2, show increased electrical conductivity, reduced Seebeck coefficient and increased total thermal conductivity arising from gradual increase in the carrier concentration for composites. A drastic reduction ({approx}55%) in {kappa}{sub l} was observed for the composite with y=0.6 and is attributed to enhanced phonon scattering due to mass fluctuations between FH and HH, and high density of HH/FH interfaces. - Graphical abstract: Large reduction in the lattice thermal conductivity of bulk nanostructured half-Heusler/full-Heusler (Zr{sub 0.25}Hf{sub 075}NiSn/ Zr{sub 0.25}Hf{sub 075}Ni{sub 2}Sn) composites, obtained by solid-state diffusion at 1073 K of elemental Ni into vacant sites of the half-Heusler structure, arising from the formation of regions of spinodally decomposed HH and FH phases with a spatial composition modulation of {approx}2 nm. Highlights: > Bulk composites from solid state transformation of half-Heusler matrix through Ni diffusion. > Formation of coherent phase boundaries between half-Heusler matrix and full-Heusler inclusion. > Alteration of thermal and electronic transports with increasing full-Heusler inclusion. > Enhanced phonon scattering at half-Heusler/ full-Heusler phase boundaries.

  11. Highly effective strain-induced band-engineering of (111) oriented, direct-gap GeSn crystallized on amorphous SiO2 layers

    NASA Astrophysics Data System (ADS)

    Li, Haofeng; Wang, Xiaoxin; Liu, Jifeng

    2016-03-01

    We demonstrate highly effective strain-induced band-engineering of (111) oriented direct-gap Ge1-xSnx thin films (0.074 < x < 0.085) crystallized on amorphous SiO2 towards 3D photonic integration. Due to a much smaller Poisson's ratio for (111) vs. (100) orientation, 0.44% thermally induced biaxial tensile strain reduces the direct-gap by 0.125 eV towards enhanced direct-gap semiconductor properties, twice as effective as the tensile strain in Ge(100) films. Correspondingly, the optical response is extended to λ = 2.8 μm. A dilatational deformation potential of a = -12.8 ± 0.8 eV is derived. These GeSn films also demonstrate high thermal stability, offering both excellent direct-gap optoelectronic properties and fabrication/operation robustness for integrated photonics.

  12. Thermoelectric properties of metallic antiperovskites AXD3 (A=Ge, Sn, Pb, Al, Zn, Ga; X=N, C; D=Ca, Fe, Co)

    NASA Astrophysics Data System (ADS)

    Bilal, Muhammad; Ahmad, Iftikhar; Asadabadi, Saeid Jalali; Ahmad, Rashid; Maqbool, Muhammad

    2015-05-01

    In this paper we communicate the thermoelectric properties of carbon and nitrogen based metallic antiperovskites ANCa3 (A=Ge, Sn, Pb), BCFe3 (B=Al, Zn, Ga) and SnCD3 (D=Co and Fe) using the ab-initio calculations to explore efficient metallic thermoelectric materials. The consistency of the calculated results of SnCCo3 and SnCFe3 with the experimental results confirms the reliability of our theoretical calculations for the other investigated metallic antiperovskites. The results indicate that the thermopower of these materials can be enhanced by changing the chemical potential. The dimensionless figure of merit for the three nitrides approaches 0.96 at room temperature, which proves the usefulness of these materials in thermoelectric generators. Furthermore, the thermal conductivity is minimum at room temperature for chemical potential values between -0.25 μ(eV) and 0.25 μ(eV), and provides the maximum values of dimensionless figure of merit in this range. The striking feature of these studies is identifying a metallic compound, SnNCa3, with the highest value of Seebeck coefficient at room temperature out of all metals. The results anticipate that these materials could be efficient in thermoelectric generators; however, this needs experimental verification.[Figure not available: see fulltext.

  13. Li4Ge2B as a new derivative of the Mo2B5 and Li5Sn2 structure types.

    PubMed

    Pavlyuk, Volodymyr; Ciesielski, Wojciech; Rozdzynska-Kielbik, Beata; Dmytriv, Grygoriy; Ehrenberg, Helmut

    2016-07-01

    Binary and multicomponent intermetallic compounds based on lithium and p-elements of Groups III-V of the Periodic Table are useful as modern electrode materials in lithium-ion batteries. However, the interactions between the components in the Li-Ge-B ternary system have not been reported. The structure of tetralithium digermanium boride, Li4Ge2B, exhibits a new structure type, in the noncentrosymmetric space group R3m, in which all the Li, Ge and B atoms occupy sites with 3m symmetry. The title structure is closely related to the Mo2B5 and Li5Sn2 structure types, which crystallize in the centrosymmetric space group R-3m. All the atoms in the title structure are coordinated by rhombic dodecahedra (coordination number = 14), similar to the atoms in related structures. According to electronic structure calculations using the tight-binding-linear muffin-tin orbital-atomic spheres approximation (TB-LMTO-ASA) method, strong covalent Ge-Ge and Ge-B interactions were established. PMID:27377278

  14. A Stannyl-Decorated Zintl Ion [Ge18Pd3(Sn(i)Pr3)6](2-): Twinned Icosahedron with a Common Pd3-Face or 18-Vertex Hypho-Deltahedron with a Pd3-Triangle Inside.

    PubMed

    Perla, Luis G; Sevov, Slavi C

    2016-08-10

    We report the synthesis and characterization of the title anion which has a germanium/palladium cluster core of [Ge18Pd3] and six tri-isopropyl tin substituents. Its two Ge9-halves are the first examples of germanium deltahedra with three nonsilyl substituents, tri-isopropyl tin in this case. The new cluster is made by a reaction of an acetonitrile suspension of K4Ge9 with (i)Pr3SnCl that generates primarily tristannylated 9-atom clusters [Ge9{Sn(i)Pr3}3](-), followed by addition of Pd(PPh3)4 to the reaction mixture. It was structurally characterized by single-crystal X-ray diffraction in [K(222crypt)]2[Ge18Pd3{Sn(i)Pr3}6]·(i)Pr2O and was also confirmed in solution by ESI-MS and NMR. The new anion can be viewed both as a dimer of face-fused icosahedra (twinned icosahedron) with a common Pd3-face, i.e., [((i)Pr3Sn)3Ge9Pd3Ge9(Sn(i)Pr3)3](2-) that resembles but is not isoelectronic with the known borane version B21H18(-) or as a large hypho-deltahedron of 18 Ge-atoms with a triangle of Pd3 inside, i.e., [Pd3@Ge18(Sn(i)Pr3)6](2-). DFT calculations show a very large HOMO-LUMO gap of 2.42 eV. PMID:27466825

  15. Investigating the Structural, Thermal, and Electronic Properties of the Zircon-Type ZrSiO4, ZrGeO4 and HfSiO4 Compounds

    NASA Astrophysics Data System (ADS)

    Chiker, Fafa; Boukabrine, Fatiha; Khachai, H.; Khenata, R.; Mathieu, C.; Bin Omran, S.; Syrotyuk, S. V.; Ahmed, W. K.; Murtaza, G.

    2016-07-01

    In the present study, the structural, thermal, and electronic properties of some important orthosilicate dielectrics, such as the ZrSiO4, ZrGeO4, and HfSiO4 compounds, have been investigated theoretically with the use of first-principle calculations. We attribute the application of the modified Becke-Johnson exchange potential, which is basically an improvement over the local density approximation and the Perdew-Burke-Ernzerhof exchange-correlation functional, for a better description of the band gaps of the compounds. This resulted in a good agreement with our estimated values in comparison with the reported experimental data, specifically for the ZrSiO4, and HfSiO4 compounds. Conversely, for the ZrGeO4 compound, the calculated electronic band structure shows a direct band gap at the Γ point with the value of 5.79 eV. Furthermore, our evaluated thermal properties that are calculated by using the quasi-harmonic Debye model indicated that the volume variation with temperature is higher in the ZrGeO4 compound as compared to both the ZrSiO4 and HfSiO4 compounds, which is ascribed to the difference between the electron shells of the Si and Ge atoms. Therefore, these results also indicate that while the entropy (S) and enthalpy (U) parameters increase monotonically, the free energy (G), in contrast, decreases monotonically with increasing temperature, respectively. Moreover, the pressure and temperature dependencies of the Debye temperature Θ, thermal expansion coefficient, and heat capacities C V were also predicted in our study.

  16. Thermodynamic stability, magnetism and half-metallicity of Heusler alloy Co2MnX(X = Si, Ge, Sn)(1 0 0) surface

    NASA Astrophysics Data System (ADS)

    Wu, Bo; Yuan, Hongkuan; Kuang, Anlong; Chen, Hong; Feng, Yu

    2012-03-01

    The thermodynamic stability, magnetism and half-metallicity of Heusler alloy Co2MnX(X = Si, Ge, Sn)(1 0 0) surface are comprehensively investigated from the first-principles calculations. The calculated phase diagram indicates that with increasing core electrons of X atoms in Co2MnX(1 0 0) the CoCo termination will be faded out of the thermodynamic equilibrium region gradually. Due to the difference of Cosbnd X bonding the surface Co and Mn atoms prefer to move towards the slab and vacuum, respectively. By comparing with the bulk, the surface Co and Mn atomic magnetic moments (AMMs) are enhanced obviously because of the significant surface d-electronic localization. Further investigations of the partial density of states (PDOS) show that the half-metallicity observed in bulk has been destroyed by the surface states in deficient-Mn atomic terminated surface, only the terminations capped pure Mn atoms in Co2MnSi(1 0 0) and Co2MnGe(1 0 0) surfaces preserve spin-polarization of 100% instead of the Co2MnSn(1 0 0) surface, which is a possible explanation for low experimental tunnel magnetoresistance (TMR) value in Co2MnSn(1 0 0)-based magnetic tunnel junctions (TMJs).

  17. Effect of a carbon additive on the TbCu7-type melt-spun Sm(Co, M)7 (M=Ti, Zr, Hf, V and Ge) ribbons

    NASA Astrophysics Data System (ADS)

    Hsieh, Chih-Chieh; Huang, Shih-Teng; Guo, Jin-Sheng; Shih, Chih-Wei; Chang, Wen-Cheng; Chang, Huang-Wei; Shaw, Chun-Chung

    2013-08-01

    The effect of a carbon additive on the microstructure and the magnetic properties of melt-spun SmCo7- x M x C y (M=Ti, Zr, Hf, V and Ge; x = 0-0.3 and y = 0-0.1) ribbons was studied. Based on the XRD and the TEM analyses, a pure 1:7 phase could be formed for the C-containing ribbons with M= Ti and Ge. However, carbide phases, i.e., Sm2C3 for M=Zr and Hf, and SmCoC2 for M=V, respectively, were found. Nevertheless, a slight C addition may effectively refine the microstructure and improve both the intrinsic coercvity and the magnetic energy product in all the studied ribbons. Among them, the SmCo6.9V0.1C0.1 ribbons with σ r = 58.7 emu/g, i H c = 13.5 kOe and ( BH) max = 9.3 MGOe, and the SmCo6.9Hf0.1C0.1 ribbons with σ r = 61.6 emu/g, i H c = 11.8 kOe and ( BH) max = 10.3 MGOe are most suitable for the bonded magnet applications.

  18. Electronic band structure of compressively strained Ge{sub 1−x}Sn{sub x} with x < 0.11 studied by contactless electroreflectance

    SciTech Connect

    Zelazna, K.; Polak, M. P.; Scharoch, P.; Gladysiewicz, M.; Misiewicz, J.; Kudrawiec, R.; Serafinczuk, J.

    2015-04-06

    Contactless electroreflectance is applied to study direct optical transitions from the heavy hole, light hole, and spin-orbit split-off band to the conduction band in compressively strained Ge{sub 1−x}Sn{sub x} layers of various Sn concentrations at room temperature. It is shown that the energies of these transitions are in very good agreement with theoretical predictions, which take into account non-linear variation of bandgap and spin-orbit splitting plus the strain-related shifts obtained from the Bir-Pikus theory. The bowing parameter for the direct bandgap has been determined to be 1.8 ± 0.2 eV and agree with this one obtained within ab initio calculations, which is 1.97 eV (for indirect bandgap the bowing parameter is 0.26 eV)

  19. Infrared nonlinear optical properties of lithium-containing diamond-like semiconductors Li2ZnGeSe4 and Li2ZnSnSe4.

    PubMed

    Zhang, Jian-Han; Clark, Daniel J; Brant, Jacilynn A; Sinagra, Charles W; Kim, Yong Soo; Jang, Joon I; Aitken, Jennifer A

    2015-06-28

    Two new lithium-containing diamond-like semiconductors, Li2ZnGeSe4 and Li2ZnSnSe4, have been prepared by high-temperature, solid-state synthesis. Single crystal X-ray diffraction reveals that both compounds adopt the wurtz-kesterite structure type, crystallizing in the noncentrosymmetric space group Pn. X-ray powder diffraction coupled with Rietveld refinement indicates the high degree of phase purity in which the materials are prepared. Both compounds display optical bandgaps around 1.8 eV, wide optical transparency windows from 0.7 to 25 μm and type-I phase matched second harmonic generation starting at 2500 nm and persisting deeper into the infrared. Using the Kurtz powder method, the second-order nonlinear optical coefficient, χ((2)), was estimated to be 19 and 23 pm V(-1) for Li2ZnGeSe4 and Li2ZnSnSe4, respectively. Using a 1064 nm incident laser beam with a pulse width (τ) of 30 ps both compounds exhibit a laser damage threshold of 0.3 GW cm(-2), which is higher than that of the AgGaSe2 reference material measured under identical conditions. Differential thermal analysis shows that the title compounds are stable up to 684 and 736 °C, respectively. These properties collectively demonstrate that Li2ZnGeSe4 and Li2ZnSnSe4 have great potential for applications in tunable laser systems, especially in the infrared and even up to the terahertz regime. Electronic structure calculations using a plane-wave pseudopotential method within density functional theory provide insight regarding the nature of the bandgap and bonding. PMID:26006322

  20. Hybrid surface roughening modes during low-temperature heteroepitaxy: Growth of fully-strained metastable Ge{sub 1-x}Sn{sub x} alloys on Ge(001)2x1

    SciTech Connect

    Desjardins, P.; Spila, T.; Guerdal, O.; Taylor, N.; Greene, J. E.

    1999-12-15

    Fully-strained single-crystal metastable Ge{sub 1-x}Sn{sub x} alloys were grown on Ge(001) up to their critical epitaxial thickness values t{sub epi}(x) in order to probe surface roughening pathways leading to heteroepitaxial breakdown during low-temperature molecular-beam epitaxy under large compressive strain. All films with x>0.09 have comparable roughnesses while films with x<0.09 are considerably rougher with larger lateral feature sizes. Roughening rates increase with increasing x for films with x>0.09 due to a new hybrid relaxation path which only becomes accessible under high strain as kinetic roughening provides surface oscillations on lateral length scales that allow bulk relaxation through strain-induced islanding at growth temperatures where it could not otherwise proceed. (c) 1999 The American Physical Society.

  1. First principle study of structural, electronic and magnetic properties of half-Heusler IrCrZ (Z=Ge, As, sn and sb) compounds

    NASA Astrophysics Data System (ADS)

    Allaf Behbahani, Marzieh; Moradi, Mahmood; Rostami, Mohammad; Davatolhagh, Saeed

    2016-05-01

    First-principle calculations based on the density functional theory for new half-Heusler IrCrZ (Z=Ge, As, Sn and Sb) alloys are performed. It is found that the half-Heusler IrCrGe and IrCrSn compounds have an antiferromagnetic ground state while the ferromagnetic state is more stable than the antiferromagnetic and non-magnetic states for both IrCrAs and IrCrSb compounds. IrCrAs and IrCrSb exhibit half-metallic property with integer magnetic moments of 2.00 μB per formula unit and half-metallic gaps of 0.28 and 0.27 eV at their equilibrium volume, respectively. In addition, the density of states (DOSs) and band structures of IrCrAs and IrCrSb compounds are studied and the origin of their half-metallic gaps are discussed in detail. The estimation of Curie temperatures of IrCrAs and IrCrSb compounds is performed within the mean field approximation (MFA). The Curie temperatures of IrCrAs and IrCrSb are estimated to be 1083 and 1470 K, respectively. The stability of the half-metallicity in IrCrAs and IrCrSb compounds with the variation of lattice constant are also investigated.

  2. Enhancement of thermoelectric figure-of-merit at low temperatures by titanium substitution for hafnium in n-type half-Heuslers Hf0.75-xTixZr0.25NiSn0.99Sb0.01

    SciTech Connect

    Joshi, Giri; Dahal, Tulashi; Chen, Shuo; Wang, Hengzhi Z; Shiomi, Junichiro; Chen, Gang; Ren, Zhifeng F.

    2012-08-08

    The effect of titanium (Ti) substitution for hafnium (Hf) on thermoelectric properties of (Hf, Zr)-based n-type half-Heuslers: Hf0.75-xTixZr0.25NiSn0.99Sb0.01, has been studied. The samples are made by arc melting followed by ball milling and hot pressing via the nanostructuring approach. A peak thermoelectric figure-of-merit (ZT) of ~1.0 is achieved at 500 °C in samples with a composition of Hf0.5Zr0.25Ti0.25NiSn0.99Sb0.01 due to a slight increase in carrier concentration and also a lower thermal conductivity caused by Ti. TheZT values below 500 °C of hot pressed Hf0.5Zr0.25Ti0.25NiSn0.99Sb0.01 samples are significantly higher than those of the same way prepared Hf0.75Zr0.25NiSn0.99Sb0.01samples at each temperature, which are very much desired for mid-range temperature applications such as waste heat recovery in automobiles.

  3. New members of the A{sub 2}M′M{sub 2}{sup ″} structure family (A=Ca, Sr, Yb, La; M′=In,Sn,Pb; M″=Si,Ge)

    SciTech Connect

    Jehle, Michael; Dürr, Ines; Fink, Saskia; Lang, Britta; Langenmaier, Michael; Steckhan, Julia; Röhr, Caroline

    2015-01-15

    The new mixed tetrelides Sr{sub 2}PbGe{sub 2} and Yb{sub 2}SnGe{sub 2}, several mixed Ca/Sr (A{sup II}) germanides A{sub 2}{sup II}(Sn,Pb)Ge{sub 2} and two polymorphs of La{sub 2}InSi{sub 2} represent new members of the general structure family of ternary alkaline-earth/lanthanoid main group silicides/germanides A{sub 2}M′M{sub 2}{sup ″}(M′=In,Sn,Pb;M″=Si,Ge). All compounds were synthesized from melts of the elements and their crystal structures have been determined by means of single crystal X-ray diffraction. Sr{sub 2}PbGe{sub 2} (Cmmm, a=402.36(11), b=1542.3(4), c=463.27(10) pm) crystallizes with the Mn{sub 2}AlB{sub 2}-type structure. In exhibiting infinite planar Ge zig-zag chains, it represents one border of the compound series. The other borderline case, where only [Ge{sub 2}] dumbbells are left as Ge building units, is represented by the Ca/Yb tin germanides Ca{sub 2}SnGe{sub 2} and Yb{sub 2}SnGe{sub 2} (Mo{sub 2}FeB{sub 2}-type; P4/mbm, a=748.58(13)/740.27(7), c=445.59(8)/435.26(5) pm). In between these two border structures compounds with variable Si/Ge chain lengths could be obtained by varying the averaged size of the A{sup II} cations: Ca{sub 0.45}Sr{sub 1.55}PbGe{sub 2} (new structure type; Pbam, a=791.64(5), b=2311.2(2), c=458.53(3) pm) contains planar six-membered chain segments [Ge{sub 6}]. Tetrameric pieces [Ge{sub 4}] are the conspicuous structure elements in Ca{sub 1.16}Sr{sub 0.84}SnGe{sub 2} and La{sub 2}InSi{sub 2} (La{sub 2}InNi{sub 2}-type; Pbam, a=781.01(2)/762.01(13), b=1477.95(3)/1494.38(6), c=457.004(9)/442.1(3) pm). The tetragonal form of ’La{sub 2}InSi{sub 2}{sup ′} (exact composition: La{sub 2}In{sub 1.07}Si{sub 1.93}, P4/mbm, a=1309.11(12), c=443.32(4) pm) also crystallizes in a new structure type, containing only [Si{sub 3}] trimers as cutouts of the planar chains. In all structures the Si/Ge zig-zag chains/chain segments are connected by In/Sn/Pb atoms to form planar M layers, which are separated by pure A layers. Band

  4. Origin of the granites and related Sn and Pb-Zn polymetallic ore deposits in the Pengshan district, Jiangxi Province, South China: constraints from geochronology, geochemistry, mineral chemistry, and Sr-Nd-Hf-Pb-S isotopes

    NASA Astrophysics Data System (ADS)

    Xu, Bin; Jiang, Shao-Yong; Luo, Lan; Zhao, Kui-Dong; Ma, Liang

    2016-05-01

    The Pengshan Sn and Pb-Zn polymetallic deposits are located in the south margin of the Jiujiang-Ruichang (Jiurui) district of the Middle-Lower Yangtze River Metallogenic Belt in South China. Four large deposits include Huangjinwa, Zengjialong, Jianfengpo, and Zhangshiba, the former three are Sn-dominant deposits which occur as stratiform orebodies in the contact zones of the Pengshan granites and within the country rock strata, whereas Zhangshiba consists of stratiform Pb-Zn orebodies within the Precambrian metasedimentary strata. In this study, we present results on zircon U-Pb ages, major and trace elements, and mineral chemistry as well as Sr-Nd-Hf isotope data of the granites, Pb and S isotopes of both the Sn-dominant and Pb-Zn dominant deposits, and U-Pb dating of cassiterite from the Pengshan district. SHRIMP and LA-ICP-MS zircon U-Pb dating shows that the Pengshan granites were emplaced in the Early Cretaceous (129-128 Ma), which is in good agreement with the U-Pb dating (130-128 Ma) of cassiterite from the Jianfengpo Sn deposit. The Pengshan granites consist mainly of weakly peraluminous highly fractionated I-type affinity granitic rocks. Detailed elemental and isotopic data suggest that the granites formed by partial melting of Mesoproterozoic metamorphic basement materials with minor input of mantle-derived melts. The mineral chemistry of biotite demonstrates that the Pengshan granitic magma had a low oxygen fugacity, thereby precluding the tin dominantly partitioning into the rock-forming silicate minerals and favoring accumulation in the exsolved residual liquid during magma crystallization stages. Sulfur isotopes show a relatively heavy sulfur isotopic composition from 5.8 to 17.6 ‰, and no difference for sulfur isotopes between the Sn deposits (5.8-13.4 ‰, Huangjinwa, Zengjialong, Jianfengpo) and the Pb-Zn deposit (mostly 7.1-13.0 ‰, except for one 17.6 ‰, Zhangshiba). The sulfur isotope data of pyrite from the host sedimentary rocks show

  5. Measurement of inclusive spectra of protons emitted in interactions between /sup 12/C nuclei of energy 3. 6 GeV/nucleon and C, Cu, Sn, and Pb nuclei

    SciTech Connect

    Ad'yasevich, B.P.; Antonenko, V.G.; Vinogradov, A.A.; Grigor'yan, Y.I.; Ippolitov, M.S.; Karadzhev, K.V.; Lebedev, A.L.; Man'ko, V.I.; Nikolaev, S.A.; Polunin, Y.P.; Tsvetkov, A.A.

    1984-08-01

    The inclusive spectra of protons emitted when carbon ions of energy 3.6 GeV/nucleon are used to bombard C, Cu, Sn, and Pb targets are investigated. Data are presented on the invariant cross sections for proton emission in a wide range of emission angles and momenta. The observed empirical relations are discussed.

  6. TbNb6Sn6: the first ternary compound from the rare earth–niobium–tin system

    PubMed Central

    Oshchapovsky, Igor; Pavlyuk, Volodymyr; Fässler, Thomas F.; Hlukhyy, Viktor

    2010-01-01

    The title compound, terbium hexa­niobium hexastannide, TbNb6Sn6, is the first ternary compound from the rare earth–niobium–tin system. It has the HfFe6Ge6 structure type, which can be analysed as an inter­growth of the Zr4Al3 and CaCu5 structures. All the atoms lie on special positions; their coordination geometries and site symmetries are: Tb (dodeca­hedron) 6/mmm; Nb (distorted icosa­hedron) 2mm; Sn (Frank–Caspar polyhedron, CN = 14–15) 6mm and m2; Sn (distorted icosa­hedron) m2. The structure contains a graphite-type Sn network, Kagome nets of Nb atoms, and Tb atoms alternating with Sn2 dumbbells in the channels. PMID:21589205

  7. Crystal Structure, Chemical Bonding and Magnetism Studies for Three Quinary Polar Intermetallic Compounds in the (Eu1−xCax)9In8(Ge1−ySny)8 (x = 0.66, y = 0.03) and the (Eu1−xCax)3In(Ge3−ySn1+y) (x = 0.66, 0.68; y = 0.13, 0.27) Phases

    PubMed Central

    Woo, Hyein; Jang, Eunyoung; Kim, Jin; Lee, Yunho; Kim, Jongsik; You, Tae-Soo

    2015-01-01

    Three quinary polar intermetallic compounds in the (Eu1−xCax)9In8(Ge1−ySny)8 (x = 0.66, y = 0.03) and the (Eu1−xCax)3In(Ge3-ySn1+y) (x = 0.66, 0.68; y = 0.13, 0.27) phases have been synthesized using the molten In-metal flux method, and the crystal structures are characterized by powder and single-crystal X-ray diffractions. Two orthorhombic structural types can be viewed as an assembly of polyanionic frameworks consisting of the In(Ge/Sn)4 tetrahedral chains, the bridging Ge2 dimers, either the annulene-like “12-membered rings” for the (Eu1−xCax)9In8(Ge1−ySny)8 series or the cis-trans Ge/Sn-chains for the (Eu1−xCax)3In(Ge3−ySn1+y) series, and several Eu/Ca-mixed cations. The most noticeable difference between two structural types is the amount and the location of the Sn-substitution for Ge: only a partial substitution (11%) occurs at the In(Ge/Sn)4 tetrahedron in the (Eu1−xCax)9In8(Ge1−ySny)8 series, whereas both a complete and a partial substitution (up to 27%) are observed, respectively, at the cis-trans Ge/Sn-chain and at the In(Ge/Sn)4 tetrahedron in the (Eu1−xCax)3In(Ge3−ySn1+y) series. A series of tight-binding linear muffin-tin orbital calculations is conducted to understand overall electronic structures and chemical bonding among components. Magnetic susceptibility measurement indicates a ferromagnetic ordering of Eu atoms below 5 K for Eu1.02(1)Ca1.98InGe2.87(1)Sn1.13. PMID:25913380

  8. Vibrationally high-resolved electronic spectra of MCl2 (M=C, Si, Ge, Sn, Pb) and photoelectron spectra of MCl2(.).

    PubMed

    Ran, Yibin; Pang, Min; Shen, Wei; Li, Ming; He, Rongxing

    2016-10-01

    We systematically studied the vibrational-resolved electronic spectra of group IV dichlorides using the Franck-Condon approximation combined with the Duschinsky and Herzberg-Teller effects in harmonic and anharmonic frameworks (only the simulation of absorption spectra includes the anharmonicity). Calculated results showed that the band shapes of simulated spectra are in accordance with those of the corresponding experimental or theoretical ones. We found that the symmetric bend mode in progression of absorption is the most active one, whereas the main contributor in photoelectron spectra is the symmetric stretching mode. Moreover, the Duschinsky and anharmonic effects exert weak influence on the absorption spectra, except for PbCl2 molecule. The theoretical insights presented in this work are significant in understanding the photophysical properties of MCl2 (M=C, Si, Ge, Sn, Pb) and studying the Herzberg-Teller and the anharmonic effects on the absorption spectra of new dichlorides of this main group. PMID:27280730

  9. MAX phase - Alumina composites via elemental and exchange reactions in the Tin+1ACn systems (A=Al, Si, Ga, Ge, In and Sn)

    NASA Astrophysics Data System (ADS)

    Cuskelly, Dylan; Richards, Erin; Kisi, Erich

    2016-05-01

    Extension of the aluminothermal exchange reaction synthesis of Mn+1AXn phases to systems where the element 'A' is not the reducing agent was investigated in systems TiO2-A-Al-C for A=Al, Si, Ga, Ge, In and Sn as well as Cr2O3-Ga-Al-C. MAX phase-Al2O3 composites were made in all systems except those with A=Ga or In. The effectiveness of conversion to MAX phases was generally in the range 63-96% without optimisation of starting ratios. Optimisation in the Ti-Si-C system gave a MAX phase component with >98% Ti3SiC2.

  10. Structural anisotropy results in strain-tunable electronic and optical properties in monolayer GeX and SnX (X = S, Se, Te)

    NASA Astrophysics Data System (ADS)

    Huang, Le; Wu, Fugen; Li, Jingbo

    2016-03-01

    Using first-principles calculations, the structural and electronic properties of group-IV monochalcogenide monolayers are investigated. It is demonstrated that all the monolayers employed here possess moderate indirect bandgaps. In-plane elastic stiffness calculation demonstrates the structural anisotropy in these materials, further resulting in anisotropic response to in-plane strains in their electronic properties and anisotropic optical properties. The bandgaps of GeX and SnX monolayers can be linearly reduced by applied in-plane compressive strains and the semiconductor-to-metal transition can be realized under large compressive strains; while tensile strains exert less influence on the electronic properties in comparison to compressive strains. Some monolayers will experience indirect-to-direct bandgap transition when subjected to proper strains. A further insight into the variation of bandgaps of these monolayers can be obtained from the changing band edges.

  11. All-electron molecular Dirac-Hartree-Fock calculations: Properties of the group IV monoxides GeO, SnO and PbO

    NASA Technical Reports Server (NTRS)

    Dyall, Kenneth G.

    1991-01-01

    Dirac-Hartree-Fock calculations have been carried out on the ground states of the group IV monoxides GeO, SnO and PbO. Geometries, dipole moments and infrared data are presented. For comparison, nonrelativistic, first-order perturbation and relativistic effective core potential calculations have also been carried out. Where appropriate the results are compared with the experimental data and previous calculations. Spin-orbit effects are of great importance for PbO, where first-order perturbation theory including only the mass-velocity and Darwin terms is inadequate to predict the relativistic corrections to the properties. The relativistic effective core potential results show a larger deviation from the all-electron values than for the hydrides, and confirm the conclusions drawn on the basis of the hydride calculations.

  12. Nonlinear structure-composition relationships in the Ge1-ySny/Si(100) (y<0.15) system

    SciTech Connect

    Beeler, R.; Roucka, R.; Chizmeshya, A. V. G.; Kouvetakis, J.; Menéndez, J.

    2011-07-26

    The compositional dependence of the cubic lattice parameter in Ge1-ySny alloys has been revisited. Large 1000-atom supercell ab initio simulations confirm earlier theoretical predictions that indicate a positive quadratic deviation from Vegard's law, albeit with a somewhat smaller bowing coefficient, θ = 0.047 Å, than found from 64-atom cell simulations (θ = 0.063 Å). On the other hand, measurements from an extensive set of alloy samples with compositions y < 0.15 reveal a negative deviation from Vegard's law. The discrepancy with earlier experimental data, which supported the theoretical results, is traced back to an unexpected compositional dependence of the residual strain after growth on Si substrates. The experimental bowing parameter for the relaxed lattice constant of the alloys is found to be θ = -0.066 Å. Possible reasons for the disagreement between theory and experiment are discussed in detail.

  13. Experimental data on inclusive spectra of protons in interaction of 3. 6-GeV/nucleon. cap alpha. particles with Cu and Sn nuclei

    SciTech Connect

    Ad'yasevich, B.P.; Antonenko, V.G.; Vinogradov, A.A.; Grigor'yan, Y.I.; Dukhanov, V.I.; Ippolitov, M.S.; Karadzhev, K.V.; Lebedev, A.L.; Man'ko, V.I.; Nikolaev, S.A.

    1983-07-01

    Results are reported on the study of inclusive spectra of protons emitted in interaction of 3.6-GeV/nucleon ..cap alpha.. particles with Cu and Sn nuclei. Proton angular distributions are given for three intervals of velocities: 0.325< or approx. =..beta..< or approx. =0.425, 0.425< or approx. =..beta..< or approx. =0.525, and 0.525< or approx. =..beta..< or approx. =0.625. The nature of the angular distributions is practically independent of the combination of colliding nuclei but is substantially different for different velocity intervals. Total cross sections and average charged-particle multiplicities are found in the velocity interval ..beta..> or approx. =0.32. Rapidity distributions are obtained for the invariant cross sections for proton production in the rapidity range -0.2< or approx. =Y< or approx. =0.6 for 0.35< or approx. =p/sub perpendicular//mc< or approx. =0.7.

  14. The study on SiO2 pattern fabrication using Ge1.5Sn0.5Sb2Te5 as resists.

    PubMed

    Xi, Hongzhu; Liu, Qian; Tian, Ye; Guo, Shengming; Cu, Maoyou; Zhang, Gengmin

    2013-02-01

    Ge1.5Sn0.5Sb2Te5 (GSST) can be easily induced to phase transition from amorphous state to crystalline state by a laser direct writing (LDW) system. The results show that the crystalline phase of GSST is more durable against acid solution corrosion than the amorphous phase. So nano-scale patterns and structures can be formed on the GSST film resists using laser-induced phase change and wet etching. Moreover, reactive ion etching (RIE) technology was applied to transfer these patterns onto the SiO2 substrate. The result shows to the extent that GSST material has thermal resist characteristics with high resolution and well etching selectivity to SiO2 when etched in the CHF3, which is compatibility with the future nanofabricate processing. PMID:23646524

  15. Elastic and electronic properties of the Ti{sub 5}X{sub 3} (X=Si, Ge, Sn, Pb) compounds from first-principles calculations

    SciTech Connect

    Chen, Xiao-Jun; Mo, Zhou-Sheng; Wang, Ren-Nian; Zeng, Meng-Xue; Tang, Bi-Yu; Peng, Li-Ming; Ding, Wen-Jiang

    2012-10-15

    The structural stabilities, elastic and electronic properties of Ti{sub 5}X{sub 3} (X=Si, Ge, Sn, Pb) compounds with D8{sub 8} structure have been systematically investigated within the frame work of density functional theory. With increase of atomic number of the element X, the calculated lattice constants of Ti{sub 5}X{sub 3} compounds are found to increase, while stabilities of these compounds decrease because the formation enthalpies increase. Moreover, with exception of C{sub 12}, the calculated elastic constants C{sub ij} are reduced with increase of atomic number of element X, the bulk, shear, Young's modulus and Debye temperature are also lowered, while Poisson's ratio is larger, and the ductility is slightly improved. The elastic anisotropies were further studied, especially the 3D direction dependence of these elastic modulus was visually described. The density of states and charge density distribution reveal bonding feature of Ti{sub 5}X{sub 3}. Especially, the X-X and Ti-X covalent bonding strength is found to decrease with increase of atomic number of element X. - Graphical abstract: The charge density contour plots on the (0 0 0 1) plane for Ti{sub 5}Si{sub 3} (a), Ti{sub 5}Ge{sub 3} (b), Ti{sub 5}Sn{sub 3} (c) and Ti{sub 5}Pb{sub 3} (d). Highlights: Black-Right-Pointing-Pointer The elastic constants except C{sub 12} were lowered with increase of atomic number of X. Black-Right-Pointing-Pointer The bulk and shear modulus as well as Young's modulus was also decreased. Black-Right-Pointing-Pointer The elastic anisotropies of Ti{sub 5}X{sub 3} were further studied visually. Black-Right-Pointing-Pointer The X-X and Ti-X covalent bonding strength was lowered.

  16. Antiferromagnetism in R u2Mn Z (Z =Sn ,Sb ,Ge ,Si ) full Heusler alloys: Effects of magnetic frustration and chemical disorder

    NASA Astrophysics Data System (ADS)

    Khmelevskyi, Sergii; Simon, Eszter; Szunyogh, László

    2015-03-01

    We present systematic theoretical investigations to explore the microscopic mechanisms leading to the formation of antiferromagnetism in R u2Mn Z (Z =Sn ,Sb ,Ge ,Si ) full Heusler alloys. Our study is based on first-principles calculations of interatomic Mn-Mn exchange interactions to set up a suitable Heisenberg spin model and on subsequent Monte Carlo simulations of the magnetic properties at finite temperature. The exchange interactions are derived from the paramagnetic state, while a realistic account of long-range chemical disorder is made in the framework of the coherent potential approximation. We find that in the case of the highly ordered alloys (Z =Sn and Sb), the exchange interactions derived from the perfectly ordered L 21 structure lead to Néel temperatures in excellent agreement with the experiments, whereas, in particular in the case of Si, the consideration of chemical disorder is essential to reproduce the experimental Néel temperatures. Our numerical results suggest that by improving a heat treatment of the samples to suppress the intermixing between the Mn and Si atoms, the Néel temperature of the Si-based alloys can potentially be increased by more than 30%. Based on calculated biquadratic exchange couplings, we evidence a lifting of degeneracy of the antiferromagnetic ground states on a frustrated face-centered-cubic lattice in the fully ordered compounds. Furthermore, we show that in strongly disordered R u2MnSi alloys, a distinct change in the antiferromagnetic ordering occurs.

  17. Reaction Mechanism of the Hydrogermylation/Hydrostannylation of Unactivated Alkenes with Two-Coordinate E(II) Hydrides (E=Ge, Sn): A Theoretical Study.

    PubMed

    Zhao, Lili; Hermann, Markus; Jones, Cameron; Frenking, Gernot

    2016-08-01

    Quantum chemical calculations using density functional theory with the TPSS+D3(BJ) and M06-2X+D3(ABC) functionals have been carried out to understand the mechanisms of catalyst-free hydrogermylation/hydrostannylation reactions between the two-coordinate hydrido-tetrylenes :E(H)(L(+) ) (E=Ge or Sn, L(+) =N(Ar(+) )(SiiPr3 ); Ar(+) =C6 H2 {C(H)Ph2 }2 iPr-2,6,4) and a range of unactivated terminal (C2 H3 R, R=H, Ph, or tBu) and cyclic [(CH)2 (CH2 )2 (CH2 )n , n=1, 2, or 4] alkenes. The calculations suggest that the addition reactions of the germylenes and stannylenes to the cyclic and acyclic alkenes occur as one-step processes through formal [2+2] addition of the E-H fragment across the C-C π bond. The reactions have moderate barriers and are weakly exergonic. The steric bulk of the tetrylene amido groups has little influence on the activation barriers and on the reaction energies of the anti-Markovnikov pathway, but the Markovnikov addition is clearly disfavored by the size of the substituents. The addition of the tetrylenes to the cyclic alkenes is less exergonic than the addition to the terminal alkenes, which agrees with the experimentally observed reversibility of the former reactions. The hydrogermylation reactions have lower activation energies and are more exergonic than the stannylene addition. An energy decomposition analysis of the transition state for the hydrogermylation of cyclohexene shows that the reaction takes place with simultaneous formation of the Ge-C and (Ge)H-C' bonds. The dominant orbitals of the germylene are the σ-type lone pair MO of Ge, which serves as a donor orbital, and the vacant p(π) MO of Ge, which acts as acceptor orbital for the π* and π MOs of the olefin. Inspection of the transition states of some selected reactions suggests that the differences between the activation energies come from a delicate balance between the deformation energies of the interacting species and their interaction energies. PMID:27403941

  18. Phase Stability and Electronic Structure of In-Free Photovoltaic Materials: Cu2ZnSiSe4, Cu2ZnGeSe4, and Cu2ZnSnSe4

    NASA Astrophysics Data System (ADS)

    Nakamura, Satoshi; Maeda, Tsuyoshi; Wada, Takahiro

    2010-12-01

    We have theoretically evaluated phase stability and electronic structure of Cu2ZnSiSe4 and Cu2ZnGeSe4 and compared the results with those of Cu2ZnSnSe4. The enthalpies of formation for kesterite (KS), stannite (ST), and wurtz-stannite (WST) phases of Cu2ZnSiSe4, Cu2ZnGeSe4, and Cu2ZnSnSe4 (CZTSe) were calculated by first-principles calculations. In these three compounds, the KS phase is more stable than the ST and WST phases. The theoretical band gaps of KS-type Cu2ZnSiSe4 (1.48 eV) and Cu2ZnGeSe4 (1.10 eV) are wider than that of KS-type Cu2ZnSnSe4 (0.63 eV). The valence band maximum (VBM) of KS-type Cu2ZnIVSe4 consists of antibonding orbital of Cu 3d and Se 4p, while the conduction band minimum (CBM) consist of antibonding orbital of IV ns and Se 4p. The VBMs of Cu 3d + Se 4p in Cu2ZnSiSe4 and Cu2ZnGeSe4 are similar to that in Cu2ZnSnSe4. Therefore, the energy levels of VBMs in Cu2ZnIVSe4 (IV = Si, Ge) do not change so much compared with that of CZTSe. On the other hand, the energy levels of CBMs of IV ns + Se 4p in Cu2ZnSiSe4 and Cu2ZnGeSe4 become higher than that in Cu2ZnSnSe4. These trends in the electronic structures are explained by the schematic molecular orbital diagrams of tetrahedral CuSe47-, ZnSe46-, and IVSe44- (IV = Si, Ge, Sn) clusters.

  19. Effects of Rh on the thermoelectric performance of the p-type Zr{sub 0.5}Hf{sub 0.5}Co{sub 1-x}Rh{sub x}Sb{sub 0.99}Sn{sub 0.01} half-Heusler alloys

    SciTech Connect

    Maji, Pramathesh; Takas, Nathan J.; Misra, Dinesh K.; Gabrisch, Heike; Stokes, Kevin; Poudeu, Pierre F.P.

    2010-05-15

    We show that Rh substitution at the Co site in Zr{sub 0.5}Hf{sub 0.5}Co{sub 1-x}Rh{sub x}Sb{sub 0.99}Sn{sub 0.01} (0<=x<=1) half-Heusler alloys strongly reduces the thermal conductivity with a simultaneous, significant improvement of the power factor of the materials. Thermoelectric properties of hot-pressed pellets of several compositions with various Rh concentrations were investigated in the temperature range from 300 to 775 K. The Rh 'free' composition shows n-type conduction, while Rh substitution at the Co site drives the system to p-type semiconducting behavior. The lattice thermal conductivity of Zr{sub 0.5}Hf{sub 0.5}Co{sub 1-x}Rh{sub x}Sb{sub 0.99}Sn{sub 0.01} alloys rapidly decreased with increasing Rh concentration and lattice thermal conductivity as low as 3.7 W/m*K was obtained at 300 K for Zr{sub 0.5}Hf{sub 0.5}RhSb{sub 0.99}Sn{sub 0.01}. The drastic reduction of the lattice thermal conductivity is attributed to mass fluctuation induced by the Rh substitution at the Co site, as well as enhanced phonon scattering at grain boundaries due to the small grain size of the synthesized materials. - Graphical abstract: Significant reduction of the lattice thermal conductivity with increasing Rh concentration in the p-type Zr{sub 0.5}Hf{sub 0.5}Co{sub 1-x}Rh{sub x}Sb{sub 0.99}Sn{sub 0.01} half-Heusler materials prepared by solid state reaction at 1173 K.

  20. Thermal stability and radiation resistance of tin valent states in the structure of the (As{sub 2}Se{sub 3}){sub 1-z}(SnSe){sub z-x}(GeSe){sub x} semiconductor glasses

    SciTech Connect

    Bordovskii, G. A.; Kastro, R. A.; Marchenko, A. V.; Nemov, S. A.; Seregin, P. P.

    2007-12-15

    The ratio between the content of bivalent and tetravalent tin atoms in the (As{sub 2}Se{sub 3}){sub 1-z}(SnSe){sub z-x}(GeSe){sub x} glasses depends on the rate of quenching of the alloy and on its temperature. Irradiation of these glasses with {gamma}-ray photons brings about a partial oxidation of bivalent tin with formation of amorphous (finely divided) SnO{sub 2} phase blocked by the glass, so that the physicochemical properties of the glasses (density, microhardness, glassformation temperature, and the electrical-conductivity activation energy) are virtually unaffected by irradiation.

  1. Crystal structure and thermal expansion of the low- and high-temperature forms of BaM{sup IV}(PO{sub 4}){sub 2} compounds (M=Ti, Zr, Hf and Sn)

    SciTech Connect

    Bregiroux, D.; Popa, K.; Jardin, R.; Raison, P.E.; Wallez, G.; Quarton, M.; Brunelli, M.; Ferrero, C.; Caciuffo, R.

    2009-05-15

    The crystal structure of beta-BaZr(PO{sub 4}){sub 2}, archetype of the high-temperature forms of BaM(PO{sub 4}){sub 2} phosphates (with M=Ti, Zr, Hf and Sn), has been solved ab initio by Rietveld analysis from synchrotron X-ray powder diffraction data. The phase transition appears as a topotactic modification of the monoclinic (S.G. C2/m) lamellar alpha-structure into a trigonal one (S.G. P3-barm1) through a simple mechanism involving the unfolding of the [Zr(PO{sub 4}){sub 2}]{sub n}{sup 2-} layers. The thermal expansion is very anisotropic (e.g., -4.1

  2. Insight into the pseudo π-hole interactions in the M3H6(NCF)n (M = C, Si, Ge, Sn, Pb; n = 1, 2, 3) complexes.

    PubMed

    Li, Wei; Zeng, Yanli; Li, Xiaoyan; Sun, Zheng; Meng, Lingpeng

    2016-09-21

    For cyclopropane and its derivatives M3H6 (M = C, Si, Ge, Sn, Pb), "pseudo π-hole" regions above and below the M-M-M three-membered ring have been discovered, and pseudo π-hole interactions between M3H6 and F-CN have been designed and investigated by MP2/aug-cc-pVTZ and MP2/aug-cc-pVTZ-pp calculations. To investigate the enhancing effects of FN halogen bonds on the pseudo π-hole interactions, the termolecular and tetramolecular complexes M3H6(NCF)n (n = 2, 3) were constructed. Energy decomposition analysis shows that the dispersion term contributes the most among the three attractive components in the C3H6(NCF)n (n = 1, 2, 3) complexes while in the Si3H6(NCF)n and Ge3H6(NCF)n complexes, the electrostatic term has the largest contribution. The electrostatic and polarization energies have more effect than the dispersion energy for the enhancement of the FN halogen bond on the pseudo π-hole interactions. With the increase in the number of NCF units from 1 to 3, the VS,min values outside the nitrogen atom of NCF become increasingly negative, the electric field of the lone pair of nitrogen becomes greater and causes a further increase of electron density outside the nitrogen atom and a further decrease of electron density outside the pseudo π-hole region, resulting in a stronger pseudo π-hole interaction. PMID:27545836

  3. Calcium hexa-kis(dihydrogen-phosphito)-stannate(IV), Ca[Sn(H2PO2)6], with some remarks on the so-called Ge2(H2PO2)6 structure type.

    PubMed

    Gieschen, Tobias; Reuter, Hans

    2013-01-01

    The title compound, Ca[Sn(H2PO2)6], was formed after a few days when tin(II) fluoride was allowed to react with phosphinic acid at ambient conditions. The structure consists of chains of Ca(2+) and Sn(4+) cations in octa-hedral sites with -3 symmetry bridged by bidentate hypophosphite anions. The chains are hexa-gonally close packed along [001]. The discovery of the compound and the successful structure refinement provides strong evidence that an isostructural compound, originally described as the mixed-valence compound, Ge2[H2PO2]6 [Weakley (1983 ▶). J. Chem. Soc. Pak. 5, 279-281], must be reformulated as Ca[Ge(H2PO2)6]. PMID:24109251

  4. Calcium hexa­kis(dihydrogen­phosphito)­stannate(IV), Ca[Sn(H2PO2)6], with some remarks on the so-called Ge2(H2PO2)6 structure type

    PubMed Central

    Gieschen, Tobias; Reuter, Hans

    2013-01-01

    The title compound, Ca[Sn(H2PO2)6], was formed after a few days when tin(II) fluoride was allowed to react with phosphinic acid at ambient conditions. The structure consists of chains of Ca2+ and Sn4+ cations in octa­hedral sites with -3 symmetry bridged by bidentate hypophosphite anions. The chains are hexa­gonally close packed along [001]. The discovery of the compound and the successful structure refinement provides strong evidence that an isostructural compound, originally described as the mixed-valence compound, Ge2[H2PO2]6 [Weakley (1983 ▶). J. Chem. Soc. Pak. 5, 279–281], must be reformulated as Ca[Ge(H2PO2)6]. PMID:24109251

  5. Memory type switching behavior of ternary Ge20Te80‑x Sn x (0  ⩽  x  ⩽  4) chalcogenide compounds

    NASA Astrophysics Data System (ADS)

    Jeevan Fernandes, Brian; Sridharan, Kishore; Munga, Pumlian; Ramesh, K.; Udayashankar, N. K.

    2016-07-01

    Chalcogenide compounds have gained huge research interest recently owing to their capability to transform from an amorphous to a crystalline phase with varying electrical properties. Such materials can be applied in building a new class of memories, such as phase-change memory and programmable metallization cells. Here we report the memory type electrical switching behavior of a ternary chalcogenide compound synthesized by doping Tin (Sn) in a germanium–telluride (Ge20Te80) host matrix, which yielded a composition of Ge20Te80‑x Sn x (0  ⩽  x  ⩽  4). Results indicate a remarkable decrease in the threshold switching voltage (V T) from 140 to 61 V when the Sn concentration was increased stepwise, which is attributed to the domination of the metallicity factor leading to reduced amorphous network connectivity and rigidity. Variation in the threshold switching voltage (V T) was noticed even when the sample thickness and temperature were altered, confirming that the memory switching process is of thermal origin. Investigations using x-ray diffraction (XRD) and scanning electron microscopy (SEM) revealed the formation of a crystalline channel that acts as the conduction path between the two electrodes in the switched region. Structural and morphological studies indicated that Sn metal remained as a micro inclusion in the matrix and hardly contributed to the rigid amorphous network formation in Ge20Te80‑x Sn x . Memory type electrical switching observed in these ternary chalcogenide compounds synthesized herein can be explored further for the fabrication of phase-change memory devices.

  6. Theoretical analysis of NMR shieldings in XSe and XTe (X = Si, Ge, Sn and Pb): the spin-rotation constant saga.

    PubMed

    Demissie, Taye Beyene

    2016-01-28

    The nuclear spin-rotation (NSR) and absolute nuclear magnetic resonance (NMR) shielding tensors of the nuclei in the series of X(77)Se and X(125)Te (X = (29)Si, (73)Ge, (119)Sn and (207)Pb) are calculated using four-component relativistic density functional theory (DFT) and coupled-cluster singles-doubles with a perturbative triples correction (CCSD(T)). The results for the NSR constants are compared to available experimental data. The best theoretical estimates are obtained when relativistic corrections from DFT are added to the accurate non-relativistic CCSD(T) results. All the calculated NSR constants are in excellent agreement with the corresponding experimental values. Even though there are previously estimated absolute shielding constants and spans from experimental NSR tensors, new accurate values are reported following the same approach used to calculate the NSR constants in this study. The main reasons for the discrepancy between the previously reported NMR properties and the accurate results obtained in this study are also discussed. PMID:26741559

  7. Electronic structure and low temperature thermoelectric properties of In₂₄M₈O₄₈ (M = Ge(4+), Sn(4+), Ti(4+), and Zr(4+)).

    PubMed

    Yan, Yu Li; Wang, Yuan Xu

    2012-01-01

    The electronic structure and transport properties of In₂₄M₈O₄₈ (M = Ge(4+), Sn(4+), Ti(4+), and Zr(4+)) have been studied by using the full-potential linearized augmented plane-wave method and the semiclassical Boltzmann theory, respectively. It is found that the magnitude of powerfactor with respect to relation time follows the order of In₂₄Sn₈O₄₈ > In₂₄Zr₈O₄₈ > In₂₄Ge₈O₄₈ > In₂₄Ti₈O₄₈. The largest powerfactor is 2.7 × 10¹² W/K² ms for In₂₄Sn₈O₄₈ at 60 K, which is nearly thirty times larger than those of conventional n-type thermoelectric materials. The origin of the different thermoelectric behavior for these compounds is discussed from the electronic structure level. It is found that, at low temperature, the dopant strongly affect the bands near the Fermi level, which consequently leads to their different thermoelectric properties. The electronic configuration and the difference in atomic number between the dopant and the host atom also play an important role on the thermoelectric properties of In₂₄M₈O₄₈. Our calculations give a valuable insight on how to enhance the thermoelectric performance of In₃₂O₄₈. PMID:21952977

  8. Nanostructured rocksalt-type solid solution series (Ge{sub 1−x}Sn{sub x}Te){sub n}Sb{sub 2}Te{sub 3} (n=4, 7, 12; 0≤x≤1): Thermal behavior and thermoelectric properties

    SciTech Connect

    Rosenthal, Tobias; Neudert, Lukas; Ganter, Pirmin; Boor, Johannes de; Stiewe, Christian; Oeckler, Oliver

    2014-07-01

    Solid solutions (Ge{sub 1−x}Sn{sub x}Te){sub n}Sb{sub 2}Te{sub 3} (n=4, 7, 12; 0≤x≤1) represent stable high-temperature phases and can be obtained as metastable compounds by quenching. High-resolution transmission electron microscopy reveals that the quenched (pseudo-)cubic materials exhibit parquet-like nanostructures comparable to, but especially for n=4 more pronounced than in (GeTe){sub n}Sb{sub 2}Te{sub 3} (GST materials). The temperature-dependent phase transitions are comparable; however, substitution with Sn significantly lowers the transition temperatures between cubic high-temperature phase and the long range ordered layered phases that are stable at ambient conditions. In addition, the metrics of the quenched Sn-containing materials remains closer to cubic, especially for samples with n=7 or 12. For samples with high defect concentrations (n=4, 7), Sn-substituted samples exhibit electrical conductivities up to 3 times higher than those of corresponding GST materials. Since the difference in thermal conductivity is much less pronounced, this results in a doubling of the thermoelectric figure of merit (ZT) at high temperatures for (Ge{sub 0.5}Sn{sub 0.5}Te){sub 4}Sb{sub 2}Te{sub 3} as compared to (GeTe){sub 4}Sb{sub 2}Te{sub 3}. Sn doping in (GeTe){sub 7}Sb{sub 2}Te{sub 3} increases the ZT value by a factor of up to 4 which is also due to an increased Seebeck coefficient. - Graphical abstract: High-resolution transmission electron micrographs of (GeTe){sub 4}Sb{sub 2}Te{sub 3} (top) and (Ge{sub 0.5}Sn{sub 0.5}Te){sub 4}Sb{sub 2}Te{sub 3} (bottom) with different nanostructures and thermoelectric figures of merit (ZT) of these samples. - Highlights: • Representative samples of solid solutions of (Ge{sub 1−x}Sn{sub x}Te){sub n}Sb{sub 2}Te{sub 3} were synthesized. • Sn substitution leads to more pronounced nanostructures in defect-rich compounds. • Phase transitions are comparable to (GeTe){sub n}Sb{sub 2}Te{sub 3} but occur at lower temperatures

  9. Room-temperature electroluminescence from Ge/Ge1-xSnx/Ge diodes on Si substrates

    NASA Astrophysics Data System (ADS)

    Du, Wei; Zhou, Yiyin; Ghetmiri, Seyed A.; Mosleh, Aboozar; Conley, Benjamin R.; Nazzal, Amjad; Soref, Richard A.; Sun, Greg; Tolle, John; Margetis, Joe; Naseem, Hameed A.; Yu, Shui-Qing

    2014-06-01

    Double heterostructure Ge/Ge1-xSnx/Ge light-emitting diodes (LEDs) with 6% and 8% Sn were grown on Si substrates using chemical vapor deposition. The electroluminescence emission spectra from the fabricated LEDs were investigated at room-temperature under different injection levels. The observed emission peaks at 0.645 eV and 0.601 eV are attributed to the direct bandgap transition of the Ge0.94Sn0.06 and Ge0.92Sn0.08 layers, respectively. Moreover, the integrated emission intensity increases as the Sn composition increases under the same injection condition.

  10. [Zr 0.72Y 0.28]Al 4C 4: A new member of the homologous series ( MC) l( T4C 3) m ( M=Zr, Y and Hf, T=Al, Si and Ge)

    NASA Astrophysics Data System (ADS)

    Sugiura, Keita; Iwata, Tomoyuki; Nakano, Hiromi; Fukuda, Koichiro

    2009-07-01

    A new layered carbide, [Zr 0.72(3)Y 0.28(3)]Al 4C 4, has been synthesized and characterized by X-ray powder diffraction, transmission electron microscopy and energy dispersive X-ray spectroscopy (EDX). The atom ratios [Zr:Y] were determined by EDX, and the initial structure model was derived by the direct methods, and further refined by Rietveld method. The crystal is trigonal (space group P3¯m1, Z=1) with lattice dimensions of a=0.333990(5) nm, c=1.09942(1) nm and V=0.106209(2) nm 3. This compound shows an intergrowth structure with [Zr 0.72Y 0.28C 2] thin slabs separated by Al 4C 3-type [Al 4C 4] layers. It is a new member with l=1 and m=1 of the homologous series, the general formula of which is ( MC) l( T4C 3) m ( l=1, 2 and 3, m=1 and 2, M=Zr, Y and Hf, T=Al, Si and Ge).

  11. Phase stabilities of pyrite-related MTCh compounds (M=Ni, Pd, Pt; T=Si, Ge, Sn, Pb; Ch=S, Se, Te): A systematic DFT study

    SciTech Connect

    Bachhuber, Frederik; Krach, Alexander; Furtner, Andrea; Söhnel, Tilo; Peter, Philipp; Rothballer, Jan; Weihrich, Richard

    2015-03-15

    Pyrite-type and related systems appear for a wide range of binary and ternary combinations of transition metals and main group elements that form Zintl type dumbbell anion units. Those representatives with 20 valence electrons exhibit an extraordinary structural flexibility and interesting properties as low-gap semiconductors or thermoelectric and electrode materials. This work is devoted to the systematic exploration of novel compounds within the class of MTCh compounds (M=Ni, Pd, Pt; T=Si, Ge, Sn, Pb; Ch=S, Se, Te) by means of density functional calculations. Their preferred structures are predicted from an extended scheme of colored pyrites and marcasites. To determine their stabilities, competing binary MT{sub 2} and MCh{sub 2} boundary phases are taken into account as well as ternary M{sub 3}T{sub 2}Ch{sub 2} and M{sub 2}T{sub 3}Ch{sub 3} systems. Recently established stability diagrams are presented to account for MTCh ordering phenomena with a focus on a not-yet-reported ordering variant of the NiAs{sub 2} type. Due to the good agreement with experimental data available for several PtTCh systems, the predictions for the residual systems are considered sufficiently accurate. - Graphical abstract: Compositional and structural stability of MTCh compounds is investigated from first principle calculations. A conceptional approach is presented to study and predict novel stable and metastable compounds and structures of low gap semiconductors with TCh dumbbell units that are isoelectronic and structurally related to pyrite (FeS{sub 2}). - Highlights: • Study of compositional stability of MTCh vs. M{sub 3}T{sub 2}Ch{sub 2} and M{sub 2}T{sub 3}Ch{sub 3} compounds. • Study of structural stability of known and novel MTCh compounds. • Prediction of novel stable and metastable structures and compounds isoelectronic to pyrite, FeS{sub 2}.

  12. Ground state properties and thermoelectric behavior of Ru2VZ (Z=Si, ge, sn) half-metallic ferromagnetic full-Heusler compounds

    NASA Astrophysics Data System (ADS)

    Yalcin, Battal Gazi

    2016-06-01

    The ground state properties namely structural, mechanical, electronic and magnetic properties and thermoelectric behavior of Ru2VZ (Z=Si, Ge and Sn) half-metallic ferromagnetic full-Heusler compounds are systematically investigated. These compounds are ferromagnetic and crystallize in the Heusler type L21 structure (prototype: Cu2MnAl, Fm-3m 225). This result is confirmed for Ru2VSi and Ru2VSn by experimental work reported by Yin and Nash using high temperature direct reaction calorimetry. The studied materials are half-metallic ferromagnets with a narrow direct band gap in the minority spin channel that amounts to 31 meV, 66 meV and 14 meV for Ru2VSi, Ru2VGe, and Ru2VSn, respectively. The total spin magnetic moment (Mtot) of the considered compounds satisfies a Slater-Pauling type rule for localized magnetic moment systems (Mtot=(NV-24)μB), where NV=25 is the number of valence electrons in the primitive cell. The Curie temperature within the random phase approximation (RPA) is found to be 23 K, 126 K and 447 K for Ru2VSi, Ru2VGe and Ru2VSn, respectively. Semi-classical Boltzmann transport theories have been used to obtain thermoelectric constants, such as Seebeck coefficient (S), electrical (σ/τ) and thermal conductivity (κ/τ), power factor (PF) and the Pauli magnetic susceptibility (χ). ZTMAX values of 0.016 (350 K), 0.033 (380 K) and 0.063 (315 K) are achieved for Ru2VSi, Ru2VGe and Ru2VSn, respectively. It is expected that the obtained results might be a trigger in future experimentally interest in this type of full-Heusler compounds.

  13. Exploration of R2XM2 (R=Sc, Y, Ti, Zr, Hf, rare earth; X=main group element; M=transition metal, Si, Ge): Structural Motifs, the novel Compound Gd2AlGe2 and Analysis of the U3Si2 and Zr3Al2 Structure Types

    SciTech Connect

    Sean William McWhorter

    2006-05-01

    In the process of exploring and understanding the influence of crystal structure on the system of compounds with the composition Gd{sub 5}(Si{sub x}Ge{sub 1-x}){sub 4} several new compounds were synthesized with different crystal structures, but similar structural features. In Gd{sub 5}(Si{sub x}Ge{sub 1-x}){sub 4}, the main feature of interest is the magnetocaloric effect (MCE), which allows the material to be useful in magnetic refrigeration applications. The MCE is based on the magnetic interactions of the Gd atoms in the crystal structure, which varies with x (the amount of Si in the compound). The crystal structure of Gd{sub 5}(Si{sub x}Ge{sub 1-x}){sub 4} can be thought of as being formed from two 3{sup 2}434 nets of Gd atoms, with additional Gd atoms in the cubic voids and Si/Ge atoms in the trigonal prismatic voids. Attempts were made to substitute nonmagnetic atoms for magnetic Gd using In, Mg and Al. Gd{sub 2}MgGe{sub 2} and Gd{sub 2}InGe{sub 2} both possess the same 3{sup 2}434 nets of Gd atoms as Gd{sub 5}(Si{sub x}Ge{sub 1-x}){sub 4}, but these nets are connected differently, forming the Mo{sub 2}FeB{sub 2} crystal structure. A search of the literature revealed that compounds with the composition R{sub 2}XM{sub 2} (R=Sc, Y, Ti, Zr, Hf, rare earth; X=main group element; M=transition metal, Si, Ge) crystallize in one of four crystal structures: the Mo{sub 2}FeB{sub 2}, Zr{sub 3}Al{sub 2}, Mn{sub 2}AlB{sub 2} and W{sub 2}CoB{sub 2} crystal structures. These crystal structures are described, and the relationships between them are highlighted. Gd{sub 2}AlGe{sub 2} forms an entirely new crystal structure, and the details of its synthesis and characterization are given. Electronic structure calculations are performed to understand the nature of bonding in this compound and how electrons can be accounted for. A series of electronic structure calculations were performed on models with the U{sub 3}Si{sub 2} and Zr{sub 3}Al{sub 2} structures, using Zr and A1 as

  14. The structural, electronic, magnetic and mechanical properties of quaternary Heusler alloys ZrTiCrZ (Z  =  Al, Ga, In, Si, Ge, Sn): a first-principles study

    NASA Astrophysics Data System (ADS)

    Yan, Peng-Li; Zhang, Jian-Min; Zhou, Bo; Xu, Ke-Wei

    2016-06-01

    The structural, electronic, magnetic and mechanical properties of the quaternary Heusler alloys ZrTiCrZ (Z  =  Al, Ga, In, Si, Ge, Sn) have been investigated firstly by using the first-principles calculations. The preferred configurations of the ZrTiCrZ alloys are all Y-type (I). At their equilibrium lattice constants, the ZrTiCrZ alloys are half-metallic (HM) ferrimagnets for Z  =  Al, Ga and In, while spin-gapless semiconductor (SGS) antiferromagnets (AFM) for Z  =  Si, Ge and Sn. The total magnetic moments {μt} of the ZrTiCrZ alloys are  ‑1 {μ\\text{B}}/\\text{f}\\text{.u}\\text{.} for Z  =  Al, Ga and In, while 0 {μ\\text{B}}/\\text{f}\\text{.u}\\text{.} for Z  =  Si, Ge and Sn, both linearly scaled with the total number of valence electrons {{Z}\\text{t}} by Slater–Pauling rule {μ\\text{t}}={{Z}\\text{t}}-18 . The elastic constants {{C}11} , {{C}12} and {{C}44} of the single crystal and the related elastic moduli G , B , E , \\upsilon and A of the polycrystalline aggregates are also calculated and used to study the mechanical stability of these alloys. Although the Curie temperatures {{T}\\text{C}} of the ZrTiCrZ alloys are overestimated by using the mean field approximation (MFA), they can be better estimated by including the exchange interactions. Finally, the HM stabilities as well as the total and atomic magnetic moments of the ZrTiCrZ alloys (Z  =  Al, Ga, In) under either hydrostatic strain or tetragonal strain are also discussed.

  15. All-electron molecular Dirac-Hartree-Fock calculations: The group 4 tetrahydrides CH4, SiH4, GeH4, SnH4 and PbH4

    NASA Technical Reports Server (NTRS)

    Dyall, Kenneth G.; Taylor, Peter R.; Faegri, Knut, Jr.; Partridge, Harry

    1990-01-01

    A basis-set-expansion Dirac-Hartree-Fock program for molecules is described. Bond lengths and harmonic frequencies are presented for the ground states of the group 4 tetrahydrides, CH4, SiH4, GeH4, SnH4, and PbH4. The results are compared with relativistic effective core potential (RECP) calculations, first-order perturbation theory (PT) calculations and with experimental data. The bond lengths are well predicted by first-order perturbation theory for all molecules, but non of the RECP's considered provides a consistent prediction. Perturbation theory overestimates the relativistic correction to the harmonic frequencies; the RECP calculations underestimate the correction.

  16. Conventional and stuffed Bergman-type phases in the Na-Au-T (T = Ga, Ge, Sn) systems: syntheses, structures, coloring of cluster centers, and Fermi sphere-brillouin zone interactions.

    PubMed

    Lin, Qisheng; Smetana, Volodymyr; Miller, Gordon J; Corbett, John D

    2012-08-20

    Bergman-type phases in the Na-Au-T (T = Ga, Ge, and Sn) systems were synthesized by solid-state means and structurally characterized by single-crystal X-ray diffraction studies. Two structurally related (1/1) Bergman phases were found in the Na-Au-Ga system: (a) a conventional Bergman-type (CB) structure, Na(26)Au(x)Ga(54-x), which features empty innermost icosahedra, as refined with x = 18.1 (3), Im3, a = 14.512(2) Å, and Z = 2; (b) a stuffed Bergman-type (SB) structure, Na(26)Au(y)Ga(55-y), which contains Ga-centered innermost icosahedra, as refined with y = 36.0 (1), Im3, a = 14.597(2) Å, and Z = 2. Although these two subtypes have considerable phase widths along with respective tie lines at Na ≈ 32.5 and 32.1 atom %, they do not merge into a continuous solid solution. Rather, a quasicrystalline phase close to the Au-poor CB phase and an orthorhombic derivative near the Au-rich SB phase lie between them. In contrast, only Au-rich SB phases exist in the Ge and Sn systems, in which the innermost icosahedra are centered by Au rather than Ge or Sn. These were refined for Na(26)Au(40.93(5))Ge(14.07(5)) (Im3, a = 14.581(2) Å, and Z = 2) and Na(26)Au(39.83(6))Sn(15.17(6)) (Im3, a = 15.009(2) Å, and Z = 2), respectively. Occupations of the centers of Bergman clusters are rare. Such centering and coloring correlate with the sizes of the neighboring icosahedra, the size ratios between electropositive and electronegative components, and the values of the average valence electron count per atom (e/a). Theoretical calculations revealed that all of these phases are Hume-Rothery phases, with evident pseudogaps in the density of states curves that arise from the interactions between Fermi surface and Brillouin zone boundaries corresponding to a strong diffraction intensity. PMID:22862775

  17. Conventional and Stuffed Bergman-Type Phases in the Na-Au-T (T=Ga, Ge, Sn) Systems: Synthesis, Structures, Coloring of Cluster Centers, and Fermi Sphere - Brillouin Zone Interactions

    SciTech Connect

    Lin, Qisheng; Smetana, Volodymur; Miller, Gordon J.; Corbett, John D

    2012-08-03

    Bergman-type phases in the Na−Au−T (T = Ga, Ge, and Sn) systems were synthesized by solid-state means and structurally characterized by single-crystal X-ray diffraction studies. Two structurally related (1/1) Bergman phases were found in the Na− Au−Ga system: (a) a conventional Bergman-type (CB) structure, Na26AuxGa54−x, which features empty innermost icosahedra, as refined with x = 18.1 (3), Im3̅, a = 14.512(2) Å, and Z = 2; (b) a stuffed Bergman-type (SB) structure, Na26AuyGa55−y, which contains Gacentered innermost icosahedra, as refined with y = 36.0 (1), Im3̅, a = 14.597(2) Å, and Z = 2. Although these two subtypes have considerable phase widths along with respective tie lines at Na ≈ 32.5 and 32.1 atom %, they do not merge into a continuous solid solution. Rather, a quasicrystalline phase close to the Au-poor CB phase and an orthorhombic derivative near the Au-rich SB phase lie between them. In contrast, only Au-rich SB phases exist in the Ge and Sn systems, in which the innermost icosahedra are centered by Au rather than Ge or Sn. These were refined for Na26Au40.93(5)Ge14.07(5) (Im3̅, a = 14.581(2) Å, and Z = 2) and Na26Au39.83(6)Sn15.17(6) (Im3̅, a = 15.009(2) Å, and Z = 2), respectively. Occupations of the centers of Bergman clusters are rare. Such centering and coloring correlate with the sizes of the neighboring icosahedra, the size ratios between electropositive and electronegative components, and the values of the average valence electron count per atom (e/a). Theoretical calculations revealed that all of these phases are Hume−Rothery phases, with evident pseudogaps in the density of states curves that arise from the interactions between Fermi surface and Brillouin zone boundaries corresponding to a strong diffraction intensity.

  18. Pseudo Jahn-Teller effect and natural bond orbital analysis of structural properties of tetrahydridodimetallenes M2H4, (M = Si, Ge, and Sn).

    PubMed

    Nori-Shargh, Davood; Mousavi, Seiedeh Negar; Boggs, James E

    2013-02-21

    The structural properties of ethene (1) and tetrahydridodimetallenes M(2)H(4) [M = Si (2), Ge (3), and Sn (4)] have been examined by means of CCSD(T)/Def2-TZVPP, MP4(SDTQ)/Def2-TZVPP, and B3LYP/Def2-TZVPP levels of theory and natural bond orbital analysis (NBO) interpretations. The results obtained showed the expected planar ground state structure for compound 1 (D(2h) symmetry) but trans-bent ground state structures for compounds 2-4 (C(2h) symmetry). The distortions of the high-symmetry configurations of compounds 2-4 are due to the pseudo Jahn-Teller effect (PJTE), which is the only source of instability of high-symmetry configurations in nondegenerate states. The distortions are due to the mixing of the ground A(g) and excited B(2g) states [i.e., HOMO(B(3u)) → LUMO + 3(B(1u)) for compound 1, HOMO(B(3u)) → LUMO + 2(B(1u)) for compound 2, and HOMO(B(3u)) → LUMO + 1(B(1u)) for compounds 3 and 4]. Importantly, the higher-lying B(1g), B(2u), and B(2g) states are not involved in the PJT interactions. The energy gaps between reference states (Δ) in the undistorted configurations decrease from compound 1 to compound 4, and the PJT stabilization energies increase. Therefore, the primary force constant of the ground state in the Q((b2g)) direction (K(0)) decreases from compound 1 to compound 4. This fact can be justified by the valence isoelectronic systems of these compounds (having similar vibronic coupling constants, F). For the purpose of more chemical transparency, the NBO results were analyzed, and their relation to the PJT interactions has been revealed. The NBO analysis showed that stabilization energy associated with π(M-H) (b(u)) → σ*(M═M) (b(u)) electron delocalization (i.e., the mixing of the distorted b(u) molecular orbitals along the b(2g) bending distortions) increases from compound 1 to compound 4. Also, by using the hybridized orbitals obtained, an n parameter is defined. The NBO results revealed that the n values in the mean hybrid orbitals

  19. Tunable electronic properties and low thermal conductivity in synthetic colusites Cu{sub 26−x}Zn{sub x}V{sub 2}M{sub 6}S{sub 32} (x ≤ 4, M = Ge, Sn)

    SciTech Connect

    Suekuni, K. Kim, F. S.; Takabatake, T.

    2014-08-14

    We have first synthesized Cu{sub 26−x}Zn{sub x}V{sub 2}M{sub 6}S{sub 32} (x ≤ 4, M = Ge, Sn) with the cubic colusite structure and measured the thermoelectric properties. For both M = Ge and Sn, the samples with x = 0 show moderately large thermopower of +27 μV/K at 300 K. The metallic conduction of p-type carriers and Pauli-paramagnetic behavior are consistent with the electron-deficient character expected from the formal charge Cu{sub 26}{sup 1+}V{sub 2}{sup 5+}M{sub 6}{sup 4+}S{sub 32}{sup 2−}. The substitution of Zn for Cu results in significant increases in both the electrical resistivity and thermopower. The resistivity of the samples with x = 4 displays a three-dimensional variable-range hopping behavior at low temperatures. These facts indicate that the doped electrons fill the unoccupied states in the valence band and thereby the Fermi level moves to the localized electronic states at the top of the band. The lattice thermal conductivity is as low as ∼1 W/Km at 300 K for all samples. The structural and thermoelectric properties of the colusites are discussed in comparison with those of doped tetrahedrite Cu{sub 12−x}Zn{sub x}Sb{sub 4}S{sub 13}.

  20. A first-principles study on the negative thermal expansion material: Mn3(A0.5B0.5)N (A=Cu, Zn, Ag, or Cd; B=Si, Ge, or Sn)

    NASA Astrophysics Data System (ADS)

    Qu, Bingyan; He, Haiyan; Pan, Bicai

    2016-07-01

    In this paper, using the first-principles calculations, we systemically study the magnetic and the negative thermal expansion (NTE) properties of Mn3(A0.5B0.5)N (A = Cu, Zn, Ag, or Cd; B = Si, Ge, or Sn). From the calculated results, except Mn3(Cu0.5Si0.5)N, all the doped compounds considered would exhibit the NTE. For the dopants at B sites, the working temperature of the NTE shifts to higher temperature range from Si to Sn, and among the compounds with these dopants, Mn3(A0.5Ge0.5)N has the largest amplitude of the NTE coefficient. As to the dopants at A sites, compared to Mn3(Cu0.5B0.5)N, Mn3(A0.5B0.5)N (A = Ag or Cd) exhibit the NTE with higher temperature ranges and lower coefficient of the thermal expansion. In a word, these compounds would have different working temperatures and coefficients of the NTE, which is important for the applications in different conditions.

  1. Molecular structure of trichloroethenylgermane, CH2=CH-GeCl3, as studied by gas-phase electron diffraction. experimental determination of the barrier of internal rotation of the trichlorogermyl group supplemented with quantum chemical calculations on CH2=CH-MX3 (M = C, Si, Ge, Sn, and X = H, Cl).

    PubMed

    Samdal, Svein; Guillemin, Jean-Claude; Gundersen, Snefrid

    2010-06-01

    The molecular structure of trichloroethenylgermane, CH(2)=CH-GeCl(3), has been determined by electron diffraction and supported by quantum chemical calculations on CH(2)=CH-MX(3) (M = C, Si, Ge, Sn and X = H, Cl). An equilibrium syn conformation with C(s) symmetry is obtained both experimentally and theoretically where one of the Ge-Cl bonds eclipses the C=C bond. The barrier of internal rotation about the C-Ge bond is determined to be V(3) = 5.3(7) kJ mol(-1) using a dynamic model to simulate the internal motion. The most important structure parameters (estimated r(e)/A and angle/degree) are: r(C-Ge) = 1.911(5), r(C=C) = 1.345(5), r(Ge-Cl7) = 2.122(2), Ge = 120.4(5), Ge-Cl7 = 111.0(2), and Ge-Cl8) = 109.4(5) where the Cl7 atom is in the C=C-Ge plane and the Cl8 atom is out of the C=C-Ge plane. Uncertainties are estimated total standard deviations (sigma(tot)) given as: sigma(tot) = [sigma(2)(scale) + (2sigma(lsq))(2)](1/2) for bond lengths where sigma(scale) = 0.001r and sigma(lsq) is the least-squares standard deviation using a diagonal weight matrix and sigma(tot) = 2sigma(lsq) for the other parameters. The assignment of some of the fundamental frequencies has been discussed. The internal agreement between the calculated molecular geometry obtained from B3LYP and MP2(F) using the cc-pVQZ basis set and to the experimental geometry is not good, whereas the molecular geometry obtained from a CCSD/cc-pVTZ calculation is in very good agreement with experimental geometry. This investigation shows that the gas electron-diffraction method is capable of determining the rotational barrier for small suitable molecules with acceptable accuracy. PMID:20459079

  2. Field-induced spin-flop in antiferromagnetic semiconductors with commensurate and incommensurate magnetic structures: Li2FeGeS4 (LIGS) and Li2FeSnS4 (LITS).

    PubMed

    Brant, Jacilynn A; dela Cruz, Clarina; Yao, Jinlei; Douvalis, Alexios P; Bakas, Thomas; Sorescu, Monica; Aitken, Jennifer A

    2014-12-01

    Li2FeGeS4 (LIGS) and Li2FeSnS4 (LITS), which are among the first magnetic semiconductors with the wurtz-kesterite structure, exhibit antiferromagnetism with TN ≈ 6 and 4 K, respectively. Both compounds undergo a conventional metamagnetic transition that is accompanied by a hysteresis; a reversible spin-flop transition is dominant. On the basis of constant-wavelength neutron powder diffraction data, we propose that LIGS and LITS exhibit collinear magnetic structures that are commensurate and incommensurate with propagation vectors km = [1/2, 1/2, 1/2] and [0, 0, 0.546(1)], respectively. The two compounds exhibit similar magnetic phase diagrams, as the critical fields are temperature-dependent. The nuclear structures of the bulk powder samples were verified using time-of-flight neutron powder diffraction along with synchrotron X-ray powder diffraction. (57)Fe and (119)Sn Mössbauer spectroscopy confirmed the presence of Fe(2+) and Sn(4+) as well as the number of crystallographically unique positions. LIGS and LITS are semiconductors with indirect and direct bandgaps of 1.42 and 1.86 eV, respectively, according to optical diffuse-reflectance UV-vis-NIR spectroscopy. PMID:25397682

  3. Ab initio CASSCF study of the electronic structure of the transition-metal alkylidene-like complexes Mo-M[prime]H[sub 2] (M[prime] = C, Si, Ge, and Sn)

    SciTech Connect

    Marquez, A.; Sanz, J.F. )

    1992-12-02

    Experimental and theoretical research on the electronic and geometric structure of transition-metal-carbenes and -alkylidenes is an active area in chemistry nowadays due to their potential activity in catalysis and in organic and organometallic synthesis. A theoretical investigation of the electronic structure of the high-valent, transition-metal, alkylidene-like complexes MoM[prime]H[sub 2] (M[prime] = C, Si, Ge, and Sn) is reported. Based on ab initio calculations carried out at the complete active space multiconfiguration self-consistent field (CASSCF) level, the molecular structure of the ground state and some low-lying excited states have been determined. For M[prime] = C, Si, and Ge, the ground state has C[sub 2v] symmetry (state [sup 5]B[sub 1]) and corresponds to pairing each electron of the M[prime]H[sub 2] triplet [sup 3]B[sub 1] with an electron of Mo ([sup 7]S). In the case of MoSnH[sub 2], the lowest state is bent (C[sub s] symmetry, state [sup 7]A[prime]), the out-of-plane angle being 68[degrees], and dissociates into SnH[sub 2] ([sup 1]A[sub 1]) + Mo ([sup 7]S). Dissociation energies, potential energy profiles for the dissociation, harmonic force constants in terms of internal symmetry coordinates, and vibrational frequencies are reported. The comparison of these properties with those of their pentacarbonylated homologous (CO)[sub 5]M[double bond]M[prime]H[sub 2] shows that the carbene-like (Fischer) type of complexation is stronger than the alkylidene-like one (Schrock). 28 refs., 4 figs., 6 tabs.

  4. Local density functional calculations of the electronic structures of the intermetallic systems U{sub 2}Fe{sub 2}Sn and UFe{sub 2}Ge{sub 2}

    SciTech Connect

    Matar, S.F.; Chevalier, B.; Etourneau, J.; Eyert, V.

    1997-02-05

    The electronic structures of U{sub 2}Fe{sub 2}Sn and UFe{sub 2}Ge{sub 2} are self-consistently calculated within the local density functional theory using the augmented spherical wave (ASW) method. Calculations are scalar relativistic. The experimentally observed Pauli paramagnetic behavior of the two systems is accounted for and the influence of hybridization between the different l-states on the chemical bonding is discussed from the site-projected densities of states (DOS) as well as from the modulation of the DOS by the sign and magnitude of the overlap integral, i.e., with the so-called COOP. From this, we propose a mechanism for the evolution of bonding within the series to which the two compounds belong. 12 refs., 3 figs.

  5. SrZn2Sn2 and Ca2Zn3Sn6 — two new Ae-Zn-Sn polar intermetallic compounds (Ae: alkaline earth metal)

    NASA Astrophysics Data System (ADS)

    Stegmaier, Saskia; Fässler, Thomas F.

    2012-08-01

    SrZn2Sn2 and Ca2Zn3Sn6, two closely related new polar intermetallic compounds, were obtained by high temperature reactions of the elements. Their crystal structures were determined with single crystal XRD methods, and their electronic structures were analyzed by means of DFT calculations. The Zn-Sn structure part of SrZn2Sn2 comprises (anti-)PbO-like {ZnSn4/4} and {SnZn4/4} layers. Ca2Zn3Sn6 shows similar {ZnSn4/4} layers and {Sn4Zn} slabs constructed of a covalently bonded Sn scaffold capped by Zn atoms. For both phases, the two types of layers are alternatingly stacked and interconnected via Zn-Sn bonds. SrZn2Sn2 adopts the SrPd2Bi2 structure type, and Ca2Zn3Sn6 is isotypic to the R2Zn3Ge6 compounds (R=La, Ce, Pr, Nd). Band structure calculations indicate that both SrZn2Sn2 and Ca2Zn3Sn6 are metallic. Analyses of the chemical bonding with the electron localization function (ELF) show lone pair like basins at Sn atoms and Zn-Sn bonding interactions between the layers for both title phases, and covalent Sn-Sn bonding within the {Sn4Zn} layers of Ca2Zn3Sn6.

  6. Morphotropy, isomorphism, and polymorphism of Ln{sub 2}M{sub 2}O{sub 7}-based (Ln = La-Lu, Y, Sc; M = Ti, Zr, Hf, Sn) oxides

    SciTech Connect

    Shlyakhtina, A. V.

    2013-07-15

    Structural studies of compounds of variable composition and measurements of their conductivity have made it possible to identify new oxygen-ion-conducting rare-earth pyrochlores, Ln{sub 2}Ti{sub 2}O{sub 7} (Ln = Dy-Lu) and Ln{sub 2}Hf{sub 2}O{sub 7} (Ln = Eu, Gd), with intrinsic high-temperature oxygen ion conductivity (up to 1.4 Multiplication-Sign 10{sup -2} S/cm at 800 Degree-Sign C). Twenty six systems have been studied, and more than 50 phases based on the Ln{sub 2}M{sub 2}O{sub 7} (Ln= La-Lu; M = Ti, Zr, Hf) oxides have been synthesized and shown to be potential oxygen ion conductors. The morphotropy and polymorphism of the Ln{sub 2}M{sub 2}O{sub 7} (Ln = La-Lu; M = Ti, Zr, Hf) rare-earth pyrochlores have been analyzed in detail for the first time. Thermodynamic and kinetic (growth-related) phase transitions have been classified with application to the pyrochlore family.

  7. Effects of cerium substitution on magnetic properties of naturally layered TbMn6Sn6 compound

    NASA Astrophysics Data System (ADS)

    Chen, X. X.; Zhao, M.; Liu, G. Z.; Yao, J. L.; Gao, J.

    2016-04-01

    The Tb1‑xCexMn6Sn6 compounds with x = 0 ‑ 0.3 crystallize in the hexagonal HfFe6Ge6-type structure (space group P6/mmm). The cerium (Ce) substitution for Tb increases the magnetization while reduces the Curie and spin-orientation temperatures. The hard magnetic properties are enhanced by the Ce substitution, e.g., from a coercivity of ˜ 5.4 kOe for TbMn6Sn6 to ˜ 7.6 kOe for the Ce-substituted compounds with x = 0.2 at 5 K. The role of Ce substitution in the magnetocrystalline anisotropy is discussed based on the single-ion anisotropy model. The substitution of Ce for critical rare-earth atoms provides an opportunity of improving hard magnetic properties of the rare-earth-based intermetallics.

  8. Supermarine Spitfire HF VII

    NASA Technical Reports Server (NTRS)

    1944-01-01

    Supermarine Spitfire HF VII: This Supermarine Spitfire HF VII was one of high-altitude versions of the famous fighter, its normal elliptical wingtips replaced by extended 'pointed' tips for its high-altitude role. This is one of the Langley aircraft that has survived. It is in the Smithsonian Institution's National Air and Space Museum's collection.

  9. Composition-tunable Cu2(Ge(1-x),Sn(x))(S(3-y),Se(y)) colloidal nanocrystals: synthesis and characterization.

    PubMed

    Wu, Yihui; Zhou, Bin; Li, Mingrun; Yang, Chi; Zhang, Wen-Hua; Li, Can

    2014-10-28

    A facile colloidal approach was developed to prepare cubic Cu2(Ge1-x,Snx)(S3-y,Sey) nanocrystals (NCs) (0 ≤ x ≤ 1, 0 ≤ y ≤ 3). The band gaps of the NCs can be tuned in the range of 1.35-2.45 eV by varying the chemical compositions, and the NCs display promising applications in solar energy utilization. PMID:25198654

  10. Reaction Mechanism of the Symmetry-Forbidden [2+2] Addition of Ethylene and Acetylene to Amido-Substituted Digermynes and Distannynes Ph2N-EE-NPh2, (E = Ge, Sn): A Theoretical Study.

    PubMed

    Zhao, Lili; Jones, Cameron; Frenking, Gernot

    2015-08-24

    Quantum chemical calculations of reaction mechanisms for the formal [2+2] addition of ethylene and acetylene to the amido-substituted digermyne and distannyne Ph2N-EE-NPh2 (E = Ge, Sn) have been carried out by using density functional theory at the BP86/def2-TZVPP level. The nature and bonding situations were studied with the NBO method and with the charge and energy decomposition analysis EDA-NOCV. The addition of ethylene to Ph2N-EE-NPh2 takes place through an initial [2+1] addition to one metal atom and consecutive rearrangement to four-membered cyclic species, which feature a weak E-E bond. Rotation about the C-C bond with concomitant rupture of the E-E bond leads to the 1,2-disubstituted ethanes, which have terminal E(NPh2) groups. The overall reaction Ph2N-EE-NPh2+C2H4→(Ph2N)E-C2H4-E(NPh2) has very low activation barriers and is slightly exergonic for E = Ge but slightly endergonic for E = Sn. The analysis of the electronic structure shows that there is charge donation of nearly one electron to the ethylene moiety already in the first part of the reaction. The energy partitioning analysis suggests that the HOMO(Ph2N-EE-NPh2)→LUMO(C2H4) interaction has a similar strength as the HOMO(C2H4)→LUMO(Ph2N-EE-NPh2) interaction. The [2+2] addition of acetylene to Ph2N-EE-NPh2 also takes place through an initial [2+1] approach, which eventually leads to 1,2-disubstituted olefins (Ph2N)E-C2H2-E(NPh2). The formation of the energetically lowest lying conformations of cis-(Ph2N)E-C2H2-E(NPh2), which occurs with very low activation barriers, is clearly exergonic for the germanium and the tin compound. The trans-coordinated isomers of (Ph2N)E-C2H2-E(NPh2) are slightly lower in energy than the cis form but they are separated by a substantial energy barrier for the rotation about the C-C bond. The energy decomposition analysis indicates that the initial reaction takes place under formation of electron-sharing bonds between triplet fragments rather than HOMO

  11. Epitaxial growth of Ge1-xSnx films with x up to 0.14 grown on Ge (00l) at low temperature

    NASA Astrophysics Data System (ADS)

    Tao, Ping; Huang, Lei; Cheng, H. H.; Wang, Huan-Hua; Wu, Xiao-Shan

    2014-08-01

    We characterize the structures of Ge1-xSnx films with x up to 0.14 grown on Ge (00l) by molecular-beam epitaxy at low temperature. The results show that Ge1-xSnx films are fully strained even at high Sn composition. The in-plane lattice parameters remain exactly the same as that of the substrate. Depth sensitivity analysis of the lattice parameters indicates that the strains of the epitaxial films are all in homogeneity. The films are fully strained. Poisson ratios, the force constants for the bonds between Ge and Sn are estimated and discussed in the present paper. Raman results show Ge—Ge, Ge—Sn, Sn—Sn vibrational modes. The Sn—Sn bond aggregation may respond to the high quality of our films. The fully strained epitaxy films with high content of Sn may be useful in designing the high quality GeSn films.

  12. Electronic and atomic structures of a Sn induced 3√{ 3} × 3√{ 3} superstructure on the Ag/Ge(111) √{ 3} ×√{ 3} surface

    NASA Astrophysics Data System (ADS)

    Sohail, Hafiz M.; Uhrberg, R. I. G.

    2016-02-01

    We have investigated sub-monolayer coverages of Sn on the Ag/Ge(111) √{ 3} ×√{ 3} surface. It was found that ≈ 0.45 monolayer (ML) resulted in a new, well-defined, reconstruction with a 3√{ 3} × 3√{ 3} periodicity. The periodic structure of the surface atoms was verified by low-energy electron diffraction and scanning tunneling microscopy. The electronic structure was studied in detail using angle-resolved photoelectron spectroscopy and core level spectroscopy at a temperature of 100 K. Several surface bands were identified and their dispersions are presented along the Γbar -Mbar -Γbar and Γbar -Kbar -Mbar high symmetry lines of the 3√{ 3} × 3√{ 3} surface Brillouin zone (SBZ). The 3√{ 3} × 3√{ 3} surface has a metallic character since there is a strong surface band crossing the Fermi level near Γbar points coinciding with Kbar points of the 1 × 1 SBZ. The Fermi contour of the metallic band showed a hexagonal shape in contrast to the circular shaped Fermi contour of the initial √{ 3} ×√{ 3} surface. Both empty and filled state STM images showed a hexagonal arrangement of protrusions with a local √{ 3} ×√{ 3} periodicity and a superimposed modulation of the apparent heights resulting in a 3√{ 3} × 3√{ 3} periodicity.

  13. Hierarchical assembly of Ti(IV)/Sn(II) co-doped SnO₂ nanosheets along sacrificial titanate nanowires: synthesis, characterization and electrochemical properties.

    PubMed

    Wang, Hongkang; Xi, Liujiang; Tucek, Jiri; Zhan, Yawen; Hung, Tak Fu; Kershaw, Stephen V; Zboril, Radek; Chung, C Y; Rogach, Andrey L

    2013-10-01

    Hierarchical assembly of Ti(IV)/Sn(II)-doped SnO₂ nanosheets along titanate nanowires serving as both sacrificial templates and a Ti(IV) source is demonstrated, using SnCl2 as a tin precursor and Sn(II) dopants and NaF as the morphology controlling agent. Excess fluoride inhibits the hydrolysis of SnCl2, promoting heterogeneous nucleation of Sn(II)-doped SnO₂ on the titanate nanowires due to the insufficient oxidization of Sn(II) to Sn(IV). Simultaneously, titanate nanowires are dissolved forming Ti(4+) species under the etching effect of in situ generated HF resulting in spontaneous Ti(4+) ion doping of SnO₂ nanosheets formed under hydrothermal conditions. Compositional analysis indicates that Ti(4+) ions are incorporated by substitution of Sn sites at a high level (16-18 at.%), with uniform distribution and no phase separation. Mössbauer spectroscopy quantified the relative content of Sn(II) and Sn(IV) in both Sn(II)-doped and Ti(IV)/Sn(II) co-doped SnO₂ samples. Electrochemical properties were investigated as an anode material in lithium ion batteries, demonstrating that Ti-doped SnO₂ nanosheets show improved cycle performance, which is attributed to the alleviation of inherent volume expansion of the SnO₂-based anode materials by substituting part of Sn sites with Ti dopants. PMID:23904051

  14. Experimental and theoretical characterization of MSi16(-), MGe16(-), MSn16(-), and MPb16(-) (M = Ti, Zr, and Hf): the role of cage aromaticity.

    PubMed

    Furuse, Shunsuke; Koyasu, Kiichirou; Atobe, Junko; Nakajima, Atsushi

    2008-08-14

    Silicon (Si), germanium (Ge), tin (Sn), and lead (Pb) clusters mixed with a group-4 transition metal atom [M = titanium (Ti), zirconium (Zr), and hafnium (Hf)] were generated by a dual-laser vaporization method, and their properties were analyzed by means of time-of-flight mass spectroscopy and anion photoelectron spectroscopy together with theoretical calculations. In the mass spectra, mixed neutral clusters of MSi(16), MGe(16), and MSn(16) were produced specifically, but the yield of MPb(16) was low. The anion photoelectron spectra revealed that MSi(16), MGe(16), and MSn(16) neutrals have large highest occupied molecular orbital-lowest unoccupied molecular orbital gaps of 1.5-1.9 eV compared to those of MPb(16) (0.8-0.9 eV), implying that MSi(16), MGe(16), and MSn(16) are evidently electronically stable clusters. Cage aromaticity appears to be an important determinant of the electronic stability of these clusters: Calculations of nucleus-independent chemical shifts (NICSs) show that Si(16)(4-), Ge(16)(4-), and Sn(16)(4-) have aromatic characters with negative NICS values, while Pb(16)(4-) has an antiaromatic character with a positive NICS value. PMID:18715073

  15. Mechanisms for the reactions of group 10 transition metal complexes with metal-group 14 element bonds, Bbt(Br)E═M(PCy3)2 (E = C, Si, Ge, Sn, Pb; M = Pd and Pt).

    PubMed

    Liao, Wei-Hung; Ho, Pei-Yun; Su, Ming-Der

    2013-02-01

    The electronic structures of the Bbt(Br)E═M(PCy(3))(2) (E = C, Si, Ge, Sn, Pb and M = Pt, Pd) complexes and their potential energy surfaces for the formation and water addition reactions were studied using density functional theory (B3LYP/LANL2DZ). The theoretical evidence suggests that the bonding character of the E═M double bond between the six valence-electron Bbt(Br)E: species and the 14 valence-electron (PCy(3))(2)M complexes has a predominantly high s-character. That is, on the basis of the NBO, this theoretical study indicates that the σ-donation from the E element to the M atom prevails. Also, theoretical computations suggest that the relative reactivity decreases in the order: Bbt(Br)C═M(PCy(3))(2) > Bbt(Br)Si═M(PCy(3))(2) > Bbt(Br)Ge═M(PCy(3))(2) > Bbt(Br)Sn═M(PCy(3))(2) > Bbt(Br)Pb═M(PCy(3))(2), irrespective of whether M = Pt or M = Pd is chosen. Namely, the greater the atomic weight of the group 14 atom (E), the larger is the atomic radius of E and the more stable is its Bbt(Br)E═M(PCy(3))(2) doubly bonded species toward chemical reactions. The computational results show good agreement with the available experimental observations. The theoretical results obtained in this work allow a number of predictions to be made. PMID:23339483

  16. Development of epitaxial growth technology for Ge1-xSnx alloy and study of its properties for Ge nanoelectronics

    NASA Astrophysics Data System (ADS)

    Nakatsuka, Osamu; Shimura, Yosuke; Takeuchi, Wakana; Taoka, Noriyuki; Zaima, Shigeaki

    2013-05-01

    We have recently developed an epitaxial growth technique for Ge1-xSnx layers with an especially high Sn content, and we investigated the crystalline properties of the Ge1-xSnx epitaxial layers. In this report, we describe our recent achievements for improving the crystalline quality of the epitaxial growth of Ge1-xSnx layers on various substrates. We also demonstrate the impacts of Sn incorporation on the defect and dopant behaviors and electrical properties of Ge1-xSnx epitaxial layers. Sn incorporation improves on the issue of unintentional hole generation due to vacancy defects and enhances the dopant activation of Ga atoms in the Ge matrix. In addition, we introduce a recent study of the optical properties of Ge1-xSnx epitaxial layers with very high Sn contents.

  17. Electronic, optical, structural, and elastic properties of MAX phases and (Cr2Hf)2Al3C3

    NASA Astrophysics Data System (ADS)

    Mo, Yuxiang

    The term "MAX phase" refers to a very interesting and important class of layered ternary transition-metal carbides and nitrides with a novel combination of both metal- and ceramic-like properties that have made these materials highly regarded candidates for numerous technological and engineering applications. In the present dissertation work, the electronic structure and optical conductivities of 20 MAX phases Ti3AC2 (A = Al, Si, Ge), Ti2AC (A = Al, Ga, In, Si, Ge, Sn, P, As, S), Ti2AlN, M2AlC (M = V, Nb, Cr), and Tan+1AlC n (n = 1 to 4) are studied using the first-principles orthogonalized linear combination of atomic orbitals (OLCAO) method. It is confirmed that the N(Ef) (total density of states at the Fermi level Ef) increases as the number of valence electrons of the composing elements increases. The local feature of total density of states (TDOS) near Ef is used to predict structural stability. The calculated effective charge on each atom shows that the M (transition-metal) atoms always lose charge to the X (C or N) atoms, whereas the A-group atoms mostly gain charge but some lose charge. Bond order values are obtained and critically analyzed for all types of interatomic bonds in the 20 MAX phases. Also included in this work is the exploration [using (Cr2Hf)2Al3C3 as an example] of the possibility of incorporating more types of elements into a MAX phase while maintaining the crystallinity, instead of creating solid solution phases. The crystal structure and elastic properties of (Cr2Hf)2Al 3C3 are studied using the Vienna ab initio Simulation Package. Unlike MAX phases with a hexagonal symmetry ( P63/mmc, #194), (Cr 2Hf)2Al3C3 crystallizes in the monoclinic space group of P21/m (#11). Its structure is found to be energetically much more favorable against the allotropic segregation and solid solution phases. Calculations using a stress versus strain approach and the VRH approximation for polycrystals also show that (Cr2Hf)2Al3C3 has outstanding elastic moduli.

  18. Large grain growth of Ge-rich Ge1-xSnx (x ≈ 0.02) on insulating surfaces using pulsed laser annealing in flowing water

    NASA Astrophysics Data System (ADS)

    Kurosawa, Masashi; Taoka, Noriyuki; Ikenoue, Hiroshi; Nakatsuka, Osamu; Zaima, Shigeaki

    2014-02-01

    We investigate Sn incorporation effects on the growth characteristics of Ge-rich Ge1-xSnx (x < 0.02) on SiO2 crystallized by pulsed laser annealing (PLA) in air and water. Despite the very low Sn content of 2%, Sn atoms within the GeSn layers play a role in preventing ablation and aggregation of the layers during these PLA. Raman and electron backscatter diffraction measurements demonstrate achievement of large-grain (˜800 nmϕ) growth of Ge0.98Sn0.02 polycrystals by using PLA in water. These polycrystals also show a tensile-strain of ˜0.68%. This result opens up the possibility for developing GeSn-based devices fabricated on flexible substrates as well as Si platforms.

  19. First-Principles Study of Electronic Structure and Thermoelectric Properties of Ge-Doped Tin Clathrates

    NASA Astrophysics Data System (ADS)

    Akai, K.; Kishimoto, K.; Koyanagi, T.; Kono, Y.; Yamamoto, S.

    2014-06-01

    We calculated the electronic structure and thermoelectric properties of the Ge-doped quaternary clathrate Ba-Ga-Sn-Ge. The electronic structure was calculated by using the WIEN2k code, which is based on the full-potential augmented plane-wave method. Using this method, we calculated the total energies for several Ge configurations to determine the positions of Ge atoms in the unit cell. The calculated Ge positions were in good agreement with the experimental results. Based on the resulting Ge positions, the band structure and thermoelectric properties of the Ba-Ga-Sn-Ge clathrates were calculated.

  20. Study of HfO2 films deposited on strained Si1-xGex layers by atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Damlencourt, J.-F.; Weber, O.; Renault, O.; Hartmann, J.-M.; Poggi, C.; Ducroquet, F.; Billon, T.

    2004-11-01

    This paper focuses on the growth of HfO2 by atomic layer deposition (ALD) at 350°C on pseudomorphic Si1-xGex thin films (x =15% and 25%). Two different Si1-xGex surface preparations (chemical oxidation and HF "last" treatment) have been investigated to obtain the highest HfO2 film quality with the thinnest interfacial layer possible. The initial stages of the ALD growth on these different surfaces (i.e., hafnium adsorption and chlorine contamination) analyzed by total x-ray fluorescence show that HF last treated Si1-xGex surfaces are more convenient than chemically oxidized ones to grow high quality HfO2 layers. This result is confirmed by x-ray photoelectron spectroscopy investigations of the interfacial layer structure as a function of the surface treatment. As-deposited and annealed thin HfO2 layers (2.5, 3.5, 5, and 8nm) grown on HF last treated Si0.75Ge0.25 strained layers were analyzed by mercury probe. An equivalent oxide thickness as low as 0.7nm was obtained for a 2.5nm as-deposited HfO2 film. Mobility results show that a 22% mobility enhancement is obtained in the entire effective field range with HfO2/SiGe compared to the HfO2/Si reference.

  1. Effects of metal/Ge contact and surface passivation on direct band gap light emission and detection for asymmetric metal/Ge/metal diodes

    NASA Astrophysics Data System (ADS)

    Maekura, Takayuki; Yamamoto, Keisuke; Nakashima, Hiroshi; Wang, Dong

    2016-04-01

    Direct band gap electroluminescence (EL) and light detection were studied at room temperature for n-type bulk germanium (Ge) by using fin-type asymmetric lateral metal/Ge/metal diodes. HfGe/Ge and PtGe/Ge contacts were used for injecting holes. Electron cyclotron resonance plasma oxidation and physical vapor deposition bilayer passivation (BLP) methods were employed for passivating the surface of the active region. A high EL intensity and a low dark current intensity were observed for the sample with PtGe/Ge contact and BLP, owing to the small/large barrier height of holes/electrons for PtGe/Ge contact, respectively, and the low density of interface states for the active region with BLP. The local-heating-induced redshift of the EL peak for the sample with PtGe/Ge contact is smaller than that for the sample with HfGe/Ge contact, owing to the lower parasitic resistance of PtGe/Ge contact. The diode with PtGe/Ge contact and BLP shows an on/off ratio of ∼104 and a responsivity of 0.70 A/W, corresponding to an external quantum efficiency of 56.0% under a wavelength of 1.55 µm.

  2. Characterization of locally strained Ge1-xSnx/Ge fine structures by synchrotron X-ray microdiffraction

    NASA Astrophysics Data System (ADS)

    Ike, Shinichi; Nakatsuka, Osamu; Moriyama, Yoshihiko; Kurosawa, Masashi; Taoka, Noriyuki; Imai, Yasuhiko; Kimura, Shigeru; Tezuka, Tsutomu; Zaima, Shigeaki

    2015-05-01

    We have investigated the formation of the locally strained Ge nanostructure with epitaxial Ge1-xSnx stressors and characterized the microscopic strain field in the Ge1-xSnx/Ge fine-heterostructures by synchrotron X-ray microdiffraction and finite element method (FEM) calculations. We achieved local epitaxial growth of Ge1-xSnx with Sn contents of 2.9% and 6.5%, sandwiching the 25 nm-wide Ge fine line structure. Microdiffraction measurements revealed that out-of-plane tensile strain induced in the Ge line effectively increased with decreasing Ge width and increasing Sn content of Ge1-xSnx stressors, which is in good agreement with FEM calculations. An out-of-plane tensile strain of 0.8% along the Ge[001] direction is induced in a 25 nm-wide Ge line, which corresponds to an in-plane uniaxial compressive strain of 1.4% in the Ge line sandwiched between Ge0.935Sn0.065 stressors.

  3. Structural Changes of Amorphous Ge1-xSnx Alloy Films by Annealing

    NASA Astrophysics Data System (ADS)

    Fukumoto, Hirofumi; Myoren, Hiroaki; Nakashita, Toshio; Imura, Takeshi; Osaka, Yukio

    1986-09-01

    Microcrystalline (μc-) grains of Ge1-ySny (0.1≲ y≲ 0.4) were precipitated by thermal treatments of amorphous films of a Ge1-xSnx(x≲ 0.4) alloy deposited by co-sputtering. At higher temperatures grains of β-Sn came out, co-existing with those of μc-Ge1-ySny. Mössbauer spectroscopy was used to characterize states of Sn in a Ge-Sn alloy film. Optical properties, such as the real part \\varepsilon1 of the complex dielectric constant for Ge0.65Sn0.35, also changed as the structure change, especially at a photon energy of 1.6˜ 1.8 eV, where \\varepsilon1 took a maximum. It was suggested that an amorphous Ge-Sn alloy might be a good material for archival-type optical storage.

  4. Pulsed inductive HF laser

    NASA Astrophysics Data System (ADS)

    Razhev, A. M.; Churkin, D. S.; Kargapol'tsev, E. S.; Demchuk, S. V.

    2016-03-01

    We report the results of experimentally investigated dependences of temporal, spectral and spatial characteristics of an inductive HF-laser generation on the pump conditions. Gas mixtures H2 – F2(NF3 or SF66) and He(Ne) – H2 – F2(NF3 or SF6) were used as active media. The FWHM pulse duration reached 0.42 μs. This value corresponded to a pulsed power of 45 kW. For the first time, the emission spectrum of an inductive HF laser was investigated, which consisted of seven groups of bands with centres around the wavelengths of 2732, 2736, 2739, 2835, 2837, 2893 and 2913 nm. The cross section profile of the laser beam was a ring with a diameter of about 20 mm and width of about 5 mm. Parameters of laser operation in the repetitively pulsed regime were sufficiently stable. The amplitude instability of light pulses was no greater than 5% – 6%.

  5. Hierarchical assembly of Ti(iv)/Sn(ii) co-doped SnO2 nanosheets along sacrificial titanate nanowires: synthesis, characterization and electrochemical properties

    NASA Astrophysics Data System (ADS)

    Wang, Hongkang; Xi, Liujiang; Tucek, Jiri; Zhan, Yawen; Hung, Tak Fu; Kershaw, Stephen V.; Zboril, Radek; Chung, C. Y.; Rogach, Andrey L.

    2013-09-01

    Hierarchical assembly of Ti(iv)/Sn(ii)-doped SnO2 nanosheets along titanate nanowires serving as both sacrificial templates and a Ti(iv) source is demonstrated, using SnCl2 as a tin precursor and Sn(ii) dopants and NaF as the morphology controlling agent. Excess fluoride inhibits the hydrolysis of SnCl2, promoting heterogeneous nucleation of Sn(ii)-doped SnO2 on the titanate nanowires due to the insufficient oxidization of Sn(ii) to Sn(iv). Simultaneously, titanate nanowires are dissolved forming Ti4+ species under the etching effect of in situ generated HF resulting in spontaneous Ti4+ ion doping of SnO2 nanosheets formed under hydrothermal conditions. Compositional analysis indicates that Ti4+ ions are incorporated by substitution of Sn sites at a high level (16-18 at.%), with uniform distribution and no phase separation. Mössbauer spectroscopy quantified the relative content of Sn(ii) and Sn(iv) in both Sn(ii)-doped and Ti(iv)/Sn(ii) co-doped SnO2 samples. Electrochemical properties were investigated as an anode material in lithium ion batteries, demonstrating that Ti-doped SnO2 nanosheets show improved cycle performance, which is attributed to the alleviation of inherent volume expansion of the SnO2-based anode materials by substituting part of Sn sites with Ti dopants.Hierarchical assembly of Ti(iv)/Sn(ii)-doped SnO2 nanosheets along titanate nanowires serving as both sacrificial templates and a Ti(iv) source is demonstrated, using SnCl2 as a tin precursor and Sn(ii) dopants and NaF as the morphology controlling agent. Excess fluoride inhibits the hydrolysis of SnCl2, promoting heterogeneous nucleation of Sn(ii)-doped SnO2 on the titanate nanowires due to the insufficient oxidization of Sn(ii) to Sn(iv). Simultaneously, titanate nanowires are dissolved forming Ti4+ species under the etching effect of in situ generated HF resulting in spontaneous Ti4+ ion doping of SnO2 nanosheets formed under hydrothermal conditions. Compositional analysis indicates that Ti4

  6. Discovery of Nuwaite, Ni6GeS2, a New Alteration Mineral in Allende

    NASA Astrophysics Data System (ADS)

    Ma, C.

    2015-07-01

    Nuwaite is likely the first solar mineral with high Ge, Sn and Te concentrations. It is a late-stage alteration product, probably derived from a sulfidation process, where Ni-Fe metals react with a low-temperature fluid enriched in S, Ge, Sn and Te.

  7. Ge1-xSnx alloys pseudomorphically grown on Ge(001)

    NASA Astrophysics Data System (ADS)

    Ladrón de Guevara, H. Pérez; Rodríguez, A. G.; Navarro-Contreras, H.; Vidal, M. A.

    2003-12-01

    Ge1-xSnx alloys were grown on Ge(001) substrates in a conventional rf sputtering system. We determined the in-plane and in-growth lattice parameters, as well as the alloy bulk lattice parameter of the alloys for different Sn concentrations by high resolution x-ray diffraction. The Sn concentration was determined assuming Vegard's law for the alloy lattice parameter. At low concentrations, we observed that Ge1-xSnx layers have pseudomorphic characteristics for layer thickness from 320 to 680 nm. These characteristics of Ge1-xSnx layers agree with the People and Bean critical thickness model. This structural study opens the possibility of growing dislocation-free Ge1-xSnx alloys below the critical thickness.

  8. The Likely Fermi Detection of the Supernova Remnant SN 1006

    NASA Astrophysics Data System (ADS)

    Xing, Yi; Wang, Zhongxiang; Zhang, Xiao; Chen, Yang

    2016-05-01

    We report the likely detection of γ-ray emission from the northeast shell region of the historical supernova remnant (SNR) SN 1006. Having analyzed seven years of Fermi Large Area Telescope Pass 8 data for the region of SN 1006, we found a GeV gamma-ray source detected with ∼ 4σ significance. Both the position and spectrum of the source match those of HESS J1504‑418, respectively, which is TeV emission from SN 1006. Considering the source as the GeV γ-ray counterpart to SN 1006, the broadband spectral energy distribution is found to be approximately consistent with the leptonic scenario that has been proposed for the TeV emission from the SNR. Our result has likely confirmed the previous study of the SNRs with TeV shell-like morphology: SN 1006 is one of them sharing very similar peak luminosity and spectral shape.

  9. Marburg Hemorrhagic Fever (Marburg HF)

    MedlinePlus

    ... The CDC Cancel Submit Search The CDC Marburg hemorrhagic fever (Marburg HF) Note: Javascript is disabled or is ... was first recognized in 1967, when outbreaks of hemorrhagic fever occurred simultaneously in laboratories in Marburg and Frankfurt, ...

  10. Raman scattering from fully strained Ge1-xSnx (x<=0.22) alloys grown on Ge(001)2×1 by low-temperature molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Rojas-López, M.; Navarro-Contreras, H.; Desjardins, P.; Gurdal, O.; Taylor, N.; Carlsson, J. R. A.; Greene, J. E.

    1998-08-01

    Fully strained single-crystal Ge1-xSnx alloys (x⩽0.22) deposited on Ge(001)2×1 by low-temperature molecular beam epitaxy have been studied by Raman scattering. The results are characterized by a Ge-Ge longitudinal optical (LO) phonon line, which shifts to lower frequencies with increasing x. Samples capped with a 200-Å-thick Ge layer exhibit a second Ge-Ge LO phonon line whose position remains close to that expected from bulk Ge. For all samples, capped and uncapped, the frequency shift ΔωGeSn of the Ge-Ge LO phonon line from the Ge1-xSnx layer, with respect to the position for bulk Ge, is linear with the Sn fraction x (ΔωGeSn=-76.8x cm-1) over the entire composition range. Using the elastic constants, the Grüneisen parameter, and the shear phonon deformation parameter for Ge, we calculate the contribution of compressive strain to the total frequency shift to be Δωstrain=63.8x cm-1. Thus, the LO phonon shift in Ge1-xSnx due to substitutional-Sn-induced bond stretching in fully relaxed alloys is estimated to be Δωbond =-140.6x cm-1.

  11. Properties of slow traps of ALD Al2O3/GeOx/Ge nMOSFETs with plasma post oxidation

    NASA Astrophysics Data System (ADS)

    Ke, M.; Yu, X.; Chang, C.; Takenaka, M.; Takagi, S.

    2016-07-01

    The realization of Ge gate stacks with a small amount of slow trap density as well as thin equivalent oxide thickness and low interface state density (Dit) is a crucial issue for Ge CMOS. In this study, we examine the properties of slow traps, particularly the location of slow traps, of Al2O3/GeOx/n-Ge and HfO2/Al2O3/GeOx/n-Ge MOS interfaces with changing the process and structural parameters, formed by atomic layer deposition (ALD) of Al2O3 and HfO2/Al2O3 combined with plasma post oxidation. It is found that the slow traps can locate in the GeOx interfacial layer, not in the ALD Al2O3 layer. Furthermore, we study the time dependence of channel currents in the Ge n-MOSFETs with 5-nm-thick Al2O3/GeOx/Ge gate stacks, with changing the thickness of GeOx, in order to further clarify the position of slow traps. The time dependence of the current drift and the effective time constant of slow traps do not change among the MOSFETs with the different thickness GeOx, demonstrating that the slow traps mainly exist near the interfaces between Ge and GeOx.

  12. Deposition of HfO2 on germanium and the impact of surface pretreatments

    NASA Astrophysics Data System (ADS)

    Van Elshocht, S.; Brijs, B.; Caymax, M.; Conard, T.; Chiarella, T.; De Gendt, S.; De Jaeger, B.; Kubicek, S.; Meuris, M.; Onsia, B.; Richard, O.; Teerlinck, I.; Van Steenbergen, J.; Zhao, C.; Heyns, M.

    2004-10-01

    The deposition behavior of HfO2 by metalorganic chemical vapor deposition on germanium has been investigated. HfO2 films can be deposited on Ge with equally good quality as compared to high-k growth on silicon. Surface preparation is very important: compared to an HF-last, NH3 pretreatments result in smoother films with strongly reduced diffusion of germanium in the HfO2 film, resulting in a much better electrical performance. We clearly show that much thinner interfacial layers can be obtained, approximately half the thickness of what is typically found for depositions on silicon, suggesting the possibility of more aggressive equivalent oxide thickness/leakage scaling.

  13. Development of NTD Ge Sensors for Superconducting Bolometer

    NASA Astrophysics Data System (ADS)

    Garai, A.; Mathimalar, S.; Singh, V.; Dokania, N.; Nanal, V.; Pillay, R. G.; Ramakrishnan, S.; Shrivastava, A.; Jagadeesan, K. C.; Thakare, S. V.

    2016-08-01

    Neutron transmutation-doped (NTD) Ge sensors have been prepared by irradiating device-grade Ge with thermal neutrons at Dhruva reactor, BARC, Mumbai. These sensors are intended to be used for the study of neutrinoless double beta decay in ^{124}Sn with a superconducting Tin bolometer. Resistance measurements are performed on NTD Ge sensors in the temperature range 100-350 mK. The observed temperature dependence is found to be consistent with the variable-range hopping mechanism.

  14. Generalized current-voltage analysis and efficiency limitations in non-ideal solar cells: Case of Cu2ZnSn(SxSe1-x)4 and Cu2Zn(SnyGe1-y)(SxSe1-x)4

    NASA Astrophysics Data System (ADS)

    Hages, Charles J.; Carter, Nathaniel J.; Agrawal, Rakesh; Unold, Thomas

    2014-06-01

    Detailed electrical characterization of nanoparticle based Cu2ZnSn(SxSe1-x)4 (CZTSSe) and Cu2Zn(SnyGe1-y)(SxSe1-x)4 (CZTGeSSe) solar cells has been conducted to understand the origin of device limitations in this material system. Specifically, temperature dependent current-voltage analysis has been considered, with particular application to the characterization of solar cells with non-ideal device behavior. Due to the presence of such non-ideal device behavior, typical analysis techniques—commonly applied to kesterite-type solar cells—are found to be insufficient to understand performance limitations, and an analysis methodology is presented to account for the non-idealities. Here, the origin of non-ideal device behavior is chiefly considered in terms of electrostatic and band gap potential fluctuations, low minority carrier lifetimes, temperature dependent band edges, high surface/bulk recombination rates, and tunneling enhanced recombination. For CZTSSe and CZTGeSSe, the main limitations to improved device performance (voltage limitations) are found to be associated with significant EA deficits (EA-EG) at 300 K, large ideality factors, and voltage-dependent carrier collection, which we associate with the bulk material properties of the absorbers. The material origin of these non-ideal electrical properties is considered. Additionally, for CZTGeSSe, the effect of Ge-incorporation on the electrical properties of the solar cells is discussed, with improvements in the electrical properties characterized for the Ge-alloyed devices.

  15. Synthesis of the first fluoro(phosphanyl)- and diphosphanyl-stannanes and surprising formation of [P(SnMe3)4]+ SiF5-.

    PubMed

    Driess, Matthias; Merz, Klaus; Monsé, Christian

    2003-10-21

    Monophosphanylation of the difluorostannane Is2SnF2 (Is = 2,4,6-triisopropylphenyl) with Si(PH2)4 furnishes the first isolable fluoro(phosphanyl)stannane Is2Sn(F)PH2 1, which readily undergoes unique SiO2-assisted decompostion to [Is2Sn(PH)]2 2 and HF, while further phosphanylation of 1 leads to the remarkably stable diphosphanylstannane Is2Sn(PH2)2 3; the latter reacts with Me3SnF at the glass-wall to give the first perstannylphosphonium pentafluorosilicate [P(SnMe3)4]+ SiF5- 4. PMID:14594304

  16. SrZn{sub 2}Sn{sub 2} and Ca{sub 2}Zn{sub 3}Sn{sub 6} - two new Ae-Zn-Sn polar intermetallic compounds (Ae: alkaline earth metal)

    SciTech Connect

    Stegmaier, Saskia; Faessler, Thomas F.

    2012-08-15

    SrZn{sub 2}Sn{sub 2} and Ca{sub 2}Zn{sub 3}Sn{sub 6}, two closely related new polar intermetallic compounds, were obtained by high temperature reactions of the elements. Their crystal structures were determined with single crystal XRD methods, and their electronic structures were analyzed by means of DFT calculations. The Zn-Sn structure part of SrZn{sub 2}Sn{sub 2} comprises (anti-)PbO-like {l_brace}ZnSn{sub 4/4}{r_brace} and {l_brace}SnZn{sub 4/4}{r_brace} layers. Ca{sub 2}Zn{sub 3}Sn{sub 6} shows similar {l_brace}ZnSn{sub 4/4}{r_brace} layers and {l_brace}Sn{sub 4}Zn{r_brace} slabs constructed of a covalently bonded Sn scaffold capped by Zn atoms. For both phases, the two types of layers are alternatingly stacked and interconnected via Zn-Sn bonds. SrZn{sub 2}Sn{sub 2} adopts the SrPd{sub 2}Bi{sub 2} structure type, and Ca{sub 2}Zn{sub 3}Sn{sub 6} is isotypic to the R{sub 2}Zn{sub 3}Ge{sub 6} compounds (R=La, Ce, Pr, Nd). Band structure calculations indicate that both SrZn{sub 2}Sn{sub 2} and Ca{sub 2}Zn{sub 3}Sn{sub 6} are metallic. Analyses of the chemical bonding with the electron localization function (ELF) show lone pair like basins at Sn atoms and Zn-Sn bonding interactions between the layers for both title phases, and covalent Sn-Sn bonding within the {l_brace}Sn{sub 4}Zn{r_brace} layers of Ca{sub 2}Zn{sub 3}Sn{sub 6}. - Graphical abstract: Crystal structures of the new Ae-Zn-Sn polar intermetallic phases SrZn{sub 2}Sn{sub 2} and Ca{sub 2}Zn{sub 3}Sn{sub 6}. Highlights: Black-Right-Pointing-Pointer New polar intermetallic phases SrZn{sub 2}Sn{sub 2} and Ca{sub 2}Zn{sub 3}Sn{sub 6}. Black-Right-Pointing-Pointer Obtained by high temperature reactions of the elements. Black-Right-Pointing-Pointer Single crystal XRD structure determination and DFT electronic structure calculations. Black-Right-Pointing-Pointer Closely related crystal and electronic structures. Black-Right-Pointing-Pointer Metallic conductivity coexisting with lone pairs and covalent bonding

  17. Electrical properties of magnesium oxide layers with different surface pretreatment on high mobility Ge1-xSnx and Ge MOS capacitors

    NASA Astrophysics Data System (ADS)

    Su, Chen-Yi; Lieten, Ruben; Bakalov, Petar; Tseng, Wei-Jhih; Dillemans, Leander; Menghini, Mariela; Smets, Tomas; Seo, Jin Won; Locquet, Jean-Pierre

    2014-02-01

    Germanium based channels are interesting for high performance CMOS devices because of their high carrier mobility. In this study, the electrical properties of MgO on both GeSn and Ge MOS capacitors have been investigated. The low equivalent oxide thickness (EOT) of 2.1 nm for MgO on GeSn with a Ge cap layer indicates the high potential for MOSFET applications. A surface treatment prior to oxide deposition is found essential to reduce the gate leakage. It is shown that HCl and H2O2 dipping followed by ozone treatment improves the leakage and leads to good capacitance-voltage (C-V) behavior.

  18. Few-layer SnSe2 transistors with high on/off ratios

    NASA Astrophysics Data System (ADS)

    Pei, Tengfei; Bao, Lihong; Wang, Guocai; Ma, Ruisong; Yang, Haifang; Li, Junjie; Gu, Changzhi; Pantelides, Sokrates; Du, Shixuan; Gao, Hong-jun

    2016-02-01

    We report few-layer SnSe2 field effect transistors (FETs) with high current on/off ratios. By trying different gate configurations, 300 nm SiO2 and 70 nm HfO2 as back gate only and 70 nm HfO2 as back gate combined with a top capping layer of polymer electrolyte, few-layer SnSe2 FET with a current on/off ratio of 104 can be obtained. This provides a reliable solution for electrically modulating quasi-two-dimensional materials with high electron density (over 1013 cm-2) for field-effect transistor applications.

  19. Ge1-xSnx alloys synthesized by ion implantation and pulsed laser melting

    NASA Astrophysics Data System (ADS)

    Gao, Kun; Prucnal, S.; Huebner, R.; Baehtz, C.; Skorupa, I.; Wang, Yutian; Skorupa, W.; Helm, M.; Zhou, Shengqiang

    2014-07-01

    The tunable bandgap and the high carrier mobility of Ge1-xSnx alloys stimulate a large effort for bandgap and strain engineering for Ge based materials using silicon compatible technology. In this Letter, we present the fabrication of highly mismatched Ge1-xSnx alloys by ion implantation and pulsed laser melting with Sn concentration ranging from 0.5 at. % up to 1.5 at. %. According to the structural investigations, the formed Ge1-xSnx alloys are monocrystalline with high Sn-incorporation rate. The shrinkage of the bandgap of Ge1-xSnx alloys with increasing Sn content is proven by the red-shift of the E1 and E1 + Δ1 critical points in spectroscopic ellipsometry. Our investigation provides a chip technology compatible route to prepare high quality monocrystalline Ge1-xSnx alloys.

  20. HfS: Hyperfine Structure fitting tool

    NASA Astrophysics Data System (ADS)

    Estalella, Robert

    2016-07-01

    HfS fits the hyperfine structure of spectral lines, with multiple velocity components. The HfS_nh3 procedures included in HfS fit simultaneously the hyperfine structure of the NH3 (J,K)= (1,1) and (2,2) inversion transitions, and perform a standard analysis to derive the NH3 column density, rotational temperature Trot, and kinetic temperature Tk. HfS uses a Monte Carlo approach for fitting the line parameters, with special attention to the derivation of the parameter uncertainties. HfS includes procedures that make use of parallel computing for fitting spectra from a data cube.

  1. Stark shift of the absorption spectra in Ge/Ge1-xSnx/Ge type-I single QW cell for mid-wavelength infra-red modulators

    NASA Astrophysics Data System (ADS)

    Yahyaoui, N.; Sfina, N.; Lazzari, J.-L.; Bournel, A.; Said, M.

    2015-09-01

    For mid-wavelength infra-red (MWIR) modulation or detection applications, we propose α-Sn rich Ge/Ge1-xSnx/Ge a type-I single quantum wells (SQW) partially strain compensated on Ge1-ySny relaxed layers grown onto (0 0 1)-oriented Ge substrate. Such elementary cells with W-like potential profiles of conduction and valence bands have been modeled by solving the one-dimensional Schrödinger equation under an applied external electrical field. First, strain effects on electrons, heavy holes (hh) and light holes (lh) energy bands for strained/relaxed Ge1-xSnx/Ge1-ySny heterointerfaces are investigated using the model-solid theory in the whole ranges (0 ⩽ x, y ⩽ 1) of Sn compositions. From the obtained band-discontinuities, band gaps and effective masses, Ge1-ySny/Ge/Ge0.80Sn0.20/Ge/Ge1-ySny cells are computed as a function of the Ge0.80Sn0.20 well width for three compositions of the Ge1-ySny buffer layer (y = 0.05, 0.07 and 0.09) in order to get the optimum quantum confinement of electrons and holes levels while keeping a reasonable amount of averaged strain in the cell. The electric field effect on the absorption spectra is given. An absorption coefficient in the 6× to 3 × 103 cm-1 range is reasonably obtained for a SQW at room temperature with a rather large Stark shift of the direct transition between 0.46 and 0.38 eV (i.e., λ = 3.26-2.70 μm) at large external fields (50 kV/cm). These characteristics are attractive for the design of MWIR optical modulators.

  2. Chemical Bonding, Interfaces and Defects in Hafnium Oxide/Germanium Oxynitride Gate Stacks on Ge (100)

    SciTech Connect

    Oshima, Yasuhiro; Sun, Yun; Kuzum, Duygu; Sugawara, Takuya; Saraswat, Krishna C.; Pianetta, Piero; McIntyre, Paul C.; /Stanford U., Materials Sci. Dept.

    2008-10-31

    Correlations among interface properties and chemical bonding characteristics in HfO{sub 2}/GeO{sub x}N{sub y}/Ge MIS stacks were investigated using in-situ remote nitridation of the Ge (100) surface prior to HfO{sub 2} atomic layer deposition (ALD). Ultra thin ({approx}1.1 nm), thermally stable and aqueous etch-resistant GeO{sub x}N{sub y} interfaces layers that exhibited Ge core level photoelectron spectra (PES) similar to stoichiometric Ge{sub 3}N{sub 4} were synthesized. To evaluate GeO{sub x}N{sub y}/Ge interface defects, the density of interface states (D{sub it}) was extracted by the conductance method across the band gap. Forming gas annealed (FGA) samples exhibited substantially lower D{sub it} ({approx} 1 x 10{sup 12} cm{sup -2} eV{sup -1}) than did high vacuum annealed (HVA) and inert gas anneal (IGA) samples ({approx} 1x 10{sup 13} cm{sup -2} eV{sup -1}). Germanium core level photoelectron spectra from similar FGA-treated samples detected out-diffusion of germanium oxide to the HfO{sub 2} film surface and apparent modification of chemical bonding at the GeO{sub x}N{sub y}/Ge interface, which is related to the reduced D{sub it}.

  3. Critical thickness for strain relaxation of Ge1-xSnx (x ≤ 0.17) grown by molecular beam epitaxy on Ge(001)

    NASA Astrophysics Data System (ADS)

    Wang, Wei; Zhou, Qian; Dong, Yuan; Tok, Eng Soon; Yeo, Yee-Chia

    2015-06-01

    We investigated the critical thickness (hc) for plastic relaxation of Ge1-xSnx grown by molecular beam epitaxy. Ge1-xSnx films with various Sn mole fraction x (x ≤ 0.17) and different thicknesses were grown on Ge(001). The strain relaxation of Ge1-xSnx films and the hc were investigated by high-resolution x-ray diffraction and reciprocal space mapping. It demonstrates that the measured hc values of Ge1-xSnx layers are as much as an order of magnitude larger than that predicted by the Matthews and Blakeslee (M-B) model. The People and Bean (P-B) model was also used to predict the hc values in Ge1-xSnx/Ge system. The measured hc values for various Sn content follow the trend, but slightly larger than that predicted by the P-B model.

  4. Combined wet and dry cleaning of SiGe(001)

    SciTech Connect

    Park, Sang Wook; Kaufman-Osborn, Tobin; Kim, Hyonwoong; Siddiqui, Shariq; Sahu, Bhagawan; Yoshida, Naomi; Brandt, Adam; Kummel, Andrew C.

    2015-07-15

    Combined wet and dry cleaning via hydrofluoric acid (HF) and atomic hydrogen on Si{sub 0.6}Ge{sub 0.4}(001) surface was studied at the atomic level using ultrahigh vacuum scanning tunneling microscopy (STM), scanning tunneling spectroscopy (STS), and x-ray photoelectron spectroscopy to understand the chemical transformations of the surface. Aqueous HF removes native oxide, but residual carbon and oxygen are still observed on Si{sub 0.6}Ge{sub 0.4}(001) due to hydrocarbon contamination from post HF exposure to ambient. The oxygen contamination can be eliminated by shielding the sample from ambient via covering the sample in the HF cleaning solution until the sample is introduced to the vacuum chamber or by transferring the sample in an inert environment; however, both processes still leave carbon contaminant. Dry in-situ atomic hydrogen cleaning above 330 °C removes the carbon contamination on the surface consistent with a thermally activated atomic hydrogen reaction with surface hydrocarbon. A postdeposition anneal at 550 °C induces formation of an atomically flat and ordered SiGe surface observed by STM. STS verifies that the wet and dry cleaned surface has an unpinned Fermi level with no states between the conduction and valence band edge comparable to sputter cleaned SiGe surfaces.

  5. Environmentally friendly HF (DF) lasers

    NASA Astrophysics Data System (ADS)

    Apollonov, V. V.

    2016-08-01

    Dedicated to the 100th anniversary of the birth of Academician A M Prokhorov, this paper reviews the physics of self-sustained volume discharge without preionization—self-initiated volume discharge (SIVD)—in the working mixtures of non-chain hydrofluoride HF (deuterofluoride (DF)) lasers. The dynamics of SIVD in discharge gaps with different geometries is thoroughly described. The mechanisms for the restriction of current density in a diffuse channel in electric discharges in SF6 and SF6 based mixtures (which determines whether SIVD is possible) are proposed and analyzed using simple models. The most probable mechanisms are the electron impact dissociation of SF6 and other mixture components, electron–ion recombination and electron attachment to vibrationally excited SF6 molecules. Starting from a comparative analysis of the rate coefficients of these processes, it is shown that electron–ion recombination is capable of compensating for electron detachment from negative ions via electron impact. It is also established that SIVD is not only observed in SF6, but also in other strongly electronegative gases. The factors that determine the uniformity of the active medium in non-chain HF (DF) lasers are analyzed. Some special features of non-chain HF (DF) lasers with different apertures operating are carefully examined. Consideration is given to the problem of increasing the aperture and discharge volume of non-chain HF (DF) lasers. Based on our experimental results, the possibility of increasing the energy of such lasers to ~1 kJ and above is shown.

  6. In-beam {gamma}-ray spectroscopy in the vicinity of {sup 100}Sn.

    SciTech Connect

    Seweryniak, D.

    1998-09-29

    In recent years, in-beam x-ray experiments supplied a vast amount of data on high-spin states in nuclei in the vicinity of {sup 100}Sn. The present contribution reviews spectroscopic information obtained recently for N {ge} 50 nuclei around {sup 100}Sn, with emphasis on isomer studies, and discusses selected results in the frame of the shell model.

  7. The GEO-HF project

    NASA Astrophysics Data System (ADS)

    Willke, B.; Ajith, P.; Allen, B.; Aufmuth, P.; Aulbert, C.; Babak, S.; Balasubramanian, R.; Barr, B. W.; Berukoff, S.; Bunkowski, A.; Cagnoli, G.; Cantley, C. A.; Casey, M. M.; Chelkowski, S.; Chen, Y.; Churches, D.; Cokelaer, T.; Colacino, C. N.; Crooks, D. R. M.; Cutler, C.; Danzmann, K.; Dupuis, R. J.; Elliffe, E.; Fallnich, C.; Franzen, A.; Freise, A.; Gholami, I.; Goßler, S.; Grant, A.; Grote, H.; Grunewald, S.; Harms, J.; Hage, B.; Heinzel, G.; Heng, I. S.; Hepstonstall, A.; Heurs, M.; Hewitson, M.; Hild, S.; Hough, J.; Itoh, Y.; Jones, G.; Jones, R.; Huttner, S. H.; Kötter, K.; Krishnan, B.; Kwee, P.; Lück, H.; Luna, M.; Machenschalk, B.; Malec, M.; Mercer, R. A.; Meier, T.; Messenger, C.; Mohanty, S.; Mossavi, K.; Mukherjee, S.; Murray, P.; Newton, G. P.; Papa, M. A.; Perreur-Lloyd, M.; Pitkin, M.; Plissi, M. V.; Prix, R.; Quetschke, V.; Re, V.; Regimbau, T.; Rehbein, H.; Reid, S.; Ribichini, L.; Robertson, D. I.; Robertson, N. A.; Robinson, C.; Romano, J. D.; Rowan, S.; Rüdiger, A.; Sathyaprakash, B. S.; Schilling, R.; Schnabel, R.; Schutz, B. F.; Seifert, F.; Sintes, A. M.; Smith, J. R.; Sneddon, P. H.; Strain, K. A.; Taylor, I.; Taylor, R.; Thüring, A.; Ungarelli, C.; Vahlbruch, H.; Vecchio, A.; Veitch, J.; Ward, H.; Weiland, U.; Welling, H.; Wen, L.; Williams, P.; Winkler, W.; Woan, G.; Zhu, R.

    2006-04-01

    The GEO 600 gravitational wave detector uses advanced technologies including signal recycling and monolithic fused-silica suspensions to achieve a sensitivity close to the kilometre scale LIGO and VIRGO detectors. As soon as the design sensitivity of GEO 600 is reached, the detector will be operated as part of the worldwide network to acquire data of scientific interest. The limited infrastructure at the GEO site does not allow for a major upgrade of the detector. Hence the GEO collaboration decided to improve the sensitivity of the GEO detector by small sequential upgrades some of which will be tested in prototypes first. The development, test and installation of these upgrades are named 'The GEO-HF Project.' This paper describes the upgrades considered in the GEO-HF project as well as their scientific reasons. We will describe the changes in the GEO 600 infrastructure and the prototype work that is planned to support these upgrades. Finally, we will point to some laboratory research that identifies new technologies or optical configurations that might undergo a transition into detector subsystems within the GEO-HF project.

  8. High mobility field effect transistors of SnOx on glass substrates made by reactive sputtering of Sn metal

    NASA Astrophysics Data System (ADS)

    Ju, Chanjong; Park, Chulkwon; Yang, Hyeonseok; Kim, Useong; Kim, Young Mo; Char, Kookrin

    2015-03-01

    We report on the electrical properties of SnOx thin films and the performance of their field effect transistors on glass substrates made by reactive sputtering of a Sn metal target. We investigated the electrical properties of SnOx films as a function of the oxygen pressure. The mobility of the SnOx films on glass substrates after post-deposition annealing at 400 C was as high as 15.3 cm2/Vs while its carrier density was 4.42 × 1018 cm-3. By x-ray diffraction, we have found that the films are mixture of SnO and SnO2 phases, suggesting possibility of further enhancement of the electrical properties if the phase can be controlled. Nevertheless, we will report on the performance of thin film transistors using polycrystalline SnOx as the channel layer and the atomic-layer-deposited AlOx and HfOx as the gate oxide.

  9. Clinical trials update from the American Heart Association meeting 2010: EMPHASIS-HF, RAFT, TIM-HF, Tele-HF, ASCEND-HF, ROCKET-AF, and PROTECT.

    PubMed

    Cleland, John G F; Coletta, Alison P; Buga, Laszlo; Antony, Renjith; Pellicori, Pierpaolo; Freemantle, Nick; Clark, Andrew L

    2011-04-01

    This article provides information and a commentary on key trials relevant to the pathophysiology, prevention, and treatment of heart failure presented at the annual meeting of the American Heart Association held in Chicago in 2010. Unpublished reports should be considered as preliminary, since analyses may change in the final publication. In patients with mild heart failure (HF), EMPHASIS-HF showed that the addition of eplerenone to standard therapy was well tolerated and reduced both the risk of death and hospitalization. The addition of cardiac resynchronization therapy to implantable cardioverter defibrillator (ICD) therapy reduced the incidence of all-cause mortality and HF hospitalizations in patients with NYHA class II-III HF compared with ICD alone in RAFT. Telemonitoring failed to improve outcome compared with a high standard of conventional care in patients with chronic HF (TIM-HF study) and a telephone-based interactive voice response system failed to improve outcome in patients recently hospitalized for HF (Tele-HF study). ASCEND-HF suggested that nesiritide was ineffective but safe in patients with acute decompensated HF. ROCKET-AF suggests that the factor-Xa inhibitor rivaroxaban may be as effective as warfarin in patients with atrial fibrillation. The PROTECT study provided more data to suggest that amino-terminal B-type natriuretic peptide guided therapy may be beneficial in patients with left ventricular systolic dysfunction. PMID:21436363

  10. Stabilization of the high-k tetragonal phase in HfO2: The influence of dopants and temperature from ab initio simulations

    NASA Astrophysics Data System (ADS)

    Fischer, Dominik; Kersch, Alfred

    2008-10-01

    By means of ab initio simulations we investigate the influence of dopants (Si, C, Ge, Sn, Ti, and Ce) on the transition from the monoclinic to the tetragonal phase in HfO2. In this study we focus first on the internal energy only, an approach common to ab initio simulations. In the second step we go beyond this approach in considering the Helmholtz free energy by additionally taking into account the contribution of the phonon density of states. Finally we discuss the change in transition temperature in the regime of thin films based on an empirical model. We find that both the contributions of the internal energy and phonons can be understood in terms of a model relying on the ionic radius of the dopants. Among the investigated dopants silicon is identified to promote the tetragonal phase most efficiently. The effectiveness of the various dopants is compared on the basis of a qualitative phase diagram for doping concentrations up to ˜12%.

  11. Non-equilibrium induction of tin in germanium: towards direct bandgap Ge1-xSnx nanowires.

    PubMed

    Biswas, Subhajit; Doherty, Jessica; Saladukha, Dzianis; Ramasse, Quentin; Majumdar, Dipanwita; Upmanyu, Moneesh; Singha, Achintya; Ochalski, Tomasz; Morris, Michael A; Holmes, Justin D

    2016-01-01

    The development of non-equilibrium group IV nanoscale alloys is critical to achieving new functionalities, such as the formation of a direct bandgap in a conventional indirect bandgap elemental semiconductor. Here, we describe the fabrication of uniform diameter, direct bandgap Ge1-xSnx alloy nanowires, with a Sn incorporation up to 9.2 at.%, far in excess of the equilibrium solubility of Sn in bulk Ge, through a conventional catalytic bottom-up growth paradigm using noble metal and metal alloy catalysts. Metal alloy catalysts permitted a greater inclusion of Sn in Ge nanowires compared with conventional Au catalysts, when used during vapour-liquid-solid growth. The addition of an annealing step close to the Ge-Sn eutectic temperature (230 °C) during cool-down, further facilitated the excessive dissolution of Sn in the nanowires. Sn was distributed throughout the Ge nanowire lattice with no metallic Sn segregation or precipitation at the surface or within the bulk of the nanowires. The non-equilibrium incorporation of Sn into the Ge nanowires can be understood in terms of a kinetic trapping model for impurity incorporation at the triple-phase boundary during growth. PMID:27095012

  12. Non-equilibrium induction of tin in germanium: towards direct bandgap Ge1-xSnx nanowires

    NASA Astrophysics Data System (ADS)

    Biswas, Subhajit; Doherty, Jessica; Saladukha, Dzianis; Ramasse, Quentin; Majumdar, Dipanwita; Upmanyu, Moneesh; Singha, Achintya; Ochalski, Tomasz; Morris, Michael A.; Holmes, Justin D.

    2016-04-01

    The development of non-equilibrium group IV nanoscale alloys is critical to achieving new functionalities, such as the formation of a direct bandgap in a conventional indirect bandgap elemental semiconductor. Here, we describe the fabrication of uniform diameter, direct bandgap Ge1-xSnx alloy nanowires, with a Sn incorporation up to 9.2 at.%, far in excess of the equilibrium solubility of Sn in bulk Ge, through a conventional catalytic bottom-up growth paradigm using noble metal and metal alloy catalysts. Metal alloy catalysts permitted a greater inclusion of Sn in Ge nanowires compared with conventional Au catalysts, when used during vapour-liquid-solid growth. The addition of an annealing step close to the Ge-Sn eutectic temperature (230 °C) during cool-down, further facilitated the excessive dissolution of Sn in the nanowires. Sn was distributed throughout the Ge nanowire lattice with no metallic Sn segregation or precipitation at the surface or within the bulk of the nanowires. The non-equilibrium incorporation of Sn into the Ge nanowires can be understood in terms of a kinetic trapping model for impurity incorporation at the triple-phase boundary during growth.

  13. Non-equilibrium induction of tin in germanium: towards direct bandgap Ge1−xSnx nanowires

    PubMed Central

    Biswas, Subhajit; Doherty, Jessica; Saladukha, Dzianis; Ramasse, Quentin; Majumdar, Dipanwita; Upmanyu, Moneesh; Singha, Achintya; Ochalski, Tomasz; Morris, Michael A.; Holmes, Justin D.

    2016-01-01

    The development of non-equilibrium group IV nanoscale alloys is critical to achieving new functionalities, such as the formation of a direct bandgap in a conventional indirect bandgap elemental semiconductor. Here, we describe the fabrication of uniform diameter, direct bandgap Ge1−xSnx alloy nanowires, with a Sn incorporation up to 9.2 at.%, far in excess of the equilibrium solubility of Sn in bulk Ge, through a conventional catalytic bottom-up growth paradigm using noble metal and metal alloy catalysts. Metal alloy catalysts permitted a greater inclusion of Sn in Ge nanowires compared with conventional Au catalysts, when used during vapour–liquid–solid growth. The addition of an annealing step close to the Ge-Sn eutectic temperature (230 °C) during cool-down, further facilitated the excessive dissolution of Sn in the nanowires. Sn was distributed throughout the Ge nanowire lattice with no metallic Sn segregation or precipitation at the surface or within the bulk of the nanowires. The non-equilibrium incorporation of Sn into the Ge nanowires can be understood in terms of a kinetic trapping model for impurity incorporation at the triple-phase boundary during growth. PMID:27095012

  14. Radiation hardness of 3HF-tile/O2-WLS-fiber calorimeter

    SciTech Connect

    Han, S.W.; Hu, L.D.; Liu, N.Z.

    1993-11-01

    The radiation hardness of a 3HF-tile/O2-WLS-fiber calorimeter with two different tile/fiber patterns has been studied. Two calorimeter modules were irradiated up to 10 Mrad with the BEPC 1.3 GeV electron beam. The radiation damage of these modules is compared with our previous measurements from SCSN81-tile/BCF91A-WLS-fiber modules. The longitudinal damage profiles are fitted as a function of depth.

  15. Tin surface segregation, desorption, and island formation during post-growth annealing of strained epitaxial Ge1-xSnx layer on Ge(0 0 1) substrate

    NASA Astrophysics Data System (ADS)

    Wang, Wei; Li, Lingzi; Zhou, Qian; Pan, Jisheng; Zhang, Zheng; Tok, Eng Soon; Yeo, Yee-Chia

    2014-12-01

    Annealing of strained Ge1-xSnx epitaxial layers grown on Ge(0 0 1) substrate results in two distinctive regimes marked by changes in composition and morphology. Annealing at low temperatures (200-300 °C or Regime-I) leads to surface enrichment of Sn due to Sn segregation, as indicated by X-ray photoelectron spectroscopy (XPS) results, while the bulk Sn composition (from X-ray diffraction (XRD)) and the surface morphology (from atomic force microscopy (AFM)) do not show discernible changes as compared to the as-grown sample. Annealing at temperatures ranging from 300 °C to 500 °C (Regime-II) leads to a decrease in the surface Sn composition. While the Ge1-xSnx layer remains fully strained, a reduction in the bulk Sn composition is observed when the annealing temperature reaches 500 °C. At this stage, surface roughening also occurs with formation of 3D islands. The island size increases as the annealing temperature is raised to 600 °C. The decrease in the Sn composition at the surface and in the bulk in Regime-II is attributed to additional thermally activated kinetic processes associated with Sn desorption and formation of Sn-rich 3D islands on the surface.

  16. Germyl cations with Ge-S bond: an experimental and theoretical study on the gaseous F(n)Ge(SH)(3-n)+ (n=0-2).

    PubMed

    Antoniotti, Paola; Benzi, Paola; Operti, Lorenzo; Rabezzana, Roberto; Borocco, Stefano; Giordani, Maria; Grandinetti, Felice

    2012-01-01

    The germyl cations F(2)Ge(SH)(+), FGe(SH)(2)(+) and Ge(SH)(3)(+) were obtained from ionized mixtures of GeF(4) and H(2)S. Ion trap mass spectrometry revealed the occurrence of three consecutive addition-HF elimination reactions between GeF(3)(+), F(2)Ge(SH)(+) and FGe(SH)(2)(+) and H(2)S. The structure and the mechanism of formation of the observed F(n)Ge(SH)(3-n)(+) (n = 0-2) were investigated by ab initio calculations performed at the MP2 and coupled cluster level of theory. It was also possible to note regular trends in the geometries and Lewis acidities of the F(n)Ge(SH)(3-n)(+) (n= 0-3). PMID:23221118

  17. SN 1604 in China

    NASA Astrophysics Data System (ADS)

    Wang, Z. R.; Zhao, Y.; Li, M.; Zhou, Q. L.

    2005-06-01

    The 6th East Asian Meeting of Astronomy was held just at the time of 400 years after the discovery of SN (supernova) 1604 and its pre-maximum observation by the astronomers both from the East and the West in the 17th century. It has a special meaning and is interesting to look back on the historical observation of SN 1604. In this paper, we only limit to concern the Chinese observation on SN 1604.

  18. Precise measurement of energies in 115Sn following the (n ,γ ) reaction

    NASA Astrophysics Data System (ADS)

    Urban, W.; Köster, U.; Jentschel, M.; Mutti, P.; Märkisch, B.; RzÄ ca-Urban, T.; Bernards, Ch.; Fransen, Ch.; Jolie, J.; Thomas, T.; Simpson, G. S.

    2016-07-01

    The first measurement of γ rays from the 114Sn(n ,γ ) reaction using cold neutrons, performed with an array of Ge detectors at the PF1B facility of the Institute Laue-Langevin in Grenoble, has provided the most accurate energy, Qβ=173 (12 ) eV, of β- decay of the 115In ground state to the first excited state in 115Sn. This is the lowest of all such energies in the known nuclear landscape. The accuracy of the neutron binding energy of 115Sn and the mass of 114Sn have been improved.

  19. Suppression of tin precipitation in SiSn alloy layers by implanted carbon

    SciTech Connect

    Gaiduk, P. I.; Lundsgaard Hansen, J. Nylandsted Larsen, A.

    2014-06-09

    By combining transmission electron microscopy and Rutherford backscattering spectrometry, we have identified carbon related suppression of dislocations and tin precipitation in supersaturated molecular-beam epitaxial grown SiSn alloy layers. Secondary ion mass spectrometry has exposed the accumulation of carbon in the SiSn layers after high temperature carbon implantation and high temperature thermal treatment. Strain-enhanced separation of point defects and formation of dopant-defect complexes are suggested to be responsible for the effects. The possibility for carbon assisted segregation-free high temperature growth of heteroepitaxial SiSn/Si and GeSn/Si structures is argued.

  20. Electronic band structures of Ge1-xSnx semiconductors: A first-principles density functional theory study

    NASA Astrophysics Data System (ADS)

    Lee, Ming-Hsien; Liu, Po-Liang; Hong, Yung-An; Chou, Yen-Ting; Hong, Jia-Yang; Siao, Yu-Jin

    2013-02-01

    We conduct first-principles total-energy density functional calculations to study the band structures in Ge1-xSnx infrared semiconductor alloys. The norm-conserving optimized pseudopotentials of Ge and Sn have been constructed for electronic structure calculations. The composition-bandgap relationships in Ge1-xSnx lattices are evaluated by a detailed comparison of structural models and their electronic band structures. The critical Sn composition related to the transition from indirect- to direct-gap in Ge1-xSnx alloys is estimated to be as low as x ˜ 0.016 determined from the parametric fit. Our results show that the crossover Sn concentration occurs at a lower critical Sn concentration than the values predicted from the absorption measurements. However, early results indicate that the reliability of the critical Sn concentration from such measurements is hard to establish, since the indirect gap absorption is much weaker than the direct gap absorption. We find that the direct band gap decreases exponentially with the Sn composition over the range 0 0.375, in very good agreement with the theoretical observed behavior [D. W. Jenkins and J. D. Dow, Phys. Rev. B 36, 7994, 1987]. For homonuclear and heteronuclear complexes of Ge1-xSnx alloys, the indirect band gap at L-pointis is found to decrease homonuclear Ge-Ge bonds or increase homonuclear Sn-Sn bonds as a result of the reduced L valley. All findings agree with previously reported experimental and theoretical results. The analysis suggests that the top of valence band exhibits the localization of bond charge and the bottom of the conduction band is composed of the Ge 4s4p and/or Sn 5s5p atomic orbits.

  1. Elaboration of SnO2 Thin Films and Effect of High Pressure on their Structural Properties (abstract)

    NASA Astrophysics Data System (ADS)

    Djahmoun, M.; Sedda, K.; Zerrouki, H.; Outemzabet, R.; Kesri, N.

    2009-04-01

    Undoped films of SnO2 were prepared from SnCl2,2H2O by the chemical vapor deposition technique and by spray pyrolysis. Examinations of the structures were performed by X-ray diffraction and by scanning electron microscopy. From optical spectra we deduced thickness of the layers, optical constants, and direct and indirect gaps. The electrical resistivity was measured by the four-probe-contacts technique. We investigated theoretically the main characteristics of the ground state of the high-pressure polymorphs, such as the equilibrium volume and bulk modulus. Tin oxide exhibited extensive polymorphism at high pressures and presented a similar sequence of phase transitions to metal oxides MO2, where M can be cations from groups 4 and 14 as SiO2, TiO2, HfO2, GeO2, PbO2, and ZrO2. Ab initio calculations (density-functional theory, local-density approximation, and generalized gradient approximation) were performed to determine the ground state properties and to solve the Kohn-Sham equations. Total energy calculations and geometry optimizations were carried out for all structural phases involved. It was observed that under increasing pressure the rutile-phase (space-group P42/mmm) could be transformed to the orthorhombic in CaCl2-type (space group Pnnm), then in α-PbO2-type (Pbcn), in pyrite-type (Pa-3), in ZrO2,-type (Pbca), and finally in cotunnite-type (Pnam).

  2. The intrinsic disorder related alloy scattering in ZrNiSn half-Heusler thermoelectric materials

    PubMed Central

    Xie, Hanhui; Wang, Heng; Fu, Chenguang; Liu, Yintu; Snyder, G. Jeffrey; Zhao, Xinbing; Zhu, Tiejun

    2014-01-01

    The intrinsic structural disorder dramatically affects the thermal and electronic transport in semiconductors. Although normally considered an ordered compound, the half-Heusler ZrNiSn displays many transport characteristics of a disordered alloy. Similar to the (Zr,Hf)NiSn based solid solutions, the unsubstituted ZrNiSn compound also exhibits charge transport dominated by alloy scattering, as demonstrated in this work. The unexpected charge transport, even in ZrNiSn which is normally considered fully ordered, can be explained by the Ni partially filling interstitial sites in this half-Heusler system. The influence of the disordering and defects in crystal structure on the electron transport process has also been quantitatively analyzed in ZrNiSn1-xSbx with carrier concentration nH ranging from 5.0×1019 to 2.3×1021 cm−3 by changing Sb dopant content. The optimized carrier concentration nH ≈ 3–4×1020 cm−2 results in ZT ≈ 0.8 at 875K. This work suggests that MNiSn (M = Hf, Zr, Ti) and perhaps most other half-Heusler thermoelectric materials should be considered highly disordered especially when trying to understand the electronic and phonon structure and transport features. PMID:25363573

  3. Growth and structure evaluation of strain-relaxed Ge1-xSnx buffer layers grown on various types of substrates

    NASA Astrophysics Data System (ADS)

    Takeuchi, Shotaro; Sakai, Akira; Yamamoto, Koji; Nakatsuka, Osamu; Ogawa, Masaki; Zaima, Shigeaki

    2007-01-01

    We have performed growth and structure evaluation of strain-relaxed Ge1-xSnx buffer layers grown on Si(0 0 1), virtual Ge(0 0 1) and bulk Ge(0 0 1) substrates. In the case of Si(0 0 1), amorphous Ge1-xSnx phases are partially formed as well as many threading dislocations in Ge0.98Sn0.02 layers. Employing virtual Ge substrates to reduce the lattice mismatch at the interface leads to epitaxial Ge0.978Sn0.022 layers with a flat surface. Most of threading dislocations in the Ge0.978Sn0.022 layer comes from pre-existing ones in the virtual Ge substrate and propagates laterally, leaving misfit segments at the Ge0.978Sn0.022/virtual Ge interface, after post-deposition annealing (PDA). This simultaneously results in the reduction of threading dislocation density and the promotion of strain relaxation. In the case of bulk Ge(0 0 1), although low threading dislocation density can be achieved, less than 106 cm-2, the film exhibits surface undulation and a lesser degree of strain relaxation even after PDA.

  4. Ge1-x-ySixSny light emitting diodes on silicon for mid-infrared photonic applications

    NASA Astrophysics Data System (ADS)

    Gallagher, J. D.; Xu, C.; Senaratne, C. L.; Aoki, T.; Wallace, P. M.; Kouvetakis, J.; Menéndez, J.

    2015-10-01

    This paper reports initial the demonstration of prototype Ge1-x-ySixSny light emitting diodes with distinct direct and indirect edges and high quality I-V characteristics. The devices are fabricated on Si (100) wafers in heterostructure pin geometry [n-Ge/i-Ge1-x-ySixSny/p-Ge(Sn/Si)] using ultra low-temperature (T < 300 °C) depositions of the highly reactive chemical sources Si4H10, Ge4H10, Ge3H8, and SnD4. The Sn content in the i-Ge1-x-ySixSny layer was varied from ˜3.5% to 11%, while the Si content was kept constant near 3%. The Si/Sn amounts in the p-layer were selected to mitigate the lattice mismatch so that the top interface grows defect-free, thereby reducing the deleterious effects of mismatch-induced dislocations on the optical/electrical properties. The spectral responsivity plots of the devices reveal sharp and well-defined absorption edges that systematically red-shift in the mid-IR from 1750 to 2100 nm with increasing Sn content from 3.5% to 11%. The electroluminescence spectra reveal strong direct-gap emission peaks and weak lower energy shoulders attributed to indirect gaps. Both peaks in a given spectrum red-shift with increasing Sn content and their separation decreases as the material approaches direct gap conditions in analogy with binary Ge1-ySny counterparts. These findings-combined with the enhanced thermal stability of Ge1-x-ySixSny relative to Ge1-ySny and the observation that ternary alloy disorder does not adversely affect the emission properties—indicate that Ge1-x-ySixSny may represent a practical target system for future generations of group-IV light sources on Si.

  5. Electronic transport and atomic vibrational properties of semiconducting (Mg{sub 2}{sup 119}Sn) thin film.

    SciTech Connect

    Sahoo, B.; Adeagbo, W. A.; Stromberg, F.; Keune, W.; Schuster, E.; Peters, R.; Entel, P.; Luttjohann, S.; Gondorf, A.; Sturhahn, W.; Zhao, J.; Toellner, T.S.; Alp, E.E.; X-Ray Science Division; Univ. of Duisburg-Essen

    2006-12-26

    A polycrystalline Mg{sub 2}Sn thin film has been prepared by thermal co-evaporation in ultrahigh vacuum of Mg and Sn onto a naturally oxidized Si(100) substrate at -140 C. The structure of the sample was characterized by X-ray diffraction (XRD) and {sup 119}Sn conversion electron M{umlt o}ssbauer spectroscopy (CEMS). The semiconducting property of the Mg{sub 2}Sn thin film was confirmed by electrical resistance, magnetoresistance, Hall-effect and infrared spectroscopy measurements, and a value of {approx}0.2 eV was found for the electronic gap energy. The {sup 119}Sn-projected partial vibrational density of states (VDOS), g(E), has been measured by nuclear resonant inelastic X-ray scattering (NRIXS) of 23.878 keV synchrotron radiation. Together with g(E), other thermodynamic quantities such as the probability of recoilless absorption (f-factor), the average kinetic energy per Sn atom, the average force constant, and the vibrational entropy per Sn atom are obtained. The partial VDOS of both elements (Mg and Sn) has been calculated theoretically and reasonable agreement with the measured {sup 119}Sn-projected VDOS is observed. g(E) is characterized by a phonon energy gap ranging from {approx}17 to {approx}21 meV.

  6. Raman study of strained Ge1-xSnx alloys

    NASA Astrophysics Data System (ADS)

    Lin, Hai; Chen, Robert; Huo, Yijie; Kamins, Theodore I.; Harris, James S.

    2011-06-01

    The Ge-Ge longitudinal optical Raman peak has been measured in strained Ge1-xSnx alloy layers grown on top of relaxed InyGa1-yAs buffer layers on GaAs substrates by molecular beam epitaxy. The experimental result shows that the peak frequency shift increases linearly from the value for bulk Ge with the Sn fraction x and the strain ɛ, Δω = ω - ωGe = ax + bɛ. In these experiments alloy and strain contributions are decoupled and measured separately, and a and b are determined to be a = - 82 ± 4 cm-1 and b = - 563 ± 34 cm-1, over the entire composition and strain range investigated.

  7. Optical and electrical properties of undoped and doped Ge nanocrystals

    PubMed Central

    2012-01-01

    Size-dependent photoluminescence characteristics from Ge nanocrystals embedded in different oxide matrices have been studied to demonstrate the light emission in the visible wavelength from quantum-confined charge carriers. On the other hand, the energy transfer mechanism between Er ions and Ge nanocrystals has been exploited to exhibit the emission in the optical fiber communication wavelength range. A broad visible electroluminescence, attributed to electron hole recombination of injected carriers in Ge nanocrystals, has been achieved. Nonvolatile flash-memory devices using Ge nanocrystal floating gates with different tunneling oxides including SiO2, Al2O3, HfO2, and variable oxide thickness [VARIOT] tunnel barrier have been fabricated. An improved charge storage characteristic with enhanced retention time has been achieved for the devices using VARIOT oxide floating gate. PMID:22348653

  8. ASASSN-16hf: Discovery of A Probable Nova in M31

    NASA Astrophysics Data System (ADS)

    Nicolas, J.; Kiyota, S.; Brown, J. S.; Stanek, K. Z.; Holoien, T. W.-S.; Kochanek, C. S.; Godoy-Rivera, D.; Basu, U.; Shappee, B. J.; Prieto, J. L.; Bersier, D.; Dong, Subo; Chen, Ping; Brimacombe, J.; Fernandez, J. M.; Krannich, G.; Masi, G.; Post, R. S.; Stone, G.

    2016-07-01

    During the ongoing All Sky Automated Survey for SuperNovae (ASAS-SN or "Assassin"), using data from the quadruple 14-cm "Brutus" telescope in Haleakala, Hawaii, we discovered a new transient source, most likely a nova, in the nearby galaxy M31. ASASSN-16hf (AT 2016dah) was discovered in images obtained on UT 2016-07-14.54 at V~16.4 mag. We also detect the object in images obtained on UT 2016-07-13.52 (V~16.6).

  9. Mobility Behavior of Ge1-xSnx Layers Grown on Silicon-on-Insulator Substrates

    NASA Astrophysics Data System (ADS)

    Nakatsuka, Osamu; Tsutsui, Norimasa; Shimura, Yosuke; Takeuchi, Shotaro; Sakai, Akira; Zaima, Shigeaki

    2010-04-01

    We have investigated the behaviors of the carrier mobility and concentration of the undoped Ge1-xSnx layers epitaxially grown on silicon-on-insulator (SOI) substrates. Hall measurement revealed the conduction of holes excited from acceptor levels related to vacancy defects whose concentration was as high as 1018 cm-3 in Ge1-xSnx layers. The temperature dependences of the carrier mobility and concentration in the valence band was estimated by reducing the parallel conduction component in the impurity band. The incorporation of Sn at a content lower than 4.0% hardly degraded the hole mobility of heteroepitaxial Ge1-xSnx layers. In contrast, the mobility of the Ge1-xSnx layers was improved by reducing the carrier concentration of the Ge1-xSnx layers by Sn incorporation compared with that of the Ge layer formed under the same growth and annealing conditions. This result suggests that the incorporation of Sn into Ge leads to reducing the hole concentration of the electrically active vacancy defects due to the formation of Sn-vacancy pairs.

  10. Epitaxial growth and anisotropic strain relaxation of Ge1-xSnx layers on Ge(1 1 0) substrates

    NASA Astrophysics Data System (ADS)

    Asano, Takanori; Shimura, Yosuke; Taoka, Noriyuki; Nakatsuka, Osamu; Zaima, Shigeaki

    2013-05-01

    We have investigated the strain relaxation behavior and dislocation structures of Ge1-xSnx epitaxial layers on Ge(1 1 0) substrates. We found that the anisotropic strain relaxation of a Ge0.966Sn0.034 layer along the [0 0 1] direction preferentially occurs during postdeposition annealing over 500 °C. Transmission electron microscopy observation revealed that the anisotropic strain relaxation is attributed to the propagation of misfit dislocations along the two directions of [1¯ 1 0] and <1 1 2> at the Ge1-xSnx/Ge(1 1 0) interface. We found that the propagation of 60° dislocations preferentially occurs, which contributes to the strain relaxation only for the [0 0 1] direction.

  11. Statistical gamma transitions in {sup 174}Hf

    SciTech Connect

    Farris, L.P.; Cizewski, J.A.; Brinkman, M.J.; Henry, R.G.; Lee, C.S.; Khoo, T.L.; Janssens, R.V.F.; Moore, E.F.; Carpenter, M.P.; Ahmad, I.; Lauritsen, T.; Kolata, J.J.; Beard, K.B.; Ye, D.; Garg, U.; Kaplan, M.S.; Saladin, J.X.; Winchell, D.

    1992-08-01

    Statistical spectrum extracted from the {sup 172}Yb({alpha},2n){sup 174}Hf reaction was fit with Monte Carlo simulations using a modified GDR E1 strength function and several formulations of the level density.

  12. Statistical gamma transitions in sup 174 Hf

    SciTech Connect

    Farris, L.P.; Cizewski, J.A.; Brinkman, M.J.; Henry, R.G.; Lee, C.S. ); Khoo, T.L.; Janssens, R.V.F.; Moore, E.F.; Carpenter, M.P.; Ahmad, I.; Lauritsen, T. ); Kolata, J.J.; Beard, K.B.; Ye, D.; Garg, U. ); Kaplan, M.S.; Saladin, J.X.; Winchell, D. (Pittsburgh Univ., PA (Un

    1992-01-01

    Statistical spectrum extracted from the {sup 172}Yb({alpha},2n){sup 174}Hf reaction was fit with Monte Carlo simulations using a modified GDR E1 strength function and several formulations of the level density.

  13. Materials Growth and Optoelectronic Properties of Nano-needle Structured Sn-rich SnO Thin Films

    NASA Astrophysics Data System (ADS)

    Wong, Andrew A.

    The rising global interest in photovoltaics and consumer electronics has heightened the demand for earth-abundant optoelectronic materials. Transparent conductive oxides (TCOs) in particular have been widely studied due to their unique material properties and versatility in a variety of applications. However, many of the common TCO materials suffer tradeoffs between cost, environmental stability, and fabrication requirements in addition to their optical and electronic properties. Tin monoxide (SnO) has become an intriguing TCO candidate due to its p-type conductivity, unique among oxide semiconductors. Yet prior studies show these materials require delicate preparation conditions and result in modest electrical and optical performance. In this study, we report a novel method of preparing Sn-rich SnO thin films using a comproportionation reaction of Sn and SnO2. These thin films are fabricated through magnetron co-sputtering of Sn and SnO2 and then undergo crystallization through thermal annealing at different temperatures and in varied ambient environments. Material properties are quantified through techniques such as X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, electron backscatter diffraction, spectrophotometry (with integrating sphere), 4-point probe, hot probe and Hall effect measurements. This thesis reports the rapid (15-60 seconds), low temperature (210-300°C) crystallization of these thin films to form SnO nano-needles with embedded Sn plasmonic scatterers. Sn-rich SnO thin films can be laser pre-patterned to establish nucleation centers and control nano-needle size. These nanoscale features are advantageous for light-trapping in low temperature photovoltaic technologies such as a-Si or CIGS. Furthermore, parallel experimental-theoretical studies suggest that Sn-rich SnO thin films on thin film Ge could have 2-5x absorption increase the near infrared regime. This would be ideal for thermophotovoltaic and infrared

  14. Thermoelectric properties of Co(x)Ni(4-x)Sb(12-y)Sn(y) ternary skutterudites

    NASA Technical Reports Server (NTRS)

    Mackey, Jon A.; Dynys, Frederick W.; Sehirlioglu, Alp

    2014-01-01

    Thermoelectric materials based on the skutterudite crystal structure have demonstrated enhanced performance (ZT greater than 1), along with good thermal stability and favorable mechanical properties. Binary skutterudites, with single and multiple fillers, have been intensively studied in recent years. Compared to binary skutterudites, the ternary systems have received less attention, e.g. Ni4Sb8Sn4. Ternary skutterudites are isoelectronic variants of binary skutterudites; cation substitutions appear to be isostructural to their binary analogues. In general, ternary skutterudites exhibit lower thermal conductivity. Ternary systems of Ni4Bi8Ge4, Ni4Sb8Ge4, and Ni4Sb8Sn4 were investigated using combined solidification and sintering steps. Skutterudite formation was not achieved in the Ni4Bi8Ge4 and Ni4Sb8Ge4 systems; skutterudite formation occurred in Ni4Sb8Sn4 system. P-type material was achieved by Co substitution for Ni. Thermoelectric properties were measured from 298 K to 673 K for Ni4Sb8Sn4, Ni4 Sb7Sn5 and Co2Ni2Sb7Sn5. N-type Ni4Sb8Sn4 exhibit the highest figure of merit of 0.1 at 523 K.

  15. NiSn Half-Heusler Alloy

    NASA Astrophysics Data System (ADS)

    Appel, O.; Gelbstein, Y.

    2014-06-01

    We deal here with Sb and Bi doping effects of the n-type half-Heusler (HH) Ti0.3Zr0.35Hf0.35NiSn alloy on the measured thermoelectric properties. To date, the thermoelectric effects upon Bi doping on the Sn site of HH alloys have rarely been reported, while Sb has been widely used as a donor dopant. A comparison between the measured transport properties following arc melting and spark plasma sintering of both Bi- and Sb-doped samples indicates a much stronger doping effect upon Sb doping, an effect which was explained thermodynamically. Due to similar lattice thermal conductivity values obtained for the various doped samples, synthesized in a similar experimental route, no practical variations in the thermoelectric figure of merit values were observed between the various investigated samples, an effect which was attributed to compensation between the power factor and electrical thermal conductivity values regardless of the various investigated dopants and doping levels.

  16. Magnetoelastic properties of substituted Er1-xGdxMn6Sn6 intermetallic system

    NASA Astrophysics Data System (ADS)

    Tabatabai Yazdi, Sh.; Tajabor, N.; Roknabadi, M. Rezaee; Behdani, M.; Pourarian, F.

    2014-06-01

    The forced magnetostriction of polycrystalline samples of Er1-xGdxMn6Sn6 (0≤x≤1) intermetallics with hexagonal HfFe6Ge6-type structure is investigated in the temperature range of 77-480 K. Gd substitution has a significant effect on interatomic distances and especially on inter-sublattice R-Mn couplings. The replacement of Er by Gd results in increasing the ordering temperature followed by reinforcement of the R-Mn coupling, as well as decreasing the magnetostriction values owing to the S-state character of Gd3+ ions. The results show that the contribution of Er sublattice to anisotropic magnetoelastic effects is positive, while that of Gd and Mn is negative. All the examined samples exhibit considerable magnetovolume anomalies at the ordering temperature (TC=338, 381, 412 and 434 K for the samples with x=0, 0.2, 0.6 and 1.0, respectively). While the unsubstituted sample exhibits metamagnetic transitions, Gd-contained compounds do not show this behavior, owing to the strong Gd-Mn coupling. The experimental results obtained are discussed in the framework of the two-magnetic sublattice by bearing in mind the lattice parameter dependence of the interlayer Mn-Mn exchange interaction in these layered compounds. From the temperature dependence of magnetostriction values and considering the magnetostriction equation for a hexagonal structure, we attempt to determine the signs of some of the magnetostriction constants for these compounds and the influence of Gd substitution on them.

  17. The first principle study of magnetic properties of Mn2WSn, Fe2YSn (Y=Ti, V), Co2YSn (Y=Ti, Zr, Hf, V, Mn) and Ni2YSn (Y=Ti, Zr, Hf, V, Mn) heusler alloys

    NASA Astrophysics Data System (ADS)

    Rauf, Sana; Arif, Suneela; Haneef, Muhammad; Amin, Bin

    2015-01-01

    The spin polarized electronic band structures, density of states (DOS) and magnetic properties of Mn2WSn, Fe2YSn (Y=Ti, V), Co2YSn (Y=Ti, Zr, Hf, V, Mn) and Ni2YSn (Y=Ti, Zr, Hf, V, Mn) huesler compounds are reported. The calculations are performed by using full-potential linearized augmented plane wave method (FP-LAPW) within density functional theory. The magnetic trend in these compounds is studied using values of magnetic moments, exchange interaction and calculated band gap. The results reveal that Mn2WSn and Ni2VSn show 100% spin polarization, Co2YSn (Y=Ti, Zr, Hf, Mn), Fe2YSn (Y=Ti, V), and Ni2MnSn exhibit metallic nature and Ni2YSn (Y=Ti, Zr, Hf) and Co2VSn show semi-conducting behavior.

  18. HF Accelerated Electron Fluxes, Spectra, and Ionization

    NASA Astrophysics Data System (ADS)

    Carlson, Herbert C.; Jensen, Joseph B.

    2015-10-01

    Wave particle interactions, an essential aspect of laboratory, terrestrial, and astrophysical plasmas, have been studied for decades by transmitting high power HF radio waves into Earth's weakly ionized space plasma, to use it as a laboratory without walls. Application to HF electron acceleration remains an active area of research (Gurevich in Usp Fizicheskikh Nauk 177(11):1145-1177, 2007) today. HF electron acceleration studies began when plasma line observations proved (Carlson et al. in J Atmos Terr Phys 44:1089-1100, 1982) that high power HF radio wave-excited processes accelerated electrons not to ~eV, but instead to -100 times thermal energy (10 s of eV), as a consequence of inelastic collision effects on electron transport. Gurevich et al (J Atmos Terr Phys 47:1057-1070, 1985) quantified the theory of this transport effect. Merging experiment with theory in plasma physics and aeronomy, enabled prediction (Carlson in Adv Space Res 13:1015-1024, 1993) of creating artificial ionospheres once ~GW HF effective radiated power could be achieved. Eventual confirmation of this prediction (Pedersen et al. in Geophys Res Lett 36:L18107, 2009; Pedersen et al. in Geophys Res Lett 37:L02106, 2010; Blagoveshchenskaya et al. in Ann Geophys 27:131-145, 2009) sparked renewed interest in optical inversion to estimate electron spectra in terrestrial (Hysell et al. in J Geophys Res Space Phys 119:2038-2045, 2014) and planetary (Simon et al. in Ann Geophys 29:187-195, 2011) atmospheres. Here we present our unpublished optical data, which combined with our modeling, lead to conclusions that should meaningfully improve future estimates of the spectrum of HF accelerated electron fluxes. Photometric imaging data can significantly improve detection of emissions near ionization threshold, and confirm depth of penetration of accelerated electrons many km below the excitation altitude. Comparing observed to modeled emission altitude shows future experiments need electron density profiles

  19. Beta Decay of the Proton-Rich Nuclei 102Sn and 104Sn

    SciTech Connect

    Karny, M.; Batist, L.; Banu, A.; Becker, F.; Blazhev, A.; Brown, B. A.; Bruchle, W.; Doring, J.; Faestermann, T.; Gorska, M.; Grawe, H.; Janas, Z.; Jungclaus, A.; Kavatsyuk, M.; Kavatsyuk, O.; Kirchner, R.; La Commara, M.; Mandal, S.; Mazzocchi, C.; Miernik, K.; Mukha, I.; Muralithar, S.; Plettner, C.; Plochocki, A.; Roeckl, E.; Romoli, M.; Rykaczewski, Krzysztof Piotr; Schadel, M.; Schmidt, K.; Schwengner, R.; Zylicz, J.

    2006-01-01

    The {beta} decays of {sup 102}Sn and {sup 104}Sn were studied by using high-resolution germanium detectors as well as a Total Absorption Spectrometer (TAS). For {sup 104}Sn, with three new {beta}-delayed {gamma}-rays identified, the total Gamow-Teller strength (BGT) value of 2.7(3) was obtained. For {sup 102}Sn, the {gamma}-{gamma} coincidence data were collected for the first time, allowing us to considerably extend the decay scheme. This scheme was used to unfold the TAS data and to deduce a BGT value of 4.2(8) for this decay. This result is compared to shell model predictions, yielding a hindrance factor of 3.6(7) in agreement with those obtained previously for {sup 98}Cd and {sup 100}In. Together with the latter two, {sup 102}Sn completes the triplet of Z {le} 50, N {ge} 50 nuclei with two proton holes, one proton hole and one neutron particle, and two neutron particles with respect to the doubly magic {sup 100}Sn core.

  20. The Ho–Ni–Ge system: Isothermal section and new rare-earth nickel germanides

    SciTech Connect

    Morozkin, A.V.; Knotko, A.V.; Yapaskurt, V.O.; Yuan, Fang; Mozharivskyj, Y.; Pani, M.; Provino, A.; Manfrinetti, P.

    2015-05-15

    The Ho–Ni–Ge system has been investigated at 1070 K and up to ~60 at% Ho by X-ray diffraction and microprobe analyses. Besides the eight known compounds, HoNi{sub 5}Ge{sub 3} (YNi{sub 5}Si{sub 3}-type), HoNi{sub 2}Ge{sub 2} (CeAl{sub 2}Ga{sub 2}-type), Ho{sub 2}NiGe{sub 6} (Ce{sub 2}CuGe{sub 6}-type), HoNiGe{sub 3} (SmNiGe{sub 3}-type), HoNi{sub 0.2÷0.6}Ge{sub 2} (CeNiSi{sub 2}-type), Ho{sub 37÷34}Ni{sub 6÷24}Ge{sub 57÷42} (AlB{sub 2}-type), HoNiGe (TiNiSi-type), Ho{sub 3}NiGe{sub 2} (La{sub 3}NiGe{sub 2}-type), the ternary system contains four new compounds: Ho{sub 3}Ni{sub 11}Ge{sub 4} (Sc{sub 3}Ni{sub 11}Ge{sub 4}-type), HoNi{sub 3}Ge{sub 2} (ErNi{sub 3}Ge{sub 2}-type), Ho{sub 3}Ni{sub 2}Ge{sub 3} (Hf{sub 3}Ni{sub 2}Si{sub 3}-type) and ~Ho{sub 5}Ni{sub 2}Ge{sub 3} (unknown structure). Quasi-binary solid solutions were observed at 1070 K for Ho{sub 2}Ni{sub 17}, HoNi{sub 5}, HoNi{sub 7}, HoNi{sub 3}, HoNi{sub 2}, HoNi and Ho{sub 2}Ge{sub 3}, but no detectable solubility was found for the other binary compounds in the Ho–Ni–Ge system. Based on the magnetization measurements, the HoNi{sub 5}Ge{sub 3}, HoNi{sub 3}Ge{sub 2} and Ho{sub 3}Ni{sub 11}Ge{sub 4} (and isostructural (Tb, Dy){sub 3}Ni{sub 11}Ge{sub 4}) compounds have been found to show paramagnetic behavior down to 5 K, whereas Ho{sub 3}Ni{sub 2}Ge{sub 3} exhibits an antiferromagnetic transition at ~7 K. Additionally, the crystal structure of the new isostructural phases (Y, Yb)Ni{sub 3}Ge{sub 2} (ErNi{sub 3}Ge{sub 2}-type), Er{sub 3}Ni{sub 11}Ge{sub 4} (Sc{sub 3}Ni{sub 11}Ge{sub 4}-type) and (Y, Tb, Dy, Er, Tm){sub 3}Ni{sub 2}Ge{sub 3} (Hf{sub 3}Ni{sub 2}Si{sub 3}-type) has been also investigated. - Graphical abstract: The Ho–Ni–Ge system has been investigated at 1070 K and up to ~60 at.% Ho by X-ray and microprobe analyses. Besides the eight known compounds, i.e. HoNi{sub 5}Ge{sub 3} (YNi{sub 5}Si{sub 3}-type), HoNi{sub 2}Ge{sub 2} (CeAl{sub 2}Ga{sub 2}-type), Ho{sub 2}NiGe{sub 6} (Ce{sub 2

  1. Crystal architecture of R(2)SnS(5) (R = Pr, Nd, Gd and Tb): crystal structure relationships in chalcogenides.

    PubMed

    Daszkiewicz, Marek; Gulay, Lubomir D; Shemet, Vasylyna Ya

    2008-04-01

    The crystal structure of the R(2)SnS(5) (R = Pr, Nd, Gd and Tb) compounds has been investigated using X-ray single-crystal diffraction. Crystal architecture and structural relationships among U(3)S(5), Y(2)HfS(5), R(2)SnS(5) compounds are discussed and a structural origin is determined. It is shown that the complex architecture of the crystal structure of Eu(5)Sn(3)S(12) is a result of interweaving of the simple crystal structures. The location of the copper ions in the non-stoichiometric compound Y(2)Cu(0.20)Sn(0.95)S(5) is proposed on the basis of comparative analysis of the R-S interatomic distances in the R(2)SnS(5) series of compounds. PMID:18369288

  2. Formation of medical radioisotopes 111In, 117 m Sn, 124Sb, and 177Lu in photonuclear reactions

    NASA Astrophysics Data System (ADS)

    Danagulyan, A. S.; Hovhannisyan, G. H.; Bakhshiyan, T. M.; Avagyan, R. H.; Avetisyan, A. E.; Kerobyan, I. A.; Dallakyan, R. K.

    2015-06-01

    The possibility of the photonuclear production of radioisotopes 111In, 117 m Sn, 124Sb, and 177Lu is discussed. Reaction yields were measured by the gamma-activation method. The enriched tin isotopes 112, 118Sn and Te and HfO2 of natural isotopic composition were used as targets. The targets were irradiated at the linear electron accelerator of Alikhanian National Science Laboratory (Yerevan) at the energy of 40 MeV. The experimental results obtained in this way reveal that the yield and purity of radioisotopes 111In and 117 mSn are acceptable for their production via photonuclear reactions. Reactions proceeding on targets from Te and HfO2 of natural isotopic composition and leading to the formation of 124Sb and 177Lu have small yields and are hardly appropriate for the photoproduction of these radioisotopes even in the case of enriched targets.

  3. Comparison of HfCl4, HfI4, TEMA-Hf, and TDMA-Hf as precursors in early growing stages of HfO2 films deposited by ALD: A DFT study

    NASA Astrophysics Data System (ADS)

    Cortez-Valadez, M.; Fierro, C.; Farias-Mancilla, J. R.; Vargas-Ortiz, A.; Flores-Acosta, M.; Ramírez-Bon, R.; Enriquez-Carrejo, J. L.; Soubervielle-Montalvo, C.; Mani-Gonzalez, P. G.

    2016-06-01

    The final structure of HfO2 films grown by atomic layer deposition (ALD) after reaction with OH- ions has been analyzed by DFT (density functional theory). The interaction of the precursors: HfCl4 (hafnium tetrachloride), HfI4 (hafnium tetraiodide), TEMA-Hf (tetrakis-ethylmethylamino hafnium), and TDMA-Hf (tetrakis-dimethylamino hafnium) with HO-H was studied employing the B3LYP (Becke 3-parameter, Lee-Yang-Parr) hybrid functional and the PBE (Perdew-Burke-Ernzerhof) generalized gradient functional. The structural evolution at the Si(100) surface has been analyzed by LDA (local density approximation). The structural parameters: bond length and bond angle, and the vibrational parameters for the optimized structures are also reported. The presence of hafnium silicate at the interface was detected. The infrared spectra and structural parameters obtained in this work agree with previously reported experimental results.

  4. Direct gap Ge1-ySny alloys: Fabrication and design of mid-IR photodiodes

    NASA Astrophysics Data System (ADS)

    Senaratne, C. L.; Wallace, P. M.; Gallagher, J. D.; Sims, P. E.; Kouvetakis, J.; Menéndez, J.

    2016-07-01

    Chemical vapor deposition methods were developed, using stoichiometric reactions of specialty Ge3H8 and SnD4 hydrides, to fabricate Ge1-ySny photodiodes with very high Sn concentrations in the 12%-16% range. A unique aspect of this approach is the compatible reactivity of the compounds at ultra-low temperatures, allowing efficient control and systematic tuning of the alloy composition beyond the direct gap threshold. This crucial property allows the formation of thick supersaturated layers with device-quality material properties. Diodes with composition up to 14% Sn were initially produced on Ge-buffered Si(100) featuring previously optimized n-Ge/i-Ge1-ySny/p-Ge1-zSnz type structures with a single defected interface. The devices exhibited sizable electroluminescence and good rectifying behavior as evidenced by the low dark currents in the I-V measurements. The formation of working diodes with higher Sn content up to 16% Sn was implemented by using more advanced n-Ge1-xSnx/i-Ge1-ySny/p-Ge1-zSnz architectures incorporating Ge1-xSnx intermediate layers (x ˜ 12% Sn) that served to mitigate the lattice mismatch with the Ge platform. This yielded fully coherent diode interfaces devoid of strain relaxation defects. The electrical measurements in this case revealed a sharp increase in reverse-bias dark currents by almost two orders of magnitude, in spite of the comparable crystallinity of the active layers. This observation is attributed to the enhancement of band-to-band tunneling when all the diode layers consist of direct gap materials and thus has implications for the design of light emitting diodes and lasers operating at desirable mid-IR wavelengths. Possible ways to engineer these diode characteristics and improve carrier confinement involve the incorporation of new barrier materials, in particular, ternary Ge1-x-ySixSny alloys. The possibility of achieving type-I structures using binary and ternary alloy combinations is discussed in detail, taking into account

  5. HF Radio Wave Production of Artificial Ionospheres

    NASA Astrophysics Data System (ADS)

    Carlson, Herbert

    In 1993 it was predicted that artificial ionospheres would be produced by high power HF radio waves, once HF transmitters approached a GWatt ERP. When that threshold was very recently achieved, such production was indeed detected and published at two high latitude high power HF facilities. Here we review: the first-principles logic behind that prediction, which aspects of such production are critically dependent on magnetic latitude, and which aspects of such production depend only on physical parameters independent of latitude. These distinctions follow directly from decomposition of the problem of ionization production into its components of: radio-wave propagation, wave-particle interactions, electron transport, and quantitative elastic/inelastic cross-sections. We outline this analysis to show that, within the context of early observations, the production of ionization is inevitable, and only a question of competing instability thresholds, and scale of ionization production. This illustrates complimentary aeronomy and plasma physics to advance understanding of both.

  6. Schirmwirkung von Hochfrequenz (HF)-Schutzkleidung: Untersuchung verschiedener Konstruktionsmerkmale

    NASA Astrophysics Data System (ADS)

    Arps, V.; Scheibe, K.

    2005-05-01

    Die Messverfahren zur Bestimmung der Schutzwirkung von HF-Schutzkleidung sind in der Norm DIN 32780-100 festgelegt. Entsprechend diesen Anforderungen wird die elektrische und magnetische Schirmdämpfung bestimmt und daraus als Maß für die Schutzwirkung die elektromagnetische Schirmdämpfung berechnet. Diese ist eine der SAR vergleichbare Größe. In diesem Beitrag werden die Einflüsse verschiedener Konstruktionsmerkmale von HF-Schutzanzügen auf die elektromagnetische Schirmdämpfung untersucht. Zu diesen gehören die nach MIL STD 285 vermessene elektrische Schirmdämpfung der verwendeten Gewebe. Weiter werden verschiedene Teilbereiche der HF-Schutzkleidung auf ihre Schutzwirkung untersucht. Der Schwerpunkt liegt hierbei auf der Fragestellung inwieweit Verschlüsse, Reißverschlüsse oder leitfähiges Klettband, die Schutzwirkung beeinträchtigen. Zu diesem Zweck werden zwei Schutzanzüge unterschiedlicher Konstruktion vergleichend vermessen. Es handelt sich dabei um einen bereits im Handel befindlichen und entsprechend der Norm zertifizierten Anzug und einen neuen Prototyp, welcher nach verschiedenen Gesichtspunkten optimiert wurde. Schwachstellen der Konstruktion werden herausgearbeitet und Ansatzpunkte für weitere Verbesserungen erarbeitet. The measuring methods for determining the shielding effectiveness of radiofrequency (RF)-protective clothing are defined in German Standard DIN 32780-100. According to this standard, both the electric and the magnetic shielding effectiveness are measured in order to calculate the electromagnetic shielding effectiveness. The electromagnetic shielding effectiveness is an adequate quality criterion for the degree of protection and also compares well with the Specific Absorption Rate (SAR). In this article, the impact of different design features on the electromagnetic shielding effectiveness is analyzed. The electric shielding effectiveness of the used shielding materials is measured according to MIL STD 285 and thereupon

  7. Bridgman crystal growth of Yb{sub 2}Ru{sub 3}Ge{sub 4}-A ternary germanide with a three-dimensional network of condensed distorted RuGe{sub 5} and RuGe{sub 6} units

    SciTech Connect

    Schappacher, Falko M.; Katoh, Kenichi Poettgen, Rainer

    2007-01-15

    The germanide Yb{sub 2}Ru{sub 3}Ge{sub 4} was synthesized from the elements using the Bridgman crystal growth technique. The monoclinic Hf{sub 2}Ru{sub 3}Si{sub 4} type structure was investigated by X-ray powder and single crystal diffraction: C2/c, Z=8, a=1993.0(3) pm, b=550.69(8) pm, c=1388.0(2) pm, {beta}=128.383(9){sup o}, wR {sub 2}=0.0569, 2047 F {sup 2} values, and 84 variables. Yb{sub 2}Ru{sub 3}Ge{sub 4} contains two crystallographically independent ytterbium sites with coordination numbers of 18 and 17 for Yb1 and Yb2, respectively. Each ytterbium atom has three ytterbium neighbors at Yb-Yb distances ranging from 345 to 368 pm. The shortest interatomic distances occur for the Ru-Ge contacts. The three crystallographically independent ruthenium sites have between five and six germanium neighbors in distorted trigonal bipyramidal (Ru1Ge{sub 5}) or octahedral (Ru2Ge{sub 6} and Ru3Ge{sub 6}) coordination at Ru-Ge distances ranging from 245 to 279 pm. The Ru2 atoms form zig-zag chains running parallel to the b-axis at Ru2-Ru2 of 284 pm. The RuGe{sub 5} and RuGe{sub 6} units are condensed via common edges and faces leading to a complex three-dimensional [Ru{sub 3}Ge{sub 4}] network. - Graphical abstract: Condensation of the Ru1Ge{sub 5}, Ru2Ge{sub 6}, and Ru3Ge{sub 6} units in the structure of Yb{sub 2}Ru{sub 3}Ge{sub 4}.

  8. Ionization Energy Measurements and Spectroscopy of HfO and HfO^+

    NASA Astrophysics Data System (ADS)

    Merritt, J. M.; Bondybey, V. E.; Heaven, M. C.

    2009-06-01

    Rotationally resolved spectra of the HfO^+ cation have been recorded using the pulsed field ionization zero electron kinetic energy (PFI-ZEKE) technique. The F(0^+)← X^1Σ_g band system in HfO was resonantly excited to provide vibrational and rotational state selectivity in the two photon ionization process. Using the PFI-ZEKE technique a value of 7.91687(10) eV was determined for the ionization energy (IE) of HfO, 0.37 eV higher than the values reported previously using electron impact ionization measurements. Underestimation of the IE in the previous studies is attributed to ionization of thermally excited states. A progression in the HfO^+ stretching vibration up to ν^+ = 4 was observed in the PFI-ZEKE spectrum, allowing for determination of the ground electronic state vibrational frequency of ν_e = 1017.7(10) cm^{-1} and anharmonicity of ω_ex_e = 3.2(2) cm^{-1}. The rotational constant of HfO^+ was determined to be 0.403(5) cm^{-1}. Benchmark theoretical ab initio calculations were carried out in order to explore the effects of electron correlation on the predicted molecular properties. Survey scans utilizing laser induced fluorescence and resonance enhanced multiphoton ionization detection revealed many previously unassigned bands in the region of the F-X and G-X bands of HfO, which we attribute to nominally forbidden singlet - triplet transitions of HfO.

  9. Removal of uranium from aqueous HF solutions

    DOEpatents

    Pulley, Howard; Seltzer, Steven F.

    1980-01-01

    This invention is a simple and effective method for removing uranium from aqueous HF solutions containing trace quantities of the same. The method comprises contacting the solution with particulate calcium fluoride to form uranium-bearing particulates, permitting the particulates to settle, and separting the solution from the settled particulates. The CaF.sub.2 is selected to have a nitrogen surface area in a selected range and is employed in an amount providing a calcium fluoride/uranium weight ratio in a selected range. As applied to dilute HF solutions containing 120 ppm uranium, the method removes at least 92% of the uranium, without introducing contaminants to the product solution.

  10. Low Temperature Silicon Surface Cleaning by HF Etching/Ultraviolet Ozone Cleaning (HF/UVOC) Method (I)—Optimization of the HF Treatment—

    NASA Astrophysics Data System (ADS)

    Suemitsu, Maki; Kaneko, Tetsuya; Miyamoto, Nobuo

    1989-12-01

    Several variations of fluoric acid (HF) treatments of silicon substrates were examined for their adaptability as a pretreatment method for a silicon epitaxy process. Treatments with and without distilled, deionized (DI) water rinse, of different HF concentrations, and of different methods of HF supply were tested and their residual carbonic impurity contents were measured using RHEED. As a result, HF treatments by themselves were found to be insufficient in passivating the surface dangling bonds irrespective of the method of HF supply: dipping into the solution or exposure to the vapor. The optimum procedure of HF treatment thus proposed is a succession of (a) HF dipping, (b) DI-water rinsing, (c) nitrogen-gas blowing, and (d) UV-ozone cleaning.

  11. Synthesis, photocatalytic and antimicrobial properties of SnO2, SnS2 and SnO2/SnS2 nanostructure.

    PubMed

    Fakhri, Ali; Behrouz, Sajjad; Pourmand, Melika

    2015-08-01

    Nanoscale SnO2, SnS2 and SnO2/SnS2 were synthesized by hydrothermal treatment method and characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET), Barrett-Joyner-Halenda (BJH) and UV-vis spectra. The photocatalytic activity of SnO2, SnS2 and SnO2/SnS2 were tested with Enrofloxacin antibiotic. The tetragonal and hexagonal SnO2 and SnS2 phase was confirmed through XRD, respectively. The photocatalytic results indicated that the SnO2/SnS2 enhanced the photocatalytic activity and could be effectively used as photocatalyst for degradation of Enrofloxacin antibiotic pollutant. The results of antibacterial experiment under visible light irradiation demonstrate that the SnO2/SnS2 nanocomposite exhibit enhanced antibacterial efficiency compared with pure SnO2 and SnS2. The antifungal activity of the nanoscale SnO2, SnS2 and SnO2/SnS2 against Candida albicans was assessed using the disc-diffusion susceptibility tests. It was seen that the antifungal activity of SnO2/SnS2 nanocomposite is higher than the pure SnO2 and SnS2 toward pathogenic C. albicans. PMID:26046748

  12. Evaluation of Dislocation Density of SiGe-on-Insulator Substrates using Enhanced Secco Etching Method

    NASA Astrophysics Data System (ADS)

    Sugiyama, Naoharu; Moriyama, Yoshihiko; Tezuka, Tsutomu; Mizuno, Tomohisa; Nakaharai, Shu; Usuda, Koji; Takagi, Sin-ichi

    2003-07-01

    The dislocation density in thin SiGe on Insulator layers is evaluated, for the first time, by the enhanced secco etching method. It is found that the dislocation density in SGOI layers formed by the Ge condensation method is 6× 103 cm-2. It has also been confirmed that the different types of defects are observed by the HF defect detection method. In addition, the origin of dislocations is discussed by the diagnosis of the variation of dislocation densities during the process steps in the Ge condensation technique.

  13. SnS2- Compared to SnO2-Stabilized S/C Composites toward High-Performance Lithium Sulfur Batteries.

    PubMed

    Li, Xiaona; Lu, Yue; Hou, Zhiguo; Zhang, Wanqun; Zhu, Yongchun; Qian, Yitai; Liang, Jianwen; Qian, Yitai

    2016-08-01

    The common sulfur/carbon (S/C) composite cathodes in lithium sulfur batteries suffer gradual capacity fading over long-term cycling incurred by the poor physical confinement of sulfur in a nonpolar carbon host. In this work, these issues are significantly relieved by introducing polar SnO2 or SnS2 species into the S/C composite. SnO2- or SnS2-stabilized sulfur in porous carbon composites (SnO2/S/C and SnS2/S/C) have been obtained through a baked-in-salt or sealed-in-vessel approach at 245 °C, starting from metallic tin (mp 231.89 °C), excess sulfur, and porous carbon. Both of the in situ-formed SnO2 and SnS2 in the two composites could ensure chemical interaction with lithium polysulfide (LiPS) intermediates proven by theoretical calculation. Compared to SnO2/S/C, the SnS2/S/C sample affords a more appropriate binding effect and shows lower charge transfer resistance, which is important for the efficient redox reaction of the adsorbed LiPS intermediates during cycling. When used as cathodes for Li-S batteries, the SnS2/S/C composite with sulfur loading of 78 wt % exhibits superior electrochemical performance. It delivers reversible capacities of 780 mAh g(-1) after 300 cycles at 0.5 C. When further coupled with a Ge/C anode, the full cell also shows good cycling stability and efficiency. PMID:27419855

  14. Origin of Excess 176Hf in Meteorites

    NASA Astrophysics Data System (ADS)

    Thrane, Kristine; Connelly, James N.; Bizzarro, Martin; Meyer, Bradley S.; The, Lih-Sin

    2010-07-01

    After considerable controversy regarding the 176Lu decay constant (λ176Lu), there is now widespread agreement that (1.867 ± 0.008) × 10-11 yr-1 as confirmed by various terrestrial objects and a 4557 Myr meteorite is correct. This leaves the 176Hf excesses that are correlated with Lu/Hf elemental ratios in meteorites older than ~4.56 Ga meteorites unresolved. We attribute 176Hf excess in older meteorites to an accelerated decay of 176Lu caused by excitation of the long-lived 176Lu ground state to a short-lived 176m Lu isomer. The energy needed to cause this transition is ascribed to a post-crystallization spray of cosmic rays accelerated by nearby supernova(e) that occurred after 4564.5 Ma. The majority of these cosmic rays are estimated to penetrate accreted material down to 10-20 m, whereas a small fraction penetrate as deep as 100-200 m, predicting decreased excesses of 176Hf with depth of burial at the time of the irradiation event.

  15. Magnetism and hybridization effects in UCuSn

    NASA Astrophysics Data System (ADS)

    El-Khatib, Sami; Llobet, Anna; Purwanto, Agus; Alsmadi, A.; Nakotte, Heinz

    2006-03-01

    UCuSn crystallizes in an orthombically-distorted structure that is closely related to the hexagonal GaGeLi structure. Bulk studies reveal that UCuSn undergoes two magnetic transitions at about 60 and 25 K. Here, we present more detailed neutron-diffraction studies that performed on the High-Intensity Powder Diffractometer (HIPD) at the Manuel Lujan, Jr. Neutron Scattering Center at Los Alamos. Neutron-diffraction studies provide clear evidence for a non-collinear configuration of the magnetic moments in both magnetic phases. We propose a simultaneous existence of two magnetic allowed-symmetry structures as one possible explanation to fit the observed magnetic intensities below 25 K. We will discuss the relationship between magnetic and structural properties in UCuSn. We observe regular thermal contraction with decreasing temperature down to 60 K, below which we observe discontinuities for the interatomic spacings, dU-U, dU-Cu and the cell parameters, which provides a measure of the hybridization effects in UCuSn. We were able to correlate the structural changes with the magnetism in UCuSn.

  16. Characteristics of HfO2/Hf-based bipolar resistive memories

    NASA Astrophysics Data System (ADS)

    Jinshun, Bi; Zhengsheng, Han

    2015-06-01

    Nano-scale Hf/HfO2-based resistive random-access-memory (RRAM) devices were fabricated. The cross-over between top and bottom electrodes of RRAM forms the metal-insulator-metal sandwich structure. The electrical responses of RRAM are studied in detail, including forming process, SET process and RESET process. The correlations between SET voltage and RESET voltage, high resistance state and low resistance state are discussed. The electrical characteristics of RRAM are in a strong relationship with the compliance current in the SET process. The conduction mechanism of nano-scale Hf/HfO2-based RRAM can be explained by the quantum point contact model. Project supported by the National Natural Science Foundation of China (Nos. 11179003, 61176095).

  17. Simultaneous observation of HF-enhanced plasma waves and HF-wave self-focusing

    SciTech Connect

    Frey, A.; Duncan, L.M.

    1984-07-01

    Intense HF-radiowaves of the ordinary mode transmitted from the ground enhance plasma waves near the reflection height. These have been extensively studied in the past by the use of Incohernt-Scatter-Radars. Intense HF-radiowaves propagating in the ionosphere also produce electron density irregularities with scale sizes much larger than the HF wavelength of approx.60 m. These have been observed by radio star intensity scintillations. For the past 2 years a new method was used at Arecibo, P.R. which allows radar- and scintillation-measurements at 430 MHz to be performed simultaneously along the same line of sight. The scale sizes deduced from the scintillation measurements are shorter than the scale sizes observed with the radar and are inconsistent with the HF-power density thresholds predicted by existing theories.

  18. Concentration Dependent Physical Properties of Ge1-xSnx Solid Solution

    NASA Astrophysics Data System (ADS)

    Jivani, A. R.; Jani, A. R.

    2011-12-01

    Our own proposed potential is used to investigate few physical properties like total energy, bulk modulus, pressure derivative of bulk modulus, elastic constants, pressure derivative of elastic constants, Poisson's ratio and Young's modulus of Ge1-xSnx solid solution with x is atomic concentration of α-Sn. The potential combines linear plus quadratic types of electron-ion interaction. First time screening function proposed by Sarkar et al is used to investigate the properties of the Ge-Sn solid solution system.

  19. Comprehensive study and design of scaled metal/high-k/Ge gate stacks with ultrathin aluminum oxide interlayers

    NASA Astrophysics Data System (ADS)

    Asahara, Ryohei; Hideshima, Iori; Oka, Hiroshi; Minoura, Yuya; Ogawa, Shingo; Yoshigoe, Akitaka; Teraoka, Yuden; Hosoi, Takuji; Shimura, Takayoshi; Watanabe, Heiji

    2015-06-01

    Advanced metal/high-k/Ge gate stacks with a sub-nm equivalent oxide thickness (EOT) and improved interface properties were demonstrated by controlling interface reactions using ultrathin aluminum oxide (AlOx) interlayers. A step-by-step in situ procedure by deposition of AlOx and hafnium oxide (HfOx) layers on Ge and subsequent plasma oxidation was conducted to fabricate Pt/HfO2/AlOx/GeOx/Ge stacked structures. Comprehensive study by means of physical and electrical characterizations revealed distinct impacts of AlOx interlayers, plasma oxidation, and metal electrodes serving as capping layers on EOT scaling, improved interface quality, and thermal stability of the stacks. Aggressive EOT scaling down to 0.56 nm and very low interface state density of 2.4 × 1011 cm-2eV-1 with a sub-nm EOT and sufficient thermal stability were achieved by systematic process optimization.

  20. Versatile buffer layer architectures based on Ge1-xSnx alloys

    NASA Astrophysics Data System (ADS)

    Roucka, R.; Tolle, J.; Cook, C.; Chizmeshya, A. V. G.; Kouvetakis, J.; D'Costa, V.; Menendez, J.; Chen, Zhihao D.; Zollner, S.

    2005-05-01

    We describe methodologies for integration of compound semiconductors with Si via buffer layers and templates based on the GeSn system. These layers exhibit atomically flat surface morphologies, low defect densities, tunable thermal expansion coefficients, and unique ductile properties, which enable them to readily absorb differential stresses produced by mismatched overlayers. They also provide a continuous selection of lattice parameters higher than that of Ge, which allows lattice matching with technologically useful III-V compounds. Using this approach we have demonstrated growth of GaAs, GeSiSn, and pure Ge layers at low temperatures on Si(100). These materials display extremely high-quality structural, morphological, and optical properties opening the possibility of versatile integration schemes directly on silicon.

  1. Growth and characterization of highly tensile strained Ge1-xSnx formed on relaxed InyGa1-yP buffer layers

    NASA Astrophysics Data System (ADS)

    Wang, Wei; Loke, Wan Khai; Yin, Tingting; Zhang, Zheng; D'Costa, Vijay Richard; Dong, Yuan; Liang, Gengchiau; Pan, Jisheng; Shen, Zexiang; Yoon, Soon Fatt; Tok, Eng Soon; Yeo, Yee-Chia

    2016-03-01

    Ge0.94Sn0.06 films with high tensile strain were grown on strain-relaxed InyGa1-yP virtual substrates using solid-source molecular beam epitaxy. The in-plane tensile strain in the Ge0.94Sn0.06 film was varied by changing the In mole fraction in InxGa1-xP buffer layer. The tensile strained Ge0.94Sn0.06 films were investigated by transmission electron microscopy, x-ray diffraction, and Raman spectroscopy. An in-plane tensile strain of up to 1% in the Ge0.94Sn0.06 was measured, which is much higher than that achieved using other buffer systems. Controlled thermal anneal experiment demonstrated that the strain was not relaxed for temperatures up to 500 °C. The band alignment of the tensile strained Ge0.94Sn0.06 on In0.77Ga0.23P was obtained by high resolution x-ray photoelectron spectroscopy. The Ge0.94Sn0.06/In0.77Ga0.23P interface was found to be of the type I band alignment, with a valence band offset of 0.31 ± 0.12 eV and a conduction band offset of 0.74 ± 0.12 eV.

  2. A search for a heavy Majorana neutrino and a radiation damage simulation for the HF detector

    NASA Astrophysics Data System (ADS)

    Wetzel, James William

    A search for heavy Majorana neutrinos is performed using an event signature defined by two same-sign muons accompanied by two jets. This search is an extension of previous searches, (L3, DELPHI, CMS, ATLAS), using 19.7 fb -1 of data from the 2012 Large Hadron Collider experimental run collected by the Compact Muon Solenoid experiment. A mass window of 40-500 GeV/ c2 is explored. No excess events above Standard Model backgrounds is observed, and limits are set on the mixing element squared, |VmuN|2, as a function of Majorana neutFnrino mass. The Hadronic Forward (HF) Detector's performance will degrade as a function of the number of particles delivered to the detector over time, a quantity referred to as integrated luminosity and measured in inverse femtobarns (fb-1). In order to better plan detector upgrades, the CMS Forward Calorimetry Task Force (FCAL) group and the CMS Hadronic Calorimeter (HCAL) group have requested that radiation damage be simulated and the subsequent performance of the HF subdetector be studied. The simulation was implemented into both the CMS FastSim and CMS FullSim simulation packages. Standard calorimetry performance metrics were computed and are reported. The HF detector can expect to perform well through the planned delivery of 3000 fb-1.

  3. Collisional quenching of highly rotationally excited HF

    NASA Astrophysics Data System (ADS)

    Yang, B.; Walker, K. M.; Forrey, R. C.; Stancil, P. C.; Balakrishnan, N.

    2015-06-01

    Context. Collisional excitation rate coefficients play an important role in the dynamics of energy transfer in the interstellar medium. In particular, accurate rotational excitation rates are needed to interpret microwave and infrared observations of the interstellar gas for nonlocal thermodynamic equilibrium line formation. Aims: Theoretical cross sections and rate coefficients for collisional deexcitation of rotationally excited HF in the vibrational ground state are reported. Methods: The quantum-mechanical close-coupling approach implemented in the nonreactive scattering code MOLSCAT was applied in the cross section and rate coefficient calculations on an accurate 2D HF-He potential energy surface. Estimates of rate coefficients for H and H2 colliders were obtained from the HF-He collisional data with a reduced-potential scaling approach. Results: The calculation of state-to-state rotational quenching cross sections for HF due to He with initial rotational levels up to j = 20 were performed for kinetic energies from 10-5 to 15 000 cm-1. State-to-state rate coefficients for temperatures between 0.1 and 3000 K are also presented. The comparison of the present results with previous work for lowly-excited rotational levels reveals significant differences. In estimating HF-H2 rate coefficients, the reduced-potential method is found to be more reliable than the standard reduced-mass approach. Conclusions: The current state-to-state rate coefficient calculations are the most comprehensive to date for HF-He collisions. We attribute the differences between previously reported data and our results to differences in the adopted interaction potential energy surfaces. The new He rate coefficients can be used in a variety of applications. The estimated H2 and H collision rates can also augment the smaller datasets previously developed for H2 and electrons. Rate coefficient tables are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130

  4. Saturated hydrides in the HfV2-D system

    NASA Astrophysics Data System (ADS)

    Bogdanova, A. N.; Irodova, A. V.; André, G.

    2007-05-01

    Saturated solid solutions of hydrogen (deuterium) are synthesized up to the ratio D/HfV2 = 5.1 for the HfV2 compound with a structure of the cubic Laves phase (the C15 type) and the HfV2-based alloys (Hf0.7Zr0.3)V2 and Hf(V0.92Ti0.08)2 with partial substitution. The structure of the solid solutions is studied using neutron diffraction at room temperature. The saturated solid solutions of hydrogen are disordered: hydrogen occupies tetrahedral interstices 2Hf + 2V and 1Hf + 3V. The concentration of hydrogen in the solid solutions increases as the occupancy of the 1Hf + 3V interstices increases to the maximum value p 1Hf + 3V ˜ 0.46, whereas the occupancy of the 2Hf + 2V interstices remains constant and equal to p 2Hf + 2V ˜ 0.28. The maximum hydrogen concentration depends linearly on the lattice parameter of the initial intermetallic compound.

  5. Comet Ge-Wang

    NASA Astrophysics Data System (ADS)

    Ge, Yong-liang; Wang, Qi; Han, Tao

    1990-03-01

    Comet Ge-Wang (1988o) was discovered by GE Yong-liang and WANG Qi at Xinglong Station of Beijing Observatory on 1988 November 4. We collected 13 observations of this comet in China and abroad and calculated its orbit. It passed the perihelion on 1988 May 23. Ephemerides up to 1991 April are given.

  6. Comet Ge-Wang

    NASA Astrophysics Data System (ADS)

    Ge, Yong-Liang; Wang, Qi; Han, Tao

    1989-03-01

    Comet Ge-Wang (1988o) was discovered by GE Yong-liang and WANG Qi at Xinglong Station of Beijing Observatory on November 4, 1988. Thirteen observations of this comet were collected in China and abroad and calculated its orbit. It passed the perihelion on May 23, 1988. Ephemerides up to April 1991 are given.

  7. Pathway studies in the fragmentation of Ge(CH 3) 4 involving Ge(3d,3p,3s) and C(1s) inner-shell photoexcitation in the range 49.5-450 eV

    NASA Astrophysics Data System (ADS)

    Boo, Bong Hyun; Saito, Norio; Suzuki, Isao H.; Koyano, Inosuke

    2002-06-01

    The dissociative multiple photoionization of tetramethylgermane (Ge(CH 3) 4) in the valence, and in the Ge(3d,3p,3s) and C(1s) inner-shell regions has been studied by using time-of-flight mass spectrometry coupled to synchrotron radiation in the range 49.5-450 eV. Total and individual photoion yields have been recorded as a function of the incident photon energy. Several discrete resonances over a structureless giant resonance are observed below the Ge(3p), Ge(3s) and C(1s) threshold regions. The structureless giant resonance corresponding to the Ge(3d) presumably arises from the continuum enhancement caused by the 3d→ɛf transition. Various monocations of H +, H 2+, CH n+ ( n=0-4), C 2H n+ ( n=0-5), GeH n+, GeCH n+, GeC 2H n+, and GeC 3H n+ are detected in the whole energy range. Dissociation processes have also been investigated by photoelectron-photoion and photoion-photoion coincidence methods. The dominant dissociation channel is found to be CH n+-GeCH n+ in the whole energy examined. Specific energy dependence of dissociation processes is observed in the Ge(3p) and Ge(3s) regions. With the help of ab initio HF/6-311++G(2df,p) calculation, we roughly estimated the photoabsorption positions and symmetries for the discrete core hole states.

  8. The low-temperature form of calcium gold stannide, CaAuSn.

    PubMed

    Lin, Qisheng; Corbett, John D

    2014-08-01

    The EuAuGe-type CaAuSn phase has been synthesized and single-crystal X-ray diffraction analysis reveals that it has an orthorhombic symmetry (space group Imm2), with a = 4.5261 (7) Å, b = 7.1356 (11) Å and c = 7.8147 (11) Å. The structure features puckered layers that are connected by homoatomic Au-Au and Sn-Sn interlayer bonds. This structure is one of the two parent structures of its high-temperature polymorph (ca 873 K), which is an intergrowth structure of the EuAuGe- and SrMgSi-type structures in a 2:3 ratio. PMID:25093357

  9. The low-temperature form of calcium gold stannide, CaAuSn

    SciTech Connect

    Lin, Qisheng; Corbett, John D

    2014-07-19

    The EuAuGe-type CaAuSn phase has been synthesized and single-crystal X-ray diffraction analysis reveals that it has an ortho­rhom­bic symmetry (space group Imm2), with a = 4.5261 (7) Å, b = 7.1356 (11) Å and c = 7.8147 (11) Å. The structure features puckered layers that are connected by homoatomic Au-Au and Sn-Sn inter­layer bonds. This structure is one of the two parent structures of its high-temperature polymorph (ca 873 K), which is an inter­growth structure of the EuAuGe- and SrMgSi-type structures in a 2:3 ratio.

  10. Phase equilibria, formation, crystal and electronic structure of ternary compounds in Ti-Ni-Sn and Ti-Ni-Sb ternary systems

    SciTech Connect

    Romaka, V.V.; Rogl, P.; Romaka, L.; Stadnyk, Yu.; Melnychenko, N.; Grytsiv, A.; Falmbigl, M.; Skryabina, N.

    2013-01-15

    The phase equilibria of the Ti-Ni-Sn and Ti-Ni-Sb ternary systems have been studied in the whole concentration range by means of X-ray and EPM analyses at 1073 K and 873 K, respectively. Four ternary intermetallic compounds TiNiSn (MgAgAs-type), TiNi{sub 2-x}Sn (MnCu{sub 2}Al-type), Ti{sub 2}Ni{sub 2}Sn (U{sub 2}Pt{sub 2}Sn-type), and Ti{sub 5}NiSn{sub 3} (Hf{sub 5}CuSn{sub 3}-type) are formed in Ti-Ni-Sn system at 1073 K. The TiNi{sub 2}Sn stannide is characterized by homogeneity in the range of 50-47 at% of Ni. The Ti-Ni-Sb ternary system at 873 K is characterized by formation of three ternary intermetallic compounds, Ti{sub 0.8}NiSb (MgAgAs-type), Ti{sub 5}Ni{sub 0.45}Sb{sub 2.55} (W{sub 5}Si{sub 3}-type), and Ti{sub 5}NiSb{sub 3} (Hf{sub 5}CuSn{sub 3}-type). The solubility of Ni in Ti{sub 0.8}NiSb decreases number of vacancies in Ti site up to Ti{sub 0.91}Ni{sub 1.1}Sb composition. - Graphical abstract: Isothermal section of the Ti-Ni-Sn phase diagram and DOS distribution in hypothetical TiNi{sub 1+x}Sn solid solution. Highlights: Black-Right-Pointing-Pointer Ti-Ni-Sn phase diagram was constructed at 1073 K. Black-Right-Pointing-Pointer Four ternary compounds are formed: TiNiSn, TiNi{sub 2-x}Sn, Ti{sub 2}Ni{sub 2}Sn, and Ti{sub 5}NiSn{sub 3}. Black-Right-Pointing-Pointer Three ternary compounds exist in Ti-Ni-Sb system at 873 K. Black-Right-Pointing-Pointer The TiNi{sub 2}Sb compound is absent.

  11. Atomic layer etching of Al2O3 using sequential, self-limiting thermal reactions with Sn(acac)2 and hydrogen fluoride.

    PubMed

    Lee, Younghee; George, Steven M

    2015-02-24

    The atomic layer etching (ALE) of Al2O3 was demonstrated using sequential, self-limiting thermal reactions with tin(II) acetylacetonate (Sn(acac)2) and hydrogen fluoride (HF) as the reactants. The Al2O3 samples were Al2O3 atomic layer deposition (ALD) films grown using trimethylaluminum and H2O. The HF source was HF-pyridine. Al2O3 was etched linearly with atomic level precision versus number of reactant cycles. The Al2O3 ALE was monitored at temperatures from 150 to 250 °C. Quartz crystal microbalance (QCM) studies revealed that the sequential Sn(acac)2 and HF reactions were self-limiting versus reactant exposure. QCM measurements also determined that the mass change per cycle (MCPC) increased with temperature from -4.1 ng/(cm(2) cycle) at 150 °C to -18.3 ng/(cm(2) cycle) at 250 °C. These MCPC values correspond to etch rates from 0.14 Å/cycle at 150 °C to 0.61 Å/cycle at 250 °C based on the Al2O3 ALD film density of 3.0 g/cm(3). X-ray reflectivity (XRR) analysis confirmed the linear removal of Al2O3 and measured an Al2O3 ALE etch rate of 0.27 Å/cycle at 200 °C. The XRR measurements also indicated that the Al2O3 films were smoothed by Al2O3 ALE. The overall etching reaction is believed to follow the reaction Al2O3 + 6Sn(acac)2 + 6HF → 2Al(acac)3 + 6SnF(acac) + 3H2O. In the proposed reaction mechanism, the Sn(acac)2 reactant donates acac to the substrate to produce Al(acac)3. The HF reactant allows SnF(acac) and H2O to leave as reaction products. The thermal ALE of many other metal oxides using Sn(acac)2 or other metal β-diketonates, together with HF, should be possible by a similar mechanism. This thermal ALE mechanism may also be applicable to other materials such as metal nitrides, metal phosphides, metal sulfides and metal arsenides. PMID:25604976

  12. Dynamics of the F(-) + CH3I → HF + CH2I(-) Proton Transfer Reaction.

    PubMed

    Zhang, Jiaxu; Xie, Jing; Hase, William L

    2015-12-17

    Direct chemical dynamics simulations, at collision energies Erel of 0.32 and 1.53 eV, were performed to obtain an atomistic understanding of the F(-) + CH3I reaction dynamics. There is only the F(-) + CH3I → CH3F + I(-) bimolecular nucleophilic substitution SN2 product channel at 0.32 eV. Increasing Erel to 1.53 eV opens the endothermic F(-) + CH3I → HF + CH2I(-) proton transfer reaction, which is less competitive than the SN2 reaction. The simulations reveal proton transfer occurs by two direct atomic-level mechanisms, rebound and stripping, and indirect mechanisms, involving formation of the F(-)···HCH2I complex and the roundabout. For the indirect trajectories all of the CH2I(-) is formed with zero-point energy (ZPE), while for the direct trajectories 50% form CH2I(-) without ZPE. Without a ZPE constraint for CH2I(-), the reaction cross sections for the rebound, stripping, and indirect mechanisms are 0.2 ± 0.1, 1.2 ± 0.4, and 0.7 ± 0.2 Å(2), respectively. Discarding trajectories that do not form CH2I(-) with ZPE reduces the rebound and stripping cross sections to 0.1 ± 0.1 and 0.7 ± 0.5 Å(2). The HF product is formed rotationally and vibrationally unexcited. The average value of J is 2.6 and with histogram binning n = 0. CH2I(-) is formed rotationally excited. The partitioning between CH2I(-) vibration and HF + CH2I(-) relative translation energy depends on the treatment of CH2I(-) ZPE. Without a CH2I(-) ZPE constraint the energy partitioning is primarily to relative translation with little CH2I(-) vibration. With a ZPE constraint, energy partitioning to CH2I(-) rotation, CH2I(-) vibration, and relative translation are statistically the same. The overall F(-) + CH3I rate constant at Erel of both 0.32 and 1.53 eV is in good agreement with experiment and negligibly affected by the treatment of CH2I(-) ZPE, since the SN2 reaction is the major contributor to the total reaction rate constant. The potential energy surface and reaction dynamics for F

  13. Heterogeneous chemistry of HBr and HF

    SciTech Connect

    Hanson, D.R.; Ravishankara, A.R.

    1992-11-12

    The authors present information on heterogeneous chemistry of HF and HBr on glass and ice surfaces at a temperature of 200K. Their objective is to study whether heterogeneous reactions of these species could be important in the atmospheric chemistry occuring on NAT particles or cloud condensation nuclei, and be a contributor to ozone depletion. HF showed no significant uptake or reactions with ClONO{sub 2} or HOCl. HBr was found to adsorb on these surfaces, and did not exhibit saturation for even relative high concentrations. In addition it showed reactivity with ClONO{sub 2}, Cl{sub 2} and N{sub 2}O{sub 5} on ice surfaces.

  14. Site Dependency of the High Conductivity of Ga 2 In 6 Sn 2 O 16 : The Role of the 7-Coordinate Site

    DOE PAGESBeta

    Rickert, Karl; Huq, Ashfia; Lapidus, Saul H.; Wustrow, Allison; Ellis, Donald E.; Poeppelmeier, Kenneth R.

    2015-11-11

    In 6-coordinated cation sites, we find that it is the fundamental building block of the most effective transparent conducting oxides. Ga2In6SnO16, however, maintains 4-, 6-, 7-, and 8-coordinated cation sites and still exhibits desirable transparency and high conductivity. To investigate the potential impact of these alternative sites, we partially replace the Sn in Ga2In6Sn2O16 with Ti, Zr, or Hf and use a combined approach of density functional theory-based calculations, X-ray diffraction, and neutron diffraction to establish that the substitution occurs preferentially on the 7-coordinate site. Conversely to Sn, the empty d orbitals of Ti, Zr, and Hf promote spd covalencymore » with the surrounding oxygen, which decreases the conductivity. Pairing the substitutional site preference with the magnitude of this decrease demonstrates that the 7-coordinate site is the V major contributor to conductivity. The optical band gaps, in contrast, are shown to be site-independent and composition-dependent. After all 7-coordinate Sn has been replaced, the continued substitution of Sn results in the formation of a 7-coordinate In antisite or replacement of 6-coordinate Sn, depending on the identity of the d(0) substitute.« less

  15. SERVE-HF: More Questions Than Answers.

    PubMed

    Javaheri, Shahrokh; Brown, Lee K; Randerath, Winfried; Khayat, Rami

    2016-04-01

    The recent online publication of the SERVE-HF trial that evaluated the effect of treating central sleep apnea (CSA) with an adaptive servoventilation (ASV) device in patients with heart failure and reduced ejection fraction (HFrEF) has raised serious concerns about the safety of ASV in these patients. Not only was ASV ineffective but post hoc analysis found excess cardiovascular mortality in treated patients. The authors cited as one explanation an unfounded notion that CSA is a compensatory mechanism with a protective effect in HFrEF patients. We believe that there are several possible considerations that are more likely to explain the results of SERVE-HF. In this commentary, we consider methodological issues including the use of a previous-generation ASV device that constrained therapeutic settings to choices that are no longer in wide clinical use. Patient selection, data collection, and treatment adherence as well as group crossovers were not discussed in the trial as potential confounding factors. We have developed alternative reasons that could potentially explain the results and that can be explored by post hoc analysis of the SERVE-HF data. We believe that our analysis is of critical value to the field and of particular importance to clinicians treating these patients. PMID:26836904

  16. Metal-assisted chemical etching of Ge surface and its effect on photovoltaic devices

    NASA Astrophysics Data System (ADS)

    Lee, Seunghyo; Choo, Hyeokseong; Kim, Changheon; Oh, Eunseok; Seo, Dongwan; Lim, Sangwoo

    2016-05-01

    Ge surfaces were etched by means of metal-assisted chemical etching (MaCE). The behavior of the MaCE reaction in diluted H2O2 was compared with that of a conventional etchant of HF/H2O2/H2O mixture (FPM). Herein we first report that a pyramidal structure on Ge (0 0 1) can be prepared by MaCE in dilute H2O2 solution, without the use of HF. Contrastingly, an octagonal trench structure was prepared by 4/5/1 FPM treatment of Ge (0 0 1) surface. This octagonal structure consisted of a square base, four large facets connected to the base, and other four small facets adjacent to the four large facets, which were considered to be (0 0 1), {1 1 0}, and {1 1 1}, respectively. The octagonal trench was formed as a result of the difference in etch rate of Ge depending on the orientation: {1 0 0} > {1 1 0} > {1 1 1}. Ge surfaces treated by MaCE exhibited improved solar cell efficiency due to their improved light absorption, which led to significant increases in the cells' short circuit current and fill factor. The results suggest that optimized MaCE procedures can be an effective method to improve the performance of Ge-based photovoltaic devices.

  17. Measurement of the thermodynamic properties of saturated solid solutions of compounds in the Ag-Sn-Se system by the EMF method

    NASA Astrophysics Data System (ADS)

    Moroz, M. V.; Prokhorenko, M. V.

    2015-08-01

    The dependence of the EMF ( E) of galvanic cells Ag|AgI|Ag2GeS3 glass| D on temperature (where Ag, D denotes the electrodes of an electrochemical cell; D represents equilibrium two- and three-phase alloys of the Ag-Sn-Se system; and AgI|Ag2GeS3 glass is a bilayer membrane with purely ionic (Ag+) conductivity) is studied in the range of 480-580 K. Analytical equations of E( T) are used to calculate the values of the thermodynamic functions of saturated solid solutions of the SnSe, β-Ag2Se, AgSnSe2, and Ag8SnSe6 phases of the Ag-Sn-Se system in the standard state.

  18. Materials Data on HfCo2Sn (SG:225) by Materials Project

    SciTech Connect

    Kristin Persson

    2015-03-09

    Computed materials data using density functional theory calculations. These calculations determine the electronic structure of bulk materials by solving approximations to the Schrodinger equation. For more information, see https://materialsproject.org/docs/calculations

  19. Materials Data on HfNiSn (SG:216) by Materials Project

    SciTech Connect

    Kristin Persson

    2015-03-24

    Computed materials data using density functional theory calculations. These calculations determine the electronic structure of bulk materials by solving approximations to the Schrodinger equation. For more information, see https://materialsproject.org/docs/calculations

  20. Materials Data on HfSn (SG:198) by Materials Project

    SciTech Connect

    Kristin Persson

    2015-02-09

    Computed materials data using density functional theory calculations. These calculations determine the electronic structure of bulk materials by solving approximations to the Schrodinger equation. For more information, see https://materialsproject.org/docs/calculations

  1. Materials Data on HfSnPd (SG:216) by Materials Project

    SciTech Connect

    Kristin Persson

    2015-02-09

    Computed materials data using density functional theory calculations. These calculations determine the electronic structure of bulk materials by solving approximations to the Schrodinger equation. For more information, see https://materialsproject.org/docs/calculations

  2. LU-HF Age and Isotope Systematics of ALH84001

    NASA Technical Reports Server (NTRS)

    Righter, M.; Lapen, T. J.; Brandon, A. D.; Beard, B. L.; Shafer, J. T.; Peslier, A. H.

    2009-01-01

    Allan Hills (ALH) 84001 is an orthopyroxenite that is unique among the Martian meteorites in having the oldest inferred crystallization age (approx..4.5 to 4.0 Gyr) [e.g., 1-6 and references therein 7]. Its ancient origin makes this stone a critical constraint on early history of Mars, in particular the evolution of different planetary crust and mantle reservoirs. However, because there is significant variability in reported crystallization ages, determination of initial isotope compositions is imprecise making assessment of planetary reservoirs difficult. Here we report a new Lu-Hf mineral isochron age, initial Hf-176/Hf-177 isotope composition, and inferred Martian mantle source compositions for ALH84001 that place constraints on longlived source reservoirs for the enriched shergottite suite of Martian meteorites including Shergotty, Zagami, NWA4468, NWA856, RBT04262, LAR06319, and Los Angeles. Sm-Nd isotope analyses are under way for the same mineral aliquots analyzed for Lu-Hf. The Lu-Hf system was utilized because Lu and Hf are both lithophile and refractory and are not easily redistributed during short-lived thermal pulses associated with shock metamorphism. Moreover, chromite has relatively modest Hf concentrations with very low Lu/Hf ratios [9] yielding tight constraints on initial Hf-176/Hf-177 isotope compositions

  3. Electric Field Gradients at Hf and Fe Sites in Hf2Fe Recalculated

    NASA Astrophysics Data System (ADS)

    Belošević-Čavor, J.; Cekić, B.; Novaković, N.; Koteski, V.; Milošević, Z.

    2004-11-01

    The electric field gradients (EFG) of the Hf2Fe intermetallic compound were calculated using the full-potential linearized augmented plain-wave (FP-LAPW) method as embodied in the WIEN 97 code. The obtained values are compared with other ab-initio calculations and on a qualitative basis with the previously reported experimental data obtained from TDPAC. The calculated results, -23.1·1021 V/m2 and 2.7·1021 V/m2 for Hf 48f and Fe 32e position, respectively, are in excellent agreement with experimental data (23.4·1021 V/m2 and 2.7·1021 V/m2), better than those reported in earlier calculations. The calculated EFG for Hf 16c position (4.2·1021 V/m2) is stronger than the experimental one (1.1·1021 V/m2).

  4. Investigation on the effective mass of Ge1-xSnx alloys and the transferred-electron effect

    NASA Astrophysics Data System (ADS)

    Liu, Lei; Liang, Renrong; Wang, Jing; Xu, Jun

    2015-03-01

    The electron band structures of Ge1-xSnx alloys were calculated using the nonlocal empirical pseudopotential method. The electron and hole effective masses were extracted, and the mobility enhancement over Ge was comprehensively analyzed. For the direct gap Ge1-xSnx with high Sn compositions, only a small fraction of electrons occupy the Γ valley with high mobility at room temperature. Hence, the negative differential mobility resulting from the transferred-electron effect may not be observed, and the electron mobility enhancement over Ge is only two-fold. Low temperature conditions may lead to the transferred-electron effect and a significantly enhanced electron mobility.

  5. Pirquitasite, Ag2ZnSnS4

    PubMed Central

    Schumer, Benjamin N.; Downs, Robert T.; Domanik, Kenneth J.; Andrade, Marcelo B; Origlieri, Marcus J.

    2013-01-01

    Pirquitasite, ideally Ag2ZnSnS4 (disilver zinc tin tetra­sulfide), exhibits tetra­gonal symmetry and is a member of the stannite group that has the general formula A2BCX 4, with A = Ag, Cu; B = Zn, Cd, Fe, Cu, Hg; C = Sn, Ge, Sb, As; and X = S, Se. In this study, single-crystal X-ray diffraction data are used to determine the structure of pirquitasite from a twinned crystal from the type locality, the Pirquitas deposit, Jujuy Province, Argentina, with anisotropic displacement parameters for all atoms, and a measured composition of (Ag1.87Cu0.13)(Zn0.61Fe0.36Cd0.03)SnS4. One Ag atom is located on Wyckoff site Wyckoff 2a (symmetry -4..), the other Ag atom is statistically disordered with minor amounts of Cu and is located on 2c (-4..), the (Zn, Fe, Cd) site on 2d (-4..), Sn on 2b (-4..), and S on general site 8g. This is the first determination of the crystal structure of pirquitasite, and our data indicate that the space group of pirquitasite is I-4, rather than I-42m as previously suggested. The structure was refined under consideration of twinning by inversion [twin ratio of the components 0.91 (6):0.09 (6)]. PMID:23424398

  6. Stellar Laboratories: New GeV and Ge VI Oscillator Strengths and their Validation in the Hot White Dwarf RE0503-289

    NASA Technical Reports Server (NTRS)

    Rauch, T.; Werner, K.; Biemont, E.; Quinet, P.; Kruk, J. W.

    2013-01-01

    State-of-the-art spectral analysis of hot stars by means of non-LTE model-atmosphere techniques has arrived at a high level of sophistication. The analysis of high-resolution and high-S/N spectra, however, is strongly restricted by the lack of reliable atomic data for highly ionized species from intermediate-mass metals to trans-iron elements. Especially data for the latter has only been sparsely calculated. Many of their lines are identified in spectra of extremely hot, hydrogen-deficient post-AGB stars. A reliable determination of their abundances establishes crucial constraints for AGB nucleosynthesis simulations and, thus, for stellar evolutionary theory. Aims. In a previous analysis of the UV spectrum of RE 0503-289, spectral lines of highly ionized Ga, Ge, As, Se, Kr, Mo, Sn, Te, I, and Xe were identified. Individual abundance determinations are hampered by the lack of reliable oscillator strengths. Most of these identified lines stem from Ge V. In addition, we identified Ge VI lines for the first time. We calculated Ge V and Ge VI oscillator strengths in order to reproduce the observed spectrum. Methods. We newly calculated Ge V and Ge VI oscillator strengths to consider their radiative and collisional bound-bound transitions in detail in our non-LTE stellar-atmosphere models for the analysis of the Ge IV-VI spectrum exhibited in high-resolution and high-S/N FUV (FUSE) and UV (ORFEUS/BEFS, IUE) observations of RE 0503-289. Results. In the UV spectrum of RE 0503-289, we identify four Ge IV, 37 Ge V, and seven Ge VI lines. Most of these lines are identified for the first time in any star. We can reproduce almost all Ge IV, GeV, and Ge VI lines in the observed spectrum of RE 0503-289 (T(sub eff) = 70 kK, log g = 7.5) at log Ge = -3.8 +/- 0.3 (mass fraction, about 650 times solar). The Ge IV/V/VI ionization equilibrium, that is a very sensitive T(sub eff) indicator, is reproduced well. Conclusions. Reliable measurements and calculations of atomic data are a

  7. Thermoelectric properties of doped BaHfO3

    NASA Astrophysics Data System (ADS)

    Dixit, Chandra Kr.; Bhamu, K. C.; Sharma, Ramesh

    2016-05-01

    We have studied the structural stability, electronic structure, optical properties and thermoelectric properties of doped BaHfO3 by full potential linearized augmented plane wave (FP-LAPW) method. The electronic structure of BaHfO3 doped with Sr shows enhances the indirect band gaps of 3.53 eV, 3.58 eV. The charge density plots show strong ionic bonding in Ba-Hf, and ionic and covalent bonding between Hf and O. Calculations of the optical spectra, viz., the dielectric function, refractive index and extinction coefficient are performed for the energy range are calculated and analyzed. Thermoelectric properties of semi conducting are also reported first time. The doped BaHfO3 is approximately wide band gap semiconductor with the large p-type Seebeck coefficient. The power factor of BaHfO3 is increased with Sr doping, decreases because of low electrical resistivity and thermal conductivity.

  8. Structure-property relationships in lithium superionic conductors having a Li10GeP2S12-type structure.

    PubMed

    Hori, Satoshi; Taminato, Sou; Suzuki, Kota; Hirayama, Masaaki; Kato, Yuki; Kanno, Ryoji

    2015-12-01

    The crystal structures of the superionic conductors Li9.81Sn0.81P2.19S12 and Li10.35Si1.35P1.65S12, both having a Li10GeP2S12 (LGPS)-type structure, were determined by neutron diffraction analysis over the temperature range 12-800 K. The maximum entropy method was also employed to clarify the lithium distribution in these materials. The Sn system showed one-dimensional diffusion in the c direction over a wide temperature range, even though the Ge-based system typically exhibits three-dimensional conduction at higher temperatures. The ionic conduction mechanisms of analogous Si, Ge and Sn phases with LGPS-type structures are discussed on the basis of the observed structural parameter changes. PMID:26634730

  9. Competition of optical transitions between direct and indirect bandgaps in Ge1-xSnx

    NASA Astrophysics Data System (ADS)

    Du, Wei; Ghetmiri, Seyed A.; Conley, Benjamin R.; Mosleh, Aboozar; Nazzal, Amjad; Soref, Richard A.; Sun, Greg; Tolle, John; Margetis, Joe; Naseem, Hameed A.; Yu, Shui-Qing

    2014-08-01

    Temperature-dependent photoluminescence (PL) study has been conducted in Ge1-xSnx films with Sn compositions of 0.9%, 3.2%, and 6.0% grown on Si. The competing between the direct and indirect bandgap transitions was clearly observed. The relative peak intensity of direct transition with respect to the indirect transition increases with an increase in temperature, indicating the direct transition dominates the PL at high temperature. Furthermore, as Sn composition increases, a progressive enhancement of direct transition was observed due to the reduction of direct-indirect valley separation, which experimentally confirms that the Ge1-xSnx could become the group IV-based direct bandgap material grown on Si by increasing the Sn content.

  10. Improvements in the electrical properties of high-k HfO2 dielectric films on Si1-xGex substrates by postdeposition annealing

    NASA Astrophysics Data System (ADS)

    Park, Tae Joo; Kim, Jeong Hwan; Jang, Jae Hyuk; Seo, Minha; Hwang, Cheol Seong; Won, Jeong Yeon

    2007-01-01

    The changes in atomic-layer-deposited HfO2 films on Si and Si1-xGex (x =0.1, 0.2, and 0.3) substrates by postdeposition annealing were studied. The migration of Ge reduced the capacitance equivalent thickness while keeping the leakage current density almost invariant after annealing. High resolution x-ray photoelectron spectroscopy and secondary ion mass spectroscopy analyses confirmed that Ge atoms which had diffused into the HfO2 layer during the deposition were drawn back to the substrate by annealing which was accompanied by the decrease in the interfacial strain energy. A very low interface trap density (1.3×1010cm-2eV-1) was obtained when x =0.3.

  11. The Inhibition of Tin Whiskers on the Surface of Sn-8Zn-3Bi-0.5Ce Solders

    NASA Astrophysics Data System (ADS)

    Jain, C. C.; Chen, C. L.; Lai, H. J.; Chuang, T. H.

    2011-08-01

    Through the refinement of the (Ce, Zn)Sn3 intermetallic phase, the formation of tin whiskers, previously observed on the surface of a Sn-3Ag-0.5Cu-0.5Ce solder, was prevented in a Sn-9Zn-0.5Ce alloy. However, whisker growth can still occur on the surface of Sn-8Zn-3Bi-0.5Ce solder after air storage at room temperature and at 150 °C due to the formation of large (Ce, Zn)Sn3 intermetallic clusters. Further experiments showed that decreasing the Bi-content in this Sn-8Zn-0.5Ce alloy to 1 and 2 wt.% can recover the beneficial effects of Zn additions on the refinement of the (Ce, Zn)Sn3 phase and obviously reduce the appearance of tin whiskers. In addition, alloying the Sn-8Zn-3Bi-0.5Ce solder with 0.5 wt.% Ge, which increases the oxidation resistance of the (Ce, Zn)Sn3 intermetallic clusters, can also effectively inhibit tin whisker growth.

  12. HF sounding of the auroral magnetosphere

    NASA Astrophysics Data System (ADS)

    Gurevich, A. V.; Babichenko, A. M.; Karashtin, A. N.; Rapoport, V. O.

    1992-06-01

    Results are presented from incoherent scatter radar measurements in the magnetosphere, using the Radiophysical Research Institute 'Sura' heating facility operated in the frequency range 4.5-9 MHz. The first magnetosphere sounding experiments were carried out on February 21, 1989; a frequency of 9.310 MHz was used for the sounding, while the effective radiated power was about 30 MW. The results of analyses of the scattered signal spectra showed that, in the auroral region of the polar magnetosphere, ion acoustic oscillations are excited and that the HF sounding technique used in this study was an effective method for magnetosphere sounding.

  13. The demonstration of significant ferroelectricity in epitaxial Y-doped HfO2 film

    PubMed Central

    Shimizu, Takao; Katayama, Kiliha; Kiguchi, Takanori; Akama, Akihiro; Konno, Toyohiko J.; Sakata, Osami; Funakubo, Hiroshi

    2016-01-01

    Ferroelectricity and Curie temperature are demonstrated for epitaxial Y-doped HfO2 film grown on (110) yttrium oxide-stabilized zirconium oxide (YSZ) single crystal using Sn-doped In2O3 (ITO) as bottom electrodes. The XRD measurements for epitaxial film enabled us to investigate its detailed crystal structure including orientations of the film. The ferroelectricity was confirmed by electric displacement filed – electric filed hysteresis measurement, which revealed saturated polarization of 16 μC/cm2. Estimated spontaneous polarization based on the obtained saturation polarization and the crystal structure analysis was 45 μC/cm2. This value is the first experimental estimations of the spontaneous polarization and is in good agreement with the theoretical value from first principle calculation. Curie temperature was also estimated to be about 450 °C. This study strongly suggests that the HfO2-based materials are promising for various ferroelectric applications because of their comparable ferroelectric properties including polarization and Curie temperature to conventional ferroelectric materials together with the reported excellent scalability in thickness and compatibility with practical manufacturing processes. PMID:27608815

  14. The demonstration of significant ferroelectricity in epitaxial Y-doped HfO2 film.

    PubMed

    Shimizu, Takao; Katayama, Kiliha; Kiguchi, Takanori; Akama, Akihiro; Konno, Toyohiko J; Sakata, Osami; Funakubo, Hiroshi

    2016-01-01

    Ferroelectricity and Curie temperature are demonstrated for epitaxial Y-doped HfO2 film grown on (110) yttrium oxide-stabilized zirconium oxide (YSZ) single crystal using Sn-doped In2O3 (ITO) as bottom electrodes. The XRD measurements for epitaxial film enabled us to investigate its detailed crystal structure including orientations of the film. The ferroelectricity was confirmed by electric displacement filed - electric filed hysteresis measurement, which revealed saturated polarization of 16 μC/cm(2). Estimated spontaneous polarization based on the obtained saturation polarization and the crystal structure analysis was 45 μC/cm(2). This value is the first experimental estimations of the spontaneous polarization and is in good agreement with the theoretical value from first principle calculation. Curie temperature was also estimated to be about 450 °C. This study strongly suggests that the HfO2-based materials are promising for various ferroelectric applications because of their comparable ferroelectric properties including polarization and Curie temperature to conventional ferroelectric materials together with the reported excellent scalability in thickness and compatibility with practical manufacturing processes. PMID:27608815

  15. Epitaxial Thin Films of Y doped HfO2

    NASA Astrophysics Data System (ADS)

    Serrao, Claudy; Khan, Asif; Ramamoorthy, Ramesh; Salahuddin, Sayeef

    Hafnium oxide (HfO2) is one of a few metal oxides that is thermodynamically stable on silicon and silicon oxide. There has been renewed interest in HfO2 due to the recent discovery of ferroelectricity and antiferroelectricity in doped HfO2. Typical ferroelectrics - such as strontium bismuth tantalate (SBT) and lead zirconium titanate (PZT) - contain elements that easily react with silicon and silicon oxide at elevated temperatures; therefore, such ferroelectrics are not suited for device applications. Meanwhile, ferroelectric HfO2 offers promise regarding integration with silicon. The stable phase of HfO2 at room temperature is monoclinic, but HfO2 can be stabilized in the tetragonal, orthorhombic or even cubic phase by suitable doping. We stabilized Y-doped HfO2 thin films using pulsed laser deposition. The strain state can be controlled using various perovskite substrates and controlled growth conditions. We report on Y-doped HfO2 domain structures from piezo-response force microscopy (PFM) and structural parameters via X-ray reciprocal space maps (RSM). We hope this work spurs further interest in strain-tuned ferroelectricity in doped HfO2.

  16. Mitigating Doppler shift effect in HF multitone data modem

    NASA Astrophysics Data System (ADS)

    Sonlu, Yasar

    1989-09-01

    Digital communications over High Frequency (HF) radio channels are getting important in recent years. Current HF requirements are for data transmission at rates 2.4 kbps or more to accommodate computer data links and digital secure voice. HF modems which were produced to meet these speeds are, serial modems and parallel modems. On the other hand, the HF sky-wave communication medium, the ionosphere, has some propagation problems such as multipath and Doppler shift. The effect of Doppler shift in a parallel modem which employs Differential Quadrature Phase Shift Keying (DQPSK) modulation is considered and a correction method to mitigate the Doppler Shift effect is introduced.

  17. Comparative analysis of cross sections of residual nuclei on separated tin isotopes at a beam energy of protons and deuterons 3.65 GeV/nucleon

    SciTech Connect

    Balabekyan, A. R.; Demekhina, N. A.; Simonyan, A. E.

    2013-03-15

    The cross sections of residual nuclei in the separated tin isotopes ({sup 112}Sn, {sup 118}Sn, {sup 120}Sn, and {sup 124}Sn), irradiated with proton and deuteron beams with energy 3.65 GeV/nucleon, are investigated. Parametrization by ten parametric semi-empirical formula was conducted with the aim of determining the total cross sections and analyzing the measurement results. The dependence of total inelastic cross sections on the mass number of the target and the structure of the incoming particle was investigated via the comparison of the obtained data.

  18. Nonlinear behavior of the energy gap in Ge1-xSnx alloys at 4 K

    NASA Astrophysics Data System (ADS)

    Pérez Ladrón de Guevara, H.; Rodríguez, A. G.; Navarro-Contreras, H.; Vidal, M. A.

    2007-10-01

    The optical energy gap of Ge1-xSnx alloys (x⩽0.14) grown on Ge substrates has been determined by performing transmittance measurements at 4K using a fast fourier transform infrared interferometer. The direct energy gap transitions in Ge1-xSnx alloys behave following a nonlinear dependence on the Sn concentration, expressed by a quadratic equation, with a so called bowing parameter b0 that describes the deviation from a simple linear dependence. Our observations resulted in b0RT=2.30±0.10eV and b04K=2.84±0.15eV, at room temperature and 4K, respectively. The validity of our fit is limited for Sn concentrations lower than 15%.

  19. Band gap engineering of Si-Ge alloys for mid-temperature thermoelectric applications

    SciTech Connect

    Pulikkotil, J. J.; Auluck, S.

    2015-03-15

    The viability of Si-Ge alloys in thermoelectric applications lies in its high figure-of-merit, non-toxicity and earth-abundance. However, what restricts its wider acceptance is its operation temperature (above 1000 K) which is primarily due to its electronic band gap. By means of density functional theory calculations, we propose that iso-electronic Sn substitutions in Si-Ge can not only lower its operation to mid-temperature range but also deliver a high thermoelectric performance. While calculations find a near invariance in the magnitude of thermopower, empirical models indicate that the materials thermal conductivity would also reduce, thereby substantiating that Si-Ge-Sn alloys are promising mid-temperature thermoelectrics.

  20. Compositional dependence of the band-gap of Ge1-x-ySixSny alloys

    NASA Astrophysics Data System (ADS)

    Wendav, Torsten; Fischer, Inga A.; Montanari, Michele; Zoellner, Marvin Hartwig; Klesse, Wolfgang; Capellini, Giovanni; von den Driesch, Nils; Oehme, Michael; Buca, Dan; Busch, Kurt; Schulze, Jörg

    2016-06-01

    The group-IV semiconductor alloy Ge1-x-ySixSny has recently attracted great interest due to its prospective potential for use in optoelectronics, electronics, and photovoltaics. Here, we investigate molecular beam epitaxy grown Ge1-x-ySixSny alloys lattice-matched to Ge with large Si and Sn concentrations of up to 42% and 10%, respectively. The samples were characterized in detail by Rutherford backscattering/channeling spectroscopy for composition and crystal quality, x-ray diffraction for strain determination, and photoluminescence spectroscopy for the assessment of band-gap energies. Moreover, the experimentally extracted material parameters were used to determine the SiSn bowing and to make predictions about the optical transition energy.

  1. Ferroelectricity of nondoped thin HfO2 films in TiN/HfO2/TiN stacks

    NASA Astrophysics Data System (ADS)

    Nishimura, Tomonori; Xu, Lun; Shibayama, Shigehisa; Yajima, Takeaki; Migita, Shinji; Toriumi, Akira

    2016-08-01

    We report on the impact of TiN interfaces on the ferroelectricity of nondoped HfO2. Ferroelectric properties of nondoped HfO2 in TiN/HfO2/TiN stacks are shown in capacitance–voltage and polarization–voltage characteristics. The Curie temperature is also estimated to be around 500 °C. The ferroelectricity of nondoped HfO2 clearly appears by thinning HfO2 film down to ∼35 nm. We directly revealed in thermal treatments that the ferroelectric HfO2 film on TiN was maintained by covering the top surface of HfO2 with TiN, while it was followed by a phase transition to the paraelectric phase in the case of the open surface of HfO2. Thus, it is concluded that the ferroelectricity in nondoped HfO2 in this study was mainly driven by both of top and bottom TiN interfaces.

  2. Electronic Structure and Defect Physics of Tin Sulfides: SnS, Sn2S3 , and Sn S2

    NASA Astrophysics Data System (ADS)

    Kumagai, Yu; Burton, Lee A.; Walsh, Aron; Oba, Fumiyasu

    2016-07-01

    The tin sulfides SnS, Sn2S3 , and Sn S2 are investigated for a wide variety of applications such as photovoltaics, thermoelectrics, two-dimensional electronic devices, Li ion battery electrodes, and photocatalysts. For these applications, native point defects play important roles, but only those of SnS have been investigated theoretically in the literature. In this study, we consider the band structures, band-edge positions, and thermodynamical stability of the tin sulfides using a density functional that accounts for van der Waals corrections and the G W0 approximation. We revisit the point-defect properties, namely, electronic and atomic structures and energetics of defects, in SnS and newly examine those in Sn S2 and Sn2S3 with a comparison to those in SnS. We find that Sn S2 shows contrasting defect properties to SnS: Undoped SnS shows p -type behavior, whereas Sn S2 shows n type, which are mainly attributed to the tin vacancies and tin interstitials, respectively. We also find that the defect features in Sn2S3 can be described as a combination of those in SnS and Sn S2 , intrinsically Sn2S3 showing n -type behavior. However, the conversion to p type can be attained by doping with a large monovalent cation, namely, potassium. The ambipolar dopability, coupled with the earth abundance of its constituents, indicates great potential for electronic applications, including photovoltaics.

  3. Materials Data on HfGePd (SG:11) by Materials Project

    SciTech Connect

    Kristin Persson

    2015-05-31

    Computed materials data using density functional theory calculations. These calculations determine the electronic structure of bulk materials by solving approximations to the Schrodinger equation. For more information, see https://materialsproject.org/docs/calculations

  4. Materials Data on Hf5Ge3 (SG:193) by Materials Project

    SciTech Connect

    Kristin Persson

    2015-05-16

    Computed materials data using density functional theory calculations. These calculations determine the electronic structure of bulk materials by solving approximations to the Schrodinger equation. For more information, see https://materialsproject.org/docs/calculations

  5. Materials Data on Hf3(NiGe)4 (SG:71) by Materials Project

    SciTech Connect

    Kristin Persson

    2015-02-09

    Computed materials data using density functional theory calculations. These calculations determine the electronic structure of bulk materials by solving approximations to the Schrodinger equation. For more information, see https://materialsproject.org/docs/calculations

  6. Materials Data on HfGeTe (SG:129) by Materials Project

    SciTech Connect

    Kristin Persson

    2015-03-24

    Computed materials data using density functional theory calculations. These calculations determine the electronic structure of bulk materials by solving approximations to the Schrodinger equation. For more information, see https://materialsproject.org/docs/calculations

  7. Hf isotope and concentration systematics of the Mariana arc

    NASA Astrophysics Data System (ADS)

    Tollstrup, D. L.; Gill, J. B.

    2004-12-01

    Negative Hf concentration anomalies are common but little-discussed geochemical features of island arcs. Because both light rare earth elements (LREE) and Hf may be mobile even in `fluid-dominated' island arcs, it is important to relate their isotopic and elemental ratios to models of slab-mantle mixing. We report new Hf isotope and trace element data for K-rich submarine basalts from the Kasuga seamounts located 10-20 km behind the volcanic front of the southern Northern Seamount Province (NSP) of the Mariana arc. These data, when combined with published data for other Mariana samples, span the full range from low-K tholeiites to high-K shoshonites. Rear-arc Kasuga seamounts seamounts of the NSP have lower 143Nd/144Nd and 176Hf/177Hf ratios than arc-front volcanoes of the Mariana Central Island Province (CIP). Within the CIP, Hf concentration anomalies correlate positively with 176Hf/177Hf ratios. Radiogenic Hf and little or no concentration anomalies characterize samples from fluid-dominated volcanoes (Guguan and Maug), whereas samples from sediment-melt dominated volcanoes (Anatahan and Sarigan) have less radiogenic Hf and larger concentration anomalies. Samples from the Kasuga and Hiyoshi seamounts have even larger negative concentration anomalies and less radiogenic Hf, although the two are not always correlated. These data are consistent with mixing between a depleted mantle and a partial melt of subducted sediment that is saturated with trace accessory phases including zircon, rutile, and monazite. A more volcaniclastic source is needed for the NSP than the CIP. Implications of these findings are three-fold. Partial melts of subducting sediment affect the HFSE and REE budgets of even fluid-dominated island arcs. Slab temperatures must be high enough for a peraluminous melt to be present, even where old, cold slabs are subducting. Refractory accessory phases have the potential to become exotic "nuggets" in the convecting mantle, potentially controlling the

  8. EPR spectroscopic characterization of persistent germyl-substituted Pb(III)- and Sn(III)-radicals.

    PubMed

    Kurzbach, Dennis; Yao, Shenglai; Hinderberger, Dariush; Klinkhammer, Karl W

    2010-07-28

    In this report we present the synthesis and the detailed electron paramagnetic resonance (EPR) spectroscopic characterization of novel trivalent lead- and tin-based radicals comprising sterically demanding germyl substituents. The investigated radicals are derived from the recently reported trihypersilyl-substituted tetryl radicals *PbHyp3 and *SnHyp3. The tetryl radicals *Pb(Ge(SiMe3)3)3 (8), *Pb(Ge(SiMe3)3)2Si(SiMe3)3 (9), *PbGe(SiMe3)3(Si(SiMe3)3)2 (10), and *Sn(Ge(SiMe3)3)3 (11) show substitution patterns derived from stepwise (9, 10) or complete (8, 11) substitution of hypersilyl groups (Hyp = Si(SiMe3)3) in *PbHyp3 and *SnHyp3 by homologous hypergermyl groups (Hge = Ge(SiMe3)3). They were generated through oxidation of the corresponding potassium tetranides KPbR3 and KSnR3 (R = Hyp, Hge), which in turn had been synthesized employing nucleophilic addition of KHyp or KHge to PbHyp2 or to the novel tetrylenes PbHge2 (1) and SnHge2 (12). The gained EPR spectroscopic data give insights into the influence of the substitution pattern on the geometric and electronic properties of the lead-centered species. With an increasing number of germyl substituents, the spin-orbit coupling to the central atom increases resulting in larger g(iso)-values and larger g-anisotropies while the 209Pb hyperfine splitting constants A(iso) decrease. These decreasing splitting constants are indicative of a diminished s-character of the singly occupied molecular orbital (SOMO) and to a molecular geometry running from slightly pyramidal to almost planar. Interestingly, already one germyl substituent (for radical 10) dominates most of the mentioned properties. For stannyl radical 11 a similar trend is seen for the spin-orbit coupling, while the (117/119)Sn hyperfine splittings unexpectedly increase from SnHyp3 to SnHge3. PMID:20532294

  9. Magnetic properties and complex magnetic phase diagram in non-centrosymmetric EuRhGe3 and EuIrGe3 single crystals

    NASA Astrophysics Data System (ADS)

    Maurya, Arvind; Bonville, P.; Kulkarni, R.; Thamizhavel, A.; Dhar, S. K.

    2016-03-01

    We report the magnetic properties of two Eu based compounds, single crystalline EuIrGe3 and EuRhGe3, inferred from magnetisation, electrical transport, heat capacity and 151Eu Mössbauer spectroscopy. These previously known compounds crystallise in the non-centrosymmetric, tetragonal, I4 mm, BaNiSn3-type structure. Single crystals of EuIrGe3 and EuRhGe3 were grown using a high temperature solution growth method using In as flux. EuIrGe3 exhibits two magnetic transition temperatures TN1 = 12.4 K, and TN 2 = 7.3 K, whereas EuRhGe3 presents a single one at TN = 12 K. 151Eu Mössbauer spectra show evidence for a cascade of transitions from paramagnetic to incommensurate amplitude modulated followed by an equal moment phase at lower temperature in EuIrGe3. This latter phase alone occurs in EuRhGe3. In both compounds, the magnetisation measured up to 14 T suggests that the equal moment magnetic phase has a spiral spin arrangement. The field induced reorientations are also well documented in the magnetotransport data. A superzone gap is observed for the current density J ∥ [001], which is enhanced by a transverse magnetic field. The magnetic phase diagram constructed from all the data is complex, revealing the presence of many phases in the H - T space.

  10. Gas-phase chemistry of ionized and protonated GeF4: a joint experimental and theoretical study.

    PubMed

    Antoniotti, Paola; Bottizzo, Elena; Operti, Lorenza; Rabezzana, Roberto; Borocci, Stefano; Grandinetti, Felice

    2011-05-01

    The gas-phase ion chemistry of GeF(4) and of its mixtures with water, ammonia and hydrocarbons was investigated by ion trap mass spectrometry (ITMS) and ab initio calculations. Under ITMS conditions, the only fragment detected from ionized GeF(4) is GeF(3)(+). This cation is a strong Lewis acid, able to react with H(2)O, NH(3) and the unsaturated C(2)H(2), C(2)H(4) and C(6)H(6) by addition-HF elimination reactions to form F(2)Ge(XH)(+), FGe(XH)(2)(+), Ge(XH)(3)(+) (X = OH or NH(2)), F(2)GeC(2)H(+), F(2)GeC(2)H(3)(+) and F(2)GeC(6)H(5)(+). The structure, stability and thermochemistry of these products and the mechanistic aspects of the exemplary reactions of GeF(3)(+) with H(2)O, NH(3) and C(6)H(6) were investigated by MP2 and coupled cluster calculations. The experimental proton affinity (PA) and gas basicity (GB) of GeF(4) were estimated as 121.5 ± 6.0 and 117.1 ± 6.0 kcal mol(-1), respectively, and GeF(4)H(+) was theoretically characterized as an ion-dipole complex between GeF(3)(+) and HF. Consistently, it reacts with simple inorganic and organic molecules to form GeF(3)(+)-L complexes (L = H(2)O, NH(3), C(2)H(2), C(2)H(4), C(6)H(6), CO(2), SO(2) and GeF(4)). The theoretical investigation of the stability of these ions with respect to GeF(3)(+) and L disclosed nearly linear correlations between their dissociation enthalpies and free energies and the PA and GB of L. Comparing the behavior of GeF(3)(+) with the previously investigated CF(3)(+) and SiF(3)(+) revealed a periodically reversed order of reactivity CF(3)(+) < GeF(3)(+) < SiF(3)(+). This parallels the order of the Lewis acidities of the three cations. PMID:21500305

  11. Calculation of NMR lineshapes for Ba-Al-Ge clathrates

    NASA Astrophysics Data System (ADS)

    Rodriguez, Sergio; Gou, Weiping; Ross, Joseph

    2008-10-01

    Clathrates consist of Si, Ge, or Sn cages in a crystalline framework, with guest atoms inside the cages. They have gained interest due to thermoelectric properties suitable for potential device application. To understand Al substitutional configurations, we calculated Al NMR line shapes for several structures with compositions Ba8Ge46-x-yAlxy for x=3,8,11,12,16,24; y=2,3; where represents a vacancy. The results were obtained by calculating Electric Field Gradients (EFG) for Al sites of type-I clathrates assuming an ordered superstructure of vacancies and framework occupation. We used ab initio methods in the Generalized Gradient Approximation as implemented by the WIEN2k program, and used the results to simulate NMR lineshapes numerically. These were compared to our previously reported NMR lineshapes. In the case of Ba8Ge31Al123 four Al sites in the superstructure include two sites with small EFG where the vacancy is far away and two sites with large EFG with a vacancy adjacent to Al. Assuming a larger Knight shift for sites next to vacancies, we obtain good agreement with NMR experimental results for reduced-Al Ba8Ge34Al12, while for the Zintl phase Ba8Ge30Al16 we obtain good agreement with no spontaneous vacancies. We infer that Al prefers locations close to vacancies rather than random occupation. This work was supported by Robert A. Welch Foundation (Grant A-1526).

  12. Kinetics of Hydrogen Diffusion in LaNi(sub 5-x)Sn(sub x) Alloys

    NASA Technical Reports Server (NTRS)

    Ratnakumar, B. V.; Hightower, A.; Witham, C.; Bowman, R. C.; Fultz, B.

    1996-01-01

    Solid-state diffusion of hydrogen in metal hydride (MH) alloys is recognized as the rate determining step in the discharge of MH alloys in alkaline Ni-MH rechargeable cells. In our pursuit of new ternary solutes in LaNi(sub 5) for extended cycle lifetimes, we have observed noticeable improvement in the cycle life with small substitutions of Sn and Ge for Ni. Furthermore, these substituents also facilitate enhanced charge transfer kinetics for hydriding-dehydriding process. In this paper, we report our studies on the kinetics of hydrogen diffusion in LaNi(sub 5-x) Sn(sub x) alloys by electrochemical pulse techniques, chronoamperometry and chronocoulometry.

  13. In-beam studies of {sup 98}Cd and {sup 102}Sn

    SciTech Connect

    Lipoglavsek, M. |; Gorska, M.; Schubart, R.

    1996-12-31

    For the first time excited states of the neutron deficient nuclei {sup 98}Cd and {sup 102}Sn were identified using in-beam spectroscopy following fusion evaporation reactions. Half lives of long lived isomeric states in both nuclei were also measured. Due to very low cross sections for producing {sup 98}Cd and {sup 102}Sn with stable beams and targets, a special detector setup utilizing NORDBALL ancillary detectors and a recoil catcher device was used. High {gamma}-ray detection efficiency was achieved with two EUROBALL Ge cluster detectors.

  14. Fractionation of Zr and Hf in surface processes

    SciTech Connect

    Chyi, L.L.; Garg, A.N.

    1985-01-01

    Zircons from a pegmatite near Tuxedo, North Carolina were crushed and treated with different reagents under different conditions. The treated and untreated samples were determined for Zr and Hf with radiochemical neutron activation analysis. Zircons treated with 50% sulfuric acid were having lowered Zr content and Zr/Hf ratio. The conclusions are that a portion of Zr and Hf in zircons is sensitive to leaching, and Zr appears to be selectively leached over Hf. The conclusions of this work support the observations of small dissolutions of Zr in both acidic podzolic soils and in alkaline laterites, of lower Zr content in soils on glacial drift, and of lower Zr/Hf ratios in loess deposits from various parts of the world. The fractionation of Zr and Hf in surface processes appears to be due to selective leaching. Weakening of Zr-O over Hf-O bonds in zircon by fission projectiles is postulated to be the viable process. The observed fractionation from leaching experiments suggest that areas receiving leachates such as swamps, lakes, and oceans should have high to very high Zr/Hf ratios preserved in rocks. High ratios are found in the Springfield (No. 9) Coal, the Green River Shale, and various limestones. High ratio is also found in orchard leaves, which grow by absorbing leachate from soil.

  15. Ge1-ySny (y = 0.01-0.10) alloys on Ge-buffered Si: Synthesis, microstructure, and optical properties

    NASA Astrophysics Data System (ADS)

    Senaratne, C. L.; Gallagher, J. D.; Jiang, Liying; Aoki, Toshihiro; Smith, D. J.; Menéndez, J.; Kouvetakis, J.

    2014-10-01

    Novel hydride chemistries are employed to deposit light-emitting Ge1-ySny alloys with y ≤ 0.1 by Ultra-High Vacuum Chemical Vapor Deposition (UHV-CVD) on Ge-buffered Si wafers. The properties of the resultant materials are systematically compared with similar alloys grown directly on Si wafers. The fundamental difference between the two systems is a fivefold (and higher) decrease in lattice mismatch between film and virtual substrate, allowing direct integration of bulk-like crystals with planar surfaces and relatively low dislocation densities. For y ≤ 0.06, the CVD precursors used were digermane Ge2H6 and deuterated stannane SnD4. For y ≥ 0.06, the Ge precursor was changed to trigermane Ge3H8, whose higher reactivity enabled the fabrication of supersaturated samples with the target film parameters. In all cases, the Ge wafers were produced using tetragermane Ge4H10 as the Ge source. The photoluminescence intensity from Ge1-ySny/Ge films is expected to increase relative to Ge1-ySny/Si due to the less defected interface with the virtual substrate. However, while Ge1-ySny/Si films are largely relaxed, a significant amount of compressive strain may be present in the Ge1-ySny/Ge case. This compressive strain can reduce the emission intensity by increasing the separation between the direct and indirect edges. In this context, it is shown here that the proposed CVD approach to Ge1-ySny/Ge makes it possible to approach film thicknesses of about 1 μm, for which the strain is mostly relaxed and the photoluminescence intensity increases by one order of magnitude relative to Ge1-ySny/Si films. The observed strain relaxation is shown to be consistent with predictions from strain-relaxation models first developed for the Si1-xGex/Si system. The defect structure and atomic distributions in the films are studied in detail using advanced electron-microscopy techniques, including aberration corrected STEM imaging and EELS mapping of the average diamond-cubic lattice.

  16. 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.

  17. Improved interfacial and electrical properties of Ge MOS capacitor by using TaON/LaON dual passivation interlayer

    NASA Astrophysics Data System (ADS)

    Cheng, Z. X.; Xu, J. P.; Liu, L.; Huang, Y.; Lai, P. T.; Tang, W. M.

    2016-07-01

    The effects of TaON/LaON dual passivation interlayer on the interfacial and electrical properties of Ge metal-oxide-semiconductor (MOS) capacitor with HfO2 gate dielectric are investigated. As compared to its counterpart with only LaON as passivation interlayer, the formation of HfGeOx and LaHfOx, which would degrade the interfacial quality, is effectively suppressed due to the strong blocking role of the TaON barrier layer against Hf diffusion. As a result, excellent interfacial and electrical properties are achieved for the Ge MOS device with the TaON/LaON dual passivation interlayer: high k value (20.9), low interface-state density (5.32 × 1011 cm-2 eV-1) and oxide-charge density (-3.90 × 1012 cm-2), low gate leakage current density (1.77 × 10-4 A/cm2 at Vg = Vfb + 1 V), and high reliability under high-field stress.

  18. Effect of mixed Ge/Si cross-linking on the physical properties of amorphous Ge-Si-Te networks

    SciTech Connect

    Gunasekera, K.; Boolchand, P.; Micoulaut, M.

    2014-04-28

    Amorphous Ge{sub x}Si{sub x}Te{sub 1−2x} glasses are studied as a function of composition by a combination of experimental and theoretical methods, allowing for a full description of the network structure in relationship with physico-chemical properties. Calorimetric and thermal measurements reveal that such glasses display an anomalous behavior across a range of compositions x{sub c1}=7.5% and Ge, Si) are increased. The structural manifestation of these anomalies is understood from  {sup 119}Sn Mössbauer spectroscopy and First Principles Molecular Dynamics at selected compositions (Ge{sub 20}Te{sub 80}, Si{sub 20}Te{sub 80}, and Ge{sub 10}Si{sub 10}Te{sub 80}). The numerical models reveal the quite different roles played by the modifier or network cross-linker Ge or Si atoms, Si being more tetrahedral in sp{sup 3} geometry, whereas Mössbauer spectroscopy shows that the nature of chemical bonding is dramatically changed around x≃ 8%. The precise evolution of the local structure and chemical bonding ultimately allows understanding the origin of the intermediate phase in these complex tellurides.

  19. Crystal structure of Si-doped HfO2

    NASA Astrophysics Data System (ADS)

    Zhao, Lili; Nelson, Matthew; Aldridge, Henry; Iamsasri, Thanakorn; Fancher, Chris M.; Forrester, Jennifer S.; Nishida, Toshikazu; Moghaddam, Saeed; Jones, Jacob L.

    2014-01-01

    Si-doped HfO2 was prepared by solid state synthesis of the starting oxides. Using Rietveld refinement of high resolution X-ray diffraction patterns, a substitutional limit of Si in HfO2 was determined as less than 9 at. %. A second phase was identified as Cristobalite (SiO2) rather than HfSiO4, the latter of which would be expected from existing SiO2-HfO2 phase diagrams. Crystallographic refinement with increased Si-dopant concentration in monoclinic HfO2 shows that c/b increases, while β decreases. The spontaneous strain, which characterizes the ferroelastic distortion of the unit cell, was calculated and shown to decrease with increasing Si substitution.

  20. SAR/InSAR observation by an HF sounder

    NASA Astrophysics Data System (ADS)

    Kobayashi, T.; Ono, T.

    2007-03-01

    Application of SAR imaging algorithm to spaceborne HF sounder observation was studied. Two types of image ambiguity problems were addressed in the application. One is surface/subsurface image ambiguity arising from deep penetration of HF wave, and another is mirror image ambiguity that is inherent to dipole antenna SAR. A numerical model demonstrated that the surface/subsurface ambiguity can be mitigated by taking a synthetic aperture large enough to defocus subsurface objects. In order to resolve the mirror image ambiguity problem, an image superposition technique was proposed. The performance of the technique was demonstrated by using simulation data of the HF sounder observation to confirm the feasibility of HF SAR and HF InSAR observation.