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Sample records for alloy-ge

  1. High thermoelectric potential of Bi2Te3 alloyed GeTe-rich phases

    Science.gov (United States)

    Madar, Naor; Givon, Tom; Mogilyansky, Dmitry; Gelbstein, Yaniv

    2016-07-01

    In an attempt to reduce our reliance on fossil fuels, associated with severe environmental effects, the current research is focused on the identification of the thermoelectric potential of p-type (GeTe)1-x(Bi2Te3)x alloys, with x values of up to 20%. Higher solubility limit of Bi2Te3 in GeTe, than previously reported, was identified around ˜9%, extending the doping potential of GeTe by the Bi2Te3 donor dopant, for an effective compensation of the high inherent hole concentration of GeTe toward thermoelectrically optimal values. Around the solubility limit of 9%, an electronic optimization resulted in an impressive maximal thermoelectric figure of merit, ZT, of ˜1.55 at ˜410 °C, which is one of the highest ever reported for any p-type GeTe-rich alloys. Beyond the solubility limit, a Fermi Level Pinning effect of stabilizing the Seebeck coefficient was observed in the x = 12%-17% range, leading to stabilization of the maximal ZTs over an extended temperature range; an effect that was associated with the potential of the governed highly symmetric Ge8Bi2Te11 and Ge4Bi2Te7 phases to create high valence band degeneracy with several bands and multiple hole pockets on the Fermi surface. At this compositional range, co-doping with additional dopants, creating shallow impurity levels (in contrast to the deep lying level created by Bi2Te3), was suggested for further electronic optimization of the thermoelectric properties.

  2. A low-temperature fabricated gate-stack structure for Ge-based MOSFET with ferromagnetic epitaxial Heusler-alloy/Ge electrodes

    Science.gov (United States)

    Fujita, Yuichi; Yamada, Michihiro; Nagatomi, Yuta; Yamamoto, Keisuke; Yamada, Shinya; Sawano, Kentarou; Kanashima, Takeshi; Nakashima, Hiroshi; Hamaya, Kohei

    2016-06-01

    A possible low-temperature fabrication process of a gate-stack for Ge-based spin metal–oxide–semiconductor field-effect transistor (MOSFET) is investigated. First, since we use epitaxial ferromagnetic Heusler alloys on top of the phosphorous doped Ge epilayer as spin injector and detector, we need a dry etching process to form Heusler-alloy/n+-Ge Schottky-tunnel contacts. Next, to remove the Ge epilayers damaged by the dry etching process, the fabricated structures are dipped in a 0.03% diluted H2O2 solution. Finally, Al/SiO2/GeO2/Ge gate-stack structures are fabricated at 300 °C as a top gate-stack structure. As a result, the currents in the Ge-MOSFET fabricated here can be modulated by applying gate voltages even by using the low-temperature formed gate-stack structures. This low-temperature fabrication process can be utilized for operating Ge spin MOSFETs with a top gate electrode.

  3. Formation, crystalline structure, and optical properties of Ge1-x-ySnxCy ternary alloy layers

    International Nuclear Information System (INIS)

    We have investigated the crystalline and optical properties of epitaxial layers of the ternary alloy Ge1-x-ySnxCy grown on a Si substrate. We achieved the formation of epitaxial Ge1-x-ySnxCy layers with a C content as high as 2% even with a high C incorporation efficiency. X-ray photoemission spectra and Raman scattering spectroscopy measurements revealed that C atoms preferentially bond with Sn atoms in the Ge matrix, which is considered to enhance C introduction into substitutional sites in Ge with local strain compensation. We also demonstrated the control of the energy bandgaps of epitaxial Ge1-x-ySnxCy layers by controlling Sn and C contents. (author)

  4. Compositional dependence of the band-gap of Ge1-x-ySixSny alloys

    Science.gov (United States)

    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.

  5. Analysis of switching conditions of chalcogenide alloys during crystallization

    Institute of Scientific and Technical Information of China (English)

    Wanhua Yu; C.D. Wright

    2006-01-01

    To understand the principle and limitation of chalcogenide alloy Ge2Sb2Te5 (GST) in solid-state memory devices during crystallization, it was necessary to develop a physically realistic model that could reflect the electrical and thermal properties of these media. A novel comprehensive numerical model has been developed for simulating these memory devices, which describes the electrical and thermal behavior using the solution of the nonlinear, time-dependent electrical and heat conduction equation. The finite-difference-time-domain technique was adopted to compute the electrical field and heat distribution in the device. Several contributing factors that affect the crystallization switching process such as the geometry of the GST layer, temperature and electric field dependency of the electrical conductivity have been discussed. The results of the simulations were then used to provide critical guidelines for fabrication and optimization of the device performance.

  6. Effects of Mn substitution on the phases and thermoelectric properties of Ge{sub 0.8}Pb{sub 0.2}Te alloy

    Energy Technology Data Exchange (ETDEWEB)

    Lu, Z.W.; Li, J.Q., E-mail: junqinli@szu.edu.cn; Wang, C.Y.; Li, Y.; Liu, F.S.; Ao, W.Q.

    2015-02-05

    Highlights: • Effects of Mn substitution on the thermoelectric properties in Ge{sub 0.8}Pb{sub 0.2}Te were studied. • All Mn atoms dissolved in the PbTe-based and GeTe-based phases up to 18% Mn substitution. • The alloys kept layer-like microstructures formed by the spinodal decomposition. • The thermal conductivity is reduced significantly by Mn substitution. • The maximum ZT of 1.3 at 723 K was obtained in the alloy (Ge{sub 0.8}Pb{sub 0.2}){sub 0.9}Mn{sub 0.1}Te. - Abstract: The series of (Ge{sub 0.8}Pb{sub 0.2}){sub 1−x}Mn{sub x}Te alloys with x = 0, 0.03, 0.05, 0.08, 0.10, 0.13 and 0.18 were prepared by melting, quenching and spark plasma sintering (SPS) techniques. The effects of Mn on the phases and thermoelectric properties of the alloys were investigated. Experimental results show that all alloys are composites containing minor NaCl-type structure PbTe-based and major GeTe-based phases with the rhombohedral and the cubic structures without any phase arising from Mn. All Mn atoms were dissolved in these phases and reduce their unit cell. Mn atoms in GeTe-based phase can stabilize its high temperature cubic structure. The layer-like microstructures are formed by the Spinodal decomposition. All the samples show p-type conduction. Although the electrical resistivity for the alloy (Ge{sub 0.8}Pb{sub 0.2}){sub 1−x}Mn{sub x}Te increases, its Seebeck coefficient increases while its thermal conductivity reduces significantly as Mn content x increases due to the enhanced phonon scattering from the solute atoms Mn in these three phases and the microstructures. As a result, the figure of merit ZT of the (Ge{sub 0.8}Pb{sub 0.2}){sub 1−x}Mn{sub x}Te composites can be enhanced with proper Mn content. The maximum ZT of 1.3 was obtained in the sample (Ge{sub 0.8}Pb{sub 0.2}){sub 0.9}Mn{sub 0.1}Te at 723 K, which is much higher than that of Ge{sub 0.8}Pb{sub 0.2}Te alloy.

  7. Post-growth annealing of germanium-tin alloys using pulsed excimer laser

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Lanxiang; Wang, Wei; Zhou, Qian; Yeo, Yee-Chia, E-mail: yeo@ieee.org [Department of Electrical and Computer Engineering, National University of Singapore, Singapore 117582 (Singapore); Pan, Jisheng; Zhang, Zheng [Institute of Materials Research and Engineering, A*STAR (Agency for Science, Technology and Research), Singapore 117602 (Singapore); Tok, Eng Soon [Department of Physics, National University of Singapore, Singapore 117551 (Singapore)

    2015-07-14

    We investigate the impact of pulsed excimer laser anneal on fully strained germanium-tin alloys (Ge{sub 1−x}Sn{sub x}) epitaxially grown on Ge substrate by molecular beam epitaxy. Using atomic force microscopy, X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy, the morphological and compositional evolution of Ge{sub 1−x}Sn{sub x} with Sn content up to 17% after annealing using various conditions is studied. Ge{sub 0.83}Sn{sub 0.17} samples annealed at 80 mJ/cm{sup 2} or 150 mJ/cm{sup 2} have no observable changes with respect to the as-grown sample. However, Ge{sub 0.83}Sn{sub 0.17} samples annealed at 250 mJ/cm{sup 2} or 300 mJ/cm{sup 2} have Sn-rich islands on the surface, which is due to Sn segregation in the compressively strained epitaxial film. For Ge{sub 0.89}Sn{sub 0.11}, significant Sn redistribution occurs only when annealed at 300 mJ/cm{sup 2}, indicating that it has better thermal stability than Ge{sub 0.83}Sn{sub 0.17}. A mechanism is proposed to explain the formation of Sn-rich islands and Sn-depleted regions.

  8. Post-growth annealing of germanium-tin alloys using pulsed excimer laser

    International Nuclear Information System (INIS)

    We investigate the impact of pulsed excimer laser anneal on fully strained germanium-tin alloys (Ge1−xSnx) epitaxially grown on Ge substrate by molecular beam epitaxy. Using atomic force microscopy, X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy, the morphological and compositional evolution of Ge1−xSnx with Sn content up to 17% after annealing using various conditions is studied. Ge0.83Sn0.17 samples annealed at 80 mJ/cm2 or 150 mJ/cm2 have no observable changes with respect to the as-grown sample. However, Ge0.83Sn0.17 samples annealed at 250 mJ/cm2 or 300 mJ/cm2 have Sn-rich islands on the surface, which is due to Sn segregation in the compressively strained epitaxial film. For Ge0.89Sn0.11, significant Sn redistribution occurs only when annealed at 300 mJ/cm2, indicating that it has better thermal stability than Ge0.83Sn0.17. A mechanism is proposed to explain the formation of Sn-rich islands and Sn-depleted regions

  9. An optoelectronic framework enabled by low-dimensional phase-change films

    Science.gov (United States)

    Hosseini, Peiman; Wright, C. David; Bhaskaran, Harish

    2014-07-01

    The development of materials whose refractive index can be optically transformed as desired, such as chalcogenide-based phase-change materials, has revolutionized the media and data storage industries by providing inexpensive, high-speed, portable and reliable platforms able to store vast quantities of data. Phase-change materials switch between two solid states--amorphous and crystalline--in response to a stimulus, such as heat, with an associated change in the physical properties of the material, including optical absorption, electrical conductance and Young's modulus. The initial applications of these materials (particularly the germanium antimony tellurium alloy Ge2Sb2Te5) exploited the reversible change in their optical properties in rewritable optical data storage technologies. More recently, the change in their electrical conductivity has also been extensively studied in the development of non-volatile phase-change memories. Here we show that by combining the optical and electronic property modulation of such materials, display and data visualization applications that go beyond data storage can be created. Using extremely thin phase-change materials and transparent conductors, we demonstrate electrically induced stable colour changes in both reflective and semi-transparent modes. Further, we show how a pixelated approach can be used in displays on both rigid and flexible films. This optoelectronic framework using low-dimensional phase-change materials has many likely applications, such as ultrafast, entirely solid-state displays with nanometre-scale pixels, semi-transparent `smart' glasses, `smart' contact lenses and artificial retina devices.

  10. Self-assembly of tin wires via phase transformation of heteroepitaxial germanium-tin on germanium substrate

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Wei; Li, Lingzi; Yeo, Yee-Chia, E-mail: yeo@ieee.org [Department of Electrical and Computer Engineering, National University of Singapore, Singapore 117576 (Singapore); Tok, Eng Soon [Department of Physics, National University of Singapore, Singapore 117551 (Singapore)

    2015-06-14

    This work demonstrates and describes for the first time an unusual strain-relaxation mechanism by the formation and self-assembly of well-ordered tin wires during the thermal annealing of epitaxial Ge{sub 0.83}Sn{sub 0.17}-on-Ge(001) substrate. Fully strained germanium-tin alloys (Ge{sub 0.83}Sn{sub 0.17}) were epitaxially grown on Ge(001) substrate by molecular beam epitaxy. The morphological and compositional evolution of Ge{sub 0.83}Sn{sub 0.17} during thermal annealing is studied by atomic force microscopy, X-ray diffraction, transmission electron microscopy. Under certain annealing conditions, the Ge{sub 0.83}Sn{sub 0.17} layer decomposes into two stable phases, and well-defined Sn wires that are preferentially oriented along two orthogonal 〈100〉 azimuths are formed. The formation of the Sn wires is related to the annealing temperature and the Ge{sub 0.83}Sn{sub 0.17} thickness, and can be explained by the nucleation of a grain with Sn islands on the outer front, followed by grain boundary migration. The Sn wire formation process is found to be thermally activated, and an activation enthalpy (E{sub c}) of 0.41 eV is extracted. This thermally activated phase transformation, i.e., 2D epitaxial layer to 3D wires, occurs via a mechanism akin to “cellular precipitation.” This synthesis route of Sn wires opens new possibilities for creation of nanoscale patterns at high-throughput without the need for lithography.

  11. Electronic transport in amorphous phase-change materials

    Energy Technology Data Exchange (ETDEWEB)

    Luckas, Jennifer Maria

    2012-09-14

    Phase change materials combine a pronounced contrast in resistivity and reflectivity between their disordered amorphous and ordered crystalline state with very fast crystallization kinetics. Due to this exceptional combination of properties phase-change materials find broad application in non-volatile optical memories such as CD, DVD or Bluray Disc. Furthermore, this class of materials demonstrates remarkable electrical transport phenomena in their disordered state, which have shown to be crucial for their application in electronic storage devices. The threshold switching phenomenon denotes the sudden decrease in resistivity beyond a critical electrical threshold field. The threshold switching phenomenon facilitates the phase transitions at practical small voltages. Below this threshold the amorphous state resistivity is thermally activated and is observed to increase with time. This effect known as resistance drift seriously hampers the development of multi-level storage devices. Hence, understanding the physical origins of threshold switching and resistance drift phenomena is crucial to improve non-volatile phase-change memories. Even though both phenomena are often attributed to localized defect states in the band gap, the defect state density in amorphous phase-change materials has remained poorly studied. Starting from a brief introduction of the physics of phase-change materials this thesis summarizes the most important models behind electrical switching and resistance drift with the aim to discuss the role of localized defect states. The centerpiece of this thesis is the investigation of defects state densities in different amorphous phase-change materials and electrical switching chalcogenides. On the basis of Modulated Photo Current (MPC) Experiments and Photothermal Deflection Spectroscopy, a sophisticated band model for the disordered phase of the binary phase-change alloy GeTe has been developed. By this direct experimental approach the band-model for a

  12. Electronic transport in amorphous phase-change materials

    International Nuclear Information System (INIS)

    Phase change materials combine a pronounced contrast in resistivity and reflectivity between their disordered amorphous and ordered crystalline state with very fast crystallization kinetics. Due to this exceptional combination of properties phase-change materials find broad application in non-volatile optical memories such as CD, DVD or Bluray Disc. Furthermore, this class of materials demonstrates remarkable electrical transport phenomena in their disordered state, which have shown to be crucial for their application in electronic storage devices. The threshold switching phenomenon denotes the sudden decrease in resistivity beyond a critical electrical threshold field. The threshold switching phenomenon facilitates the phase transitions at practical small voltages. Below this threshold the amorphous state resistivity is thermally activated and is observed to increase with time. This effect known as resistance drift seriously hampers the development of multi-level storage devices. Hence, understanding the physical origins of threshold switching and resistance drift phenomena is crucial to improve non-volatile phase-change memories. Even though both phenomena are often attributed to localized defect states in the band gap, the defect state density in amorphous phase-change materials has remained poorly studied. Starting from a brief introduction of the physics of phase-change materials this thesis summarizes the most important models behind electrical switching and resistance drift with the aim to discuss the role of localized defect states. The centerpiece of this thesis is the investigation of defects state densities in different amorphous phase-change materials and electrical switching chalcogenides. On the basis of Modulated Photo Current (MPC) Experiments and Photothermal Deflection Spectroscopy, a sophisticated band model for the disordered phase of the binary phase-change alloy GeTe has been developed. By this direct experimental approach the band-model for a