Effect of gravity on InGaSb crystal growth

The effect of gravity on dissolution of GaSb in InSb melt and growth of InGaSb was experimentally investigated. Experiments were carried out in a GaSb(seed)/InSb/GaSb(feed) sandwich system under an imposed temperature gradient. In the experiments, the GaSb feed crystal dissolved into the InSb melt to supply the required GaSb component for the growth of In_0.1Ga_0.9Sb crystal. Two parameters were considered: (1) the inclination angle (θ) of the sample for gravity as 0° and 53°, and (2) the sample diameter (D) as 9 mm and 5mm. When θ was 0°, the interface was almost flat, indicating that convection was axisymmetric and stable. Whereas the interface was distorted towards gravitational direction when θ was 53°, indicating that solutal convection was dominant. The decrease of growth temperature and sample diameter reduced the distortion of interface and the dissolution amount of GaSb feed. The homogeneous crystals were grown at the initial growth stage by supplying the GaSb component during growth.     

Enhancement of Rashba Spin–Orbit Interaction Due to Wave Function Engineering

We have demonstrated an enhancement of Rashba spin–orbit interaction (SOI) in In_0.53Ga_0.47As/In_0.7Ga_0.3As/In_0.53Ga_0.47As double-step structure in comparison with In_0.53Ga_0.47As normal quantum well. In the double-step structure, high electron probability density is located on the In_0.53Ga_0.47As/In_0.7Ga_0.3As heterointerface to enhance the interface contribution of Rashba SOI. The double-step structure is designed based on k⋅p formalism considering field and interface contributions separately. The Rashba parameter α calculated by the k⋅p formalism shows good agreement with the experimental value by analyzing weak antilocalization. The large carrier density dependence of α is due to the In_0.53Ga_0.47As/In_0.7Ga_0.3As heterointerface contribution as well as the energy-band bending in the In_0.7Ga_0.3As quantum well. The results of this study suggest that the precise control of interface and field contributions in Rashba SOI will make its application to semiconductor spintronics.     

Development of refractory ohmic contact materials for gallium arsenide compound semiconductors

Recent strong demands for optoelectronic communication and portable telephones have encouraged engineers to develop optoelectronic devices, microwave devices, and high-speed devices using hetero-structural GaAs-based compound semiconductors. Although the GaAs crystal growth techniques had reached a level to control the compositional stoichiometry and crystal defects on a nearly atomic scale by the advanced techniques such as molecular beam epitaxy and metal organic chemical vapor deposition techniques, development of ohmic contact materials (which play a key role to inject external electric current from the metals to the semiconductors) was still on a trial-and-error basis.Our research efforts have been focused to develop low resistance, refractory ohmic contact materials to n-type GaAs using the deposition and annealing techniques, and it was found the growth of homo-or hetero-epitaxial intermediate semiconductor layers (ISL) on the GaAs surface was essential for the low resistance ohmic contact formation. In this paper, two typical examples of ohmic contact materials developed by forming ISL were given. The one was refractory NiGe-based ohmic contact material, which was developed by forming the homo-epitaxial ISL doped heavily with donors. This heavily doped ISL was discovered to be formed through the regrowth mechanism of GaAs layers at the NiGe/GaAs interfaces during annealing at elevated temperatures. To reduce the contact resistance further down to a value required by the device designers, an addition of small amounts of third elements to NiGe, which have strong binding energy with Ga, was found to be essential. These third elements contributed to increase the carrier concentration in ISL. The low resistance ohmic contact materials developed by forming homo-epitaxial ISL were Ni/M/Ge where a slash ‘/’ denotes the deposition sequence and M is an extremely thin (∼5 nm) layer of Au, Ag, Pd, Pt or In. The other was refractory In_xGa_1−xAs-based ohmic contact materials which were developed by forming the hetero-epitaxial ISL with low Schottky barrier to the contacting metals by growing the In_xGa_1−xAs layers on the GaAs substrate by sputter-depositing In_xGa_1−xAs targets and subsequently annealing at elevated temperatures. To reduce the contact resistance, it was found that this In_xGa_1−xAs (ISL) layer had to have In compositional gradient normal to the GaAs surface: the In concentration being rich at the metal/In_xGa_1−xAs interface and poor close to the In_xGa_1−xAs/GaAs interface. This concentration graded ISL reduced both the barrier heights at the metal/ISL and ISL/GaAs interfaces and reduced the contact resistance. The ohmic contact materials developed by forming hetero-epitaxial ISL was In_0.7Ga_0.3As/Ni/WN₂/W. These contact materials formed refractory compounds at the interfaces, which was also found to be essential to improve thermal stability of ohmic contacts used in the GaAs devices.     

Features of Fermi-level pinning at the interface of Al0.3Ga0.7As with anodic oxide and stabilized zirconia

In the metal-oxide-semiconductor structures based on the Al_0.3Ga_0.7As films prepared by metal-organic epitaxy, Fermi-level pinning at the Al_0.3Ga_0.7As/oxide interface at a distance of 1.1 eV from the top of the Al_0.3Ga_0.7As conduction band was observed. In these structures, a long-term memory phenomenon was found that was caused by the inflow of electrons from Al_0.3Ga_0.7As to the anodic oxide and their capture by deep traps. The reversible change in the states of the structures due to this memory effect under the action of an electric field or light was observed.     

Solution growth of n-type GaxIn1−xSb crystals and application to gunn effect

n type Ga_xIn_1?xSb crystals with 0 ? x ? 0.45 have been elaborated by mean of a solution growth method (T.G.Z.M.) using Indium as solvent and Indium antimonide as seed. The growth processus and resulting homogeneous material elaboration are described with the aid of the ternary phase diagram of the GaInSb system. Ga_xIn_1?xSb Gunn diodes were prepared. Current instabilities were obtained on some samples. The conditions for the Gunn effect observation in the alloy are given.     

Synthesis of GaN nanorods by ammoniating Ga2O3 films on In2O3 layer deposited on Si (111) substrates

GaN nanorods were synthesized by ammoniating Ga₂O₃/In₂O₃ thin films deposited on Si (111) with magnetron sputtering. X-ray diffraction, Scanning electronic microscope and high-resolution TEM results show that they are GaN single crystals, the sizes of which vary from 2 to 7 μm in length and 200 to 300 nm in diameter. In₂O₃ middle layer plays an important role in the GaN nanorod growth.     

Degradation and Fracture of Crystals of Gallium and Indium Selenides

In the Laue patterns of crystals of gallium selenide, we experimentally established the blurring of diffraction spots in the radial direction (asterism). The elongation of tails depends on the number, shape, and dimensions of fragments. The isomorphic substitution of elements results in the appearance of Ga _x In_1 – x Se and (In_0.6Ga_0.4)₂Se₃ solid solutions. In the course of deformation and fracture of mixed (In_0.6Ga_0.4)₂Se₃ crystals, slip bands reach the surface due to mechanical stresses. The spalling of crystals occurs at an angle about 45° to the direction of applied tensile stresses. Brittle fracture of the alloy is accompanied by the simultaneous disintegration of a crystal at several sites.     

Low thermal drift in highly sensitive doped channel Al0.3Ga0.7As/GaAs/In0.2Ga0.8As micro-Hall element

Micro-Hall sensors with high sensitivity, low noise, and high thermal stability, 5 μm square, are fabricated using pseudomorphic Al_0.3Ga_0.7As/GaAs/In _y Ga_1-y As (0.2 ≤ y ≤ 0.3) heterostructures with Si-doped channels. The structures were optimized for thermal stability using a calculation of the self-consistent solution of Schrödinger-Poisson equations and Fermi-Dirac statistics in Hartree approximation. The optimized structure based on a Si-δ-doped 144 Å In_0.2Ga_0.8As quantum well embedded into uniformly doped GaAs channel showed thermal drifts of only 90 ppm·K^?1 in current drive mode and 192 ppm K^?1 in voltage drive mode. The measurements of the absolute magnetic sensitivity and the low frequency noise were done. The micro-Hall sensor, optimized for thermal drift, is able to resolve the magnetic field of 438 nT.     

Effect of starting melt composition on growth of La3Ta0.5Ga5.5O14 crystal

The phase diagram of the La₂O₃-Ta₂ O₅-Ga₂ O₃ system around La₃ Ta_0.5 Ga_5.5 O₁₄ (LTG) was investigated by a differential thermal analysis and the quenching method. La₃ Ta_0.5 Ga_5.5 O₁₄ single crystals were subsequently grown from different starting melt compositions using the Czochralski technique. The effect of the starting melt composition on crystal quality was examined by measuring the variation in the chemical composition and lattice parameters along the growth axis. On the basis of these experimental results, we have grown LTG single crystals over 2 inches in diameter.     

GaN single crystal growth from a Na-Ga melt

GaN single crystals were prepared in a sealed stainless-steel tube container at 650–840°C for 6–300 h using Ga, NaN₃, and Na as starting materials. A thin GaN layer covered Na-Ga melt surface at the initial stage of reaction between Ga in the Na-Ga melt and N₂ given by the thermal decomposition of NaN₃ around 300°C. In the next stage, pyramidal and prismatic GaN single crystals grew under the layer. Prismatic and platelet crystals also grew from the melt which wetted the tube wall. The reaction rate was enhanced by increasing temperature and by increasing Na content in the melt. The maximum size of pyramidal crystals was about 0.7 mm. The platelet crystals were 1–2 mm in one direction and <0.05 mm thick. The platelet single crystals prepared at 650°C exhibited the sharpest cathodoluminescence peak with the strongest intensity at 362 nm.     

Influence of In0.56Ga0.44P/Ge heterostructure on diffusion of phosphorus in germanium during the formation of multiple solar cells

Phosphorus profiles in germanium doped with gallium obtained within the formation of the first stage of a three-stage solar cell based on A³B⁵/Ge (Ga) have been studied. Secondary-ion mass spectroscopy has been applied to obtain profiles of phosphorus and gallium in germanium in flow of phosphine and in In_0.01Ga_0.99As/In_0.56Ga_0.44P/ Ge. It is observed that most of the phosphorus is supplied from In_0.56Ga_0.44P along with diffusion of gallium. The diffusion profiles of phosphorus in germanium have been calculated. It has been shown that diffusion of phosphorus from an In_0.56Ga_0.44P buffer layer, which is at the same time a source of gallium, depends on the coordinates, and, in order to describe this dependence, it is necessary to use mathematical models that take into account not only diffusion, but also the drift component of flow of phosphorus atoms.     

Growth of large LiNbO3〈Mg〉 crystals

We have analyzed conditions for the growth of large (≥80 mm in diameter) LiNbO₃〈Mg〉 crystals in a wide range of dopant concentrations in the melt (2.9–5.8 mol % MgO). We have established conditions for the growth of large LiNbO₃〈Mg〉 crystals uniform in doping level from melts containing magnesium concentrations above a certain threshold (C _melt 5.0–5.8 mol % MgO) and optimized the high-temperature electrodiffusion annealing process, which allowed us to obtain single-domain, microstructurally homogeneous, large LiNbO₃〈Mg〉 crystals containing 4.9–5.15 mol % magnesium.     

Power and gas pressure effects on properties of amorphous In–Ga–ZnO films by magnetron sputtering

Amorphous In–Ga–ZnO thin films were deposited on quartz glass substrate at room temperature utilizing radio frequency magnetron sputtering technique. Sputtering power and oxygen flow rate effects on the physical properties of the In–Ga–ZnO films were systematically investigated. It is shown the film deposition rate and the conductivity of the In–Ga–ZnO films increased with the sputtering power. The as-grown In–Ga–ZnO films deposited at 500 W exhibited the Hall mobility of 17.7 cm²/Vs. Average optical transmittance of the In–Ga–ZnO films is greater than 80% in the visible wavelength. The extracted optical band gap of the In–Ga–ZnO films increased from 3.06 to 3.46 eV with increasing the sputtering power. The electrical properties of the In–Ga–ZnO films are greatly dependent on the O₂/Ar gas flow ratio and post-growth annealing process. Increasing oxygen flow rate converted the In–Ga–ZnO films from semiconducting to semi-insulating, but the resistivity of the films was significantly reduced after being annealed in vacuum. Both the as-grown and annealed In–Ga–ZnO films show n-type electrical conductivity.     

The effect of growth temperature on the coaxial InxGa1 − xN/GaN nanowires grown by metalorganic chemical vapor deposition

We report on the growth of coaxial In_xGa_1 − xN/GaN nanowires (NWs) on Si(111) substrates by using pulsed flow metalorganic chemical vapor deposition. The coaxial In_xGa_1 − xN/GaN NWs were grown by a two step process in which the core (GaN) structure was grown at a higher temperature followed by the shell (In_xGa_1 − xN) structure at a lower temperature. Dense and well-oriented coaxial In_xGa_1 − xN/GaN NWs were grown with an average diameter and length of about 300 ± 50 nm and 1.5-2.0 μm, respectively. The coaxial In_xGa_1 − xN/GaN NW was confirmed by cathodoluminescence mapping and high-resolution transmission electron microscopy. It is proposed that the critical dissociation of precursors at an elevated growth temperature can lead to a clear formation of an outer-shell in coaxial In_xGa_1 − xN/GaN NWs.     

Flow-induced crystallization of polyethylene melts

In situ optical observations have been made of the way polyethylene melt can crystallize whilst subject to certain longitudinal velocity gradients. In general crystallization is seen to occur as the generation of fibres 5 to 50 μm in diameter. Hydrodynamic considerations lead to the conclusion that the externally applied velocity field is responsible for the nucleation of the fibrous crystals, subsequent growth is then influenced by both the local streaming of polymer melt around the growing tip of the fibre and the external velocity field. The effect enhanced pressure has on flow induced crystallization is also examined.     

Effect of growth conditions on the compositional homogeneity of Cd<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Zn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Te crystals

A crystal growth unit has been designed for Cd_{1 − x} Zn _x Te growth by the axial-heat-flux-close-to-the-phase-interface (AHP) method at argon overpressures of up to 12 MPa. The influence of melt superheating, growth rate, melt layer thickness, argon pressure, and growth mode on the Zn distribution in 21- to 45-mm-diameter crystals and defect formation in Cd_{1 − x} Zn _x Te ingots has been investigated. The results demonstrate that the AHP method offers the possibility of effectively controlling the shape of the solid-liquid interface and ensures low fluid velocity and high radial compositional homogeneity. The feeding method used markedly improves the axial Zn profile and ensures low dislocation density (5 × 10³ cm⁻²) in the grown crystal.     

An investigation on preparation of CIGS targets by sintering process

Pressureless sintering process was used to fabricate CIGS targets with Cu₂Se, In₂Se₃, and Ga₂Se₃ as raw powders mixed according to the stoichiometry of CuIn_0.72Ga_0.28Se₂ (CIGS). The results showed that only CuIn_0.7Ga_0.3Se₂ phase can be detected in the sintered targets. The pores in sintered specimen become smaller and distribute more homogenously under the conditions of finer powders and higher cold pressure. Both mass loss caused by the formation of volatile phase relating to Ga and volume expansion occur during the sintering process, which result in the decrease of density. The tendency of anti-densification becomes stronger under the conditions of coarser powders and higher cold pressure. The sintering process and causes for anti-densification were discussed. Finally, a hot pressing process was carried out, which was proved to be fairly effective to increase the density of CIGS target. The fabricated target can be used for magnetron-sputtering deposition of CIGS absorbers.     

Synthesis and characterization of LiCo0.3−xGaxNi0.7O2 (x = 0, 0.05) as a cathode material for lithium ion battery

The single phase of LiCo_0.3−xGa_xNi_0.7O₂ (x = 0, 0.05) was synthesized by a sol–gel method. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical performance. The powders are homogeneous and have a good-layered structure. The synthesized LiCo_0.25Ga_0.05Ni_0.7O₂ exhibits better electrochemical performance with an initial discharge capacity of 180.0 mAh g⁻¹ and a capacity retention of 95.2% after 50 cycles between 2.8 and 4.4 V at 0.2C rate. The study on the structural evolution of the material during the cycling shows that Ga-doping improves the structure stability of LiCo_0.3Ni_0.7O₂ at ambient temperature and 55 °C. Meanwhile, Ga-doping not only suppresses the alternating current (AC) impedance of LiCo_0.3Ni_0.7O₂ but also promotes the Li⁺ diffusion in LiCo_0.3Ni_0.7O₂. Furthermore, thermal stability of the charged LiCo_0.25Ga_0.05Ni_0.7O₂ is improved, which may be attributed to the retard of O₂ evolution in LiCo_0.3Ni_0.7O₂ and the suppression of electrolyte oxidation during cycling by Ga-doping_.     

Homogeneous Si0.5Ge0.5 bulk crystal growth as substrates for strained Ge thin films by the traveling liquidus-zone method

Compositionally uniform Si_0.5Ge_0.5 bulk crystals were grown by the traveling liquidus-zone method which we developed for alloy crystal growth. Grown crystals were characterized as substrates for compressive-strained Ge thin films for high mobility p-channels of complementary metal oxide semiconductor transistors. Compositional uniformity was excellent and crystallinity was also excellent for 10 mm diameter crystals. However, crystallinity was degraded for 30 mm diameter crystals although compositional uniformity was excellent. Transmission electron microscope (TEM) observation showed high dislocation density at the interface between a Si seed and a grown crystal due to lattice mismatch. However, the dislocation density decreased as crystal growth proceeded. High quality 30 mm diameter crystals will be grown when the single crystal length is extended judging from TEM results. In this paper, we report on the growth and characterization of Si_0.5Ge_0.5 crystals as substrates for strained Ge thin films.     

熔体内重力对流速度场的实验研究及其理论分析

应用最近开发的高温光学实时观察法研究了铌酸钾熔体的重力对流现象．通过加热直径为2．5mm的圆环形坩埚,形成厚度为0．2mm的圆形KNbO₃熔液．实验测量了熔体内温度和流体速度的分布,并从理论上对速度场的分布给出了定量分析．