GaAs Single Crystals Research Articles

Effect of a traveling magnetic field on the parameters of doped tellurium gallium arsenide single crystals grown by the chokhralsky method

The effect of a traveling magnetic field on the parameters of Te-doped GaAs single crystals in the carrier density range of 5 × 1017–2 × 1018 cm–3 has been studied. A traveling magnetic field was induced in a melt by a graphite inductor located in the setup chamber around the main heater. It is shown that a high-frequency magnetic field slightly reduces the dislocation density in the crystals without changing the shape of the dislocation distribution over their cross sections. The magnetic field affects the impurity distribution along the crystal axis, almost doubling the distance between the striation bands from 9 µm in the absence of magnetic field to 17 µm in a field with a frequency of 300 Hz.

Atomistic understanding of ductile-to-brittle transition in single crystal Si and GaAs under nanoscratch

Ensuring ductile removal in a grinding process is crucial for achieving the desired finish on a hard and brittle single crystal. This study provides new insights into the material removal processes in Si and GaAs single crystals, exploring their deformation behaviour using Berkovich and Conical tips to replicate contact from a fixed abrasive grit. Experimental observations are compared with Molecular Dynamic (MD) simulations to uncover the atomistic deformation mechanisms during the ductile-to-brittle transition (DBT). Notable plastic deformation and minimal cracking were consistently observed in Si, irrespective of the tips used. MD simulations supported this observation, revealing pronounced chip formation indicative of ductile material removal. The resistance to cracking in Si was attributed to amorphization induced by localized high contact stresses. In contrast, GaAs showed a propensity for cracking, with MD simulations revealing dislocation and slip band formation, and cracks emerging in the areas of substantial plastic deformation. These findings address phenomena not previously discernible in experimental studies due to the challenge of real-time observation. Moreover, the tip geometry was shown to significantly influence stress distribution, impacting deformation and crack formation in GaAs. This study also reveals limitations in predicting the critical depth for DBT in both Si and GaAs throught the amended Bifano, Dow, and Scattergood (aBDS) models and MD simulation, offering nuanced insights into these challenges that have not been extensively explored. It was found that the experimental results exceeded predictions by an order of magnitude. These discrepancies underscore the aBDS model's disregard for essential material properties and tip geometry, while the disparities between MD simulation and experiment are primarily attributed to the inherent limitations in the simulated length scales and challenges in detecting initial subsurface cracks.

Method for Low-Temperature Vacuum-Thermal Cleaning of Surface Single Crystals Si and GaAs

The paper reports on a method of low-temperature vacuum-thermal cleaning of the surface of Si and GaAs single crystals developed by the authors, which consists in implanting Ba+ ions (or alkaline elements) into Si and GaAs crystals preliminarily cleaned by ultra-high vacuum by ion etching and subsequent annealing in two stage at 800 K - 15 minutes and at 1000 K for 30 minutes. The effect of effective cleaning is achieved due to the fact that the introduced ions of Ba+ and alkaline elements, being active, form compounds with impurity atoms (O, C, S, N, etc.) at the first stage and are removed together with impurities after the second stage of heating.

Light–induced transition of charged carrier transport in symmetric metal–semiconductor–metal contacts

Metal–semiconductor (M–S) contact is a basic element in semiconductor integrated circuit. Recent studies on photodetectors extensively focus on M–S contact owing to the easy fabrication and superior performance. Here, we report a light–induced transition of charged carrier transport in planar Cu/Si–doped GaAs single crystal (Si:GaAs) symmetric double Schottky contacts. Different from conventional photodetector, illumination not only gains the carrier concentration but also changes the charged carrier transport mechanism at Cu/Si:GaAs contact. The light-induced transition of charged carrier transport is reflected by the change of shape of current–voltage (I–V) curve caused by illumination. By the construction of theoretical model and its fitting to experimental data, we point out that carrier transport mechanism at Cu/Si:GaAs contact changes from tunneling effect to thermionic emission by illumination. Among that, photovoltaic effect is the crucial driving force. This study presents a novel mechanism for converting optical signal to electrical signal by tailoring Schottky contact in photodetector, which provide a design prototype to new–type optoelectronic device.

Substrate and Excitation Intensity Dependence of Saturable Absorption in Perovskite Quantum Dot Films.

Saturable absorption in perovskite quantum dot (PQD) films, leading to saturation in photoluminescence (PL), is reported. PL of drop-casting films was used to probe how excitation intensity and host-substrate influence the growth of PL intensity. The PQD films were deposited on single-crystal GaAs, InP, Si wafers and glass. Saturable absorption was confirmed through PL saturation in all films, with different excitation intensity thresholds, suggesting strong substrate-dependent optical properties, resulting from absorption nonlinearities in the system. The observations extend our former studies (Appl. Phys. Lett., 2021, 119, 19, 192103), wherein we pointed out that the PL saturation in QDs can be used to create all-optical switches in combination with a bulk semiconductor host.

Conversion efficiency improvement of ELO GaAs solar cell, deposited on water soluble sacrificial buffer

We demonstrate the improvement of power conversion efficiency of an epitaxially-lifted-off single junction GaAs solar cell deposited on a water-soluble sacrificial buffer architecture by introducing an additional germanium (Ge) interlayer between GaAs and the fluoride buffer. The epitaxial lift-off (ELO) technique has been extensively used to separate III-V device layers from their single crystal GaAs substrates. However, conventional ELO requires the use of concentrated hydrofluoric acid (HF) for extended times to etch out the sacrificial layer, subsequently degrading the surface roughness of the parent wafer. As a result, the wafer has to undergo expensive and intensive chemical mechanical polishing (CMP) processes, costing about 25 % of a pristine 6-inch GaAs substrate. In our previous work, we demonstrated a method to eliminating the need for CMP post-processing by using water-assisted ELO (H2O-ELO). A water-soluble, 3-layer buffer architecture was developed using alkaline earth compounds. However, devices suffered low performance due to a high defect density in the GaAs active layers. A Ge interlayer was introduced to provide a more favorable surface energy for GaAs growth, which leads to an improvement of GaAs crystal quality. The Ge deposition conditions were optimized to achieve a high-quality Ge layer on triple-layer fluoride buffer. Single junction GaAs devices fabricated on Ge/(Ca,Sr)F2/BaF2/(Ca,Sr)F2 showed improvement of solar cell performance parameters featuring increases in Voc by 23.7 %, and fill factor (F.F.) by 4.9 %, which results in an overall improvement of power conversion efficiency from 10.3 % to 12.69 %.

Influence of dopants on spin-charge conversion in GaAs

The practical applications for spintronic semiconductors requires the control of spin to charge current conversion. The ratio of spin current to charge current in a material can be determined from the inverse spin Hall angle (θISHE) and can be experimentally extracted. However, the reported results on the magnitude and the sign of θISHE in various semiconductors are rather diversed in association with the difference in the details of material properties. In this study, we focus on the dopant effects on the θISHE of GaAs. We adopted the technique of ferromagnetic resonance driven spin-pumping to accurately determine the θISHE in the GaAs single crystals with different type of dopants. We found that the magnitude of θISHE is sensitive to the atomic number of dopant (Z), but the sign of θISHE is independent on the dopant type. In addition, the relationship between θISHE and Z follows the Landau-Lifshitz Z2 scaling.

Defect seeded remote epitaxy of GaAs films on graphene

Remote epitaxy is an emerging materials synthesis technique which employs a 2D interface layer, often graphene, to enable the epitaxial deposition of low defect single crystal films while restricting bonding between the growth layer and the underlying substrate. This allows for the subsequent release of the epitaxial film for integration with other systems and reuse of growth substrates. This approach is applicable to material systems with an ionic component to their bonding, making it notably appealing for III–V alloys, which are a technologically important family of materials. Chemical vapour deposition growth of graphene and wet transfer to a III–V substrate with a polymer handle is a potentially scalable and low cost approach to producing the required growth surface for remote epitaxy of these materials, however, the presence of water promotes the formation of a III–V oxide layer, which degrades the quality of subsequently grown epitaxial films. This work demonstrates the use of an argon ion beam for the controlled introduction of defects in a monolayer graphene interface layer to enable the growth of a single crystal GaAs film by molecular beam epitaxy, despite the presence of a native oxide at the substrate/graphene interface. A hybrid mechanism of defect seeded lateral overgrowth with remote epitaxy contributing the coalescence of the film is indicated. The exfoliation of the GaAs films reveals the presence of defect seeded nucleation sites, highlighting the need to balance the benefits of defect seeding on crystal quality against the requirement for subsequent exfoliation of the film, for future large area development of this approach.

Molecular beam epitaxy of GaAs templates on water soluble NaCl thin films

Expensive III-V substrates are cost limiting for the adoption of many technologies. Thus, being able to reuse the original substrate is highly desirable. Existing substrate reuse techniques have significant drawbacks, but this work discusses a new method using molecular beam epitaxy deposition of water soluble NaCl thin films on commonly employed (001) GaAs substrates. Single-crystal GaAs templates are grown on continuous NaCl layers utilizing careful exposure of the NaCl to an in-situ electron beam and a low temperature nucleation layer. The template layers can be quickly removed from the substrate via dissolution of the NaCl. After liftoff, the original wafer shows an increase in rms surface roughness of only 0.2 nm.

Material-related fundamentals of cutting techniques for GaAs wafer manufacturing

Abstract Driven by the requirement of high cutting efficiency and improvement of wafer flatness, wire sawing of GaAs single crystals under brittle material removal conditions has been studied. Crack nucleation and crack propagation were investigated by indentation and scratching tests on polished {100}-oriented semi-insulating GaAs wafers. Based on these results a concept has been developed that allows to control the force balance in the cutting slits so that the deflection of the wires perpendicular to the cutting planes is minimal resulting in cuts of high flatness. The concept has been successfully introduced in mass production of GaAs wafers.

Структура, морфология и фотоэлектрические свойства гетероструктуры n-GaAs--p-(GaAs)1--x(Ge2)х

The paper studies the structural properties of the thin-film (GaAs)1--х(Ge2)x solid solutions grown by liquid-phase epitaxy on single crystal GaAs substrates. The obtained epitaxial layers were 10 μm thick, had a 0.17 Ω · cm resistivity of p-type conductivity. X-ray diffraction analysis showed that the obtained films are monocrystalline with nanoinclusions with block sizes up to 49 nm, with a crystallographic orientation (100), and have a sphalerite structure of the ZnS type. Morphological studies using AFM showed that the nanocones on the surface of the epitaxial (GaAs)1--х(Ge2)x layers are due to Ge atoms in them. The analysis revealed that the diameter of the nanocones' bases is in the range from 70 to 90 nm, and the height is from 3 to 12 nm. The sizes of such nanocones, determined by the X-ray diffraction method, were close to these values. The photosensitivity spectra of these solid solutions exhibit peculiar fluctuations due to various complexes of charged atoms in them. Analysis of the photosensitivity spectrum of n-GaAs--p-(GaAs)1--х(Ge2)x heterostructures using the Wolfram Mathematics 7 program showed that the spectrum consists of three peaks due to As--Ge, Ge--Ge and Ga--Ge

Резонансная микроволновая спектроскопия полупроводников с микронным разрешением

We have proposed and experimentally verified a local method of microwave resonant spectroscopy of semiconductors. The microwave circuit of the spectrometer based on the Cascade Microtech probe station is equipped with a coaxial resonator of special geometry. As result, the measurement accuracy of the previously developed volt-impedance spectroscopy method was greatly increased. A technique for spectrometer calibration and resonant measurements of the complex impedance of the probe-sample system has been developed. We have measured the impedance of test structures with Schottky contacts of 30 - 60 μm in diameter on a single-crystal GaAs wafer at several discrete frequencies in the range of 50 - 250 MHz. The nontrivial resistive properties of the structures are studied, which consist of the excess resistance that is 1–2 orders higher than the spreading resistance for the alternating current in the unperturbed region of the semiconductor. The discovered effect is presumably associated with the a.c. charge modulation on deep levels of the semiconductor. A model calculation of the impedance spectrum has been performed, which demonstrates a good agreement with the experimental spectra.

Microwave Resonant Spectroscopy of Semiconductors with Micrometer Resolution

We have proposed and experimentally verified a local method of microwave resonant spectroscopy of semiconductors. The microwave circuit of the spectrometer based on the Cascade Microtech probe station is equipped with a coaxial resonator of special geometry. As result, the measurement accuracy of the previously developed volt-impedance spectroscopy method was greatly increased. A technique for spectrometer calibration and resonant measurements of the complex impedance of the probe-sample system has been developed. We have measured the impedance of test structures with Schottky contacts of 30-60 μm in diameter on a single-crystal GaAs wafer at several discrete frequencies in the range of 50-250 MHz. The nontrivial resistive properties of the structures are studied, which consist of the excess resistance that is 1-2 orders higher than the spreading resistance for the alternating current in the unperturbed region of the semiconductor. The discovered effect is presumably associated with the a.c. charge modulation on deep levels of the semiconductor. A model calculation of the impedance spectrum has been performed, which demonstrates a good agreement with the experimental spectra. Keywords: Microwave microscope, near field, probe, resonator, impedance, semiconductor.

Microwave Resonant Spectroscopy of Semiconductors with MicrometerResolution

We have proposed and experimentally verified a local method ofmicrowave resonant spectroscopy of semiconductors. The microwave circuit ofthe spectrometer based on the Cascade Microtech probe station is equippedwith a coaxial resonator of special geometry. As result, the measurementaccuracy of the previously developed volt-impedance spectroscopy method wasgreatly increased. A technique for spectrometer calibration and resonantmeasurements of the complex impedance of the probe-sample system has beendeveloped. We have measured the impedance of test structures with Schottkycontacts of 30-60 μm in diameter on a single-crystal GaAs wafer at severaldiscrete frequencies in the range of 50-250 MHz . The nontrivial resistiveproperties of the structures are studied, which consist of the excessresistance that is 1-2 orders higher than the spreading resistance for thealternating current in the unperturbed region of the semiconductor. Thediscovered effect is presumably associated with the a.c. charge modulationon deep levels of the semiconductor. A model calculation of the impedancespectrum has been performed, which demonstrates a good agreement with theexperimental spectra. Keywords: Microwave microscope, near field, probe, resonator, impedance, semiconductor.\

РОЗРОБКА МЕТОДУ ВИЗНАЧЕННЯ ТЕРМОПРУЖНІХ НАПРУГ У ПЛАСТИНАХ GAAS

Purpose. А study of the temperature field of the melt during the cultivation of GaAs single crystals from under a layer of liquid flux. Thermoplastic stresses were measured on plates cut from the upper, middle and lower part of the ingot of undoped GaAs.Methodology. Finite element method is used to calculate temperature profiles and internal thermoplastic stresses. The mechanism of theoretical and experimental researches which allow to predict thermoplastic stresses in the course of cultivation of ingots is offered. For the analysis and mathematical calculations of the stationary differential equation in partial derivatives and the equations of thermoelasticity, respectively, use the finite element method, the calculations were performed in the programs THERMIX and INCA. Temperature profiles and internal thermoplastic stresses were calculated. Thermoplastic stresses were measured on plates cut from the upper, middle and lower part of the ingot of undoped GaAs (cm-3) with a thickness of 1 mm with a resistivity of 108 Ohm x cm, diameter 50 mm, orientation (111).The axial temperature gradient is determined. Experimentally obtained values of ison voltage lines along the plane of GaAs plates cut from different parts of the ingot. To measure the internal (thermoplastic) stresses in the work used the method of photoelastic-guests in infrared polarized light. The integrated picture of thermoplastic stresses was obtained using the "Polaron" installation, and the point measurement with the construction of the iso-voltage line was obtained on the "Polaron-2" installation. Originality. As a result of the research it can be concluded that the mechanism of theoretical and experimental researches is offered in the work, which allows to predict thermoplastic stresses in the process of growing GaAs ingots and, finally, to develop a procedure for reducing dislocation density in GaAs ingots. The practical value. the proposed method will improve the technology of growing ingots of gallium arsenide with a more homogeneous technology, which will be a good indicator for the future creation of gas sensors from this material.

Thermal Oxidation of a Single-Crystal GaAs Surface Treated in Sulfur Vapor

Thermal Oxidation of a Single-Crystal GaAs Surface Treated in Sulfur Vapor

The structural evolution of light-ion implanted into GaAs single crystal after annealing

Four groups of He+ and H+ with different dose combinations are implanted into GaAs crystal. After annealing, different phenomena of blisters and exfoliation appear on the surface. High resolution X-ray diffraction (HRXRD) is used to irradiate the surfaces of the four samples, and the diffraction satellite peaks are observed to move to the lower angles. The surface morphology of the four samples after annealing is observed by optical microscope. The depth of craters and the height of blisters are measured by atomic force microscope (AFM), and the critical pressure and internal stress of blisters are calculated. The damage microstructure induced by ion implantation after annealing is observed by transmission electron microscope (TEM), and the stress intensity factor at the crack tip is calculated. The different mechanisms of He+ and H+ in GaAs single crystal are compared. The dose combination of He+ and H+ is optimized to explore a more cost-effective way for GaAs film exfoliation.

Superior Mechanical Properties of GaAs Driven by Lattice NanotwinningSupported by the National Key Research and Development Program of China (Grant No. 2018YFA0703400), the National Natural Science Foundation of China (Grant Nos. 11704044 and 11974134), the Jilin Province Outstanding Young Talents Project (Grant No. 20190103040JH), and the China Postdoctoral Science Foundation (Grant No. 2018M631870).

Gallium arsenide (GaAs), a typical covalent semiconductor, is widely used in the electronic industry, owing to its superior electron transport properties. However, its brittle nature is a drawback that has so far significantly limited its application. An exploration of the structural deformation modes of GaAs under large strain at the atomic level, and the formulation of strategies to enhance its mechanical properties is highly desirable. The stress-strain relations and deformation modes of single-crystal and nanotwinned GaAs under various loading conditions are systematically investigated, using first-principles calculations. Our results show that the ideal strengths of nanotwinned GaAs are 14% and 15% higher than that of single-crystal GaAs under pure and indentation shear strains, respectively, without producing a significantly negative effect in terms of its electronic performance. The enhancement in strength stems from the rearrangement of directional covalent bonds at the twin boundary. Our results offer a fundamental understanding of the mechanical properties of single crystal GaAs, and provide insights into the strengthening mechanism of nanotwinned GaAs, which could prove highly beneficial in terms of developing reliable electronic devices.

Molecular dynamics simulation of AFM tip-based hot scratching of nanocrystalline GaAs

GaAs is a hard, brittle material and its cutting at room-temperature is rather difficult, so the work explored whether hot conditions improve its cutting performance or not. Atomic force microscope (AFM) tip-based hot machining of the (0 1 0) oriented single crystal GaAs was simulated using molecular dynamics (MD). Three representative temperatures 600 K, 900 K and 1200 K (below the melting temperature of ~1511 K) were used to cut GaAs to benchmark against the cutting performance at 300 K using indicators such as the cutting forces, kinetic coefficient of friction, cutting temperature, shear plane angle, sub-surface damage depth, shear strain in the cutting zone, and stress on the diamond tip. Hotter conditions resulted in the reduction of cutting forces by 25% however, the kinetic coefficient of friction went up by about 8%. While material removal rate was found to increase with the increase of the substrate temperature, it was accompanied by an increase of the sub-surface damage in the substrate. Simulations at 300 K showed four major types of dislocations with Burgers vector 1/2<110>, 1/6<112>, <0–11> and 1/2<1–12> underneath the cutting zone and these were found to cause ductile response in zinc-blende GaAs. Lastly, a phenomenon of chip densification was found to occur during hot cutting which referred to the fact that the amorphous cutting chips obtained from cutting at low temperature will have lower density than the chips obtained from cutting at higher temperatures.

Origins of ductile plasticity in a polycrystalline gallium arsenide during scratching: MD simulation study

This paper used molecular dynamics simulation to reveal the origins of the ductile plasticity in polycrystalline gallium arsenide (GaAs) during its nanoscratching. Velocity-controlled nanoscratching tests were performed with a diamond tool to study the friction-induced deformation behaviour of polycrystalline GaAs. Cutting temperature, sub-surface damage depth, cutting stresses, the evolution of dislocations and the subsequent microstructural changes were extracted from the simulation. The simulated MD data indicated that the deformation of polycrystalline GaAs is accompanied by dislocation nucleation in the grain boundaries (GBs) leading to the initiation of plastic deformation. Furthermore, the 1/2〈110〉 is the main type of dislocation responsible for ductile plasticity in polycrystalline GaAs. The magnitude of cutting forces and the extent of sub-surface damage were both observed to reduce with an increase in the scratch velocity whereas the cutting temperature scaled with the cutting velocity. As for the depth of the scratch, an increase in its magnitude increased the cutting forces, temperature and damage-depth. A phenomenon of fluctuation from wave crests to wave troughs in the cutting forces was observed only during the cutting of polycrystalline GaAs and not during the cutting of single-crystal GaAs.