Determination of Band Structure of Gallium-Arsenide and Aluminium-Arsenide Using Density Functional Theory

This research paper is on Density Functional Theory (DFT) within Local Density Approximation. The calculation was performed using Fritz Haber Institute Ab-initio Molecular Simulations (FHIAIMS) code based on numerical atomic-centered orbital basis sets. The electronic band structure, total density of state (DOS) and band gap energy were calculated for Gallium-Arsenide and Aluminium-Arsenide in diamond structures. The result of minimum total energy and computational time obtained from the experimental lattice constant 5.63 A for both Gallium Arsenide and Aluminium Arsenide is -114,915.7903 eV and 64.989 s, respectively. The electronic band structure analysis shows that Aluminium-Arsenide is an indirect band gap semiconductor while Gallium-Arsenide is a direct band gap semiconductor. The energy gap results obtained for GaAs is 0.37 eV and AlAs is 1.42 eV. The band gap in GaAs observed is very small when compared to AlAs. This indicates that GaAs can exhibit high transport property of the electron in the semiconductor which makes it suitable for optoelectronics devices while the wider band gap of AlAs indicates their potentials can be used in high temperature and strong electric fields device applications. The results reveal a good agreement within reasonable acceptable errors when compared with the theoretical and experimental values obtained in the work of Federico and Yin wang [1] [2].

Preparation, characterization and nonlinear optical properties of colloidal gallium arsenide nanocrystals

GaAs nanocrystals were prepared via a simple mechanical ball milling technique. The prepared GaAs nanocrystals have high purity and could form colloidal ethanol suspension without any surfactant additives. The colloidal GaAs nanocrystal suspension displayed excellent two-photon absorption property over the visible and near-infrared region from 490 nm to 1064 nm, which enables it to become a promising broadband optical limiting material.

Burst mode enabled ultrafast laser inscription inside gallium arsenide

Ultrafast laser inscription(ULI)inside semiconductors offers new perspectives for 3D monolithic structures to be fabricated and new functionalities to be added in electronic and photonic microdevices.However,important challenges remain because of nonlinear effects such as strong plasma generation that distort the energy delivery at the focal point when exposing these materials to intense infrared light.Up to now,the successful technological demonstrations have primarily concentrated on silicon(Si).In this paper,we target at another important semiconductor:gallium arsenide(GaAs).With nonlinearities higher than those of Si,3D-machining of GaAs with femtosecond pulses becomes even harder.However,we show that the difficulty can be circumvented by burst-mode irradiation.We generate and apply trains of pulses at terahertz repetition rates for efficient pulse-to-pulse accumulation of laser-induced free carriers in the focal region,while avoiding an overdose of prefocal excitations.The superior performance of burst-mode irradiation is confirmed by a comparative study conducted with infrared luminescence microscopy.The results indicate a successful reduction of the plasma density in the prefocal region so that higher pulse energy reaches the focal spot.The same method is applied to identify optimum irradiation conditions considering particular cases such as asymmetric pulse trains and aberrated beams.With 64-pulse trains,we successfully manage to cross the writing threshold providing a solution for ULI inside GaAs.The application potential is finally illustrated with a stealth dicing demonstration by taking benefit of the burst mode.The irradiation method opens wide possibilities for 3D structuring inside GaAs by ULI.

NMR and NQR studies on transition-metal arsenide superconductors LaRu2As2,KCa2Fe4As4F2,and A2Cr3As3

We report 75As-nuclear magnetic resonance(NMR)and nuclear quadrupole resonance(NQR)measurements on transition-metal arsenides LaRu2As2,KCa2Fe4As4F2,and A2Cr3As3.In the superconducting state of LaRu2As2,a Hebel–Slichter coherence peak is found in the temperature dependence of the spin-lattice relaxation rate 1/T1 just below Tc,which indicates that LaRu2As2 is a full-gap superperconducor.For KCa2Fe4As4F2,antiferromagnetic spin fluctuations are observed in the normal state.We further find that the anisotropy rate RAF=Tc 1/Tab 1 is small and temperature independent,implying that the low energy spin fluctuations are isotropic in spin space.Our results indicate that KCa2Fe4As4F2 is a moderately overdoped iron-arsenide high-temperature superconductor with a stoichiometric composition.For A2Cr3As3(A=Na,K,Rb,Cs),we calculate the electric field gradient by first-principle method and assign the 75As-NQR peaks to two crystallographically different As sites,paving the way for further NMR investigation.

Effect of transport agent boron triiodide on the synthesis and crystal quality of boron arsenide

Cubic boron arsenide(BAs)has attracted great attention due to its high thermal conductivity,however,its controllable,stable,and ideal preparation remains challenging.Herein,we investigated the effect of iodine-containing transport agents I_(2) and boron triiodide(BI_(3))on BAs synthesized and grown through chemical vapor transport.Results show that similar to the commonly used I_(2),BI_(3) accelerates the synthesis and improves the mass fraction of BAs from ~12% to over 90% at 820℃ and 1.5 MPa,a value beyond the promoting effect of only increasing temperature and pressure.Both agents enhance the quality of BAs crystals by reducing the full width at half maximum by up to 10%-20%.I_(2) agglomerates the grown crystals with twin defects(~50 nm wide),and BI_(3) improves the crystal anisotropy and element uniformity of BAs crystals with narrow twins(~15 nm wide)and increases the stoichiometry ratio(~0.990)to almost 1.Owing to the boron interstitials from the excessive boron supply,the spacing of layers in {111} increases to 0.286 nm in the presence of I_(2).Owing to its coordinated effect,BI_(3) only slightly influences the layer spacing at 0.275 nm,which is close to the theoretical value of 0.276 nm.In the chemical vapor transport,the anisotropic crystals with flat surfaces exhibit single-crystal characteristics under the action of BI_(3).Different from that of I_(2),the coordinated effect of BI_(3) can promote the efficient preparation of high-quality BAs crystal seeds and facilitate the advanced application of BAs.

Epitaxial fabrication of monolayer copper arsenide on Cu(111)

We report the epitaxial growth of monolayer copper arsenide(CuAs)with a honeycomb lattice on Cu(111)by molecular beam epitaxy(MBE).Scanning tunneling microscopy(STM),low energy electron diffraction(LEED),x-ray photoelectron spectroscopy(XPS),and density functional theory(DFT)verify the√3×√3 superlattice of monolayer CuAs on Cu(111)substrate.Angle-resolved photoemission spectroscopy(ARPES)measurements together with DFT calculations demonstrate the electronic band structures of monolayer CuAs and reveal its metallic nature.Further calculations show that charge transfer from Cu(111)substrate to monolayer CuAs lifts the Fermi level and tunes the band structure of the monolayer CuAs.This high-quality epitaxial monolayer CuAs with potential tunable band gap holds promise on the applications in nano-electronic devices.

Accurate Electronic, Transport, and Bulk Properties of Zinc Blende Gallium Arsenide (Zb-GaAs)

We report accurate, calculated electronic, transport, and bulk properties of zinc blende gallium arsenide (GaAs). Our ab-initio, non-relativistic, self-con-sistent calculations employed a local density approximation (LDA) potential and the linear combination of atomic orbital (LCAO) formalism. We strictly followed the Bagayoko, Zhao, and William (BZW) method, as enhanced by Ekuma and Franklin (BZW-EF). Our calculated, direct band gap of 1.429 eV, at an experimental lattice constant of 5.65325 Å, is in excellent agreement with the experimental values. The calculated, total density of states data reproduced several experimentally determined peaks. We have predicted an equilibrium lattice constant, a bulk modulus, and a low temperature band gap of 5.632 Å, 75.49 GPa, and 1.520 eV, respectively. The latter two are in excellent agreement with corresponding, experimental values of 75.5 GPa (74.7 GPa) and 1.519 eV, respectively. This work underscores the capability of the local density approximation (LDA) to describe and to predict accurately properties of semiconductors, provided the calculations adhere to the conditions of validity of DFT.

Evaluation of Gallium Arsenide Thermal Expansion Coefficient by Extended X-Ray Absorption Fine Structure

Negative thermal expansion of gallium arsenide has been investigated through temperature dependent Extended X-ray Absorption Fine Structure (EXAFS) measurements. The bond thermal expansion coefficient αbond has been evaluated and compared to negative expansion coefficient αtens due to tension effects. The overall thermal expansion coefficient is the sum?of?αbond?and αtens. Below 60 K, αtens is greater than αbond? yielding to a negative expansion in this temperature region. Tension effects are progressively overcome by the stretching effects in the region 60 - 300 K. The asymmetry of nearest neighbors distribution is not negligible since the gaussian approximation underestimates the bond expansion by about 0.00426 Å. This error decreases when the temperature is lowered. The accuracy in the thermal expansion evaluation and the connection between third cumulant and thermal expansion are discussed.

Dark Current Compensation and Sensitivity Adjustment on Gallium Arsenide Linear Array Detector for X-Ray Imaging

For the last several years, the linear array x-ray detector for x-ray imaging with gallium arsenide direct conversion sensitive elements has been developed and tested at the In-stitute for High Energy Physics. The array consists of 16 sensitive modules. Each module has 128 gallium arsenide (GaAs) sensitive elements with 200 μm pitch. Current article describes two key program procedures of initial dark current compensation of each sensitive element in the linear array, and sensitivity adjustment for alignment of strip pattern in the raw image data. As a part of evaluation process a modular transfer function (MTF) was measured with the slanted sharp-edge object under RQA5 technique as it described in the International Electrotechnical Commission 62220-1 standard (high voltage 70 kVp, additional aluminium filter 21 mm) for images with compensated dark currents and adjusted sensitivity of detector elements. The 10% level of the calculated MTF function has spatial resolution within 2 - 3 pair of lines per mm for both vertical and horizontal orientation.

Realizing ultra-low thermal conductivity by strong synergy of asymmetric geometry and electronic structure in boron nitride and arsenide

The design of novel devices with specific technical interests through modulating structural properties and bonding characteristics promotes the vigorous development of materials informatics.Boron arsenide and boron nitride,as remarkably high thermal conductivity(κ)materials,are unfavorable for thermal insulation applications as well as thermoelectric devices.In this study,based on first-principles calculations,we identify a group of novel borides with ultra-lowκ,i.e.,g-B_(3)X_(5)(X=N,P,and As).Theκof g-B_(3)N_(5),g-B_(3)P_(5),and g-B_(3)As_(5)are 21.08,2.50,and 1.85 W·m^(-1)·K^(-1),respectively,which are boron nitride and boron arsenide systems with the lowestκreported so far.The ultra-lowκis attributed to the synergy effect of electronics(lone-pair electrons)and geometry(buckling structures)on thermal transport.The discovery of the ultralowκof boron nitride and boron arsenide systems can well fill the gaps in applications of thermal insulation and thermoelectric devices.

Pressure-driven anomalous thermal transport behaviors in gallium arsenide

High-pressure has been widely utilized to improve material performances such as thermal conductiv-ityκand interfacial thermal conductance G.Gallium arsenide(GaAs)as a functional semiconductor has attracted extensive attention in high-pressure studies for its technological importance and complex structure transitions.Thermal properties of GaAs under high pressure are urgent needs in physics but remain elusive.Herein,we systematically investigateκGaAs and G Al/GaAs of multi-structure up to -23 GPa.We conclude that:(1)in pressurization,phonon group velocity,lattice defects,and electrons play a central role inκGaAs in elastic,plastic,and metallization regions,respectively.The increased phonon density of states(PDOS)overlap,group velocity,and interfacial bonding enhances G Al/GaAs.(2)In depressurization,electrons remain the dominant factor on κ GaAs from 23 to 13.5 GPa.G Al/GaAs increases dramatically at -12 GPa due to the larger PDOS overlap.With decompressing to ambient,lattice defects including grain size reduction,arsenic vacancies,and partial amorphization reduce κ GaAs to a glass-like value.Remarkably,the released G Al/GaAs is 2.6 times higher than that of the initial.Thus our findings open a new dimension in synergistically realizing glass-like κ and enhancing G,which can facilitate thermoelectric performance and its potential engineering applications.

Enhanced thermal emission from metal-free,fully epitaxial structures with epsilon-near-zero InAs layers

We introduce a novel method to create mid-infrared(MIR)thermal emitters using fully epitaxial,metal-free structures.Through the strategic use of epsilon-near-zero(ENZ)thin films in InAs layers,we achieve a narrow-band,wide-angle,and p-polarized thermal emission spectra.This approach,employing molecular beam epitaxy,circumvents the complexities associated with current layered structures and yields temperature-resistant emission wavelengths.Our findings contribute a promising route towards simpler,more efficient MIR optoelectronic devices.

Behavior of exciton in direct−indirect band gap Al_(x)Ga_(1−x)As crystal lattice quantum wells

Excitons have significant impacts on the properties of semiconductors.They exhibit significantly different properties when a direct semiconductor turns in to an indirect one by doping.Huybrecht variational method is also found to influence the study of exciton ground state energy and ground state binding energy in Al_(x)Ga_(1−x)As semiconductor spherical quantum dots.The Al_(x)Ga_(1−x)As is considered to be a direct semiconductor at AI concentration below 0.45,and an indirect one at the concentration above 0.45.With regards to the former,the ground state binding energy increases and decreases with AI concentration and eigenfrequency,respectively;however,while the ground state energy increases with AI concentration,it is marginally influenced by eigenfrequency.On the other hand,considering the latter,while the ground state binding energy increases with AI concentration,it decreases with eigenfrequency;nevertheless,the ground state energy increases both with AI concentration and eigenfrequency.Hence,for the better practical performance of the semiconductors,the properties of the excitons are suggested to vary by adjusting AI concentration and eigenfrequency.

Atomic-Scale Friction Studies on Single-Crystal Gallium Arsenide Using Atomic Force Microscope and Molecular Dynamics Simulation

This paper provides a fresh perspective and new insights into nanoscale friction by investigating it through molecular dynamics(MD)simulation and atomic force microscope(AFM)nanoscratch experiments.This work considered gallium arsenide,an importantⅢ-Ⅴdirect bandgap semiconductor material residing in the zincblende structure,as a reference sample material due to its growing usage in 5G communication devices.In the simulations,the scratch depth was tested as a variable in the fine range of 0.5-3 nm to understand the behavior of material removal and to gain insights into the nanoscale friction.Scratch force,normal force,and average cutting forces were extracted from the simulation to obtain two scalar quantities,namely,the scratch cutting energy(defined as the work performed to remove a unit volume of material)and the kinetic coefficient of friction(defined as the force ratio).A strong size effect was observed for scratch depths below 2 nm from the MD simulations and about 15 nm from the AFM experiments.A strong quantitative corroboration was obtained between the specific scratch energy determined by the MD simulations and the AFM experiments,and more qualitative corroboration was derived for the pile-up and the kinetic coefficient of friction.This conclusion suggests that the specific scratch energy is insensitive to the tool geometry and the scratch speed used in this investigation.However,the pile-up and kinetic coefficient of friction are dependent on the geometry of the tool tip.

GaAs-based resonant tunneling diode:Device aspects from design,manufacturing,characterization and applications

This review article discusses the development of gallium arsenide(GaAs)-based resonant tunneling diodes(RTD)since the 1970s.To the best of my knowledge,this article is the first review of GaAs RTD technology which covers different epitaxialstructure design,fabrication techniques,and characterizations for various application areas.It is expected that the details presented here will help the readers to gain a perspective on the previous accomplishments,as well as have an outlook on the current trends and future developments in GaAs RTD research.

HIGH-ENERGY PROTON IRRADIATION EFFECTS ON GaAs/Ge SPACE SOLAR CELLS

This paper reports the high-energy proton irradiation effects on GaAs/Ge space solar cells. The solar cells were irradiated by protons with energy of 5-20 MeV at fluence ranging from 1×109 to 7×1013 cm-2, and then their electric parameters were measured at AM0. It was shown that the Isc, Voc and Pmax decrease as the proton energy increasing, and the degradation is relative to proton irradiation-induced defect with a level of Ec-0.41 eV in irradiated GaAs/Ge cells.

High-Quality InSb Grown on Semi-Insulting GaAs Substrates by Metalorganic Chemical Vapor Deposition for Hall Sensor Application

High-quality InSb epilayers are grown on semi-insulting GaAs substrates by metalorganic chemical vapor deposition using an indium pre-deposition technique. The influence of Ⅴ/Ⅲ ratio and indium pre-deposition time on the surface morphology, crystalline quality and electrical properties of the InSb epilayer is systematically investigated using Nomarski microscopy, atomic force microscopy, high-resolution x-ray diffraction, Hall measurement and contactless sheet resistance measurement. It is found that a 2-μm-thick InSb epilayer grown at 450℃ with a Ⅴ/Ⅲ ratio of 5 and an indium pre-deposition time of 2.5s exhibits the optimum material quality, with a root-meansquare surface roughness of only 1.2 nm, an XRD rocking curve with full width at half maximum of 358 arcsec and a room-temperature electron mobility of 4.6 × 10~4 cm^2/V·s. These values are comparable with those grown by molecular beam epitaxy. Hall sensors are fabricated utilizing a 600-nm-thick InSb epilayer. The output Hall voltages of these sensors exceed 10 mV with the input voltage of 1 V at 9.3 mT and the electron mobility of 3.2 × 10~4 cm^2/V·s is determined, which indicates a strong potential for Hall applications.

A STUDY OF THE PIEZOELECTRIC PROPERTIES OF GaAs

The origin of the piezoelectric effect of GaAs is discussed in some detail.TheGa atoms are negatively charged and As atoms positively charged.The piezoelectric con-stant tensors for arbitrarily oriented GaAs have been obtained.It is verified that for nor-mal stress when the GaAs samples are oriented in the 〈111〉 direction the maximumpiezoelectric effect occurs.As far as the piezoelectric properties and fabrication technologyare concerned,〈100〉 oriented GaAs substratcs are fit for the force sensors.

High Quality Zinc Sulfide Epitaxial Layers Grown by Metalorganic Chemical Vapour Deposition

ZnS films were successfully grown by metallorganic chemical vapour deposition (MOCVD) at atmospheric pressure on (100) GaAs substrates. The deposition was carried out at a substrate temperature between 280 approximately 550°C with optimisation of reactor design and growth conditions. The gas phase prereaction is effectively restrained. These epilayers exhibit high crystallographic quality and reveal a mirror surface morphology. The peak halfwidths of X-ray diffraction patterns from their (400) faces are within 0.06 approximately 0.09°. The epilayers grown on (111) GaAs, (112ˉ0) Al2O3 and (100) Si have proven to be single crystalline feature. The optical and electrical characteristics of ZnS epilayers are measured by photoluminescence, cathodeluminescence, and the Van der Pauw method. The results indicate that there are not a large number of deep centers that could be detected both at 77K and at room temperature. A broad CL peak around 2.897eV and 2.672eV was observed only under very strong excitation. Their origin has not been examined. All epilayers present high resistivities up to 1013Ω&middotcm.

Analysis of silicon-based integrated photovoltaic–electrochemical hydrogen generation system under varying temperature and illumination

Last decade witnessed tremendous research and development in the area of photo-electrolytic hydrogen generation using chemically stable nanostructured photo-cathode/anode materials. Due to intimately coupled charge separation and photo-catalytic processes, it is very difficult to optimize individual components of such system leading to a very low demonstrated solar-to-fuel efficiency (SFE) of less than 1%. Recently there has been growing interest in an integrated photovoltaic–electrochemical (PV–EC) system based on GaAs solar cells with the demonstrated SFE of 24.5% under concentrated illumination condition. But a high cost of GaAs based solar cells and recent price drop of poly-crystalline silicon (pc-Si) solar cells motivated researchers to explore silicon based integrated PV–EC system. In this paper a theoretical framework is introduced to model silicon-based integrated PV–EC device. The theoretical framework is used to analyze the coupling and kinetic losses of a silicon solar cell based integrated PV–EC water splitting system under varying temperature and illumination. The kinetic loss occurs in the range of 19.1%–27.9% and coupling loss takes place in the range of 5.45%–6.74% with respect to varying illumination in the range of 20–100?mW/cm2. Similarly, the effect of varying temperature has severe impact on the performance of the system, wherein the coupling loss occurs in the range of 0.84%–21.51% for the temperature variation from 25 to 50?°C. ? 2016 Science Press