Monolayers Of GaAs Research Articles

Enhanced spin Hall ratio in two-dimensional semiconductors

The conversion efficiency from charge current to spin current via the spin Hall effect is evaluated by the spin Hall ratio (SHR). Through state-of-the-art ab initio calculations involving both charge conductivity and spin Hall conductivity, we report the SHRs of the III-V monolayer family, revealing an ultrahigh ratio of 0.58 in the hole-doped GaAs monolayer. In order to find more promising 2D materials, a descriptor for high SHR is proposed and applied to a high-throughput database, which provides the fully relativistic band structures and Wannier Hamiltonians of 216 exfoliable monolayer semiconductors and has been released to the community. Among potential candidates for high SHR, the MXene monolayer Sc2CCl2 is identified with the proposed descriptor and confirmed by computation, demonstrating the descriptor validity for high SHR materials discovery.

Strain controllable band alignment and the interfacial and optical properties of tellurene/GaAs van der Waals heterostructures.

By using first principles calculations, we theoretically investigate the electronic structures and the interfacial and optical properties of the two-dimensional tellurene (Te)-gallium arsenide (GaAs) van der Waals heterostructures (vdWHs), i.e., α-Te/GaAs and γ-Te/GaAs, formed using Te and GaAs monolayers. It has been demonstrated that, the semiconductor-semiconductor contacted α-Te/GaAs vdWH exhibits a type-II band alignment with a direct band gap of 0.28 eV while the metal-semiconductor contacted γ-Te/GaAs vdWH has a p-type Schottky contact with a Schottky barrier height (SBH) of 0.36 eV at the interface. The transition from type-II to type-III band alignment is observed firstly in the α-Te/GaAs vdWH when the in-plane biaxial strain is less than -5.2% and larger than 4.4%, meanwhile, the p-type Schottky contact to Ohmic contact transition may be realized in the γ-Te/GaAs vdWH when the in-plane biaxial strain is less than -2.4%. Finally, the maximum optical absorption coefficients of the α- and γ-Te/GaAs vdWHs have been found to be up to 31% and 29%, respectively, and may be modulated effectively by applying in-plane biaxial strain. The obtained results may be of importance in the design of nanoelectronic devices based on the proposed tellurene/GaAs vdWHs.

Performance Limit of Ultrathin GaAs Transistors.

High-electron-mobility group III-V compounds have been regarded as a promising successor to silicon in next-generation field-effect transistors (FETs). Gallium arsenide (GaAs) is an outstanding member of the III-V family due to its advantage of both good n- and p-type device performance. Monolayer (ML) GaAs is the limit form of ultrathin GaAs. Here, a hydrogenated ML GaAs (GaAsH2) FET is simulated by ab initio quantum-transport methods. The n- and p-type ML GaAsH2 metal-oxide-semiconductor FETs (MOSFETs) can well satisfy the on-state current, delay time, power dissipation, and energy-delay product requirements of the International Technology Roadmap for Semiconductors until the gate length is scaled down to 3/4 and 3/5 nm for the high-performance/low-power applications, respectively. Therefore, ultrathin GaAs is a prominent channel candidate for devices in the post-Moore era. The p-type ML GaAsH2 MOSFETs with a 2% uniaxially compressive strain and the unstrained n-type counterparts have symmetrical performance for the high-performance application, making ultrathin GaAs applicable for complementary MOS integrated circuits.

Two-dimensional XY monolayers (X = Al, Ga, In; Y = N, P, As) with a double layer hexagonal structure: A first-principles perspective

In this paper, we systematically investigate the structural, mechanical, optical and electronic properties of novel two-dimensional XY (X= Al, Ga, In; Y= N, P, As) monolayers in the double layer hexagonal structure (DLHS) using first-principles calculations. Our calculations show that single-layers of XY are stable, with the exception of GaP monolayer, which is unstable with its phonon spectrum containing negative frequencies. Also, the linear elastic parameters confirm the Born conditions for mechanical stability of XY monolayers and they are brittle structures. Most XY monolayers have indirect semiconductor characteristics with band gaps of 3.54 eV, 1.78 eV, 0.18 eV, 1.68 eV and 1.28 eV for AlN, GaN, InN, AlP, and AlAs monolayers. However the GaAs monolayer has a metallic character. The optical results indicate the InN and AlAs monolayers have ability to absorb the visible light spectra. We expect that our findings will point the way forward for the use of these structures in microelectronics and optoelectronics devices.

Adsorption of gas molecules on buckled GaAs monolayer: a first-principles study.

The design of sensitive and selective gas sensors can be significantly simplified if materials that are intrinsically selective to target gas molecules can be identified. In recent years, monolayers consisting of group III–V elements have been identified as promising gas sensing materials. In this article, we investigate gas adsorption properties of buckled GaAs monolayer using first-principles calculations within the framework of density functional theory. We examine the adsorption energy, adsorption distance, charge transfer, and electron density difference to study the strength and nature of adsorption. We calculate the change in band structure, work function, conductivity, density of states, and optical reflectivity for analyzing its prospect as work function-based, chemiresistive, optical, and magnetic gas sensor applications. In this regard, we considered the adsorption of ten gas molecules, namely NH3, NO2, NO, CH4, H2, CO, SO2, HCN, H2S, and CO2, and noticed that GaAs monolayer is responsive to NO, NO2, NH3, and SO2 only. Specifically, NH3, SO2 and NO2 chemisorb on the GaAs monolayer and change the work function by more than 5%. While both NO and NO2 are found to be responsive in the far-infrared (FIR) range, NO shows better spin-splitting property and a significant change in conductivity. Moreover, the recovery time at room temperature for NO is observed to be in the sub-millisecond range suggesting selective and sensitive NO response in GaAs monolayer.

Laser-driven anisotropic and nonlinear Rashba spin splitting in GaAs monolayer

We investigate the electronic properties of the buckled honeycomb GaAs monolayer under a periodically circularly polarized laser (CPL) by first-principles calculations and Floquet theory. Under the irradiation of CPL with propagation direction in the $xy$ plane, a remarkable Rashba spin splitting (RSS) is induced in the valence and conduction bands at $\mathrm{\ensuremath{\Gamma}}$ point. The laser-driven RSS deviates from the classical linear Rashba model in a wide range of wave vectors, and can be interpreted by a nonlinear model involving the third-order terms. The phase diagram of Rashba effect with laser amplitude and propagation direction is worked out. The anisotropy of the nonlinear RSS is mainly determined by the laser propagation direction, providing the possibility of controlling the Rashba anisotropy characteristics. By carefully choosing the laser frequency and amplitude, giant anisotropic RSS can be obtained, which allows the generation of spin-polarized electrons via doping and facilitates the flexibility of spintronic devices.

The optimization of InGaAs/InGaP quantum wells grown by gas source molecular beam epitaxy

We report on the great improvement of optical properties of a InGaAs quantum well structure by inserting ultra-thin GaAs layers between the InGaAs well and the InGaP barrier grown by molecular beam epitaxy. The room temperature photoluminescence from the quantum well structure with insertion of 3 monolayers GaAs shows 1.5 times enhancement in peak intensity, as well as a drastic reduction of peak linewidth from 46 nm to 30 nm. The dependence of the quantum well optical properties has been investigated with inserted GaAs thickness in the range of 0–12 MLs, and optimized GaAs thickness has been obtained. This methodology might be beneficial for growth of high quality quantum well optical devices.

First Principles Calculation for Photocatalytic Activity of GaAs Monolayer

Solar energy hydrogen production is one of the best solutions for energy crisis. Therefore, finding effective photocatalytic materials that are able to split water under the sunlight is a hot topic in the present research fields. In addition, theoretical prediction is a present low-cost important method to search a new kind of materials. Herein, with the aim of seeking efficient photocatalytic material we investigated the photocatalytic activity of GaAs monolayer by the first principles calculation. According to the obtained electronic and optical properties, we primarily predicted the photocatalytic water splitting activity of GaAs monolayer, which the result further confirmed by the calculated reaction free energy. More remarkably, predicted carrier mobility of GaAs monolayer 2838 cm2V−1s−1 is higher than 200 cm2V−1s−1 of MoS2. Our finding provides a promising material for the development of renewable energy conversion and a new outlook for better designing of a superior photocatalyst for water splitting.

Exciton-driven giant nonlinear overtone signals from buckled hexagonal monolayer GaAs

We report here a giant $\left|\chi_{baa}^{2}\right|=$780 pm/V second harmonic and $\left|\chi_{aaaa}^{3}\right|=$1.4$\times$10$^{-17}$ m$^{2}$/V$^{2}$ third harmonic signal from single atomic sheet of buckled hexagonal GaAs. We demonstrate this through the solution of an ab-initio real-time Bethe-Salpeter equation by including the electron-hole screened-exchange self-energy. The coupling between time-dependent external electric field and correlated electrons is treated within the modern theory of polarization. The result of our calculation envisage monolayer GaAs to be a prominent member in the material library of non-linear signal generations.

Growth and evaluation of GaAsN films with different N distribution grown by atomic layer epitaxy method

GaAsN films with different N distributions have been grown using the atomic layer epitaxy method to evaluate the effects of N distribution on the electrical properties of GaAsN. Three films, which had the same N composition with different N distribution were fabricated by alternate stack of GaAsN 1 monolayer (ML) and GaAs (0, 3, 5) ML. According to the X-ray diffraction measurement, periodicity and small N interdiffusion between GaAs and GaAsN layers in grown GaAsN films were confirmed. Thus, N distribution in the films were successfully modified in the order of a few unit lattice. Contribution of each scattering mechanisms on carrier mobility and densities of scattering centers in grown GaAsN films were evaluated. Compared with the film with 0 ML of GaAs, the density of N induced scattering center decreased with insertion of GaAs 3 ML between GaAsN 1 ML. It again increased the film with insertion of GaAs 5 ML. These results suggest that controlling N distribution intentionally not only degraded but also improved the electrical properties of GaAsN films.

Spin-polarized magneto-electronic properties in buckled monolayer GaAs

We develop the generalized tight-binding model to fully explore the magneto-electronic properties of monolayer GaAs, where the buckled structure, multi-orbital chemical bondings, spin-orbit coupling, electric field, and magnetic field are considered simultaneously. The diverse magnetic quantization covers three groups of spin-polarized Landau levels (LLs) near the Fermi level, with the unique initial energies, LL degeneracy, energy spacings, magnetic-field-dependence, and spin splitting. Furthermore, the Landau state probabilities exhibit specific oscillation patterns, being composed of the localization centers, node regularities, and energy-dependent variations of the dominating orbitals. The density of states directly reflects the main features of the LL energy spectra in the form, height, number, and frequency of the spin-split delta-function-like prominent peaks. The electric field leads to the monotonous/nonmonotonous LL energy dispersions, LL crossing behavior, gap modulation, phase transition and enhancement of spin splitting. The complex gap modulations and even semiconductor-semimetal transitions are attributed to the strong competition among the intrinsic interactions, magnetic field, and electric field. Such predicted magneto-electronic properties could be verified by scanning tunneling spectroscopy and are helpful in designing the top-gated and phase-change electronic devices.

High piezoelectricity in the buckled V-structure monolayers of group III-V: An Ab initio calculation

Using first-principles plane-wave calculations in the framework of density functional theory, we calculated the coefficients of elasticity, piezoelectric strain and stress tensors for the buckled V-structure group III-V monolayer materials (GaP, GaAs, InP, InAs). We demonstrated that these compounds have four independent elastic coefficients (c11, c21, c22, c66) and three piezoelectric coefficients (d11, d12, d26). Our analysis shows that the InAs (d11 = 64.47 p.m./V) and the GaAs (d11 = 35.39 p.m./V) monolayers exhibit much stronger piezoelectricity than reported two-dimensional materials such as the h-BN and the MoS2 monolayers. These nanomaterials that have simultaneously piezoelectricity and semiconducting behavior are promising candidates for piezotronics and piezo-phototronics applications.

GaAs monolayer: Excellent SHG responses and semi metallic to metallic transition modulated by vacancy effect

Monolayer materials are considered as a promising candidate for novel applications due to their attractive magnetic, electronic and optical properties. Investigation on nonlinear optical (NLO) properties and effect of vacancy on monolayer materials are vital to property modulations of monolayers and extending their applications. In this work, with the aid of first-principles calculations, the crystal structure, electronic, magnetic, and optical properties of GaAs monolayers with the vacancy were investigated. The result shows gallium arsenic (GaAs) monolayer produces a strong second harmonic generation (SHG) response. Meanwhile, the vacancy strongly affects structural, electronic, magnetic and optical properties of GaAs monolayers. Furthermore, arsenic vacancy (VAs) brings semi metallic to metallic transition, while gallium vacancy (VGa) causes nonmagnetic to magnetic conversion. Our result reveals that GaAs monolayer possesses application potentials in Nano-amplifying modulator and Nano-optoelectronic devices, and may provide useful guidance in designing new generation of Nano-electronic devices.

Electronic and Optical Properties of GaAs Bilayer

In the present work, we have systematically studied structural, electronic and optical properties of buckled GaAs bilayer with and without spin‐orbit coupling by density functional theory. Buckled GaAs bilayer have direct band gap of 0.70 eV at high symmetric Г‐point which is low as compare to GaAs monolayer. Optical properties such as real and imaginary part of dielectric functions, refractive index, extinction coefficient, absorption spectrum and reflectivity are well studied using density function theory. The calculated optical properties show that the buckled GaAs bilayer can be beneficial for optoelectronic and light emitting devices.

Quantum Monte Carlo Study of Buckled GaAs Monolayer

We have investigated the ground state properties of buckled GaAs monolayer using density functional theory (DFT) and quantum Monte Carlo (QMC) method. Standard first‐principles approaches such as DFT with approximate exchange‐correlation functionals do not describe the correlation effect accurately and hence, usually cannot predict results within the chemical accuracy. In order to accurate evaluation of correlation energy that makes a small but very important contribution to the total energy of an electronic system, the quantum Monte Carlo methods are used which include the correlation effect of electron‐electron using Jastrow function. We found QMC energies are few tenths eV lower than the DFT energies and the buckled GaAs monolayer have direct the band gap of 1.46 eV within DFT calculations, whereas quasiparticle gap is 3.4(8) eV within QMC calculations. We have also calculated the electron affinity and ionization potential as a function of system size.

Sub-Poissonian Narrowing of Length Distributions Realized in Ga-Catalyzed GaAs Nanowires.

Herein, we present experimental data on the record length uniformity within the ensembles of semiconductor nanowires. The length distributions of Ga-catalyzed GaAs nanowires obtained by cost-effective lithography-free technique on silicon substrates systematically feature a pronounced sub-Poissonian character. For example, nanowires with the mean length ⟨L⟩ of 2480 nm show a length distribution variance of only 367 nm2, which is more than twice smaller than the Poisson variance h⟨L⟩ of 808 nm2 for this mean length (with h = 0.326 nm as the height of GaAs monolayer). For 5125 nm mean length, the measured variance is 1200 nm2 against 1671 nm2 for Poisson distribution. A supporting model to explain the experimental findings is proposed. We speculate that the fluctuation-induced broadening of the length distribution is suppressed by nucleation antibunching, the effect which is commonly observed in individual vapor-liquid-solid nanowires but has never been seen for their ensembles. Without kinetic fluctuations, the two remaining effects contributing to the length distribution width are the nucleation randomness for nanowires emerging from the substrate and the shadowing effect on long enough nanowires. This explains an interesting time evolution of the variance that saturates after a short incubation stage but then starts increasing again due to shadowing, remaining, however, smaller than the Poisson value for a sufficiently long time.

Electric field effect of GaAs monolayer from first principles

Using first-principle calculations, we investigate two-dimensional (2D) honeycomb monolayer structures composed of group III-V binary elements. It is found that such compound like GaAs should have a buckled structure which is more stable than graphene-like flat structure. This results a polar system with out-of-plane dipoles arising from the non-planar structure. Here, we optimized GaAs monolayer structure, then calculated the electronic band structure and the change of buckling height under external electric field within density functional theory using generalized gradient approximation method. We found that the band gap would change proportionally with the electric field magnitude. When the spin-orbit coupling (SOC) is considered, we revealed fine spin-splitting at different points in the reciprocal space. Furthermore, the valence and conduction bands spin-splitting energies due to SOC at the K point of buckled GaAs monolayers are found to be weakly dependent on the electric field strength. Finally electric field effects on the spin texture and second harmonic generation are discussed. The present work sheds light on the control of physical properties of GaAs monolayer by the applied electric field.

1.5 μm InAs/InGaAsP/InP quantum dot laser with improved temperature stability

Temperature characteristics of InAs/InGaAsP quantum dot (QD) lasers synthesized on InP (001) substrate are presented. The lasers demonstrate high temperature stability: a threshold current characteristic temperature as high as 205 K in the temperature range between 20 to 50°C was measured. Lasing wavelength of 1.5 μm was achieved by covering QDs with 1.7 monolayers of GaAs.

Structural, electronic, and magnetic properties of transition-metal atom adsorbed two-dimensional GaAs nanosheet**Project supported by the National Natural Science Foundation of China (Grant No. 11174212).

By using first-principles calculations within the framework of density functional theory, the electronic and magnetic properties of 3d transitional metal (TM) atoms (from Sc to Zn) adsorbed monolayer GaAs nanosheets (GaAsNSs) are systematically investigated. Upon TM atom adsorption, GaAsNS, which is a nonmagnetic semiconductor, can be tuned into a magnetic semiconductor (Sc, V, and Fe adsorption), a half-metal (Mn adsorption), or a metal (Co and Cu adsorption). Our calculations show that the strong p–d hybridization between the 3d orbit of TM atoms and the 4p orbit of neighboring As atoms is responsible for the formation of chemical bonds and the origin of magnetism in the GaAsNSs with Sc, V, and Fe adsorption. However, the Mn 3d orbit with more unpaired electrons hybridizes not only with the As 4p orbit but also with the Ga 4p orbit, resulting in a stronger exchange interaction. Our results may be useful for electronic and magnetic applications of GaAsNS-based materials.

GaAs/GaP quantum dots: Ensemble of direct and indirect heterostructures with room temperature optical emission

We describe the optical emission and the carrier dynamics of an ensemble of self-assembled GaAs quantum dots embedded in GaP(001). The QD formation is driven by the 3.6% lattice mismatch between GaAs and GaP in the Stranski-Krastanow mode after deposition of more than 1.2 monolayers of GaAs. The quantum dots have an areal density between 6 and 7.6 × 1010 per cm−2 and multimodal size distribution. The luminescence spectra show two peaks in the range of 1.7 and 2.1 eV. The samples with larger quantum dots have red emission and show less thermal quenching compared with the samples with smaller QDs. The large QDs luminescence up to room temperature. We attribute the high energy emission to indirect carrier recombination in the thin quantum wells or small strained quantum dots, whereas the low energy red emission is due to the direct electron-hole recombination in the relaxed quantum dots.