GaAs System Research Articles

Underlying mechanism of structural transformation between GaSb and GaAs response to intense electronic excitation

Ion irradiation of semiconductors has emerged as a promising approach for fabricating self-organized nanosystems with high atomic precision, despite often being accompanied by undesirable phenomena. Exploring the mechanisms underlying structural transformations is crucial for assessing nanostructure array types under complex irradiation environments. By quantitatively calculating the thermodynamically driven processes and analyzing the impact of intrinsic structural parameters, distinct structural transformations in response to intense electronic excitation are systematically investigated in gallium antimonide (GaSb) and gallium arsenide (GaAs) systems. In high-energy regimes, the nanofibers layer of GaSb exhibits intriguing structural discrepancy, characterized by partial nanofibers with coherent boundaries, interspersed nanopores accompanied by antisite defects and Ga precipitates, distinguishing to a series of discontinuous latent tracks that emerged within cylindrical trajectories in GaAs. Furthermore, significant diffusion behaviors of the nanohillocks are discovered in GaAs, with higher average roughness than GaSb, driven by the gradient stress distribution influenced by the free-surface effects. The deposition energy for melting phase formation, Gibbs free energy, and Ga diffusion coefficients contribute to the distinctive structural features, evidencing relatively stable morphological configurations and higher irradiation resistance in GaAs. Consequently, special optoelectronic properties associated with structural discrepancies facilitate the design and optimization of material functionalities by irradiation technologies.

Explanation of puzzling FQHE at the filling fraction 3/4 in a band-hole 2D system in GaAs

A recent experiment revealed an unexpected FQHE at filling fraction 3/4 in a GaAs 2D hole system, which contradicts the composite fermion model prediction and the observation of a compressible Hall metal-type state in a twin 2D electron system in GaAs at the same filling fraction 3/4 at almost same other conditions. This finding challenges conventional effective single-quasiparticle model for FQHE exposing its limitations. We explain this experimental observation within a multiparticle approach based on a topological cyclotron commensurability criterion. This allows to generalize Laughlin function for filling fractions from the complete FQHE hierarchy including observable FQHE states at even denominator fractions. The topological multiparticle approach helps to decipher a structure of composite fermions and provides their generalization for so-called enigmatic states including even denominator filling fractions, and also for quantum fractional Hall-type behavior in Chern topological insulators without a magnetic field.

Fractional Quantum Hall States of the A Phase in the Second Landau Level.

A proposal of the existence of an Anomalous phase (A phase) [Das etal., Phys. Rev. Lett. 131, 056202 (2023)PRLTAO0031-900710.1103/PhysRevLett.131.056202] at the experimental range of moderate Landau-level-mixing strength has recently been made for the 5/2 state. We here report that the gapped A phase is generic to the sequence of spin-polarized fractional quantum Hall states with filling fractions ν=n/(nm-1) and ν=1-n/(nm-1), (n≥1,m≥3), that exhausts almost all the observed states and also predicts some states in the second Landau level for GaAs systems. Our proposed trial wave functions for all these states have remarkably high overlaps with the corresponding exact ground states and can support non-Abelian quasiparticle excitations with charge e/[2(nm-1)]. By analyzing edge modes, we predict experimentally verifiable thermal Hall conductance 2.5(π^{2}k_{B}^{2}T/3h) for all the states in these sequences.

Influence of cooling rate on microstructure and defect evolution in GaAs during solidification

The fabrication of high-quality GaAs crystals is essential to approach optimal performance in optoelectronic and microelectronic devices. In this study, a molecular dynamics simulation study was conducted for the solidification of liquid GaAs at three cooling rates (1010 K s−1, 1011 K s−1, and 1012 K s−1) at 300 K. The structural evolution in terms of crystal structure and defect formation in GaAs was thoroughly investigated using pair distribution function, average atomic energy, the largest standard cluster analysis, and visualization techniques. The results showed that the cooling rate of 1010 K s−1 led to the development of the best crystal quality with ease of eutectic twin grain boundary coherent twin boundary formation. Increasing the cooling rates to 1011 K s−1 and 1012 K s−1 resulted in the amorphous structure. Both high and low cooling rates profoundly affected the formation of As8 structure, but a maximum amount of 2.2% of As8 crystal structure was formed at a cooling rate of 1011 K s−1. The reduction in cooling rate to 1010 K s−1 induced the formation of numerous Schottky and Frenkel types of partial dislocations in the GaAs system. Results of this study can serve as potential guidelines to the theory of crystal growth and may be implemented in the fabrication of high-quality GaAs crystals for optimal device performance.

Recombination mechanism of heavily Be-doped GaAsN by time-resolved photoluminescence

The optical properties of GaAsN system alloys have not been clarified, particularly for the localized level around the bottom of the conduction band induced by nitrogen atoms. Herein, the recombination mechanism is systematically investigated for heavily Be-doped p-type GaAsN using both continuous-wave (CW) and time-resolved (TR) photoluminescence (PL) characteristics, which is expected to be applied to devices such as a p+-n+ tunnel diode inserted into a multijunction solar cell composed of GaAs system alloys and as the base layer of a heterojunction bipolar transistor. The S-shape characteristic weakened with increasing hole concentration (p) in the CW-PL spectra of Be-doped GaAsN. Both short and long lifetimes were evaluated using TR-PL decay curves. Specifically, the long lifetime was distributed between 0.7 and 1 ns independent of temperature and p. This long lifetime corresponds to radiative recombination lifetime from a localized level, supporting that a localized level is formed in Be-doped GaAsN despite high p on the order of 1019 cm−3. Electrons are tightly bound at a localized level, equivalent to this long lifetime, whereas the electron lifetime decreases with increasing p, resulting in the S-shape characteristic vanishing in the temperature dependence of the CW-PL spectra for ultraheavily Be-doped GaAsN with p of 5 × 1019 cm−3. Moreover, this S-shape characteristic vanished in the temperature dependence of TR-PL spectra for moderately Be-doped GaAsN with p of 8 × 1018 cm−3, indicating that the density of states is limited for a localized level.

Electronic structure and imaginary dielectric function for 2D GaAs doped with Si amphoteric impurities: A DFT study

Without a doubt, the impact of the discovery of 2D systems such as graphene has led to both theoretical and experimental investigations of a large number of materials such as Silicene, Borene, Arsenene, Phosphorene, just to mention some of the most emblematic ones, but other materials and its heterostructures are also of interest. From this point of view, in this work we present the band structure, density of states as well as the imaginary part of the dielectric function of a 2D GaAs system, by means of a density functional theory implementation. The aim of this study is to investigate the basic physical properties for a freestanding 2D GaAs sheet, as well as the effect of Si substitutional atoms, since it has an amphoteric nature in the GaAs, which means that depending on which atom is substituted, this can be an n- or p-type impurity atom. We report, as expected, that the levels do indeed appear near the conduction band (or valence) if the impurity is n-type (or p-type), respectively. Also the density of states due to the impurity is modified as well as the imaginary part of the dielectric function

Determination of a High-Power THz Detector for EA-FEL Radiation Using Optical Sampling of GaAs and ZnTe Crystals

This paper presents a diagnostic method for THz pulses produced by EA-FEL. Experimental results present a comparison between ZnTe and GaAs crystals for the detection of a single terahertz pulse using electro-optic sampling. In order to match an electro-optic detector for the EA-FEL radiation, the THz pulse from a source was simultaneously detected by ZnTe and GaAs electro-optic detectors. The GaAs detection system was found to have a shorter response time but low signal-to-noise ratio (SNR) compared to the ZnTe system. The GaAs crystal is suitable for the detection of short THz pulses due to fiber coupling, and the SNR of the GaAs system can be improved using a faster and more sensitive photodetector.

Hydrodynamics, viscous electron fluid, and Wiedeman-Franz law in two-dimensional semiconductors

Considering theoretically the transition between hydrodynamic and ballistic regimes in 2D semiconductors, we show that electrons in high-mobility 2D GaAs are by far the best system for the direct observation of collective hydrodynamic effects even in bulk transport properties independent of complicated transport features in narrow constrictions and small systems where Gurzhi phenomena are typically studied experimentally. We predict a strong hydrodynamics-induced generic violation of the Wiedeman-Franz law in bulk 2D GaAs systems for mobilities as modest as ${10}^{6}{\mathrm{cm}}^{2}/\text{Vs}$ and densities $1--5\ifmmode\times\else\texttimes\fi{}{10}^{11}{\mathrm{cm}}^{\ensuremath{-}2}$ in the temperature range of $T=1--40\phantom{\rule{0.16em}{0ex}}\text{K}$.

Band Flattening and Landau Level Merging in Strongly-Correlated Two-Dimensional Electron Systems

We review recent experimental results indicating the band flattening and Landau level merging at the chemical potential in strongly-correlated two-dimensional (2D) electron systems. In ultra-clean, strongly interacting 2D electron system in SiGe/Si/SiGe quantum wells, the effective electron mass at the Fermi level increases monotonically in the entire range of electron densities, while the energy-averaged mass saturates at low densities. The qualitatively different behavior of the two masses reveals a precursor to the interaction-induced single-particle spectrum flattening at the chemical potential in this electron system, in which case the fermion “condensation” at the Fermi level occurs in a range of momenta, unlike the condensation of bosons. In strong magnetic fields, perpendicular to the 2D electron layer, a similar effect of different fillings of quantum levels at the chemical potential—the merging of the spin- and valley-split Landau levels at the chemical potential—is observed in Si inversion layers and bilayer 2D electron system in GaAs. Indication of merging of the quantum levels of composite fermions with different valley indices is also reported in ultra-clean SiGe/Si/SiGe quantum wells.

Nature of the anomalous 4/13 fractional quantum Hall effect in graphene

Extensive fractional quantum Hall effect (FQHE) has been observed in graphene-based materials. Some of the observed fractions are anomalous in that FQHE has not been established at these fractions in conventional GaAs systems. One such fraction is $4/13$, where incompressibility has recently been reported in graphene [Kumar et al., Nat. Comm. 9, 2776 (2018)]. We propose a partonic wave function at $4/13$ and show it to be a viable candidate to describe the Coulomb ground state. Using the effective edge theory, we make predictions for experimentally measurable properties of the state.

Characterization of a GaAs photon-counting detector for mammography.

Purpose: The purpose of this study was to evaluate the potential of a prototype gallium arsenide (GaAs) photon-counting detector (PCD) for imaging of the breast. Approach: First, the contrast-to-noise ratio (CNR) using different aluminum/poly(methyl methacrylate) (PMMA) phantoms of different thicknesses were measured. Second, microcalcification detection accuracy using a receiver operating characteristic study with three observers reading an ensemble of images was measured. Finally, the feasibility of using a GaAs system with two energy bins for contrast-enhanced mammography was investigated. Results: For the first two studies, the GaAs detector was compared with a commercial mammography system. The CNR was estimated by imaging 18-, 36-, and -thick aluminum targets placed on top of 6cm of PMMA plates and was found to be similar or better over a range of exposures. We observed a similar performance of detecting microcalcifications with the GaAs detector over a range of clinically applicable dose levels with a small increase at lower dose levels. The results also showed that contrast-enhanced spectral mammography using a GaAs PCD is feasible and beneficial. Conclusions: Results from this study suggest that performance with this new detector seems either slightly improved or equivalent to a commercial mammography system that used an energy-integrated detector. No attempt at optimizing exposure techniques for the GaAs detector was performed. Further research is needed to determine optimal acquisition parameters for the GaAs detector and to develop more sophisticated material decomposition algorithms that promise to provide improved quantitative estimates of iodine uptake.

Unconventional Zn parton states at ν=7/3 : Role of finite width

A recent work [Balram, Jain, and Barkeshli, Phys. Rev. Res. ${\bf 2}$, 013349 (2020)] has suggested that an unconventional state describing $\mathbb{Z}_{n}$ superconductivity of composite bosons, which supports excitations with charge $1/(3n)$ of the electron charge, is energetically better than the Laughlin wave function at $\nu=7/3$ in GaAs systems. All experiments to date, however, are consistent with the latter. To address this discrepancy, we study the effect of finite width on the ground state and predict a phase transition from an unconventional $\mathbb{Z}_{n}$ state at small widths to the Laughlin state for widths exceeding $\sim$ 1.5 magnetic lengths. We also determine the parameter region where an unconventional state is stabilized in the one third filled zeroth Landau level in bilayer graphene. The roles of Landau level mixing and spin are also considered.

Импульсное лазерное облучение светоизлучающих структур со слоем (Ga,Mn)As

InGaAs/GaAs heteronanostructures with a (Ga,Mn)As layer on the surface were fabricated by MOCVD epitaxy and pulsed laser deposition, and the effect of a pulsed excimer laser (wavelength 248 nm, pulse duration ~ 30 ns) on their radiative, structural and galvanomagnetic properties was studied. The radiation energy density was varied in the range from 200 to 360 mJ/cm2. In the studies, photoluminescence spectroscopy was used, which makes it possible to analyze the polarization characteristics of the radiation of the structures. The crystalline perfection of the initial and laser-irradiated samples was studied using Raman spectroscopy. The elemental composition of the structures and its depth distribution were studied by secondary ion mass spectrometry. The effect of pulsed laser annealing on the ferromagnetic properties of heteronanostructures was characterized by the behavior of the magnetic field dependences of the Hall resistance and magnetoresistance at temperatures of 10–300 K in the range of magnetic fields ± 3600 Oe. At room temperature, the study was carried out in magnetic fields reaching values of ± 28000 Oe. To obtain the calculated temperature distributions along the sample thickness and in time using a model of the laser annealing process based on solving the problem of heat propagation in a one-dimensional GaAs system taking into account the (Ga,Mn)As layer on the surface, we used the original data on the thermal conductivity coefficient of structures with a layer (Ga,Mn)As obtained using a modified frequency separation technique (3ω-method).

Воздействие импульсов эксимерного лазера на светоизлучающие InGaAs/GaAs-структуры с (Ga, Mn)As-слоем

It was studied the possibility of laser annealing modification of the properties of the (Ga,Mn)As layer located on the surface of a quantum-well InGaAs/GaAs structure, while retaining its radiative properties. The structures with four InGaAs/GaAs quantum wells (indium content was varied from 0.08 to 0.25), located at different distances from the (Ga,Mn)As layer, were fabricated by combining the methods of MOCVD-hydride epitaxy and pulsed laser deposition. The LPX-200 excimer laser pulse energy density was varied from 200 to 360 mJ/cm2, and the depth of laser action was determined from the change in the photoluminescence spectra of the quantum wells. In describing the results obtained, a model of the laser annealing process was used, based on solving the problem of heat propagation in a one-dimensional GaAs system, taking into account the (Ga,Mn)As layer on the surface. Changes in the structural and galvanomagnetic properties of the samples as a result of laser irradiation were analyzed. It is shown that as a result of pulsed laser action at a laser energy density range of 250 - 300 mJ/cm2, it is possible to preserve the emissive properties of the active region (InGaAs/GaAs quantum well) located at a distance of 10 - 12 nm from the (Ga,Mn)As layer and modify ferromagnetic properties of the semiconductor (Ga,Mn)As, namely: to increase the temperature of the ferromagnet-paramagnetic phase transition to values of at least 120 K. The results obtained are promising for the development of technology for devices of spin optoelectronics.

The influence of the Cu doping position on GaAs: First-principles calculations

The structural, electronic, and optical properties of GaAs doped with two Cu atoms at different depths was studied using first-principles calculations based on the HSE hybrid density functional theory. The optical properties, including the complex dielectric function, optical refractive index, extinction coefficient, and absorption coefficient were computed for radiation with an energy of up to 6.7 eV. The results show that the characteristics of the GaAs system change when the Cu atoms are doped at different depths. When the two Cu atoms are placed 5.653 Å or 2.827 Å from the surface of the GaAs crystal, it exhibits typical semi-metallic properties. However, the Cu doping depth has little effect on the band structure and properties of the materials. When Cu atoms are doped onto the GaAs surface, the material shows the band structure characteristics of a metal conductor. The linear optical behavior of the GaAs system, which corresponds to its electronic structure, also varies depending on the doping position. The contribution of Cu-3d orbital electrons to the material properties varies with the doping position. In addition, copper atoms doped at a greater depth have a greater influence on the absorption wavelength and intensity of the material.

Efros–Shklovskii hopping in the electronic transport in 2D p-GaAs

We have investigated the resistivity of a 2D hole system in GaAs in the temperature range 200 mK < T < 800 mK at zero magnetic field and low hole densities when the system is near the metal–insulator transition in the insulating side. We have found that the resistivity follows the Efros–Shklovskii variable range hopping (ES-VRH) law, this behaviour is consistent with the existence of a Coulomb gap. The resistivity scales with temperature and the prefactor has been found independent of temperature and density, thus confirming the dominance of hole–hole interaction.

Two-dimensional hydrogenated buckled gallium arsenide: an ab initio study

First-principles calculations have been carried out to investigate the stability, structural and electronic properties of two-dimensional (2D) hydrogenated GaAs with three possible geometries: chair, zigzag-line and boat configurations. The effect of van der Waals interactions on 2D H–GaAs systems has also been studied. These configurations were found to be energetic and dynamic stable, as well as having a semiconducting character. Although 2D GaAs adsorbed with H tends to form a zigzag-line configuration, the energy differences between chair, zigzag-line and boat are very small which implies the metastability of the system. Chair and boat configurations display a – direct bandgap nature, while pristine 2D-GaAs and zigzag-line are indirect semiconductors. The bandgap sizes of all configurations are also hydrogen dependent, and wider than that of pristine 2D-GaAs with both PBE and HSE functionals. Even though DFT-vdW interactions increase the adsorption energies and reduce the equilibrium distances of H–GaAs systems, it presents, qualitatively, the same physical results on the stability and electronic properties of our studied systems with PBE functional. According to our results, 2D buckled gallium arsenide is a good candidate to be synthesized by hydrogen surface passivation as its group III–V partners 2D buckled gallium nitride and boron nitride. The hydrogenation of 2D-GaAs tunes the bandgap of pristine 2D-GaAs, which makes it a potential candidate for optoelectronic applications in the blue and violet ranges of the visible electromagnetic spectrum.

Model of n-type quadruple δ-doped GaAs quantum wells

Thomas Fermi (TF) approach was used to represent a model for the n-type quadruple δ-doped (QDD) system in GaAs. This is the first physical model in the literature for the QDD system. The energies, the wave functions and the Fermi energy (EF) were calculated. These calculations were performed for different density of impurities in the doped layer (N2D) and for different separation distances (d) between the doped layers. Preliminary results show that the value of the Fermi level for the first proposed model is well below its expected value. This observation is exploited for a second model consistent with the expected values of the EF. Our results indicate that there is a limit at the bottom of the potential profile for a multilayered doped delta system. This has a great importance for calculations in optoelectronic and transport properties.

Characterization of defects and strain in the (AlxGa(1−x))0.5In0.5P/ GaAs system by synchrotron X-ray topography

Abstract Synchrotron white beam X-ray topography and monochromatic beam topography have been applied to study GaAs substrates and (AlxGa(1−x))0.5In0.5P epitaxial layers grown on them that are being developed for LEDs. The GaAs substrates are 15° offcut toward [1 1 0] and mainly consist of dislocations in the {1 1 1} slip planes and low angle grain boundaries. The nominally lattice matched (AlxGa(1−x))0.5In0.5P layers contain defects such as threading dislocations replicated from the substrates, inclusions and misfit dislocations generated during organometallic vapor phase epitaxy (OMVPE) growth. The existence of misfit dislocations (MDs) indicates that strain relaxation has taken place to accommodate the in-plane lattice mismatch between epitaxial layer and substrate. The driving force for the glide of threading dislocations and relaxation efficiency of dislocations with different Burgers vectors and glide planes has been analyzed in the wafers with 15° offcut to predict the Burgers vectors and line directions of dislocations that dominate strain relaxation. Burgers vectors have been determined using ray tracing simulations. Reciprocal space maps (RSMs) recorded from the wafers to measure the strain and tilt of the epilayers show both in-plane and out-of-plane lattice mismatch as well as tilt between epilayer and substrate. A modified Nagai′s model has been developed to analyze and account for in-plane and out-of-plane tilt.

Interlayer distance effects on absorption coefficient and refraction index change in p-type double-δ-doped GaAs quantum wells**Project supported by PISA 2016–1 UJAT and PRODEP Folio UJAT-245 of México.

In the framework of the Thomas–Fermi (TF) approach, a model for the p-type double-δ-doped (DDD) system in GaAs is presented. This model, unlike other works in the literature, takes into account that the Poisson equation associated with the system is nonlinear. The electronic structure is calculated for heavy and light holes. The changes in the electronic structure result of the distance d between the doped layers are studied. In particular, the relative absorption coefficient as well as the relative refractive index change is calculated as a function of the incident photon energy for heavy holes. The effect of the interlayer distance exhibits, in the absorption coefficient, a red shift of the peak position and a decrease in amplitude when the distance increases. In addition, the relative refractive index change node has a red shift as well as the interlayer distance increases. The calculations show that the effect of the separation between layers has a greater influence on the linear terms. These results are very important for theoretical calculations and engineering of optical and electronic devices based in δ-doped GaAs.