Gallium Arsenide Crystals Research Articles

A Novel Proposal of an Electro-Optical Sensor to Measure Various Levels of an Electric Field Using Pockels Effect Photonic Crystals

Electro-optic sensors based on the Pockels effect are key components for optical instrumentation due to their speed and accuracy. In this work, we propose a new electro-optic platform using two-dimensional photonic crystals of gallium arsenide and barium titanate (GaAs-BTO). This structure allows for the measurement of various electric field levels, from 0 kV/mm to 50 kV/mm, with a very high sensitivity and a compact size. The opto-geometric parameters of this sensor were chosen, optimized, and analyzed numerically using the Plane Wave Expansion (PWE) and Finite-Difference Time-Domain (FDTD) methods.

Anisotropic fracture energy and toughness of single crystal gallium arsenide by microindentation

Although single crystal gallium arsenide (GaAs) is a technologically important semiconductor material, its mechanical behavior is poorly understood. In this study, the Vickers microindentation technique was leveraged with a quantitative fractographic approach to determine the fracture energy and toughness corresponding to various crystal planes. Cracks preferentially propagated along the {110} planes associated with the primary crack system {110} / 〈110〉. The normalized fracture toughness was used to calculate the directional fracture energy on the {001} plane and was consistent with a theoretical model based on calculating the number of broken bonds.

Ultrafast quantum path interferometry to determine the electronic decoherence time of the electron-phonon coupled system in n -type gallium arsenide

Quantum coherence is the key to new quantum technologies, although the details of decoherence processes and times are still not well understood in solids. We demonstrate how to measure the decoherence time of electronic excited states in $n$-type gallium arsenide ($n$-GaAs) crystals using a relative-phase locked double pulse excitation method and quantitatively evaluate with a simple model including temperature dependence. The interference patterns of both electronic and phonon coherence are observed in $n$-GaAs using ultrafast quantum path interferometry with $\ensuremath{\pi}/4$ polarized femtosecond pulses, via the amplitude of longitudinal optical phonons as a function of pump-pump delay. The electronic coherence shows uplifting and splitting in the collapse and revival of the electronic interference, which is sensitive to temperature, and these features are well reproduced using a simple quantum mechanical model. The decoherence time is determined using quantum calculations, from the splitting and uplifting in the interference shape, to be $27.8\ifmmode\pm\else\textpm\fi{}0.5, 23.0\ifmmode\pm\else\textpm\fi{}0.3$, and $12.9\ifmmode\pm\else\textpm\fi{}0.3$ fs at 10, 90, and 290 K, respectively. The temperature dependence of the decoherence time is well reproduced by the density of electrons in the conduction band with the group velocity of the photoinduced electrons.

Anticariogenic Sanative Effect of Aluminum Gallium Arsenide Crystals on Hydroxyapatite Crystals

Dental caries is a progressive disease with varying phases of demineralization and remineralization, and the scope of reversing the carious lesion is increased if it is diagnosed before there is surface cavitation. Preventive management strategies are directed towards making the enamel more resistant towards acid dissolution. The caries preventive protocol has always been fluoride-centric. Repeated application of fluoride gives rise to acquired fluoride resistance strains of Streptococci mutans which can be transient or permanent. The need of the hour is an effective remineralizing protocol which is one which brings about a change in enamel crystal and makes it more resistant to the acidic challenges of the oral cavity. The authors have devised a protocol in which irradiation with aluminum gallium arsenide crystals LASER can bring about a sanative change in crystal and lead to greater acid resistance of the enamel crystal and thus potentiate the remineralization of non-cavitated lesions. The concept of aluminum gallium arsenide–assisted caries inhibition and the proposed hypothesis of the mechanism of action is discussed.

A mid-IR laser diagnostic for HCN detection

Hydrogen cyanide (HCN) is a major source of prompt-NOx formation especially in fuel-bound nitrogen systems. To date, there is still a significant disagreement between experimental data and theoretical predictions of the rate coefficients of combustion reactions involving HCN as a prompt-NOx precursor. Accurate modeling of NOx formation would greatly benefit from a diagnostic capable of performing high-fidelity measurements of HCN formation/consumption time-histories. In this study, a laser diagnostic is developed for sensitive and selective HCN sensing by probing its most intense absorption feature in the mid-infrared (MIR). The diagnostic is based on difference-frequency generation (DFG) between a CO2 gas laser and an external-cavity quantum cascade laser in a nonlinear orientation-patterned gallium arsenide crystal which results in a DFG laser tunable over 11.56 − 15 µm. HCN measurements were carried out at the peak of the Q-branch of its strong ν2 vibrational band near 14 µm. Pressure dependence of the absorption cross-section was investigated at room temperature over the pressure range of 0.07 − 1.07 bar. Temperature-dependent absorption cross-section measurements were conducted behind reflected shock waves over the temperature range of 850 − 3000 K. The diagnostic was demonstrated in reactive experiments in a shock tube where HCN mole fraction time-histories were measured during the thermal decomposition of isoxazole (C3H3NO) and the first-order rate coefficients of C3H3NO → HCN + CH2CO reaction were determined.

Polarization spectroscopy of high-order harmonic generation in gallium arsenide.

An interesting property of high harmonic generation in solids is its laser polarization dependent nature which in turn provides information about the crystal and band structure of the generation medium. Here we report on the linear polarization dependence of high-order harmonic generation from a gallium arsenide crystal. Interestingly, we observe a significant evolution of the anisotropic response of above bandgap harmonics as a function of the laser intensity. We attribute this change to fundamental microscopic effects of the emission process comprising a competition between intraband and interband dynamics. This intensity dependence of the anisotropic nature of the generation process offers the possibility to drive and control the electron current along preferred directions of the crystal, and could serve as a switching technique in an integrated all-solid-state petahertz optoelectronic device.

Improving the efficiency of photopiezoelectric induction acoustic waves in semi-insulating single crystals of gallium arsenide

The work is devoted to the analysis of the influence of acoustic losses on the efficiency of inducing resonant acoustic waves in single-crystal gallium arsenide plastids using infrared light pulses. It is established that the amplitude of the excited mechanical vibrations depends on the magnitude and position of the internal friction in the crystal on the temperature scale due to acousto-electronic relaxation. Recommendations on the choice of the element of the alloying admixture of gallium arsenide are formulated. Keywords: optical absorption, piezoelectric effect, relaxation, optical pulses.

Mechanisms of Atomic–Molecular Processes Underlying Si and GaAs Nanowire Crystallization

We analyze atomic–molecular processes underlying Si and GaAs nanowire growth. The atomic structure of the crystal–melt interface has been shown to lead to poorer wettability of the (111) Si and $$\left( {\bar {1}\bar {1}\bar {1}} \right)$$ В GaAs faces by metal solvent droplets, Si and GaAs nanowire growth in the 〈111〉 and $$\left\langle {\bar {1}\bar {1}\bar {1}} \right\rangle $$ В directions, and the formation of gallium arsenide crystals with cubic and hexagonal lattices.

Real Time Predictions of VGF-GaAs Growth Dynamics by LSTM Neural Networks

The aim of this study was to assess the aptitude of the recurrent Long Short-Term Memory (LSTM) neural networks for fast and accurate predictions of process dynamics in vertical-gradient-freeze growth of gallium arsenide crystals (VGF-GaAs) using datasets generated by numerical transient simulations. Real time predictions of the temperatures and solid–liquid interface position in GaAs are crucial for control applications and for process visualization, i.e., for generation of digital twins. In the reported study, an LSTM network was trained on 1950 datasets with 2 external inputs and 6 outputs. Based on network performance criteria and training results, LSTMs showed the very accurate predictions of the VGF-GaAs growth process with median root-mean-square-error (RMSE) values of 2 × 10−3. This deep learning method achieved a superior predictive accuracy and timeliness compared with more traditional Nonlinear AutoRegressive eXogenous (NARX) recurrent networks.

Structural Features Associated with Twinning in the Growth of Gallium Arsenide Single Crystals by the Czochralski Method

The structural features induced by twinning in tin- and tellurium-doped gallium arsenide crystals during their growth by the Czochralski method with liquid melt sealing by boric anhydride have been considered. It is shown that growth twins and edge facets arise at the crystal periphery in the region of supercooled melt. The dopant concentration near a twin is always higher than in the region free of twins. A change is observed in the dislocation-growth direction in crystal during twinning.

An atomistic investigation on the wear of diamond during atomic force microscope tip-based nanomachining of gallium arsenide

This paper investigated the wear mechanism of diamond during the atomic force microscope (AFM) tip-based nanomachining of Gallium Arsenide (GaAs) using molecular dynamics (MD) simulations. The elastic–plastic deformation at the apex of the diamond tip was observed during the simulations. Meanwhile, a transition of the diamond tip from its initial cubic diamond lattice structure sp3 hybridization to graphite lattice structure sp2 hybridization was revealed. Graphitization was, therefore, found to be the dominant wear mechanism of the diamond tip during the nanometric cutting of single crystal gallium arsenide for the first time. The various stress states, such as hydrostatic stress, shear stress, and von Mises stress within the diamond tip and the temperature distribution of the diamond tip were also estimated to find out the underlying mechanism of graphitization. The results showed that the cutting heat during nanomachining of GaAs would mainly lead to the graphitization of the diamond tip instead of the high shear stress-induced transformation of the diamond to graphite. The paper also proposed a new approach to quantify the graphitization conversion rate of the diamond tip.

Localization by an external magnetic field of electrons on the ions of hydrogen-like donors in non-degenerate semiconductors

In the quasi-classical approximation of quantum mechanics a model for the localization of conduction electrons on the ions of hydrogen-like donors in an external magnetic field was developed. The thermal ionization energy of donors in lightly doped and moderately compensated crystals of gallium arsenide and indium antimonide of n-type was calculated depending on the induction of the external magnetic field. In contrast to the known theoretical works (which use variational methods for solving the Schrödinger equation), a simple analytical expression is proposed for the ionization energy of the donor in the magnetic field, which quantitatively agrees with the known experimental data. It is shown that the magnitude of the magnetic field induced by the orbital motion of the electron around the ion core of the donor is negligible compared to the external field and does not contribute to the ionization energy of donors.

Estimation of the magnitude of the Ruderman-Kittel interaction in 3d and 2d GaAs crystals

In this paper, estimates are made of the Ruderman-Kittel interaction in a gallium arsenide crystal and in GaAs quantum wells of varying widths. The calculation results indicate that this interaction may be weaker than the magnetic dipole-dipole interaction by an order of magnitude. Also discovered was a relatively strong dependence of this interaction on the level of doping.

Application of multiple correlation analysis method to modeling the physical properties of crystals (on the example of gallium arsenide)

The use of modern applied computer programs expands the possibility of multicomponent statistical analysis in materials science. The procedure for applying the method of multiple correlation and regression analysis for the study and modeling of multifactorial relationships of physical characteristics in crystalline structures is considered. The consideration is carried out using single crystals of undoped gallium arsenide as an example. The statistical analysis involved a complex of seven physical characteristics obtained by non-destructive methods for each of 32 points along the diameter of the crystal plate. The data array is investigated using multiple correlation analysis methods. A computational model of regression analysis is built. Based on it, using the programs Excel, STADIA and SPSS Statistics 17.0, statistical data processing and analytical study of the relationships of all characteristics are carried out. Regression relationships are obtained and analyzed in determining the concentration of the background carbon impurity, residual mechanical stresses, and the concentration of the background silicon impurity. The ability to correctly conduct multiple statistical analysis to model the properties of a GaAs crystal is established.New relationships between the parameters of the GaAs crystal are revealed. It is found that the concentration of the background silicon impurity is related to the vacancy composition of the crystal and the concentration of cents EL2. It is also found that there is no relationship between the silicon concentration and the value of residual mechanical stresses. These facts and the thermal conditions for the formation of point defects during the growth of a single crystal indicate the absence of a redistribution of background impurities during cooling of an undoped GaAs crystal.The use of the multiple regression analysis method in materials science allows not only to model multifactor bonds in binary crystals, but also to carry out stochastic modeling of factor systems of variable composition

Research into effect of electrochemical etching conditions on the morphology of porous gallium arsenide

The method for the formation of porous gallium arsenide in a solution of hydrochloric acid was improved. The goal of present research was to establish correlation between conditions of electrochemical etching of gallium arsenide crystals and morphology of low-dimensional structures. Porous layers were formed by the method of electrochemical etching in a solution of hydrochloric acid. The mode of electrolyte agitation was applied. This makes it possible to avoid the formation of bubbles on the surface of the crystal during etching and leads to the formation of regular porous space. Basic regularities in the formation of porous spaces were studied. It was shown that morphological properties of por-GaAs depend on etching conditions. The effect was explored of current density on the thickness of a porous layer and diameter of pores. It was established that the composition and concentration of electrolyte correlate with surface porosity and affect the rate of crystal dissolution reaction. Etching time determines thickness of a porous layer and surface porosity. Chemical composition of por-GaAs was explored. An oxide layer was not formed on the surface of the examined samples; oxygen was present only in small concentrations. Stoichiometry of the samples was disrupted towards an excess of gallium atoms

Confinement of generated terahertz waves between two metal surfaces by a nanowaveguide

In this study, a new nanowaveguide is designed and modeled. Light confinement by the nanowaveguide generates a 1-terahertz (THz) wave with narrow bandwidth. A difference-frequency generation (DFG) technique based on the nonlinear property of a gallium arsenide crystal is used in the model for generation of the THz wave. All calculations are based on the method of finite difference time domain. The feasible conditions of phase matching are evaluated, and the structural parameters of the nanowaveguide are optimized. It was found that the simultaneous use of two parallel plasmonic surfaces in the structure improves THz output power of the nanowaveguide in comparison with that of other similar waveguides. The nanowaveguide output power is several times larger than the output power of the other waveguides based on DFG technique in all scales.

Low-power optical technique using semiconductors modulates terahertz radiation

Exploiting impurities in a gallium arsenide crystal, a new approach allows for modifying waveforms of difficult-to-control terahertz radiation without bulky macroscopic modulators.

Characterization of defect states in Ga-rich gallium arsenide crystals by thermally stimulated current

The trap levels in Ga-rich GaAs crystals were studied in the temperature range of 10–300 K using thermally stimulated currents (TSC) technique. During the experiments we utilized a constant heating rate of 0.2 K/s. Experimental evidence is found for two electron trapping centers in the crystal with activation energies of 44 and 50 meV. The analysis of the experimental TSC curve suggests slow retrapping. The capture cross sections of the traps were determined as 8.8 × 10−25 and 1.0 × 10−25 cm2 with concentrations of 2.7 × 1011 and 1.3 × 1011 cm−3, respectively.

Bench testing of a heterodyne CO2 laser dispersion interferometer for high temporal resolution plasma density measurements.

A heterodyne detection scheme is combined with a 10.59 μm CO2 laser dispersion interferometer for the first time to allow large bandwidth measurements in the 10-100 MHz range. The approach employed utilizes a 40 MHz acousto-optic cell operating on the frequency doubled CO2 beam which is obtained using a high 2nd harmonic conversion efficiency orientation patterned gallium arsenide crystal. The measured standard deviation of the line integrated electron density equivalent phase resolution obtained with digital phase demodulation technique, is 4 × 1017 m-2. Air flow was found to significantly affect the baseline of the phase signal, which an optical table cover was able to reduce considerably. The heterodyne dispersion interferometer (DI) approach is found to be robustly insensitive to motion, with measured phase shifts below baseline drifts even in the presence of several centimeters of retroreflector induced path length variations. Plasma induced dispersion was simulated with a wedged ZnSe plate and the measured DI phase shifts are consistent with expectations.

Improvement of radiation stability of semi-insulating gallium arsenide crystals by deposition of diamond-like carbon films

We studied the properties of optical elements for the IR spectral range based on semi-insulating gallium arsenide (SI-GaAs) and antireflecting diamond-like carbon films (DLCF). Particular attention has been paid to the effect of penetrating γ-radiation on transmission of the developed optical elements. A Co60 source and step-by-step gaining of γ-irradiation dose were used for treatment of both an initial SI-GaAs crystal and DLCF/SI-GaAs structures. It was shown that DLCF deposition essentially increases degradation resistance of the SI-GaAs-based optical elements to γ-radiation. Particularly, the transmittance of the DLCF/SI-GaAs structure after γ-irradiation with a dose 9⋅104 Gy even exceeds that of initial structures. The possible mechanism that explains the effect of γ-radiation on the SI-GaAs crystals and the DLCF/SI-GaAs structures at different irradiation doses was proposed. The effect of small doses is responsible for non-monotonic transmission changes in both SI-GaAs crystals and DLCF/SI-GaAs structures. At further increasing the γ-irradiation dose, the variation of properties of both DLCF and SI-GaAs crystal influences on the transmission of DLCF/SI-GaAs system. At high γ-irradiation dose 1.4⋅105 Gy, passivation of radiation defects in the SI-GaAs bulk by hydrogen diffused from DLCF leads to increasing the degradation resistance of the SI-GaAs crystals coated with DLCF as compared with the crystals without DLCF.