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Detection of terahertz radiation by GaAs transistor structures has been studied experimentally. The two types of samples under study included dense arrays of HEMTs and large-apertures detectors. Arrays consisted of parallel and series chains with asymmetric gate transistors for enhanced photoresponse on terahertz radiation. We investigated two types of wide-aperture detectors: grating gate detector, and single gate detector with bow-tie antenna. Wide-aperture detectors were symmetrical. Studies of transistor chains have shown that two essential features for this type of detector are the presence of asymmetry in the gate, and the type of connection between individual transistors themselves. Wide-aperture detectors have also been tested by narrow beams of terahertz radiation, which allows analyzing the role influence of individual parts of the detector for total sensitivity to terahertz excitation. The sensitivity and noise equivalent power of the detectors were evaluated.

THz response of AlGaAs/InGaAs/GaAs HEMT structure has been investigated. The structure consists of the serpentine chain of series connected HEMTs. The source of one is the drain for the subsequent transistor. Experiments have been showed THz response peculiarities of such structures and enhanced noise equivalent power.

A survey of recent Raman scattering studies on the interstitial hydrogen molecule (H₂) in Si and GaAs is presented. It is shown that properties of H₂ strongly depend on the nuclear spin state I. In either material, para-H₂ (I=0) is unstable against irradiation with band gap light. In the case of Si, para-H₂ also preferentially disappears from the Raman spectra in the course of storage at room temperature in the dark. Possible explanations for this surprising behavior are discussed and compared with the latest infrared absorption studies.

While the As-rich 2 × 4 reconstruction of GaAs(001) is well explained by the so-called β₂ structure, the atomic structure of the Ga-rich 4 × 2 phase has been discussed for a long time. In this review, the most important structural models for the GaAs(001) (4 × 2)/c(8 × 2) surface are compared from different theoretical and experimental points of view. The selected reconstructions include the recently proposed ζ model, a new mixed dimer model, and the well-known β, β₂, Cerdà and Skala models. The different structures are compared on the basis of total energy calculations, simulations of STM experimental images and interpretation of X-ray diffraction data. Only the ζ model satisfies all criteria, and provides therefore a satisfactory explanation of the atomic structure of GaAs(001)-(4 × 2).

ZnSe epilayers have been grown under various Se/Zn atomic flux ratios in the range of 0.22–2.45 at a substrate temperature of 350°C on Zn pre-exposed GaAs (111) A surfaces. Real time reflection high energy electron diffraction (RHEED) observations have shown a transition from a two-dimensional (2D) to a three-dimensional (3D) growth mode. The transition time depends directly upon the growth rate. A detailed discussion is presented to explore the cause of this change in the growth mode.

A numerical study is needed to gain insight into the growth mechanism and improve the reactor design or optimize the deposition condition in chemical vapor deposition (CVD). In this study, we have performed a numerical analysis of the deposition of gallium arsenide (GaAs) from trimethyl gallium (TMG) and arsine in a vertical CVD reactor. The effects of operating parameters, such as the rotation velocity of susceptor, inlet velocity, and inlet TMG fraction, are investigated and presented. The three-dimensional model which is used in this investigation includes complete coupling between the thermal-fluid transport and species transport with chemical reaction.

A full, three-dimensional (3D) ray tracing approach is developed to simulate the caustics visible in mirror electron microscopy (MEM). The method reproduces MEM image contrast resulting from 3D surface relief. To illustrate the potential of the simulation methods, we study the evolution of crater contrast associated with a movie of GaAs structures generated by the droplet epitaxy technique. Specifically, we simulate the image contrast resulting from both a precursor stage and the final crater morphology which is consistent with an inverted pyramid consisting of (111) facet walls. The method therefore facilities the study of how self-assembled quantum structures evolve with time and, in particular, the development of anisotropic features including faceting.

We fabricated an FePt/MgO tunneling junction (Fe 55 atomic %) on a GaAs-based light-emitting-diode structure. The out-of-plane magnetization of the FePt thin film was confirmed by a magneto-optical measurement. The electrical spin injection from FePt into GaAs at room temperature was studied using the technique of spin-polarized electroluminescence. The spin polarization of the injected electrons under the magnetic field of 1 T was at least 6.0%. The remnant polarization at 0 T, which indicates the spin injection without a magnetic field, was at least 3.3%.

This paper analyzes the effect of 100keV silicon negative ion implantation in semi-insulating gallium arsenide sample for the fluences varying between $1\times 10^{15}$ and $2\times 10^{17}$ioncm${}^{-2}$ using Raman spectroscopy, Rutherford backscattering spectroscopy and Electron spin resonance spectroscopy. The gallium arsenide sample implanted with silicon negative ion for different fluences showed shift in the TO peak position with respect to unimplanted gallium arsenide sample. Increase in the broadening of TO peak was observed in the as-implanted samples, indicating development of stress and phonon confinement due to the incorporation of silicon in gallium arsenide crystal lattice. Annealing of as-implanted samples showed stress relaxation. Increase in RBS backscattering yield was observed in the as-implanted samples. Annealing of as-implanted (with high fluence) sample showed flat RBS yield response. ESR measurement study revealed restructuring of defects in the gallium arsenide sample implanted with fluence of $1\times 10^{17}$ioncm${}^{-2}$ after annealing to the temperature of $300^{\circ }$C.

The surface morphology modification and optical property modification of semi-insulating gallium arsenide sample implanted with 100 keV silicon ions with the fluences ranging between 5 × 10${}^{15}$ and 4 × 10${}^{17}$ ion cm${}^{-2}$ were analyzed using scanning electron microscopy and UV–Vis–NIR spectroscopy study. Scanning electron microscopy study revealed pore-like structure formation on the surface of gallium arsenide samples after silicon ion implantation. The size of these pore-like structures was found to increase with increasing ion fluence. Energy dispersive X-ray analysis showed an increase in silicon concentration in the gallium arsenide sample after silicon ion implantation with increasing ion fluence. The UV–Vis–NIR spectroscopy study revealed a decrease in optical transmission for silicon ion implanted gallium arsenide sample with increasing ion fluence. An additional absorption band was observed for the gallium arsenide sample implanted with the highest fluence (4 × 10${}^{17}$ ion cm${}^{-2})$. Urbach tail energy was found to increase with respect to ion fluence.

A molecular dynamics model of the epitaxial growth of gallium arsenide has been written. The results from the model will be used to obtain parametric growth data including layer thickness and doping concentration. Initially it was necessary to check the potential, which was developed for bulk gallium arsenide, for its applicability to surface growth. The resultant continuum model, when integrated with Stanford University’s SUPREM 3.5 code, will simulate gallium arsenide processing based on epitaxial material.

The anisotype HJ 𝜌-cu₂ZnSnSe₄/ n-GaAs was obtained, for the first time, by selenization of base metal layers that were previously thermally deposited on a GaAs substrate. The heterostructures created discuss both current-voltage properties and current transmission mechanisms. The forward bias was found to be characterized by currents limited by space charge, tunneling and recombination processes. In the case of reverse bias, currents predominate, which are limited by the space charge in mobility mode.

THz response of AlGaAs/InGaAs/GaAs HEMT structure has been investigated. The structure consists of the serpentine chain of series connected HEMTs. The source of one is the drain for the subsequent transistor. Experiments have been showed THz response peculiarities of such structures and enhanced noise equivalent power.

Detection of terahertz radiation by GaAs transistor structures has been studied experimentally. The two types of samples under study included dense arrays of HEMTs and large-apertures detectors. Arrays consisted of parallel and series chains with asymmetric gate transistors for enhanced photoresponse on terahertz radiation. We investigated two types of wide-aperture detectors: grating gate detector, and single gate detector with bow-tie antenna. Wide-aperture detectors were symmetrical. Studies of transistor chains have shown that two essential features for this type of detector are the presence of asymmetry in the gate, and the type of connection between individual transistors themselves. Wide-aperture detectors have also been tested by narrow beams of terahertz radiation, which allows analyzing the role influence of individual parts of the detector for total sensitivity to terahertz excitation. The sensitivity and noise equivalent power of the detectors were evaluated.