Semi-insulating Gallium Arsenide Research Articles

Distribution of Carbon in Large Diameter Semi-Insulating Gallium Arsenide Grown by Liquid Encapsulated Czochralski Technique

Carbon impurity concentration and dislocation density were investigated with optical microscopy and Fourier transform infrared absorption spectrometer in radial direction of large diameter (6-inch) undoped semi-insulating Gallium Arsenide (SI-GaAs) grown by liquid encapsulated Czochralski (LEC). The experimental results showed that their distributions are both “W”-shaped along wafer diameter, which is relatively higher on the center and lower near the center, but highest on the edge of the wafer. The nonuniformity distribution of thermal stress from growth process leads to the “W”-shaped distribution of dislocations in radial direction. The adsorption of matrix elastic strain field around dislocations induces the “W”-shaped distribution of carbon impurity. Dislocations adsorb carbon impurity and carbon impurity decorates dislocations. Dislocation density distribution affects carbon behavior.

Experimental Research on Inhibition of Surface Flashover Based on High Power Gallium Arsenide Photoconductive Switches Triggered by Laser

Semi-insulating gallium arsenide (GaAs) photoconductive semiconductor switches (PCSS) have great potential for high voltage switching application, however, the utility is restricted by surface flashover which would result in breakdown. In this paper, a model of photo-activated charge wave was proposed based on the theory of photo-activated charge domain (PACD) in GaAs PCSS, and moderate suppression of PACD formation by loading the semiconductor surface with dielectric material was investigated theoretically and experimentally. Current as high as 3.7 kA was obtained at 28 kV, implying that this method can effectively inhibit the surface flashover and improve the service life of DC charged GaAs PCSS.

Photopiezoelectric induction of resonant acoustic waves in semi-insulating gallium arsenide single crystals

The effect of resonant acoustic wave excitation in semi-insulating gallium-arsenide single crystals is investigated by means of light pulses. The peak amplitude of excited elastic oscillations is observed in a temperature range, where small values of the internal friction and electrical conductivity of the semiconductor take place simultaneously. The effect is related to the inverse piezoelectric conversion of the bulk-photovoltage energy into the mechanical deformation of the semiconductor crystal. The results of the investigations can be used for designing semiconductor photodetectors with high modulation-frequency selectivity.

Waveguide-to-microstrip transition at G-band using elevated E-plane probe

A rectangular waveguide-to-microstrip transition operating at G-band is presented. The E-plane probe, used in the transition, is fabricated on semi-insulating gallium arsenide (SI-GaAs) and it is elevated on the substrate. This configuration reduces interaction with semiconductor material. The elevated probe is suitable for direct integration with monolithic microwave integrated circuits. Measured results show S11 better than −10dB between 150 and 200 GHz and S21=−4dB at centre band (180GHz) for two transitions in back-to-back configuration.

Growth of silver nanowires on GaAs wafers

Silver (Ag) nanowires with chemically clean surfaces have been directly grown on semi-insulating gallium arsenide (GaAs) wafers through a simple solution/solid interfacial reaction (SSIR) between the GaAs wafers themselves and aqueous solutions of silver nitrate (AgNO(3)) at room temperature. The success in synthesis of Ag nanowires mainly benefits from the low concentration of surface electrons in the semi-insulating GaAs wafers that can lead to the formation of a low-density of nuclei that facilitate their anisotropic growth into nanowires. The resulting Ag nanowires exhibit rough surfaces and reasonably good electric conductivity. These characteristics are beneficial to sensing applications based on single-nanowire surface-enhanced Raman scattering (SERS) and possible surface-adsorption-induced conductivity variation.

Nitrogen incorporation into GaAs lattice as a result of the surface cavitation effect

Semi-insulating gallium arsenide was exposed to cavitation impact initiated by focusing a high-frequency acoustic wave into liquid nitrogen. Optical and atomic force microscopy methods were used for the analysis of surface morphology. Formation of microstructures as well as change in the chemical composition of the surface are observed. The morphology of the structures is highly dependent on the acoustic parameters. Raman spectroscopy data have confirmed the incorporation of nitrogen atoms into the GaAs lattice and Ga–N bond formation in the region of maximal structural change due to the cavitation impact.

Characteristics of Terahertz Radiation Emitted From Fractal Photoconductive Antennas

We study the terahertz (THz) emission characteristics of a photoconductive antenna comprising a metallic fractal pattern fabricated on a semi-insulating gallium arsenide substrate. multifrequency emission peaks were observed owing to the property of the multifrequency resonances of our fractal structures. The number of emission peaks increases with the number of fractal levels, attributable to the attendant increase in the number of localized resonances. We have also found that the emission intensity of the THz radiation can be enhanced by modifying part of the fractal pattern.

High Current Operation of a Semi-insulating Gallium Arsenide Photoconductive Semiconductor Switch Triggering a Spark Gap

A transient peak current as high as 5.6 kA is obtained by a GaAs photoconductive semiconductor switch (PCSS) in series with a spark gap. Based on the characteristics of the GaAs PCSS, mechanisms of discharge between the PCSS and the spark gap are discussed. It is implied that a hybrid operation mode of photo-activated charge domain occurs due to the superposition of the bias voltage and the instantaneous radio frequency voltage.

Emission of terahertz radiations from fractal antennas

We investigate the emission of terahertz radiation from a photoconductive fractal antenna fabricated on a semi-insulating gallium arsenide substrate. Owing to the self-similarity of fractal structures, our fractal antenna shows a multiband emission of terahertz radiation. The emission intensity at peak frequency is about twice that from a bow-tie antenna. We also investigate the mechanism of the multiband emission by using the finite-difference time-domain calculation.

Photoresistances of semi-insulating GaAs photoconductive switch illuminated by 1.064 μm laser pulse

The Shockley–Read–Hall model (SRHM) and its simplified model (SSRHM) were used to describe the characteristics of a photoconductive semiconductor switch (PCSS) made from a semi-insulating (SI) gallium arsenide (GaAs) chip, biased at low voltage, and illuminated by a 1.064 μm laser pulse. These characteristics include the free carrier densities, dynamic photoresistance, and time evolution of output pulses of the PCSS. The deep donor EL2 centers in SI GaAs play a dominant role in both the SRHM and SSRHM as electrons at EL2 unionized centers are strongly excited by the subband-gap photons at the wavelength of 1.064 μm. Theoretical modeling on the evolution of the experimental measured output pulses led to a two-step micromechanism of electron excitation process within the GaAs chip. The minimum photoresistances predicted by the SSRHM are in good agreement with experimental measurements, which confirms the dominant role of EL2 in the generation of electric pulses from a SI GaAs photoconductivity switch on which the 1064 nm laser pulse is illuminated.

Characterization of CdTe, Cd xZn 1−xTe and GaAs detectors

We report space-and-time current spectroscopy for characterization of high-quality GaAs thin films grown on semi-insulating gallium arsenide substrates. The approach is based on illumination of semiconductor material with an oscillating interference pattern formed of two light waves, one of which is phase modulated with frequency ω. The non-steady-state photocurrent flowing through the short-circuited semiconductor is the measurable quantity in this technique. The alternating current resulted from the periodic relative shifts of the photoconductivity and space charge electric field gratings arising in the crystal's volume under illumination. The results of measurements of semiconductor material's parameters of CdTe and Cd x Zn 1− x Te detectors are presented. The experiments are carried out for the diffusion regime of signal excitation at light wavelength λ=1.15 μm. The sign, conductivity and diffusion length are estimated from the dependencies of the signal on the temporal and spatial frequencies. The high-quality GaAs thin films grown on semi-insulating gallium arsenide substrates are characterized. The experiments are carried out in the geometry of the Michelson interferometer at the illumination wavelength of 532 nm. The dependence of the non-steady-state photocurrent on spatial frequency of the interference pattern is measured, allowing estimation of the diffusion length of photoelectrons in GaAs thin film L D=40 μm.

Angular dependence of terahertz emission from semiconductor surfaces photoexcited by femtosecond optical pulses

In this paper, the angular dependence of terahertz (THz) emission from semiconductor surfaces photoexcited by femtosecond optical pulses is reported. Time-domain waveforms of THz emission from (100) surfaces of semi-insulating gallium arsenide (si-GaAs) and p-type indium arsenide (p-InAs) are measured at various angles after careful suppression of the nonlinear optical rectification effect. THz emission angle-frequency patterns under focusing conditions of the excitation beam are regarded as radiation from an electric dipole moment located on the semiconductor surface. Based on the experimental results in the magnetic field parallel to the semiconductor surface, we discuss the ultrafast carrier dynamics on the surfaces of both semiconductors.

Transformation of GaAs surface during the vacuum deposition of Au films studied with surface acoustic waves

Surface acoustic waves are used to study the transformation of the surface of a high-resistance (semi-insulating) gallium arsenide in situ in the course of the thermal deposition of gold in vacuum. It is demonstrated that the surface modifications that involve the formation of the Au-Ga liquid phase and solid solutions based on Au3Ga, Au7Ga2, etc. result in variations in the parameters (amplitude and phase) of the transmitted acoustic wave and can be identified using such variations.

Near band-edge luminescence of semi-insulating undoped gallium arsenide at high levels of excitation

The dependences of the maximum and the half-width of near band-edge photoluminescence of semi-insulating undoped-GaAs crystals at 77 K on the concentration of background acceptor impurities and the level of excitation in the range from 3×10 21 to 6×10 22 quantum/(cm 2 s) are investigated. The observed dependences are explained by formation of the density tails of states as a result of fluctuations of impurity concentration and participation of localized states of the donor impurity band in radiative transitions. Reduction of many-particle interaction at increasing of N can be connected with increasing of shielding of charge carriers by atoms of impurity.

Complex periodic structures in bi-dimensional bifurcation diagrams of a RLC circuit model with a nonlinear NDC device

We report the existence of complex periodic structures, forming intricate periodic networks, embedded in chaotic regions of bi-dimensional bifurcation diagrams (parameter spaces) of a chaotic circuit model. Such circuit is composed by a negative differential conductivity (NDC) device coupled with a three variable RLC tank circuit. Particularly, we focused on a semi-insulating Gallium Arsenide (GaAs) model of nonlinear NDC device which is capable of oscillating at low frequencies. We show the presence of many types of orbits regarding their topological structures, indicating that there are topological transitions in the parameter space.

Effects of thermal annealing on the electrical properties of large diameter semi-insulating gallium arsenide

In this paper, the effects of thermal annealing on the electrical parameters in semi-insulating gallium arsenide (SI-GaAs) at 1200 and 1400 K under vacuum conditions were studied. It was found that the electrical parameters of SI-GaAs crystal change with thermal annealing in comparison with as-grown samples. The conductive type changes from n-type to p-type; the Hall mobility and the resistivity decrease, while the carrier concentration increases dramatically. The phenomenon was considered to be associated with the evaporation of arsenic (As) on surface of the sample and the out-diffusion of As interstitial atoms. The related formation mechanisms were also discussed.

On the modelling of semi-insulating GaAs including surface tension and bulk stresses

The necessary heat treatment of single-crystal semi-insulating gallium arsenide (GaAs), which is deployed in micro- and optoelectronic devices, generates undesirable liquid precipitates in the solid phase. The appearance of precipitates is influenced by surface tension at the liquid–solid interface and deviatoric stresses in the solid.The central quantity for the description of the various aspects of phase transitions is the chemical potential, which can be additively decomposed into a chemical and a mechanical part. In particular, the calculation of the mechanical part of the chemical potential is of crucial importance. We determine the chemical potential in the framework of the St. Venant–Kirchhoff law, which gives an appropriate stress–strain relation for many solids in the small-strain regime. We establish criteria that allow the correct replacement of the St. Venant–Kirchhoff law by the simpler Hooke law.The main objectives of this study are the following: (i) we develop a thermo-mechanical model that describes diffusion and interface motions, which are both strongly influenced by surface tension effects and deviatoric stresses, (ii) we give an overview and outlook on problems that can be posed and solved within the framework of the model, and (iii) we calculate non-standard phase diagrams for GaAs above 1059 K, i.e. those that take into account surface tension and deviatoric stresses, and we compare the results with classical phase diagrams without these phenomena.

Use of Whispering-Gallery Modes and Quasi-${\rm TE}_{0{ np}}$ Modes for Broadband Characterization of Bulk Gallium Arsenide and Gallium Phosphide Samples

The complex permittivity of bulk crystals of semiinsulating gallium arsenide (GaAs) and gallium phosphide (GaP) were measured over the frequency range from 4 to 30 GHz and at temperatures from 30 up to 300 K employing whispering-gallery-mode (WGM) and quasi-TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">np</i> -mode dielectric-resonator techniques. At temperatures about 40 K, dielectric loss tangent values were below 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> for GaAs and below 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup> for GaP. The use of several WGMs, as well as TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">np</i> modes excited in the same test sample enabled a broad frequency range of measurements (one decade). The real part of the permittivity of GaP and GaAs proved to be frequency independent at microwave frequencies. The dielectric loss tangents of GaAs and GaP increase with temperature and frequency.

The investigation of a novel approach in the simulation of the trap levels effect on the conduction in a GaAs P +νN + diode

A numerical simulation using C ++ language, allowing the store of big size information (presented as ( X × Y × Z) matrix) is realized, and a theoretical modelling of the charges transport in the semiconductor devices made in materials presenting a significant concentration of impurities whose energy levels are deep is implemented. The results are validated on a semi-insulating gallium arsenide (SI-GaAs) PIN structure. The numerical simulation is made by the resolution of the phenomenological transport's equations by adopting a new approach permitting to study the conduction phenomena through all the structure. From the 3D modelling, the variation of the potential profile, the free carriers and the space charge distributions, and the electrical field inside the structure are simulated. The effects of the traps are taken into account through the mechanisms of recombination and storage of a significant space charge, where the influence of the presence of these levels on the above factors is seen. Through this work a physical model intended for the study of the influence of the trap levels on the potential and the free carrier density distributions for weak lifetime semiconductors, more particularly on semi-insulating GaAs is introduced. Taking into account the trap centres is essential for a good comprehension and explanation of the transport phenomena. The present study consists to do a simulation and a modelisation of structures based on materials presenting a deep and a trap centres. A trapping model based on a combined numerical method Gummel and Newton is adopted to reduce both the run time and to reach convergence in the process when working not with one junction but with two.

Dynamics of formation of photoresponse in a detector structure made of gallium arsenide

The influence of capture effects on the characteristics of detectors of the ionizing radiation based on semi-insulating gallium arsenide is considered. Generation of nonequilibrium electrons and holes along the entire thickness of the active region was performed under illumination with an infrared light-emitting diode with a wavelength of 0.9 µm. In this case, the situation emerging in the device structure under the effect of X-ray radiation or a high-energy electron beam was simulated. It is shown that the variation in the shape of the output signal with time in this case is caused by variation in the electric field profile due to the capture of holes at deep centers in gallium arsenide. An absolutely different distribution of the electric field emerges in the structure under irradiation of a semitransparent cathode of the structure with a red light-emitting diode, emission of which penetrates into the active region for mere 1 μm. In this case, the transformation of the electric field is caused by the capture of electrons. Under the prolonged effect of such radiation, a space-charge-limited current mode emerges in the device.