Semi-insulating GaAs Research Articles

Carbon irradiated semi insulating GaAs for photoconductive terahertz pulse detection.

We report here a photoconductive material for THz detection with sub-picosecond carrier lifetime made by C(12) (Carbon) irradiation on commercially available semi-insulating (SI) GaAs. We are able to reduce the carrier lifetime of SI-GaAs down to sub-picosecond by irradiating it with various irradiation dosages of Carbon (C(12)) ions. With an increase of the irradiation dose from ~10(12) /cm(2) to ~10(15) /cm(2) the carrier lifetime of SI-GaAs monotonously decreases to 0.55 picosecond, whereas that of usual non-irradiated SI-GaAs is ~70 picosecond. This decreased carrier lifetime has resulted in a strong improvement in THz pulse detection compared with normal SI-GaAs. Improvement in signal to noise ratio as well as in detection bandwidth is observed. Carbon irradiated SI-GaAs appears to be an economical alternative to low temperature grown GaAs for fabrication of THz devices.

Analysis of the photocurrent relaxation in semi-insulating GaAs in the temperature range of 150–200 K

The specific features of detecting the contribution of the characteristic intrinsic defect in semi-insulating GaAs to photocurrent relaxation are considered. A detailed analysis of the relaxation kinetics based on approximation by the sum of exponential components is presented. The approximation results are compared with the data of photo-induced current transient spectroscopy.

High-Performance In0.23Ga0.77 As Channel MOSFETs with High Current Ratio Ion/Ioff Grown on Semi-insulating GaAs Substrates by MOCVD

We demonstrate high-performance In0.23 Ga0.77 As channel metal-oxide-semiconductor field-effect transistors (MOSFETs) with high on-current to off-current (Ion/Ioff) ratio grown on semi-insulating GaAs wafers by metal-organic chemical vapor deposition (MOCVD). The 2 μm channel-length devices exhibit a peak extrinsic transconductance of 150 mS/mm and a drain current up to 500 mA/mm. The maximum effective mobility is 1680 cm2/Vs extracted by the split C-V method. Furthermore, the Ion/Ioff ratio is significantly improved from approximately 4.5 × 103 up to approximately 4.32 × 104 by controlling the etch thickness of In0.49 Ga0.51 P. The high drain current and high Ion/Ioff ratio of the In0.23 Ga0.77 As channel MOSFETs are achieved due to the high effective mobility and the low gate leakage current density.

Investigation of electrochemical etch differences in AlGaAs heterostructures using Cl2 ion beam assisted etching

A deeply etched, anisotropic 45° and 90° mirror technology is developed for AlxGa1−xAs heterostructures using a Cl2 ion beam assisted etching system. When etching vertically, using a conductive low-erosion Ni mask, electrochemical etch differences between layers with various Al mole fractions caused nonuniform sidewall profiles not seen in semi-insulating GaAs test samples. These variations, based on alloy composition, were found to be negligible when etching at a 45°. A Si3N4-Ni etch mask is designed in order to electrically isolate charge buildup caused by the incoming Ar+ ion beam to the Ni layer, preventing conduction to the underlying epitaxial layers. This modification produced smoothly etched facets, up to 8 μm in depth, enabling fabrication of substrate–surface-emitting slab-coupled optical waveguide lasers and other optoelectronic devices.

Oscillation characteristics in terahertz transmission through a dipole-based metamaterial

A dual-film metamaterial is proposed that presents oscillation characteristics during terahertz transmission. An n-type gallium arsenide (n-GaAs) film with a free electron density of 4.7 × 1017 cm−3 is grown on a semi-insulating GaAs wafer. Then, a metallic film, which is fabricated on the n-GaAs film, is patterned into an arrayed single-gap microstructure with narrowed edges using traditional ultraviolet photolithography methods. The metal and n-GaAs films form a Schottky junction. The transmission frequency spectrum of the dual-film metamaterial contains an obvious fluctuation with a frequency interval of f = 0.15 THz in the 0.1–1 THz range, and the experimental results show that the frequency region of the locally intensive oscillatory signal essentially agrees with that of the characteristic transmission spectrum of the dual-film metamaterial in the 0.1–1 THz range. The terahertz characteristic transmission spectrum of the fabricated metamaterial is measured at the central frequency of ∼0.515 THz, and the observed oscillation characteristics can be explained using the dipole resonance. The measured time-domain transmission signals and the corresponding frequency responses from a metamaterial that is constructed using split-ring resonators (SRRs) agree well with the simulation results.

Dynamical observation of photo-Dember effect on semi-insulating GaAs using femtosecond core-level photoelectron spectroscopy

We investigated ultrafast photogenerated carrier dynamics on a semi-insulating GaAs surface using femtosecond time-resolved core-level photoelectron spectroscopy. We observed a transient change in the surface potential where the Ga-3d core-level peak instantaneously shifted by ∼350 meV toward a higher binding energy within 2 ps of a 100 fs laser irradiation. A comparison of the experimental results with numerical simulations based on a drift-diffusion model of a semi-insulating semiconductor revealed that the transient surface potential change was mainly due to the photo-Dember effect, whereby the large difference in the carrier diffusion between the electron and hole instantaneously induced a surface photovoltage.

Influence of Substrate Material on Radiation Characteristics of THz Photoconductive Emitters

We present in this paper spectral and spatial characteristics of terahertz emission from standard dipole antenna structures used as emitters depending on the substrate material. All antenna structures were lithographically fabricated on low-temperature (LT) grown, few-micrometers-thick gallium arsenide (GaAs) layers. To investigate the effect of the substrate material on the radiation pattern of terahertz beams, either semi-insulating gallium arsenide or high-resistivity silicon substrate wafers have been used. As detector a standard 40 µm long dipole antenna on a semi-insulating GaAs substrate with a low-temperature grown gallium arsenide layer on it has been employed; this configuration allows for broadband detection and is still efficient enough for the characterization purpose. Strong dependence of the radiation pattern on the substrate used for the terahertz source is demonstrated. The measured patterns and differences between the two cases of substrates are well explained by means of classical diffraction.

Hot Wall Epitaxy(HWE)법에 의한 MnAl2S4단결정 박막 성장과 광전도 특성

수평 전기로에서 <TEX>$MnAl_2S_4$</TEX> 다결정을 합성하여 HWE(Hot Wall Epitaxy)방법으로 <TEX>$MnAl_2S_4$</TEX> 단결정 박막을 반절연성 GaAs(100)기판에 성장시켰다. <TEX>$MnAl_2S_4$</TEX> 단결정 박막의 성장 조건은 증발원의 온도 <TEX>$630^{\circ}C$</TEX>, 기판의 온도 <TEX>$410^{\circ}C$</TEX>였고 성장 속도는 <TEX>$0.5{\mu}m/hr$</TEX>였다. 이때 <TEX>$MnAl_2S_4$</TEX> 단결정 박막의 결정성의 조사에서 이중결정 X-선 요동곡선(DCRC)의 반폭치(FWHM)도 132 arcsec로 가장 작아 최적 성장 조건임을 알 수 있었다. <TEX>$MnAl_2S_4$</TEX>/SI(Semi-Insulated) GaAs(100) 단결정 박막의 광흡수를 293 K에서 10 K까지 측정하였다. 광흡수 스펙트럼으로부터 band gap <TEX>$E_g(T)$</TEX>는 Varshni 공식에 따라 계산한 결과 <TEX>$E_g(T)=3.7920eV-(5.2729{\times}10^{-4}eV/K)T^2/(T+786K)$</TEX>였다. <TEX>$MnAl_2S_4$</TEX> 단결정 박막의 응용소자인 photocell로 사용할 수 있는 pc/dc 값이 가장 큰 광전도셀은 S 증기분위기에서 열처리한 셀로 <TEX>$1.10{\times}10^7$</TEX>이었으며, 광전도 셀의 감도(sensitivity)도 S 증기분위기에서 열처리한 셀이 0.93로 가장 좋았다. 또한 최대 허용소비전력(MAPD)값도 S 증기분위기에서 열처리한 셀이 316 mW로 가장 좋았으며, S 증기분위기에서 열처리한 셀의 응답시간은 오름시간 14.8 ms, 내림시간 12.1 ms로 가장 빠르게 나타나, <TEX>$MnAl_2S_4$</TEX> 단결정 박막을 S 분위기에서 <TEX>$290^{\circ}C$</TEX>로 30분 열처리한 photocell이 상용화가 가능할 것으로 여겨진다. A stoichiometric mixture of evaporating materials for <TEX>$MnAl_2S_4$</TEX> single crystal thin films was prepared from horizontal electric furnace. To obtain the single crystal thin films, <TEX>$MnAl_2S_4$</TEX> mixed crystal was deposited on thoroughly etched semi-insulating GaAs(100) substrate by the Hot Wall Epitaxy (HWE) system. The source and substrate temperatures were <TEX>$630^{\circ}C$</TEX> and <TEX>$410^{\circ}C$</TEX>, respectively. The crystalline structure of the single crystal thin films was investigated by the photoluminescence and double crystal X-ray diffraction (DCXD). The temperature dependence of the energy band gap of the <TEX>$MnAl_2S_4$</TEX> obtained from the absorption spectra was well described by the Varshni's relation, <TEX>$E_g(T)=3.7920eV-5.2729{\times}10^{-4}eV/K)T^2/(T+786 K)$</TEX>. In order to explore the applicability as a photoconductive cell, we measured the sensitivity (<TEX>${\gamma}$</TEX>), the ratio of photocurrent to dark current (pc/dc), maximum allowable power dissipation (MAPD) and response time. The results indicated that the photoconductive characteristic were the best for the samples annealed in S vapour compare with in Mn, Al, air and vacuum vapour. Then we obtained the sensitivity of 0.93, the value of pc/dc of <TEX>$1.10{\times}10^7$</TEX>, the MAPD of 316 mW, and the rise and decay time of 14.8 ms and 12.1 ms, respectively.

Near-infrared metal-semiconductor-metal photodetector based on semi-insulating GaAs and interdigital electrodes

Metal-semiconductor-metal photodetectors on semi-insulating GaAs with interdigital electrodes showed significant enhancement in the spectral response in the near-infrared region as the electrode spacing is reduced. The photocurrent for the device with 5 μm interdigital spacing is five orders of magnitude higher than the dark current, and the room temperature detectivity is on the order of 2.4×1012 cmHz1/2 W−1 at 5 V bias. Furthermore, the spectral response of this device possesses strong dependence on the polarization of incident light showing potential plasmonic effects with only microscale dimensions. These experimental data were analyzed using optical simulation to confirm the response of the devices.

GaAs detectors irradiated by electrons at different dose rates

The radiation hardness of Semi-Insulating (SI) GaAs detectors against high-energy electrons was investigated. The detectors were irradiated by 5 MeV electrons. The influence of two irradiation parameters, the total absorbed dose (up to 24 kGy) and the applied dose rate (20, 40 and 80 kGy/h), on their spectrometric properties was studied. An 241Am gamma-ray source was used to evaluate the spectrometric properties. The applied dose has negatively affected the detector CCE (Charge Collection Efficiency) and has influenced also the energy resolution. Nevertheless, a global increase of detection efficiency with the dose was observed. Three different dose rates used during irradiation did not affect the CCE, but in the range of doses from 4 to 16 kGy an influence of the applied dose rate upon two other parameters was observed. With higher dose rates, a steeper increase in the detection efficiency and significant worsening of energy resolution were achieved.

Influence of electron irradiation on properties of semi-insulating GaAs detectors

The effects of electron beam irradiation on electrical and spectrometric properties of semi-insulating (SI) GaAs detectors were studied. The electric properties were monitored by reverse and forward current–voltage characteristics. In general, a breakdown voltage decrease with the dose was observed. However, some samples showed a local increase in the breakdown voltage at doses between 5 and 10 kGy. The detector spectrometric properties (the charge collection efficiency (CCE), the energy resolution and the detection efficiency) were evaluated from measured spectra of the 241Am radionuclide gamma source before and after electron irradiation. The CCE and energy resolution showed minor changes after irradiation. The detection efficiency noticed an initial increase (up to a dose of 5 kGy) followed by a permanent decrease. At 30 kGy, the overall degradation of detector functionality was observed with all samples.

Large Current GaAs PCSS Triggered by a Laser Diode

We have fabricated a 2-mm gap semi-insulating GaAs photoconductive semiconductor switch (PCSS), and obtained a 1.45-kA large current under a bias voltage of 6 kV when the PCSS was triggered by a 4- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">\(\mu \) </tex-math></inline-formula> J commercial laser diode. An RLC transient circuit model was employed to get the electrical properties of the PCSS in the transient discharge process. The reason for the switch exiting from nonlinear operating mode was that the electric field across the switch dropped below the lock-on field. This letter shows the attractive prospect of a low-cost compact high-power pulse source with the GaAs PCSS.

20 THz broadband generation using semi-insulating GaAs interdigitated photoconductive antennas.

We demonstrate broadband (20 THz), high electric field, terahertz generation using large area interdigitated antennas fabricated on semi-insulating GaAs. The bandwidth is characterized as a function of incident pulse duration (15-35 fs) and pump energy (2-30 nJ). Broadband spectroscopy of PTFE is shown. Numerical Drude-Lorentz simulations of the generated THz pulses are performed as a function of the excitation pulse duration, showing good agreement with the experimental data.

Investigation of GaAs PCSS Triggered by Laser Pulses With Different Parameters

Photoconductive semiconductor switch (PCSS) has many advantages, such as low time jitter, fast response, high repetition rate, compact size, easy integration, and so on. It has extensive applications in the field of pulse power. The laser pulse adopted to trigger the PCSS exerts significant influences to its output characteristics. The parameters to characterize a laser pulse include rise time, pulsewidth, laser energy, wavelength, and so on. In this paper, a new concept of laser power is proposed and the influences that laser pulse exerts to the PCSSs output characteristics are studied. A laser diode that emits laser pulse with a dominant wavelength of 905 ns is employed to trigger a semi-insulating GaAs PCSS, which is vertical structure. Laser energy is fixed to 6.4 μJ by synchronous adjustment of both laser pulsewidth and laser power. Thus, the influences of triggering laser power to the PCSS are studied. The rise times of triggering laser pulses include 10 and 80 ns. The experiment results show that the influences that laser power exerts to the PCSS vary when the rise time of laser pulses differs.

Impact of donor compensation ratio on photorefractive two–wave mixing dynamics in multiple quantum wells structures

The kind of defects and their concentration have a significant impact on photorefractive phenomena taking place within the structure of semi-insulating GaAs / AlGaAs multiple quantum wells. In this paper, the impact of donor-to-acceptor concentration ratio on the grating in photorefractive two-waves mixing was examined. The formation of the space charge field for different defect concentrations as well as different external electric field intensities are analyzed.

Analysis of the influence of nonlinear carrier transport on the photorefractive response in GaAs with applied alternating electric field

Abstract The photorefractive response in semi-insulating GaAs:Cr is theoretically studied when an alternating electric field is applied to a crystal. The calculations are based on material equations including electron and hole currents, nonlinear hot-electron transport and field-enhanced recombination rates. The generalized solutions for the fundamental amplitude of the space-charge field are given. It is shown that for an AC sine-wave field the hot-electron effect reveals in a very small degree. A comparison of the obtained solutions with available experimental data indicates recombination coefficient values of the order of 10−6–10−5 cm3/s which can be attributed to the field-enhanced capture cross section effect.

(Invited) Nature of Point Defects at High-Mobility Semiconductor/Interfaces Probed by Electron Spin Resonance: Thermal GaAs/GaAs-Oxide Structures

Electron spin resonance study of (100)GaAs/native oxide structures thermally grown in the range 350-615 °C on both powders and slices of semi-insulating (100)GaAs compellingly reveals substantial generation (~ 1´1013 cm-2) of interfacial 75AsGa + antisites in registry with the GaAs substrate layer. This provides solid evidence of substantial interfacial As enrichment, appearing as endemic to thermal oxidation of GaAs. Given the known electrical deep double donor attribute of AsGa +, direct identification is thus established of a major system of detrimental interface traps. Additionally observed are centers at g=2.063 and g=1.937, where the former is speculated to originate from an unpaired bond defect located in the thermal GaAs film.

Simulating and modeling the breakdown voltage in a semi-insulating GaAs P+N junction diode

This work aims to determine the characteristic I (breakdown voltage) of the inverse current in a GaAs PN junction diode, subject to a reverse polarization, while specifying the parameters that influence the breakdown voltage of the diode. In this work, we simulated the behavior of the ionization phenomenon by impact breakdown by avalanche of the PN junctions, subject to an inverse polarization.We will take into account both the trapping model in a stationary regime in the P+N structure using like material of basis the III–V compounds and mainly the GaAs semi-insulating in which the deep centers have in important densities. We are talking about the model of trapping in the space charge region (SCR) and that is the trap density donor and acceptor states.The carrier crossing the space charge region (SCR) of W thickness creates N electron—hole pairs: for every created pair, the electron and the hole are swept quickly by the electric field, each in an opposite direction, which comes back, according to an already accepted reasoning, to the crossing of the space charge region (SCR) by an electron or a hole. So the even N pair created by the initial particle provoke N2 ionizations and so forth.The study of the physical and electrical behaviour of semiconductors is based on the influence of the presence of deep centers on the characteristic I(V) current-tension, which requires the calculation of the electrostatic potential, the electric field, the integral of ionization, the density of the states traps, the diffusion current of minority in the regions (1) and (3), the current thermal generation in the region (2), the leakage current in the surface, and the breakdown voltage.

Growth of Semi-Insulating GaAs Crystal with Uniform Si Doping

An improved double crucible method of melt replenishing to counteract the dopant segregation effect in order to grow homogeneous doped GaAs crystals is brought forward, and its validity and feasibility are demonstrated by analytical and numerical study. The numerical results show that the new method can suppress the increase of dopant concentration near the growth interface and can maintain the homogeneity of dopant distribution along the radial direction. The positions of replenishing melt exit almost have no effects on the axial and radial distribution homogeneity of dopant Si in the crystal. So the new method has many distinct advantages: it can improve the crystallization rate and size, the operation is flexible, etc.

Optically Controllable Composite Dielectric Based on Photo-Conductive Particulates

We report a method to optically control the effective permittivity of a composite dielectric in which the active inclusions are fabricated from pulverized semi-insulating GaAs. The electric dipoles from the inclusions are controlled by photo-generation of charge carriers using infrared light. An infrared transparent binder provides the matrix material. Our primary purpose is to develop a low-cost pigment-based ink, or paint, for optically tuning electromagnetic devices including metamaterials, frequency-selective surfaces, filters, phase delays, and antennas. In bulk form, applications of the optically controllable dielectric are imagined including a gradient index lens in which inhomogeneous light intensity can provide a dynamic response for focusing or steering of beams. An important feature is that the effective permittivity is linear with electric field intensity over a usable parameter space. We present experimental results as well as a simple model to describe the behavior qualitatively.