1-mm gate periphery AlGaN/AIN/GaN HEMTs on SiC with output power of 9.39 W at 8 GHz

AlGaN/AlN/GaN high electron mobility transistor (HEMT) structures with high mobility GaN channel layer were grown on 50 min diameter semi-insulating (SI) 6H-SiC substrates by metalorganic chemical vapor deposition and large periphery HEMT devices were fabricated and characterized. High two-dimensional electron gas mobility of 2215 cm(2)/V s at room temperature with sheet electron concentration of 1.044 x 10(13)/cm(2) was achieved. The 50 mm diameter HEMT wafer exhibited a low average sheet resistance of 251.0 Omega/square, with the resistance uniformity of 2.02%. Atomic force microscopy measurements revealed a smooth AlGaN surface with a root-mean-square roughness of 0.27 nm for a scan area of 5 mu mi x 5 pm. The 1-mm gate width devices fabricated using the materials demonstrated a very high continuous wave output power of 9.39 W at 8 GHz, with a power added efficiency of 46.2% and power gain of 7.54 dB. A maximum drain current density of 1300 mA/mm, an extrinsic transconductance of 382 mS/mm, a current gain cutoff frequency of 31 GHz and a maximum frequency of oscillation 60 GHz were also achieved in the same devices. (C) 2007 Elsevier Ltd. All rights reserved.

AlGaN/AlN/GaN/SiC HEMT structure with high mobility GaN thin layer as channel grown by MOCVD

Enhancement of the electrical properties in an AlGaN/GaN high electron mobility transistor (HEMT) structures was demonstrated by employing the combination of a high mobility GaN channel layer and an AlN interlayer. The structures were grown on 50 mm semi-insulating (SI) 6H-SiC substrates by metalorganic chemical vapor deposition (MOCVD). The room temperature (RT) two-dimensional electron gas (2DEG) mobility was as high as 2215 cm(2)/V s, with a 2DEG concentration of 1.044 x 10(13)cm(-2). The 50 mm HEMT wafer exhibited a low average sheet resistance of 251.0 Omega/square, with a resistance uniformity of 2.02%. The 0.35 Pin gate length HEMT devices based on this material structure, exhibited a maximum drain current density of 1300 mA/mm, a maximum extrinsic transconductance of 314 mS/mm, a current gain cut-off frequency of 28 GHz and a maximum oscillation frequency of 60 GHz. The maximum output power density of 4.10 W/mm was achieved at 8 GHz, with a power gain of 6.13 dB and a power added efficiency (PAE) of 33.6%. (c) 2006 Elsevier B.V. All rights reserved.

Influences of As flux on the lattice constants, magnetic and transport properties of (Ga, Mn)As epilayers

A series of (Ga, Mn)As epilayers have been prepared on semi-insulating GaAs (001) substrates at 230 degrees C by molecular-beam epitaxy under fixed temperatures of Ga and Mn cells and varied temperatures of the As cell. By systematically studying the lattice constants, magnetic and magneto-transport properties in a self-consistent manner, we find that the concentration of As antisites monotonically increases with increasing As flux, while the concentration of interstitial Mn defects decreases with it. Such a trend sensitively affects the properties of (Ga, Mn)As epilayers. (c) 2006 Elsevier Ltd. All rights reserved.

Fabrication and properties of Sb-doped ZnO thin films grown by radio frequency (RF) magnetron sputtering

Sb-doped and undoped ZnO thin films were deposited on Si (100) substrates by radio frequency (RF) magnetron sputtering. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses revealed that all the films had polycrystalline wurtzite structure and c-axis preferred orientation. Room temperature Hall measurements showed that the as-grown films were n-type and conducting (rho similar to 1-10 Omega cm). Annealing in a nitrogen ambient at 400 degrees C for 1 h made both samples highly resistive (rho > 10(3) Omega cm). Increasing the annealing temperature up to 800 C, the resistivity of the ttndoped ZnO film decreased gradually, but it increased for the Sb-doped ZnO film. In the end, the Sb-doped ZnO film annealed at 800 C became semi-insulating with a resistivity of 10(4)Omega cm. In addition, the effects of annealing treatment and Sb-doping on the structural and electrical properties are discussed. (c) 2006 Elsevier B.V. All rights reserved.

Comparison of field effect transistor characteristics between space-grown and earth-grown gallium arsenide single crystal substrates

Semi-insulating gallium arsenide single crystal grown in space has been used in fabricating low noise field effect transistors and analog switch integrated circuits by the direct ion-implantation technique. All key electrical properties of these transistors and integrated circuits have surpassed those made from conventional earth-grown gallium arsenide. This result shows that device-grade space-grown semiconducting single crystal has surpassed the best terrestrial counterparts. (C) 2001 American Institute of Physics.

Point defects in III-V compound semiconductors

Point defects in III-V compound semiconductors were analyzed systematically in this paper. The effects of substitutes, antisites, interstitials, and vacancies on lattice parameters in III-V compound semiconductors were calculated with a simple model. The formation energies of vacancies in compound semiconductors can be obtained by this calculation. A practical technique established on this model has been utilized for measuring the stoichiometry in GaAs. The relationship between stoichiometry and deep level centers in GaAs was also investigated.

Photonic switch and NOT logic gate based on the hybrid integration of a GaAsVCSEL and a GaAs MISS

The hybrid integrated photonic switch and not logic gate based on the integration of a GaAs VCSEL (Vertical Cavity Surface Emitting Lasers) and a MISS (Metal-Insulator-Semiconductor Switches) device are reported. The GaAs VCSEL is fabricated by selective etching and selective oxidation. The Ultra-Thin semi-Insulating layer (UTI) of the GaAs MISS is formed by using oxidation of A1As that is grown by MBE. The accurate control of UTI and the processing compatibility between VCSEL and MISS are solved by this procedure. Ifa VCSEL is connected in series with a MISS, the integrated device can be used as a photonic switch, or a light amplifier. A low switching power (10 mu W) and a good on-off ratio (17 dB contrast) have been achieved. If they are connected in parallel, they perform a photonic NOT gate operation.

Effect of arsenic precipitates on Fermi level in GaAs grown by molecular-beam epitaxy at low temperature

A simple model is presented to discuss the effect of As precipitates on the Fermi level in GaAs grown by molecular-beam epitaxy at low temperature (LT-GaAs). This model implements the compensation between point defects and the depletion of arsenic precipitates. The condition that the Fermi level is pinned by As precipitates is attained. The shifts of the Fermi level in LT-GaAs with annealing temperature are explained by our model. Additionally, the role of As precipitates in conventional semi-insulating GaAs is discussed. (C) 2000 American Institute of Physics. [S0021-8979(00)09905-9].

Structural properties of SI-GaAs grown in space

The structural properties of Semi-insulating gallium arsenide (SI-GaAs) crystal grown with power-travelling technique in space have been studied by double-crystal x-ray diffractometry and chemical etching. The quality of the crystal was first evaluated by x-ray rocking-curve method. The full width at half maximum of x-ray rocking curve in space-grown SI-GaAs is 9.4+/-0.08 are seconds. The average density of dislocations revealed by molten KOH is 2.0 X 10(4) cm(-2), and the highest density is 3.1 X 10(4) cm(-2). The stoichiometry in the single crystal grown in space is improved as well. Unfortunately, the rear of the ingot grown in space is polycrystalline owing to being out of control of power. (C) 1999 COSPAR. Published by Elsevier Science Ltd.

Photoluminescence properties of nitrogen-doped ZnSe epilayers

The photoluminescence (PL) properties of nitrogen-doped ZnSe epilayers grown on semi-insulating GaAs(100) substrates by MBE using a rf-plasma source for N doping were investigated. The PL peak which can be related to N acceptor was observed in the PL spectra of ZnSe:N smaples. At 10K, as the excitation power density increases, the energy of donor-acceptor pair(DAP) emission shows a blue-shift and its intensity tends to saturate. As the temperature increases over a range from 10K to 300K, the relative PL intensity of donor bound exciton to that of the acceptor bound exciton increases due to the transfer between two bound excitons.

Growth and transport properties of InAs thin films on GaAs

High-quality InAs epitaxial layers have been grown on (1 0 0) oriented semi-insulating GaAs substrates by MBE. The transport properties of largely lattice mismatched InAs/GaAs heterojunctions have been investigated by Hall effect measurements down to 10 K. In spite of a high dislocation density at the heterointerface, very high electron mobilities are obtained in the InAs thin films. By doping Si into the layer far from the InAs/GaAs interface, we found that the doped samples have higher electron mobility than that of the undoped samples with the same thickness. The mobility demonstrates a pronounced minimum around 300 K for the undoped sample. But for Si-doped samples, no pronounced minimum has been found. Such abnormal behaviours are explained by the parallel conduction from the quasi-bulk carriers and interface carriers. These high-mobility InAs thin films are found to be suitable materials for making Hall elements. (C) 1998 Elsevier Science B.V. All rights reserved.

Terahertz pulse generation with LT-GaAs photoconductive antenna

Low-temperature-grown GaAs (LT-GaAs) of 1-um thickness was grown at 250 degrees C on semi-insulating GaAs (001) substrate using EPI GEN-II solid-source MBE system. The sample was then in situ annealed for 10 min at 600 degrees C under As-rich condition. THz emitters were fabricated on this LTGaAs with three different photoconductive dipole antenna gaps of 1-mm, 3-mm, and 5-mm, respectively. The spectral bandwidth of 2.75 THz was obtaind with time domain spectroscopy. It is found that THz emission efficiency is increased with decreasing antenna gap. Two carrier lifetimes, 0.469 ps and 3.759 ps, were obtained with time-resolved transient reflection-type pump-probe spectroscopy.

THEORETICAL INVESTIGATION OF THE DYNAMIC PROCESS OF THE ILLUMINATION OF GAAS

The dynamic process of light illumination of GaAs is studied numerically in this paper to understand the photoquenching characteristics of the material. This peculiar behavior of GaAs is usally ascribed to the existence of EL2 states and their photodriven metastable states. To understand the conductivity quenching, we have introduced nonlinear terms describing the recombination of the nonequilibrium free electrons and holes into the calculation. Though some photoquenching such as photocapacitance, infrared absorption, and electron-paramagnetic-resonance quenching can be explained qualitatively by only considering the internal transfer between the EL2 state and its metastability, it is essential to take the recombination into consideration for a clear understanding of the photoquenching process. The numerical results and approximate analytical approach are presented in this paper for the first time to our knowledge. The calculation gives quite a reasonable explanation for n-type semiconducting GaAs to have infrared absorption quenching while lacking photoconductance quenching. Also, the calculation results have allowed us to interpret the enhanced photoconductance phenomenon following the conductance quenching in typical semi-insulating GaAs and have shown the expected thermal recovery temperature of about 120 K. The numerical results are in agreement with the reported experiments and have diminished some ambiguities in previous works.

RADIATIVE RECOMBINATION IN N-TYPE AND P-TYPE GAAS COMPENSATED WITH LI

We report fundamental changes of the radiative recombination in a wide range of n-type and p-type GaAs after diffusion with the group-I element Li. These optical properties are found to be a bulk property and closely related to the electrical conductivity of the samples. In the Li-doped samples the radiative recombination is characterized by emissions with excitation-dependent peak positions which shift to lower energies with increasing degree of compensation and concentration of Li. These properties are shown to be in qualitative agreement with fluctuations of the electrostatic potential in strongly compensated systems. For Li-diffusion temperatures above 700-800-degrees-C semi-insulating conditions with electrical resistivity exceeding 10(7) OMEGA cm are obtained for all conducting starting materials. In this heavy Li-doping regime, the simple model of fluctuating potentials is shown to be inadequate for explaining the. experimental observations unless the number of charged impurities is reduced through complexing with Li. For samples doped with low concentrations of Li, on the other hand, the photoluminescence properties are found to be characteristic of impurity-related emissions.

SHIFTING PHOTOLUMINESCENCE BANDS IN HIGH-RESISTIVITY LI-COMPENSATED GAAS

It is shown that Li diffusion of GaAs can give rise to semi-insulating samples with electrical resistivity as high as 10(7) OMEGAcm in undoped, n-type, and p-type starting materials. The optical properties of the compensated samples are correlated with the depletion of free carriers caused by the Li diffusion. The radiative recombination of the Li-compensated samples is dominated by emissions with excitation-dependent peak positions that shift to lower energies with increasing compensation. The photoluminescence properties are characteristic of fluctuations of the electrostatic potential in strongly doped, compensated crystals.