Optical-Electrical Characteristics and Carrier Dynamics of Semi-Insulation GaAs by Terahertz Spectroscopic Technique

OaAs has been widely used to fabricate a variety of optoelectronic devices by virtue of its superior performance, and it is very important to accurately measure its electrical and optical properties. In this study, a semi- insulation （SI） GaAs wafer is investigated by the terahertz （THz） non-destructive testing technology. Using an air biased coherent generation and detection THz time domain spectroscopy system, the THz time domain waveform and spectrum of SI-GaAs are obtained by the time domain spectroscopy module, and its optical- electrical characteristics including complex refractive index, permittivity and dielectric loss angle are calculated. Its carrier lifetime is measured by the optical-pump THz-probe module, and the THz pulse induced intervalley scattering in photo-excited SI-GaAs is discussed.

Advanced BCD technology with vertical DMOS based on a semi-insulation structure

A new semi-insulation structure in which one isolated island is connected to the substrate was pro- posed. Based on this semi-insulation structure, an advanced BCD technology which can integrate a vertical de- vice without extra internal interconnection structure was presented. The manufacturing of the new semi-insulation structure employed multi-epitaxy and selectively multi-doping. Isolated islands are insulated with the substrate by reverse-biased PN junctions. Adjacent isolated islands are insulated by isolation wall or deep dielectric trenches. The proposed semi-insulation structure and devices fixed in it were simulated through two-dimensional numerical computer simulators. Based on the new BCD technology, a smart power integrated circuit was designed and fabri- cated. The simulated and tested results of Vertical DMOS, MOSFETs, BJTs, resistors and diodes indicated that the proposed semi-insulation structure is reasonable and the advanced BCD technology is validated.

Fabrication and characterization of one-port surface acoustic wave resonators on semi-insulating GaN substrates

One-port surface acoustic wave resonators(SAWRs) are fabricated on semi-insulating high-quality bulk GaN and GaN film substrates, respectively. The semi-insulating GaN substrates are grown by hydride vapor phase epitaxy(HVPE)and doped with Fe. The anisotropy of Rayleigh propagation and the electromechanical coupling coefficient in Fe-doped GaN are investigated. The difference in resonance frequency between the SAWs between [1120] GaN and [1100] GaN is about 0.25% for the Rayleigh propagation mode, which is smaller than that of non-intentionally doped GaN film(~1%)reported in the literature. The electromechanical coupling coefficient of Fe-doped GaN is about 3.03%, which is higher than that of non-intentionally doped GaN film. The one-port SAWR fabricated on an 8-μm Fe-doped GaN/sapphire substrate has a quality factor of 2050, and that fabricated on Fe-doped bulk GaN has a quality factor as high as 3650. All of our results indicate that high-quality bulk GaN is a very promising material for application in SAW devices.

Vanadium-Doped Semi-Insulating 6H-SiC for Microwave Power Device Applications

Two-inch semi-insulating SiC bulk crystals with resistivity higher than 1 × 10^6 Qcm were achieved by vanadium doping during sublimation. Secondary-ion-mass-spectrometry （SIMS） was employed to determine the concentration of impurities in the crystals, such as B, AI, V and N. These results indicated that the concentration of nitrogen and aluminum kept on decreasing and the concentration of B and V was almost constant during the whole growth. An inner crucible was used to control the exhausting of vanadium, which made the uniformity of the high resistivity （〉1×10^6 Ωcm） in the wafer up to 80%. High-performance AlGaN/GaN high-electronmobility-transistor （HEMT） materials and devices were grown and fabricated on semi-insulating 6H-SiC sub- strates. The two-dimensional electron gas （2DEG） mobility at room-temperature was 1795 cm^2/V-s. The charge carrier concentration of the substrate determined by capacitance-voltage （C-V） test was 7.3×10^15 cm^-3. The device with a gate width of I mm exhibits a maximum output power of 5.5 W at 8 GHz, which proves the semi-insulating property of the substrates indirectly.

Effect of As Interstitial Diffusionon on the Properties of Undoped Semi-insulating LECGaAs

Annealing was carried out at 950 and 1120 degreesC under various As pressure for undoped (ND) semi-insulating (SI) LECGaAs. The effects of annealing on native defects and electrical properties were investigated. Experimental results indicate that, after an annealing at 950 degreesC for 14 h under low As pressure, the Hall mobility decreases and the resistivity increases dramatically for the samples. These changes in electrical properties are due to the generation of intrinsic acceptor defects, and the generation of the intrinsic acceptor defects originates from the outdiffusion of As interstitial at high temperature. The generation of the intrinsic defects and these changes in electrical properties can be suppressed by increasing the applied As pressure during annealing. The concentration of the main donor defect E12 (AsGaVGa) can be decreased by about one order of magnitude by an evacuated annealing at 1120 degreesC for 2-8 h followed by a fast cooling. The decrease in E12 concentration can also be suppressed by increasing the As pressure during annealing.

High-Performance In0.23Ga0.77As 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 （ MOS- FETs） with high on-current to off-current （Ion/Ioff） ratio grown on semi-insulating GaAs wafers by metal-organic chemical vapor deposition （MOCVD）. The 2μm channel-length devices exhibit a peak extrinsic transeonductance 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 × 10^3 up to approximately 4.32 × 10^4 by controlling the etch thickness of In0.49Ga0.51P, The high drain current and high Ion/Ioff ratio of the In0.23Ga0.77As channel MOSFETs are achieved due to the high effective mobility and the low gate leakage current density.

4H-SiC Schottky barrier diodes with semi-insulating polycrystalline silicon field plate termination

Based on the theoretical analysis of the 4H-SiC Schottky-barrier diodes （SBDs） with field plate termination, 4H-SiC SBD with semi-insulating polycrystalline silicon （SIPOS） FP termination has been fabricated. The relative dielectric con-stant of the SIPOS dielectric first used in 4H-SiC devices is 10.4, which is much higher than that of the SiO2 dielectric, leading to benefitting the performance of devices. The breakdown voltage of the fabricated SBD could reach 1200 V at leak-age current 20 μA, about 70% of the theoretical breakdown voltage. Meanwhile, both of the simulation and experimental results show that the length of the SIPOS FP termination is an important factor for structure design.

Microprecipitates in Semi-Insulating GaAs Single Crystals

The microprecipitates in the as-grown undoped and In-doped semi-insulating GaAs single crystals have been ex- amined by JEM 200 CX transmission electron microscope.The microprecipitates consist of GaAs polycrystalline grains of 5～100nm in size have been evidenced in dislocated crystals.Energy dispersive X-ray analysis shows that the mieropreeipitates are predominately arsenic-rich GaAs.The As/Ga atomic ratio of the microprecipitates in In-doped crystal is higher than that of undoped crystal.It is suggested that the formation of the microprecipitates may be induced by the local fluctuation of compositional undercooling during crystal growth.

Electrical and optical characteristics of vanadium in 4H-SiC

A semi-insulating layer is obtained in n-type 4H-SiC by vanadium-ion implantation. A little higher resistivity is obtained by increasing the annealing temperature from 1450 to 1650 ℃. The resistivity at room temperature is as high as 7.6 ×10^6 Ω. cm. Significant redistribution of vanadium is not observed even after 1650 ℃ annealing. Temperaturedependent resistivity and optical absorption of V-implanted samples are measured. The activation energy of vanadium acceptor level is observed to be at about Ec - 1.1 eV.

Dynamic Behavior and Its Consideration of EHD Liquid Extraction Phenomenon Causing under DC or Low-Frequency AC Voltage

This paper describes an experimental and theoretical study on an extraction phenomenon of liquids occurring at an air gap between the liquid surface and the electrode by applying a direct current (DC) or low-frequency alternating current (AC) voltage. Three liquids with a different physical property;2,3-dihydrodecafluoropenten, palm fatty acid ester oil and crude rapeseed oil are used as working liquids. The electrode configuration is the sphere or plane (high voltage electrode) to grounded plane electrode. The grounded plane electrode is fixed to the bottom of the test vessel with working liquid and the high voltage electrode is installed in an air above the liquid surface against the grounded plane electrode. The liquid surface swells towards the high voltage electrode by the increase of voltage and the liquid is extracted in a short time, thereafter the air gap between the liquid surface and the high voltage electrode is bridged at a thick liquid column. Such the liquid behavior displays unique features with voltage polarity effect for each working liquid. The relationship between the applied voltage, current variation, height of swollen liquid, force pulling liquid and dynamic feature of liquid is examined experimentally. The liquid behavior is considered theoretically based on experimental observations.

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

Metal-semiconductor-metal photodetectors on semi-insulating Ga As 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 × 1012cm Hz1∕2W-1at 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.

ESR characters of intrinsic defects in epitaxial semi-insulating 4H-SiC illuminated by Xe light

The intrinsic defects in epitaxial semi-insulating 4H-SiC prepared by low pressure chemical vapor deposition （LPCVD） are studied by electron spin resonance （ESR） with different illumination times. The results show that the intrinsic defects in as-grown 4H-SiC consist of carbon vacancy （Vc） and complex-compounds-related Vc. There are two other apexes presented in the ESR spectra after illumination by Xe light, which are likely to be Vsi and VcCsi. Illumination time changes the relative density of intrinsic defects in 4H-SiC; the relative density of intrinsic defects reaches a maximum when the illumination time is 2.5 min, and the ratio of Vc to complex compounds is minimized simultaneously. It can be deduced that some Vsi may be transformed to the complex-compounds-related Vc because of the illumination.

Influence of Zn Diffusion on Bandwidth and Extinction in MQW Electroabsorption Modulators Buried with Semi-Insulating InP

A comprehensive analysis of multi-quantum-well electroabsorption modulators buried with semi-insulating (SI)-InP is presented. We quantitatively demonstrate that suppression of Zn diffusion into the burying and optical core layers plays a key role in high-speed and high-extinction operation.