Monolithic Integration of InGaP/AlGaAs/InGaAs Enhancement/Depletion-Mode PHEMTs

The monolithic integration of enhancement- and depletion-mode （E/D-mode） InGaP/AIGaAs/InGaAs pseudomorphic high electron mobility transistors （PHEMTs） with a 1.0μm gate length is presented. Epilayers are grown on SI GaAs substrates using MBE. For this structure, a mobility of 5410cm^2/（V · s） and a sheet density of 1.34 × 10^12 cm^-2 are achieved at room temperature. During the gate fabrication of E/D-mode PHEMTs,a novel twostep technology is applied. The devices with a gate dimension of 1μm × 100μm exhibit good DC and RF performances. Threshold voltages of 0. 2 and -0. 4V,maximum drain current densities of 300 and 340mA/mm,and extrinsic transconductances of 350 and 300mS/mm for E- and D-mode PHEMTs are obtained, respectively. The reverse gatedrain breakdown voltage is -14V for both E- and D-mode. Current-gain cutoff frequencies of 10. 3 and 12.4GHz and power-gain cutoff frequencies of 12.8 and 14.7GHz for E- and D-mode are reported, respectively.

Device Characteristics Comparison Between GaAs Single and Double Delta-Doped Pseudomorphic High Electron Mobility Transistors

The Al 0.24Ga 0.76As/In 0.22Ga 0.78As single delta-doped PHEMT (SH-PHEMT) and double delta-doped PHEMT (DH-PHEMT) are fabricated and investigated.Based on the employment of double heterojunction,double delta doped design,the DH-PHEMT can enhance the carrier confinement,increase the electron gas density,and improve the electron gas distribution,which is beneficial to the device performance.A high device linearity,high transconductance over a large gate voltage swing,high current drivability are found in DH-PHEMT.These improvements suggest that DH-PHEMT is more suitable for high linearity applications in microwave power device.

Ice-wedge Pseudomorphs Showing Climatic Change Since the Late Pleistocene in the Source Area of the Yellow River, Northeast Tibet

The source area of the Yellow River is located in the northeastern Tibetan Plateau, and is a high-elevation region with the annual mean temperature of -3.9℃. The ice-wedge pseudomorphs discovered in this region are recognized as two types. One was found in sandy gravel beds of the second terrace of the Yellow River. This ice-wedge pseudomorph is characterized by higher ratio of breadth/depth, and are 1-1.4 m wide and about 1 m deep. The bottom border of the ice-wedge pseudomorph is round arc in section. Another discovered in the pedestal of the second terrace has lower ratio of width/depth, and is o.3-1.0 m wide and 1-2 m deep. Its bottom border is sharp. Based on the TL dating, the former was formed at the middleHolocene （5.69±0.43 ka BP and 5.43±0.41 ka BP）, that is, the Megathermal, and the latter was formed at the late Last Glacial Maximum （13.49±1.43 ka BP）. Additionally, the thawing-freezing folders discovered in the late Late Pleistocene proluvium are 39.83±3.84 ka BP in age. The study on the ice-wedge pseudomorphs showed that the air temperature was lowered by up to 6-7℃ in the source area of the Yellow River when the ice-wedge pseudomorphs and thawing-freezing folds developed.

Kinetics of celestite conversion to acidic strontium oxalate hydrate in aqueous solution of oxalic acid

Conversion of SrSO4 to acidic strontium oxalate hydrate(H[Sr(C2O4)1.5(H2O)]) in aqueous H2C2O4 solutions proceeds as a consecutive reaction. In the first step of the consecutive reaction, SrSO4 reacts with H2C2O4 and pseudomorphic conversion to SrC2 O4·H2O occurs. In the second step, SrC2 O4·H2O reacts with H2C2O4 to form H[Sr(C2 O4)1.5(H2O)]. Sr(HC2 O4)(C2 O4)0.5·H2 O crystallizes during cooling of the reaction mixture to room temperature if the solution reaches the saturation concentration of (H[Sr(C2O4)1.5(H2O)]. The aims of this study are the derivation of reaction rate equations and the determination of the kinetic parameters such as pre-exponential factor, apparent activation energy and order of H2C2O4 concentration for each reaction step.Fractional conversions of SrSO4 were calculated using the quantitative amounts of dissolved S and Sr. It was determined that the reaction rate increased at the initial time of reaction by increasing the temperature using solutions with approximately same H2C2O4 concentrations. The reaction extends very slowly after a certain time in solutions with low H2C2O4 concentration and ends by the formation of a protective layer of SrC2O4-H2O around the surfaces of solid particles. Fractional conversion of SrSO4 is increased by increasing concentration of H2C2O4 at constant temperature. Kinetic model equations were derived using shrinking core model for each step.

C band microwave damage characteristics of pseudomorphic high electron mobility transistor

The damage effect characteristics of GaAs pseudomorphic high electron mobility transistor(pHEMT)under the irradiation of C band high-power microwave(HPM)is investigated in this paper.Based on the theoretical analysis,the thermoelectric coupling model is established,and the key damage parameters of the device under typical pulse conditions are predicted,including the damage location,damage power,etc.By the injection effect test and device microanatomy analysis through using scanning electron microscope(SEM)and energy dispersive spectrometer(EDS),it is concluded that the gate metal in the first stage of the device is the vulnerable to HPM damage,especially the side below the gate near the source.The damage power in the injection test is about 40 dBm and in good agreement with the simulation result.This work has a certain reference value for microwave damage assessment of pHEMT.

Design of 35 GHz 1 Watt GaAs pHEMT Power Amplifier MMIC

By using 0.15 μm GaAs pHEMT （pseudomorphic high electron mobility transistor） technology,a design of millimeter wave power amplifier microwave monolithic integrated circuit （MMIC） is presented.With careful optimization on circuit structure,this two-stage power amplifier achieves a simulated gain of 15.5 dB with fluctuation of 1 dB from 33 GHz to 37 GHz.A simulated output power of more than 30 dBm in saturation can be drawn from 3 W DC supply with maximum power added efficiency （PAE） of 26%.Rigorous electromagnetic simulation is performed to make sure the simulation results are credible.The whole chip area is 3.99 mm2 including all bond pads.

Preparation of Magnesium Oxide Whisker by MgSO4·5Mg（OH）2·2H2O Whisker ＂Pseudomorph＂ Technique

To promote the scale-up production and industrial application of magnesium oxide （MgO） whiskers, MgO whiskers were prepared by the calcination method of the precursor. The precursor MgSO4·5Mg（OH）2·2H2O （152 MOS） single component was prepared by hydrothermal synthesis reaction in MgSO4 solution and NaOH solution. MgO whisker was prepared by heating treatment of the precursor at low heating speed to keep the structure of the precursor not be destroyed. The composition, the morphology and the structure of these whiskers were characterized by X-ray diffraction （XRD） and scanning electron microscopy （SEM）. The results indicate that the MgO whisker was about 0.5-1.2 μm in diameter and 20-80 μm in length, with an aspect ratio no less than 100.

<i>In Situ</i>Atomic Force Microscopy Observation of Octacalcium Phosphate (100) Face Dissolution in Weak Acidic Solutions

Dissolution of the (100) face of octacalcium phosphate (OCP) single crystal in weak acidic solutions (pH = 6.5;25&deg;C) was observed in situ using atomic force microscopy. Monomolecular steps (2.0 nm high) were observed;they originated from etch pits or crystal edges. Advancement of the dissolution process led to precipitation of nanoparticles as small as ~10 nm even though the solution was undersaturated with respect to OCP. This precipitation of nanoparticles was accompanied by a drastic decrease in the dissolution rate;however, the substrate OCP continued to dissolve, indicating that dissolution and growth occurred simultaneously on the same surface. The precipitated nanoparticles coalesced and eventually covered the entire surface without changing the surface morphology of the substrate crystal. The step height after complete coverage was ~2.0 nm, the same as that observed on the dissolving OCP surface. These findings indicate that the precipitated phase was a pseudomorph of OCP crystal.

Evidence from pseudomorphous β-quartz phenocryst for decompression of rock-forming and ore-forming processes in Shapinggou porphyry Mo deposit

The Shapinggou porphyry molybdenum(Mo) deposit, located in Jinzhai County, Anhui Province, China, is the largest in the Qinling-Dabie Mo Metallogenic Belt. The intrusive rocks in the Shapinggou Mo ore district formed in the Yanshanian can be divided into two stages based on zircon U-Pb dating and geochemical features. This study focuses on the late stage intrusions(quartz syenite and granite porphyry), which are closely genetically related to molybdenum mineralization. Petrographic observations identified two quartz polymorphs in the quartz syenite and granite porphyry, which were derived from the same magmatic sources and similar evolutionary processes. The quartzes were identified as a xenomorphic β-quartz within quartz syenite, while the quartz phenocrysts within the granite porphyry were pseudomorphous b-quartz, characterized by a hexagonal bipyramid crystallography. The pseudomorphous b-quartz phenocrysts within the granite porphyry were altered from b-quartz through phase transformation. These crystals retained b-quartz pseudomorph. Combined with titanium-inzircon thermometry, quartz phase diagrams, and granitic Q-Ab-Or-H_2O phase diagrams, it is suggested that the quartz syenite and granite porphyry were formed under similar magmatic origins, including similar depths and magmatic crystallization temperatures. However, the β-quartz within quartz syenite indicated that the crystallization pressure was greater than 0.7 GPa, while the original b-quartz within the granite porphyry was formed under pressures between 0.4 and 0.7 GPa. The groundmass of the granite porphyry which formed after the phenocryst indicated a crystallizing pressure below 0.05 GPa. This indicates that the granite porphyry was formed under repetitive and rapid decompression. The decompression was significant as it caused the exsolution of the ore-forming fluids, and boiling and material precipitation during the magmatic-fluid process. The volumetric difference during the phase transformation from b-quartz to β-quartz caused extensive fracturing on the granite porphyry body and the wall rocks. As the main ore-transmitting and ore-depositing structures, these fractures benefit the hydrothermal alteration and stockwork-disseminated mineralization of the porphyry deposit. It is considered that the pseudomorphous β-quartz phenocrysts of the porphyritic body are metallogenic indicators within the porphyry deposits. The pseudomorphous β-quartzes therefore provide evidence for the formation of the porphyry deposit within a decompression tectonic setting.

ON THE OCCURRENCE OF SPINIFEX TEXTURE IN PRO-TEROZOIC KOMATIITES AT YIYANG. HUNAN

At Shizuitang-Taohulun, south suburb of Yiyang City, Hunan Province, a set of metamorphic basic volcanic rocks, with more than 2000-m thickness and 20 km^2 in surficial area, occurs in lower part of Lengjiaxi Group of the Proterozoic era. In this set of volcanic rocks the lava flows came first and tuff, tuffite, volcanic