Effects of atmospheric species and vacancy defect on electron transfer between diamond (0 0 1) surface and adlayer

The electron transfer between diamond (0 0 1) surface without and with various vacancy defects and adlayer with various adsorbed atmospheric species is examined based on first-principles calculations, which plays an important role for the conductivity of diamond (0 0 1) surface. The results show that the electron transfer from the perfect diamond surface (without defect in diamond surface or subsurface layer) to the adlayer varies with the adlayer adsorbed on the surface. The largest electron transfer is about 1.08e from the perfect surface to the adlayer (10) (O2, H3O+) among the possible adlayers, such as (1) (H2O, H2O), (2) (H2O, H3O+), (3) (H2O, CO2) … (20) (N2, O2), (21) (N2, N2) layers. It is found that the vacancy defect in surface or subsurface layer also affects the diamond (0 0 1) surface conductivity by increasing or reducing the electron transfer from the surface to the adlayer. It is also noted that the electron transfer increases largely in the case that the (10) (O2, H3O+) system is adsorbed on the diamond (0 0 1) surface with vacancy defect in the surface or subsurface layer, in which the electron transfer is largest with 1.27e when the monovacancy defect forms in the subsurface layer. Our study is useful to understand the conductivity of diamond surface

The transport mechanism of gate leakage current in AlGaN/GaN high electron mobility transistors

The temperature dependence of the I-V characteristics on Au/Ni-HEMT Schottky contacts was measured and analyzed. Large deviations from the thermionic emission and thermionic-field emission model were observed in the I-V-T characteristics. The thin surface barrier model only fits the measured curves in the high bias region, but deviates drastically in the low bias region. Using a revised thin surface barrier model, the calculated curves match well with the measured curves. It is also found that tunneling emission model is the dominant current transport mechanism at low temperature, yet thermionic-field emission model is the dominant current transport mechanism at high temperature

Development of ECE/ECEI diagnostics and MHD-related studies on HL-2A tokamak

A novel 60-channel electron cyclotron emission (ECE) radiometer has been designed and tested for the measurement of electron temperature profiles on the HL-2A tokamak. This system is based on the intermediate frequency division technique, and has the features of wide working frequency range (60−90 GHz) and high temporal-spatial resolution (3 µs, 1 cm), which covers almost the entire plasma region. Also, an electron cyclotron emission imaging (ECEI) system has been developed for studying two dimensional electron temperature fluctuations. It is comprised of several front-end quasi-optical lenses, a 24 channel heterodyne imaging array with a tunable RF frequency range spanning 60−135 GHz, and a set of back-end ECEI electronics that together generate two 24×8 array images of the 2nd harmonic X-mode electron cyclotron emission from the HL-2A plasma. The measurement region can be flexibly shifted due to two independent local oscillator sources, and the field of view can be adjusted easily by changing the position of the zoom lenses as well. The temporal resolution is about 2.5 µs and the achievable spatial resolution is 1 cm. The ECE/ECEI diagnostics have been demonstrated to be powerful tools to study MHD-related physics including the multi-scale interaction between macro-scale MHD and micro-scale turbulence on the HL-2A tokamak