Jisheng Han

Bio: Jisheng Han is an academic researcher from Griffith University. The author has contributed to research in topics: Capacitor & Gate oxide. The author has an hindex of 20, co-authored 98 publications receiving 1426 citations. Previous affiliations of Jisheng Han include University of South Australia & Vanderbilt University.

Mechanism of Threshold Voltage Shift in ${p}$ -GaN Gate AlGaN/GaN Transistors

Abstract: In this letter, we investigate the threshold voltage ( ${V}_{\text {TH}}$ ) shift in a p-GaN gate AlGaN/GaN transistor by designed gate-bias pulse measurements. It was found that the forward gate bias causes positive ${V}_{\text {TH}}$ shift. The dynamics of electron trapping was revealed from the dependences of the consequent ${V}_{\text {TH}}$ shift on the bias duration at different voltages. A time constant smaller than 0.1 ms for the ${V}_{\text {TH}}$ shift saturation at 6-V gate bias was obtained. It was also found that the ${V}_{\text {TH}}$ became inversely proportional to the gate-bias voltages exceeding 7 V. This inverse proportionality of the ${V}_{\text {TH}}$ shift resulted from the threshold of the hole-injection/electroluminescence (EL) and the sequential optical pumping effect on the electron traps. The EL emission was confirmed by a self- and in-situ photon detection measurement.

The effect of Al addition on the gas sensing properties of Fe2O3-based sensors

Abstract: Gas sensors based on α-Fe 2 O 3 (Al) have been studied experimentally and theoretically. Those with 9 mol% Al-added, sintered at 850°C, exhibit good gas sensing responses to CO and CH 4 . Well formed polycrystalline particles, essential to good gas sensing properties, are observed. XRD data show that the Al is dissolved into the material. The improvement in the gas sensing performance is attributed to the increase of the specific surface area caused by this aluminum addition. Variation of surface energy due to the Al-doped iron(III) oxide is modeled with two- and three-dimensional periodic structures. The results show that stronger relaxation leads to a stabilization of the surface in the case of Al addition compared to that without Al addition. Without relaxation, the non Al-added surface has a much lower surface energy than the Al-added surface. Although the energy difference between the relaxed surfaces is small, it indicates that the growth of Al-added iron oxide is less exothermic than that of pure iron oxide, which would explain the smaller particle size and hence the increased surface area observed after Al addition.

Electrical and physical characterization of gate oxides on 4H-SiC grown in diluted N2O

Abstract: A systematic electrical and physical characterization of gate oxides on 4H-SiC, grown in diluted N2O at 1300 °C, has been performed. Electrical characterization by the high-frequency C-V technique, conductance technique, and slow trap profiling method reveals that the densities of interface and near-interface traps, and the effective oxide charge for gate oxides grown in 10% N2O are the lowest, compared to gate oxides grown in 100% and 0.5% N2O. These results are supported by physical characterizations using x-ray photoelectron spectroscopy, secondary ion mass spectroscopy, and atomic force microscopy. It has been shown that carbon clusters, accumulated at the SiC-SiO2 interface, directly influence the roughness of the interface and the densities of the interface and near-interface traps.

Surface-Passivation Effects on the Performance of 4H-SiC BJTs

Abstract: In this brief, the electrical performance in terms of maximum current gain and breakdown voltage is compared experimentally and by device simulation for 4H-SiC BJTs passivated with different surface-passivation layers. Variation in bipolar junction transistor (BJT) performance has been correlated to densities of interface traps and fixed oxide charge, as evaluated through MOS capacitors. Six different methods were used to fabricate SiO2 surface passivation on BJT samples from the same wafer. The highest current gain was obtained for plasma-deposited SiO2 which was annealed in N2O ambient at 1100°C for 3 h. Variations in breakdown voltage for different surface passivations were also found, and this was attributed to differences in fixed oxide charge that can affect the optimum dose of the high-voltage junction-termination extension (JTE). The dependence of breakdown voltage on the dose was also evaluated through nonimplanted BJTs with etched JTE.

Material science and device physics in SiC technology for high-voltage power devices

Abstract: Power semiconductor devices are key components in power conversion systems. Silicon carbide (SiC) has received increasing attention as a wide-bandgap semiconductor suitable for high-voltage and low-loss power devices. Through recent progress in the crystal growth and process technology of SiC, the production of medium-voltage (600?1700 V) SiC Schottky barrier diodes (SBDs) and power metal?oxide?semiconductor field-effect transistors (MOSFETs) has started. However, basic understanding of the material properties, defect electronics, and the reliability of SiC devices is still poor. In this review paper, the features and present status of SiC power devices are briefly described. Then, several important aspects of the material science and device physics of SiC, such as impurity doping, extended and point defects, and the impact of such defects on device performance and reliability, are reviewed. Fundamental issues regarding SiC SBDs and power MOSFETs are also discussed.

Controlled growth of large-area, uniform, vertically aligned arrays of alpha-Fe2O3 nanobelts and nanowires.

Abstract: Vertically aligned iron oxide nanobelt and nanowire arrays have been synthesized on a large-area surface by direct thermal oxidation of iron substrates under the flow of O2. The effects of reactive gas pressure, composition, and temperature have been systematically studied. It was found that nanobelts (width, tens of nanometers; thickness, a few nanometers) are produced in the low-temperature region (∼700 °C) whereas cylindrical nanowires tens of nanometers thick are formed at relatively higher temperatures (∼800 °C). Both nanobelts and nanowires are mostly bicrystallites with a length of tens of micrometers which grow uniquely along the [110] direction. The growth habits of the nanobelts and nanowires in the two temperature regions indicate the role of growth rate anisotropy and surface energy in dictating the ultimate nanomorphologies.

The General Theory

Abstract: The concept of invariance with respect to transformations of a group is one of the most important and successful ideas of nineteenth century mathematics. After the use of coordinates had dominated many branches of mathematics and physics for centuries, a critical review of these methods was initiated by a new look on its foundations.

IBM journal of research and development: information for authors

Abstract: This paper combines background information about the IBM Journal of Research and Development with guidelines for the preparation of Journal manuscripts. The purpose is to acquaint authors with the Journal as a primary, professional publication and to present suggestions to ease the work of author and editor in preparing clear, concise, and useful manuscripts.