Jisheng Han

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

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

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.

Thickness dependence of the piezoresistive effect in p-type single crystalline 3C-SiC nanothin films

This paper reports, for the first time, the piezoresistive effect of p-type single crystalline 3C-SiC nanothin films grown by LPCVD at low temperature. Compared to thick SiC films, the gauge factors of the 80 nm and 130 nm films decreased remarkably. This result indicates that the crystal defect at the SiC/Si interface has a significant influence on the piezoresistive effect of ultra-thin film p-type 3C-SiC.

Anchoring ultra-fine TiO2–SnO2 solid solution particles onto graphene by one-pot ball-milling for long-life lithium-ion batteries

A low cost, up-scalable and one-pot wet-mechanochemical approach is designed for fabricating TiO2–SnO2@graphene nanocomposites where TiO2 and SnO2 solid solution nanoparticles are evenly anchored on graphene sheets. As an anode material of lithium ion batteries (LIBs), the as-prepared nanocomposites deliver a superior rate performance of 388 mA h g−1 at 1.5 A g−1 and an outstanding reversible cycling stability (617 mA h g−1 at 0.4 A g−1 after 750 cycles, 92.2% capacity retention), due to the synergistic effects contributed from individual components, i.e., high specific capacity of SnO2, excellent conductivity of 3D porous graphene networks, good rate capability and structural stability of TiO2 structures.

Effects of nitrogen incorporation on the interfacial layer between thermally grown dielectric films and SiC

C-containing interlayers formed between the SiC substrate and dielectric films thermally grown in O2, NO, and in O2 followed by annealing in NO were investigated. X-ray reflectometry and x-ray photoelectron spectroscopy were used to determine N and C incorporation in dielectric films and interlayers, as well to determine their mass densities and thicknesses. The thickest C-containing interlayer was observed for films thermally grown in O2, whereas the thinnest one was observed for films directly grown in NO, evidencing that the presence of N decreases the amount of carbonaceous compounds in the dielectric/SiC interface region.

Properties of Nitrided Oxides on SiC

If there is a singular property of silicon that has contributed to its success as a semiconductor material, it is the native oxide, SiO2. This oxide can be thermally grown to form an effective insulating layer as part of the gate in a metal-oxide-semiconductor field-effect transistor (MOSFET) structure. Silicon Carbide also has the ability to grow a similar oxide, and when combined with the bulk properties of wide bandgap, high thermal conductivity and extremely low intrinsic free carrier concentration, will lead to an enormous number of applications. This means that as far as the gate oxide is concerned SiC can be processed in much the same way as Si, the exception being that the processing temperatures are generally higher.

Effects of Initial Nitridation on the Characteristics of SiC-SiO2 Interfaces

The reasons for inferior electrical properties of nitric oxide (NO) annealed gate oxides compared to gate oxides directly grown in NO are investigated in this paper. Interface roughness is identified as one of the main issues. A significant improvement of the annealed gate oxides is achieved by introducing an initial nitridation step, prior to oxidation and NO annealing. With this additional step, a sandwich (nitridation-oxidation-nitridation) process is developed to improve the SiC-SiO2 interface without the need for lengthy and expensive direct growth in NO.

Orientation dependence of the pseudo-Hall effect in p-type 3C–SiC four-terminal devices under mechanical stress

This paper presents for the first time the orientation dependence of the pseudo-Hall effect in p-type 3C–SiC four-terminal devices under mechanical stress. Experimental results indicate that the offset voltage of p-type 3C–SiC four-terminal devices significantly depends on the directions of the applied current and stress. We also calculated the piezoresistive coefficients π61, π62, and π66, showing that π66 with its maximum value of approximately 16.7 × 10−11 Pa−1 plays a more dominant role than π61 and π62. The magnitude of the offset voltage in arbitrary orientation under stress was estimated based on these coefficients. The finding in this study plays an important role in the optimization of Microelectromechanical Systems (MEMS) mechanical sensors utilizing the pseudo-Hall effect in p-type 3C–SiC.

The effect of device geometry and crystal orientation on the stress-dependent offset voltage of 3C–SiC(100) four terminal devices

This communication reports for the first time, the impact of device geometry on the stress-dependent offset voltage of single crystal p-type 3C–SiC four terminal devices. Single crystal p-type 3C–SiC(100) was grown by low pressure chemical vapor deposition and three different device geometries (cross, rectangle and square) were fabricated using the conventional photolithography and dry etching processes. It was observed that the stress-dependent offset voltage of the devices strongly depends upon the device geometry and it can be increased by almost 100% by just selecting the appropriate device geometry. We also found that as the device is rotated within the (100) crystal plane its stress sensitivity varies from ≈0 to 9 × 10−11 Pa−1.

Effect of the pH value of the precipitation solution on the CO sensitivity of α-Fe2O3

Abstract Using Fe(NO3)3·9H2O as raw material, α-Fe2O3 was prepared by the precipitation method. The CO sensitivities of sensors made from the product both in air and N2 backgrounds were tested. It was found that the sensitivities are significantly affected by the pH value of the precipitation solution. The CO gas sensitivity of sensors prepared from materials with different precipitation pH values varies in a manner indicating predominance of different gas sensing mechanisms. The response is also dependent on the operating temperature and the nature of the background stream gas. Based on the experimental results, combined with studies using Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction and scanning electron microscopy, the possible sensing mechanisms are discussed. It seems that the chemically bonded free cluster OH plays a key role in the improved CO gas sensitivity. The BET method was employed for specific surface area determination.