The Impact of Surface Defects on SiC Schottky and Ohmic Contact Formation
Silicon carbide is a leading semiconductor for high power, high temperature electronics, yet SiC devices still face problems of electrical contact control and reproducibility. Recent work worldwide shows that point and extended defects in SiC as well as chemical reactions at metal-SiC interfaces can influence contact transport properties. Yet Schottky barrier and ohmic contact formation at the intimate metal-SiC junction are relatively unexplored on the microscopic level. We have used depth-resolved cathodoluminescence spectroscopy (DRCLS) and Auger electron spectroscopy (AES) to measure the optical emissions of defects near 4H-SiC surfaces and metallized interfaces on a nanometer scale. These techniques reveal that a variety of metals on clean 4H-SiC surfaces in ultrahigh vacuum (UHV) promote the formation of mid-gap defects extending only nanometers away from the junction. These states vary in their ranges of depth and depend sensitively on interface reactivity and subsequent UHV annealing
An Evaluation for Quality Inspection of Epitaxial Layer and Heavily-doped 4H-SiC Substrate by Simple Schottky Barrier Diode and MOS Capacitor
Reducing the crystal defects in SiC is an important issue. In this work, we propose a short turn-around method using simple SBD and MOSC devices to reflect the electrically-active defect density in the substrate. Simple SBD and MOSC structures are fabricated on n− epi-layer/n+ substrate or pure n+ substrate that have different defect densities. The n− epi-layer SBDs for high-defect wafers generate high yield loss, a more comprehensive leakage current distribution, and a stronger bias-dependent leakage current than low-defect alternatives. The pure n+ substrate SBDs of high-defect wafers only reveal a higher leakage level than the low-defect alternatives. This phenomenon may be caused by the variation of doping concentration or Schottky barrier height. The pure n+ substrate MOSCs show a higher yield loss than the n− epi-layer MOSCs based on TZDB, where the leakage level is identical for both the high-defect and the low-defect wafers. It is suggested that the epitaxial quality can be evaluated by using the simple SBD, where the heavily-doped substrate is not suitable. Both the n− epi-layer and the pure n+ substrate MOSCs cannot reflect electrically-active defect densities for the TZDB phenomena.
Finite Difference Modeling on the Temperature Field of Substrate in Friction Surfacing
Friction surfacing is an advanced process of great potential, especially in the field of repair and reclamation of worn and damaged components. As a kind of thermal processing technology, the temperature profile and changes of the substrate in friction surfacing are important factors to get coatings of high quality. In this paper, the temperature field of the substrate during the process is simulated by finite difference method. The results are consistent with experiments, reappearing the temperature change of the substrate during friction surfacing, allowing further study on figuration and quality of coatings.