Papers by Author: Z.Q. Fang

Abstract: Thermally stimulated current spectroscopy (TSC) has been applied to characterize deep traps in high-purity semi-insulating 6H-SiC substrates. By using above bandgap to sub-bandgap light for illumination at 83 K and different applied biases, at least nine TSC traps in the temperature range of 80 to 400 K can be consistently observed. It is found that TSC peaks for T < 130 K are significantly affected by light and some peaks are strongly enhanced by the applied bias. Measured trap activation energies range from 0.15 eV to 0.76 eV. Theoretical fittings of selected traps give more accurate trap parameters. Based on literature results connected with deep traps in conductive 6H-SiC, the origin of these TSC traps is discussed.

Abstract: A variety of 4H-SiC samples from undoped crystals grown by the physical vapor transport technique have been studied by temperature dependent Hall effect, optical and thermal admittance spectroscopy and thermally stimulated current. In most samples studied the activation energies were in the range 0.9 - 1.6 eV expected for commercial grade HPSI 4H-SiC. However, in several samples from developmental crystals a previously unreported deep level at EC-0.55 ± 0.01 eV was observed. Thermal admittance spectroscopy detected one level with an energy of about 0.53 eV while optical admittance spectroscopy measurements resolved two levels at 0.56 and 0.64 eV. Thermally stimulated current measurements made to study compensated levels in the material detected several peaks at energies in the range 0.2 to 0.6 eV.