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
Thermal and doping dependence of 4H-SiC polytype transformation
We have observed characteristic temperatures, anneal times, and doping densities that lead to stacking faults and 3C-SiC-like bands in 4H-SiC epilayers. Low energy cathodoluminescence spectroscopy measurements reveal a temperature threshold of 800 °C for emergence of these features in thermally oxidized or argon annealed 4H-SiC with an activation energy ≈2.5 eV. Stacking fault generation and polytype transformation exhibits a strong doping dependence, appearing only in a range of highly doped n-type 4H-SiC. Systematics of these strain and/or electronic effects induced by high N concentrations can be used to control structural instabilities during SiC device fabrication.
Polytypic transformations in SiC: the role of TEM
Abstract In this paper, the structure of SiC is briefly reviewed and a recent dislocation model for polytypic transformation is explained. The model is based on the asymmetry in the mobility of partial dislocations in SiC. For this reason, the nature of dislocations in SiC is also considered and the asymmetry in dislocation velocity is attributed to the different core structure of the two partial dislocations. Following the description of the polytypic transformation model, some experiments in its support that employ transmission electron microscopy are presented.