Papers by Keyword: Shallow Impurities

Abstract: Large group-I elements such as sodium, rubidium and cesium have recently been incorporated in the gate oxide of SiC power MOSFETs. In the case of sodium incorporation, enhanced field effect mobilities have been definitively observed. Based on density functional calculations, we find large group-I elements serve as a shallow impurities near the interface. The enhanced mobility, observed in the case of sodium, can be explained in terms of an impurity band model.

Abstract: For undoped 6H-SiC boules grown by physical vapor transport the variations of resistivity, of the type and density of deep electron and hole traps, and of the concentration of nitrogen and boron were studied as a function of position in the cross section normal to the growth axis and along the growth direction. It was observed that the concentrations of all deep electron and hole traps decreased when moving from seed to tail of the boule and from the center to the edge of the wafers. Modeling of the growth process suggests that the C/Si ratio increases in a similar fashion and could be responsible for observed changes. We also discuss the implications of such stoichiometry changes on compensation mechanisms rendering the crystals semi-insulating and on electrical uniformity of SI-SiC wafers.