Papers by Author: Valeri F. Tsvetkov

Abstract: Availability of high-quality, large diameter SiC wafers in quantity has bolstered the commercial application of and interest in both SiC- and nitride-based device technologies. Successful development of SiC devices requires low defect densities, which have been achieved only through significant advances in substrate and epitaxial layer quality. Cree has established viable materials technologies to attain these qualities on production wafers and further developments are imminent. Zero micropipe (ZMP) 100 mm 4HN-SiC substrates are commercially available and 1c dislocations densities were reduced to values as low as 175 cm-2. On these low defect substrates we have achieved repeatable production of thick epitaxial layers with defect densities of less than 1 cm-2 and as low as 0.2 cm-2. These accomplishments rely on precise monitoring of both material and manufacturing induced defects. Selective etch techniques and an optical surface analyzer is used to inspect these defects on our wafers. Results were verified by optical microscopy and x-ray topography.

Abstract: DC characteristics and reverse recovery performance of 4H-SiC Junction Barrier Schottky (JBS) diodes capable of blocking in excess of 10 kV with forward conduction of 20 A at a forward voltage of less than 4 V are described. Performance comparisons are made to a similarly rated 10 kV 4H-SiC PiN diode. The JBS diodes show a significant improvement in reverse recovery stored charge as compared to PiN diodes, showing half of the stored charge at 25°C and a quarter of the stored charge at 125°C when switched to 3 kV blocking. These large area JBS diodes were also employed to demonstrate the tremendous advances that have recently been made in 4H-SiC substrate quality.

Abstract: Recent advances in PVT c-axis growth process have shown a path for eliminating micropipes in 4HN-SiC, leading to the demonstration of zero micropipe density 100 mm 4HN-SiC wafers. Combined techniques of KOH etching and cross-polarizer inspections were used to confirm the absence of micropipes. Crystal growth studies for 3-inch material with similar processes have demonstrated a 1c screw dislocation median density of 175 cm-2, compared to typical densities of 2x103 to 4x103 cm-2 in current production wafers. These values were obtained through optical scanning analyzer methods and verified by x-ray topography.