Epitaxial growth and characterization of 4H-silicon carbide on low off-axis substrates for high-power devices

Silicon carbide (SiC) is the one of most attractive materials for electronic devices in high-power and high-frequency operations due to its outstanding electrical properties. The high breakdown field and high thermal conductivity of SiC coupled with high operational junction temperature theoretically permit extremely high power densities and efficiencies to be realized in SiC devices. The wide bandgap energy and low intrinsic carrier concentration allow SiC based semiconductor electronic devices to operate in high-temperature high-radiation conditions under which conventional semiconductors cannot perform adequately.;Over the last few years, significant improvements have been made in bulk and epitaxial growth of 4H-SiC. As the 4H-SiC technology is moving towards larger substrate sizes the importance of optimizing epilayer growth on lower off-axis growth is gaining momentum. However, epitaxial growth on lower off-axis wafers suffers from step bunching as well as the formation of triangular and inverted pyramid type defects thereby preventing the realization of high performance electronic devices. These defects are believed to adversely influence the performance of various SiC devices, especially high power devices operating at high blocking voltages and current levels. Therefore their elimination is of primary importance, and can be achieved via (a) understanding the origin of this defect, and (b) identification and optimization of the growth parameters responsible for defect formation. The epilayer growth was optimized on low off-axis substrates by eliminating and/or minimizing the density of these defects. Another problem in SiC epitaxial growth is the lower growth rates which increases the growth duration and therefore cost of production. Moreover, longer growth duration also introduces newer defects affecting the device performance. Therefore, one of the foci was to increase the growth rate by introducing an alternative chlorine-based silicon precursor compared to conventional Silane precursor. High growth rates (> 50 mum/hr) were achieved.;The development of SiC based bipolar devices has been rather slow till date and the problem is attributed to the poor minority carrier lifetime on as-grown epilayer affecting the modulation of conductivity. The challenge is not only to increase the carrier lifetime (for bipolar devices) but also to control the carrier lifetime (for unipolar switching applications). A technology was developed and very high carrier lifetime (∼ 10 mus) was demonstrated using CVD.