Novel type of macroscopic defects embedded in AlGaN-based buffer layers of GaN-on-Si wafers

A novel macroscopic defect, which is observed as a microcrystal grain embedded in AlGaN buffer layers, was found in rapid-grown GaN-on-Si substrates. Leakage analysis using photoemission microscopy combined with cross-sectional transmission electron microscopy showed that the embedded grains acted as killer defects, and this was also confirmed by a statistical correlation between grain density and device yield. Electron diffraction analysis indicated that the embedded grain had a crystallographic axis tilted relative to the surrounding epilayer, suggesting its origin from semipolar planes during early buffer growth. Comparing the grain density with buffer growth conditions, we think that the grain formation was due to a rapid growth rate under low temperature. Furthermore, high growth temperature during initial buffer deposition significantly suppressed the grain formation and improved device yield under high-voltage stress. These findings highlight the essential role of buffer layer growth conditions in enhancing the yield of GaN-on-Si power devices.