Growth Characteristics of AlGaN/GaN HEMTs on Patterned Si (111) Substrates Using Double AlN Interlayers by MOCVD

AlGaN/GaN high electron mobility transistors (HEMTs) were grown on un-patterned, patterned without mask, and patterned with mask Si (111) substrates by metal organic chemical vapor deposition (MOCVD). The patterns on the Si substrates were fabricated by SiO2 masks and wet etching. Double AlN interlayers grown at high temperature were employed to relax the tensile stress induced by the large mismatches in the lattice constants and the thermal expansion coefficients. Growth characteristics of AlGaN/GaN HEMTs were discussed and analyzed. Before achieving optimized growth conditions, more cracking lines were observed on patterns along the [1-100] orientation than along the [11-20] orientation, resulted from more stable GaN (1-100) facets than GaN (11-20) facets. It is suggested that long patterns should be made along the [11-20] orientation. Micro-Raman measurements showed that Raman shifts at the concave corners are bigger than those at the convex corners, indicating the presence of the larger stress at the concave corners.