On the link between electroluminescence, gate current leakage, and surface defects in AlGaN/GaN high electron mobility transistors upon off-state stress

The degradation of AlGaN/GaN high electron mobility transistors after off-state stress is studied by means of electroluminescence (EL) analysis, gate leakage current (I-g) monitoring, and atomic force microscopy (AFM) mapping of the semiconductor surface. It is found that the degradation of I-g upon stress is due to the combined effect of the individual defects underlying each of the EL spots, which contribute a few mu A each to the total I-g. After removal of contacts and passivation, a direct one-to-one correspondence between EL spots and pits on the semiconductor surface is found. Reverse bias, conducting-tip AFM imaging showed that these surface pits do indeed act as leakage paths. Thus, the direct relationship between EL hot spots, surface pits, and gate current leakage is demonstrated. Discussion on the morphology of the surface pits and their possible origin is also provided.