Effect of a trace of water vapor on Ohmic contact formation for AlGaN/GaN epitaxial wafers

The authors observed that a trace of water vapour can have a significant degradation effect on Ohmic contact formation for AlGaN/GaN high electron mobility transistors (HEMTs). The degradation effect due to a trace of water vapour is less serious for n-GaN. This is a more serious problem for AlGaN/GaN HEMT than AlGaAs/GaAs HEMT or InP based HEMT because of the higher temperature needed for Ohmic contact annealing when AlGaN or GaN are involved. Using cooling water with a temperature slightly higher than the ambient temperature during rapid thermal annealing (RTA) appears to be the best approach.