AlGaN/GaN HEMT device reliability and degradation evolution: Importance of diffusion processes

A methodology based on combined electrical trapping analysis with UV-assisted preparation of trap states and electroluminescence analysis was developed to gain detailed understanding of trap generation in AlGaN/GaN HEMTs during off and on-state stress. This is used to identify electronic trap location laterally and vertically in a device structure and the nature of the degradation mechanism. We identify the generation of traps with activation energies in the range from 0.45 to 0.65 eV near the gate edge on its drain side in AlGaN/GaN HEMTs as electronic traps in the AlGaN device layer, as a result of on- and off-state stress. Degradation studied on devices subjected to stress under different backplate temperatures, points to diffusion processes playing an important role for early device degradation. Diffusion constants showed thermal activation energies of ∼0.26 eV consistent with diffusion processes along dislocations, with possible additional contributions from bulk diffusion accelerated by converse/inverse piezo-electric strain and leakage currents.