Theoretical analysis of buffer trapping effects on off-state breakdown between gate and drain in AlGaN/GaN HEMTs

In this paper, AlGaN/GaN HEMTs with different device dimensions were designed and fabricated to investigate the relationship between off-state breakdown voltage and gate-to-drain spacing. It is found that the off-state breakdown voltage increases almost linearly with gate-to-drain spacing with the slop of about 46.8V/gm. Sentaurus software was used to find the physical mechanism of this phenomenon. By comparing the simulation results of devices with and without deep-level acceptor traps in GaN buffer layer, it is found that the deep-level acceptor traps in GaN buffer layer underneath the gate-to-drain channel could be occupied by hot electrons created in channel, which would extend the channel depletion region and then alleviate the maximum channel electric field. The theoretical and simulation analysis show that there is a positive correlation between the depletion length and the off-state gate-drain breakdown voltage. The simulation results show that with gate-to-drain spacing increasing, the negatively charged buffer traps region spread wider and the depletion region length becomes longer, playing a key role in the linear dependence of off-state gate-drain breakdown voltage on gate-to-drain spacing.