Electronic transport mechanism for nonalloyed Ti-based ohmic contacts to strained n-AlGaN/GaN heterostructure

We report on the electronic transport mechanism for nonalloyed Ti-based ohmic contacts to strained n-AlGaNGaN heterostructure. Based on current-voltage-temperature and specific contact resistance-temperature characteristics, deep-donor-assisted tunneling (DDAT) and shallow-donor-assisted tunneling (SDAT) models are proposed to describe carrier conduction mechanisms. It is shown that for T 298 K, the theoretical results obtained not from the DDAT simulation but the SDAT are in good agreement with the experimental data. It is, however, further shown that for T298 K, most of the carriers tunnel through the barrier via deep energy levels. The carrier conduction mechanism for the contacts to the AlGaNGaN is described in terms of tunneling or carrier-hopping conduction, depending on temperatures.