Transient Simulation of GaN HEMTs

Subthreshold drain leakage can be suppressed in GaN HEMTs by intentionally doping the GaN buffer with deep acceptor dopants such as C and Fe or by using a double heterostructure. In this thesis, both concepts, doping and using double heterostructure were investigated using numerical device simulation. The main focus was on the study of transient electrical behaviour and the understanding of trapping behaviour of deep acceptor dopants which causes current collapse. It was found that current collapse is dependent on dopant concentration and is worse with Fe doping than with C doping. These results were explained by considering the potential barrier formed in the GaN buffer due to electron trapping. Transistors with an undoped GaN channel layer on top of a doped GaN buffer layer had a small current collapse but much a higher drain current