Study of Magnesium Activation Effect on Pinch-Off Voltage of Normally-Off p-GaN HEMTs for Power Applications

The role of the magnesium (Mg) doping and its electrical activation on the off-state of p-GaN/AlGaN/GaN HEMTs has been investigated in this work. Firstly, the effect of different Mg doping profiles has been studied via the help of Technology Computer-Aided Design (TCAD) simulations, with the objective of analyzing the band diagrams of the structure. Then, it has been shown how experimental Capacitance-Voltage measurements can be useful to obtain information on the net acceptor concentration in the p-GaN. As a result, devices with an undoped (magnesium-free) GaN gate have been experimentally compared to devices whose p-GaN gate has been activated via a reference annealing process. Finally, results on a device characterized by an improved p-GaN activation have been presented and compared, showing improvements on several parameters of both off- and on-state, thus underlining the key role of the Mg activation process in the overall performances of normally-off GaN HEMTs.