Current transport dynamics and stability characteristics of the NiO<i> <sub>x</sub> </i> based gate structure for normally-off GaN HEMTs
Yonghao Du, Weizong Xu, Hehe Gong, Jiandong Ye, Feng Zhou, Fangfang Ren, Dong Zhou, Dunjun Chen, Rong Zhang, Youdou Zheng, H. J. Lü
Abstract
Abstract The application of p-type oxide typified with NiO x as cap layer in AlGaN/GaN high electron mobility transistor for normally-off operation has specific benefits, including etching free fabrication process, high hole density and elimination of Mg dopants diffusion effects. This work presents a device configuration exploration combining the p-NiO x gate cap layer and a thin AlGaN barrier layer. Calculation method for the threshold voltage has been discussed, which obtains good consistence with the experimental measurements. In addition, a nitrogen based post-annealing process was developed to improve the film stoichiometry for elevated gate controllability, realizing normally-off operation with enhanced channel conduction capability. The current transport dynamics in the gate stack as coupled with the NiO x /AlGaN interface states have also been studied, where a deep level trap was recognized in dominating the gate current characteristics and the gate stability performance under different forward gate bias conditions.