Effects of SiNX passivation on GaN-HEMT DC characteristics

In this paper, the effects of tensile/compressive stress induced charge by silicon nitride (SiNX) passivation on electrical characteristics of D-mode high electron mobility transistor (HEMT), i.e., GAN were investigated by SILVACO simulation tools and fabrication results were also shown as its counterpart. The influence of Al-fraction and surface state were also discussed and analyzed. The results of stress-induced SiNx impact shows the tensile stress increase the 2-dimensional electron gases (2DEG) density. The compressive stress will not only decrease the sheet charge density but also format 2-dimensional hole gases (2DHG) at the heterojunction of GaN/AlGaN. Besides, the possible mechanism of breakdown resulting from 2DHG is discussed which results in the breakdown of device more easily. This study also shows the performance of the real device based on the design of the simulation model. Finally, D-mode GaN MIS-HEMTs was fabricated to verify the physical model. We also designed different kinds of Gate-to-Drain length in this study. The Ron of LGD = 5, 10 and 15 mu m were 12.9, 15.04 and 16.48 m omega cm2, respectively. The highest breakdown voltage was observed for LGD = 10 mu m because of the field plate.