Enhanced Performance of Low-Leakage-Current Normally off p-GaN Gate HEMTs Using NH3 Plasma Pretreatment

In this article, a low-leakage-current and high-breakdown-voltage normally OFF p-GaN gate high-electron-mobility transistor (HEMT) on a Si substrate with low-damage NH3 plasma pretreatment was investigated. NH3 plasma pretreatment was performed in a plasma-enhanced chemical vapor deposition (PECVD) system before PECVD-SiNx deposition, which effectively removed surficial oxides and other impurities, suppressed the interface traps between those of SiNx and (Al)GaN, and reduced the overall drain leakage current of devices in the OFF-state. In comparison to the device without pretreatment, the normally OFF p-GaN gate HEMTs pretreated with NH3 plasma exhibited a high ON/OFF-current ratio of <inline-formula> <tex-math notation="LaTeX">$10^{{9}}$ </tex-math></inline-formula>, a low reverse gate leakage current of <inline-formula> <tex-math notation="LaTeX">$2.86\times 10^{-{8}}$ </tex-math></inline-formula> mA/mm, a high gate breakdown voltage of 9.1 V, and a high breakdown voltage of 690 V at <inline-formula> <tex-math notation="LaTeX">$1~\mu \text{A}$ </tex-math></inline-formula>/mm. Furthermore, NH3 plasma pretreatment effectively suppressed the threshold voltage shift induced by the charge/discharge effect in p-GaN. It was found that NH3 plasma pretreatment is effective in improving device performance, such as the leakage current, breakdown voltage, and threshold voltage stability.