900-V active-passivation p-GaN gate HEMT with suppressed floating Si substrate induced back-gating effect

Abstract

The development of high-voltage GaN-on-Si power devices is hindered by vertical breakdown of buffer layer. Implementing a floating substrate configuration could improve vertical breakdown voltage. Despite this advantage, devices with a floating substrate exhibit severe dynamic RON degradation due to the back-gating effect and the consequent severe buffer trapping. In this work, a 900-V GaN-on-Si power device is demonstrated on floating Si substrate using active passivation p-GaN gate HEMT technology (AP-HEMT). As the active passivation is connected to gate, the AP-HEMT facilitates effective hole injection in both p-GaN gate and active passivation, thereby significantly suppressing negative buffer trapping. Additionally, the injected holes contribute to light emission, as evidenced by CCD camera that detect photon generation, which effectively pumps electrons out from buffer traps. Consequently, the AP-HEMT shows a superior dynamic RON/static RON ratio of 1.42 after a drain stress of 900 V with a floating substrate. To investigate the effectiveness of hole injection/light pumping effects, positive back-gating sweep is employed to induce buffer trapping to mimic the floating substrate effects. For conventional p-GaN gate HEMT, the drain current is significantly reduced after positive substrate stress. In contrast, for the AP-HEMT with sufficient hole injection (VGS = 3.5 V), the device presents no drain current reduction. These results prove that the active passivation technology improves stability against floating substrate-induced dynamic degradation, which is advantageous for development of high-voltage GaN-on-Si power devices.