Device engineering for stable and reliable gate operation in Schottky-type p-GaN gate HEMTs

Abstract

Schottky-type p-GaN gate high electron mobility transistors (HEMTs) are commercially promising power devices due to their balance of performance and fabrication cost. However, the stability and reliability of gate operation in Schottky-type p-GaN gate HEMTs remain significant limiting factors that hinder the widespread adoption of this device. To enable a widespread adoption of this device, it is crucial to increase the threshold voltage (V_TH), strengthen the gate p-GaN/metal Schottky junction, stabilize the V_TH, and boost the short-circuit robustness. In this thesis, approaches that address the aforementioned aspects have been proposed and thoroughly studied. First, a p-FET bridge (PFB) structure is introduced to elevate and partially stabilize the V_TH. By integrating a normally-ON p-FET between the gate and source, the PFB prevents false turn-on during switching transients. It also decouples V_TH from the reverse turn-on voltage, improving reverse conduction performance. Mixed-mode TCAD simulations confirm that PFB-HEMTs enhance efficiency in buck converter applications. Second, a voltage seatbelt structure is developed to eliminate V_TH instability induced by drain-bias stress. This design shields the p-GaN layer from high drain voltages, mitigating charge imbalance in floating p-GaN layer, and electron trapping at the drain-side gate corner. The voltage seatbelt concurrently enhances short-circuit robustness by limiting saturation current while maintaining reasonable ON-resistance, achieving a balance between reliability and performance. Third, a GaON nanolayer that can effectively passivate the GaN surface has been demonstrated and systematically studied, which can be used to strengthen the gate p-GaN/metal Schottky junction. The structure of the GaON nanolayer is elucidated, and the energy band alignment between GaN and GaON is clarified. Based on this band diagram and unique features of GaON nanolayer, various applications for the GaON nanolayer are reviewed and proposed.

Date of Award	2025
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology
Supervisor	Kevin Jing CHEN (Supervisor) & Mengyuan HUA (Supervisor)