Progress and Perspectives on p-GaN Cap Layer Etching Engineering Over p-GaN/AlGaN/GaN Heterojunctions

Gallium nitride (GaN)-based transistors withp-type GaN (p-GaN) gates are widely recognized as promising devices for power converter applications, due to their positive and stable threshold voltage, low on-resistance, and high breakdown field. However, the fabrication ofp-GaN gate high electron mobility transistors (HEMTs) faces several key process challenges, among which the etching of thep-GaN layer has recently become particularly important. Given the emergence of novelp-GaN etching techniques, a comprehensive review that encompasses scientific classification and systematic evaluation of these methods is essential. This paper aims to fill this gap by reviewing the latest fabrication technologies for formingp-GaN gates inp-GaN/aluminum gallium nitride (AlGaN)/GaN heterojunctions.Firstly, the etching methods are categorized into self-terminating etching, dual-step cyclic etching, and plasma treatment techniques. These three classes are comprehensively summarized and compared in terms of etching rate, mechanisms, selectivity, and applicability. Self-terminated etching methods are divided into oxygen-based and fluorine-based systems, with a focus on the influence of critical process parameters on etch rate and selectivity. Subsequently, repetitive self-limiting etching techniques, including digital etching (DE) and atomic layer etching (ALE), are reviewed, with an emphasis on oxide-chloride and chloride-inert gas systems. Finally, plasma passivation processes are introduced as an alternative approach for achieving enhancement-modep-GaN gate HEMTs.This paper provides a summary and discussion of the key fabrication process ofp-GaN gate devices—namely, thep-GaN cap layer etching engineering. It offers guidance for selecting appropriate etching methods under different application scenarios and provides valuable insights for the future development of GaN HEMTs.