Charge Control in Schottky-Type p-GaN Gate HEMTs With Partially and Fully Depleted p-GaN Conditions

• Published in: IEEE transactions on electron devices Vol. 69; no. 5; pp. 2262 - 2269
• Main Authors: Wu, Qianshu, Chen, Jia, He, Liang, Zhang, Jinwei, Qiu, Qiuling, Feng, Chenliang, Li, Liuan, Que, Taotao, Liu, Zhenxing, Wu, Zhisheng, He, Zhiyuan, Liu, Yang
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.05.2022; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Aluminum gallium nitride; Aluminum gallium nitrides; Analytical models; Capacitors; Charge control; Depletion; gallium nitride (GaN); Gallium nitrides; HEMTs; High electron mobility transistors; high-electron-mobility transistors (HEMTs); Logic gates; Mathematical models; MODFETs; multi-series-capacitance-charge model; Optimization; p-gate; Semiconductor devices; Thickness; threshold voltage; Valence band; Wide band gap semiconductors
• ISSN: 0018-9383; 1557-9646
• DOI: 10.1109/TED.2021.3130848

The Schotty-type p-GaN gate high-electron-mobility transistors (HEMT) feature a unique gate structure. A comprehensive understanding of the charge control mechanism in the p-GaN gate region is a fundamental step for the optimization of this technology. In this work, a physics-based analytical model is presented which takes into consideration all the capacitive effects from gate metal deep into the GaN buffer. According to our analysis, the p-GaN layer can be either partially depleted by the metal/p-GaN Schottky junction or fully depleted, depending on the doping concentration and thickness of the p-GaN layer. Our model accurately captures the charge control properties under both conditions and is validated against TCAD numerical simulations. For a certain p-GaN thickness, a lightly doped p-GaN leads to a full-depletion condition, such that the acceptor concentration directly affects the band diagram at AlGaN/GaN interface. The <inline-formula> <tex-math notation="LaTeX">{V}_{\text {th}} </tex-math></inline-formula> of the HEMT increases quickly with acceptor concentration in p-GaN. With sufficiently high acceptor concentration in p-GaN, the device reaches the partial-depletion condition, the acceptor concentration loses its influence over the band diagram at the location of the AlGaN/GaN interface, since the Fermi-level at the AlGaN surface is pinned near the valence band of p-GaN. The <inline-formula> <tex-math notation="LaTeX">{V}_{\text {th}} </tex-math></inline-formula> starts to decrease with acceptor concentration, but at a relatively slow rate. The maximum <inline-formula> <tex-math notation="LaTeX">{V}_{\text {th}} </tex-math></inline-formula> is obtained near the boundary between partial-and full-depletion conditions. In consideration of the process margin, the device designed with a partially depleted p-GaN is preferable, since it ameliorated the <inline-formula> <tex-math notation="LaTeX">{V}_{\text {th}} </tex-math></inline-formula> sensibility against acceptor concentration.