Channel Engineering of Normally-OFF AlGaN/GaN MOS-HEMTs by Atomic Layer Etching and High-κ Dielectric

On July 18, 2018, IEEE Electron Device Letters published the research results of high-performance normally-off AlGaN/GaN MOS-HEMTs by Professor Yanqing Wu from Wuhan National High Magnetic Field Center. The paper entitled “Channel Engineering of Normally-OFF AlGaN、GaN MOS-HEMTs by Atomic Layer Etching and High-κ Dielectric”. The first author of this paper is Qianlan Hu, a PhD student of Grade 2017 from school of optical and electronic information. The other authors from group members including Sichao Li, Tiaoyang Li, Xin Wang, and Xuefei Li.

Gallium Nitride (GaN) is emerging wide-bandgap semiconductor for high-frequency microwave RF devices and high-temperature power devices due to their superior physical properties, including high electron mobility, high critical electric field, high thermal conductivity and low ON-resistance, etc. Numerical works have been developed for E-mode devices in order to achieve fail-safe operation and simply circuit design. In this work, normally-off AlGaN/GaN MOS-HEMTs with a threshold voltage of 2.2 V have been achieved by an atomic layer etching (ALE) technique. Combined with surface passivation by atomic layer deposition of composite HfSiO high-κ gate dielectric, well-controlled gate-recess process with minimized surface damage results in improved interface properties with a low interface trap density of 2.8×10¹¹ eV-¹cm^-2 and suppressed gate leakage current with a high current on/off ratio over 10¹¹. Maximum current density of 518 mA/mm with on-resistance of 10.1 Ω∙mm and high breakdown voltage of 1456 V at an OFF-state current density of 1 μA/mm are also achieved. In the meantime, the dynamic R_on is only 1.2 times the static Ron after off-state drain voltage stress of 120 V and 2.6 times after 300 V stress. 

Paper link: https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=8412537&tag=1