AlGaN/GaN MOS-HFETs based on InGaN/GaN MQW structures with Ta₂O₅ dielectric

¹ National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan, P.R. China
² Department of Electro-Optical Engineering, Kun Shan University, Yung-Kang Dist., Tainan City 71003, Taiwan, P.R. China
³ Institute of Microelectronics and Department of Electrical Engineering, Center for Micro/Nano Science and Technology, Advanced Optoelectronic Technology Center, National Cheng Kung University, Tainan City 70101, Taiwan, P.R. China
⁴ Department of Electrical Engineering, Fu Jen Catholic University, Zhong-Zheng Rd. 510, 24205 New Taipei City, Taiwan, P.R. China

^a e-mail: lee.kh@nsrrc.org.tw

Received: 7 July 2011
Revised: 19 January 2012
Accepted: 8 February 2012
Published online: 1 March 2012

Abstract

We report on metal-oxide-semiconductor (MOS) AlGaN/GaN heterostructure field effect transistors (HFETs) based on InGaN/GaN multiple quantum well (MQW) structure using Ta₂O₅ dielectric deposited by electron beam evaporation (EBE) simultaneously for surface passivation and as a gate insulator. The device features a 5-pair MQW layer inserted into the AlGaN/GaN two-channel HFET structure. It results in a raised potential barrier, which leads to better carrier confinement and effective access to the InGaN layer. However, it revealed a pronounced leakage current which may be generated from the bottom Si-doped GaN and/or the sidewall leakage paths due to the exposure of channels after mesa etching. Both passivated MQW-HFET and MOS MQW-HFET present enhanced dc- and pulsed-mode performance compared to unpassivated one. In terms of transfer characteristics, MOS MQW-HFET exhibits the larger and broader main peak yet smaller satellite peak relative to passivated MQW-HFET. The reduced gate and mesa-to-mesa leakage current indicates the successful passivation effect from EBE-Ta₂O₅ dielectric.