Au-free normally-off AlGaN/GaN-on-Si MIS-HEMTs using combined partially recessed and fluorinated trap-charge gate structures

Abstract

In this letter, partially recessed gate structures in conjunction with negative trap charges by F- plasma treatments both at AlGaN barrier and on gate dielectric surface are employed to realize the normally-OFF operation for AlGaN/GaN Metal-Insulator-Semiconductor High Electron Mobility Transistors in Au-free scheme. A partial gate recessed trench is designed to effectively reduce the 2-D electron gas (2DEG) density and achieve positive threshold voltage Vth without severe degradation in 2-DEG channel mobility. Furthermore, the fixed trap charges are innovatively placed at the gate AlGaN and Si3N4 layers by a two-stage F- plasma treatment to further increase the Vth , without mobility degradation. A high Vth of 1.9 V and a drain current ∼200~mA/mm are achieved in the fabricated device, which also has a lower leakage current and the higher breakdown voltage of 580 V. © 2014 IEEE.