DC and RF Characteristics of Enhancement-Mode Al2O3/AlGaN/GaN MIS-HEMTs Fabricated by Shallow Recess Combined with Fluorine-Treatment and Deep Recess

Abstract

Enhancement-mode (E-mode) Al2O3/AlGaN/GaN MISHEMTs were fabricated by shallow recess combined with CF4 plasma treatment (SR/F) and deep recess (DR) to compare the effect of each process technique on the device performance. To prevent the device performance degradation induced by plasma damage during gate recess, the digital etch technique was employed. The fabricated E-mode devices have positively shifted threshold voltage, and exhibit lower transconductance (gm) and saturation drain current than depletion-mode devices. Due to the CF4 plasma damage during F-treatment, SR/F shows a sharp drop of gm curve and low saturation drain current. In contrast, DR presents broad gm and high saturation drain current. It is also revealed that the digital etch for gate recess exhibits an isotropic etch profile, consequently increasing the on-resistance. There is no remarkable difference between SR/F and DR in fT and fmax, but DR has a better linearity over SR/F owing to the absence of plasma damage during F-treatment. This results reveal that the DR using digital etch is promising technique to obtain the high performance E-mode MISHEMTs compared to the F-treatment.