Oxygen Plasma Treated Aluminum as a Gate Dielectric for AlGaN/GaN High Electron Mobility Transistors

Abstract

AlGaN/GaN high electron mobility transistors (HEMTs) grown on 4 in. silicon substrates were demonstrated using different treatments at the Schottky gate terminal, namely (i) a regular Schottky contact made of Pd/Ti/Au (HEMT), (ii) an Al-based metal-oxide-semiconductor high electron mobility transistor (MOS-HEMT) using 3 nm Al/Pd/Ti/Au, and (iii) a plasma oxidized 3 nm Al/Pd/Ti/Au (plasma treated MOS-HEMT). A high drain current density (Idsmax)(Idsmax) of 1086 mA/mm and a transconductance (gmmax)(gmmax) of 209 mS/mm were obtained for Al-based MOS-HEMTs. In the process of plasma oxidized Al, the aluminum-based oxide formed was identified as Al2O3Al2O3 by X-ray photoelectron spectrum measurements. For HEMTs with regular Schottky contact, a gate bias beyond +1.5V+1.5V leads to excess gate leakage limiting the gate bias application. However, for the MOS-HEMTs, a gate bias as high as +3.5V+3.5V could be applied without any gate leakage. Further, a low two-terminal gate leakage was observed for our MOS-HEMTs. A two-dimensional electron gas channel at an increased depth was observed for the MOS-HEMTs because of an insulating oxide layer at the Schottky contact. The out-diffusion of oxide states at the AlGaN barrier layer into thin Al facilitates the formation of Al2O3Al2O3 as a gate dielectric for AlGaN/GaN HEMTs.