Effects of surface passivation films on AlGaN/GaN HEMT with MIS gate structure

We investigated the effect of ebeam-deposited SiNx, SiO2, and TiO2 passivation films on the AlGaN/GaN HEMT structure. The AlGaN/GaN heterojunction structure was grown on a sapphire substrate by. metal organic chemical vapor deposition. The sheet resistance of the AlGaN/GaN HEMT structure was 420-510 Omega/square. TiO2, SiNx and SiO2 passivation films were employed as the insulator in MIS gate structure. All passivation films were deposited by electron beam evaporation at 200 degrees C. The thickness of SiNx SiO2 and TiO2 passivation films were 15, 10 and 15 run, respectively. The relative dielectric constants of the deposited SiNx, SiO2 and TiO2 were measured to be 4, 7 and 80, respectively by fabricating the capacitance structures. The sheet resistance was changed after the deposition of the insulator films. We found to be 512, 628 and 992 Omega/square for the SiNx, SiO2 and TiO2 films, respectively. We considered that the surface passivation using the TiO2 and SiO2 films reduces the carrier density in the AlGaN/GaN channel.