Off-state Drain Leakage Reduction by Post Metallization Annealing for Al2O3/GaN/AlGaN/GaN MOSHEMTs on Silicon

AlGaN/GaN-based high electron mobility transistors (HEMTs) have demonstrated great potential for power switching and high frequency power amplifier applications. Use of Al2O3 gate dielectric by atomic layer deposition (ALD) to form metal-oxide-semiconductor HEMTs (MOSHEMTs) has been adopted to block the gate leakage and suppress drain current collapse[1-2]. However, adding an insulator between the gate metal and barrier layer creates an extra dielectric/AlGaN or GaN interface which could be problematic. High density interface states at the dielectric/semiconductor interface can lead to serious surface leakage current [3], leading to an increase of the off-state drain leakage current. In this work, we investigated the effects of post metallization annealing (PMA) on the reduction of Ioff for Al2O3/GaN/AlGaN/GaN MOSHEMTs. It was found that a PMA at 500 °C can reduce the Ioff by 3 orders of magnitude. A high on/off current ratio of 108 and a steep subthreshold swing (SS) of 71 mV/dec were achieved. A reduction in the accumulation capacitance of the MOS capacitor (MOSCAP) after 500 °C PMA revealed partial oxidation of the GaN surface. This suggests that elimination of the conduction path at the Al2O3/GaN interface by annealing might be the reason for the significantly reduced Ioff. The AlGaN/GaN heterostructure was grown on a 6-inch n-type Si wafer by metal-organic chemical vapor deposition (MOCVD). As shown in Fig.1. (a), the epilayer, from bottom to top, consists of 1.7 µm graded AlGaN buffer, 1.2 µm undoped GaN buffer, 1 nm AlN spacer and 30 nm Al0.25Ga0.75N barrier and 2 nm GaN cap. Hall measurements showe