MOCVD grown normally-OFF type AlGaN/GaN HEMTs on 4 inch Si using p-InGaN cap layer with high breakdown

Abstract

Enhancement mode AlGaN/GaN HEMT devices with a positive threshold voltage and higher gate voltage operation still remains a major issue and challenges the integration of simplified circuit design. The demonstration of normally-OFF operation is difficult because of large amount of polarization charges in AlGaN/GaN hetero-structures. However today it is imperative to demonstrate normally-OFF type transistors in order to simplify the driving circuits for power applications. The already reported devices for enhancement mode have smaller gate bias (VG) swing and quasi-normally-OFF operation. Further, most of the reports on enhancement mode AlGaN/GaN HEMTs were demonstrated on expensive SiC or sapphire substrates. To this day, only one report [1] is available demonstrating the normally-OFF type AlGaN/GaN HEMTs on Si substrate with a maximum possible gate bias of 1 V, threshold voltage (Vth) at 0 V and drain current maximum (IDmax) of 30 mA/mm. The normally-OFF AlGaN/GaN HEMTs grown on Si needs to be improved to give a large VG swing and high IDmax. Therefore here in this report, we are reporting a p-InGaN cap layered AlGaN/GaN normally-OFF type HEMTs on silicon substrate with VG applicable as high as +3.5V without gate leakage. Further we achieved a high breakdown for relatively a small gate-drain length (Lgd) of 3 µm. Demonstrating a normally-OFF type AlGaN/GaN HEMTs on low cost Si substrate, coupled with high breakdown is an important step forward to integrate enhancement and depletion mode devices on Si.