Charge injection in normally-off p-GaN gate AlGaN/GaN-on-Si HFETs

We present an experimental and theoretical investigation aimed at a full understanding of the main charge injection mechanisms involved in enhancement-mode p-GaN gate AlGaN/GaN-on-Si HFETs: Substrate leakage in the off state for large drain-to-source voltage and charge injection in the p-GaN gate in the on state. We find that the leakage current from the substrate in the off state is sustained by field-enhanced carrier generation in the p-type Si substrate and is limited by electron injection through the AIN barrier/silicon interface. We also find that charge injection in the p-GaN during on state can lead to positive or negative variations of the threshold voltage, depending on the occurrence of hole depletion or accumulation in the p-GaN region, respectively, which in turn depends on the balance between hole injection in the p-GaN region through the Schottky gate contact and charge leakage from the p-GaN region to the channel.