Near-Ideal Subthreshold Swing in InAlN/GaN Schottky Gate High Electron Mobility Transistor Using Carbon-Doped GaN Buffer

This work presents a comparative study of the subthreshold swing (SS) in InAlN/GaN-based high electron mobility transistor (HEMT), with and without carbon doping in the buffer layer. It is observed that devices with carbon-doped (C-doped) buffer exhibit near-ideal SS of close to 60-mV/decade over a wide range of drain voltage for both up and downsweep. The C-doped buffer layer reduces the OFF-state drain leakage current and increases the drain current ON/OFF ratio. TCAD simulation of the vertical electric field under the gate shows that the sample with a C-doped buffer layer has a much lower value of the peak electric field at the drain side edge of the gate, resulting in lower reverse-biased gate leakage current and smaller SS compared to that of the undoped buffer. Moreover, the junction capacitance at the interface of the unintentionally doped GaN (UID:GAN) and the C-doped buffer layer, in series with the depletion capacitance, reduces the overall capacitance, which further improves the SS in the C-doped wafer.