Optimized Buffer Stack with Carbon-Doping for Performance Improvement of GaN HEMTs

This paper focuses on determining an optimized value of carbon-doping level in the buffer and corresponding channel thickness to improve the performance of GaN HEMTs in terms of subthreshold slope $(SS)$, breakdown voltage $(V_{BD})$ and transit frequency $(f_{t})$. With the increase in carbon-doping, we observe improvements in $SS$ and $V_{BD}$ while the $f_{t}$ is reduced. However, as the channel thickness increases above a certain thickness, no significant impact of carbon-doping is observed on the characteristics. TCAD simulation is calibrated using experimental data for a device with carbon-doping level of $3\times 10^{18}cm^{-3}$ in the buffer with channel thickness of 500 nm. Using the calibrated device in TCAD, the carbon-doping level and channel thickness are varied to see the effects on different parameters. We observed that an optimized channel thickness of 200 nm with carbon-doping level of $1\times 10^{19}cm^{-3}$ in the buffer yields the best results in terms of $V_{BD}$ and $f_{t}$.