Study of the Effect of Etching Under the Source/Drain Area on the DC Characteristics of GaN HEMTs

In this study, we employed Silvaco TCAD simulation software to conduct numerical simulations on the DC characteristics of conventional and circular p-GaN AlGaN/GaN HEMTs. The influence of etching under the source/drain area the current characteristics of HEMTs with three different structures was investigated, and the effects of varying etching depths were compared. The results indicate that, at a gate voltage of 5V, etching increased the maximum saturated drain current of the conventional HEMT from 884 mA/mm to 1285 mA/mm, and the maximum transconductance from 245 mS/mm to 318 mS/mm, with a slight increase in on-state conductance. For the source-centered circular HEMT, the maximum saturated drain current rose from 870 mA/mm to 1190 mA/mm, and the maximum transconductance increased from 284 mS/mm to 336 mS/mm, while the on-state conductance remained nearly unchanged. Due to the concentrated electric field distribution in the central region of the drain-centered circular HEMT, the improvement from etching was less pronounced. Comparison of device performance at different etching depths revealed that the optimization effect was diminished when the metalsemiconductor interface was etched down to the AlGaN/GaN heterojunction interface. The simulation results suggest that proper selection of etching depth can significantly enhance the DC performance of the devices. Considering both performance improvements and breakdown voltage, the etched source-centered circular HEMT is expected to offer the best practical performance.