AlN Spacer-Induced Improvement in DC, RF, and Breakdown Characteristics of AlN Buffered AlGaN/GaN HEMTs

This work presents a comprehensive DC and AC performance analysis of AlN buffered AlGaN/GaN HEMTs without (w/o) and with an AlN spacer using TCAD simulations. The incorporation of the AlN spacer substantially enhances the HEMT performance through improved polarization induced charge confinement in the channel. The spacer HEMT demonstrates an increased drain current (Ids) of 391 mA/mm as relative to 321 mA/mm in the typical device i.e., w/o a spacer HEMT. Furthermore, the introduction of the AlN spacer improves the transconductance from 121 mS/mm for the conventional HEMT without an AlN spacer to 147 mS/mm for the spacer engineered HEMT. A substantial reduction in the OFF-state leakage current from 9.05 × 10–7 2.87 × 10–7 A/mm which leads to nearly one order of magnitude enhancement in the Ion/Ioff current ratio. The breakdown voltage is also enhanced significantly from 586 to 813 V that indicates the superior high voltage capability of a spacer HEMT. In the AC domain, the reduction in gate capacitances including Cgs, Cgd, and Cgg contributes to an improved cut-off frequency (ft) from 1.17 to 1.42 GHz. The observed improvements are primarily attributed to enhanced polarization effects, increased two-dimensional electron gas (2DEG) density, and a reduced parasitic effect because of the AlN spacer. These results highlight the effectiveness of AlN spacer engineering in advancing high RF/frequency and power GaN based HEMT devices.