Barrier and channel thickness engineering to optimize fin height for enhancement mode Al_0.3Ga_0.7N/GaN FinHEMT

Abstract

In this work, a thorough analysis of the Al0.3Ga0.7N/GaN FinHEMT structure has been performed using three‐dimensional numerical simulations to achieve enhancement mode (E‐mode) operation. In the proposed optimized structure, the fin height (HFin) is comprised of 7 nm critical strained AlGaN barrier layer with 30% Al mole fraction and 63 nm GaN channel layer having a fixed fin width (WFin) of 160 nm. The two‐dimensional electron gas (2DEG) concentration near the hetero interface is found to vary inversely with HFin of the proposed structure. The 2DEG variation was compared between fin‐shaped full tri‐gate approach and variable side gate length tri‐gate design counterpart for a fixed HFin of 70 nm. We achieved an improved threshold voltage of −0.2 V in the optimized HFin structure as compared to −1.45 V obtained in the unoptimized structure as reported earlier. Further, upon decreasing WFin to 40 nm in the same structure having optimized HFin of 70 nm, an E‐mode operation was achieved with a positive threshold voltage of 0.4 V. The positive shift in threshold voltage is explained with the help of necessary energy band diagram.