Operational frequency degradation induced trapping in scaled GaN HEMTs

Cut-off frequency increase from 12.1 GHz to 26.4 GHz, 52.1 GHz and 91.4 GHz is observed when the 1 μm gate length GaN HEMT is laterally scaled down to L_G = 0.5 μm, L_G = 0.25 μm and L_G = 0.125 μm, respectively. The study is based on accurately calibrated transfer characteristics (I_D-V_GS) of the 1 μm gate length device using Silvaco TCAD. If the scaling is also performed horizontally, proportionally to the lateral (full scaling), the maximum drain current is reduced by 38.2% when the gate-to-channel separation scales from 33 nm to 8.25 nm. Degradation of the RF performance of a GaN HEMT due to the electric field induced acceptor traps experienced under a high electrical stress is found to be about 8% for 1 μm gate length device. The degradation of scaled HEMTs reduces to 3.5% and 7.3% for the 0.25 μm and 0.125 gate length devices, respectively. The traps at energy level of E_T = E_V + 0.9 eV (carbon) with concentrations of N_IT = 5 × 10¹⁶cm^? 3, N_IT = 5 × 10¹⁷cm^? 3 and N_IT = 5 × 10¹⁸cm^? 3 are located in the drain access region where highest electrical field is expected. The effect of traps on the cut-off frequency is reduced for devices with shorter gate lengths down to 0.125 μm.