The Impact of Non-Uniform Distribution of Radiation-Induced Defects on the Electrical Performance of AlGaN/GaN HEMTs

This study investigates AlGaN/GaN high-electron-mobility transistors (HEMTs) irradiated with chlorine ions of varying energies, which introduces depth-dependent non-uniform defects beneath the gate electrode. By combining experimental and simulation methods, we systematically analyze three distinct degradation phenomena: non-uniform degradation in transfer characteristics, threshold voltage (V_th) shift saturation, and peak transconductance (G_M) collapse. Through current deep-level transient spectroscopy (I-DLTS), electrical performance measurement, and technology computer aided design (TCAD) device simulation, along with band theory analysis, it is found that high fluence chlorine irradiation generates Fe_Ga-V_N defects (E_C-0.5 eV) in the GaN layer, inducing Fermi-level pinning at these trap states. The increased defect concentration causes interfacial band bending and reduces Two-dimensional electron gas (2DEG) density. Donor defect E1 near the AlGaN/GaN interface is identified as the primary contributor to V_th shift saturation behavior. Additionally, VN- V_N (+1/+2) defects (EC -0.77 eV) in the AlGaN barrier layer become activated when the gate voltage exceeds a critical value, significantly enhancing electron capture from the conduction band. This spatially non-uniform trapping process leads to gate-voltage-dependent degradation of drain current (I_ds) and ultimately results in the phenomenon of peak G_M collapse.