Characterization of trap states in AlN/GaN superlattice channel high electron mobility transistors under total-ionizing-dose with ⁶⁰Co γ-irradiation

In this Letter, the effects of trap states in AlN/GaN superlattice channel HEMTs (high electron mobility transistors) under total ionizing dose with γ-irradiation have been systematically investigated. After 1 Mrad γ-irradiation with a dose rate of 50 rad/s, negative drifts in threshold voltage and C–V characteristics are observed. Simultaneously, the two-dimensional electron gas sheet density of the upper channel increases from 5.09 × 10¹² to 5.47 × 10¹² cm⁻², while that of the lower channel decreases from 4.41 × 10¹² to 3.86 × 10¹² cm⁻², respectively. Furthermore, frequency-dependent capacitance and conductance measurements are adopted to investigate the evolution of trap states in an electron channel. The trap state density (D_T = 0.21–0.88 × 10¹³ cm⁻² eV⁻¹) is over the E_T range from 0.314 to 0.329 eV after irradiation for the upper channel, while the trap state in the lower channel decreases from 4.54 × 10¹¹ cm⁻² eV⁻¹ at E_T = 0.230 eV to 2.38 × 10¹¹ cm⁻² eV⁻¹ at E_T = 0.278 eV. The density (1.39–1.54 × 10¹¹ cm⁻² eV⁻¹) of trap states with faster τ_T (0.033–0.037 μs) generated in a lower channel is located at shallower E_T between 0.227 and 0.230 eV. The results reveal the mechanism of trap states in the channel, affecting the performance of HEMTs, which can provide a valuable understanding for hardening in space radiation.