Defect evolution of oxygen induced Vth-shift for ON-state biased AlGaN/GaN HEMTs.

The origin of the threshold voltage (V_th) shift that occurs in ON-state biased AlGaN/GaN high-electron mobility transistors (HEMTs) is proposed in terms of experimental researches and first-principles calculations. Experimentally, ∼20% negative shift of the V_th is found for the 0.2 μm gate length T-gate AlGaN/GaN HEMT under the ON-state stress. 1/f noise measurements are carried out to investigate the evolution of defect distribution in the GaN channel, which indicates that the V_th shift is accompanied by the diminishing of the defect level of E_v + 0.8 eV. Combined with first-principles studies based on hybrid functionals defect calculations, we find that the defect evolution of O from negatively charged V_Ga-O_N to neutral O_N-H gives rise to the decrease in acceptors in the GaN channel and thus the negative shift of V_th. Our work indicates that the strengthening of oxygen-related defects in GaN during material growth and device fabrication would improve the reliability of AlGaN/GaN HEMTs. [ABSTRACT FROM AUTHOR]