Remarkable Reduction in I G with an Explicit Investigation of the Leakage Conduction Mechanisms in a Dual Surface-Modified Al 2 O 3 /SiO 2 Stack Layer AlGaN/GaN MOS-HEMT.

We demonstrated the performance of an Al 2 O 3 /SiO 2 stack layer AlGaN/GaN metal-oxide semiconductor (MOS) high-electron-mobility transistor (HEMT) combined with a dual surface treatment that used tetramethylammonium hydroxide (TMAH) and hydrochloric acid (HCl) with post-gate annealing (PGA) modulation at 400 °C for 10 min. A remarkable reduction in the reverse gate leakage current (I G ) up to 1.5×10-12 A/mm (@ V G = -12 V) was observed in the stack layer MOS-HEMT due to the combined treatment. The performance of the dual surface-treated MOS-HEMT was significantly improved, particularly in terms of hysteresis, gate leakage, and subthreshold characteristics, with optimized gate annealing treatment. In addition, an organized gate leakage conduction mechanism in the AlGaN/GaN MOS-HEMT with the Al 2 O 3 /SiO 2 stack gate dielectric layer was investigated before and after gate annealing treatment and compared with the conventional Schottky gate. The conduction mechanism in the reverse gate bias was Poole-Frankel emission for the Schottky-gate HEMT and the MOS-HEMT before annealing. The dominant conduction mechanism was ohmic/Poole-Frankel at low/medium forward bias. Meanwhile, gate leakage was governed by the hopping conduction mechanism in the MOS-HEMT without gate annealing modulation at a higher forward bias. After post-gate annealing (PGA) treatment, however, the leakage conduction mechanism was dominated by trap-assisted tunneling at the low to medium forward bias region and by Fowler-Nordheim tunneling at the higher forward bias region. Moreover, a decent product of maximum oscillation frequency and gate length (f max × L G ) was found to reach 27.16 GHz∙µm for the stack layer MOS-HEMT with PGA modulation. The dual surface-treated Al 2 O 3 /SiO 2 stack layer MOS-HEMT with PGA modulation exhibited decent performance with an I DMAX of 720 mA/mm, a peak extrinsic transconductance (G MMAX ) of 120 mS/mm, a threshold voltage (V TH ) of -4.8 V, a higher I ON /I OFF ratio of approximately 1.2×109, a subthreshold swing of 82 mV/dec, and a cutoff frequency(f t )/maximum frequency of (f max ) of 7.5/13.58 GHz.