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

We demonstrated the performance of an Al[sub.2]O[sub.3]/SiO[sub.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[sub.G]) up to 1.5×10[sup.−12]A/mm (@ V[sub.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[sub.2]O[sub.3]/SiO[sub.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[sub.max] × L[sub.G]) was found to reach 27.16 GHz∙µm for the stack layer MOS-HEMT with PGA modulation. The dual surface-treated Al[sub.2]O[sub.3]/SiO[sub.2] stack layer MOS-HEMT with PGA modulation exhibited decent performance with an I[sub.DMAX] of 720 mA/mm, a peak extrinsic transconductance (G[sub.MMAX]) of 120 mS/mm, a threshold voltage (V[sub.TH]) of −4.8 V, a higher I[sub.ON]/I[sub.OFF] ratio of approximately 1.2×10[sup.9], a subthreshold swing of 82 mV/dec, and a cutoff frequency(f[sub.t])/maximum frequency of (f[sub.max]) of 7.5/13.58 GHz.