Performance Enhancement in N Plasma Modified AlGaN/AlN/GaN MOS-HEMT Using HfAlO Gate Dielectric with Γ-Shaped Gate Engineering.

In this paper, we have demonstrated the optimized device performance in the Γ-shaped gate AlGaN/AlN/GaN metal oxide semiconductor high electron mobility transistor (MOS-HEMT) by incorporating aluminum into atomic layer deposited (ALD) HfO and comparing it with the commonly used HfO gate dielectric with the N surface plasma treatment. The inclusion of Al in the HfO increased the crystalline temperature (~1000 °C) of hafnium aluminate (HfAlO) and kept the material in the amorphous stage even at very high annealing temperature (>800 °C), which subsequently improved the device performance. The gate leakage current (I) was significantly reduced with the increasing post deposition annealing (PDA) temperature from 300 to 600 °C in HfAlO-based MOS-HEMT, compared to the HfO-based device. In comparison with HfO gate dielectric, the interface state density (D) can be reduced significantly using HfAlO due to the effective passivation of the dangling bond. The greater band offset of the HfAlO than HfO reduces the tunneling current through the gate dielectric at room temperature (RT), which resulted in the lower I in Γ-gate HfAlO MOS-HEMT. Moreover, I was reduced more than one order of magnitude in HfAlO MOS-HEMT by the N surface plasma treatment, due to reduction of N vacancies which were created by ICP dry etching. The N plasma treated Γ-shaped gate HfAlO-based MOS-HEMT exhibited a decent performance with I of 870 mA/mm, G of 118 mS/mm, threshold voltage (V) of -3.55 V, higher I/I ratio of approximately 1.8 × 10, subthreshold slope (SS) of 90 mV/dec, and a high V of 195 V with reduced gate leakage current of 1.3 × 10 A/mm.