Change of characteristics of n-GaN MOS capacitors with Hf-rich HfSiO_x gate dielectrics by post-deposition annealing

We investigated the characteristics of n-GaN/Hf_0.64Si_0.36O_x/Pt MOS capacitors fabricated by post-deposition annealing (PDA) at 800 °C in O₂ (PDO), N₂ (PDN), and 3%H₂ (PDH) ambients. After PDO, the Hf_0.64Si_0.36O_x film was partially crystallized and had a thick interfacial layer (6.3 nm) at the n-GaN/Hf_0.64Si_0.36O_x interface, while the Hf_0.64Si_0.36O_x films after PDN and PDH maintained an amorphous structure. Furthermore, the n-GaN/Hf_0.64Si_0.36O_x/Pt MOS capacitors produced by PDN and PDH exhibited superior characteristics, such as a small flat-band voltage (V_fb) hysteresis of +50 mV and + 25 mV, a small V_fb shift of 0.74 V and − 0.06 V, high dielectric constants of 15.1 and 16.0, and high breakdown electric fields of 8.7 and 9.1 MV/cm, respectively. However, the PDH capacitor exhibited an order of magnitude larger D_it than the PDN capacitor, suggesting that a Ga₂O₃ intermediate layer at n-GaN/Hf_0.64Si_0.36O_x interface may be decomposed after PDH and results in significant Ga diffusion into the Hf_0.64Si_0.36O_x films and electrical defects generation at n-GaN/Hf_0.64Si_0.36O_x interface. These strongly indicate that the PDN process can produce superior Hf_0.64Si_0.36O_x films for use as gate dielectrics in GaN power devices.