Influence of post-deposition annealing on characteristics of Pt/Al₂O₃/β-Ga₂O₃ MOS capacitors

We investigated the influence of post-deposition annealing (PDA) temperature on the characteristics of Pt/Al₂O₃/n-β-Ga₂O₃ MOS capacitors. Electrical properties such as the flatband voltage (V_fb) shift, V_fb hysteresis, fixed charge (Q_IL), interface state density (D_it) and leakage current could be divided into two groups such as a low PDA temperature range below 600 °C and a high temperature range above 700 °C. The capacitors with a low PDA temperature exhibited superior electrical properties compared to the capacitors with a high PDA temperature, excluding leakage current property. We found that 700 °C is a critical PDA temperature because Al₂O₃ film starts to crystallize and solid-solution reaction of Al₂O₃ gate insulator and β-Ga₂O₃ substrate also occurs, resulting in Ga diffusion into the Al₂O₃ film and large roughness at Al₂O₃/β-Ga₂O₃ interface. These lead to a large D_it and positive V_fb shift at 700 °C. Even in a low PDA temperature range, it is clear that capacitor at 300 °C exhibited superior electrical properties of V_fb shift of −0.23 V, Q_IL of 4.1 × 10¹¹ cm⁻², and D_it (1.6 × 10¹² eV⁻¹ cm⁻² at E_c-E = 0.4 eV). Based on these experimental data, lower PDA temperature of 300 °C is suitable.