Interface characteristics of β-Ga₂O₃/Al₂O₃/Pt capacitors after postmetallization annealing

Interface characteristics of frequency dispersion, flatband voltage (Vfb) shift, fixed charge (QIL), and interface state density (Dit) in β-Ga2O3/Al2O3/Pt capacitors were investigated after postmetallization annealing (PMA) at 300 °C in N2 using a conductance method and a photo-assisted capacitance-voltage technique. After PMA, no frequency dispersion was observed, and the QIL and Dit values related to interface states near the conduction band edge (Ec) were significantly reduced to the ranges of -4 to +1 × 1011 cm-2 and 3 to 8 × 1011 cm-2 eV-1 at Ec - E = 0.4 eV, respectively, in the capacitors subjected to a low postdeposition annealing (PDA) temperature region of 300-600 °C. In contrast, a large frequency dispersion, and high QIL (-2 × 1012 cm-2), and Dit (4-5 × 1012 cm-2 eV-1 at Ec - E = 0.4 eV) of the capacitors with a high PDA temperature region of 700-900 °C remained. This difference is considered to be due to hard structural changes at the multilayer level by the interdiffusion of Ga and Al at the β-Ga2O3/Al2O3 interface caused by PDA above 700 °C. In contrast, the average Dit values due to the electrons deeply trapped below the midgap between 2.6 and 3.3 eV decreased from 2 × 1012 to 1 × 1011 cm-2 eV-1 as the PDA temperature was increased from 300 to 900 °C, respectively, before PMA. No significant change in Dit below the midgap was observed, regardless of the PDA temperature after PMA. Note that the PMA treatment effectively improved only the interface properties near the Ec after treatment in the low PDA temperature region below 600 °C.