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

Interface characteristics of frequency dispersion, flatband voltage (V-fb) shift, fixed charge (Q(IL)), and interface state density (D-it) in beta-Ga2O3/Al2O3/Pt capacitors were investigated after postmetallization annealing (PMA) at 300 degrees C in N-2 using a conductance method and a photo-assisted capacitance-voltage technique. After PMA, no frequency dispersion was observed, and the Q(IL) and D-it values related to interface states near the conduction band edge (E-c) were significantly reduced to the ranges of -4 to +1 x 10(11) cm(-2) and 3 to 8 x 10(11) cm(-2) eV(-1) at E-c - E = 0.4 eV, respectively, in the capacitors subjected to a low postdeposition annealing (PDA) temperature region of 300-600 degrees C. In contrast, a large frequency dispersion, and high Q(IL) (-2 x 10(12) cm(-2)), and D-it (4-5 x 10(12) cm(-2) eV(-1) at E-c - E = 0.4 eV) of the capacitors with a high PDA temperature region of 700-900 degrees 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 beta-Ga2O3/Al2O3 interface caused by PDA above 700 degrees C. In contrast, the average D-it values due to the electrons deeply trapped below the midgap between 2.6 and 3.3 eV decreased from 2 x 10(12) to 1 x 10(11) cm(-2) eV(-1) as the PDA temperature was increased from 300 to 900 degrees C, respectively, before PMA. No significant change in D-it 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 E-c after treatment in the low PDA temperature region below 600 degrees C.