Effect of postdeposition annealing on the electrical properties of β-Ga₂O₃ thin films grown on p-Si by plasma-enhanced atomic layer deposition

Ga₂O₃ dielectric thin films were deposited on (111)-oriented p-type silicon wafers by plasma-enhanced atomic layer deposition using trimethylgallium and oxygen plasma. Structural analysis of the Ga₂O₃ thin films was carried out using grazing-incidence x-ray diffraction. As-deposited films were amorphous. Upon postdeposition annealing at 700, 800, and 900 °C for 30 min under N₂ ambient, films crystallized into β-form monoclinic structure. Electrical properties of the β-Ga₂O₃ thin films were then investigated by fabricating and characterizing Al/β-Ga₂O₃/p-Si metal–oxide-semiconductor capacitors. The effect of postdeposition annealing on the leakage current densities, leakage current conduction mechanisms, dielectric constants, flat-band voltages, reverse breakdown voltages, threshold voltages, and effective oxide charges of the capacitors were presented. The effective oxide charges (Q_eff) were calculated from the capacitance–voltage (C-V) curves using the flat-band voltage shift and were found as 2.6 × 10¹², 1.9 × 10¹², and 2.5 × 10¹² cm⁻² for samples annealed at 700, 800, and 900 °C, respectively. Effective dielectric constants of the films decreased with increasing annealing temperature. This situation was attributed to the formation of an interfacial SiO₂ layer during annealing process. Leakage mechanisms in the regions where current increases gradually with voltage were well fitted by the Schottky emission model for films annealed at 700 and 900 °C, and by the Frenkel–Poole emission model for film annealed at 800 °C. Leakage current density was found to improve with annealing temperature. β-Ga₂O₃ thin film annealed at 800 °C exhibited the highest reverse breakdown field value.