Effect of pulse time control on the structural growth characteristics and optical properties of Ga2O3 thin films prepared by thermal atomic layer deposition (T-ALD)

The synthesis of gallium oxide (Ga₂O₃) thin films has predominantly utilized ozone (O₃) or O₂ plasma as oxygen sources. However, the impact of H₂O as an oxygen precursor on the properties of Ga₂O₃ films has not been extensively explored. In this study, we employ thermal atomic layer deposition (T-ALD) with trimethylgallium (TMG) and water (H₂O) as precursors to systematically investigate the growth characteristics of Ga₂O₃ films on sapphire substrates at a constant temperature of 450 °C. The H₂O pulse duration is varied between 0.1 and 0.5 s. Our results reveal that the Ga₂O₃ films exhibit the α-phase when the H₂O pulse duration ranges from 0.1 to 0.3 s. As the H₂O pulse duration increases, the films undergo a transition to an amorphous structure, accompanied by the formation of significant oxygen vacancies. The maximum film roughness of 0.531 nm is observed at a pulse duration of 0.2 s, while the highest bandgap of 5.53 eV is achieved at a pulse duration of 0.3 s. Under ultraviolet illumination with a power intensity of 224 μW/cm², the solar-blind ultraviolet detector demonstrates a photocurrent of 4.7 × 10⁻⁷ A, a dark current of 4.2 × 10⁻⁹ A, and a maximum on/off ratio of 112, with a responsivity of 0.6 mA/W. The device exhibits a response time (τ_r) of 0.08 s and a decay time (τd) of 5.20 s at a bias voltage of 5 V, along with persistent photoconductivity (PPC).