MOCVD growth of (AlxGa1−x)2O3 (x = 0–0.77) alloyed films for deep UV photodetection applications

(AlxGa1−x)2O3 alloy thin films with the tuning bandgap in a range of 4.95–6.26 eV have been achieved by adjusting the Al composition (x ≈ 0–0.77) grown on a c-plane sapphire substrate via metal-organic chemical vapor deposition. With the increase in the bandgap, the fabricated metal–semiconductor–metal (MSM) photodetectors exhibit a gradual blueshift of the spectral response wavelengths from 250 to 198 nm. X-ray diffraction characterization results indicated that the crystal structure of the films transformed from a single monoclinic β-phase (x ≤ 0.57) to a β/γ dual-phase coexistence state (x ∼ 0.67–0.77) with increasing Al composition. The optimal surface morphology and crystalline quality of the films were obtained at an Al composition of 0.20. Combined with the valence-band x-ray photoelectron spectroscopy and bandgap analysis results, it is found that the introduction of Al causes an upward shift of the conduction band minimum relative to the Fermi level, which is consistent with the observed increase in the optical bandgap and blueshift of the spectral response edge. Oxygen vacancy (VO) analysis demonstrates that the VO defect concentration first decreases and then increases with increasing Al composition. Based on these results, the evolution mechanism of VO defects is elucidated, and their intrinsic correlations with lattice strain, phase transition, and thin-film crystalline quality are discussed. The fabricated MSM photodetectors exhibited an excellent comprehensive performance at a bias of 10 V, with the dark current below 10 fA, the specific detectivity of 6.58 × 1014 Jones, and the UV-visible rejection ratio as high as 9.07 × 107. Under 185 nm illumination, the photocurrent to dark current ratio of the device with a high Al composition (x = 0.77) still remains around 1.18 × 102, indicating its excellent detection sensitivity and anti-interference capability in the deep ultraviolet to vacuum ultraviolet wavebands.