Thickness effect on solar-blind photoelectric properties of ultrathin β-Ga ₂O ₃ films prepared by atomic layer deposition

The β-Ga ₂O ₃ films with different thicknesses are prepared by an atomic layer deposition system. The influence of film thickness on the crystal quality is obvious, indicating that the thicker films perform better crystal quality, which is verified from x-ray diffraction (XRD) and scanning electron microscope (SEM) results. The Ga ₂O ₃-based solar blind photodetectors with different thicknesses are fabricated and studied. The experimental results show that the responsivity of the photodetectors increases exponentially with the increase of the film thickness. The photodetectors with inter-fingered structure based on 900 growth cycles β-Ga ₂O ₃ active layers (corresponding film thickness of 58 nm) exhibit the best performances including a low dark current of 134 fA, photo-to-dark current ratio of 1.5 × 10 ⁷, photoresponsivity of 1.56 A/W, detectivity of 2.77 × 10 ¹⁴ Jones, and external quantum efficiency of 764.49% at a bias voltage of 10 V under 254-nm DUV illumination. The photoresponse rejection ratio ( R ₂₅₄/ R ₃₆₅) is up to 1.86 × 10 ⁵. In addition, we find that the photoelectric characteristics also depend on the finger spacing of the MSM structure. As the finger spacing decreases from 50 μm to 10 μm, the photoresponsivity, detectivity, and external quantum efficiency increase significantly.