Spectrally Distinguished Solar-Blind and Visible Photodetector Based on MOCVD-Grown (111) Facet Single-Crystalline ZnGa₂O₄

ZnGa₂O₄ demonstrates excellent crystalline quality, establishing a heteroepitaxial relationship with the sapphire substrate and exhibiting a 6-fold harmonic symmetry corresponding to the sapphire lattice planes. Cross-sectional transmission electron microscopy analysis reveals the single-crystalline nature of ZnGa₂O₄ films grown on a sapphire substrate using MOCVD. These findings emphasize the critical role of film uniformity in enhancing the performance metrics of unipolar Schottky photodiodes. This unipolar photodiode technique, in which asymmetric Ni/Au and Ti/Au electrodes are on MOCVD-grown single-crystalline ZnGa₂O₄, provides excellent rectification and high-performance solar-blind detection with a selective nature for the solar-blind and visible spectrum in reverse bias. Its exceptional forward bias operation and robust sensitivity make it excellent for sophisticated UV detection systems in harsh situations, improving security, environmental monitoring, and space applications. The photodiode works in forward bias with a rectification ratio of 1 × 10⁵ (±6 V) for the solar-blind spectrum. The photodiode showed a Schottky behavior with an ultralow dark current of 0.2 <i>p</i>A in the forward direction and exhibited an exceptional dual-band UV-vis response with a photoresponsivity of 370 A/W and -3.6 μA/W, a notable photo-to-dark current ratio of 10, a switching speed of 50 ms, ultralow noisy detection with a noise equivalent power of 2.44 × 10^-19 W/Hz^1/2, and an ultrahigh detectivity of 1.23 × 10¹⁷ Jones observed for the solar-blind spectrum. Additionally, the unipolar photodiode showed a unique dual-mode operation: in forward bias, it exhibits positive photoconductivity (PPC) across the spectrum; in reverse bias, it detects ultraviolet light with PPC and visible light with negative photoconductivity. This unique characteristic enables selective detection with rectification ratios of 10⁵ for UV and 74 for visible light, providing a technique for sophisticated photodetection applications that need accurate solar-blind and visible distinction.