Solar-Blind Photodetector with High Avalanche Gains and Bias-Tunable Detecting Functionality Based on Metastable Phase α-Ga₂O₃/ZnO Isotype Heterostructures

The metastable α-phase Ga₂O₃ is an emerging material for developing solar-blind photodetectors and power electronic devices toward civil and military applications. Despite its superior physical properties, the high quality epitaxy of metastable phase α-Ga₂O₃ remains challenging. To this end, single crystalline α-Ga₂O₃ epilayers are achieved on nonpolar ZnO (112̅0) substrates for the first time and a high performance Au/α-Ga₂O₃/ZnO isotype heterostructure-based Schottky barrier avalanche diode is demonstrated. The device exhibits self-powered functions with a dark current lower than 1 pA, a UV/visible rejection ratio of 10³ and a detectivity of 9.66 × 10¹² cm Hz1/2 W⁻¹. Dual responsivity bands with cutoff wavelengths at 255 and 375 nm are observed with their peak responsivities of 0.50 and 0.071 A W⁻¹ at -5 V, respectively. High photoconductive gain at low bias is governed by a barrier lowing effect at the Au/Ga₂O₃ and Ga₂O₃/ZnO heterointerfaces. The device also allows avalanche multiplication processes initiated by pure electron and hole injections under different illumination conditions. High avalanche gains over 10³ and a low ionization coefficient ratio of electrons and holes are yielded, leading to a total gain over 10⁵ and a high responsivity of 1.10 × 10⁴ A W⁻¹. Such avalanche heterostructures with ultrahigh gains and bias-tunable UV detecting functionality hold promise for developing high performance solar-blind photodetectors.