Modulating Oxygen Vacancies in β-Ga2O3 Microflake for High-Responsivity Solar-Blind Photodetectors

Oxygen vacancies are critical in modulating the performance of optoelectronic devices that are based on micro-nano structured oxide semiconductors, primarily owing to the large surface-to-volume ratio of such structures. In this work, we tailored the concentration of oxygen vacancies in $\beta $ -Ga2O3 microflakes through oxygen annealing, thereby significantly improved the responsivity in a metal-semiconductor-metal configurated photodetector. Remarkably, the photodetector, annealed at $400~^{\circ }$ C, exhibited a peak responsivity of 96.40 A/W at 247 nm with a −3 dB cut-off wavelength of 267 nm under 25 V. This remarkable performance exceeds that of most reported metal–semiconductor–metal structured $\beta $ -Ga2O3 micro-and nanostructured photodetectors. The X-ray photoelectron spectroscopy (XPS) together with photoluminescence (PL) spectra reveal that the annealing process contributes to increased oxygen vacancies on the $\beta $ -Ga2O3 surface, indicating that the enhanced responsivity and the improved photosensitivity gain are attributed to more photoionized holes being trapped at the metal/ $\beta $ –Ga2O3 interface under illumination, which reduces the Schottky barrier height (SBH). This is also confirmed by the increase in the contact potential difference (CPD) between metal and $\beta $ -Ga2O3 in Kelvin probe force microscope, which means that the Fermi level of Ga2O3 shifts upward after annealing. The model that explains the significantly enhanced photosensitivity gain through carrier trapping with deep centers is also validated by the concurrently observed longer photocurrent decay time. Our work provided a readily feasible method to improve the photograph response of $\beta $ -Ga2O3 solar blind photodetectors (SBPDs) through modulating oxygen vacancies.