Modulating Oxygen Vacancies in <i>β</i>-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 β-Ga<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>O<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> microflakes through oxygen annealing, thereby significantly improved the responsivity in a metal-semiconductor-metal configurated photodetector. Remarkably, the photodetector, annealed at 400°C, exhibited a peak responsivity of 96.40 A/W at 247 nm with a -3dB cut-off wavelength of 267 nm under 25 V. This remarkable performance exceeds that of most reported metal-semiconductor-metal structured β-Ga<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>O<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> micro- and nanostructured photodetectors. The X-ray photoelectron spectroscopy together with Photoluminescence spectra reveal that the annealing process contributes to increased oxygen vacancies on the β-Ga<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>O<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> surface, indicating that the enhanced responsivity and the improved photosensitivity gain are attributed to more photoionized holes being trapped at the metal/β-Ga<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>O<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> interface under illumination, which reduces the Schottky barrier height. This is also confirmed by the increase in the contact potential difference between metal and β-Ga<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>O<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> in Kelvin probe force microscope, which means that the Fermi level of Ga<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>O<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> 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 photo response of β-Ga<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>O<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> solar blind photodetectors through modulating oxygen vacancies.