Self-Powered Solar-Blind Photodetectors Based on α/β Phase Junction of Ga 2 O 3

TLDR: In this paper, two different types of self-powered solar-blind photodetectors, in the form of solid-state type and photoelectrochemical type, are constructed and realized.

Abstract: Self-powered ${\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$-based solar-blind photodetectors have received attention recently due to the increased demand for energy saving, miniaturization, and high efficiency in devices. An ideal device structure consisting of a ${\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$-based p-n junction is still difficult to obtain, since p-type doping is a major challenge. Although self-powered devices based on heterojunction are promising, there are two fatal disadvantages: (1) photosensitivity of the non-solar-blind region, on account of the narrower band gap of the heterojunction materials; and (2) poor quality of the epitaxial film due to lattice mismatch. In view of the various polymorphs of ${\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$, we propose constructing a structure consisting of a ${\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$ phase junction with \ensuremath{\alpha} and \ensuremath{\beta} phases (\ensuremath{\alpha}/\ensuremath{\beta} phase junction) for self-powered solar-blind photodetectors. The small lattice mismatch and similar band gap between \ensuremath{\alpha}- and \ensuremath{\beta}-${\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$ will solve the two problems outlined above. The formation of \ensuremath{\alpha}- and \ensuremath{\beta}-${\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$ is expected to result in a type-II band alignment, promoting separation of photogenerated carriers, which transfer through the junction to the corresponding electrodes. Herein, the \ensuremath{\alpha}/\ensuremath{\beta} phase junction of ${\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$ vertically aligned nanorod arrays with a thickness-controllable \ensuremath{\beta}-${\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$ shell layer are fabricated by a low-cost and simple process of hydrothermal and postannealing treatment. Two different types of self-powered \ensuremath{\alpha}/\ensuremath{\beta}-${\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$ phase junction-based photodetectors, in the form of solid-state type and photoelectrochemical type, are constructed and realized. Our analysis shows that the constructed photodetectors are capable of highly efficient detection of solar-blind signal without any bias voltage. This work demonstrates the usefulness of using the \ensuremath{\alpha}/\ensuremath{\beta}-${\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$ phase junction in a self-powered solar-blind photodetector, which is not only energy efficient, but also potentially workable in outer space, at the south and north pole, and other harsh environments without external power for a long time.