Deep-Ultraviolet Photodetectors Based on Epitaxial ZnGa2O4 Thin Films

Abstract

A single-crystalline ZnGa2O4 epilayer was successfully grown on c-plane (0001) sapphire substrate by metal-organic chemical vapor deposition. This epilayer was used as a ternary oxide semiconductor for application in high-performance metal–semiconductor–metal photoconductive deep-ultraviolet (DUV) photodetectors (PDs). At a bias of 5 V, the annealed ZnGa2O4 PDs showed better performance with a considerably low dark current of 1 pA, a responsivity of 86.3 A/W, cut-off wavelength of 280 nm, and a high DUV-to-visible discrimination ratio of approximately 107 upon exposure to 230 nm DUV illumination than that of as-grown ZnGa2O4 PDs. The as-grown PDs presented a dark current of 0.5 mA, a responsivity of 2782 A/W at 230 nm, and a photo-to-dark current contrast ratio of approximately one order. The rise time of annealed PDs was 0.5 s, and the relatively quick decay time was 0.7 s. The present results demonstrate that annealing process can reduce the oxygen vacancy defects and be potentially applied in ZnGa2O4 film-based DUV PD devices, which have been rarely reported in previous studies.

Zinc Gallium Oxide—A Review from Synthesis to Applications

“…MSM photodetectors possess low capacitance and have the potential for large-area detectors [89]. Therefore, MSM ZnGa 2 O 4 photodetectors in Reference [20,85,90,91] are taken into consideration. Their process parameters and optimized performances are listed in Tables 7 and 8, respectively.…”

“…With the application of forward and reverse bias, the MSM structure may have an almost identical I-V curve. The current increases with the applied bias voltage due to the increased carrier drift velocity [91]. With no light illumination on a semiconductor, a current exists in MSM PDs called dark current (I dark ).…”

“…For better photodetector performance, the ratio of I ph /I dark should be as large as possible. Tsai et al found that the dark current of ZnGa 2 O 4 MSM PD fabricated with as-deposited film exhibited the I ph /I dark of one order (~10 1 order) of magnitude, while ZnGa 2 O 4 MSM PD fabricated with post-annealed ZnGa 2 O 4 film at a temperature of 800 • C exhibited the ratio I ph /I dark of 8 orders (~10 8 order) [91]. The reason behind the reduction of the dark current is post-annealing, which reduced the defects and improved the ZnGa 2 O 4 MSM PDs performance.…”

“…where, P inc is the incident optical power in Watts (W), I ph is the photocurrent in amperes (A) [91].…”

Structural Characteristics and Photoluminescence Properties of Sputter-Deposition ZnGa2O4 Thin Films on Sapphire and Si(100) Substrates

“…Wu et al discussed the gas sensor properties based on epitaxial ZnGa 2 O 4 thin film grown on sapphire substrate by MOCVD [13]. Tsai et al reported that the successful manufacture of deep-UV ZnGa 2 O 4 photodetectors and investigate the effect of annealing temperature on the devices electrical properties [14]. Shen et al showed that metal-oxide-semiconductor field-effect transistor films are a promising option in power device applications [15].…”