Effect of film thickness on photoelectric properties of <inline-formula><tex-math id="Z-20220216211654">\begin{document}${\boldsymbol{\beta}} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="4-20211744_Z-20220216211654.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="4-20211744_Z-20220216211654.png"/></alternatives></inline-formula>-Ga₂O₃ films prepared by radio frequency magnetron sputtering

Abstract

In this work, β-Ga₂O₃ films with different thickness are prepared on (001) sapphire substrates at room temperature by the radio frequency magnetron sputtering technology, then the samples are annealed in an Ar atmosphere at 800 ℃ for 1h. The effects of film thickness on the phase composition, surface morphology, optical property, and photoelectric detection performance are investigated using XRD, SEM, UV-Vis spectrophotometer, PL photoluminescence spectrometer, and Keithley 4200-SCS semiconductor characterization system. The results show that as the film thickness increases, the film crystallinity is improved, films with a thickness of 840 nm exhibit best quality, while those with a thickness of 1050 nm declines a little in quality. The β-Ga₂O₃ films with different thickness exhibit obvious ultraviolet light absorption in the solar-blind region with wavelengths of 200–300 nm, and the bandgap width increases with the film thickness increasing. All the β-Ga₂O₃ films show a broad UV-green light emission peaks in a wavelength range of 350–600 nm. As the film thickness increases, the intensities of the emission peaks of ultraviolet, violet, and blue light are greatly reduced, indicating that oxygen vacancy-related defects (<i>V</i>_O, <i>V</i>_Ga–<i>V</i>_O) are greatly suppressed with film thickness increasing. Solar-blind ultraviolet photodetector is fabricated based on the β-Ga₂O₃ film. Its photoelectric detection performances (the photo-to-dark current ratio, responsivity, detectivity, and external quantum efficiency) also increase first and decrease then with the increase of film thickness. The β-Ga₂O₃ ultraviolet photodetector prepared by a thin film with a thickness of 840 nm exhibits a very low dark current (4.9 × 10^–12 A) under a 5 V bias voltage and an ultraviolet light with a wavelength of 254 nm (600 μW/cm²). It exhibits a high photo-to-dark current ratio of 3.2 × 10⁵, and a short response time of 0.09/0.80 s (rising time) and 0.06/0.53 s ratio (falling time). Its responsivity (<i>R</i>), detectivity (<i><u>D</u></i>^*), and the external quantum efficiency (EQE) are 1.19 mA/W, 1.9 × 10¹¹ Jones, and 0.58%, respectively. The prepared device has quantifiable characteristics, and its photocurrent increases almost linearly with the increase of applied voltage and optical power density, and therefore can work in a linear dynamic region, which indicates that it is very suitable for fabricating the solar-blind ultra-violet detectors.