In this study, magnesium-doped gallium oxide (Ga2O3:Mg) films with various Mg contents were deposited by a plasma-enhanced atomic layer deposition (PE-ALD) system and were used as an active layer of metal-semiconductor-metal ultraviolet C photodetectors (MSM UVC-PDs). Compared with Ga element, owing to the lower electronegativity of Mg element, Mg–O bonds were more easily formed than Ga–O bonds. Consequently, oxygen vacancies could be reduced to improve properties. By using the measurement of X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL), the results verified that Ga2O3:Mg films with Mg content of 3.28 at.% had the lowest oxygen vacancy density. The cut-off wavelength of the devices was blue-shifted from 250 nm to 220 nm by increasing Mg content from 0 at.% to 5.22 at.%. The maximum photoresponsivity of 22.06, 10.24, 6.89, and 1.67 A/W was obtained for the devices with the Mg content of 0 at.%, 1.91 at.%, 3.28 at.%, and 5.22 at.%, respectively. The corresponding UV–visible rejection ratio was 3.56 × 104, 3.86 × 104, 4.42 × 104, and 3.48 × 103, respectively. The flicker noise was the dominant noise. By appropriately doping the Mg content in Ga2O3 films, the detectivity of the MSM UVC-PDs was effectively improved.
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