Investigation on AZO/4H-SiC n-i-p ultraviolet photodiodes with high response via Al-composition engineering

Transparent conductive materials can be employed in advanced ultraviolet (UV) photodetectors for high performance. To fabricate an Al-doped ZnO (AZO)/4H-SiC n-i-p UV photodiode, an ultrathin AZO film is studied and utilized. A range of Al in AZO content from 3.46% to 7.36% is investigated. As the Al content increases, the bandgap of the AZO film expands, resulting in higher UV transmittance. However, the film's resistivity increased correspondingly. By optimization, A 25 nm thick AZO film with a 6.00% Al content demonstrates a notable 92% transmittance at 280 nm wavelength and an electrical resistivity of 0.131 Ω cm. By using the AZO film as the n-type layer, the AZO/4H-SiC n-i-p ultraviolet photodiode achieved a low dark current of 0.245 pA at −10 V and a high spectral response peak of 0.181 A/W at 290 nm wavelength, corresponding to a quantum efficiency of 77.5%, which is better than that of the conventional pure 4H-SiC n-i-p UV photodiode.