Effect of epitaxial layer's thickness on spectral response of 4H-SiC p-i-n ultraviolet photodiodes

4H-SiC ultraviolet p-i-n photodiodes with four different epitaxial structures were fabricated. The experimental results prove that both a thin P+-type Ohmic contact layer and a thick intrinsic layer were indispensible for a high-performance ultraviolet p-i-n photodiode. A 4H-SiC p-i-n photodiode with responsivity as high as 0.139 A/W at 278 nm incident wavelength was achieved. Meanwhile, within a certain wavelength range, the peak response wavelength of an ultraviolet p-i-n photodiode would be modulated by properly varying the thicknesses of P+-type layer and the intrinsic layer. Moreover, the theoretical calculation was carried out to further authorise the experimental results.