Patent ID: 6885075

Claim:
A photodiode of a bottom incidence type for sensing signal light having a wavelength denoted by λ 2 which is longer than a wavelength of noise denoted by λ 1 (λ 2 >λ 1 ) in an optical communication system using light having wavelengths λ 1 and λ 2 , comprising: a substrate having a top surface and a bottom surface and having a bandgap wavelength shorter than λ 1 and λ 2 ; an annular electrode formed on the bottom surface of the substrate, the annular electrode allowing the signal light λ 2 and the noise λ 1 to enter the substrate; at least an epitaxially-grown absorption layer on the substrate, the absorption layer having a band gap wavelength λg which satisfies λ 1 <λg<λ 2 , whereby the absorption layer absorbs the noise λ 1 and passes the signal light λ 2 ; an epitaxially-grown light receiving layer on the light absorbing layer, the light receiving layer including a pn-junction, a p-region and an n-region having a bandgap wavelength longer than λ 1 and λ 2 , to detect the signal light λ 2 passed by the absorption layer; and a holeless top electrode formed above the p-region of the light receiving layer.