Patent ID: 7829915

Claim:
An avalanche photodiode, comprising an n-type ohmic contact layer; a transport layer; a first graded bandgap layer; an absorption layer; a second graded bandgap layer; an n-type charge layer; a multiplication layer; and a p-type ohmic contact layer, wherein, from top to bottom, said avalanche photodiode comprises said n-type ohmic contact layer, said transport layer, said first graded bandgap layer, said absorption layer, said second graded bandgap layer, said n-type charge layer, said multiplication layer and said p-type ohmic contact layer, and said avalanche photodiode thus obtains an epitaxial structure having an n-i-n-i-p junction; wherein said epitaxial structure of said avalanche photodiode is grown on a diode substrate; wherein said n-type ohmic contact layer is made of an n + -type doped semiconductor and is grown on said transport layer to be an n-type electrode; wherein each of said transport layer, said first graded bandgap layer, said absorption layer and said second graded bandgap layer is made of a semiconductor selected from a group consisting of an undoped semiconductor and an n − -type doped semiconductor; wherein said transport layer is grown on said first graded bandgap layer to reduce capacitance; wherein said first graded bandgap layer is grown on said absorption layer to change a wide energy gap into a narrow energy gap; wherein said absorption layer is grown on said second graded bandgap layer to absorb incident light to obtain carrier; wherein said second graded bandgap layer is grown on said n-type charge layer to change a narrow energy gap in to a wide energy gap; wherein said n-type charge layer is made of an n + -type doped semiconductor and is grown on said multiplication layer to concentrate electric field on said multiplication layer; wherein said multiplication layer is made of an undoped semiconductor and is grown on said p-type ohmic contact layer to amplify a current by accepting said carrier; wherein said p-type ohmic contact layer is made of a p + -type doped semiconductor and is grown on said semiconductor substrate to be a p-type electrode; and wherein said semiconductor substrate is selected from a group consisting of a semi-insulating substrate and a conductive substrate.