Hiraku Kozuka

Amorphous Avalanche Photodiode with Large Conduction Band Edge Discontinuity

An amorphous avalanche photodiode (APD) with a heterojunction of hydrogenated amorphous silicon carbide (a-SiC:H) and hydrogenated amorphous silicon germanium (a-SiGe:H) was formed. The band gaps of a-SiC:H and a-SiGe:H are 3.5 eV and 1.55 eV, respectively. The discontinuity of conduction bands at the heterojunction is larger than the band gap of a-SiGe:H. In this amorphous APD, photocurrent multiplication is observed under low electric field. The quantum efficiency starts to exceed unity when the conduction band discontinuity becomes larger than the band gap of a lower-gap material, and it is likely to saturate at 2. The slope of photoelectric conversion characteristics is 1.00. The multiplication is explained by the impact ionization process at the band edge discontinuity region.