Optimum carrier concentration of the substrate for avalanche photocurrent multiplication in an amorphous SiC:H/amorphous Si:H/crystalline Si heterojunction photodiode

Conditions for the photocurrent multiplication have been investigated for amorphous SiC:H/amorphous Si:H/crystalline Si heterojunction photodiodes, which were fabricated on n-type crystalline Si substrates with different carrier concentrations using an electron cyclotron resonance (ECR) plasma enhanced chemical vapor deposition (CVD) system. The photocurrent multiplication was observed only in the sample on the substrate of carrier concentration of 2×1016 cm−3, while other samples on the substrates of larger and smaller carrier concentration showed no indication of photocurrent multiplication. The multiplication phenomenon depends on the incident light wavelength as that the shorter the wavelength, the larger the multiplication factor. This dependence suggests that the photocurrent increase was caused by the avalanche multiplication in the amorphous Si:H layer. The reason for this phenomenon can be explained by the electric field in the amorphous Si:H layer.