Mechanism of charge transfer in injection photodetectors based on the M(In)-n-CdS-p-Si-M(In) structure

Abstract

The mechanism of charge transfer in a new-type selective (with a tunable spectrum) injection photodetector based on the M(In)-n-CdS-p-Si-M(In) structure with the internal amplification has been analyzed. It has been shown that, in this structure, there is a mutual compensation of the drift and diffusion fluxes of charge carriers. The counter drift and diffusion fluxes of nonequilibrium carriers at reverse current densities I ∼ 10−8–10−7 A/cm2 lead to the appearance of sign-reversal points of the photosensitivity in the short-wavelength and long-wavelength regions of the spectrum. The mutual compensation of the counter drift and diffusion current fluxes at current densities of the order of ∼10−6 A/cm2 leads to the appearance of a sublinear section in the reverse current-voltage characteristic over a wide range of bias voltages. It has been found that the n-SdS-p-Si heterojunction has a low density of surface states at the interface. This makes it possible to develop an injection photodetector based on the considered structure with a high spectral sensitivity Sλ = 5.0 × 104 A/W) and a high integrated sensitivity Sint = 2.8 × 104 A/lm or 4.5 × 106 A/W in the for-ward direction of the current.