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

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 $I\sim$ 10$^{-8}$–10$^{-7}$ A/cm$^2$ 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 $\sim$ 10$^{-6}$ A/cm$^2$ 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 $S_\lambda$ = 5.0 $\times$ 10$^4$ A/W) and a high integrated sensitivity ($S_{\text{int}}$ = 2.8 $\times$ 10$^4$ A/lm or 4.5 $\times$ 10$^6$ A/W) in the for-ward direction of the current.