Mechanism of charge transfer in injection photodiodes based on the In–$n^+$–CdS-$n$-CdS$_x$Te$_{1-x}$–$p$-Zn$_x$Cd$_{1-x}$Te–Mo structure

Photosensitive In–$n^+$–CdS-$n$-CdS$_x$Te$_{1-x}$–$p$-Zn$_x$Cd$_{1-x}$Te–Mo film structures based on II–VI semiconductors and operating in the wavelength range $\lambda$ = 0.490–0.855 $\mu$m have been fabricated. These structures in the forward current direction at high bias voltages operate as injection photodiodes and exhibit a high integrated sensitivity $S_{\mathrm{int}}\approx$ 700 A/lm (14500 A/W) at room temperature. It has been found that, in the fabricated structures at low illuminance levels and low forward bias voltages (0.05–0.50 V), the diffusion and drift fluxes of nonequilibrium charge carriers are directed toward each other. This effect leads to the sign reversal of the photocurrent, which makes it possible on the basis of these structures to create selective photodetectors with injection properties. In the reverse direction of the photocurrent, these structures also operate in the mode of internal amplification of the primary photocurrent, but the integrated sensitivity in this mode is considerably less than that in the forward current direction.