Injection photodiode based on a $p$-Si–$n$-CdS–$n^+$-CdS structure

An injection photodiode with a high room-temperature rectification factor (10$^5$) is developed based on a $p$-Si–$n$-CdS–$n^+$-CdS structure. It is shown that the light and dark current-voltage characteristics of the structure have identical features. It is found that the mode of “long” diodes is implemented in the structure at current densities of $I$ = 10$^{-2}$ – 5 $\times$ 10$^{-4}$ A/cm$^2$; in this case, the integral $(S_{\mathrm{int}})$ and spectral $(S_{\lambda})$ sensitivities sharply increase. It is shown that $S_{\mathrm{int}}$ = 2.8 $\times$ 10$^4$ A/lm (3 $\times$ 10$^6$ A/W) for an illuminance of $E$ = 0.1 lux and $S_{\lambda}$ = 2.3 $\times$ 10$^4$ A/W under laser irradiation with $\lambda$ = 625 nm and a power of $P$ = 10 $\mu$W/cm$^2$ at a bias voltage of $V$ = 20 V. It is shown that the mechanism of photocurrent amplification is predominantly associated with ambipolar carrier-mobility modulation.