Characteristics of Near-Infrared n-Type Nanocrystalline FeSi$_{2}$/i-Si/p-Type Si Heterojunctions prepared by Facing-Targets Direct Current Sputtering

Nanocrystalline (NC) iron disilicide (FeSi$_{2})$, which comprises crystals with diameters ranging of 3-5 nm, is a new semiconducting material. NC FeSi$_{2}$ possesses the similar semiconducting properties to $\beta $-FeSi$_{2}$. In our previous research, we have successfully deposited NC FeSi$_{2}$ films by facing-targets direct current sputtering using sintered FeSi$_{2}$ targets with a chemical composition between Fe and Si of 1:2. In this study, near-infrared n-type nanocrystalline FeSi$_{2}$/i-Si/p-type Si heterojunction photodiodes were prepared by the same sputtering method. The current-voltage characteristics were measured in the temperature range of 60 - 300 K. With a decrease in the temperature, the dark current was markedly reduced and at 60 K a rectifying current ratio in the dark became more than three orders of magnitude at between applied voltages of $\pm$1 V. The ratio of the photocurrent to the dark current was also dramatically enhanced to be more than three orders of magnitude, and the device detectivity was estimated to be 3.0 $\times$ 10$^{11}$ cm Hz$^{1/2}$/W for 1.31-$\mu $m light at 60 K.