Tunnelling in heterojunction of n-type hydrogenated nanocrystalline silicon film with p+-type crystal silicon

Abstract

N-type hydrogenated nanocrystalline silicon (nc-Si:H) films were deposited by the plasma-enhanced chemical vapour deposition (PECVD) technique on p+-type crystal silicon (c-Si) substrates; then a kind of heterojunction structure of (n)nc-Si:H/(p+)c-Si was obtained. Both negative resistance in forward current–voltage (I–V) measurements and current staircases in reverse I–V experimental curves were observed from this heterojunction of (n)nc-Si:H/(p+)c-Si at 77 K. It was verified by the electrical experiments that this structure is a semiconductor heterojunction tunnelling diode. The forward current was considered to be dominated by interband tunnelling, excess and thermionic emission component. Within the reverse bias ranging from around 0 to −13 V, the reverse leakage current can be attributed to minority carriers instead of majority carriers tunnelling across the depletion layer of the heterojunction. By increasing the reverse applied voltage from about −13 V to −37 V, the reverse current can be ascribed to the injection of electrons via sequent resonant tunnelling through the Si nanocrystals quantum dots into the substrate. By further increasing the reverse bias, the reverse current can be assigned to carrier avalanche multiplication within the amorphous buffer layer in the depletion region to enhance the electron resonant tunnelling in the nc-Si:H layer. The results indicate that the (n)nc-Si:H/(p+)c-Si structure is a promising candidate for digital circuit applications.