Ultraviolet electroluminescence from ZnO∕p-Si heterojunctions

Nominally undoped ZnO films were deposited by reactive sputtering on the lightly boron-doped (p−) and heavily boron-doped (p+) silicon substrates. The sputtered ZnO films were identified to be highly ⟨002⟩ oriented in crystallinity and n type in electrical conductivity. The current-voltage (I-V) characteristics revealed that the ZnO∕p−-Si heterojunction exhibited well-defined rectifying behavior while the ZnO∕p+-Si heterojunction did not possess rectifying function. As for the ZnO∕p+-Si heterojunction, it was electroluminescent to a certain extent in the visible region under sufficient forward bias with the positive voltage on the silicon substrate, while it emitted ultraviolet light characteristics of near-band-edge emission of ZnO under the reverse bias, which significantly dominated the visible emission. In contrast to the ZnO∕p+-Si heterojunction, the ZnO∕p−-Si heterojunction did not exhibit detectable electroluminescence (EL) under either forward or reverse bias. The I-V characteristics and EL mechanism of the above-mentioned heterojunctions have been tentatively explained in terms of the energy-band structures of the heterojunctions.