High photo-responsivity ZnO UV detectors fabricated by RF reactive sputtering

High performance ultraviolet (UV) detectors based on ZnO metal–semiconductor–metal (MSM) and p–n heterojunctions, p-NiO/n-ZnO, were fabricated and their UV photo-responsivity was measured at room temperature. High-quality ZnO and NiO thin films were deposited on quartz substrates at room temperature under optimized RF reactive sputtering conditions. For ZnO-based MSM UV detectors using Al as a contact metal, the linear current–voltage (I–V) characteristics under a forward bias exhibited ohmic metal–semiconductor contact. A maximum photocurrent and photo-responsivity of 2.5 mA and 1410 A/W, respectively, at 365 nm under 5 V bias was observed, indicating the high photo-responsivity of the ZnO MSM detector. In comparison, a p-NiO/n-ZnO p–n heterojunction UV detector demonstrated clear rectifying I–V characteristics with an ideality factor, forward threshold voltage and photo-responsivity of 2, 0.9 V and 0.09 A/W, respectively, at 362 nm under a reverse bias of 4 V, which is close to that of the commercial GaN UV detector (∼0.1 A/W).