Improving The Property Of ZnO Microwire UV Sensor Using Heterojunction

Because of its wide band gap(Eg =3.37 eV), large exciton binding energy(60 meV), low cost, ease of manufacturing, high thermal stability and biological compatibility, ZnO is emerging as an exciting new material for a wide range of applications. Especially, it draws a great deal of attention in the area of ultraviolet(UV) detection. However, the ZnO based UV detector always has the disadvantages of low respond speed and poor stability owing to the defect states on the surface of ZnO. So finding a new way to solve these problems is a great challenge for us.So far, many attempts have been made for the purpose of improving the performance of ZnO based UV detector. Some researchers studied on the contact mode between mental and semiconductor of UV detector. They tried to use schottky contact instead of ohmic contact to improve the performance of ZnO based UV detector. Others compounded two kinds of semiconductor materials with similar energy band structure together to form heterojunction. And it can also significantly improve the performance of ultraviolet detector. It has been proved that by coating a shell on the surface of ZnO material, the surface state of ZnO will be passivated. As a consequence, the bandwidth of two semiconductors will be adjusted and the ultraviolet emission of ZnO material will be simultaneously improved.In this paper, the performance of ZnO microwire based UV detector is improved by decorating a ZnS shell on the surface of ZnO, which can be explained by heterojunction formation and surface passivation. Here, ZnS is a good choice for the heterojunction formation because its band structure and lattice constant are matching well with ZnO. We designed two kinds of UV detectors including ZnO/ZnS heterojunction UV detector and ZnO/ZnS field effect transistor(FET) UV detector. We also studied the performance of these UV detectors under 365 nm UV illumination. The results show that the dark current of ZnO/ZnS heterojunction UV detectors is four order’s lower than ZnO UV detectors. And the current on/off ratio of ZnO/ZnS heterojunction UV detectors is 15132 times higher than ZnO’s. This design can also improve detector’s response speed. Its response time is 1.7 s and its recovery time is 1.1 s. By forming a FET UV detector, the dark current is 1/1209 of pure ZnO’s. And the current on/off ratio of FET UV detector is 253 times than ZnO’s. The response time of this kind of detector is 6.6 s and its recovery time is 2.2 s.