| ZnO is a II-VI semiconductor material with a direct wide band gap of3.37eV and a large exciton binding energy of60meV at room temperature. It is an ideal semiconductor material for making optoelectronic devices. Due to the unique properties, such as the large surface-to-volume ratio and the quantum confinement effect, ZnO nanostructures have potential applications in nano-photoelectric device, piezoelectric device, nano-laser, nano-motor and sersor. The quantum confinement effect makes ID ZnO nanowires not only act as direct waveguides but also provide the gain for the waveguide mode. In this way, the light could transfer along the axial of nanowires, which will be benefit for light extraction. Therefore, ZnO nanowires-based photodiodes or lasers have become one of the hot spot in the reaearch.In this article, we pay more attention to the ZnO nanowires arrays synthesized by the hythermal method. The ZnO seed layers were prepared to tune the structures of ZnO nanowires arrays by using magnetron sputtering. Then the ZnO nanowire/p-Si heterojunction structure was fabricated on p-Si substrate. The electrical and optical properties were also analysized. The main contents are summarized as follows:Firstly, from the growth mechanism of ZnO nanowire arrays by the hythermal method, we mainly focused on the analysis of effects of seed layer and solution concentration on the growth of ZnO nanowire arrays. As a buffer layer, the ZnO seed layer can not only control orientation but also limit diameter of the nanowires. The diameter of ZnO nanowires increases with increasing precursor concentration. It is, therefore, that the space between nanowires become smaller and smaller, which will eventually form a dense film. We also analyzed the optical properties of ZnO nanowires with different growth time. It has shown that the ZnO nanowires array grown at the beginning of period has certain defects, and high-quality ZnO nanowire arrays have been obtained with increasing reaction time.Secondly, in order to prepare the ZnO nanowire/Si heterojunction photodiode, the ITO films were fabricated at the top of the ZnO nanowires by electron beam evaporation as the negative electrode. Annealing treatment was carried out firstly on the ITO film prepared on glass substrate. It has been shown that annealing treatment can improve the characteristics of the ITO film. In other word, the light transmittance of the ITO film is highly increased and the resistivity decreased. The electrical properties of the ITO film at the top of the ZnO nanowires were also studied. After annealing treatment, we could obtain a perfect ohmic contact between the ITO and the ZnO nanowires.At the end, we prepared the ITO/ZnO nanowires/p+-Si/Al heterojunction diode. The electrical and optical characteristics of the undoped ZnO/p+-Si heterojunction diode were investigated by current-voltage (I-V), capacitance-voltage (C-V), and EL spectrum. The diode exhibited a typical rectifying characteristic. The built-in electric potential analyzed by C-V was0.60eV, which approximately equaled the0.61eV analyzed by I-V. However, the result has certain deviation compared with the theoretical value due to some interface states existed in the heterojunction interface. EL spectrum has a peak around710nm in the red region, which may be attributed to oxygen related deep-level defects. |
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