Study On The Growth Of NiO-based Films By Magnetron Sputtering And The Photoelectric Devices

The NiO has a stable NaCl cubic crystal structure,belonging to the transition metal oxide with a typicl 3d electronics structure.NiO of stoichiometric ratio is insulative at room temperature.However,it is usually difficult to obtain pure NiO,which exhibits p-type conductivity because of presence of intrinsic acceptor defects.NiO is a wide bandgap material with a 3.6~4.0 eV forbidden band width at room temperature,so it has excellent visible light transmittance and UV response characteristics.Li doping could improve the p-type conductivity of NiO,and Mg doping could increase its bandgap width.NiO has potential application value and brod application prospects due to its unique magnetic,gas sensitivity,resistance switch,electrochromic and other features.In particular,NiO is often used as transparent electrodes,hole transport layers and electron blocking layers in the study of optoelectronic devices such as ultraviolet light emitting devices,ultraviolet detectors and solar cells,which is based on its wide bandgap p-type transparent conductive properties.ZnO is a direct wide bandgap semiconductor material with relatively large bandgap and exciton binding energy(3.37 eV and 60 meV at room temperature)and is widely applied in short wavelength light emitting devices.Besed on the radio frequency(RF)magnetron sputtering technology,this paper has carried out a detailed study in two aspects,focusing on the preparation and characterization of NiO:Li and NiMgO:Li thin films materials,and the analysis of photoelectric properties NiO:Li(NiMgO:Li)/ZnO heterojunction devices.The specific content is as follws:NiO:Li thin films were deposited on the sapphire substrates by RF magnetron sputtering method with a purity of 99.9% Li-doped target(Li2O:NiO=1.04:98.96 wt%).We systematically investigated the effects of different growth parameters(substrate temperature,sputtering power and oxygen flow ratio)on the morphology,crystal structure,electrical and optical properties of NiO:Li thin films.The growth conditions were optimized step by step to improve the quality of NiO:Li thin films.A batch of NiO:Li thin films samples were prepared by selecting the appropriate sputtering conditions,which was based on three series experiments of changing the substrate temperature,the sputtering power and the oxygen flow tatio,and balancing the properties of films.After this,the annealing experiment of NiO:Li thin films was carried out.Firstly,the films were annealed under nitrogen and oxygen atmosphere respectively.It was found that the hole concentration in NiO:Li thin films was significantly reduced after annealing in nitrogen.Therefore,we also studied the effect of different annealing temperatures on the properties of films in oxygen atmosphere.The results showed that annealing at 500 ? in oxygen could improve the crystal qulity and optical of NiO:Li thin film while ensuring the film had a high hole concentration of 1018 cm-3.NiMgO:Li thin films were grown by using high purity MgO target and combining the NiO:Li and MgO materials.With increasing MgO deposited,the bandgap of NiMgO:Li was widened,the optical transmittance increased continuously and the range of high transmittance gradually extends to ultraviolet direction,the ultraviolet absorption characteristic was gradually enhanced.But the p-type conductivity of NiMgO:Li than that of NiO:Li because the introduction of MgO drastically reduced the hole concentration to 1016 cm-3.Annealing in oxygen increased the hole concentration of NiMgO:Li thin films to 1017 cm-3 and improved its optical properties with high visible transmittance above 80%,and the phase separation almost disappeared in the films.The p-NiO:Li/n-ZnO heterojunction device was fabricated on the ITO substrate and its photoelectric properties were studied in detail.There were light quenching and leakage in the electroluminescence test,since the ZnO nanowall net work was directly covered by NiO:Li and the gaps between the nanowall were completely bridged.So the device performed poor photoelectric characteristics.Subsequently,a p-NiMgO:Li/MgO/n-ZnO heterojunction device was prepared on the ITO substrate.The MgO insulation layer not only avoided leakage and light quenching phenomena,but also played a role with the regulation of the energy band.In addition,the transmiscence of NiMgO:Li was relatively high.These could improve the performce of the device.The random laser radiation was achieved nearly 400 nm.