Preparation And Properties Of P-type ZnMgO Films For Device Fabrication And Study On The Surface Treatment Of GZO Films

Compared with GaN, ZnO has unique advantages such as:the exciton energy is two times of that of GaN, ZnO is environment-friendly with low cost and high-resist to the radiation. The advantages promote ZnO as a promising material instead of GaN for short-wavelength optoelectronic devices. Due to the asymmetric doping limitations, p-type ZnO is hard to realize and has been thought to be a bottleneck in the development of ZnO-based devices, one of which is the device properties of p-type ZnO thin films. Therefore, in this work, we concentrated on the device properties of p-type ZnO thin films.The transparent conducting oxides (TCOs) are widely used as transparent electrodes in optoelectronic devices owing to the unique combination of high electrical conductivity and excellent visible transparency. ZnO based TCOs possess the advantages of low cost, earth abundant, and non-toxicity compared with the most popular indium oxide based TCOs, i.e. tin doped indium oxide (ITO). Many research groups demonstrated that Ga is a decent dopant for producing high quality n-type ZnO because Ga atoms cause little distortion of the ZnO lattices when they are in substitutional sites. In this study, we utilized oxygen plasma treatment to modify the surfaces of GZO thin films.The detailed investigations included:1) Na doped ZnMgO thin films with excellent structural and electrical properties were prepared on quartz substrates by pulsed laser deposition.2) In this study, we have presented results for fabricated ZnO based FET. The electrical measurements confirmed that the conductivity of the Na doped ZnMgO thin film was P-type, and the carrier mobility was estimated to be2.3cm2V-1S-1. Moreover, after exposed to the365nm ultraviolet light, the Na doped ZnMgO thin films still exhibited p-type behavior under gate voltage ranging from-5to2V.3) The effects of rapid thermal annealing (RTA) on the structural and electrical properties of Na-doped ZnMgO films grown by pulsed laser deposition have been studied. Conclusively, a wide temperature window for achieving reasonable p-type by RTA was found, which was important because RTA was generally needed to get p-type Ohmic contact when fabricating LED.4) Photocurrents were measured under a bias of6V in air at room temperature when the Na doped ZnMgO thin film was irradiated by red laser beam,365nm and254nm ultraviolet beam for20s. The film exhibited a higher current intensity after illumination. The photocurrent exhibited after red laser irradiation because of the existence of the defects and surface states. The carrier recombination rate was smaller and the photocurrent changed more significantly when the film was exposed to the254nm ultraviolet beam than that of the film exposed to the365nm ultraviolet beam.5) Na-doped ZnMgO thin films were grown on quartz substrates, Ni/Pt multilayer films and Ni/Pt films were deposited sequentially by electron-beam evaporation and patterned by photoresist lift-off to form circular transmission line model (CTLM) patterns. The specific contact resistivity of Ni/Pt multilayer films was relatively low compared with Ni/Pt films.6) The oxygen plasma treatment significantly changed the surface properties of the Ga doped ZnO thin films, leading to an increase of work function and a large reduction in contact angles. We attributed the increase of work function of the GZO thin films after oxygen plasma treatment to both the lowering of the Fermi level and the shift in ionization potential.