Preparation And Characterization Of P-type SnO₂ Thin Films By DC Magnetron Sputtering

Wide band-gap semiconductor materials are a kind of hottest semiconductor materials in recent years, such as GaN, ZnO, etc. Tin dioxide (SnO₂) is a kind of wide band gap semiconductor material with bandgap E_g³.6-4.0 eV. Due to its high optical transparency, low resistivity, thermal and chemical stabilities, and low cost of the source materials, SnC>2 has been widely used in many applications such as gas sensors, solar cells, transparent electrodes, electric heating devices, and etc. However, almost all the transparent conductive oxide (TCO) films (e.g., In₂O₃∶Sn, SnO₂∶F) are n-type conducting, and the p-type TCO films are mostly in research to fabricate transparent pn junctions which are necceary for transparent electronic devices.In this thesis, the preparation technology, property, application and p-type doping mechanism of SnO₂ were introduced. P-type transparent SnO₂ thin films were successfully fabricated by two-step method: alloy films deposited by DC magnetron sputtering (doped with In, Ga/Sn=0.2, respectively), and then thermally oxidized in the air at high temperature. In-doped SnO₂ with transmittance over 80% in the visible region and hole concentration as high as 9.61×10¹⁸cm^-3 were obtained after oxidized between 600 ℃ and 700 ℃, which are superior to Ga-doped SnO₂ films fabricated by the exactly same process. It shows that indium doping is more effective than Ga doping for p-type doping in SnO₂. In addition, SnO₂:In films were prepared by reactive DC magnetron sputtering under different parameters, but the electrical properties of the films are inferior to the films fabricated by the two-step method mentioned above. Cu-doped SnO₂ thin films were also tested to realize p-type conduction, but the results showed that Cu did not substitute Sn to behave as a bi-acceptor as expected, only weak p-type conductance of the film was observed after thermal oxidation, which was possibly due to the existence of some Cu₂O phase in the films. However, the crystallinity of SnO₂ thin films was improved and phase transformation was found.