Growth And Physical Properties Of Nitrogen-doped SnO₂ Thin Films

SnO₂ is a promising candidate for constructing ultraviolet optoelectronics devices, such as UV LEDs and photodetector. The aims of this thesis are to grow nitrogen-doped SnO₂ films by reactive magnetron sputtering, to study optical and electrical properties of the films, to explore the feasibility of achieving p-type SnO₂ by nitrogen doping, and therefore provide some basic results for SnO₂-based optoelectronic devices building.Nitrogen-doped SnO₂ films have been prepared by reactive magnetron sputtering. It has been proved that the N3- ion partially replaces O₂-, and forms N-Sn-O chemical bond via XRD, XPS and optical properties analysis. The orientation of nitrogen-doped SnO₂ films is thickness-dependent, and the film shows [110]-oriented when the film thickness is thinner than 80 nm and poly-orientation when film is thicker than 170 nm. A thin film with thickness of 20 nm was deposited as a seed layer before main film growth, and the main film with a thickness of 320 nm shows a highly [110]-oriented growth, the seed layer also has a great influence on the film microstructure. The indirect allowed transition of nitrogen-doped SnO₂ films can be tuned from UV to visible region, and the refractive index and extinction coefficient determined by spectroscopy ellipsometry increase as the nitrogen content increasing, which is due to the replacement of O₂^- by N₃^- ion in SnO₂ lattice and the formation of N-Sn-O chemical bond with higher polarizability. For the first time, the localized exciton recombination photoluminescence in nitrogen-doped SnO₂ is observed, and the PL peak shifts toward higher energy side with sample temperature decreasing or excitation intensity increasing. The exciton localization is attributed to the potential fluctuation due to the disturbed distribution of chemical composition and/or the microstructure disorders in polycrystalline nitrogen-doped SnO₂ films. The angular-dependent photoluminescence of the highly [110]-oriented nitrogen-doped SnO₂ films with the seed layer due to Fabry-Pérot microcavity interference has been observed. An obvious photoresponse of nitrogen-doped SnO₂ films in UV region also has been observed. Undoped n-type SnO₂ films have been grown epitaxially on sapphire substrates, and the carrier concentration and mobility are 2.1×10¹⁶ cm^-3and 10.3 cm²/Vs, respectively.