Preparation And Characterization Of Doped SnO₂ Films By MOCVD

Along with science and technology developing,semiconductor material development has gone through the first-generation element semiconductor and the second-generation compound semiconductor.Now there has been increasing interest in the third-generation semiconductor.The third-generation semiconductor,namely wide band gap semiconductor,has a potential that the first two generations cannot be compared with in some respects,including high temperature and high frequency powered devices and short wavelength optoelectronic devices.In the field of electronic devices,study on the SiC and GaN has been relatively mature.In the respect of light-emitting devices,much work has been done onⅢ-nitride semiconductors and ZnO based compounds.Now,there is more attention being paid to SnO₂.SnO₂ is a wide band gap semiconductor with direct band gap and has some notable advantages.It has a wide band gap of 3.6eV and a high exciton binding energy of 130meV,but has a low growth temperature and good chemical stability.So SnO₂ is a promising candidate for short wavelength light-emitting material.As a key functional material,SnO₂ has been widely used in the fields of transparent conducting oxides(TCOs) and gas sensors.But there is no study reported on the light-emitting devices of SnO₂ material.One cause may be that the SnO₂ films deposited by common methods such as magnetron sputtering,CVD and spray pyrolysis are difficult to manufacture luminescent devices due to film defects and bad PL properties. Another cause may be that it is difficult to prepare p-type SnO₂ film.Although some study has reported p-type SnO₂,the bad film quality and poor electrical properties make it impossible to manufacture luminescent devices.One cheering thing is great progress has been made in preparing high quality SnO₂ film.Single crystal SnO₂ film and single crystal In-doped SnO₂ film have been deposited and ultraviolet photoluminescence peak caused by electron transitions from conduction band to valance band was observed at room temperature.However,how the dopants affect the electrical properties was not reported.Based on this background,the preparation and characterization of doped SnO₂ films by MOCVD are investigated in this article. The major work and results are as follows:1.1%(atomic ratio)Zn-doped SnO₂ films were prepared on sapphire(0001),Si (111)and quartz substrates using an MOCVD system.High purity(C₂H₅)₄Sn was employed as Sn organometallic(OM) source,(C₂H₅)₂Zn as Zn OM source,O₂ as oxidant and N₂ as carrier gas.The XRD spectra showed that the films deposited on Si (111)and quartz substrates were polycrystalline films with rutile structure.The two films both had(110)(211)(220)(321) diffraction peaks.The film deposited on sapphire(0001)substrate only had a(200) diffraction peak.The film had preferred orientation along a-axis.The results indicated the film deposited on sapphire(0001) had better crystalline quality.2.1-10%Zn-doped SnO₂ films were prepared on sapphire(0001) substrate by MOCVD method.All the films were tetragonal crystal with rutile structure and had preferred orientation along a-axis.The film transmittance in visible region was over 80%.The optical band gap was about 3.55eV.The film thickness calculated according to interference pattem was 1-1.4μm.The refractive index dispersion curves of different doping level films were calculated.The composition of samples was determined by XPS technology.The film electrical properties were measured by four-probe technology and van der Pauw method.Affect of annealing in air on the structural and optical properties was analyzed.3.Un-doped and 1-12%In-doped SnO₂ films were deposited on sapphire(0001) substrate by MOCVD method.XRD results showed that all the films were tetragonal crystal with rutile structure and had preferred orientation along a-axis.SEM image and HRTEM image showed that the prepared films were single crystalline films.XPS results indicated that some non-stoichiometric oxide existed on the surface of 3% In-doped SnO₂ film and the atomic ratio of In over Sn was 3.16:97.The film transmittance in visible region was over 88%.The optical band gap decreased with In content increasing.The film electrical properties were measured by four-probe technology and van der Pauw method and then analyzed.