Research On Optical And Electrical Properties Of Metallic Element Doped Wide Band Gap Oxide Semiconductors(SnO₂,ZnO)

Wide-bandgap oxide semiconductors have been widely studied and applied in various optoelectronic and energy fields due to its excellent electrical and optical properties.As typical wide-bandgap oxide semiconductors,Zn O and Sn O₂ have been widely used in the field of transparent conductive films due to their suitable band gap,high visible light transparency,high electrical conductivity and excellent chemical stability.However,it is still difficult to obtain reproducible p-type Zn O with high quality and high hole concentration due to the high formation energy and deep acceptor level of acceptor impurities in Zn O.For Sn O₂,the performance of optoelectronic devices can be optimized via modulating bandgap based on band-gap engineering.However,there is still a lack of suitable alloys to realize bandgap engineering for Sn O₂.In this thesis,the following studies have been carried out:(i)Sb-doped Zn O was prepared using high-temperature and high-pressure technique.The structure,composition,optical,electrical and magnetic properties of Sb-doped Zn O are characterized;(ii)Ti-doped Sn O₂(Ti_xSn_1-xO₂)thin films were prepared using sol-gel method.The band gap engineering of Ti_xSn_1-xO₂ was realized via altering Ti content.The physical mechanism of the effect of Ti content on the optical and electrical properties of Ti_xSn_1-xO₂ thin films were investigated in detail.The obtained research results are as follows:1.Sb-doped p-type Zn O with high hole concentration was synthesized by high-temperature and high-pressure method with thermodynamic quasi-equilibrium state.It is found that Sb-doped Zn O exhibits a room temperature ferromagnetism.Temperature-dependent resistance measurements indicate that the conduction mechanism of Sb-doped Zn O follows the thermal activation model and the nearest neighbor hopping(NNH)conduction at high temperature,and gradually changes to the Mott variable range hopping(VRH)conduction and Ebros-Shklovskii VRH conductivity as the temperature decreases.Furthermore,first-principles calculations suggest that the Sb impurities between two zinc vacancies(V_Zn)can stabilize the stability of the ferromagnetic coupling between the two V_Zn,well supporting the experimental results.2.Ti_xSn_1-xO₂(0?x?0.12)thin film was prepared using sol-gel method combined with annealing process.The experimental results illustrate that the optical bandgap of Ti_xSn_1-xO₂thin films becomes narrower with increasing Ti content,which is in accordance with the absorption spectra from first-principles calculations.The calculated electronic band structures of perfect and Ti-doped Sn O₂ demonstrate that the fundamental bandgap(the energy difference between the conduction-band minimum and valence-band maximum)becomes wider as Ti is alloyed into Sn O₂,which is opposite in change trend of the optical bandgap.Based on the first-principle calculations,the physical mechanism of the difference in change trend of fundamental and optical band gap is also discussed.