Study On The Stress And Optical Properties Of Ti-buffered ZnO Films

ZnO is a direct band-gap semiconductor(Eg=3.37eV at RT) with a high exciton binding energy of about 60meV.The feasibility of using excitionic lasers of ZnO at RT has been demonstrated.Besides,ZnO thin films can be prepared at temperature lower than 600℃,its growth temperature is lower than GaN,SiC and otherâ…¡-â…¥semiconductor materials.Owing to these properties,ZnO can be used as room temperature short wavelength ophotoelectron material.It has been investigated extensively because of its interesting electrical,optical and piezoelectric properties making suitable for many applications such as light emitting diodes, photodetectors,electroluminescence,transparent conductive film,surface acoustic waves device and so on.The renewed interest of ZnO film is fueled since room temperature lasing was reported by Tang et al.In this thesis,the reactive radio-frequency(RF) magnetron sputtering method is used to deposite ZnO films.This work focuses on the growth behavior and the optical properties influenced by anneal,buffer layer and N doped.The results are summarized as follows:1.ZnO thin films with highly c-axis preferred orientation have been deposited on Ti buffered Si(111) substrate and MgO buffered Si(111) substrate by reactive ratio-frequency magnetron sputtering.With x-ray diffraction analysis and photoluminescence(PL) measurement,the structure and PL emission properties of Ti-buffered ZnO films and MgO-buffered ZnO films are studied and the effects of Ti-layer thickness and MgO-layer thickness are discussed.It is found that the PL properties of the films are improved after the introduction of buffer layer and an optimized thickness of buffer layer is given.2.Annealing treatment can improve the properties of Si(111)/Ti-buffer/ZnO films further.The residual stress is found to be an important factor influencing the emission properties of ultraviolet light.It is helpful for the emission of ultraviolet light if the films have a small residual stress.The residual stress can also change the transition energy of excitons. With the increase of annealing temperature,the increase of tension strain in films reduces the band gap of ZnO,hence results in the shift of the excitonic peak to the lower energy.3.N-doped films have good transmittance,which is 90%or more.With the N content increasing,the thickness of film decreases while the band gap width increases,which may be due to the smaller O content.With the increase of N₂O partial pressure,the optical band gap increases.The optical band-gap width reach 3.24eV when N₂O partial pressure is 0.4Pa,It is also found the optical property can be improved by increasing the N₂O partial pressure.