Study On Preparation And Luminescence Properties Of ZnO:Al-Eu Thin Film

As a wide band gap direct band gap semiconductor material,ZnO has high exciton binding energy,more matching substrate materials and lower production costs,which makes people increasingly interested in ZnO materials.However,ZnO can only emit purple light,blue light and green light under the excitation of ultraviolet light.Only the lack of red-light emission among the three primary colors severely restricts its application in flat display,night coating and commercial LED fields.The rare earth Eu³⁺ions have abundant energy levels,temperature-independent luminescence,and a narrow and strong red emission line derived from the 4f inner shell transition,making the rare earth Eu³⁺ions a good red-light luminescence center.The inorganic luminescent material is obtained by doping ZnO with rare earth Eu³⁺ions.However,the radius of Eu³⁺ions is larger than that of Zn²⁺ions,and the charges are not matched,which makes it difficult for Eu³⁺ions to be incorporated into the ZnO matrix.Co-doping may be an effective strategy.With reference to other element-doped zinc oxide studies,it is found that the addition of group III Al elements in zinc oxide can form n-type semiconductors,with high crystallinity and improved conductivity,and the Al³⁺radius is smaller than Zn²⁺.Therefore,Al and Eu co-doped with ZnO can obtain better film properties.In this thesis,ZnO:Al-Eu(AEZO)films were deposited on p-Si(100)and c-plane sapphire(Al₂O₃)substrates by radio frequency magnetron sputtering,and the effects of substrate materials and annealing process on the lattice structure,surface morphology,photoelectric properties and luminescent properties of the films were investigated.XRD and EDS spectra confirmed that Al³⁺and Eu³⁺ions were successfully incorporated into the ZnO matrix,and all AEZO films had high texture.From the perspective of crystallinity and surface morphology,AEZO film is more suitable to grow on sapphire substrate,and the film can obtain good crystal quality after annealing process.The PL spectra show that although the emission spectra of AEZO films deposited on sapphire and silicon substrates are very similar,from the perspective of relative luminescence intensity,sapphire substrates are more conducive to AEZO films to achieve red light emission of Eu³⁺ions at 615nm.This is because the sapphire substrate has a higher lattice match with ZnO.And comparing the intensity of orange-red light and red light,it can be concluded that the transition intensity of ⁵D₀-⁷F₂is greater than that of ⁵D₀-⁷F₁,indicating that the lattice position of Eu³⁺ions in the nano-ZnO matrix mainly occupies the lattice site without inversion center.Next,this thesis uses the first-principles method and the Materials Studio software CASTEP module to calculate the optoelectronic properties of intrinsic ZnO,Al-ZnO,Eu-ZnO and ZnO:Al-Eu(AEZO),such as lattice structure,and bind energy,band structure,density of states,differential charge density and optical properties.From the analysis of the results before and after doping,it is found that the conduction band of the system after doping moves to the lower energy direction,the Fermi level enters the conduction band,and the system exhibits n-type semiconductor properties.Moreover,the band structure of Eu-ZnO and AEZO has a donor energy level introduced by Eu4f state near the Fermi level,which also confirms that Eu³⁺ion is the activator and Al³⁺ion is the sensitizer.In terms of optical properties,there is a big difference between the doped system and pure ZnO in the low-energy region.The imaginary part of the dielectric function of Eu-ZnO has a new peak at 0.149 e V,which is caused by the transition between Eu's 4f orbital electrons.This thesis combines experiment and simulation.Firstly,the ZnO:Al-Eu film was deposited on different substrates by radio frequency magnetron sputtering,and the substrate suitable for the growth of AEZO film was sought.Then,the photoelectric properties of the ZnO:Al-Eu system were calculated using first principles.From the perspective of simulation theory,explain the internal reasons why Al and Eu doped ZnO change their photoelectric properties,and provide a theoretical basis for the experimental results.