Study On Preparation And Optical Of Cu-doped ?-Ga2O3 Thin Films

Gallium oxide?Ga₂O₃?,with a band gap of 4.9 eV?²50nm?,is a promising wide band gap material.It has many excellent properties such as high deep UV transmittance,high breakdown field?⁸ MV/cm?and low conduction loss.So Ga₂O₃ is a multifunctional optoelectronic material with great application potential in many fields such as deep-ultraviolet transparent electrode,solar blind ultraviolet photodetector,field effect transistors,gas sensors,and so on.Ga₂O₃ has five different polymorphs,including?,?,?,?and?.?-Ga₂O₃ is the stable form of these five phases,while all of the other forms would transform into the?phase at high temperature.Almost of researches are mainly focused on?phase in the past few years.In fact,the metastable cubic?phase presents several fascinating properties,that is blue light emission from nanocrystals,room temperature ferromagnetism on Mn doping,and selective catalytic reduction of NO in the?-Ga₂O₃-Al₂O₃ system,which may be a more attractive material than the stable?form.Therefore,the study of?-Ga₂O₃ has both important scientific significance and great application value.However,the current reports of?-Ga₂O₃ are mainly concentrated on nanomaterials,and it is rarely reported that the single-phase?-Ga₂O₃ based on the film type is difficult to obtain.T.Oshima et al.obtained?-Ga₂O₃ epitaxial film on?100?MgAl₂O₄ substrates by mist chemical vapor deposition.H.Hayashi et al.investigated the growth,microstructure and ferromagnetism of Mn-doped Ga₂O₃ thin film grown on a sapphire?0001?plane by using a pulsed-laser deposition technique.However,the above preparation process is relatively complicated and the cost is high.In this paper,the conditions of preparation of?-Ga₂O₃ were investigated by Cu doping method and the performance was studied.The specific work is as follows:1.Firstly,the structural model of?-Ga₂O₃ was constructed by first-principles principle.The crystal structure was optimized,the electronic structure of?-Ga₂O₃ was calculated,and the lattice matched elements were selected for doping calculation.The calculationresults show that Cu doping can exist stably in?-Ga₂O₃ and can fill a part of Gavacancies.After Cu doping,the formation energy of O₃₂Ga₂₁Cu system is lower thanthat of O₃₂Ga₂₂ system.This means that Cu doping can reduce the formation energy ofthe system and stabilize the metastable phase?-Ga₂O₃.This part of the work providesclear direction guidance for the experiment,and can also analyze the experimentalresults,establish a reasonable theoretical model,and accurately understand theexperimental results.2.Secondly,the preparation conditions of?-Ga₂O₃ thin films were investigated by Cusputtering using magnetron sputtering.We found that the doping amount of Cu affectsthe structure of Ga₂O₃,by continuously changing the experimental parameters such asthe doping amount of Cu and the annealing temperature.When the doping amount ofCu is 1.2 at.%-4.6 at.%,a pure?-Ga₂O₃ film is obtained.When the doping amount ofCu increases to 8.5 at.%-14.9 at.%,the structure of the film becomes CuGa₂O₄,whichis very similar to?-Ga₂O₃.We also studied the effect of annealing temperature on thestructure of the film.It is found that as the annealing temperature increases,theCuGa₂O₄ film begins to transform to?-Ga₂O₃,and a small amount of Cu starts toprecipitate.The optimum annealing temperature for maintaining the CuGa₂O₄structure is 750°C.Although the?-Ga₂O₃ film was not successfully produced,astructurally similar CuGa₂O₄ was obtained.The range of effects of temperature andCu doping on the structure of Ga₂O₃ was mastered,which provided a solid foundationfor the next experiment.3.Finally,the?-Ga₂O₃ thin films were successfully prepared by Cu doping with sol-gel method,and the corresponding preparation conditions were studied.We have found that when the Cdoping amount is 12.5 at.%and annealing at 700°C in a nitrogen atmosphere,a single-phase?-Ga₂O₃ film having a high crystal quality can be obtained.When the annealing temperatureis raised to 800°C,the metastable phase?-Ga₂O₃ will be converted into a stable phase?-Ga₂O₃.At the same time,we carried out the optical properties and component testing of theprepared?-Ga₂O₃.XPS analysis showed that the Cu ion in the Cu-doped?-Ga₂O₃ film was+2 valence.The band gap of the Ga₂O₃ film shows a significant red shift with Cu doping.Compared with undoped?-Ga₂O₃,the photoluminescence intensity of Cu-doped?-Ga₂O₃film is enhanced in ultraviolet-blue light due to the presence of more oxygen vacancies in?-Ga₂O₃.