The Structure And Optical Properties Of Ga-Al Co-doped ZnO Thin Films

Zinc oxide,is one of the important members,who is from the family of the?-VI,has a wide band gap?3.37eV?and large exciton binding energy?60meV?,plays a key role in the fields of both a variety of technologies,such as:flat-panel displays,solar cells,ultraviolet detector,short wavelength light-emitting materials,etc.Various methods have been used to prepare ZnO films,such as molecular beam epitaxy?MBE?,magnetron sputtering,chemical vapor deposition,spray pyrolysis,sol-gel method,etc.Among these technologies,sol-gel method is highly concerned due to its many advantages,such as:low cost,simple deposition process,easy control,low processing temperature,simple manufacture of large-area thin films,etc.In this paper,the intrinsic ZnO films,Ga-doped ZnO films and Ga-Al co-doped ZnO films were prepared on glass and Si substrates by sol-gel spin coating method.Meanwhile,the influences of different preparation conditions and doping amounts on the crystal properties,surface morphology,optical transmittance and photoluminescence properties of the films were investigated.The best preparation conditions of ZnO thin films is determined,by means of the study of solution concentration and pretreatment temperature,sol concentration is 0.4mol/L,the pretreatment temperature is 120?,the annealing temperature is 500?,spin six floors.The effect of Ga doping amount on ZnO thin film is under review.Ga doping does not change the structure of ZnO hexagonal wurtzite.There is small amount of Ga added in the films which will make the grains grow optimally along the c axis,the grain size becomes smaller,and the film surface becomes smoother and smoother.However,when Ga doping amount is too much,the growth of thin film grains is inhibited instead,and the surface starts to appear cluster phenomenon,and the?002?diffraction peak intensity of XRD gradually decreases.It can be concluded from the test of transmittance that,when the doping amount of Ga is 3at%,the transmittance of visible light region of the film is the highest,reaching about85%,and at this time,the band gap width of the film is the largest,which is 3.88eV.The influences of different Al doping amounts on Ga-Al co-doped ZnO films are investigated,and it is found that the addition of a certain amount of Al³⁺would improve the crystal and optical properties of the films.Through XRD analysis,the?100?diffraction peak of thin film is the strongest when Ga doping amount is 3.0at%and Al doping amount is2.0at%.Combined with the characterization results of SEM,it can be seen that appropriate addition of Al³⁺can make the film grain grow along the horizontal direction,reduce the grain gap on the film surface,make the surface smooth and smooth,and improve the crystal quality of the film.The optical properties of the thin film were investigated by means of transmittance and photoluminescence spectrum.It has been found that,with the increase of Al doping amount,the transmittance of the thin film shows a trend of increase initially and decrease afterwards.The near ultraviolet luminescence peak intensity of the thin film first increased and then decreased.There is a slight blue shift on the whole,and the luminescence band in the visible region is weakened.When the doping amount of Al is 2.0at%,the average transmittance of the film in the visible light region is the highest?92%?,the forbidden band width is the largest?about 3.95ev?,the near band edge emission peak of the film is the strongest,and the defect emission peak is the weakest.