Study On Optical Properties Of Transparent Conductive Oxide La_2/3Sr_1/3VO₃ And PtCoO₂ Thin Films

After the third scientific and technological revolution,the electronic information technology has been developed significantly.Among them,electronic devices developed based on various oxide materials are commonly used in many fields.As an important branch of oxide materials,transparent conductive oxides have received strong attention because of their excellent optical and electrical properties.Today,electronic information technology is developing rapidly,materials and devices are also developing towards ultra-high integration and miniaturization,and thin film technology is one of the most important means to achieve these two goals.In the future,thin film materials will play an increasingly important role in meeting the needs of miniaturization and ultra-high integration.Therefore,the study of the optical constants,band transitions,dielectric function and other properties of transparent conductive oxides has very important practical significance for broadening the application of these transparent conductive oxide materials in the field of optoelectronics.In view of this,this thesis focuses on two different transparent conducting oxide thin films,namely the perovskite La_2/3Sr_1/3VO₃(LSVO)thin film and delafossite PtCoO₂ thin film,the specific research contents are as follows:(i)The optical dielectric response of the LSVO thin film was analyzed and studied by using a spectroscopic ellipsometry.First of all,the LSVO thin film was successfully prepared on(LaAlO₃)_0.3(Sr₂AlTaO₆)_0.35(LSAT)substrate by using pulsed laser deposition(PLD),and then the ellipsometric data of LSVO thin film was measured with an ellipsometry,and the corresponding three-phase optical model(air/LSVO thin film/LSAT substrate)was selected to the ellipsometric data.The ellipsometric data were first forced to fit with the B-sample function to obtain the numerically optimum solution,and then we used the joint dispersion model(1Drude+1Lorentz+2Tauc-Lorentz)to replace B-sample model to obtain the real optimal solution.by fitting each parameter,we finally obtained the optical constants of the LSVO thin film with wavelength variation(245-1000 nm)and the thickness of the sample.On this basis,we plotted the dielectric function graph,the transition in the high-energy region was found,and we made a theoretical explanation for the origin of this transition.Furthermore,the optical band gap of the LSVO film was found by plotting the(?h?)²?h?graph,and then we compared it with the band gap of the undoped material LaVO₃,and the reason for the red shift of the band gap of the LSVO thin film was analyzed.(ii)The optical dielectric response of delafossite PtCoO₂ thin film was analyzed and studied by the spectroscopic ellipsometry.First of all,the PtCoO₂thin film was successfully prepared on Al₂O₃(0001)substrate by chemical solvation deposition,and the general properties of the sample were measured by X-ray diffraction,X-ray photoelectron spectroscopy,and atomic force microscopy,respectively.Then,the ellipsometric data of PtCoO₂ thin film was measured by ellipsometry,the corresponding three-phase model(air/PtCoO₂ thin film/Al₂O₃ substrate)was established,and the ellipsometric data were fitted by the joint dispersion model(1Drude+5Lorentz),then we finally obtained the optical constants of the PtCoO₂ thin film.In order to analyze the possible transitions in the spectra,the standard critical point model was applied to fit the second derivative of dielectric function(d²(E²?)/d E²).The fitting results show there exist six transitions in the spectra,and we analyzed the origin of this transition.It is worth noting that we found double-peak transition among these six peaks,which was not mentioned in the previous studies.Finally,a first-principles calculation is performed for PtCoO₂ thin film,and we plotted the density of states and energy band structure graph.The calculation results are basically consistent with the ellipsometric analysis,which provides theoretical support for our previous analysis.