| Transparent conductive oxide(TCO)thin films have important applications in modern society,such as solar cells,thin film transistors,flat panel displays and so on.Common TCOs,such as ITO,are faced with problems such as shortage of raw materials,complex preparing process and difficulty in performance improvement.Therefore,it is necessary to find new TCOs to meet the increasing market demand.Perovskite stannate ASnO3(A=Ba,Sr)is a kind of semiconductor oxide with wide band gap and high carrier mobility.Doping can result in very good conductivity without damaging its wide band gap.It is very suitable for the application in the field of TCOs.By combining with other perovskite optoelectronic materials,it is expected to realize the application of all perovskite optoelectronic devices.So it has become one of the research hotspots in the field of TCO.SrSnO3 has a band gap as large as 4.1eV and enhanced thermal stability.It has the advantage of better matching lattice constants with commercial substrates such as SrTiO3,LaAlO3,GdScO3.So it has great research and application prospects.However,SrSnO3 will form a variety of different phases at different growth temperatures,and it is difficult to grow epitaxial films with good crystallinity.There are still many problems to overcome in large-scale applications.In this paper,we choose La doped SrSnO3 thin film as the research material High quality films were prepared by Pulse Laser Deposition.The effects of growth temperature and oxygen partial pressure on crystal quality,doping ratio on electrical conductivity and optical transmittance,lattice strain on electrical conductivity and optical transmittance were systematically studied in details.The main contents are as follows:1.The chemical composition of La doped SrSnO3 films grown by pulsed laser deposition was measured by EDS.Then,the crystal quality of La:SrSnO3 films grown by pulsed laser deposition at different temperatures was optimized by XRD and AFM.The results show that the optimized temperature window for La:SrSnO3 is about 750?-850?.We studied the effect of oxygen partial pressure on the quality of the films.It was found that the samples with good crystallinity could be easily obtained at high oxygen partial pressure,while the films with good crystallinity and conductivity could not be prepared at low oxygen pressure and vacuum2.The temperature dependent electrical transport of 5%La doped SrSnO3 was studied.We use van der Pauw method to measure the resistivity and magnetoresistance of the sample.The curve of resistivity versus temperature shows that the resistance of the sample first decreases and then increases with the decrease of temperature.It is a typical heavily doped semiconductor behavior.Further analysis of p-logT curve indicated that EEI effect and WL effect might play a role at low temperature.The measurement results of electrical properties of samples at low temperature show that the linear variation of resistivity versus logT is the result of the joint influence of these two effects.3.The change of conductivity with La doping ratio was studied.The results show that with the increase of doping ratio,the conductivity of the samples increases first and then decreases slightly.The lattice structure of samples with different thickness was studied.La0.05Sr0.95SnO3 samples with different thickness were grown on SrTiO3(001)and LaAlO3(001)substrates respectively.It was found that with the decrease of thickness,the samples will be subjected to stronger lattice compressive strain.When the lattice strain reaches to a certain degree,the conductivity of samples will be significantly reduced,which is due to the change of physical properties caused by the change of lattice structure.Finally,we measured the optical transmittance of different thickness samples grown on different substrates,the results show that the strain can significantly affect the band gap size of La doped SrSnO3 samples. |
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