Stduy On Preparation And Physical Properties Of P-type Transparent Conductive CuCrO₂ Thin Films

In the field of display,energy,catalysis,and sensing technology,etc,we can see the background of the use of Transparent Conductive Oxides(TCOs)materials,which is due to their good photoelectric properties.The exploration and development of TCOs materials has attracted the attention of scientific researchers correspondingly.So far,relevant reports on TCOs semiconductor materials are mainly N-type,and the development of advanced electronic devices also requires P-type semiconductor materials with excellent performance.Therefore,P-type delafossites materials have set off a research boom as soon as they were reported,and CuCrO₂stands out in a series of delafossites materials with its relatively low synthesis temperature and excellent thermal stability.In this paper,we take the sol-gel method to synthesize the CuCrO₂thin film materials were synthesized through a two-step annealing process on Al₂O₃substrate,after that a series of physical properties including microstructure,stress,surface morphology,optical properties,and electrical transport mechanism were characterized and analysized.The influence mechanism of the annealing temperature on the CuCrO₂films prepared were discussed from multiple aspects.Finally,on the basis of the best annealing process,comprehensive influence of Ni ion doping on CuCrO₂ thin film samples was discussed from the above-mentioned perspectives.The main work results include the following three aspects:(1)Through theoretical calculation,it is found that CuCrO₂ is an indirect bandgap semiconductor.Through experimental measurement,it is determined that the film quality is the best when the annealing process is kept at 800°C with two hours.This paper uses theoretical calculations to simply simulate the energy band structure and density of states of CuCrO₂ materials,and then determines the best process flow for preparing CuCrO₂ thin films.During the preparation of CuCrO₂ thin film materials,two major factors affecting the quality of the thin film were paid attention to:annealing temperature and annealing time.Various heating curves were set using the controlled variable method,and the thin films under different process parameters were analyzed by XRD and Raman spectroscopy to explore the best process flow,and on this basis,for the first time,the sol-gel method was used to prepare Cu Cr_1-xNi_xO₂(x=0,2%,4%,6%,8%)samples doped with trace Ni ions on the sapphire substrate.(2)Properly increasing the annealing temperature can promote the crystal growth of the film.The morphology of the film becomes more clearly visible as the annealing temperature rises.All films possess a relatively high transparency of around 75%in the visible region.In addition,the conductivity of theses samples show different characteristics of changes in different temperature ranges.Through various characterization methods,the performance characteristics of CuCrO₂ films under different annealing temperature treatments are systematically analyzed and discussed.The CuCrO₂ films after two-step annealing treatment are all polycrystalline materials,which were confirmed by XRD and Raman results.The two-step annealing treatment successfully converted Cu²⁺into Cu¹⁺.As the annealing temperature gradually increased,the film crystallinity gradually improved.Besides,we can see that as the annealing temperature rised,the grains began to gradually aggregate from the SEM characterization results,which made the average particle size of the CuCrO₂ film increase,the grain boundaries became obvious,the density decreased,and the film thickness increased slightly.In addition,the element distribution and the composition of different elements of theses films are proved to meet our calculated stoichiometry from the SEM-EDS test results.These films with high transparency in the visible range were detected by transmission spectra.Finally,the electrical transport mechanism of CuCrO₂ film in different temperature ranges is discussed.It is found that the electrical transport performance shows different features as the temperature ranging from low to high,which can be explained by the crystal defects of the CuCrO₂films and the fluctuation of the Fermi level.The results of the Hall test further confirmed the P-type semiconductor properties of CuCrO₂.(3)The Ni ions introduced in CuCrO₂are well absorbed into the lattice of CuCrO₂,and the grain size of the film surface is affected by Ni ions.The grain size varies as the increase of the Ni content.That is,first increases and then decreases.And the inflection is when the doping content at x=2%,Doping can effectively improve the conductivity of CuCrO₂ films.The physical properties of these samples including microstructure,stress,surface morphology,optical properties and electrical transport mechanism of CuCrO₂ thin film are investigated in detail.The XRD test results show that Ni ions are well absorbed into the CuCrO₂ crystal lattice.All samples have well c-axis preferred orientation.Since the radius of Ni ions is slightly larger than that of Cr,as the doped content of Ni ions increases,the lattice of CuCrO₂ will expand to a certain extent.The test results of Raman spectroscopy show that the doping of Ni ions has little damage to the structural integrity of CuCrO₂.In addition,it can be seen from the results of variable temperature Raman spectra that Cu Cr_1-xNi_xO₂(0?x?8%)films have excellent thermal stability properties.The relatively flat and smooth surfaces of all film samples were confirmed by SEM and AFM.The grain size increases firstly and then decrease with increasing the Ni content at the inflection point at x=2%.Since the grain size is opposite to the grain boundary change law and the roughness of these samples is exactly the opposite of the corresponding grain size change law.XPS and SEM-EDS further determined the composition and valence of the chemical elements of the Cu Cr_1-xNi_xO₂(0?x?8%)films.The transparency in the visible region of these samples is declined with increasing the Ni ions content,which is characterized by transmission spetra.Besides,we can also see that the absorption edge of the CuCrO₂film to move toward the infrared range,which is mainly caused by the scattering effect and the formation of more defect centers.The Hall test shows that all Cu Cr_1-xNi_xO₂(0?x?8%)films are P-type semiconductor materials,the conductivity together with carrier concentration of these samples improve orders of magnitude with increasing the Ni content,it shows that the doping of Ni ions cause the holes in CuCrO₂ films increase,leading to a surge of carriers.However,doping also promote the growth of grain boundaries and defect centers in the film,resulting in a decrease in carrier mobility.But overall,the CuCrO₂ films with doping Ni ions obtain an enhanced electrical properties,which further improve its application potential in various electronic devices.