Preparation And Photoelectric Properties Of Infrared Transparent Conductive Oxychalcogenide Films

With a more complicated war environment,infrared photoelectric detection system,such as airborne infrared search and tracking system or missile accurate guidance system,is required to have a better electromagnetic shielding ability to improve its survivability in the complex electromagnetic environment.Infrared transparent conductive films（ITCFs）are a new kind of photoelectric films which can achieve both high transmittance in infrared detection band and electromagnetic shielding performance.In recent years,ITCFs have attracted extensive attention from researchers and major aerospace institutions.The application of high-performance ITCFs in the dome of infrared photoelectric detection system can greatly improve the ability of anti-electromagnetic interference and speed up the upgrading of weapons and equipment.However,there have been no significant breakthroughs in the research on ITCFs.The main reason is that the synergistic regulation mechanism of ITCFs is unclear and no transparent conductive materials with excellent infrared photoelectric properties have been found.In order to solve the pressing needs of scientific and technical problems mentioned above,this thesis carried out research on the mid-infrared transparent conductive films and wide-band infrared transparent conductive material from visible range to mid-infrared range.Firstly,the P-type La Se₂ films were prepared using a two-step method by combining the RF magnetron sputtering with selenization,and the infrared photoelectric properties were studied.Secondly,the wide-band LaCuOS films were prepared by two different methods,i.e.,ink method and co-sputtering combined with sulfurization.The growth process of LaCuOS films was investigated and the absorption and regulation mechanism of mid-infrared range was explained.The research in this thesis can be divided into the following parts:Firstly,P-type mid-infrared transparent conductive La Se₂ films were prepared by reactive RF magnetron sputtering combined with selenization.The effect of different selenization conditions on the infrared photoelectrical properties of La Se₂ films was studied.and the obtained La Se₂ films possess a conductivity of about 3.6 S/cm.The excellent electrical properties of La Se₂ films are attributed to the high carrier concentration of 10¹⁹ cm^-3.Compared with traditional P-type mid-infrared transparent conductive films,the hole effective mass of La Se₂ films（about 0.348）₀))is much lower than that of traditional P-type transparent conductive films（about 38）₀)).The mid-infrared transmittance of La Se₂ films is about 75%,which has broad application prospects.Secondly,the wide-band transparent conductive LaCuOS films were prepared by a simple and low-cost ink method.The photoelectric properties of LaCuOS films were investigated under different sulfurization time at 860℃.The transmittance of LaCuOS films was more than 70%and the conductivity was about 89 S/cm after sulfurization for a short time.The photoelectric properties of LaCuOS films decreased with the increase in sulfurization time.Nonetheless,the average transmittance of LaCuOS films is above60%and the conductivity is above 5 S/cm regardless of the wavelength range（visible or mid-infrared）.Thirdly,a new two-step process of preparing LaCuOS thin films by co-sputtering combined with sulfurization was developed.At a sulfurization temperature of 860℃and a sulfurization time of 1 hour,the LaCuOS thin film has excellent optical transmittance in visible range and mid-infrared range.The transmittance of visible light is above 60%,the transmittance in mid-infrared band is above 40%,and the conductivity is as high as about 70 S/cm.The electrical properties are better than that of most P-type transparent conductive materials.The conductive mechanism of LaCuOS films was explained by PPMS method.When the sulfurization temperature is higher than 860℃,the conductive mechanism of LaCuOS films is the same as that of metals,and the main carrier transport mechanism is ionized impurity scattering.When the temperature is 810℃,the main transport mechanism of carriers in LaCuOS films is grain boundary tunneling.When the temperature is 760℃,the carrier transport of LaCuOS thin films is affected by both grain boundary tunneling and mott transition jump conductance mechanism,with the former being the main mechanism.When the sulfurization time is more than 1h,LaCuOS films have the metal conductive properties mainly due to the scattering transport mechanism of ionized impurities.The main transport mechanism of carriers in LaCuOS films is grain boundary tunneling when sulfurized at 0.5h.Finally,the interstitial O point defect in LaCuOS films was identified by combining TEM-Mapping,HRTEM and DFT calculation.By constructing supercell with different interstitial O point defects concentrations,the regulation mechanism of interstitial O point defects on the transparent conductivity of LaCuOS films in infrared range was revealed.A higher concentration of interstitial O point defects could increase the hole effective mass of LaCuOS films.Thus,the absorption effect in the infrared range of the LaCuOS films caused by the increase of carrier concentration is weakened,which is conducive to the coupling of the transparent and conductive properties in the infrared range.The imaginary part of the dielectric constant of the high conductivity LaCuOS films was obtained by fitting the transmission spectrum.It was revealed that the main absorption mechanism of the high conductivity LaCuOS films in the mid-infrared range is the intra-band transition absorption of carriers.