Study On The Texture Of Scandium-doped ZnO Films

ZnO is a II-VI compound semiconductor material with hexagonal wurtzitestructure, and it has3.37ev band gap at room temperature. ZnO is widely applied inUV detector, SAW device and window layer in thin-film solar cells due to its low cost,outstanding photoelectric and non-toxic properties.Compared with AZO, ⅢB rare earth element Sc doped ZnO has causedextensive concern not only because the Sc3+(0.0745nm) has the nearest ionic radius toZn2+(0.0740nm which leads to a smaller lattice distortion, a decreased defect and aimproved crystal quality when it is doped into ZnO lattice, but also because SZO hasa the more excellent corrosion resistance than AZO. Surface textured ZnO thin filmhas a great light trapping effect and light scattering capacity, so it has an increasedtransmittance, an increased incident light’s utilization rate and optical path in thethin-film solar cells, which can improve the Iscand efficiency of thin-film solar cells.In this work, surface textured SZO thin films are successfully prepared bymagnetron sputtering method with varied deposition temperature, sputtering pressureand power. The crystal structure, surface topography and optical and electricalproperties of the surface textured SZO are investigated by XRD, SEM, UVspectrophotometer, Hall measurement instrument and so on. The effects ofpreparation condition on the textured structure of SZO thin film are also analyzed.Firstly, in order to study the influence of deposition temperature on the SZOtextured structure, SZO thin films are prepared at room temperature,250℃,350℃and450℃separately, and the related properties are measured. It is found that theSZO thin film shows the (100) preferred orientation which is parallel to the substrateat250℃, the surface presents a pyramid structure, and it has the greatestlight-trapping effect and light scattering capacity, which lead to the highest totaltransmittance, diffusion transmittance and haze coefficient. With the increase ofdeposition temperature, the growth direction of SZO thin films changed graduallyfrom (100) to (002), which is perpendicular to the substrate with a smoother filmsurface, the light-trapping effect and light scattering capacity are weak, which cause the reduction of total transmittance, diffusion transmittance and haze coefficient. Thecarrier concentration of SZO thin film increases with the increase of depositiontemperature. The Hall mobility and the resistivity decrease due to the predominanceof the changes in the carrier concentration.Secondly, in order to study the influence of sputtering pressure on the SZOtextured structure, the SZO thin films are prepared at0.5pa,1.0pa1.5pa and2.0paseparately, and the related properties are measured. It is found that the SZO thin filmshows the (002) preferred orientation which is perpendicular to the substrate when thesputtering pressure is low. The surface is smooth, which has the lowest totaltransmittance and diffusion transmittance. Meanwhile, it has the excellent electricalproperty due to the high carrier concentration and the low hall mobility. As thesputtering pressure increased, the growth direction of SZO thin films changedgradually from (002) to (110), which is parallel to the substrate. It has the greatestlight-trapping effect and light scattering capacity with a pyramid structure and lead tothe highest total transmittance(87.21%), diffusion transmittance(5.49%) and hazecoefficient. With the further increase of sputtering pressure, the crystal qualitybecomes poorer, optical and electrical properties degenerate, haze coefficientdecreases.Finally, to study the influence of sputtering power on the SZO textured structure,the SZO thin films are prepared at60w,90w,120w and150w separately, and therelated properties are measured. It is found that the SZO thin film shows the (100)preferred orientation which is parallel to the substrate when the deposition power is90w, the grain size is larger, the surface presents the pyramid structure, and it has thegreatest light-trapping effect and light scattering capacity, which lead to the highesttotal transmittance(85.50%), diffusion transmittance(7.93%) and haze coefficient. Asthe sputtering power increased, the growth direction of SZO thin films changedgradually from (100) to (002), which is perpendicular to the substrate, the grain size issmaller, and the surface is smoother, the light-trapping effect and light scatteringcapacity are weaken, which cause the reduction of total transmittance, diffusiontransmittance and haze coefficient. Meanwhile, the carrier concentration of SZO thin film increases with the rise of sputtering power, the hall mobility and the resistivitydecrease.