Study On Properties Of Y Doped Cadmium Oxide Thin Films

Transparent conductive oxides?TCO?have attracted a lot of attentions due to their high conductivity as well as high transparency in the visible and NIR wavelength region.Due to the rapid development of photovoltaic devices and displays,traditional transparent conductive oxide materials can no longer meet the demand.Compared with these traditional TCOs,CdO can achieve even higher conductivity?>1x104 S/cm?due to its much higher electron mobility?>100 cm²/Vs?with electron concentration>1021/cm³.However,the intrinsic band gap of CdO is only 2.2 eV,which limits its optical transparency in the ultra-violet?UV?region.To solve this problem,metal elements can be doped into CdO thin films and the band gap size can be tuned by the Burstein-Moss effect.In this dissertation,Y-doped CdO thin films were synthesized by RF sputtering.The effects of different Y doping concentrations and rapid thermal processing on the properties of thin films were studied.In addition,indium and yttrium co-doped CdO thin films have been studied for their properties and annealing effects on the co-doped thin films.The Y-doped CdO thin films we prepared by RF sputtering method are all cubic rock salt CdO phases.Y replaces the Cd site in the CdO lattice,providing a free electron to the conduction band,increasing the carrier concentration of the film.The average transmittance of the film in the visible and near-infrared regions is between 75%and 95%.9%Y doped CdO thin film has an optical bandgap of 3.09 eV and widens the intrinsic bandgap?0.4 eV.The decrease in the carrier concentration of the 9%doped film is due to that Y have two existing forms,Y atoms and Y3+.The rapid drop in mobility with Y concentration can be understood in terms of the anticrossing interaction between localized d-states of Y and extended conduction band states of CdO.After annealing,the carrier concentration rapidly increases and the resistivity decreases.YCO films with low resistivity of 1.5×10^-4?· cm and high mobility of 122 cm²/Vs was obtained with 1.4%Y doping after RTP at 500°C.The average grain size of the film increases during annealing,which reduces the scattering of grain boundaries and increases the mobility of the film.Co-doping of In and Y can effectively increase the carrier concentration of CdO thin film to 1021/cm³,At the same time,the resistivity is 1-4?·cm.when the sputtering power of In2O3 is l0W,the film carrier concentration n?8.66 × 1020/cm³,mobility ??52.3cm²/Vs,Iesistivity ??1.36 × 10^-4?·cm.After annealing at 500 ?,carrier concentration?1021/cm³,the mobility and conductivity also increased slightly.The doping of Y can effectively improve the performance and optical bandgap of CdO thin films.We note that after RTP at temperatures>?500?,YCO thin films with[Y]?2.4%has an n?6.3×1020/cm³ and ??75 cm²/Vs,corresponding to a??1.3×lV-4?·cm.This is comparable or better than most conventional TCO available.