Dependence of Thermal Annealing on Transparent Conducting Properties of HoF3-Doped ZnO Thin Films

A kind of n-type HoFa-doped zinc oxide-based transparent conductive film has been developed by electron beam evaporation and studied under thermal annealing in air and vacuum at temperatures 100-500℃.Effective substitutional dopings of F to O and Ho to Zn are realized for the films with smooth surface morphology and average grain size of about 50 nm.The hall mobility,electron concentration,resistivity and work function for the as-deposited films are 4 7.89 cm2 /Vs,1.39× 1020 cm-3,9.37× 10-4 Ω·cm and 5.069eV,respectively.In addition,the average transmittance in the visible region (400 700 nm) approximates to 87％.The HoF3 ∶ZnO films annealed in air and vacuum can retain good optoelectronic properties under 300℃,thereinto,more stable electrical properties can be found in the air-annealed fihns than in the vacuum-annealed films,which is assumed to be a result of improved nano-crystalline lattice quality.The optimized films for most parameters can be obtained at 200℃ for the air-annealing case and at room temperature for the vacuum annealing case.The advisable optoelectronic properties imply that HoF3 ∶ZnO can facilitate carrier injection and has promising applications in energy and light sources as transparent electrodes.