Transparent and electrical properties of Ga-doped Zn1−x Cd x O films post-annealed in vacuum and nitrogen

Abstract

(Cd,Ga)-codoped ZnO films were prepared by sol–gel method. The codoping films retained wurtzite structure of ZnO, and showed preferential c-axis orientation. The transparent and electrical properties of the films post-annealed in vacuum and nitrogen were investigated. The transmittances of the films were degraded to 60–70 % by vacuum annealing, but enhanced to 80–90 % by nitrogen annealing. The carrier concentration increased, while resistivity decreased with the narrowing band gap, i.e. Cd doping could increase the conductivity of the Ga-doped Zn1−x Cd x O films by narrowing their band gap. The band gap modification was attributed to both Cd doping (majority) and Burstein–Moss effect (minority). The resistivity of nitrogen annealing films was one order higher than that of vacuum annealing films. It seemed that the transmittance and conductivity was irreconcilable, while the trade-off between them might be modulated by different post-annealing ambient.