Electrical and optical properties of ZnO:Al thin films prepared by the spray pyrolysis technique

Highly transparent conducting ZnO:Al thin films have been produced by the spray pyrolysis technique on glass substrates at a substrate temperature T-s = 450 degrees C by a home-made spraying system. The electrical and optical properties of the films were investigated at room temperature before and after annealing in nitrogen atmosphere. The electrical properties were studied by recording and analyzing the I-V measurements. All the curves were linear, so the resistivity was estimated from the slopes. The resistivity was found to be 133 Omega cm for the undoped ZnO films, but 90 Omega cm for the Al-doped films before annealing and 84 Omega cm after annealing. The optical properties were investigated by measuring the transmittance curves that were used to find the optical bandgap energy. The bandgap energy was found to be 3.27 eV for the undoped ZnO films and 3.28 eV for the Al-doped ZnO films before and after annealing. Therefore the electro-optical properties of the films had improved with Al doping and annealing in nitrogen atmosphere.