Electrical and optical properties of ZnO films grown on GaAs substrates

Undoped ZnO films were deposited on GaAs substrates by conventional rf magnetron sputtering technique. After thermal annealing at temperatures of 500degreesC and higher for 20 min, the Hall coefficient of ZnO films on GaAs substrate becomes positive. The long-time annealing of 550 min at a temperature of 400degreesC also converts the sign of the Hall coefficient to positive. X-ray microanalysis shows that the diffusion of Zn atoms into the GaAs substrate and Ga atoms from the GaAs substrate into the ZnO film during thermal annealing occurs. The results of Hall measurements were analyzed by using the two-layer model of conductivity. It was shown that the positive sign of the Hall coefficient for the annealed ZnO film on the GaAs substrate is due to p-type conductivity of the GaAs substrate as a result of the diffusion of the Zn atoms from ZnO film into the GaAs substrate. With increasing annealing temperature or annealing time the ZnO films become more n-type due to the diffusion of Ga atoms from the GaAs substrate into the ZnO film.