Cathodoluminescence properties of undoped and Al-doped ZnO thin films deposited on glass substrate by spray pyrolysis

Abstract

Undoped and Al-doped zinc oxide (ZnO) thin films have been prepared by spray pyrolysis (SP), and the effect of doping on structural properties and cathodoluminescence (CL) imaging and spectroscopy has been investigated. These films, deposited at an optimal substrate temperature ( T s=450 °C), have a hexagonal close-packed structure. At room temperature, the CL spectra of the undoped and doped ZnO films exhibit the common near ultra-violet band gap peak at λ=382 nm, but they differ as regard to the visible emissions. The undoped ZnO emits an intensive blue-green light at λ=520 nm and a red emission at λ=672 nm. The presence of aluminium gives rise to a new light typical of the intrinsic behaviour of the material. CL imaging of the undoped ZnO films shows that the luminescence is located at defined sites with a grain-like structure inherent to the sample surface morphology. The presence of aluminium leads to a homogenous repartition of the emitting centres.