Annealing effects on the photoluminescence of terbium doped zinc oxide films

Zinc oxide (ZnO) is a transparent conductive oxide (TCO) material. It is integrated in many optoelectronic applications usually in thin films structures. ZnO is a well known, cheap and non-toxic material. Electrically or optically excited, it emits in the UV-blue spectral region. By Stark effect, rare earth doped ZnO (RE:ZnO) shows a light emissions whose wavelength depends on the RE nature considered. Based on the addition of several emissions created in the ZnO matrix by RE codoping, white light emission could be achieved. The intended application is the feasibility of a white light-emitting diode LED based on RE:ZnO. In this work, Terbium doped ZnO (Tb:ZnO) thin films have been deposited by rf-sputtering on (100) silicon substrates at low temperature (TS = 100?C). Tb:ZnO films have been annealed from Ta=400?C to 1000?C by a step of 100?C. From 400?C to 600?C, the band-gaps decrease with Ta from Eg = 3.44 eV up to Eg = 3.37 eV. Above 600?C and up to 1000?C, the band gap increases up to 3.42 eV. We present the structural changes of the films with temperature as well as their optical properties and the associated photoluminescence (PL). We compare these PL properties to those of undoped ZnO thin films fabricated with similar growth conditions. Then, we discuss the photoluminescence mechanism involved in the Tb:ZnO film.