Thermal Treatments and Photoluminescence Properties of ZnO and ZnO:Yb Films Grown by Magnetron Sputtering

This work is on ZnO and ZnO:Yb (0.3 at%) films prepared on (100) Si substrates by magnetron sputtering and deals with their structural and photoluminescence evolutions upon annealing at different temperatures from 873 to 1173 K during 1 h under N-2 atmosphere. The microstructural characterizations reveal that, for both sample series, annealing treatment improves the crystallinity of ZnO of the upper part of the films. However, (002) textured ZnO columnar growth is only observed for ZnO films. For annealing temperatures higher than 973 K, rare earth and Si diffusions toward the film/substrate interface are observed resulting in the appearance of a zinc silicate phase for ZnO films and a composite material made of nanoscale ZnO grains surrounded by an amorphous phase for ZnO:Yb films. In addition, photoluminescence measurements show that Yb doping in ZnO results in a lower integrated photoluminescence intensity compared to that of ZnO films and the photoluminescence response in the visible spectral range is also modified most probably due to the presence of dopant. Furthermore, the PL intensity at 980 nm originating from electronic transitions between F-2(5/2) and F-2(7/2) levels of Yb3+ ion increased with temperature. At last, the evolutions of the PL emissions with temperature from the ZnO defects are discussed.