Formation of size controlled Ge nanocrystals in Er-doped ZnO matrix and their enhancement effect in 1.54 μm photoluminescence

This paper investigated the controllable growth of Ge nanocrystal (nc-Ge) in (Ge, Er) co-doped ZnO film, and the relationship between the size of nc-Ge and the enhancement of Er3+ related 1.54 μm photoluminescence (PL). It was found that nc-Ge with size of ∼5 nm was formed by annealing treatment at 600 °C. The intensity of 1.54 μm was significantly enhanced due to the existence of nc-Ge and showed an obvious dependence on nanocrystal size. The size of nc-Ge increased with the increase of the annealing temperature, and the nanocrystal with size of ∼5 nm made the most obvious contribution to PL enhancement. Prolonging annealing time could improve the crystalline structure of ZnO matrix but had no effect on PL intensity. The experimental results showed that the PL enhancement was mainly achieved by transferring the energy to Er through the resonance absorption of nc-Ge.