A comparative study of 1.5 μm photoluminescence from (Er, Si) and (Er, Ge) co-sputtered with Al2O3 on Si

•An attempt to fabricate Si and Ge nanocrystals/nanoclusters in Al2O3 matrix in Si substrates.•Co-doping of Er in Si and Ge sputtered with Al2O3 matrix.•1.5 μm intense luminescence is emitted from Er ion with presence of Si nanoclusters.•Quenching of luminescence due to the presence of Ge ions in the sputtered matrix.

We present a comparative study of the 1.54 μm photoluminescence (PL) from Al2O3:(Er, Si) and Al2O3:(Er, Ge) films co-sputtered on Si substrates using a composite target. The PL yield of Si- and Ge-doped films subjected to different thermal treatment in the range 500–1100 °C is referenced against that of a control Al2O3:(Er) structure. The Er-related emission reaches maximum upon annealing at 700 °C for the Al2O3:(Er, Si) and 500 °C for the Al2O3:(Er, Ge) films, in both cases decreasing at higher annealing temperatures. Ge co-doped films are found to be approximately 20 times less luminous than the reference Al2O3:(Er) structure, whereas Si co-doping leads to greatly enhanced emission at 1.54 μm. By adapting energy filtered transmission electron microscopy (EFTEM), the presence of ∼2 nm Si nanoclusters was revealed, whereas no indications of Ge clusters or crystals could be observed implying that mere presence of Ge in the Al2O3 matrix can dramatically reduce the luminescence efficiency. We discuss the possible reasons for not forming the Ge nanoclusters in the Al2O3 host and the apparent quenching of the Er-related emission.