The impact of erbium incorporation on the structure and photophysics of silicon-germanium nanowires

摘要

In this paper, we report multi-step processes for the fabrication of Er~(3+)-doped SiGe nanowires (NWs) and characterization of their emissive properties. Three different alloyed architectures are obtained by altering the deposition sequences of Si and Er~(3+) on a Ge core NW, each involving a fixed concentration of these three elements. The deposition of Si onto the Ge NW core, followed by an Er~(3+)-rich layer on the outermost surface, permits facile formation of a SiGe alloy given the lack of an erbium diffusion barrier; yet clustering of the erbium centers on the NW surface produces the weakest emitter. For nanowires prepared by co-depositing Si and Er~(3+) on top of the Ge core, the presence of impurity Er~(3+) ions greatly reduces the alloying rate of Si and Ge such that less Si can diffuse into the Ge core. For this structure, the reduction of Er-Er interactions by a polycrystalline Si shell results in the strongest emission at 1540 nm. If an Er~(3+) layer is inserted between the Ge and Si layers (a sandwich structure), it is found that Er~(3+) ions diffuse preferentially into the SiGe core instead of the silicon-rich shell, with a correspondingly weaker luminescence intensity. A combination of high resolution transmission electron microscopy, energy dispersive X-ray mapping, micro-Raman spectroscopy, and photoluminescence spectroscopy are employed to derive these conclusions.