The Impact of Erbium Incorporation on the Structure and Photophysics of Silicon-Germanium Nanowires

In this paper, we report multi-step processes for the fabrication of Er3+-doped SiGe nanowires(NWs) and characterization of their emissive properties. Three different alloyed architectures are obtained by altering the deposition sequences of Si and Er3+ on a Ge core NW, each involving a fixed concentration of these three elements. The deposition of Si onto the Ge NWcore, followed by an Er3+-rich layer on the outermost surface, permits facile formation of a SiGealloy 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 Er3+ on top of the Ge core, the presence of impurity Er3+ ions greatly reduces the alloying rate of Si andGe 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 Er3+layer is inserted between the Ge and Si layers (a sandwich structure), it is found that Er3+ 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, andphotoluminescence spectroscopy are employed to derive these conclusions.