Impact of strain on Si and Sn incorporation in (Si)GeSn alloys by STEM analyses

Abstract

The structural properties of CVD-grown (Si)GeSn heterostructures were assessed thanks to scanning transmission electron microscopy at the nanometer scale. Quantitative energy dispersive x-ray (EDX) spectroscopy together with precession electron diffraction and geometrical phase analysis (GPA) were performed to probe the chemical and structural properties of the different layers. Results presented in this paper demonstrated the advantages of a multilayer structure, with successive layers grown at decreasing temperatures in order to gradually accommodate the in-plane lattice parameter and incorporate more and more Sn into the stack. It was shown how the GeSn emissive layer could be manufactured with low plastic deformation and a high relaxation rate, necessary for better light emission performances. SiGeSn alloys used as confinement barriers around the emissive layer were also investigated. For such thin layers, we showed the importance of the starting lattice parameter (SLP) prior to the growth on their composition. Indeed, higher SLPs resulted, for the very same process conditions, into higher Sn contents and lower Si contents. The interest in combining EDX, which was accurate enough to detect slight chemical concentration variations, and GPA, for local strain analyses, was clearly demonstrated. Present results will be very useful to predict and control the bandgap and structural quality of (Si)GeSn materials and, in turn, device properties.

Advances in In Situ Boron and Phosphorous Doping of SiGeSn

“…[47][48][49][50][51] Thin SiGeSn layers grown on top of relaxed GeSn buffers, with therefore a higher inplane lattice parameter than on Ge SRBs, were otherwise shown to be richer in Sn and poorer in Si than the very same layers grown on Ge SRBs. 52 Here, the layer was too thin to result in plastic strain relaxation, but elastic strain relaxation might have occurred. Composition changes towards the surface might also explain why the surface got drastically smoother for high diborane flows.…”