Lateral Strain Engineering of Thickness Modulated Semiconductor Nanomembranes

Strain engineering in semiconductors is an effective strategy for modifying bandgaps and, in turn, electronic and optoelectronic properties. Laterally varying strain fields offer the opportunity to create complex band alignments, varying carrier mobility, and localized regions of quantum confinement. We report our results on lateral strain engineering of thickness-modulated Si nanomembranes (NMs) via mechanical stretching. The general idea is that thin regions of the Si NM accommodate more strain than thick regions under a globally applied stress. We transfer 220 nm thick Si NM to flexible polyimide host substrates and pattern thick (220 nm) and thin (60 nm) regions of 20 µm and 1mm lateral dimensions using optical lithography and etching. We mechanically stress these thickness-modulated Si NMs and experimentally quantify the amount of local strain using in-situ Raman spectroscopy. We observe a %strain of twice the value in thin region (60 nm) as compared to thick region (220 nm) of 20um *1 mm lateral dimensions. We predict how different thicknesses influence the amount of strain stored in the film and how the energy band gap changes when one goes from thick to thin regions.In summary, we create a strain mosaic at 50 micrometer or less and use in-situ Raman spectroscopy to calculate the amount of strain, up to 1.5%, developed in thick (220 nm) and thin (60 nm) regions of the NM.