Tensile strain is a widely discussed means for inducing a direct bandgap in Ge for the realization of a semiconductor laser compatible with Si microelectronics. We present a top-down fabrication approach for creating high uniaxial tensile stress in suspended Ge structures, which enhances—by a factor of more than 20—the strain induced by thermal mismatch of Ge layers grown on silicon or silicon-on-insulator substrates. Strain values up to 3.1% are measured using Raman spectroscopy, in excellent agreement with simulations using a biaxial thermal strain of 0.15%. As expected from the high value of strain, a 210 meV peak energy shift in the emission with respect to bulk Ge and a strong increase (×25) in the integrated photoluminescence intensity are observed. Although 3.1% uniaxial strain does not transform Ge into a direct-gap material, our model calculation predicts an optical gain of 460 cm−1 for 1 × 1019 cm−3 n-doped structures at an electron–hole injection density of 3 × 1019 cm−3.
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The authors acknowledge hospitality from the IR beamline of the SLS, where some of the photoluminescence experiments were performed. Part of this work is supported by the Swiss National Science Foundation (SNF project no. 130181). The authors also acknowledge support from the CARIPLO foundation regarding the project NANOGAP.
The authors declare no competing financial interests.
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Süess, M., Geiger, R., Minamisawa, R. et al. Analysis of enhanced light emission from highly strained germanium microbridges. Nature Photon 7, 466–472 (2013) doi:10.1038/nphoton.2013.67
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