A micromachining-based technology for enhancing germanium light emission via tensile strain

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Abstract

Germanium is an attractive material for silicon-compatible optoelectronics, but in its bulk form it does not emit light efficiently because of its indirect bandgap. Applying tensile strain to germanium modifies its band structure such that radiative recombination is enhanced, leading to improved light emission. Here, we introduce the ‘suspension platform for optoelectronics under tension’, a micromachining-based technology that applies large, locally tunable tensile strains to suspended device layers. Using this approach, we demonstrate dramatically enhanced light emission from uniaxially and biaxially tensile-strained germanium-on-insulator device layers. Photoluminescence enhanced by a factor of 130 at a wavelength of 1,550 nm and integrated enhancement by greater than a factor of 260 over bulk germanium are described. The emission exhibits a superlinear dependence on optical pump power. We also report preliminary evidence for enhanced electroluminescence from suspended germanium-on-insulator light-emitting diodes.

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Figure 1: Finite-element simulations of tensile-strained suspended (100) GOI device layers with 100-nm-thick germanium on 1-µm-thick SiO2 and 1-µm-thick Si3N4 stressors with 1 GPa initial intrinsic tensile stress.
Figure 2: Spectral photoluminescence analysis of a suspended 20 µm × 100 µm (100) GOI device layer under 0.98% uniaxial tensile strain along [100] with 60-µm-wide Si3N4 stressors.
Figure 3: Photoluminescence emission at 1,550 nm with optical pump power from tensile-strained suspended (100) GOI device layers.
Figure 4: Schematic illustrations of radiative recombination in germanium.
Figure 5: Theoretical steady-state modelling of photoluminescence emission from the 0.82% biaxially tensile-strained device of Fig. 3b.
Figure 6: Preliminary electroluminescence results from tensile-strained suspended (100) GOI LEDs.

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Acknowledgements

This work was carried out at the Stanford Nanofabrication Facility of the National Nanotechnology Infrastructure Network. The authors thank D.S. Ly-Gagnon and K.C. Balram of Stanford University for useful discussions. Funding for A.H. and M.L.B. was obtained from the Si-based Laser Initiative of the Multidisciplinary University Research Initiative (MURI) under the Air Force Aerospace Research OSR (award no. FA9550-06-1-0470).

Author information

J.R.J. and R.T.H. conceived the idea for the technology. J.R.J. conducted strain simulations, device fabrication, photoluminescence and Raman measurements/analysis, theoretical modelling/analysis and manuscript preparation. A.H. contributed to photoluminescence measurements/analysis and manuscript preparation. T.M.B. contributed to photoluminescence and Raman analysis and manuscript preparation. D.A.B.M contributed to photoluminescence and Raman analysis, theoretical modelling/analysis and manuscript preparation. M.L.B contributed to photoluminescence and Raman analysis, theoretical modelling/analysis and manuscript preparation. R.T.H. also contributed to photoluminescence and Raman analysis, theoretical analysis and manuscript preparation.

Correspondence to Jinendra Raja Jain.

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Jain, J., Hryciw, A., Baer, T. et al. A micromachining-based technology for enhancing germanium light emission via tensile strain. Nature Photon 6, 398–405 (2012) doi:10.1038/nphoton.2012.111

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