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Crystals 2017, 7(6), 157;

Extended Defect Propagation in Highly Tensile-Strained Ge Waveguides

Electrical Engineering, University of Notre Dame, Notre Dame, IN 46556, USA
Uber, San Francisco, CA 94103, USA
Rigetti Quantum Computing, 775 Heinz Avenue, Berkeley, CA 94710, USA
Sandia National Laboratory, Albuquerque, NM 87185, USA
Electrical and Computer Engineering, University of California, Santa Barbara, CA 93106, USA
Institute of Solid State Physics, University Bremen, Otto-Hahn-Allee 1, Bremen 28359, Germany
Electrical and Computer Engineering, Cornell University, Ithaca, New York, NY 14853, USA
Author to whom correspondence should be addressed.
Academic Editor: Winnie Wong-Ng
Received: 8 March 2017 / Revised: 5 May 2017 / Accepted: 11 May 2017 / Published: 26 May 2017
(This article belongs to the Special Issue Crystallography of Functional Materials)
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Tensile-strained Ge is a possible laser material for Si integrated circuits, but reports of lasers using tensile Ge show high threshold current densities and short lifetimes. To study the origins of these shortcomings, Ge ridge waveguides with tensile strain in three dimensions were fabricated using compressive silicon nitride (SiNx) films with up to 2 GPa stress as stress liners. A Raman peak shift of up to 11 cm−1 was observed, corresponding to 3.6% hydrostatic tensile strain for waveguides with a triangular cross-section. Real time degradation in tensile-strained Ge was observed and studied under transmission electron microscopy (TEM). A network of defects, resembling dark line defects, was observed to form and propagate with a speed and density strongly correlated with the local strain extracted from both modeled and measured strain profiles. This degradation suggests highly tensile-strained Ge lasers are likely to have significantly shorter lifetime than similar GaAs or InGaAs quantum well lasers. View Full-Text
Keywords: strained germanium; stress liner; tensile strain; direct bandgap; dark line defects; optical waveguide; stability; silicon photonics strained germanium; stress liner; tensile strain; direct bandgap; dark line defects; optical waveguide; stability; silicon photonics

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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

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Qi, M.; O’Brien, W.A.; Stephenson, C.A.; Patel, V.; Cao, N.; Thibeault, B.J.; Schowalter, M.; Rosenauer, A.; Protasenko, V.; Xing, H.G.; Wistey, M.A. Extended Defect Propagation in Highly Tensile-Strained Ge Waveguides. Crystals 2017, 7, 157.

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