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Infrared absorption of n-type tensile-strained Ge-on-Si

Author(s)
Wang, Xiaoxin; Li, Haofeng; Cai, Yan; Kimerling, Lionel C.; Michel, Jurgen; Liu, Jifeng; Camacho-Aguilera, Rodolfo Ernesto; ... Show more Show less
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Abstract
We analyze the IR absorption of tensile-strained, n-type Ge for Si-compatible laser applications. A strong intervalley scattering from the indirect L valleys to the direct Γ valley in n[superscript +] Ge-on-Si is reported for the first time to our knowledge. The intervalley absorption edge is in good agreement with the theoretical value. On the other hand, we found that the classical λ[superscript 2]-dependent Drude model of intravalley free-carrier absorption (FCA) breaks down at λ < 15  μm. A first-principle model has to be employed to reach a good agreement with the experimental data. The intravalley FCA loss is determined to be <20  cm[superscript −1] for n = 4 × 10[superscript 19]  cm[superscript −3] at λ = 1.5–1.7  μm, an order lower than the results from Drude model. The strong L → Γ intervalley scattering favors electronic occupation of the direct Γ valley, thereby enhancing optical gain from the direct gap transition of Ge, while the low intravalley free-electron absorption at lasing wavelengths leads to low optical losses. These two factors explain why the first electrically pumped Ge-on-Si laser achieved a higher net gain than the theoretical prediction using λ[superscript 2]-dependent free-carrier losses of bulk Ge and indicate the great potential for further improvement of Ge-on-Si lasers.
Date issued
2013-02
URI
http://hdl.handle.net/1721.1/79736
Department
MIT Materials Research Laboratory; Massachusetts Institute of Technology. Department of Materials Science and Engineering; Massachusetts Institute of Technology. Microphotonics Center
Journal
Optics Letters
Publisher
Optical Society of America
Citation
Wang, Xiaoxin et al. “Infrared Absorption of N-type Tensile-strained Ge-on-Si.” Optics Letters 38.5 (2013): 652. © 2013 Optical Society of America
Version: Final published version
ISSN
0146-9592
1539-4794

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