Infrared absorption of n-type tensile-strained Ge-on-Si
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 goo...
| Main Authors: | , , , , , , |
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| Other Authors: | |
| Format: | Article |
| Language: | en_US |
| Published: |
Optical Society of America
2013
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| Online Access: | http://hdl.handle.net/1721.1/79736 https://orcid.org/0000-0002-3913-6189 |
| Summary: | 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. |
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