High Speed Circuits & Systems Laboratory

Joungwook Moon2011. 4.

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Abstract 1. Introduction 2. Material and Device Structure 3. Emission Characteristics 4. Summary

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First experimental observation of lasing from the direct gap transition of Ge-on-Si at room temperature using an edge-emitting waveguide device.

The emission exhibited a gain spectrum of 1590-1610nm, Predominantly TE with increasing gain, and a clear threshold behavior.

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monolithically integrated lasers on Si have been one of the biggest challenges

(SiGe nanostructures, Er doped Si. GeSn β-FeSi2, and Hybrid Ⅲ-Ⅴ lasers on Si )

Ge, indirect-gap meterial, can be band engineered to behave like a direct-gap material by using tensile strain and n-type doping

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Energy band engineering of Ge Why engineering Ge band structure?

Reduce band gap difference between Direct & Indirect.

Provide population inversion in the direct bandgap

Direct Indirect

136 eV

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1. Ge waveguides were selectively grown epitaxially on Si by UHVCVD. (Ultra high vacuum chemical vapor deposition)2. Ge Growth temp. 650’C , 0.24% thermally-induced tensile strain was

accumlated. shrinks the direct gap of GE to 0.76 eV3. Ge was In-situ doped with 1X1019 cm-3 phosphorous during the growth

Futher compensate the energy difference between direct and significantly enhance the direct gap light emission

Direct Band gap PL(Photoluminescence) of tensile-strained, n-type Ge-on-Si at room temperature

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A cross sectional SEM picture & Setup procesure

1. Ge waveguide Width = 1.6 um / Length=4.8mm / Hight = 500nm2. Both edges were mirror polished to obtain vertical facets for reflection mirrors

(mirror loss << 10 cm-1 , much smaller than optical gain of Ge)3. 1064nm Q-Switched laser with pulse duration of 1.5ns excited the entire

waveguide4. The pump laser was focused into a line by a cylindrical lens, and vertically

incident on top of a Ge waveguide5. The pulsed edge emission is collected into monochromator, and detected by

an InGaAs photomultiplier

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(a)

Spontaneousemission

threshold

laser emission

The threshold pumping energy is ~5uJ Increase of carrier inection Gain specturm shifts

to shorter wavelengths (occupation of higher energy stats in the direct Γ valley) ( k ∝ 1/λ )

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(b)

Periodic peaks corresponding to longitudinal Fabry-Perot modes are clearly observed.

Δλ = 0.060±0.003 nm @cavity length 4.8 mm.

Demonstrated an optically pumped edge-emitting multimode Ge-on-Si laser operating at room temperature with a gain spectrum of 1590-1610 nm.

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