Transcript Presentation

High Speed Circuits & Systems Laboratory
Joungwook Moon
2011. 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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Direct Band gap PL(Photoluminescence) of tensilestrained, n-type Ge-on-Si at room temperature
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 eV
3. 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
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A cross sectional SEM picture & Setup procesure
1. Ge waveguide Width = 1.6 um / Length=4.8mm / Hight = 500nm
2. 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
waveguide
4. The pump laser was focused into a line by a cylindrical lens, and vertically
incident on top of a Ge waveguide
5. The pulsed edge emission is collected into monochromator, and detected by
an InGaAs photomultiplier
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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 )
laser emission
threshold
Spontaneous
emission
(a)
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Periodic peaks corresponding to longitudinal
Fabry-Perot modes are clearly observed.
Δλ = 0.060±0.003 nm @cavity length 4.8 mm.
(b)
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Demonstrated an optically pumped edgeemitting multimode Ge-on-Si laser operating
at room temperature with a gain spectrum of
1590-1610 nm.
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