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Ge-on-Si laser operation at room temperaure

Ge-on-Si laser operation at room temperaure. High Speed Circuits & Systems Laboratory Joungwook Moon 2011. 4. Contents. Abstract 1. Introduction 2. Material and Device Structure 3. Emission Characteristics 4. Summary. Abstract.

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Ge-on-Si laser operation at room temperaure

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  1. Ge-on-Si laser operation at room temperaure High Speed Circuits & Systems Laboratory Joungwook Moon 2011. 4.

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

  3. Abstract • 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.

  4. 1. Introduction • 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

  5. 2. Material and Device Structure(1) • 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

  6. 2. Material and Device Structure(2) • Direct Band gap PL(Photoluminescence) of tensile-strained, n-type Ge-on-Si at room temperature • Ge waveguides were selectively grown epitaxially on Siby UHVCVD. • (Ultra high vacuum chemical vapor deposition) • Ge Growth temp. 650’C , 0.24% thermally-induced tensile strain was accumlated.  shrinks the direct gap of GE to 0.76 eV • 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

  7. 2. Material and Device Structure(3) • A cross sectional SEM picture & Setup procesure • Ge waveguide Width = 1.6 um / Length=4.8mm / Hight = 500nm • Both edges were mirror polished to obtain vertical facets for reflection mirrors • (mirror loss << 10 cm-1 , much smaller than optical gain of Ge) • 1064nm Q-Switched laser with pulse duration of 1.5ns excited the entire waveguide • The pump laser was focused into a line by a cylindrical lens, and vertically incident on top of a Ge waveguide • The pulsed edge emission is collected into monochromator, and detected by an InGaAs photomultiplier

  8. 3. Emission Characteristics(1) • 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 (a) Spontaneous emission

  9. 3. Emission Characteristics(2) • Periodic peaks corresponding to longitudinal Fabry-Perot modes are clearly observed. • Δλ = 0.060±0.003 nm @cavity length 4.8 mm. (b)

  10. 4. Summary • 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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