High Speed Circuits & Systems Laboratory Joungwook Moon

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

 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 nm, Predominantly TE with increasing gain, and a clear threshold behavior. 3

 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 4

5  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 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 1X10 19 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

7  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) nm 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

8 (a) Spontaneous emission 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 )

9 (b)  Periodic peaks corresponding to longitudinal Fabry-Perot modes are clearly observed.  Δλ = 0.060±0.003 length 4.8 mm.

 Demonstrated an optically pumped edge- emitting multimode Ge-on-Si laser operating at room temperature with a gain spectrum of nm. 10