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