Ultra-Low Threshold cw Lasing in Tensile Strained GeSn Microdisk Cavities

GeSn is proven as a good candidate to achieve CMOS-compatible laser sources on silicon. Lasing demonstrations in this alloy were based on directness of the band structure, this directness being increased with increasing the Sn content above 8 at.%. These past few years the research were consequently focused on incorporating the highest Sn content as possible to achieve high directness and high temperature laser operation. This unfortunately results is increased threshold. In this contribution we discuss the advantages in combining tensile strain engineering with lower Sn content alloys. This approach is motivated by the higher material quality in lower Sn content. The case with Sn content as small as 5.4 at.% Sn will be discussed. The alloy is initially compressively strained, and exhibits an indirect band gap that is turned to direct by applying tensile strain. A specific technology based on transfer On Insulator stressor layer on metal was developed to address strain engineering, thermal cooling and defective interface with the Ge-VS. This led to lasing in Ge0.95Sn0.05 microdisk cavities with dramatically reduced thresholds, by two order of magnitude, as compared to the case with high Sn alloys and as consequence enables cw operation

Ultra-low-threshold continuous-wave and pulsed lasing in tensile-strained GeSn alloys

Strained GeSn alloys are promising for realizing light emitters based entirely on group IV elements. Here, we report GeSn microdisk lasers encapsulated with a SiNx stressor layer to produce tensile strain. A 300 nm-thick GeSn layer with 5.4 at% Sn, which is an indirect-bandgap semiconductor as-grown, is transformed via tensile strain engineering into a direct-bandgap semiconductor that supports lasing. In this approach, the low Sn concentration enables improved defect engineering and the tensile strain delivers a low density of states at the valence band edge, which is the light hole band. We observe ultra-low-threshold continuous-wave and pulsed lasing at temperatures up to 70 K and 100 K, respectively. Lasers operating at a wavelength of 2.5 μm have thresholds of 0.8 kW cm−2 for nanosecond pulsed optical excitation and 1.1 kW cm−2 under continuous-wave optical excitation. The results offer a path towards monolithically integrated group IV laser sources on a Si photonics platform

Interplay of Order and Disorder in the High-Energy Optical Response of Three-Dimensional Photonic Crystals

21 páginasOpal-like structures, consisting of lattices of dielectrics spheres, are the most commonly studied example of three-dimensional (3D) photonic crystals (PCs). Since they were proposed as new materials to mold the flow of light, they have become an important area of research because of theit technological potential and fundamental interest. Among all fabrication techniques developed up to date to prepare opaline PCs, those based on evaporation-induced self-assembly (EISA) are some of the most frequently used and thoroughly analyzed. The advent and subsequent improvement of fabrication techniques that take advantage of self-organizing properties of dielectric spheres in the micrometer scale have permitted to obtain solid colloidal crystals that exhibit PC properties, whose optical response has been studies in depth in the low-energy range, where the lattice parameter is smaller than the incident wavelength.Peer reviewe