Physical mechanism for photon emissions from group-IV-semiconductor quantum-dots in quartz-glass and thermal-oxide layers

We experimentally studied the influence of both impurity density and dangling-bond density on PL emissions from group-IV-semiconductor quantum-dots (IV-QDs) of Si and SiC fabricated by hot-ion implantation technique, to improve the PL intensity (IPL) from IV-QDs embedded in two types of insulators of quartz glass (QZ) with low impurity density and thermal-oxide (OX) layers. First, we verified the IPL reduction in the IV-QDs in QZ. However, we demonstrated the IPL enhancement of IV-QDs in doped QZ, which is attributable to multiple-level emission owing to acceptor and donor ion implantations into QZ. Secondly, we confirmed the large IPL enhancement of IV-QDs in QZ and OX, owing to forming gas annealing with H2/N2 mixed gas, which are attributable to the reduction of the dangling-bond density in IV-QDs. Consequently, it is possible to improve the IPL of IV-QDs by increasing impurity density and reducing dangling-bond density.

GeSnOI mid-infrared laser technology

GeSn alloys are promising materials for CMOS-compatible mid-infrared lasers manufacturing. Indeed, Sn alloying and tensile strain can transform them into direct bandgap semiconductors. This growing laser technology however suffers from a number of limitations, such as poor optical confinement, lack of strain, thermal, and defects management, all of which are poorly discussed in the literature. Herein, a specific GeSn-on-insulator (GeSnOI) stack using stressor layers as dielectric optical claddings is demonstrated to be suitable for a monolithically integration of planar Group-IV semiconductor lasers on a versatile photonic platform for the near- and mid-infrared spectral range. Microdisk-shape resonators on mesa structures were fabricated from GeSnOI, after bonding a Ge0.9Sn0.1 alloy layer grown on a Ge strain-relaxed-buffer, itself on a Si(001) substrate. The GeSnOI microdisk mesas exhibited significantly improved optical gain as compared to that of conventional suspended microdisk resonators formed from the as-grown layer. We further show enhanced vertical out-coupling of the disk whispering gallery mode in-plane radiation, with up to 30% vertical out-coupling efficiency. As a result, the GeSnOI approach can be a valuable asset in the development of silicon-based mid-infrared photonics that combine integrated sources in a photonic platform with complex lightwave engineering.

Green Synthesis of Ge1-xSnx Alloy Nanoparticles for Optoelectronic Applications

Compositionally controlled, light-emitting, group IV semiconductor nanomaterials have potential to enable on-chip data communications and infrared (IR) imaging devices compatible with the complementary metal−oxide−semiconductor (CMOS) technology. The recent demonstration of a direct band gap laser in Ge-Sn alloys opens avenues to the expansion of Si-photonics. Ge-Sn alloys showed improved effective carrier mobility as well as direct band gap behavior at Sn composition above 6–11%. In this work, Ge1−xSnx alloy nanoparticles with varying Sn compositions from x = 0.124 to 0.178 were prepared via colloidal synthesis using sodium borohydride (NaBH4), a mild and non-hazardous reducing reagent. Successful removal of the synthesized long-alkyl-chain ligands present on nanoparticles’ surfaces, along with the passivation of the Ge-Sn nanoparticle surface, was achieved using aqueous (NH4)2S. The highly reactive surface of the nanoparticles prior to ligand exchange often leads to the formation of germanium oxide (GeO2). This work demonstrates that the (NH4)2S further acts as an etching reagent to remove the oxide layer from the particles’ surfaces. The compositional control and long-term stability will enable the future use of these easily prepared Ge1−xSnx nanoalloys in optoelectronic devices.