Full Picture of Lattice Deformation in a GeSn Micro-Disk by 5D X-ray Diffraction Microscopy.

Lattice strain in crystals can be exploited to effectively tune their physical properties. In microscopic structures, experimental access to the full strain tensor with spatial resolution at the (sub-)micrometer scale is at the same time very interesting and challenging. In this work, how scanning X-ray diffraction microscopy, an emerging model-free method based on synchrotron radiation, can shed light on the complex, anisotropic deformation landscape within three dimensional (3D) microstructures is shown.

Growth and Electrical Characterization of Hybrid Core/Shell InAs/CdSe Nanowires.

Core-only InAs nanowires (NWs) remain of continuing interest for application in modern optical and electrical devices. In this paper, we utilize the II-VI semiconductor CdSe as a shell for III-V InAs NWs to protect the electron transport channel in the InAs core from surface effects. This unique material configuration offers both a small lattice mismatch between InAs and CdSe and a pronounced electronic confinement in the core with type-I band alignment at the interface between both materials.

Correlations between Cascaded Photons from Spatially Localized Biexcitons in ZnSe.

Radiative cascades emit correlated photon pairs, providing a pathway for the generation of entangled photons. The realization of a radiative cascade with impurity atoms in semiconductors, a leading platform for the generation of quantum light, would therefore provide a new avenue for the development of entangled photon pair sources. Here we demonstrate a radiative cascade from the decay of a biexciton at an impurity-atom complex in a ZnSe quantum well.

Efficient Single-Photon Sources Based on Chlorine-Doped ZnSe Nanopillars with Growth Controlled Emission Energy.

Isolated impurity states in epitaxially grown semiconductor systems possess important radiative features such as distinct wavelength emission with a very short radiative lifetime and low inhomogeneous broadening, which make them promising for the generation of indistinguishable single photons. In this study, we investigate chlorine-doped ZnSe/ZnMgSe quantum well (QW) nanopillar (NP) structures as a highly efficient solid-state single-photon source operating at cryogenic temperatures. We show that single photons are generated due to the radiative recombination of excitons bound to neutral Cl atoms in ZnSe QW and the energy of the emitted photon can be tuned from about 2.

Structural Property Study for GeSn Thin Films.

The structural properties of GeSn thin films with different Sn concentrations and thicknesses grown on Ge (001) by molecular beam epitaxy (MBE) and on Ge-buffered Si (001) wafers by chemical vapor deposition (CVD) were analyzed through high resolution X-ray diffraction and cross-sectional transmission electron microscopy. Two-dimensional reciprocal space maps around the asymmetric (224) reflection were collected by X-ray diffraction for both the whole structures and the GeSn epilayers. The broadenings of the features of the GeSn epilayers with different relaxations in the direction, along the -2 direction and parallel to the surface were investigated.

Impact of tensile strain on low Sn content GeSn lasing.

In recent years much effort has been made to increase the Sn content in GeSn alloys in order to increase direct bandgap charge carrier recombination and, therefore, to reach room temperature lasing. While being successful for the former, the increase of Sn content is detrimental, leading to increased defect concentrations and a lower thermal budget regarding processing. In this work we demonstrate strong photoluminescence enhancement in low Sn content GeSn layers by implementing tensile strain.

Investigation of carrier confinement in direct bandgap GeSn/SiGeSn 2D and 0D heterostructures.

Since the first demonstration of lasing in direct bandgap GeSn semiconductors, the research efforts for the realization of electrically pumped group IV lasers monolithically integrated on Si have significantly intensified. This led to epitaxial studies of GeSn/SiGeSn hetero- and nanostructures, where charge carrier confinement strongly improves the radiative emission properties. Based on recent experimental literature data, in this report we discuss the advantages of GeSn/SiGeSn multi quantum well and quantum dot structures, aiming to propose a roadmap for group IV epitaxy.

Advanced GeSn/SiGeSn Group IV Heterostructure Lasers.

Growth and characterization of advanced group IV semiconductor materials with CMOS-compatible applications are demonstrated, both in photonics. The investigated GeSn/SiGeSn heterostructures combine direct bandgap GeSn active layers with indirect gap ternary SiGeSn claddings, a design proven its worth already decades ago in the III-V material system. Different types of double heterostructures and multi-quantum wells (MQWs) are epitaxially grown with varying well thicknesses and barriers.

Tailoring Mechanically Tunable Strain Fields in Graphene.

There are a number of theoretical proposals based on strain engineering of graphene and other two-dimensional materials, however purely mechanical control of strain fields in these systems has remained a major challenge. The two approaches mostly used so far either couple the electrical and mechanical properties of the system simultaneously or introduce some unwanted disturbances due to the substrate. Here, we report on silicon micromachined comb-drive actuators to controllably and reproducibly induce strain in a suspended graphene sheet in an entirely mechanical way.

Electrical resistance of individual defects at a topological insulator surface.

Three-dimensional topological insulators host surface states with linear dispersion, which manifest as a Dirac cone. Nanoscale transport measurements provide direct access to the transport properties of the Dirac cone in real space and allow the detailed investigation of charge carrier scattering. Here we use scanning tunnelling potentiometry to analyse the resistance of different kinds of defects at the surface of a (BiSb)Te topological insulator thin film.

SiGeSn Ternaries for Efficient Group IV Heterostructure Light Emitters.

SiGeSn ternaries are grown on Ge-buffered Si wafers incorporating Si or Sn contents of up to 15 at%. The ternaries exhibit layer thicknesses up to 600 nm, while maintaining a high crystalline quality. Tuning of stoichiometry and strain, as shown by means of absorption measurements, allows bandgap engineering in the short-wave infrared range of up to about 2.

Low V(π) Silicon photonics modulators with highly linear epitaxially grown phase shifters.

We report on the design of Silicon Mach-Zehnder carrier depletion modulators relying on epitaxially grown vertical junction diodes. Unprecedented spatial control over doping profiles resulting from combining local ion implantation with epitaxial overgrowth enables highly linear phase shifters with high modulation efficiency and comparatively low insertion losses. A high average phase shifter efficiency of VπL = 0.