Excitonic interplay between surface polar III-nitride quantum wells and MoS2_2 monolayer

III-nitride wide bandgap semiconductors exhibit large exciton binding energies, preserving strong excitonic effects at room temperature. On the other hand, semiconducting two-dimensional (2D) materials, including MoS$_2$, also exhibit strong excitonic effects, attributed to enhanced Coulomb interactions. This study investigates excitonic interactions between surface GaN quantum well (QW) and 2D MoS$_2$ in van der Waals heterostructures by varying the spacing between these two excitonic systems. Optical property investigation first demonstrates the effective passivation of defect states at the GaN surface through MoS$_2$ coating. Furthermore, a strong interplay is observed between MoS$_2$ monolayers and GaN QW excitonic transitions. This highlights the interest of the 2D material/III-nitride QW system to study near-field interactions, such as F\"orster resonance energy transfer, which could open up novel optoelectronic devices based on such hybrid excitonic structures.Comment: Corrected error bars in Fig.

Joined optical and thermal characterization of a III-nitride semiconductor membrane by micro-photoluminescence spectroscopy and Raman thermometry

We present the simultaneous optical and thermal analysis of a freestanding photonic semiconductor membrane made from wurtzite III-nitride material. By linking micro-photoluminescence ($\mu$PL) spectroscopy with Raman thermometry, we demonstrate how a robust value for the thermal conductivity $\kappa$ can be obtained using only optical, non-invasive means. For this, we consider the balance of different contributions to thermal transport given by, e.g., excitons, charge carriers, and heat carrying phonons. Further complication is given by the fact that this membrane is made from direct bandgap semiconductors, designed to emit light based on an In$_{x}$Ga$_{1-x}$N ($x=0.15$) quantum well embedded in GaN. To meet these challenges, we designed a novel experimental setup that enables the necessary optical and thermal characterizations in parallel. We perform micro-Raman thermometry, either based on a heating laser that acts as a probe laser (1-laser Raman thermometry), or based on two lasers, providing the heating and the temperature probe separately (2-laser Raman thermometry). For the latter technique, we obtain temperature maps over tens of micrometers with a spatial resolution less than $1\,\mu\text{m}$, yielding $\kappa\,=\,95^{+11}_{-7}\,\frac{\text{W}}{\text{m}\cdot \text{K}}$ for the $\textit{c}$-plane of our $\approx\,250\text{-nm}$-thick membrane at around room temperature, which compares well to our $\textit{ab initio}$ calculations applied to a simplified structure. Based on these calculations, we explain the particular relevance of the temperature probe volume, as quasi-ballistic transport of heat-carrying phonons occurs on length scales beyond the penetration depths of the heating laser and even its focus spot radius. The present work represents a significant step towards non-invasive, highly spatially resolved, and still quantitative thermometry performed on a photonic membrane.Comment: 28 pages, 14 figures, and Supplemental Materia

Magma mixing, mingling and hybridisation at different crustal levels: snapshots from 1.9 billion years of magmatism in south-eastern Greenland

During field work in 2014, we investigated a suite of igneous intrusions in south-eastern Greenland between 65° and 67°N. Many of the intrusions show widespread evidence for juxtaposition of different magmas in the liquid state and subsequent mixing, mingling and hybridisation. Here we present field evidence for these processes from three areas that differ in age and geological setting. We discuss the significance of mingling, mixing and hybridisation features in the field area, motivated by their abundance in the area, the morphological variation between intrusions that were emplaced at different crustal levels, the implications for magma genesis in collisional and rift settings, and the implications for the interior dynamics of igneous bodies

InGaN/GaN QWs on Si

<p>Dataset for the project of high TD density QWs grown on Si, published <a href="https://doi.org/10.3390/nano13182569">here</a>.</p><p>The different sub-datasets are named after:</p><ul><li>the measurement technique, from [ Atomic Force Microscopy (AFM) ; Cathodoluminescence (CL) mapping ; Power-dependent photoluminescence (PL) series (P-series) ; Scanning Electron Micrographs (SEM) ; Temperature-dependent P-series (T-P-series) ; Transmission Electron Microscopy (TEM) ; Time-resolved PL (TRPL) ];</li><li>the sample name, from [ R = A4286 ; U = A4287 ; V = A4289 ].</li></ul><p>Further relevant information can be found in the .zip folders, in README files.</p&gt

Investigation of the Impact of Point Defects in InGaN/GaN Quantum Wells with High Dislocation Densities

In this work, we report on the efficiency of single InGaN/GaN quantum wells (QWs) grown on thin (9 cm−2) is much lower than that of TD (2–3 × 1010 cm−2). Time-resolved photoluminescence and cathodoluminescence studies confirm the prevalence of point defects over TDs in QW efficiency. Interestingly, TD terminations lead to the formation of independent domains for carriers, thanks to V-pits and step bunching phenomena