Quantum Optoelectronics

Abstract:

Crystallographic point defects (PDs) can dramatically decrease the efficiency of optoelectronic semiconductor devices, many of which are based on quantum well (QW) heterostructures. However, spatially resolving individual nonradiative PDs buried in such QWs has so far not been demonstrated. Here, using high-resolution cathodoluminescence (CL) and a specific sample design, we spatially resolve, image, and analyze nonradiative PDs in InGaN/GaN QWs at the nanoscale. We identify two different types of PDs by their contrasting behavior with temperature and measure their densities from 10¹⁴ cm^–3 to as high as 10¹⁶ cm^–3. Our CL images clearly illustrate the interplay between PDs and carrier dynamics in the well: increasing PD concentration severely limits carrier diffusion lengths, while a higher carrier density suppresses the nonradiative behavior of PDs. The results in this study are readily interpreted directly from CL images and represent a significant advancement in nanoscale PD analysis.

Abstract:

Current industrial production of ammonia from the Haber-Bosch process and its transport concomitantly produces a large quantity of CO2. Herein, we successfully synthesize inorganic-structure-based catalysts with [Fe-S2-Mo] motifs with a connecting structure similar to that of FeMoco (a cofactor of nitrogenase) by placing iron atoms on a single molecular layer of MoS2 at various loadings. This type of new catalytic material functionally mimics the nitrogenase to convert N2 to ammonia and hydrogen in water without adding any sacrificial agent under visible-light illumination. Using the elevated temperature boosts the ammonia yield and the energy efficiency by one order of magnitude. The solar-to-NH3 energy-conversion efficiency can be up to 0.24% at 270°C, which is the highest efficiency among all reported photocatalytic systems. This method of ammonia production and the photocatalytic materials may open up an exciting possibility for the decentralization of ammonia production for fertilizer provision to local farmlands using solar illumination.

Abstract:

The research looks into the lasing phenomenon from the tetragonally symmetric CsPbBr3 perovskite nanocrystals. The emission has been demonstrated to originate from the triplet state via polarisation and lifetime verifications. A resonantly pumped excitation source has been adopted to tune the inter-level transition resonantly, which significantly enhances the emission characteristics. The data follows the order of the figures contained in the corresponding paper and a comment in each data file explains what each column of the data stands for. The data files cover all the experimental results presented in the main text of the paper.