A series of light-emitting diodes (LEDs) with active layers based on InAs quantum dots (QDs) covered by GaAsSb capping layers is presented. Varying the Sb content in the capping layer from ~2 to ~28%, room temperature electroluminescence (EL) from 1.15 to 1.5 μm is obtained. The external efficiency of the devices, next, increases as the Sb is increased up to ~15% and then decreases for higher Sb contents, consistently with the reported increase of QD height with the Sb content up to ~15% and the band alignment transition from type I to type II above ~15% Sb. An analysis of the EL and photocurrent spectra shows that the emission from type I LEDs originates from the recombination between electrons and holes confined in the QDs. On the other hand, the EL from the type II devices is the combination of two different processes. First, recombination between electrons confined in the QDs and holes at the capping layer. Second, a type I-like recombination of electrons from the QDs and holes residing in extended levels of the quantum well composed by the capping layer and the QDs. The mechanisms responsible for the thermal quenching of the EL are also studied. Escape of holes from the QD to the capping layer is identified as the dominant mechanism for the type I devices, whereas in type II structures it is the escape of electrons from QD excited levels to the barrier which dominates.

An extensive study on molecular beam epitaxy growth conditions of quaternary GaAsSbN as a capping layer (CL) for InAs/GaAs quantum dots (QD) was carried out. In particular, CL thickness, growth temperature, and growth rate were optimized. Problems related to the simultaneous presence of Sb and N, responsible for a significant degradation of photoluminescence (PL), are thereby solved allowing the achievement of room-temperature (RT) emission. A particularly strong improvement on the PL is obtained when the growth rate of the CL is increased. This is likely due to an improvement in the structural quality of the quaternary alloy that resulted from reduced strain and composition inhomogeneities. Nevertheless, a significant reduction of Sb and N incorporation was found when the growth rate was increased. Indeed, the incorporation of N is intrinsically limited to a maximum value of approximately 1.6% when the growth rate is at 2.0 ML s⁻¹. Therefore, achieving RT emission and extending it somewhat beyond 1.3 μm were possible by means of a compromise among the growth conditions. This opens the possibility of exploiting the versatility on band structure engineering offered by this QD-CL structure in devices working at RT. PACS 81.15.Hi (molecular beam epitaxy); 78.55.Cr (III-V semiconductors); 73.21.La (quantum dots)

Non-solid infill generation in Non-Planar Additive Manufacturing (NPAM) is still an open problem. This is due to mathematical complexities from curvature distortion, as well as bridging limitations inherent in some NPAM processes. Providing solutions to this problem may result in significant energy, build cycle time, and cost savings. In this context, the goal of this paper is to define a workflow for the generation of non-solid infill paths with quasi-uniform density within the layer. This was performed by defining the build geometry through an axisymmetric embedded map methodology, and the infill points were distributed via a geodesic repulsion energy-based algorithm. In addition to these core algorithms, several numeric optimizations were implemented to reduce runtime. The algorithm has been tested on several build platform geometries and slice polygons. The results were satisfactory, achieving a homogeneous kernel density distribution for all cases and reductions in geodesic distance standard deviations of around 70%. A first iteration of a path planning algorithm was also implemented to showcase the intended final results. This methodology is to be combined with other Design for Non-Planar Additive Manufacturing techniques to enable applications in the biomedical field, automotive and aerospace industry, or rapid mold manufacturing.

This study investigates the application of non-planar additive manufacturing (NPAM) combined with robotic systems to enhance the production of coronary stents. Traditional additive manufacturing methods typically produce planar layers, which can limit the mechanical properties and surface quality of printed objects. In contrast, NPAM allows for the creation of continuous, curved layers, reducing anisotropic mechanical properties and minimizing stress concentrations. The methodology automates the generation of non-planar, axisymmetric layers, facilitating the fabrication of complex stent geometries that closely mimic the natural anatomy of coronary arteries. By employing advanced motion planning algorithms, robotic arms can precisely deposit materials along these curved trajectories, which may result in smoother surfaces and enhanced structural integrity. The study successfully generated trajectories for the case study and designed the necessary support structures, enabling fabrication on a cylindrical build platform giving a complete perspective of the usage of this methodology.