We report a study of the emission properties of InGaN/GaN quantum wells, grown by metalorganic vapour phase epitaxy, as a function of barrier-growth temperature, using continuous wave and time-resolved photoluminescence spectroscopy. We observe that high barrier-growth temperatures lead to a blue-shift of the photoluminescence, a reduction of the recombination lifetime, and a broadening of the emission linewidth. These effects are consistent with increased indium desorption during the pause preceding the growth of the barrier at higher temperatures. The blue-shift and the reduced lifetime are consistent with a reduction of the average indium concentration, while the increase of the linewidth is caused by the increase of the indium composition fluctuations due to the randomness of the desorption process. At the same time, the high barrier temperature samples have the highest photoluminescence efficiency at room temperature due to the reduced number of defects in the barrier.

Colorizing metals using micrometer and nanometer scale surface modifications has been vastly investigated and presents many advantages for applications across scientific and technological fields. By tuning the surface chemical composition or controlling its morphology, it is possible to produce a wide range of chromatic effects. Ultrafast laser processing presents here an interesting asset, as it allows to simultaneously provide chemical and morphological modifications at the micro‐scale in a single step. In this article, the composite colorization of copper surfaces with mW‐class average power deep ultraviolet (DUV) femtosecond laser pulses is demonstrated. The advantages of this setup are twofold: first, thanks to the increased absorption of copper in the DUV, the technique allows scaling down the requirement for laser power. Second, under ultrafast short‐wavelength illumination molecular oxygen bond‐breaks occur, enhancing the oxidation rate of the copper. The technique allows for highly controllable and efficient copper oxidation with the irradiation parameters. Taking these two effects into account, the generation of a wide spectrum of colors—from dark blue to shiny red—is demonstrated, and the role of the surface oxidation rate, the laser fluence, and laser scanning strategies in the colorization of copper surfaces employing DUV lasers is discussed.

The authors have studied the diffusion of carriers in GaN by photoluminescence and pump-probe spectroscopy in an InGaN∕GaN single quantum well sample at 300K. The sample was designed with the quantum well buried beneath a thick (240nm) GaN layer. When pumping above the GaN band gap, the carriers that are excited in the GaN layer diffuse to the InGaN quantum well before recombining radiatively. The hole diffusion coefficient was determined from the rise time of the quantum well photoluminescence, together with pump-probe experiments. A value of 2.0±0.4cm2∕s is found for the diffusion coefficient.

Blazed gratings are periodic surface structures of great interest for applications such as friction control, light trapping, and spectrometry. While different laser processing methods have been explored to produce these elements, they have not yet surpassed conventional surface manufacturing techniques, often based on lithography processes or mechanical ruling. This work introduces a new approach based on the combination of ultrashort pulses and triangular beam shaping, which enables the generation of asymmetrical grooves in a single step. The main advantage of this strategy is that by simply changing the laser processing direction we can induce a significant modification in the ratio of asymmetry between the sidewall angles of the machined channels. The paper includes a comprehensive study, which has been supported by statistical tools, of the effect of this and other experimental parameters on the morphology of grooves machined on stainless steel. As a result, we achieved a wide range of geometries, with asymmetry ratios spanning from 1 to 5 and channel depths between 3 and 15 µm. Furthermore, we demonstrate the validity of the approach through the successful manufacture of blazed gratings of various slopes. The results reflect the versatility and cost-efficiency of the proposed fabrication strategy, and thus its potential to streamline the production of sawtooth gratings and other devices that are based on asymmetrical features.