GaN/InGaN nanostructures have numerous potential electronic and opto-electronic applications, such as energy-selective contacts for hot carrier solar cells and light-emitting diodes. A joint experimental and computational approach has been developed to understand the properties of GaN/InGaN nanostructures grown by selective area epitaxy (see the article by P.-C. Ku and co-workers, pp. 531–535). GaN quantum dots were grown by metal-organic chemical vapor deposition on a GaN substrate, with a SiO₂ mask patterned by electron-beam lithography used to control the initial quantum dot size and position. The morphology of the quantum dot in the early stages of deposition is non-uniform, resembling a volcano that gradually fills in and finally takes the shape of a hexagonal pyramid (inset, right). To understand the evolution of the morphology, a phase-field model was developed to simulate the growth process (inset, left), which included crystallographic orientation-dependent GaN growth and surface diffusion. Good agreement between simulation and experiment was obtained throughout the growth process. The growth of InGaN layers embedded in the quantum dots was also simulated, and the results were used to explain why the measured photoluminescence spectrum was considerably broader than expected.

Perovskite superlattices show a large variety of useful physical properties, like (anti)ferromagnetism, (anti)ferroelectricity, superconductivity and multiferroicity. These properties may strongly depend on the interface morphology. In the article by Reinald Hillebrand et al. (see pp. 536–542), high angle annular dark field scanning transmission electron micrographs (HAADF-STEM) of SrRuO₃/Pr_0.7Ca_0.3MnO₃ (SRO/PCMO) superlattices are interpreted quantitatively. The superlattices were fabricated by pulsed-laser deposition (PLD). The growth was performed at a temperature of 650 °C and in an oxygen partial pressure of 0.14 mbar. The images were taken in the probe-corrected (c_s = 0) FEI microscope TITAN 80-300 at 300 kV. The experimental studies have been substantially supported by image simulations. The specimen thickness is estimated by comparing experimental and simulated Z-contrast ratios. The quantitative image analyses proved that the intermixing at the interfaces is different for the growth of SRO on PCMO and that of PCMO on SRO. In addition, the thermal stability of SRO/PCMO superlattices is studied, based on a series of annealing experiments up to 1200 °C.

GaN nanodots with embedded InGaN layers are grown by selective area epitaxy. Photoluminescence measurements show significant energy state broadening compared to disk-shaped emitters of uniform thickness. Phase-field simulation of the growth process reveals an unexpected thickness variation in the InGaN layer. The photoluminescence spectrum calculated from the simulated InGaN layer profile agrees with the measured spectrum, demonstrating that the layer non-uniformity was the cause of the energy state broadening.

The metal-semiconductor contact plays an important role to define the performance of a device where current extraction is critical. In that regard, Mink et al. (pp. 551–554) examined a set of metals (Al, Ti, Co) fabricated as Ohmic and Schottky contact to study which can enable better performance in micro-sized microbial fuel cells fabricated on silicon. The study shows that, in general AlSi_x (Ohmic contacts) provide higher current density whereas CoSi₂ Ohmic contacts provide higher power density.