Noble metal nanoparticles such as gold and silver support localized surface plasmon resonances upon excitation by visible light. When brought into close proximity or arranged in periodic arrays, these single particle resonances interfere leading to collective, coupled optical response. Tailoring the strength and frequency of the coupled resonance is an important prerequisite for the suitability of such materials for modern nanophotonic applications including sensing, high resolution microscopy and plasmonic lasing. Here, Fitzgerald and Karg (article no. 1600947) review recent works that demonstrate defined plasmon coupling phenomena in self-assembled colloidal monolayers. Design concepts and properties of plasmonic building blocks are presented followed by an introduction to single particle and coupled plasmon resonances. Then examples for near-field, plasmonic/diffractive as well as anisotropic coupling are introduced. Overall, this review highlights the benefits of wet-chemical synthesis for the fabrication of functional building blocks in combination with the flexibility of colloidal self-assembly offering access to high-troughput nanostructuring on application-relevant, macroscopic areas.

In order to improve wafer based silicon solar cell performance with even lower costs, new methods for manufacturing the material are constantly being developed. One approach is to use low cost block casting to make material with primarily monocrystalline character, called mono-like silicon. Unfortunately, crystal faults readily form and multiply in this structure. These cause the recombination of photogenerated charge carriers lowering the efficiency of solar cells. The socalled D-line emissions are four luminescence signals (D1–D4) emanating from photoexcited silicon. They are caused by radiative recombination via traps in the band gap and are reported to always occur together in dislocated areas. The behaviour of the D-line emissions as function of position in a block of mono-like silicon has been studied by Olsen et al. (article no. 1700124). The emissions behave differently suggesting they do not have the same origin. A new signal (0.70 eV) is found in areas where the mono-like character is lost due to formation of material with multicrystalline character. These areas are highly dislocated, however do not exhibit the D1–D4 emissions.

The effects of several design geometries on the thermal resistance for a flip-chip GaN-based VCSEL with dielectric distributed Bragg reflectors was studied by Mishkat-Ul- Masabih (article no. 1600819) using finite-element analysis. The current flip-chip design suffers from high thermal resistance, preventing devices to lase under CW operation. It was found that including a patterned DBR with recessed metal, reducing the lithography alignment tolerances, and increasing the aperture size; all contributed to the reduction of the thermal resistance of the design. In addition, epitaxially increasing the cladding layer thickness on either side of the active region also lowered the thermal resistance significantly. The thermal resistance values for previously reported CW device configurations were also calculated and compared to our flip-chip design. The internal temperature changes at the threshold were estimated for the devices, indicating why previous generations of our flip-chip devices could not achieve CW lasing. Combining these techniques, the effects of thermal roll-over can be mitigated; as the reduction of the device temperature is a key consideration for obtaining high output power CW GaN-based VCSELs.

The background of this cover page shows a superimposed emission microscope image observed from backside of a GaN m-plane Schottky barrier diode with reverse biased condition. It can be observed that the epitaxial layer of m-plane GaN has pyramidal hillocks at the surface, and only facets inclined toward the [0001] direction (+c facet) have emission due to leakage current. Three images at the corner are differential interference contrast microscopy image (upper left), photoluminescence intensity mapping image (PL, upper right), and cathode luminescence image (CL, lower left), respectively, observing the same pyramidal hillocks to investigate the characteristics of each facet. The PL image indicates the intensity of near-band-edge emission (around 363 nm wavelength) of the facets. Details are discussed in the article by Tanaka et al. (no. 1600829). The +c facets have high emission intensity, indicating that there is a high impurity concentration in the +c facets. Furthermore, we consider this is the reason that +c facets have high leakage current. The CL image is a panchromatic image, and facets inclined toward [000-1] direction (−c facet) have lowest emission. Together with PL intensity mapping it can be considered that −c facets have less yellow emission and less impurity concentration.