A method to produce photonic glasses (disordered dielectric structures built from monodisperse spheres) composed of silica is discussed. This method is capable of dispensing samples in a few minutes with the help of a uniaxial press. An analytical model that accounts for the most relevant features and explains how Mie scattering is the leading phenomenon is developed.

Thermophotovoltaic (TPV) devices based on GaInAsSb lattice matched to GaSb (100) substrates have demonstrated high external quantum efficiencies (EQEs) in the mid-infrared spectral range, making them promising candidates for waste heat recovery from high temperature "blackbody" sources. In this work, the GaInAsSb alloy has been integrated onto more cost-effective GaAs (100) substrates by using advanced metamorphic buffer layer techniques in molecular beam epitaxy (MBE), which included an interfacial misfit (IMF) array at the GaSb/GaAs interface followed by GaInSb/GaSb dislocation filtering layers. The threading dislocations in the GaInAsSb region can be efficiently supressed, resulting in high quality materials for TPV applications. To determine the performance of the GaInAsSb TPV on GaAs it was compared with a cell grown lattice matched onto GaSb substrate having the same structure. The resulting TPV on GaAs exhibited similar dark current-voltage characteristics with that on GaSb. Under illumination from an 800 °C silicon nitride emitter, the short circuit current density (J sc) from the GaInAsSb TPVs on GaAs reached more than 90% of the control cell on GaSb, and the open circuit voltage (V oc) exceeded 80% of the cell on GaSb. The EQE from the TPV on GaAs reached around 62%, the highest value reported from this type of TPV on GaAs. With improved TPV structure design, large area GaInAsSb TPV panels on GaAs substrates can be realized in the future for waste heat energy recovery applications.

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Hydrostatic pressure can be used as a powerful diagnostic tool to enable the study of lattice dynamics, defects, impurities and recombination processes in a variety of semiconductor materials and devices. Here we report on intermediate band GaAs solar cells containing GaSb quantum rings which exhibit a 15% increase in open-circuit voltage under application of 8 kbar hydrostatic pressure at room temperature. The pressure coefficients of the respective optical transitions for the GaSb quantum rings, the wetting layer and the GaAs bulk, were each measured to be ~10.5±0.5 meV/kbar. A comparison of the pressure induced and temperature induced bandgap changes highlights the significance of the thermal energy of carriers in intermediate band solar cells.

A type‐II GaSb/GaAs quantum dot (QD)/quantum ring (QR) solar cell (SC) achieves higher photo‐response than its type‐I counterpart [1], as it supports an enhanced carrier recombination rate due to a larger separation between the electron and hole confinements [2]. This behavior leads to greater valence band offset [2] and, eventually, the solar cell is also able to function well into the near infrared (NIR) regions [3]. The stacking of several GaSb/GaAs QDs layers within the SC is essential to increase the photon absorption, however these heterostructures face a large lattice mismatch (7.8%) that causes a high local strain [4]. Because of this, sometimes QDs tend to relax by diffusing Sb from its center, followed by As/Sb exchange, giving place to nanostructures in the form of quantum rings (QR). [5]. In this communication, we analyze a GaSb/GaAs structure grown at 480ºC by molecular beam epitaxy (MBE) on a GaAs substrate. The GaSb layers (2.1 ML) are capped by two consecutive GaAs layers (10nm at 480ºC and 30nm at 580ºC), and this whole segment is repeated 10 times. The structural properties of this sample have been analyzed by diffraction contrast Transmission Electron Microscopy (TEM) in a JEOL 2100 LaB 6 microscope, working at 200 kV. 220 bright field (BF) images of the GaSb layers have shown that no dislocations or other type of defects appear in the structure, and only some strain contrasts due to the lattice mismatch are observed. Fig. 1 shows a 002 dark field (DF) image of the sample that clearly shows two‐lobe shaped nanostructures corresponding to the presence of QR. We have found that the average diameter of the QR is 14 ± 5 nm, with average diameter of the individual lobes of 4±2 nm and an average height of 3±2 nm. Also, it is worth highlighting that a vertical stacking of the QR is not observed which is a consequence of a reduced propagation of the strain to the subsequent QR layers because of the large thickness of the GaAs barrier layers. High angle annular dark field (HAADF) analyses using an aberration corrected electron microscope are in progress in order to obtain more detailed information about the composition and the strain in these heterostructures.