The qHAADF method allows the quantification of the composition at atomic column resolution in semiconductor materials by comparing the HAADF-STEM intensities between a region of interest to a region of the material of known composition. However, the application of this qHAADF approach requires both regions to be differentiable and included in the same micrograph at close proximity. This limits the application of this approach to certain materials and magnifications where this requirement is fulfilled. In this work, we extend the qHAADF method to analyses where the reference region is imaged in a separate micrograph. The validity of this modified method is proved by comparison to the original qHAADF approach using HAADF-STEM simulated images of the semiconductor heterostructure InSb/InAs. Additionally, the methods are applied successfully to experimental images both of a simple InSb/InAs interface and of a complex InSb/GaSb heterostructure, justifying the significance of the modified method over the original method.

InSb/InAs sub-monolayer (SML) nanostructures such as SML quantum dots offer sharper emission spectra, a better modal gain and a larger modulation bandwidth compared to its Stranski–Krastanov counterpart. In this work, the Sb distribution of SML InSb layers grown by migration enhanced epitaxy has been analyzed by transmission electron microscopy (TEM) techniques. The analysis of the material by diffraction contrast in 002 dark field conditions and by atomic column resolved high angle annular dark field-scanning TEM reveal the presence of a low Sb content InSbAs continuous layer with scarce Sb-rich InSbAs agglomerates. The intensity profiles obtained by both techniques point to Sb segregation during growth. This segregation has been quantified using the Muraki segregation model obtaining a high segregation coefficient R of 0.81 towards the growth direction. The formation of a continuous InSbAs wetting layer as a result of a SML deposition of Sb on the InAs surface is discussed.

III-Sb semiconductors cover the whole 0.29-1.64 eV bandgap range, allowing us to grow several subcells of a multi-junction solar cell lattice-matched to GaSb. Among III-Sb alloys, AlInAsSb exhibits the broadest range of direct bandgaps, making it a promising material for photovoltaic applications. In this work, the behavior of two AlInAsSb/GaSb tandem photovoltaic cells is studied. Material characterization and physics-based 1D modeling are carried out to analyze and discuss performance of the cells. An efficiency of 5.2% is achieved under 1-sun illumination, limited by the AlInAsSb quaternary-alloy properties.

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.

Sub-monolayer (SML) deposition of InSb within InAs matrix by migration enhanced epitaxy (MEE) tends to form type II SML nanostructures offering efficient light emission within the mid-infrared (MIR) range between 3-5 µm. In this work, we report on the Sb distribution in InSb/InAs SML nanostructures with InAs cap layers grown at temperatures lower than that associated with the under-grown InSb active layer. Analysis by transmission electron microscopy (TEM) in 002 dark field (DF) conditions shows that the reduction in the growth temperature of the InAs cap layer increases the amount of Sb deposited in the layers, in good agreement with the X-ray diffraction (XRD) results. TEM micrographs also show that the layers are formed by random InSbAs agglomerates, where the lower cap temperature leads to a more continuous InSb layer. Quantitative atomic column resolved high angle annular dark field (HAADF)scanning (S)TEM analyses also reveal atomic columns with larger composition of Sb for the structure with the lowest InAs cap layer temperature. The dependence of the Sb distribution on InAs cap growth temperature allows tuning the corresponding emission wavelength in the MIR range, as shown by the photoluminescence (PL) emission spectra.