Imaging shape and strain in nanoscale engineered semiconductors for photonics by coherent XRD Bragg coherent x-ray diffractive imaging stable N-H complexes that also modify the crystal lattice constant (BCDI) is a nondestructive technique that [4]. Thus, by allowing H incorporation in selected regions of the sample, it is possible to achieve a spatially tailored modulation extracts 3D electron density and strain of the band gap energy in the growth plane. This can be done maps from materials with nanometer by deposition of H-opaque masks (Fig. 1), which impede H resolution. In this work, BCDI brings new diffusion in defined regions of the crystal [2]. understanding to a novel nanofabrication For nanophotonics based on dilute nitrides, a breakthrough process for engineering the optical properties would be to push down this approach to the nanometer scale of semiconducting GaAsN. BCDI allows length. In order to control fabrication at the nanoscale, the 1-y y need of a non-destructive high-resolution imaging technique us to test the manufactured patterns. We able to visualize the obtained individual patterns and their strain show that sharp geometrical structures can distribution is mandatory. Conventional microscopy techniques be produced on a few-micron scale, and are not suitable for this task. Here, we show that Bragg coherent x-ray diffractive imaging (BCDI) [5], exploiting the contrast that the strain distribution is uniform even produced by the tiny separation of the Bragg peaks of pristine for highly strained sub-microscopic objects. and hydrogenated GaAsN, is able to extract good quality 3Dy1-y Our results pave the way for tailoring the electron density and strain maps on planar micro- and nano- structures grown on GaAs. optical properties of emitters with nanometric precision for nanophotonics and quantum FIGURE 2 technology applications. FIGURE 1 Control over size and distribution of semiconductor nanostructures is key for the fabrication of a number of innovative devices, including photonic crystals. Nonetheless, the control of the material properties in the growth plane remains challenging [1]. Recently, a method for engineering the in plane properties of a semiconductor RESULTS has been proven, by exploiting Fig. 2 (left) shows the scattered intensity around the GaAsN the effects of H irradiation in [004] reflection by the triangular feature of Fig. 1 (/home/webapps/asp_fr/data/asp/publications/synchrotron-soleil/synchrotron-soleil-2020/soleil-highlights-2020-hd-ss-tc 5 μm side),1-y y GaAsN [2]. In these alloys, they1-y when illuminated by a coherent x-ray beam; the threefold substitution of few percents of symmetry comes from the fact that the XRD pattern is given As atoms by N leads to strong by the square modulus of the Fourier transform of the function non-linear effects in the electronic describing the external shape of the micro-object. Fig. 2 (right) properties. In particular, it causes ashows the reconstruction (via retrieval procedures) of the phase giant reduction in the optical band of the complex shape function [5], which is proportional to the gap [3]. Post-growth irradiation atom displacements projected onto the reciprocal lattice vector, with atomic H reverses this band related to the out-of-plane strain for a [004] reflection. The phase gap change via the formation of is represented by the values that intersect an isosurface of the 76