3D Strain Imaging of a Heterostructured GaInP/InP Nanowire Using Bragg Coherent Diffraction X-ray Imaging: Implications for Optoelectronic Devices.

Imaging the strain in nanoscale heterostructures is challenging since it requires a combination of high strain sensitivity and spatial resolution. Here, we show that three-dimensional (3D) Bragg coherent diffraction imaging (BCDI) can be used to image the strain in a single InP segment within an axially heterostructured GaInP-InP nanowire. We use a 350 nm-diameter X-ray beam, which is smaller than the nanowire but larger than the 180 nm long InP segment. The intense nanofocused beam induced angular distortions, but these are successfully removed by a correction algorithm. Additionally, we show that data from multiple scans can be merged despite scan-to-scan variations. The reconstruction of the merged data set has a spatial resolution of approximately 14 nm, revealing the 3D morphology of the InP segment and its internal strain distribution. The measured strain shows qualitative agreement with finite element method simulations, but with slightly larger magnitude, which indicates a higher Ga composition than the nominal value. The 3D strain map suggests that the nanowire can accommodate the theoretically predicted lattice mismatch without exceeding the coherency limit. Continued development of robust BCDI measurements and reconstructions enables future studies of strain fields and coherency limits in axial nanowire heterostructures, which are critical for designing next-generation optoelectronic devices.