Multimodal Imaging of Strain and Light Emission of Core–Shell InGaN/GaN Wires under a Sub‐Micrometer Polychromatic X‐Ray Probe

ABSTRACT We present a combination of µLaue X‐ray diffraction and X‐ray excited optical luminescence (XEOL) techniques to map local strain, orientation, and light emission in metalorganic vapor phase epitaxy (MOVPE) core–shell InGaN/GaN multiple quantum wells (MQW) wires dispersed on silicon substrates. The components of the deviatoric strain tensor averaged along the beam footprint were quantified with a measurement precision better than 9 × 10 −5 and an accuracy of approximately 4 × 10 −4 . This measurement quality is achieved by carefully calibrating the analysis chain with a Ge crystal and verifying it with measurements of the unstrained Si substrate reference. The µLaue mapping of the components of the deviatoric strain confirms the high crystal quality and the impact of the MQW shell grown only in the upper part of the GaN core, as evidenced by the local variations of the full width at half maximum of the diffraction peaks and of the lattice rotation tensor. The two deviatoric tensors of the GaN core and InGaN/GaN shell can be measured independently and are in quantitative agreement with 3D finite element method (FEM) simulations. The structural information is correlated with XEOL measurements, whose spectral analysis reveals the main contributions to light emission: the major UV‐blue MQW emission from the m‐plane at the top of the wires, with a gradient varying from 406 nm at the top of the MQW to 397 nm at the bottom, with a secondary emission of a semipolar r‐plane facet at ∼470 nm; the near‐band‐edge GaN signal at ∼363 nm; and the usual yellow defect‐band luminescence, centered at 560 nm. The paper also highlights the potential of these techniques to obtain statistics on semiconductor heterostructures and their automation capabilities for measurements and analysis.