The data behind the plots in figures 3, 4, 6 & 7 in the corresponding manuscript are provided here.

The data from figure 3 captures the relationship between topographic measurements from line profiles in the atomic force microscope (AFM) and cathodoluminescence (CL) in the scanning electron microscope (SEM). The trench thickness (measured 2 nm below the higher adjoining terrace of the surrounding material) and the prominence of the enclosed material (calculated as the height of the enclosed material relative to the average height of the surrounding material to the left and right) recorded in the AFM are shown. Similarly, the calculated redshift in CL emission from the quantum wells (QWs) enclosed by the trench defect (relative to the surrounding QWs) and the ratio of the intensity of CL emission from inside and outside the defect volume are given. Definitions of these parameters are given in the methods section of the manuscript.

The data from figure 4 plotted the CL emission inside and outside the three trench defects chosen for further investigation (A, B and C) along with AFM height images of the defects, and data used to plot the CL spectra inside and outside the trench defects is given (with the relevant measured parameters given in the main manuscript text).

In Figure 6 profiles of the atomic fraction of indium measured by energy dispersive X-ray spectroscopy in the scanning transmission electron microscope (STEM-EDX) throughout the QW stack are shown for wells contained inside trench defects A, B and C along with the profile from QWs adjacent to trench C; the atomic fraction of indium vs. position (along the growth direction (nm)) is given here for each profile.

Figure 7 shows the QW width measured inside and outside trench defect C (using high-angle annular-dark-field (HAADF) imaging in STEM). Here, we provide the mean QW width measured for each QW in the stack along with the standard deviation and standard error of these measurements.