Figure summarizes the measured LO peak position (relative to the bulk LO reference ω LO,Bulk = 237.6 cm -1 ) and linewidth (full width at half maximum, Γ) for all samples grown at different applied potentials. Here, each data point represents the mean value from the fitted and deconvoluted LO peak in 10 points within each sample. We observe a clear correlation between the LO peak shift and its broadening, that can be explained by phonon confinement.