The solid curve in Figure shows the relation between the LO peak position relative to the value for bulk InAs and its linewidth as predicted by the spatial correlation model, where the intrinsic linewidth of bulk InAs is used (Γ 0 = 7.25 cm -1 ). The right-axis shows the corresponding crystal correlation size L. Figure shows that the LO peak broadening and red-shift with increasing deposition potential in our samples, clearly follows the trend given by the phonon confinement model. The match is actually more obvious if a larger intrinsic phonon linewidth is used in the model (Γ 0 = 9 cm -1 , dashed curve). The slightly larger intrinsic linewidth, or shorter phonon lifetime, in our samples as compared to bulk InAs indicates the presence of phonon scattering potentially from non-stoichiometric defects or impurities. This relatively large intrinsic linewidth can be potentially improved by, for example, using a higher purity In substrate.