To assess the formation of InAs, we probe the as-grown samples with Raman spectroscopy. Figure shows a representative Raman spectrum of a sample before and after deposition of As 3+ at -1.25 V. The details regarding the Raman set-up are described in the experimental section. Two clear prominent Raman peaks appear at ~ 216 cm -1 and ~ 236 cm -1 after deposition of As. These values are in very good agreement with the TO and LO phonon frequencies of InAs at the centre of the Brillouin zone, undoubtedly identifying the presence of crystalline InAs. We also observe additional features at higher frequencies, all of which correspond to InAs second-order peaks, as labelled in Figure . We observe the presence of crystalline InAs Raman features in all samples grown at different potentials (Figure ).