Figure 2.

Twin superlattice phonon modes and hexagonal symmetry. (a) Calculated spectrum of a GaP twin superlattice with 9 nm period length. (b) Calculated reference spectra of bulk GaP in the ZB (black solid line) and wurtzite (red solid line) crystal phase. (c) Measured spectrum of a GaP twin superlattice nanowire with 9 nm period length (open circles). Deconvoluted Lorentzian components of the data fitting arising from the superlattice are displayed, along with the fit result (solid lines). (d) Measured reference spectra of GaP from a bulk ZB substrate (black circles) and a wurtzite nanowire (red circles) with superimposed fit results (solid lines). All theoretical and experimental spectra were obtained in the x̅(yy)x configuration. All spectra in panels a–d are normalized to the most intense peak contribution. (e) Residual plot (lines + circles) of the fit of the data displayed in panel c performed excluding the modes arising from the superlattice. The fit of the residual plot along with its Lorentzian components (only those arising from the superlattice) are displayed (solid lines). (f) Residual plots (lines + circles) of the fit of the data displayed in (d). The scale of panels e and f goes between −2.5% and 5% of the scale in panels c and d.