The tuning of the optical and electronic properties of semiconductor nanowires can be achieved by crystal phase engineering. Zinc-blende and diamond semiconductors exhibit pressure-induced structural transitions as well as a strong pressure dependence of the band gaps. When reduced to nanoscale dimensions, new phenomena may appear. We demonstrate the tuning of the optical properties of GaAs nanowires and the induction of a phase transition by applying an external pressure. The dependence of the E(0) gap on the applied pressure was measured, and a direct-to-indirect transition was found. Resonant Raman scattering was obtained by pressure tuning of the E(0) and the E(0) + Δ(SO) gaps with respect to the excitation energy. The resonances of the longitudinal optical modes LO and 2LO indicate the presence of electron-phonon Fröhlich interactions. These measurements show for the first time a variation of ionicity in GaAs when in nanowire form. Furthermore, the dependence of the lattice constant on applied pressure was estimated. Finally, we found a clear indication of a structural transition above 16 GPa.

GaAs nanowires were heated locally under ambient air conditions by a focused laser beam which led to oxidation and formation of crystalline arsenic on the nanowire surface. Atomic force microscopy, photoluminescence and Raman spectroscopy experiments were performed on the same single GaAs nanowires in order to correlate their structural and optical properties. We show that the local changes of the nanowires act as a barrier for thermal transport which is of interest for thermoelectric applications.

We report on resonant Raman experiments carried out on wurtzite InAs nanowires. Resonant conditions have been obtained by tuning either the excitation energy or the band gap through external high pressure at fixed excitation energy. A complete azimuthal study of the Raman spectra with two laser excitation lines (2.41 and 1.92 eV) has also been performed on a single wire. The measured E2(H) mode resonance indicates that the E1(A) gap is about 2.4 eV, which is considerably reduced with respect to the zinc-blende InAs E1 gap. These findings confirm recent theoretical calculations of crystal phase induced bandstructure modifications.