The phonon dynamics of both the A 1(LO) and the E 1 (LO) phonons in InN has been studied by time-resolved Raman spectroscopy on a subpicosecond time scale. From the temperature-dependence of their lifetimes, we demonstrate that both phonons decay primarily into a large wavevector TO phonon and a large wavevector TA/LA phonon consistent with the accepted phonon dispersion relationship for wurtzite InN. Their lifetimes have been found to decrease from 2.2 ps, at the low electron-hole pair density of5x1017 cm -3 to 0.25 ps, at the highest density of2x1019 cm -3. Our experimental findings demonstrate that carrier-density dependence of LO phonon lifetime is a universal phenomenon in polar semiconductors.

ZnO nanorods were grown by catalyst-assisted vapor phase transport on Si(001), GaN(0001)/c-Al2O3, and bulk ZnO(0001) substrates. Morphology studies showed that ZnO nanorods grew mostly perpendicularly to the GaN substrate surface, whereas a more random directional distribution was found for nanorods on Si. Optical properties of fabricated nanorods were studied by steady-state photoluminescence and time-resolved photoluminescence. Stimulated emission was observed from ZnO nanorods on GaN substrates. Raman spectroscopy revealed biaxial strain in the nanorod samples grown on Si. Conductive atomic force microscopy was applied to study I-V spectra of individual nanorods.