Strain-modulated exciton recombination probability in low-dimensional semiconductors

We employ femtosecond laser pulses to generate coherent acoustic phonons in InP nanocrystals pinned on a regular grid of Si nanotips. These strain pulses modulate the bandstructure of the nanocrystals and in consequence the carrier recombination probability. Time-resolved optical reflectometry was used to study the structural response of these nanostructures to strong laser excitation. The Eigenmode spectrum consists of two fundamental breathing modes at low fluences. Additional modes appear after a certain threshold fluence. We interpret these modes as a nonlinear mixing of the fundamental modes. A low-frequency mode was confirmed by time-resolved X-ray diffraction on a nanosecond timescale. Time-correlated single photon counting was used to measure the acoustically modulated photoluminescence lifetime.