Resonant photoluminescence of semiconductor microcavities:The role of acoustic phonons in polariton relaxation

We have measured the resonantly excited photoluminescence (PL) from a semiconductor microcavity. At 30 K the form of the PL spectra is almost independent of excitation wavelength while at 5 K the spectra change shape depending on the excitation. We attribute this difference to the transition from multiple to single acoustic phonon scattering. An elementary model is given which agrees with the data using only the temperature as a free parameter. The results show the important role that acoustic phonons play in exciton (cavity polariton) thermalization at low temperature (T=5–30nK) and density (n=${10}^7$–${10}^9$ ${\mathrm{ncm}}^{\mathrm{-}2}$).