Direct measurement of acoustic-phonon scattering of hot quantum-well excitons

Due to their high momentum, hot excitons do not couple to photons directly. Thus, the interaction of excitons with phonons is typically studied only for zero-momentum excitons. We show here that the excitonic recombination process assisted by optical phonons provides a direct method to study the acoustic-phonon scattering of hot excitons in semiconductor quantum wells. From the thermal broadening of the hot-exciton luminescence, we obtain the broadening coefficient as a measure of the coupling strength. The coefficient is found to increase with exciton kinetic energy. This finding is in contrast to theoretical predictions taking into account only the direct exciton-phonon scattering process.