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.

Figure 1

Photoluminescence spectrum measured at $7.3\mathrm{K}$.

Figure 2

The spectra of the hot-exciton luminescence (HL) peak at different sample temperatures. The excitation-photon energy is $2.8573\text{eV}$, corresponding to an exciton kinetic energy of $12\text{meV}$.

Figure 3

Spectral linewidth of the hot-exciton luminescence as a function of sample temperature measured under different excitation-photon energies. The number in each panel indicates the corresponding kinetic energy of the excitons calculated from the excitation-photon energy.

Figure 4

Thermal broadening coefficient as a function of the exciton kinetic energy. Squares, measured from the hot-exciton luminescence; circle at $E_k=0$, measured from zero-phonon recombination of the cold excitons; solid line, calculated.