Energy relaxation of hot two-dimensional excitons in a GaAs quantum well by exciton-phonon interaction

The power loss of hot two-dimensional excitons in GaAs/Alₓ{Ga}_{1{{-}}x}$As multiple quantum wells and the corresponding energy relaxation times are calculated in the present work. A simplified variational envelope function is assumed for the 1s excitonic level in an infintely deep well and the exciton distribution is described by an effective exciton temperature. For deformation-potential acoustic-phonon scattering, a simple expression for the power loss derived by Takagahara is used, while for polar-optic-phonon scattering the expression is developed in the present paper. The calculated values indicate that for lattice and exciton temperatures below 150 K, polar-optic-phonon scattering contributes little to the power loss. The energy relaxation time due to the acoustic-phonon scattering is found to be about 3--4 times higher than the experimental estimate and hence the higher-lying states have to be considered to obtain enhanced energy relaxation rate.