Temperature-dependent linewidth of charged excitons in semiconductor quantum dots: Strongly broadened ground state transitions due to acoustic phonon scattering

We report temperature-dependent photoluminescence on neutral and charged excitons in individual InAs quantum dots. We find narrow emission lines for temperatures up to 30 K for exciton transitions where only the electron ground state is occupied. In contrast, for doubly charged excitons where the excited electron state is occupied, we observe a drastic increase of the ground state transition linewidth even at 30 K. We interpret this as evidence that the excited electron state is degenerate with the low energy tail of continuum states.