Optical spin-filtering effect in charged InAs/GaAs quantum dots

We present time resolved photoluminescence results using nonresonant polarized light which show that the electron spin-flip time is much longer than the recombination time for an ensemble of $p$-doped InAs/GaAs quantum dots. Under continuous wave excitation the degree of optical polarization of the ground state is found to be around 10%. However, the excited state polarization is twice this value. We attribute this effect to Pauli blocking of the injected spin population captured into the dots and show that the effect persists up to room temperature. For resonant excitation, values are nearly doubled in accordance with increased spin injection efficiency.