Electrical control of optical orientation of neutral and negatively   charged excitons in n-type semiconductor quantum well
  We report a giant electric field induced increase of spin orientation of excitons in n-type GaAs/AlGaAs quantum well. It correlates strongly with the formation of negatively charged excitons (trions) in the photoluminescence spectra. Under resonant excitation of neutral heavy-hole excitons, the polarization of excitons and trions increases dramatically with electrical injection of electrons within the narrow exciton-trion bias transition in the PL spectra, implying a polarization sensitivity of 200 % per Volt. This effect results from a very efficient trapping of neutral excitons by the quantum well interfacial fluctuations (so-called "natural" quantum dots) containing resident electrons. 
R.I. Dzhioev, V.L. Korenev, M.V. Lazarev, V.F. Sapega, D. Gammon, A.S.   Bracker