DIFFUSION OF FREE TRIONS IN MIXED-TYPE GAAS ALAS QUANTUM-WELLS/

We show that an emission line which depends on the simultaneous presen ce of excitons and < 2 x 10(10) cm(-2) electrons in a 20 nm GaAs quant um well is due to free negatively charged excitons or 'trions'. Using time- and spatially-resolved photoluminescence. We find that trions an d excitons are localized at 5 K, and with increasing bath temperature both species become mobile. The diffusivity of trions and excitons inc reases linearly with bath temperature, and the trion mobility is found to be about one-half the exciton mobility.