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

We have measured the radiative lifetime and diffusivity of excitons an d trions as a function of temperature and electron density. The radiat ive decay times increase linearly with temperature, as expected for fr ee particles. From time- and spatially-resolved measurements of diffus ion, we find that while trions and excitons are localized at 5K, as th e temperature is raised both become mobile. The diffusivities then inc rease linearly with bath temperature as expected for a classical gas w ith a temperature independent mobility, the trion mobility being about one half the exciton mobility. Our results are the first direct exper imental evidence for free trions. Copyright (C) 1996 Elsevier Science Ltd