ENHANCED EXCITON MOBILITIES IN GAAS/ALGAAS AND INGAAS/INP QUANTUM-WELLS

We have studied lateral exciton and electron-hole pair transport by space- and time-resolved spectroscopy under conditions where enhanced mobilities and diffusivities are observed. A transport/transfer model, including relaxation, lateral diffusion, transfer between the islands and recombination, is used to evaluate our measurements of growth-interrupted quantum wells. For 40 K < T < 180 K the variation of the diffusivities with temperature can be described by an isothermal diffusion of excitons considering various scattering mechanisms. For growth-interrupted quantum wells we found considerably higher mobilities and diffusivities at low temperatures compared to continuously grown samples. This is attributed to a partial suppression of interface roughness scattering due to island formation on growth-interrupted interfaces. Unexpectedly high diffusivities were observed for 10 K < T < 40 K which may be caused by non-equilibrium effects in the carrier and phonon system. The unexpected increase of the diffusivities with rising temperature observed in thin quantum wells for 180 K < T < 230 K is attributed to the growing thermal dissociation of excitons into free carrier pairs.