OPTICALLY DETERMINED MINORITY-CARRIER TRANSPORT IN GAAS ALXGA1-X AS HETEROSTRUCTURES/

We have studied minority-carrier electron and hole transport versus te mperature (30-300 K) in a series of undoped, ''interface-free,'' GaAs/ Al0.3Ga0.7As double heterostructures prepared by organometallic vapor- phase epitaxy, with GaAs thicknesses from 0.1 to 10 mum. This was achi eved using an all-optical, time-resolved photoluminescence-imaging tec hnique with a spatial resolution of less than or similar to 3 mum, tem poral resolution of approximately 50 ps, and spectral resolution of < 1 cm-1. This technique allows direct determination of minority-carrier transport properties, and is superior to electrical transport measure ment techniques in that it is contactless, may distinguish between dif fusive and nondiffusive carrier motion, and has high temporal and spec tral resolution. We find all transport (electron and hole) in these st ructures to be diffusive. Specifically, transport in thick structures (greater than or similar to 0.5 mum) is hole-dominated ambipolar diffu sion, whereas in thinner structures (less than or similar to 0.5 mum) we observe a time-dependent transition from ambipolar to electron-domi nated diffusion. Minority-carrier mobilities derived from these diffus ion measurements, from 300 to approximately 30 K, are in excellent agr eement with both electron and hole majority-carrier mobilities. Furthe rmore, fits to the temperature-dependent mobilities yield deformation potentials in agreement with published electrically derived values.