LONG-RANGE, MINORITY-CARRIER TRANSPORT IN HIGH-QUALITY SURFACE-FREE GAAS/ALGAAS DOUBLE HETEROSTRUCTURES

Using a novel time-resolved optical photoluminescence imaging technique, analogous to the electrical Haynes-Shockley experiment, we have measured room-temperature minority-carrier transport in a series of "surface-free" GaAs/Al0.3Ga0.7As double heterostructures. These measurements are only possible in "surface-free" samples in which the band-to-band radiative recombination lifetimes are long - here up to 2.5-mu-s. We find minority-carrier transport to be "diffusive," with diffusion lengths of up to approximately 140-mu-m. We also find transport in thick ( > 1-mu-m) structures to be mediated by hole-dominated ambipolar diffusion, whereas for thinner structures a transition from ambipolar to free-electron-dominated diffusion is observed. These results demonstrate that our heterostructures become effectively modulation doped for GaAs thicknesses less-than-or-similar-to 1-mu-m.