MINORITY-CARRIER RECOMBINATION KINETICS AND TRANSPORT IN SURFACE-FREEGAAS ALXGA1-XAS DOUBLE HETEROSTRUCTURES/

We have measured room-temperature band-to-band recombination decay kin etics in superior quality GaAs heterostructures, and have observed the longest lifetime (2.5 mus) observed for any GaAs/AlxGa1-xAs structure to date. Additionally, using a novel time-resolved optical photolumin escence imagining technique, analogous to the Haynes-Shockley experime nt, we have also measured room-temperature minority-carrier transport in this series of ''surface-free'' GaAs/Al0.3Ga0.7As double heterostru ctures, measurements only possible in high-quality samples with long l ifetimes and intense photoluminescence. We find the transport to be di ffusive with diffusion lengths of greater than or similar to 100 mum. Further, we find, for thick structures, minority-carrier transport is hole-dominated ambipolar diffusion, as expected for high-purity n-type material. However, for thinner structures, we find that the minority- carrier transport is time dependent, changing from ambipolar diffusion at early times, as in thick structures, to electron-dominated diffusi on at later times. We show that these structures become effectively p- type modulation doped due to the relative ''impurity'' and thickness o f the AlxGa1-xAs compared to the GaAs. As a result, the minority-carri er species changes from holes to electrons for decreasing GaAs layer t hicknesses. Cumulatively, we show the band-to-band recombination decay kinetics and carrier transport results to be in excellent qualitative and quantitative agreement. Moreover, our results are in excellent ag reement with electrical transport measurements of electron and hole mo bilities. Finally, with our measured room-temperature lifetimes and mi nority-carrier transport measurements versus GaAs layer thickness, we accurately calculate the interface recombination velocity for these st ructures, with the result S is similar to 40 cm/s, among the lowest ev er reported for any GaAs/AlxGa1-xAs structure.