| The ultrafast relaxation of the excitons in GaAs/AlGaAs multiple quantum well (MQW) structures and the tunneling of minority-carrier in n-doped triple-barrier GaAs/AlAs resonant tunneling structures (RTS) have been investigated by laser spectroscopy. Picosecond photoinduced reflectance (PR), time-integrated and time-resolved photoluminescence (PL) (by single-photon-correlation and excitation-correlation techniques) and photoconductance (PhC) measurements have been applied in these studies.; Three different excitation-probing configurations have been employed in time-resolved PR experiments. In medium excitation power conditions, the spectra can be fitted with a sum of two single exponential forms. The long-short components are related to exciton recombination decay and more complex processes with exciton-exciton or carrier-exciton interactions, respectively. From excitation correlation experiments, the recombination lifetimes of excitons in both thick- and thin-barrier MQWs have been obtained and are consistent with the results of the time-resolved PR.; The carrier tunneling processes in the RTS have been studied by time-resolved PL and PhC. The minority-carrier sequential tunneling was found to take a key role in the time-dependence of the PL Intensities. A model based on the minority-carrier tunneling was able to explain the time-resolved PL, and from this the hole tunneling time and the total decay time of excitons in the wells have been obtained. In the PhC experiment the tunneling information of the majority-carrier electrons has been acquired. The reasons for the absence of hole resonant tunneling have been discussed. |
