Time-resolved studies of spatially direct and indirect transitions in GaAs/AlGaAs and InGaAs/GaAs quantum wires

摘要

Laser holographic lithography and selective chemical etching have been used to create GaAs/AlGaAs and InGaAs/GaAs quantum well wires. Strong differences are observed between the photoluminescence spectra from the GaAs and InGaAs quantum wires, with the former being dominated by spatially indirect transitions, and the latter by direct transitions. Detailed time resolved photoluminescence studies show a red shift in photoluminescence energy with increasing time delay after excitation for the indirect transition in the GaAs wires. This is accompanied by a non-exponential decay time which increases from 10 ns to greater than 150 ns as the delay time is increased (in a manner similar to that observed in nipi doping superlattices). The InGaAs wires show no such behavior, with a decay time constant of 320 ps at 1.8 K, independent of time delay after excitation, both indicative of a spatially direct transition.