Time-resolved photoluminescence quenching measurements in InAs/GaAs quantum dots using terahertz laser pulses

Carrier dynamics and relaxation processes in self assembled quantum dots (QDs) are of fundamental interest due to their influences on the performances of optoelectronic devices. The intersublevel relaxation mechanisms influence the temporal response of the photoluminescence (PL). In this paper we present our work on time-resolved PL quenching measurements on QD ensembles using terahertz pulses. A Ti:Sapphire laser was used for interband excitation and the PL was measured by a streak camera. Terahertz pulses obtained from a Free Electron Laser were tuned to excite intersublevel transitions in the QDs which caused partial depletion of the electronic ground state resulting in quenching of the interband PL. The samples studied consisted of self-assembled InAs/GaAs QDs for which the intersublevel relaxation times varied from few ps to ns. Simultaneous time and wavelength resolved measurements enabled us to study the carrier redistribution by the terahertz pulse and their dynamics. The PL transients were fitted using exponential functions convoluted with a Gaussian system response and the PL quenching depth and recovery times were extracted. We present a comparative analysis for different QD samples, with emphasis on the effect of intersublevel relaxation times on the carrier dynamics.