Photoluminescence of self-assembled InAs/GaAs quantum dots excited by ultraintensive femtosecond laser

Abstract

This paper presents the ultrahigh excitation intensity-dependent photoluminescence (UEIPL) spectra of self-assembled InAs/GaAs quantum dots (QDs) excited by femtosecond laser with power intensity up to 450 kW/cm2. Upon ultraintensive excitation, many emission features from QDs and underneath wetting layer (WL) have been observed. As a result of band filling, two emission features D1 and D3 due to the ground (n=1) and second excited state (n=3) transitions, and an emission band from GaAs barrier layer state transition have been distinguished at the experimental temperature of 77K. In addition, an emission feature DD has been identified as the superposition of n=2 (first excited state) in QD and defect state transitions. Moreover, both heavy-hole (HH) and light-hole (LH) states in WL, which are usually optically inactive in emission type of experiment, have been derived from the sample subjected to ultraintensive laser excitation. The ultraintensive excitation generates ultrahigh transient carrier density in QDs and WL. As a result of very strong carrier-carrier and carrier-phonon scattering, all emission peaks shift toward lower photon energy with the increasing excitation power due to lattice heating effect. Further investigations also show that WL could effectively assist in the thermally escape of carriers in QDs; it acts as a channel to facilitate the thermal redistribution of excitons in QDs as well. The UEIPL measurement seems to be a valid alternative to photoreflectance measurements for the investigation of QD and WL system.