Abstract

We have developed an inter-/intra-band double-resonance technique that has allowed us to make an unequivocal assignment of the resonant bound-bound intersublevel absorption in self-organized InAs/GaAs quantum dots We have applied the technique to dots grown at a low growth-rate, which show well resolved photoluminescence (PL) lines The double resonance (far infrared modulated photoluminescence, FER-MPL) and its polarisation selection rules allows us to identify not only the levels involved in the PL transition but the relative importance of the causes of its inhomogeneous broadening The interband excitation was with a 4 mW c w. He:Ne laser, focussed so that the peak intensity was about 1 photon per dot every 10ns, incident on the top surface of the sample The PL was collected and focussed into a 0 5 m grating monochrometer, and detected by a liquid nitrogen cooled Ge p-i-n diode The FIR from the Dutch free-electron laser (FELIX), which is continuously tuneable from 5 μm to 250 μm, was incident normal to the substrate side of the sample The PL and the FIR-MPL were collected simultaneously to ensure the correspondence of features in each by monitoring both the de and ac outputs of the detector Spectra were obtained by scanning either the monochrometer at fixed FIR frequency or scanning FELIX at a fixed PL frequency The FIR beam was unfocussed in order to avoid heating the sample, and the intensity was estimated to be ~10¹⁶ photons/micropulse/cm², i e of the order of 10⁶ photons per dot

© 2000 IEEE