Optical saturation of mid-infrared transitions in self-assembled InAs quantum dots: evidence for an LO phonon bottleneck

Summary form only given. Semiconductor structures which are able to trap carriers in three dimensions, commonly known as quantum dots (QDs), are interesting because of their discrete state spectra and intriguing optical and electrical properties. Because of their size and discrete state spectra, it has long been predicted that phonon scattering of carriers in dots should be significantly affected. In particular, carriers in QDs with level spacings larger than the LO phonon frequency should see strongly suppressed LO phonon emission. This bottleneck in the LO-phonon relaxation implies long lifetimes and dephasing times in QD excited states, which makes QDs an interesting system for optical applications. Experimental observations of carrier relaxation have been inconsistent, however, with evidence both supporting and contradicting the existence of the bottlenecks. We present experimental observations of the saturation of mid-infrared transitions of electrons out of the dots (IR photoconductivity).