Carrier relaxation and electronic structure in InAs self-assembled quantum dots

We studied the electronic structure and relaxation processes in InAs quantum dots embedded in GaAs. Using capacitance measurements along with photoluminescence spectroscopy, we estimate the energy splitting between the ground and first excited quantum-dot state in the conduction and valence band, respectively. There are five quantum-dot transitions observable in our photoluminescence (PL) spectra, which we attribute to allowed transitions between electron and hole states of the same quantum number. Phonon-related relaxation processes were studied combining PL, resonant PL (RPL), and photoluminescence excitation (PLE) experiments. In the RPL as well as in the PLE spectra, we observed enhanced signals at twice the phonon energies available in the system. Therefore, a maximum in the intensity of the PLE and RPL signal does not necessarily occur when most of the dots are pumped resonantly into an excited state. The main criterion, however, seems to be that the energy distance between the pumped levels and the levels below matches a multiple of the available phonon energies. Changing the pump power in our resonant PL experiments corroborates that at least in the small carrier density regime phonon-related processes are important for the carrier relaxation in InAs quantum dots embedded in GaAs bulk material. © 1996 The American Physical Society.