Enhanced Polar Exciton-LO-Phonon Interaction in Quantum Dots

Phonon replicas of charged and neutral exciton complexes in single quantum dots

“…Note that the Huang-Rhys parameter of X obtained here for the pyramidal In 0.15 Ga 0.85 As/ AlGaAs QDs is only 20-30 % of the values reported for InAs/GaAs SK QDs on ͑001͒ substrates. 8 Lower values are not surprising since a lower In-concentration results in a weaker piezoelectric field. Moreover, for the high-symmetry pyramidal QDs, the piezoelectric field is directed vertically along the smallest dimension of the QD while for the low-symmetry SK QDs, grown on the ͑001͒ plane, the field is also acting laterally.…”

“…Moreover, for the high-symmetry pyramidal QDs, the piezoelectric field is directed vertically along the smallest dimension of the QD while for the low-symmetry SK QDs, grown on the ͑001͒ plane, the field is also acting laterally. Thus, the strong lateral deformation of the electron and hole wave functions present in the SK QDs, 8 dramatically enhancing the Huang-Rhys factor for dots with a wide base, is not present in the pyramidal QDs.…”

“…11 Thus, the investigations on the LO-phonon coupling of single QDs have so far been scanty and mainly limited to the neutral exciton ͑and biexciton͒. 6,8,11,12 Although a weak LO-phonon replica was interpreted as the signature of a neutral exciton, 10 no experimental studies compare neutral and charged exciton complexes in this regard. It was predicted theoretically, however, that an extra charge enhances the Huang-Rhys parameter by one order of magnitude for GaAs microcrystallites.…”

“…The experimental investigations of LO-phonon assisted recombination in III-V QDs have so far been restricted to photoluminescence ͑PL͒ spectroscopy of StranskiKrastanow ͑SK͒ grown InAs/GaAs dot ensembles. 8 In such measurements are different exciton complexes not resolved but the average value of the Huang-Rhys parameter was extracted to be ϳ0.015. 8 LO-phonon replicas have been resolved for single InAs/GaAs QDs in PL-excitation spectroscopy, but the coupling strength was not extracted, nor its association with charged excitonic states investigated.…”

“…Moreover, the piezoelectric field in strained QDs separates electrons and holes and further enhances the polar coupling. 8 In the weak-coupling regime, the LO-phonon coupling is manifested in the low-temperature optical recombination ͑absorption͒ spectrum by replicas at discrete LO-phonon energies ប LO below ͑above͒ the dominating zero-phonon transition. For the independent-boson model, 9 where the electronic wave functions are assumed to remain unchanged under phonon interaction, the intensities of the LO-phonon replicas follow the Poisson distribution characterized by the Huang-Rhys parameter, describing the polar coupling strength.…”