Exciton-phonon interaction in epitaxial CdSe/ZnSe nanostructures

The low-temperature optical properties of submonolayer CdSe/ZnSe nanostructures have been investigated with nominal layer thickness of 0.15 ML and 0.58 ML CdSe. in photoluminescence excitation spectroscopy (PLE) we observe more than 10 equidistant peaks separated by the ZnSe LO-phonon energy even at energies high above the ZnSe-band edge. The peak heights and line shapes are extremely sensitive to the monolayer coverage, have strongly different intensities in emission and PLE and deviate from the Poissonian intensity distribution expected within the concept of a constant, material specific Huang-Rhys parameter S. A bound polaron model is proposed to explain the optical properties of quantum structures for which the approach of a pure electronic quantum confinement is not appropriate. Intrinsic coherence of joint exciton-phonon modes is very promising, e.g. for application in quantum information processing or coherent population transfer.