Optical study of phonon-mediated carrier relaxation in CdTe/ZnTe self-assembled quantum dots

We report the photoluminescence and excitation spectra of CdTe self-assembled quantum dots grown by molecular beam epitaxy in ZnTe. In photoluminescence excitation spectra, multiple longitudinal-optical (LO) phonon structures Lip to the 19th order are observed even above ZnTe-matrix energy, and the wetting layer was clarified. Photoluminescence spectra of CdTe quantum dots having LO phonon structures under quasi-resonant excitation show that CdTe dots are surrounded by ZnxCd1-xTe (x similar to 0.8, where x ranges from 0.5 to 1). Phonon-mediated carrier relaxation is discussed. Photoexcited carriers forming excitons are relaxed by emitting multiple LO phonons of the ZnTe matrix successively from the higher energy state of the matrix to the wetting layer. At the wetting layer, involved LO phonons are transformed to those of ZnxCd1-xTe surrounding the CdTe dots. ZnTe-like and CdTe-like LO phonons and, lastly, acoustic phonons, are emitted in relaxation to the CdTe-dot state.