Raman spectroscopy of CdTe/ZnTe quantum dot structures

Semiconductor low-dimensional structures of CdTe quantum dots (QDs) embedded in ZnTe matrix have been investigated by micro-Raman spectroscopy. A reference ZnTe sample (without dots) was also studied for comparison. Both samples were grown by a molecular beam epitaxy technique on the p-type GaAs substrate. The Raman measurements have been performed at room temperature. The samples were excited by an Ar2+ laser of 514.5 nm wavelength. The Raman spectra have been recorded for different acquisition parameters of the measurement. For the reference and QD sample localized longitudinal (LO) phonons of 210 cm–1 wavenumber associated with the ZnTe layer are observed. In the case of QD sample another broadband corresponding to the LO CdTe phonon related to the QD-layer appears at a wavenumber of 160 cm–1. Such behaviour does not exhibit the Raman spectra of the reference sample. Thus the Raman measurements confirm the presence of CdTe layer of quantum dots in the investigated material. Additionally, Raman spectra for both samples exhibit tellurium-related peaks at wavenumbers around 120 cm–1 and 140 cm–1, significantly increasing with laser time exposure. It is shown that the peaks are associated with the formation of Te aggregates on the ZnTe surface due to the laser damage in the ZnTe layer.