Quantum confinement in CdSe-nanocrystallites synthesized by ion implantation

Nanocrystalline semiconductors offer a wide variety of possible applications in optical and optoelectronic devices. Embedding nanocrystals in compatible and stable host materials is of fundamental technical and scientific interest. In this work, buried nanocrystals of the direct band gap II–VI compound semiconductor CdSe were synthesized by sequential high dose ion beam implantation into thin thermally grown silicon dioxide layers and subsequent rapid thermal processing. Bulk CdSe has a bandgap energy of 1.75 eV that can be shifted to larger values by reducing the crystal size to dimensions smaller than the Bohr radius of the exciton. The size of the CdSe precipitates was controlled by the implantation and annealing parameters. The photoluminescence (PL) emission was exited by an Ar ion laser and measured in a temperature range between 80 and 295 K. The energy shift of the PL emission of the embedded CdSe nanocrystals is in quantitative agreement with the shift due to quantum confinement calculated from the mean size of the nanocrystals determined from thin film X-ray diffraction spectra (XRD) and transmission electron microscopy (TEM) images.