Photoluminescence and photoluminescence excitation studies of lateral size effects in Zn 1 − x Mn x S e / Z n S e quantum disk samples of different radii

Quantum disc structures (with diameters of 200 and 100 nm) were prepared from a ${\mathrm{Zn}}_{0.72}{\mathrm{Mn}}_{0.28}\mathrm{S}\mathrm{e}/\mathrm{Z}\mathrm{n}\mathrm{S}\mathrm{e}$ single quantum well structure by electron beam lithography followed by an etching procedure that combined dry and wet etching techniques. The quantum disc structures and the parent structure were studied by photoluminescence and photoluminescence excitation spectroscopy. For the light-hole excitons in the quantum well region, shifts of the energy positions are observed following fabrication of the discs, confirming that strain relaxation occurs in the pillars. The light-hole exciton lines also sharpen following disc fabrication: this is due to an interplay between strain effects (related to dislocations) and the lateral size of the discs. A further consequence of the small lateral sizes of the discs is that the intensity of the donor-bound exciton emission from the disc is found to decrease with the disc radius. These size-related effects occur before the disc radius is reduced to dimensions necessary for lateral quantum confinement to occur but will remain important when the discs are made small enough to be considered as quantum dots.