Experimental studies of the recombination processes in II-VI semiconductors (bulk crystals and epilayers) at variable excitation levels

摘要

Low-temperature luminescence spectra under broad-scale variation of anudexcitation level Iexc are studied for ZnS/ZnSe single quantum wells (QW)udand for CdS bulk crystals and epilayers. In the first case, the manifestationsudturn out to be of the heterointerface inhomogeneity - i.e. fluctuations of QWudthickness. The position of the mobility edge for excitons localized by fluctuations is determined. In the second case the effect of the increase of Iexcudis systematically studied not only for excitonic but also for impurity-relatedudedge luminescence. Contrary to the earlier and commonly assumed expectations, up to the highest Iexc close to damage threshold no saturation ofudedge luminescence intensity was observed in bulk CdS crystals, whereasudin a few thick epilayers such saturation did occur. The suggested qualitativeudexplanation takes into account diffusion (non-diffusive transport) of carriersudbeyond the excited near-surface layer.