Be-enhanced CdSe island formation in CdSe/ZnSe heterostructures

The Be-enhanced formation of CdSe quantum dots in CdSe/ZnSe heterostructures grown by migration enhanced epitaxy on (001)GaAs substrates has been investigated using photoluminescence spectroscopy, x-ray techniques (diffraction and reflectometry), and transmission electron microscopy. Coverage of the ZnSe starting surface with a fractional monolayer of beryllium selenide leads to enhanced island formation well below the CdSe thickness of 0.6 monolayer corresponding to the onset of the CdSe-rich island formation in the Be-free structures. The effect of the fractional Be coverage is demonstrated by observation of sharp lines in the photoluminescence signal from patterned mesas with dimensions down to 60 nm, which is due to the emission from individual exciton localization sites attributed to quantum dots. X-ray diffraction and reflectometry measurements on CdSe/ZnSe short-period superlattices with the submonolayer CdSe insertions confirm an enhanced roughening of the CdSe layer morphology in the case of beryllium coverage. Cross-sectional transmission electron microscopy on the SLs with BeSe fractional monolayer exhibits Cd-induced stress modulation along the CdSe sheets with a lateral scale of similar to4 nm, that can also be interpreted in favor of the BeSe-nucleated CdSe-based quantum dots. (C) 2000 American Institute of Physics. [S0021-8979(00)09101-0].