Be-enhanced CdSe island formation in CdSe/ZnSe heterostructures

The Be-enhanced formation of CdSe quantum dots in CdSe/ZnSe heterostructure s grown by migration enhanced epitaxy on (001)GaAs substrates has been inve stigated using photoluminescence spectroscopy, x-ray techniques (diffractio n and reflectometry), and transmission electron microscopy. Coverage of the ZnSe starting surface with a fractional monolayer of beryllium selenide le ads to enhanced island formation well below the CdSe thickness of 0.6 monol ayer 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 patterne d mesas with dimensions down to 60 nm, which is due to the emission from in dividual exciton localization sites attributed to quantum dots. X-ray diffr action and reflectometry measurements on CdSe/ZnSe short-period superlattic es with the submonolayer CdSe insertions confirm an enhanced roughening of the CdSe layer morphology in the case of beryllium coverage. Cross-sectiona l transmission electron microscopy on the SLs with BeSe fractional monolaye r exhibits Cd-induced stress modulation along the CdSe sheets with a latera l scale of similar to4 nm, that can also be interpreted in favor of the BeS e-nucleated CdSe-based quantum dots. (C) 2000 American Institute of Physics . [S0021-8979(00)09101-0].