Coexistence of planar and three-dimensional quantum dots in CdSe/ZnSe structures

Two well distinguishable classes of nanoscale islands were identified in Cd Se/ZnSe quantum dot structures by optical spectroscopy and transmission ele ctron microscopy. For 2.1 to 3.1 monolayer CdSe deposition, coherent three- dimensional (3D) islands, formed in the Stranski-Krastanow (SK) mode, are f ound with typical diameters of similar to 16 nm and a coverage-dependent de nsity of up to 3x10(10) cm(-2). Simultaneously, small islands with lateral extensions below 10 nm and a density of similar to 5x10(11) cm(-2) are form ed by strain-modified island growth. Whereas the 3D SK islands dominate the emission properties at room temperature, the latter smaller islands determ ine the optical properties at temperatures below 120 K. (C) 2000 American I nstitute of Physics. [S0003-6951(00)00806-8].