Observation of the 2D-3D growth mode transition in the InAs/GaAs system

Self-organized InAs quantum dot structures were prepared by low pressure metalorganic vapor phase epitaxy (MOVPE) using the Stranski-Krastanow growth mode. We present photoluminescence (PL) and atomic force microscopy (AFM) studies of the transition from a 2D InAs wetting layer to 3D quantum sized islands. The very narrow window where this transition takes place could be studied in detail by taking advantage of the slight growth rate gradient of our MOVPE system. After the growth of a critical layer thickness, first quantum dots occur. From the PL spectra obtained at different positions on the wafer, we conclude that a part of the wetting layer is consumed by the dot formation process. This is further confirmed by AFM measurements. Also a qualitative correlation between dot density and PL intensity is described. Moreover, we observed that the dot formation can be suppressed by instantaneous overgrowth. Besides the overgrowth temperature the growth interruption between the InAs film and the GaAs cap layer was found to be of great importance for the dot formation.