ENTROPY EFFECTS IN THE SELF-ORGANIZED FORMATION OF NANOSTRUCTURES

摘要

A finite-temperature thermodynamic theory is developed for arrays of submonolayer islands in heteroepitaxial systems. It is established that the temperature dependence of the average island size at temperatures of several hundred degrees Kelvin is determined by the entropy contribution to the free energy. Entropy effects lead to the shrinkage of the average island size. At moderate temperatures the islands have a bimodal size distribution, with one local maximum corresponding to nanometer-scale islands and another corresponding to single adatoms. With increasing temperature, the size distribution becomes unimodal, and no optimum island size can be resolved. A decrease of the average island size with temperature is an indication of the equilibrium nature of an array of islands and allows such arrays to be distinguished from those that are kinetically-controlled. Data from cross-sectional high-resolution transmission electron microscopy and photoluminescence spectroscopy of submonolayer arrays of InAs/GaAs islands confirm the equilibrium nature of this system.