Annealing effects on carbon-induced germanium dots in silicon

The growth of 2.4 monolayers Ge on 0.2 monolayers of predeposited C on Si results in the formation of 15 nm size Ge islands. Fifty stacked layers of these C-induced Ge dots are grown on Si (001) at 460 degrees C. Different pieces of the wafer an annealed at temperatures between 460 and 950 degrees C and for times ranging from 1 to 20 min at 850 degrees C. For temperatures higher than 550 degrees C, a pronounced energy blueshift and an evolution from one broad photoluminescence peak to two well-resolved lines reflect a gradual transition from quantum dot states to quantum well-like states. As transmission electron microscopy images illustrate, diffusion processes completely smear out the sharp interfaces between the dots and the surrounding Si. An activation energy of only 1.6 eV and temperature-dependent diffusion coefficients are derived from simple model calculations. (C) 1998 American Institute of Physics. [S0003-6951(98)04025-X].