Direct Observation of Subcritical Fluctuations during the Formation of Strained Semiconductor Islands

We have directly imaged subcritical fluctuations during the nucleation phase of three-dimensional islands in strained layer epitaxy. The fluctuations are defect mediated and are found to be large even at low growth temperatures. We attribute the existence of large fluctuations to the time dependence of the supersaturation. This indicates classical nucleation concepts are relevant, even at low growth temperatures.