Island formation during growth of Ge on Si(100): A study using photoluminescence spectroscopy

We present a photoluminescence (PL) study on the growth mode changeover during growth of Ge on Si(100) substrates. Intense PL signals originating from both the flat Ge layer and the three-dimensional (3D) Ge islands are observed from Si/Ge/Si quantum wells with various Ge coverage. The onset of the 3D island formation is determined to be 3.7 monolayers (ML). It is also found that the 3D islands grow with only 3.0 ML of the flat Ge layer retained. This implies that only the 3.0 ML Ge is thermodynamically stable on Si(100) and hence corresponds to the ‘‘equilibrium’’ critical thickness.