Two-dimensional-like nucleation of GaAs on Si by room-temperature deposition

Nucleation of GaAs on Si in molecular-beam epitaxy is studied by Auger electron spectrometry and reflection high-energy electron diffraction. It is shown that, if growth is initiated at room temperature and if a GaAs equivalent thickness of ∼15 Å is deposited on Si, an amorphous, nonstoichiometric layer is obtained which covers completely the substrate surface. Stoichiometry and monocrystallinity can be restored by thermal annealing at 350 °C by a solid-phase epitaxy mechanism. Under such conditions the initial stages of GaAs/Si growth can then proceed via two-dimensional nucleation, instead of the three-dimensional mode observed at higher growth temperatures.