Critical epitaxial thicknesses for low-temperature (20–100 °C) Ge(001)2×1 growth by molecular-beam epitaxy

The growth of Ge(001) by molecular-beam epitaxy at temperatures Ts between 20 and 100 °C, and deposition rates of 0.5 and 1 Å s−1, was investigated using a combination of in situ reflection high-energy electron diffraction and post-deposition cross-sectional transmission electron microscopy. All films consisted of three zones beginning with a defect-free epitaxial layer of thickness t1 in which ln(t1)∝(1/Ts). The second zone was a narrower intermediate layer containing {111} stacking faults and microtwins, while the third zone was amorphous. An atomistic growth model is proposed to explain the observed morphological breakdown during low-temperature growth.