On the epitaxy of germanium telluride thin films on silicon substrates

The growth by molecular beam epitaxy of GeTe thin films on highly lattice‐mismatched Si(111) substrates is reported. In situ reflection high‐energy electron diffraction and quadrupole mass spectrometry were employed to monitor the growth process in real time and tune the deposition conditions. Epitaxy was achieved in a window of substrate temperatures between 220 and 270 °C, using a Ge/Te flux ratio of ∼0.4. Extensive ex situ X‐ray diffraction characterization showed that the epitaxial layers crystallize in the rhombohedrally distorted rocksalt structure α‐GeTe, with orientation relationships to the substrate α‐GeTe[0001] ‖ Si[111] and α‐GeTe〈101̄ 0〉 ‖ Si〈112̄ 〉. ω‐scans of the α‐GeTe(000n) reflections (n = 3, 6, 9) exhibit a full width at half maximum between 10 and 20 arcsec, indicating small mosaicity. However, a large twist is observed (∼14°), pointing to the presence of rotational domains. In addition, the layer matrix is affected by twinning. The epitaxial films exhibit a slight tensile in‐plane strain, which might be due to the difference in thermal expansion coefficients between α‐GeTe and Si, and/or small deviation from stoichiometric composition, i.e., vacancies in the Ge sub‐lattice.