Influence of growth and annealing temperature on the strain and surface morphology of Ge995Sn0.005 epilayer

Ge1−xSnx alloys with low tin composition (0.5%) were grown directly on Si (1 0 0) substrates by molecular beam epitaxy at various temperatures ranging from 220 °C to 500 °C. In situ RHEED patterns, AFM images, and HR-XRD curves were measured to investigate the surface morphology and strain of the Ge0.995Sn0.005 alloys. Surface roughening, which occurred during the deposition of the alloy, was found to be enhanced with the increase of the growth temperature TG. Compressive residual strain was introduced during low-temperature heteroepitaxial growth of the alloy. As TG was increased, it was gradually released, while the tensile thermal strain was increased. As a result, tensile in-plane strain was obtained provided TG was high enough (>420 °C). The influence of annealing temperature TA was investigated as well. It was shown that both surface morphology and stain of the alloy were only slightly changed with TA ≤ 600 °C. If TA was further increased, the surface roughness was significantly increased and the residual heteroepitaxial strain substantially released.