Advances in surfactant-mediated growth of germanium on silicon: high-quality p-type Ge films on Si

The use of antimony (Sb) as a surfactant allows the growth of relaxed and smooth germanium films with low-defect density on silicon (1 1 1) substrates. We extend the possibilities of surfactant mediated epitaxy (SME) by introducing in situ boron (B) doping, thus enabling the growth of p-type Ge layers on Si(1 1 1). In Sb-SME, a lower p-doping limit in the order of 1×1016 cm−3 for B doping is set by the compensating incorporation of the surfactant Sb during growth. Above this limit, high hole Hall mobilities are reached, up to 1600 cm2/V s for a net p-doping of 1.9×1016 cm−3. Temperature-dependent Hall measurements show that the hole mobility in p-type Ge layers grown by SME is only limited by ionized impurity scattering of the dopants pointing to high material quality. The structural properties of Ge films grown by SME are characterized by cross-sectional transmission electron microscopy and high-resolution X-ray diffraction. This reveals a complete relaxation and low defect densities. A more detailed study of the Ge/Si(1 1 1) interface shows a regular dislocation array with dislocation lines oriented along the in-plane 〈1¯10〉 directions with a spacing of 8.0 nm. This indicates a practically complete relaxation of the Ge layer by a triangular network of interface misfit dislocations.