Structural and electrical properties of Ge-on-Si(0 0 1) layers with ultra heavy n-type doping grown by MBE

•Ultra heavy doped n-Ge layers grown on Si(0 0 1) by MBE are studied.•Electrically active dopant concentration exceeding 1020 cm−3 is achieved.•X-ray diffraction can reveal the electrically active part of dopant atoms.•High crystalline quality of heavy doped Ge:Sb/Si films could be maintained. In this paper we report about the formation of ultra heavy doped n-Ge layers on Si(0 0 1) substrates by molecular beam epitaxy and their characterization by different independent techniques. Combined study of structural and electrical properties of fabricated layers using secondary ion mass spectroscopy, X-ray diffraction, Hall effect and reflection measurements was carried out and it has revealed the achievable charge carrier densities exceeding 1020 cm−3 without deterioration of crystalline quality of such doped layers. It was also shown that X-ray analysis can be used as a fast, reliable and non-destructive method for evaluation of the electrically active Sb concentration in heavy doped Ge layers. The appropriate set of doping density allowed to adjust the plasmonic resonance position in Ge:Sb layers in a rather wide range reaching the wavelength of 3.6 μm for the highest doping concentration. Room temperature photoluminescence confirmed the high crystalline quality of such doped layers. Our results indicated the attainability of high electron concentration in Ge:Sb layers grown on Si substrates without crystalline quality deterioration which may find potential applications in the fields of Si-based photonics and mid-IR plasmonics.