Germanium incorporation in heavily doped molecular beam epitaxy grown GaAs:Ge

Germanium is normally an n-type dopant in MBE GaAs but compensation and p-type action has been observed under certain conditions. Studies have been made of the growth conditions under which p+ and n+ layers are obtained with heavy Ge fluxes during MBE GaAs growth on GaAs substrates at 570 °C. Both p+ and n+ dopings in excess of 1020 cm−3 have been observed. The production of p-type layers is favored by As4/Ga ratios of 2–3:1 and high Ge fluxes. For As4/Ga ratios of 4–5:1 and Ge fluxes corresponding to dopings of the order of mid-1018 cm−3 or less, the layers grown are n-type. For As4/Ga ratios greater than 6:1, the layers may be n+ type with concentrations that are 1020 cm−3 or higher as given by capacitance measurements or van der Pauw measurements. Photoluminescence studies at 4 K for 1020 cm−3 doped layers show a broadband with a maximum at 1.27–1.33 eV for n+ layers, and for p+ layers a broadband luminescence with evidence of peaking at about 1.38 and 1.35 eV. Transmission electron microscope studies show almost no tendency for the formation of a second phase or microprecipitation in the most heavily doped (2×1020 cm−3 p and n) specimens. Finally, the paper considers the possible role of the species GeGa, GeAs, (GeGaVGa), and (GeAsVGa) and other complexes in the doping effects observed.