Phosphorus atomic layer doping of germanium by the stacking of multiple δ layers.

In this paper we demonstrate the fabrication of multiple, narrow, and closely spaced δ-doped P layers in Ge. The P profiles are obtained by repeated phosphine adsorption onto atomically flat Ge(001) surfaces and subsequent thermal incorporation of P into the lattice. A dual-temperature epitaxial Ge overgrowth separates the layers, minimizing dopant redistribution and guaranteeing an atomically flat starting surface for each doping cycle. This technique allows P atomic layer doping in Ge and can be scaled up to an arbitrary number of doped layers maintaining atomic level control of the interface. Low sheet resistivities (280 Ω/ [symbol see text ) and high carrier densities (2 × 10(14) cm( - 2), corresponding to 7.4 × 10(19) cm( - 3)) are demonstrated at 4.2 K.