Growth, electrical properties and reciprocal lattice mapping characterization of heavily B-doped, highly strained silicon-molecular beam epitaxial structures

Abstract

The growth, electrical and structural characterization of heavily B-doped Si layers produced by molecular beam epitaxy is reported. B doping was obtained from an elemental B source by indirect heating of a graphite crucible in a thin, meander-shaped graphite heater. High doping levels up to 9×10 20 cm -3 were achieved in structures which showed excellent epitaxial quality and bulk-like mobilities for growth temperatures ≤500°C. The growth temperature ( T g) dependence of the electrical activation is reported in relation to the dopant incorporation and crystalline quality. At T g≥600°C and high doping levels, poor electrical activation due to dopant segregation and precipitation was observed. The B-induced lattice strain in the Si epilayer was determined by means of a two-dimensional high-resolution mapping of the reciprocal space. The lattice contraction coefficient was measured to be (6.3±0.1)× 10 -24 cm 3/ atom by considering the concentration of carriers which should be in substitutional positions. Strain characterization of samples with strongly reduced electrical activation, i.e. grown at T g≥600°C, showed that the lattice contraction is related to the effectively incorporated and activated fraction of carriers rather than to the total dopant concentration.