GROWTH, ELECTRICAL-PROPERTIES AND RECIPROCAL LATTICE MAPPING CHARACTERIZATION OF HEAVILY B-DOPED, HIGHLY STRAINED SILICON-MOLECULAR BEAM EPITAXIAL STRUCTURES

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 X 10(20) cm(-3) were achieved in structures which showed excellent epitaxial quality and bulk-like mobilities for growth temperatures less than or equal to 500 degrees 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 greater than or equal to 600 degrees 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) x 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 greater than or equal to 600 degrees C, showed that the lattice contraction is related to the effectively incorporated and activated fraction of carriers rather than to the total dopant concentration.