DETERMINATION OF THE LATTICE CONTRACTION OF BORON-DOPED SILICON

We report a study of the change in lattice constant when single-crystal silicon is substitutionally doped with boron. The measurements were made using 10-mum-thick epilayers with boron concentrations (N(B)) in the range 1.7 X 10(19)-1.2 X 10(20) cm-3. The influence of elastic strain in the epilayers and their substrates was eliminated by including Bragg reflections from planes that were inclined to the (100) surface. We obtained a value for the lattice contraction coefficient beta = (5.19 +/- 0.09) X 10(-24) cm-3, where the range is +/- one standard error. Specimens with N(B) almost-equal-to 2 X 10(19) cm-3 were strained to give coherent interfaces with their substrates. Evidence for relaxation (presumably by misfit dislocations at the interface) was observed with N(B) almost-equal-to 5 X 10(19) cm-3 (corresponding to a lattice mismatch of approximately 2.5 X 10(-4)), but this occurred in a patchy fashion and remained incomplete while N(B) was increased to 1.2 X 10(20) cm-3 (corresponding to a mismatch of 6.5 X 10(-4)) . This partial relaxation occurred at somewhat smaller mismatches than would be expected from reported studies of silicon-germanium alloy epilayers on silicon substrates. Our technique for analyzing a set of Bragg reflections to separate the effects of elastic strain and lattice mismatch appears to be novel and has general applicability to the study of epilayer/substrate combinations.