Si(001):B gas-source molecular-beam epitaxy: Boron surface segregation and its effect on film growth kinetics

B-doped Si(001) films, with concentrations C-B up to 1.7 x 10(22) cm(-3), were grown by gas-source molecular-beam epitaxy from Si2H6 and B2H6 at T-s = 500-800 degrees C. D-2 temperature-programed desorption (TPD) spectra were then used to determine B coverages theta(B) as a function of C-B and T-s. In these measurements, as-deposited films were flash heated to desorb surface hydrogen, cooled, and exposed to atomic deuterium until saturation coverage, Strong B surface segregation was observed with surface-to-bulk B concentration ratios ranging up to 1200. TPD spectra exhibited beta(2) and beta(1) peaks associated with dideuteride and monodeuteride desorption as well as lower-temperature B-induced peaks beta(2)* and beta(1)*. Increasing theta(B) increased the area under beta(2)* and beta(1)* at the expense of beta(2) and beta(1) and decreased the total D coverage theta(D). The TPD results were used to determine the B segregation enthalpy, -0.53 eV, and to explain and model the effects of high B coverages on Si(001) growth kinetics. Film deposition rates R increase by greater than or equal to 50% with increasing C-B > 1 x 10(19) cm(-3) T-s less than or equal to 550 degrees C, due primarily to increased H desorption rates from B-backbonded Si adatoms, and decrease by corresponding amounts at T-s greater than or equal to 600 degrees C due to decreased adsorption site densities. At T-s greater than or equal to 700 degrees C, high B coverages also induce {113} facetting. (C) 1997 American Institute of Physics.