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 $C_{\mathrm{B}}$ up to ${\text{1.7×10}}^{22}\hspace{0.17em}{\mathrm{cm}}^{\mathrm{-3}},$ were grown by gas-source molecular-beam epitaxy from ${\mathrm{Si}}_{\mathrm{2}}{\mathrm{H}}_{\mathrm{6}}$ and ${\mathrm{B}}_{\mathrm{2}}{\mathrm{H}}_{\mathrm{6}}$ at $T_s\text{=500–800\hspace{0.17em}°}\mathrm{C}.$ ${\mathrm{D}}_{\mathrm{2}}$ temperature-programed desorption (TPD) spectra were then used to determine B coverages ${\theta }_{\mathrm{B}}$ as a function of $C_{\mathrm{B}}$ 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 ${\theta }_{\mathrm{B}}$ increased the area under ${\beta }_2^{*}$ and ${\beta }_1^{*}$ at the expense of ${\beta }_2$ and ${\beta }_1$ and decreased the total D coverage ${\theta }_{\mathrm{D}}.$ The TPD results were used to determine the B segregation enthalpy, $\text{−0.53\hspace{0.17em}}\mathrm{eV},$ and to explain and model the effects of high B coverages on Si(001) growth kinetics. Film deposition rates $R$ increase by $\text{⩾50\%}$ with increasing $C_{\mathrm{B}}{\mathrm{>̃1\times 10}}^{\mathrm{19}}{\mathrm{\hspace{0.17em}cm}}^{\mathrm{-3}}$ at $T_s\text{⩽550\hspace{0.17em}°}\mathrm{C},$ due primarily to increased H desorption rates from B-backbonded Si adatoms, and decrease by corresponding amounts at $T_s\text{⩾600\hspace{0.17em}°}\mathrm{C}$ due to decreased adsorption site densities. At $T_s\text{⩾700\hspace{0.17em}°}\mathrm{C},$ high B coverages also induce {113} facetting.