  B-doped $\delta$-layers were fabricated in Si(100) using BCl$_{3}$ as a
dopant precursor in ultrahigh vacuum. BCl$_{3}$ adsorbed readily at room
temperature, as revealed by scanning tunneling microscopy (STM) imaging.
Annealing at elevated temperatures facilitated B incorporation into the Si
substrate. Secondary ion mass spectrometry (SIMS) depth profiling demonstrated
a peak B concentration $>$ 1.2(1) $\times$ 10$^{21}$ cm$^{-3}$ with a total
areal dose of 1.85(1) $\times$ 10$^{14}$ cm$^{-2}$ resulting from a 30 L
BCl$_{3}$ dose at 150 $^{\circ}$C. Hall bar measurements of a similar sample
were performed at 3.0 K revealing a sheet resistance of $R_{\mathrm{s}}$ = 1.91
k$\Omega\square^{-1}$, a hole concentration of $n$ = 1.90 $\times$ 10$^{14}$
cm$^{-2}$ and a hole mobility of $\mu$ = 38.0 cm$^{2}$V$^{-1}$s$^{-1}$ without
performing an incorporation anneal. Further, the conductivity of several
B-doped $\delta$-layers showed a log dependence on temperature suggestive of a
two-dimensional system. Selective-area deposition of BCl$_{3}$ was also
demonstrated using both H- and Cl-based monatomic resists. In comparison to a
dosed area on bare Si, adsorption selectivity ratios for H and Cl resists were
determined by SIMS to be 310(10):1 and 1529(5):1, respectively, further
validating the use of BCl$_{3}$ as a dopant precursor for atomic precision
fabrication of acceptor-doped devices in Si.
