  A wide range of n- and p-type doping levels in GaAs layers grown by chemical
beam epitaxy is achieved using H$_{2}$-diluted DTBSi and CBr$_{4}$ as gas
precursors for Si and C. We show that the doping level can be varied by
modifying either the concentration or the flux of the diluted precursor.
Specifically, we demonstrate carrier concentrations of
6$\times$10$^{17}$-1.2$\times$10$^{19}$ cm$^{-3}$ for Si, and
9$\times$10$^{16}$-3.7$\times$10$^{20}$ cm$^{-3}$ for C, as determined by Hall
effect measurements. The incorporation of Si and C as a function of the flux of
the corresponding diluted precursor is found to follow, respectively, a first
and a fourth order power law. The dependence of the electron and hole mobility
values on the carrier concentration as well as the analysis of the layers by
low-temperature (12 K) photoluminescence spectroscopy indicate that the use of
H$_{2}$ for diluting DTBSi or CBr$_{4}$ has no effect on the electrical and
optical properties of GaAs.
