Atomic-order surface reaction processes on the group IV semiconductor surface are formulated based on the Langmuir-type surface adsorption and reaction scheme. In in-situ doped Si1−xGex epitaxial growth on the (100) surface in a SiH4-GeH4-dopant (PH3, or B2H6 or SiH3CH3)-H2 gas mixture, the deposition rate, the Ge fraction and the dopant concentration are explained quantitatively assuming that the reactant gas adsorption/reaction depends on the surface site materials and that the dopant incorporation in the grown film is determined by Henry's law. Self-limiting formation of 1-3 monolayers of group IV or related atoms in the thermal adsorption and reaction of hydride gases (SiH4, GeH4, NH3, PH3, CH4 and SiH3CH3) on Si(100) and Ge(100) are generalized based on the Langmuir-type model. Epitaxial Si or SiGe grown on N, P or B layers already-formed on Si(100) or SiGe(100) surface is achieved. It is found that higher level of electrical active P atoms exist in such film, compared with doping under thermal equilibrium conditions. Furthermore, the capability of atomically controlled processing for doping of advanced devices with critical requirements for dopant dose and location control is demonstrated for the base doping of SiGe:C heterojunction bipolar transistors (HBTs). These results open the way to atomically controlled technology for ultra-large-scale integrations.