The surface of boron-doped layers formed by rapid vapor-phase doping was analyzed by x-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared-attenuated total reflection (FTIR-ATR), to determine the role of the hydrogen carrier gas. Boron doping was carried out with aB2H6source gas and a hydrogen carrier gas at 800 and 900 °C. A nitrogen carrier gas was also used for comparison. Using hydrogen carrier gas, no evidence of boron segregation was observed in the XPS spectra. FTIR-ATR analysis confirmed that the hydrogen termination of the surface was maintained during doping. Using nitrogen carrier gas, layers that included segregated boron and silicon nitride were produced on the surface, which led to poor controllability of the boron concentration. When a hydrogen carrier gas is used, the hydrogen termination should promote the surface migration of adsorbed species. The hydrogen carrier gas plays an important role in terminating the silicon dangling bonds, thus preventing excessive chemisorption of boron.