Abstract Boron and boron phosphide films were prepared by gas source molecular beam deposition on sapphire crystal at various substrate temperatures up to 800°C using cracked B 2H 6(2% in H 2) at 300°C and cracked PH 3(20% in H 2) at 900°C. The substrate temperatures and gas flow rates of the reactant gases determined the film growth. The boron films with amorphous structure are ptype. Increasing growth times lead to increasing mobilities and decreasing carrier concentrations. Boron phosphide film with maximum P/B ratio is obtained at a substrate temperature of 600°C, below and above which they become phosphorus deficient due to insufficient supply of phosphorus and thermal desorption of the phosphorus as P 2, respectively, but they are all ntype conductors due to phosphorus vacancies.