Disilane is presented as a new Si source gas in the metalorganic chemical vapor deposition of both GaAs and AlxGa1-xAs. The doping characteristics of disilane were studied over a wide range of growth conditions: temperature, gas phase stoichiometry, and disilane concentration in the growth ambient. Disilane exhibits several features as a doping gas which prove it superior in this application to silane, the conventional silicon source gas. Doping by means of disilane shows no dependence on growth temperature in sharp contrast to the strong temperature dependence found using silane. The decomposition reaction of disilane is very efficient, reducing the amount of dopant gas required by about two orders of magnitude at the lower growth temperatures. The doping efficiency of disilane is also independent of the aluminum content of the AlxGa1-xAs alloy layers. These results indicate that disilane may be the preferred silicon doping gas for GaAs and AlxGa1-xAs. © 1984.