An ion source for generating an ion beam containing aluminum ions is disclosed. The ion source includes a first gas source to introduce an organoaluminium compound into the arc chamber of the ion source. A second gas, different from the first gas, which is a chlorine-containing gas is also introduced to the arc chamber. The chloride co-flow reduces the buildup of decomposition material that occurs within the arc chamber. This buildup may occur at the gas bushing, the extraction aperture or near the repeller. In some embodiments, the second gas is introduced continuously. In other embodiments, the second gas is periodically introduced, based on hours of operation or the measured uniformity of the extracted ion beam. The second gas may be introduced from second gas source or from a vaporizer.