The growth of III-V Al-containing epitaxial structures by MOMBE has proven difficult due to the excessive oxygen and carbon contamination introduced by the Al source. Triethylaluminum (TEAl), the most commonly used precursor, produces unacceptable levels of both impurities in AlGaAs grown by MOMBE. We have grown AlGaAs films with excellent structural and optical properties using a novel source, trimethylamine alane (TMAAl). Photoluminescence intensities from AlGaAs grown by MOMBE at 500δC with TMAAl are comparable to those from material grown by MOCVD at 675δC using trimethylaluminum. In addition, carbon and oxygen levels in AlGaAs, as detected by SIMS, are drastically reduced in comparison to similar films produced with TEAl. We shall also discuss the effects of growth temperature and Al content on carbon and oxygen incorporation as well as crystallinity and provide preliminary device results on GaAs/AlGaAs HBTs prepared by the MOMBE technique.