High quality AlxGa1−xAs has been grown by low‐pressure (30 Torr) organometallic vapor phase epitaxy (OMVPE) using a novel precursor, trimethylamine alane (TMAAl), as the aluminum source. The epilayers exhibited featureless surface morphology, very strong room‐temperature photoluminescence (PL), and excellent compositional uniformity (x=0.235±0.002 over a 40 mm diameter). The residual carbon incorporation, which determined the background doping, depended largely upon the choice of gallium precursor. Using triethylgallium, carbon incorporation could be largely suppressed ([C]≪1016 cm−3). The carbon‐related emission intensity was less than the bound exciton emission in low‐temperature (1.6 K) PL even at excitation powers as low as 50 μW cm−2. By sharp contrast, the use of trimethylgallium led to much higher C concentrations (2–5×1017cm−3). Under appropriate conditions, therefore, the use of TMAAl produces extremely high purity AlGaAs of superior quality to AlGaAs grown using conventional precursors.