High-purity Al 0.25Ga 0.75As layer has been successfully obtained by metalorganic chemical vapor deposition (MOCVD) using new precursors of dimethylethylamine alane (DMEAA) and triethylgallium–dimethylethylamine adduct (TEG–DMEA). It is shown that the concentrations of residual carbon and oxygen in the AlGaAs layer grown at a relatively low V/III ratio were under detection limits of secondary-ion mass spectrometry (3.0×10 15 and 5.0×10 15 cm −3, respectively). In the photoluminescence spectra at 4.2 K, the peak intensity of carbon-related emission was much weaker than that of bound-exciton (BE) emission. The full-width at half-maximum for the BE peak was as narrow as 5.6 meV. Any predeposition between these precursors due to a gas-phase prereaction was not observed. These results indicate that the combination of DMEAA and TEG–DMEA are promising precursors for MOCVD growth of AlGaAs with low residual impurity concentration.