A semiquantitative low temperature (~4 K) photoluminescence technique has been used to estimate the residual carbon concentration in MBE GaAs to be ~2 × 10¹⁴ cm⁻³ . This value agrees well with the total compensating acceptor concentration calculated from electrical measurements and thus confirms that carbon is the dominant residual acceptor in MBE GaAs. In high purity MBE GaAs films grown at substrate temperatures between 545°C and 625°C a band of at least nine luminescence peaks is observed in the 1.471 eV to 1.491 eV spectral region. These peaks can be correlated with the most prominent "defect-induced" bound exciton peaks in the 1.504 eV to 1.511 eV spectral region and their transition energies follow the empirical relation This suggests that the luminescence in these two spectral regions have a common origin at a set of “defect-complexes” which involve carbon impurities.