Secondary‐ion mass spectroscopy and cathodoluminescence (CL) studies were carried out on GaAs films grown by Ar+laser‐assisted metalorganic molecular beam epitaxy. The Ar+laser irradiation leads to the formation of a 400‐&mgr;m‐diam spot. In the growth temperature range 425–500 °C, the carbon concentration within the spot is maintained at 1017cm−3, while that in the area not irradiated by the laser increases from 1017to 1019cm−3. The process of decomposition of the triethylgallium molecules and the mechanism by which the carbon concentration is maintained by the laser irradiation are discussed in detail. Low‐temperature CL spectra revealed that the CL signal intensity in the selectively grown spot was some ten times greater than that in the area not irradiated by the laser.