GaAs grown from trimethylgallium (TMG) and arsine (AsH3) countaing residual carbon C. It is mostly incorporated essentialy as acceptor. Photoluminescence spectra exhibit besides the usual features a peak at 1.477 eV the higher the greater the ratio As/Ga. Annealing under H2 + AsH3 enhances the intensity of this peak. GaAs layers were grown with excess CH4. This gives highly compensated layers ; the 1.477 eV peak appears in all these samples. The kinetics of growth is drastically changed by the excess CH4