A detailed photoluminescence study of a deep broadband emission as a function of the dopant concentration is conducted in molecular‐beam epitaxy‐grown silicon‐doped Al0.3Ga0.7As single layers. The deep broadband which is correlated to the Si concentration consists of several emissions among which three are suggested to be due to different Si complexes. The effects of annealing the samples contributed immensely to this investigation. A model to explain the direct and indirect participations of SiAsin the formation of Si complexes during heat treatment is proposed. The photoluminescence is complemented by the Hall‐effect, capacitance, and secondary‐ion‐mass spectroscopy measurements.