An experimental investigation is presented on the influence of the laser excitation on the photoluminescence (PL) linewidth in silicon-doped InAlAs layers grown lattice-matched to InP substrates by molecular beam epitaxy. It was observed that the linewidth decreases with increasing laser excitation power. A model describing an unbalanced migration of photo-generated charge carriers owing to the presence of clusters is proposed to explain the effect of the linewidth reduction. Also, the trend of the linewidth decrease becomes more pronounced in InAlAs samples with higher silicon doping concentrations. These samples have broader linewidths which is the result of poorer alloy quality owing to the presence of disorder. A similar trend of linewidth reduction was also observed at 30 K. Our results show that such a measurement of linewidth versus laser excitation power can be used as a supplementary method for InAlAs material characterization.