We present a study of Si incorporation in InAlAs layers grown lattice matched on InP substrates by low pressure metal-organic chemical vapor deposition. Distinct Si doping levels an achieved for different values of diluted flows of SiH4. Photoluminescence, capacitance-voltage, and Hall measurements are used to characterize the samples. In order to investigate a possible autocompensation effect, the samples were subjected to a heat treatment. Analysis of the photoluminescence spectra before and after annealing, with the help of a fitting procedure, reveals that Si is also incorporated as an acceptor in the sublattice V. The position of the acceptor peak is consistent with our theoretical calculations. Photoluminescence measurements as a function of temperature show the anomalous inverted S-shape behavior. The analysis of the fitted spectra gives support to a carrier localization effect.