The growth of epitaxial GaAs layers on semi-insulating substrates, using high purity GaAs as source material has been obtained by the so-called lose Space Vapor Transport technique. The thermodynamical conditions of the growth, the effect of the growth parameters : source and substrate temperatures, pressure of transporting gas (water vapor) on the growth rate were investigated. Then, the variations of the optical, electrical and deep levels properties of the layers were studied as a function of the growth parameters in order to determine the values of these parameters for which the layers present the best electronic properties. Here, we describe i) the evolution of the photoluminescence spectra versus the substrate and source temperatures, the water vapor pressure being kept constant at its best value; ii) a secondary ion mass spectroscopy analysis of the main impurities contained in the layers. The results demonstrate that the layers are homogeneously Si and S doped, the doping being slightly compensated, the layer-substrate interface is clean and the PL is characteristic of a defect free material.