The defect formation during the growth of intrinsic GaAs epitaxial layers grown by the liquid phase epitaxy technique using supercooled melts has been studied through the optical characterization of the layers using the low temperature photoluminescence (PL) and the photoreflectance (PR) spectroscopies. Different degrees of supercooling in the range Delta T : 0-15 degrees C were used to grow several GaAs layers. It was found that for growth temperatures (T-g) around the equilibrium temperature (T(eq)similar to 804 degrees C), the PL spectra showed a strong exciton peak and emission bands related to the presence of C and Si impurities; and no low-energy defect-related bands were detected. As soon as T-g falls a few degrees below T-eq(Delta T greater than or equal to 2 degrees C), an emission band centered around 855 nm appears in the PL spectra whose intensity increases as Delta T does. The corresponding PR spectra for the different samples present Franz-Keldysh oscillations which were analyzed under the intermediate-electric-field regime and showed that, as Delta T increases, there is a monotonic increase in the density of ionized impurities, in agreement with the results from the PL spectra. We have identified this defect as the cation antisite double acceptor Ga-As which is produced as a result of the increase in the density of As vacancies when the supercooling parameter increases. Results on the dependence of the ratio of the peak intensities between the exciton and the other impurity-related bands are presented and discussed.