PHOTOLUMINESCENCE AND PHOTOREFLECTANCE STUDIES OF DEFECTS IN GAAS EPITAXIAL LAYERS GROWN BY LIQUID-PHASE EPITAXY AT DIFFERENT SUPERCOOLING TEMPERATURES

The defect formation during the growth of intrinsic GaAs epitaxial lay ers grown by the liquid phase epitaxy technique using supercooled melt s has been studied through the optical characterization of the layers using the low temperature photoluminescence (PL) and the photoreflecta nce (PR) spectroscopies. Different degrees of supercooling in the rang e Delta T: 0-15 degrees C were used to grow several GaAs layers. It wa s found that for growth temperatures (T-g) around the equilibrium temp erature (T(eq)similar to 804 degrees C), the PL spectra showed a stron g exciton peak and emission bands related to the presence of C and Si impurities; and no low-energy defect-related bands were detected. As s oon as T-g falls a few degrees below T-eq(Delta T greater than or equa l to 2 degrees C), an emission band centered around 855 nm appears in the PL spectra whose intensity increases as Delta T does. The correspo nding PR spectra for the different samples present Franz-Keldysh oscil lations which were analyzed under the intermediate-electric-field regi me and showed that, as Delta T increases, there is a monotonic increas e in the density of ionized impurities, in agreement with the results from the PL spectra. We have identified this defect as the cation anti site double acceptor Ga-As which is produced as a result of the increa se in the density of As vacancies when the supercooling parameter incr eases. Results on the dependence of the ratio of the peak intensities between the exciton and the other impurity-related bands are presented and discussed. (C) 1997 American Vacuum Society.