CARBON INCORPORATION IN GAAS AND ALXGA1-XAS LAYERS GROWN BY MOLECULAR-BEAM EPITAXY

GaAs:C and AlxGa1-xAs:C films, grown by solid-source molecular-beam epitaxy with doping levels beyond 10(19) cm-3, have been studied by high-resolution double-crystal x-ray diffraction, Hall-effect measurements, and secondary-ion-mass spectroscopy (SIMS). Comparison between x-ray diffraction and Hall-effect data indicate that carbon is preferentially incorporated as acceptor on As lattice sites both in the GaAs:C and in the AlxGa1-xAs:C films. It was found that the higher the AlAs mole fraction the higher is the concentration of carbon incorporated on As sites (C(As)). Moreover, SIMS results showed that the total amount of carbon in the host lattices largely exceeds C(As). Our findings are explained by supposing that carbon atoms are incorporated on As sites and on interstitial sites. Furthermore, it is shown that the carbon interstitial concentration can be reduced growing at higher arsenic flux and higher substrate temperature in GaAs:C as well as in AlxGa1-xAs:C layers.