A first-principles study of carbon impurities in GaAs and InAs

We study the stability of carbon-related and native point defects in GaAs and InAs and compare the p-type doping levels of these two materials through first-principles pseudopotential calculations. In GaAs, a substitutional C acceptor at an As site is found to be a predominant defect, and the hole density is saturated to about 10(20) cm(-3), which is mainly caused by the compensation by [100] split-interstitial C-C complexes in the high doping regime. In InAs, the C-As acceptor is most stable among C-related defects, however, its formation energy is higher than for an As-antisite and an In vacancy in the As-rich limit. Moreover, as compared to GaAs, since C-related defects in InAs have higher formation energies, C incorporation into bulk InAs is more difficult, resulting in lower hole densities in InxGa1-xAs alloys. When C occupies an In site in InAs, the associated defect level is found to lie below the valence band maximum, but, this energy level moves above the valence band maximum with increasing of pressure.