Carbon-nitrogen molecules in GaAs and GaP

A carbon-nitrogen molecule in GaAs and GaP is investigated by using first-principles density functional pseudopotential calculations. The formation energy calculations show that the molecule favors substituting for an anion site (As or P) over being an interstitial under all equilibrium growth conditions. Under $p$-type conditions, the molecule exhibits the characteristic triple bonding and acts as a donor. When the Fermi level is higher ($n$ type), the molecule acts as an acceptor by accepting electrons into its antibonding states and exhibits double or single bonding. The bond length and vibrational frequencies for each configuration are calculated and compared to those in recent experiments. Trends in the changes in bond length and vibrational frequencies with respect to the number of electrons in the antibonding states are discussed.