Hydrogen vibration modes in GaP:N: the pivotal role of nitrogen in stabilizing the H(2)(*) complex

Atomic structures of N-related hydrogen complexes in GaP:N are calculated from first principles. As the more electronegative N bonds H stronger than P, it stabilizes the H(2)(*) complex that is otherwise unstable against the formation of an H2 molecule. This provides the first theoretical proof that H(2)(*) can be stable in a III-V semiconductor. The previously proposed H-N-H dihydride model is found to be unstable against spontaneously transforming into H(2)(*), which involves only monohydrides, H-N and H-Ga. The calculated local vibrational frequencies and isotope shifts are in good agreement with experiment.