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Configurations, energies, and thermodynamics of the neutral MgH complex in GaN

Wright, Alan F.; Myers, Samuel M.

Atomic configurations corresponding to local-energy minima for the neutral MgH complex in wurtzite GaN are identified using density-functional theory and the generalized-gradient approximation for exchange and correlation. MgH binding energies, H local-mode vibration frequencies, and configurational degeneracies for the six lowest-energy configurations are used, along with corresponding results for isolated H{sup +}, to compute equilibrium H state populations in Mg-doped GaN as a function of temperature. For a Mg concentration of 1 x 10{sup 19}/cm{sup 3} and a H/Mg concentration ratio of 0.99, MgH is found to be the majority H species at room temperature with isolated H{sup +} becoming the majority species at T {approx} 550 C. Among the MgH states, one is found to dominate at all temperatures. The dominant configuration consists of H at an antibonding site of a N neighbor of the substitutional Mg, with the Mg-N and N-H bonds nearly aligned and the N-H bond oriented at an angle of -109{sup o} with the c axis. The H stretch-mode frequency of the dominant state is consistent with the peak observed in Fourier-transform infrared reflection spectra from Mg-doped GaN samples.