Manganese-hydrogen complexes in Ga_1-x Mn_x N

The effects of hydrogenation on Mn-doped GaN are studied with electron-paramagnetic resonance (EPR), local vibrational mode (LVM) spectroscopy, and density-functional theory (DFT) calculations. With EPR, we find two distinct Mn complexes which, in particular, differ in the size and orientation of the uniaxial crystal field and are attributed to Mn-H complexes oriented along the out-of-plane Ga-N bonds parallel to the c axis and to Mn-H complexes oriented along the "in-plane" Ga-N bond directions. DFT calculations in the local spin-density approximation taking into account the self-consistent correlation parameter U predict that the in-plane back-bonded configuration and the out-of-plane bond-center configuration of the Mn-H complexes have the lowest, nearly identical total energy, in good agreement with the EPR results. The hyperfine interactions with the Mn nucleus in the different complexes are fully reproduced by the theory. Using infrared-absorption and reflection measurements, we additionally observe the stretching mode of the in-plane configuration and report the effects of H/D substitution and measurement temperature on the LVM.