Neutral Mn acceptor in bulk GaN in high magnetic fields

We present magneto-optical studies of intra-center absorption band related to neutral Mn acceptor in GaN bulk crystals. The band is built of a zero-phonon line at 1.4166 eV followed by GaN phonon spectrum. Magneto-optical experiments performed in magnetic fields up to 22 T in both Faraday and Voigt configurations revealed very small influence of magnetic field on the spectrum. In particular no splitting of the zero-phonon line was observed. The only characteristic feature recorded in high magnetic fields was a step-like behavior of the spectral position of zero-phonon line measured in Faraday configuration. The step appeared at the magnetic field of about 7 T, with a shift in energy of about 1.3 meV. We interpret the behavior of the zero-phonon line in magnetic field based on crystal-field model for Mn3+(d(4)) ion in trigonal crystal field, undergoing Jahn-Teller distortion and spin-orbit coupling. Applied model explains reasonably experimental results, supporting strongly localized character of Mn neutral acceptor in GaN.