Observation of a manganese acceptor level in ferromagnetic Ga_1-xMn_xN layers

We have observed the high-temperature (T=300 K) photoluminescence (PL) spectra from free to Mn-related acceptor pair transitions in Ga_1-xMn_xN layers (where x≈0.2%–0.6%) grown on sapphire (0001) substrates using the plasma-enhanced molecular-beam epitaxy technique. Luminescence from an Mn acceptor level in Ga_1-xMn_xN layer with a low Mn content was observed at around E=3.08 eV in the PL spectra. When compared to the PL from undoped GaN, the excitation, temperature-dependent PL at E=3.08 eV provides convincing evidence for a neutral Mn acceptor-bound hole character. The binding energy of the Mn acceptor-bound holes of E=330 meV is in good agreement with an ionization energy of E=402 meV obtained using effective mass theory of shallow impurity states for the hydrogen model. In addition, analysis of the PL intensities of an acceptor-bound hole in a Ga_1-xMn_xN layer with x≈0.6% gave an activation energy of E=310 meV, which indicates that the acceptor-bound hole with a binding energy of E=310 meV was dissociated due to thermal quenching.