The aim of the reported work was investigation of Mn/GaN and Ti/GaN interface formation in order to reveal differences and similarities between interaction of these transition metals (TM) with GaN(000-1)-(1x1) surface. In both investigated systems doping with TM atoms leads to important modifications of properties. Annealing of Mn/GaN is considered as a technique suitable for fabrication of a ferromagnetic semiconductor with a Curie temperature higher than room temperature. Ti/GaN system is important as an element of ohmic contacts in nitride-based electronic devices. Thus, knowledge of details of interaction between these TM and GaN are crucial for applications as well as for basic research of electronic structure of open-shell atoms in nitrides. Resonant photoemission experiments were performed in order to compare interactions between Mn or Ti atoms and clean GaN surface, to reveal compounds formed at the interfaces and to relate them to changes in the density of states distribution in the valence bands of Mn/GaN and Ti/GaN formed under UHV conditions.
The clean surfaces of bulk GaN crystals were prepared in situ by repeated cycles of Ar+ ion sputtering and annealing. The sets of photoemission spectra were measured for clean GaN surface, as a function of TM coverage and after annealing of these systems. Contributions of TM 3d states to the valence band of Mn/GaN and Ti/GaN systems were derived from the spectra taken for photon energies near to TM 3p-3d excitation. Mn 3d contribution to the emission from the valence band turned out to be similar to that characteristic of Mn built into tetrahedrally coordinated semimagnetic semiconductors. Ti deposition and annealing led to formation of Ti-N compound - the valence band became similar to that observed for titanium nitride. Summarizing, the acquired results enabled us to prove strong interaction of Mn and Ti with GaN, to observe GaN surface disruption and reactive interface formation in Ti/GaN and Mn/GaN.