Gallium nitride (apart from its optoelectronic applications) is a system particularly interesting from the point of view of surface physics research. Its surfaces may reconstruct in various ways depending on formation conditions (surface polarity, preparation method, and presence of impurities). Moreover, doping with transition metals may transform GaN into a ferromagnetic semiconductor. Annealing of Mn/GaN is considered as a technique suitable for fabrication of this material.
In this paper we present the results of photoemission studies of electronic structure of a GaN surface, clean and modified by deposition of manganese. Advantages of two experimental techniques based on application of synchrotron radiation manifest themselves in this report.
Details of electronic band structure of clean (000-1)-(1x1) surface of GaN bulk crystal were studied by means of angle-resolved photoelectron spectroscopy. The acquired results indicated that some part of the surface corresponds to the GaN (000-1):Ga configuration, covered with additional layer of Ga atoms bound at the "on top" positions above N atoms. However, substantially large regions have the relaxed clean GaN (000-1) configuration with a characteristic, almost dispersionless surface band occurring at the energy of the valence band maximum.
Mn/GaN interface formation on GaN(000-1)-(1x1) surface was investigated by resonant photoemission spectroscopy, as a function of Mn-coverage. A contribution of Mn 3d states to the valence band of the system was derived from photoemission spectra taken for photon energies near to Mn 3p-3d excitation. Interaction between Mn and GaN was also monitored by spectroscopy of Ga 3d core level. The results show that Mn on GaN forms a reactive interface. Moreover, annealing of Mn/GaN at 400oC makes the Mn 3d states distribution similar to that characteristic of Mn built into tetrahedrally coordinated semimagnetic semiconductors. Possible Mn atom environment will be discussed.