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MnAs has been grown by means of MBE on the GaN(000 (1) over bar)-(1x1) surface. Two options of initiating the crystal growth were applied: (a) a regular MBE procedure (manganese and arsenic were delivered simultaneously) and (b) subsequent deposition of manganese and arsenic layers. It was shown that spontaneous formation of MnAs dots with the surface density of 1x10(11) cm(-2) and 2.5x10(11) cm(-2), respectively (as observed by atomic force microscopy), occurred for the layer thickness higher than 5 ML. Electronic structure of the MnAs/GaN systems was studied by resonant photoemission spectroscopy. That led to determination of the Mn 3d-related contribution to the total density of states distribution of MnAs. It has been proven that the electronic structures of the MnAs dots grown by the two procedures differ markedly. One corresponds to metallic, ferromagnetic NiAs-type MnAs, the other is similar to that reported for half-metallic zinc-blende MnAs. Both systems behave superparamagnetically (as revealed by magnetization measurements), but with both the blocking temperatures and the intradot Curie temperatures substantially different. The intradot Curie temperature is about 260 K for the former system while markedly higher than room temperature for the latter one. Relations between growth process, electronic structure, and other properties of the studied systems are discussed. Possible mechanisms of half-metallic MnAs formation on GaN are considered.

By performing extensive angle-resolved photoemission measurements using tunable linearly polarized synchrotron radiation with photon energies from 15 to 31 eV on high quality cleaved samples we have succeeded in experimentally mapping the occupied electronic bands of GaSe(0001) along all key symmetry directions. The experimental results are in very good agreement with state-of-the-art ab initio theoretical calculations. The data were analyzed assuming a direct transition model and final-state effects are discussed in the analysis of the normal-emission data. The off-normal emission spectra accurately reproduce the gaps in the calculated projected band structure. The azimuthal symmetry of the photocurrent revealed the polytype of the samples investigated.