Electronic structure characteristics of MBE (molecular beam epitaxy)-grown diluted magnetic semiconductor Ga_1-xCr_xN films

We study the electronic structure of newly discovered MBE-grown diluted magnetic semiconductor Ga_1-xCr_xN(x = 0.0, 0.06, 0.29, 1.0) films, using X-ray absorption spectroscopy across the N 1s and Cr 2p edges. Angle-dependent N 1s absorption results of pure GaN and ferromagnetic Ga _0.94Cr_0.06N exhibit identical behaviour of the N 2p _x, 2p_y and 2p_z states, typical of the wurtzite structure. In addition, Ga_0.94Cr_0.06N shows a new feature derived from N 2p states hybridized with Cr 3d states, within the band gap of GaN. Cr 2p absorption spectra show spectral features consistent with tetrahedrally co-ordinated CrN₄ cluster calculations. Excess Cr-content shows up as cubic CrN impurity phase, which is confirmed by comparing experimentally with pure CrN spectral features as well as with cluster calculations in octahedral geometry. The results indicate that the new unoccupied states formed in the band gap of the Cr-substituted wurtzite GaN are important for ferromagnetism.