Near edge x-ray absorption fine structure characterization of polycrystalline GaN grown by nitridation of GaAs (001)

The phase composition and microcrystalline structure of thin gallium nitrid e (GaN) grown by nitridation of (001) oriented gallium arsenide (GaAs) was investigated by near edge x-ray absorption fine structure (NEXAFS) spectros copy. The GaN layer was grown by the interaction of atomic nitrogen produce d by a rf-plasma source with the clean GaAs surface at a temperature of 700 degrees C. In this way a GaN film thickness of approximate to 100 A was ob tained after 6 h of nitridation. Using surface sensitive NEXAFS at the nitr ogen K edge, the partial nitrogen p density of states was determined. Compa ring the data to reference spectra of hexagonal and cubic GaN, the amount o f cubic GaN in the nitrided film was estimated to be 20%-25%. Varying the a ngle of polarization of the synchrotron radiation with respect to the sampl e surface, the geometric anisotropy of the GaN film, and thus its crystalli ne structure, was probed, providing information on the orientation of the G aN microcrystallites. The results from the polarization dependent measureme nts suggest that the c axes of the hexagonal GaN crystallites in the film a re mainly oriented parallel to the (001) direction of the GaAs substrate. T he c axes of roughly 45% of the crystallites are tilted by 90 degrees and l ie parallel to the surface plane. (C) 1999 American Institute of Physics. [ S0021-8979(99)08513-8].