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

Abstract

The phase composition and microcrystalline structure of thin gallium nitride (GaN) grown by nitridation of (001) oriented gallium arsenide (GaAs) was investigated by near edge x-ray absorption fine structure (NEXAFS) spectroscopy. The GaN layer was grown by the interaction of atomic nitrogen produced by a rf-plasma source with the clean GaAs surface at a temperature of 700 °C. In this way a GaN film thickness of ≈100 Å was obtained after 6 h of nitridation. Using surface sensitive NEXAFS at the nitrogen K edge, the partial nitrogen p density of states was determined. Comparing the data to reference spectra of hexagonal and cubic GaN, the amount of cubic GaN in the nitrided film was estimated to be 20%–25%. Varying the angle of polarization of the synchrotron radiation with respect to the sample surface, the geometric anisotropy of the GaN film, and thus its crystalline structure, was probed, providing information on the orientation of the GaN microcrystallites. The results from the polarization dependent measurements suggest that the c axes of the hexagonal GaN crystallites in the film are mainly oriented parallel to the (001) direction of the GaAs substrate. The c axes of roughly 45% of the crystallites are tilted by 90° and lie parallel to the surface plane.