APPLICATION OF NEAR-EDGE X-RAY-ABSORPTION FINE-STRUCTURE FOR THE IDENTIFICATION OF HEXAGONAL AND CUBIC POLYTYPES IN EPITAXIAL GAN

Cubic and hexagonal GaN thin films are studied using the angular depen dence of the near-edge x-ray absorption fine structure (NEXAFS) spectr a recorded at thp N-K edge. It is shown that the energy positions of t he NEXAFS resonances are characteristic of the cubic and hexagonal str uctures and, thus, the NEXAFS spectra can be used as a fingerprint of the symmetry of the examined crystal. Deviations from the zinc-blende or wurtzite phases are clearly detectable since they lead to a systema tic energy shift in the NEXAFS resonances. Finally, a method is propos ed for the quantitative estimation of the percentages of the cubic and wurtzite phases present in a mixed crystal. (C) 1996 American Institu te of Physics.