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A synchrotron radiation and theoretical study of the UV reflectivity of wurtzite GaN films in the range 0 -30 eV is presented. First-principles calculations of the reHectivity and related optical constants are reported and used to analyze the experimental results. The calculations are performed assuming the local-density approximation and using a mufBn-tin orbital basis set. The calculated peak positions are found to be in good agreement with the experiment to within a few tenths of an eV except for a constant shift of 0.98 eV which simultaneously corrects the minimum band gap. This constant upward shift of the conduction bands of the Kohn-Sham eigenvalue band structure is in good agreement with a recently calculated self-energy gap correction of 0.95 eV. A discrepancy in absolute intensities increasing with increasing energy is found between theory and experiment, the origin of which is discussed. The imaginary part of the dielectric function e2(w) is decomposed into its most important interband contributions and the relation between the features in the optical response functions and the band structure is described. The transitions from the upper N 2p-like valence bands occur in the range 3.5 -15 eV. The transitions from the rather localized Ga 3d and N 2s bands whose energy is expected to need additional self-energy corrections are presented separately. The spectrum of the transitions from Ga 3d is closely related to the Ga 4p-like density of states in the conduction band.

The effect of ion-implantation-induced damage on the resistivity of n-type GaN has been investigated. H, He, and N ions were studied. The resistivity as a function of temperature, implant concentration, and post-implant annealing temperature has been examined. Helium implantation produced material with an as-implanted resistivity of 1010 Ω-cm. He-implanted material remained highly resistive after an 800 °C furnace anneal. The damage associated with H implantation had a significant anneal stage at 250 °C and the details of the as-implanted resistivity were sample dependent. N implants had to be annealed at 400 °C to optimize the resulting resistivity but were then thermally stable to over 800 °C. The 300 °C resistivity of thermally stabilized He- and N- implanted layers was 104 Ω-cm, whereas for H-implanted layers the 300 °C resistivity was less than 10 Ω-cm.

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Extended x-ray absorption fine structure above the Ga–K edge has been used to study the local structure of AlxGa1−xN films grown by metal organic chemical vapor deposition. With increasing Al content, x, the Ga–N bond length decreases, but much less than the average bond length. On the other hand, the x dependence of the Ga–Ga and Ga–Al distances does follow the variation of the average cation–cation distance. We conclude that bond angle distortions accommodate the differences between the Ga–N and Al–N bond lengths.