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Algorithms of deducing the refractive index of h-GaN from the optical spectra of heteroepitaxial films were critically analyzed. A one-layer model applied in most works was observed to be insufficient for real nitride films which conventionally are grown using a low temperature buffer layer or/and possess a nonabrupt substrate/film interface and surface defects. A method to characterize nitride layered structures using reflectivity studies over a wide spectral region is presented.

Comprehensive reflectivity investigations were performed on hexagonal GaN films grown by molecular beam epitaxy on GaAs substrates in the energy range of 1.4 to 3.8 eV at room temperature. Findings indicate that the reflectivity is strongly affected by a surface roughness. Also, the optical data indicate the development of an interface layer between the film and the substrate which is in agreement with findings from transmission electron microscopy studies.

An X-ray absorption study of the N-, O- and Al-K edges on hexagonal AIN, epitaxially grown on GaAs, demonstrates that the nitrogen molecules are nearer to those around them by between 0.04 and 0.13 angstroms. Al-O distance analysis shows that it is 1.67 angstroms: 0.18 smaller than the Al-N distance. Maximum electron charge densities are also established.

The processes of electron energy relaxation of GaN using pulsed transport and heat pulse phonon measurements are studied. Theoretical calculations are compared to determine the electron-phonon coupling processes in GaN.