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The effect of 6H-SiC or A12O3 substrates on the E3(high)-phonon Raman line was studied.

Hexagonal (AIGa)N heterostructures were characterized by variable angle spectroscopic ellipsometry, to determine the resulting spectra.

Optical excitation was used to study resonant Raman scattering from A1xGa1-xN (x

Research was conducted to examine Si-doped n-type GaN with free-electron concentrations up to 1.7 x 10(to the 19th power) cm-3 using temperature-dependent photoluminescence (PL) spectroscopy. Results reveal that band-filling effects dominate the PL line broadening and that dopant-induced changes in residual strain generate line shifts that are small in comparison to those that arise from band-gap renormalization.

We report on the interaction between photogenerated electron-hole pairs and surface acoustic waves (SAW) in GaN films grown on sapphire substrates. The spatial separation of photogenerated carriers by the piezoelectric field of the SAW is evidenced by the quenching of the photoluminescence (PL) intensity. The quenching levels in GaN are significantly smaller than those measured in GaAs under similar conditions. The latter is attributed to the lower exciton ionization efficiency and carrier separation probabilities mediated by the piezoelectric effect. The PL spectra also evidence energy shifts and broadenings of the electronic transitions, which are attributed to the band gap modulation by the SAW strain field. [ABSTRACT FROM AUTHOR]

Wurtzite GaN layers are commonly grown heteroepitaxially on 6H-SiC or Al[sub 2]O[sub 3] substrates, because of the lack of lattice-matched substrates. We study the influence of these substrates mainly on the E[sub 2](high)-phonon Raman line by temperature dependent Raman spectroscopy. We find that the line broadening with sample heating is predominantly caused by intrinsic phonon-phonon scattering in GaN. The small three-phonon contribution as well as the small intrinsic linewidth at low temperature are due to the rather low two-phonon density of states at the E[sub 2](high)-phonon energy. Substrates with large lattice mismatch cause inhomogeneous strain and defects in the layers, which lead to a large, temperature independent, line broadening. We show that the temperature shift of the E[sub 2](high)-phonon frequency is dominated by the GaN lattice expansion. The lattice of epilayers is strongly modified by the thermal in-plane expansion of the substrate. The degree of relaxation at the growth temperature is reflected by deviation of the E[sub 2](high)-line from the intrinsic phonon frequency. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]