Raman spectra of n-type gallium nitride with different carrier concentrations have been measured. The LO phonon band shifted towards the high-frequency side and broadened with an increase in carrier concentration. Results showed that the LO phonon was coupled to the overdamped plasmon in gallium nitride. The carrier concentrations and damping constants were determined by line-shape fitting of the coupled modes and compared to values obtained from Hall measurements. The carrier concentrations obtained from the two methods agree well. As a result, the dominant scattering mechanisms in gallium nitride are deformation-potential and electro-optic mechanisms.
Thermal stress in GaN epitaxial layers with different thicknesses grown on sapphire substrates by metalorganic vapor phase epitaxy using an AlN buffer layer was investigated. Biaxial compressive stress in the GaN layer, due to the difference in the thermal expansion coefficients between GaN and sapphire, was obtained by measuring the curvature of wafer bending, and the observed stress agreed with the calculated stress. In Raman measurements, the E2 phonon peak of GaN was found to shift and broaden with the stress as a consequence of the change of the elastic constants with strain. The frequency shift Δω (in cm−1) was obtained for the first time, given by the relation: Δω=6.2 σ, where the biaxial stress σ is expressed in GPa.
p-type conduction in InN-containing nitrides doped with Mg has been achieved by metalorganic vapor-phase epitaxy. The hole concentration at room temperature is as high as 7×1017 cm−3. The activation energy of a Mg acceptor is estimated to be 204 meV. D–A pair emission with peak wavelength of about 405 nm is enhanced by thermal annealing.
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