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GaN x As 1−x samples with x<3% grown by metalorganic vapor phase epitaxy were studied by low-temperature photoluminescence under hydrostatic pressure and photomodulated reflectance spectroscopy. The transformation from N acting as an isoelectronic impurity to N-induced band formation takes place at x≈0.2%. The N level does not shift with respect to the valence band edge of GaNxAs1−x. Concentration as well as hydrostatic-pressure dependence of the GaNxAs1−x bands can be described by a three band kp description of the conduction band state E− and E+ and the valence band at k=0. The model parameters for T<20 and T=300 K were determined by fitting the model to the experimental data. Modeling the linewidth of the E− transition by combining the kp model and ion statistics leads to the conclusion that the electron-hole pairs are strongly localized.

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We report a cross-correlated investigation, performed by means of Raman scattering and infrared spectroscopy, of coupled LO phonon-plasmon modes in bulk GaN. Using different samples with different (high) residual concentrations of free carriers, we find that the high-energy Raman mode follows closely the plasma frequency resolved from the infrared data. On the opposite, the low-frequency modes appears down shifted, with respect to the standard TO phonon frequency, by about 11 cm−1. Both findings agree satisfactorily with predictions of the linear response theory for undamped phonon-plasmon modes and establish Raman scattering as a powerful and nondestructive tool to investigate the residual doping level of GaN up to about 1020 cm−3 .

Phys. Rev. Lett. 87, 292 (1976