Abstract
We have used Raman scattering to investigate a series of undoped and As-doped GaN epilayers grown on sapphire substrates by plasma-assisted molecular beam epitaxy with different Ga-to-N ratios. We find that the frequency of the E2h phonon mode of GaN is very sensitive to the Ga-to-N ratio used to grow both types of samples, which may be attributed to strain effects arising from the different growth conditions. We observe Raman signatures corresponding to the formation of submicron cubic domains in some of the spectra of the As-doped samples. We discuss the origin of a broad band located at 232 cm−1 that appears in both the undoped and the As-doped epilayers. We speculate that this band, reported in previous Raman studies on As-doped and Bi-doped GaN, may be attributed to the formation of Ga clusters.
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