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Growth and characterization of isotopic natGa15N by molecular-beam epitaxy

Isotopically enriched gallium nitride films, Ga14N and Ga15N, have been fabricated by molecular-beam epitaxy to study the effect of nitrogen atomic mass on structures and properties of GaN. Due to the isotopic substitution, the phonon frequency shift has been clearly observed by using Raman spectroscopy. The lattice constants of Ga15N differed from Ga14N, and, actually, the unit cell volume of Ga15N was approximately 0.07% less than that of Ga14N. Temperature-dependent photoluminescence measurements revealed that recombination mechanism in Ga14N and Ga15N was the same to each other in the temperature range of 4-50 K, and the band gap energy difference between them was found to be Eg15-Eg14=6.0±0.1 meV. This Eg difference is discussed in terms of volume shrinkage and change in phonon-electron interaction due to isotopic substitution.