Nitrogen isotopic effect in Ga15N epifilms grown by plasma-assisted molecular-beam epitaxy

Ga14N and Ga15N were grown to study the isotopic effect on GaN lattice constants and band gap energy. It was shown that Ga15N has smaller lattice constants a and c at room temperature. However, the thermal expansion coefficients of Ga15N are larger than those of Ga14N up to 600 °C. Photoluminescence at 4.5–50 K implies a wider band gap in Ga15N, presumably due to its smaller unit cell at low temperature, and a weaker band gap renormalization effect via phonon–electron interaction.