Layers of C-doped material were grown by molecular-beam epitaxy and were studied using photoluminescence and positron annihilation spectroscopy. Semi-insulating layers, doped to more than 1018C/cm3, exhibited a strong luminescence band which was centered at about 2.2eV (yellow luminescence). The absolute intensity of the 2.2eV band was compared with the Ga-vacancy concentration as determined by positron annihilation spectroscopy. The results indicated that a high concentration of Ga vacancies was not necessary for yellow luminescence, and that there was a causal relationship between C and the 2.2eV band. Markedly different deep-level ionization energies were found for

high-temperature quenching of the 2.2eV photoluminescence in C-doped and reference samples. It was proposed that a new yellow luminescence mechanism was involved when the interstitial C concentration was comparable to, or exceeded, the Ga vacancy concentration.

Contributions from Gallium Vacancies and Carbon-Related Defects to the “Yellow Luminescence” in GaN. R.Armitage, W.Hong, Q.Yang, H.Feick, J.Gebauer, E.R.Weber, S.Hautakangas, K.Saarinen: Applied Physics Letters, 2003, 82[20], 3457-9