Correlation between yellow luminescence intensity and carrier lifetimes in GaN epilayers

GaN epilayers grown on sapphire and SiC substrates and exhibiting yellow and blue luminescence were studied using photoluminescence spectroscopy, light-induced grating, and Kelvin probe techniques. For epilayers on sapphire substrates, we observed practically no yellow luminescence (YL) and lifetimes exceeding 100ps in samples with the Fermi level close (∼0.5eV) to conduction band, while samples with Fermi level close to the midgap exhibited YL. A general trend is a decrease in the intensity of yellow and blue emission bands compared to the intensity of the band-to-band recombination in the samples with longer carrier lifetimes.