Photoluminescence of GaN deposited on single-crystal bulk AlN with different polarities

Photoluminescence (PL) properties of two GaN epilayers grown in identical conditions on substrates of Al face and N face of bulk single-crystal AlN are studied in the temperature range from 8 to 300 K under weak cw excitation and strong pulsed excitation up to the intensities when electron–hole heating and stimulated emission are observed. At low temperatures and pump intensities, PL of GaN on Al-face AlN is consistent with that of homoepitaxial Ga-face GaN, while GaN on N-face AlN exhibits features indicating the existence of tail localized states. At carrier densities high enough for band-to-band transitions to dominate, the room-temperature PL of GaN on N-face AlN is higher than that in GaN on Al-face AlN due to longer effective lifetime of photoexcited carriers.