Substrate roughness dependence of structural and optical properties of Eu-doped GaN grown by gas source molecular beam epitaxy

Eu-doped GaN has been grown by gas source molecular beam epitaxy on two kin ds of sapphire (0 0 0 1) substrates; one has regular atomic step (AS) surfa ce and the other one has random roughness (RR) surface. The effect of the s ubstrate on the structural and optical qualities of Eu doped GaN was invest igated. The atomic force microscope showed the epilayer on the AS substrate owns better surface morphology at each growth step such as nitridation, bu ffer layer, undoped GaN and Eu doped GaN layer. In the asymmetric X-ray dif fraction of (11 (2) over bar4), the full-width at half-maximum of the Eu.-d oped GaN on the AS substrate was almost a half value compared with that on the RR substrate. The room temperature photoluminescence spectra showed red emission due to f-f transition of Eu3+ ion from both epilayers, however, t he intensity of the red emission from the epilayer grown on the AS substrat e is five times stronger than that on the RR substrate. The cause of the im provement in the structural and optical properties of Eu-doped GaN grown on the AS substrate is discussed. (C) 2002 Elsevier Science B.V. All rights r eserved.