Abstract
Sequential multiple Eu ion implantations at low fluence (1x10(13) cm(-2) at 300 keV) and subsequent rapid thermal annealing (RTA) steps (30 s at 1000 degrees C or 1100 degrees C) were performed on high quality nominally undoped GaN films grown by metal organic chemical vapour deposition (MOCVD) and medium quality GaN: Mg grown by hydride vapour phase epitaxy (HVPE). Compared to samples implanted in a single step, multiple implantation/annealing shows only marginal structural improvement for the MOCVD samples, but a significant improvement of crystal quality and optical activation of Eu was achieved in the HVPE films. This improvement is attributed to the lower crystalline quality of the starting material, which probably enhances the diffusion of defects and acts to facilitate the annealing of implantation damage and the effective incorporation of the Eu ions in the crystal structure. Optical activation of Eu3+ ions in the HVPE samples was further improved by high temperature and high pressure annealing (HTHP) up to 1400 degrees C. After HTHP annealing the main room temperature cathodo- and photoluminescence line in Mg-doped samples lies at similar to 619 nm, characteristic of a known Mg-related Eu3+ centre, while after RTA treatment the dominant line lies at similar to 622 nm, typical for undoped GaN:Eu. (C) 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim