Persistent layer-by-layer growth is demonstrated for pulsed-laser homoepitaxy of ZnO thin films on ZnO single crystals. Employing interval pulsed-laser deposition (PLD), RHEED oscillations are stabilized over a film thickness of about 90 nm. For interval pulsed laser deposited films a considerably decreased root-mean-square surface roughness of 0.26 nm was found, in comparison to 0.74 nm for conventional PLD. A small asymmetry in the X-ray diffraction (XRD) 2θ –ω scan reveals compressive strain in the thin film being slightly larger for interval PLD as compared to conventional PLD. The FWHM of the photoluminescence (PL) I6 line is higher with about 500 µeV as compared to 350 µeV for the conventional PLD. Consequently, both XRD as well as PL indicate a slightly higher amount of charged defects for the interval PLD.
Evolution of RHEED intensity as function of time for interval PLD. The green and red line marks the start and the end of the ablation interval, respectively.
(© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)