Thermal processing induced structural changes in ZnO films grown on (11&2macr;0) sapphire substrates using molecular beam epitaxy

Abstract

We have investigated the effect of in-situ annealing and nitrogen doping on 40 nm low-temperature buffer layers in radical-source molecular beam epitaxy (RS-MBE) as well as subsequently grown high-temperature ZnO layers grown on the buffers. All layers were grown on (11&2macr;0) sapphire substrates. High resolution x-ray reciprocal space maps in the vicinity of the ZnO (0002) reciprocal lattice point (RLP) showed a sharp reduction in diffuse scattering for the thermally annealed buffer layer implying a reduction in dislocation density. X-ray lateral coherence (LC) values obtained from asymmetric diffraction near the (10&1macr;4) RLP indicated that the LC of a undoped, high-temperature ZnO layer grown on an in-situ N-doped buffer was larger than those of high-temperature ZnO layers grown on either the in-situ annealed or untreated low-temperature buffers. The increased LC was found to be correlated with in-plane twist suggesting that dislocation bunching may be present at domain boundaries in the high-temperature ZnO grown on annealed N-doped buffer layers. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)