Monocrystalline ZnO Films on GaN/Al₂O₃ by Atomic Layer Epitaxy in Gas Flow

Abstract

Atomic layer epitaxy (ALE) of ZnO on a GaN template was performed in a low-pressure gas flow system using ZnCl2 and O2 precursors, and the evidence of monocrystallinity of an ALE-grown ZnO film is presented. The growth is achieved under the pressure of about 5 mbar with 480 °C substrate temperature and the ZnCl2-source temperature of 390 °C. According to the AFM analyses, the film surface exhibits a low roughness value of 0.45 nm RMS, which fulfills the expectations with respect to high morphological quality of the ALE products. The structural properties of the produced ZnO are characterized by means of X-ray diffraction methods based on wide range 2θ/ω scans and high-resolution studies of 00.2 and 11.4 reciprocal lattice points. Lattice parameters for ALE-grown ZnO layer are a = 0.3253(1) nm and c = 0.52060(5) nm, as derived from the high-resolution data. The mosaicity level of the GaN template layer is reproduced in the grown ZnO film.