MBE growth of ZnO layers on sapphire employing hydrogen peroxide as an oxidant

The growth of ZnO epitaxial layers by using molecular beam epitaxy (MBE) is presented in this paper. We employed a modified Varian Gen II MBE system using H2O2 as an oxidant. ZnO layers with thickness from 100 to 600 nm were grown on (0 0 0 1)-sapphire using an MgO buffer. The surface morphology of the samples was studied by atomic force microscopy (AFM), optical microscopy with Nomarski contrast and scanning electron microscopy (SEM). The crystalline quality of the layers was investigated using X-ray diffractometry (XRD) and transmission electron microscopy (TEM). Optical properties of the ZnO layers were studied by photoluminescence (PL). The surface roughness (rms) measured by AFM for the best layers is about 0.2 nm. The formation of hexagonal ZnO pyramids was also observed in some cases. XRD measurements of the obtained ZnO layers show the excellent quality of the single crystalline ZnO heteroepitaxially grown on sapphire. The FWHM of the XRD (0 0 0 2) rocking curve measured for our best layers is as low as 27 arcsec.The influence of growth parameters on structural properties as well as on surface morphology of the zinc oxide layers on sapphire is investigated and discussed. High-quality ZnO-on-sapphire epiwafers with a very good lateral uniformity revealed both by XRD and PL measurements could provide an alternative to bulk ZnO wafers.