Structural, Electrical and Optical Properties of Epitaxial ZnO Layers Grownwith Various O_2 Flows by Radio-Frequency Magnetron Sputtering

摘要

High-quality epitaxial ZnO layers were grown by RF magnetron sputtering. During the ZnOgrowth, the total pressure of the Ar and/or O_2flows was kept constant. The optimum conditionsfor the substrate and the rate of O_2flow were confirmed to be 700 °C and 60 %, respectively. Thus,the base-bottom strata of the ZnO layers totally consisted of freestanding hexagonal shapes ofnucleation. As the O_2flow was increased from 0 to 100 %, the growth mode tended to change froma two-dimensional mode to a three-dimensional layered growth mode and the surface shape changedfrom films to rods following the growth mode at the initial stage of growth. During the increaseof the O_2 flow, the relative intensity of the deep-level emission decreased remarkably while thatof the near-band-edge emission increased rapidly. This is related to decrease of the concentrationof oxygen-vacancies in the ZnO layers. Furthermore, the layers recomposed following the states ofthe oxygen interstitials. Consequently, we conclude that increased O_2flow leads to a reduction ofnative point defects in the ZnO layers.