Growth condition dependence of morphology and electric properties of ZnO films on sapphire substrates prepared by molecular beam epitaxy

Abstract

Zinc oxide (ZnO) films were grown on sapphire (112̄0) substrates by molecular beam epitaxy under oxygen radical irradiation. The effect of the growth conditions, including the Zn/O ratio supplied to the film surface, on the electrical properties of ZnO films was studied in relation to the film morphology. We found that the growth rate strongly depended on the Zn flux from the Knudsen cell and the optimum condition for high growth rate was very narrow. The grain size in the lateral direction increased with increasing growth rate in the thickness direction. The increase in growth rate, especially in the lateral direction, resulted in the carrier mobility increasing up to 42 cm2 V−1 s−1. The carrier concentration N was sensitive to the substrate temperature, while the value of N was not sensitive to the source supplying ratio Zn/O. We discuss the decrease of the carrier concentration with increasing substrate temperature in regard to the formation of nonequilibrium defects.

Development of MgZnO-ZnO-AlGaN heterostructures for ultraviolet light emitting applications

“…Significantly, the former was shown to operate up to 500 K. 8 Molecular-beam epitaxy (MBE) is a versatile technique applied extensively in the formation of various heterostructures for the development of novel electronic and photonic devices. Using this technique, epitaxial ZnO films have been grown on c-plane sapphire, 10-13 a-plane sapphire, 14 and GaN-buffered c-plane sapphire. [15][16][17] Because of a large lattice mismatch between ZnO and c-plane Al 2 O 3 (ϳ18%), the crystal quality of the ZnO films is greatly limited by high-density threading dislocations.…”

Effect of deposition conditions on the growth rate and electrical properties of ZnO thin films grown by MOCVD

“…Therefore, changing VI P * in order to keep the VI/II ratio constant in this experiment, is expected to change the stoichiometry. However, no effect is observed on electron/native donor concentration, suggesting that the formation of solid nonstoichiometric defects depends on the surface reactivity or the activation of structural relaxation in the growing films, which are both thermally activated reactions [12]. Figure 4 exhibits the dependence of the ZnO film growth rate and mobility on the total reactor pressure at a temperature of 380 °C and a VI/II molar ratio of 60.…”

Growth and characterization of device quality ZnO on Si(111) and c-sapphire using a conventional rf magnetron sputtering

“…However, growth of single crystal ZnO films has been mainly achieved on Al 2 O 3 in sophisticated and finely controlled thin film growth techniques such as molecular beam epitaxy (MBE) and metal organic chemical vapor deposition (MOCVD) [3][4][5][6]. Despite the epitaxial growth of high quality ZnO using these methods, they might have disadvantage in mass production, due to high cost and low throughput.…”