Epitaxial growth of high-temperature ZnO layers on sapphire substrate by magnetron sputtering

Undoped ZnO films were grown epitaxially by magnetron sputtering on a sapphire substrate in the high-temperature range of 560-720 °C. The crystalline and optical quality was improved simultaneously with increasing growth temperature, and the dislocation density was also reduced. The surfaces of the deposited samples showed pyramidal-shaped protrusions with a hexagonal base and an increase in the density of protrusions with increasing growth temperature. The region including the surface protrusions was highly defective and had rotated grains compared with the general ZnO film. In addition, the increase in growth temperature led to a deep level photoluminescence emission related to oxygen vacancies and a change in the electronic characteristics from a semi-insulator to an n-type semiconductor.