Growth kinetic of MgO film on r-plane of sapphire: microstructural study

Abstract

MgO has been deposited on r-plane cut sapphire single crystalline substrate at temperatures between 475°C and 900°C. Transmission electron microscopy (TEM) was mainly performed to study the film microstructures and reveal the film growth kinetics. For the deposition temperatures below 875°C, the MgO film and r-plane cut sapphire substrate mainly maintain an orientation relationship, called OR 1, where [1 0 0] MgO ∥[1 1 2 ̄ 0] Al 2 O 3 and (0 1 0) MgO ∥(1 1 ̄ 0 4) Al 2 O 3 . Below 600°C the initial MgO film shows epitaxial island growth; however the epitaxy breaks down for increasing film thickness. The thickness of the epitaxial MgO film increases with deposition temperature. This effect is discussed by considering atomic diffusion and stress release during high temperature film deposition. High quality epitaxial films can only be obtained in the deposition temperature range between 600°C and 875°C. Film deposited at higher temperatures (above 900°C) are polycrystalline with a variable orientation relationships; the dominate one being [1 1 2] MgO ∥[0 1 1 ̄ 1] Al 2 O 3 , (3 1 1) MgO ∥(1 1 2 ̄ 0) Al 2 O 3 , called OR 2. A surface reconstruction and a reaction between MgO and Al 2O 3 at this high temperature are suggested to be responsible for the occurrence of these different orientation relationships.