Growth of high-quality inch-diameter heteroepitaxial diamond layers on sapphire substrates in comparison to MgO substrates

Recently, a 2-inch-diameter high-quality (001) diamond wafer was prepared that was heteroepitaxially grown on a (001) Ir buffer layer/(112¯0) A-plane sapphire substrate. Herein, we investigate residual strain and curvature of diamond in a relation with Ir/sapphire substrate and Ir/(001) MgO substrate. Diamond layers grown on Ir substrates have tensile strain, whereas Ir buffer layers on sapphire or MgO substrates have compressive strain. However, the magnitude of these strains in diamond and Ir layers grown on sapphire is considerably lower than that of the same layers grown on MgO. The lower tensile strain in the diamond on Ir/sapphire leads to the growth of a 2-inch-diameter layer without cracking. The convex curvature radius of the diamond layers grown on sapphire is larger than that observed on the MgO substrate. The difference in the coefficients of thermal expansion between the diamond and sapphire is considerably smaller than that of the MgO substrate. The low tensile strain of diamond is caused by the difference in the lattice constants of the diamond and Ir/sapphire substrate.