Initial growth mechanism of high-quality CVD diamond on Ir/sapphire substrate compared with Ir/MgO substrate

Abstract

We demonstrate the growth of the highest-quality 2-in-diameter (001) diamond on a (112¯0) sapphire substrate. To elucidate the mechanism of the formation of this diamond, we observe the surfaces of the Ir buffer layer, bias-enhanced nucleation (BEN)-treated Ir surfaces, and diamond surfaces grown at the initial stage with different diamond growth times on both the (112¯0) sapphire and (001) MgO substrates. The (001) Ir buffer surface exhibits atomically flat terraces with atomic steps. However, after the BEN treatment, a ridge surface appears and diamond island growth begins from the bottom of the ridges during the diamond chemical vapor deposition growth. On Ir/sapphire, quadrangular-pyramid diamond three-dimensional (3D) islands with {111} sidewalls grow first. Subsequently, the sidewall facet changes from {111} to {011} and preferentially coalesced in the 〈010〉 direction. In contrast, on Ir/MgO, quadrangular-pyramid diamond 3D islands with {111} sidewalls grow first. Subsequently, the columnar growth proceeds. Consequently, the coalescence of diamond 3D islands on Ir/MgO requires a longer time than that on Ir/sapphire. We detect Ir on the top and sidewalls of the diamond 3D islands. This suggests that the Ir buffer can promote diamond growth at the initial stage as a catalytic effect. The X-ray rocking curve full width at half maximum for the 311 Bragg reflection is roughly proportional to the etch pit density. This is in accord with the transmission electron microscopy observation that the etch pits are of point-bottom-type and originated from a pure edge-type dislocation.