Growth Process of 2-In-Diameter High-Quality CVD Diamond on Ir/Sapphire Substrate Compared with Ir/MgO Substrate

Diamond is expected to be high power and high efficient devices<u>,</u> superior to SiC and GaN, because diamond possesses higher critical field strength, and thermal conductivity. For the power-device application, the inch-diameter high-quality diamond wafer has been a big challenge. Recently, we have demonstrated the growth of the highest-quality 2-inch-diameter (001) diamond on a (11-20) sapphire substrate.<br/>In this study, we investigate the crystal properties of diamond wafer mainly by XRD in both out-of-plane and in-plane conditions, and 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 (11-20) sapphire and (001) MgO substrates by AFM, XTEM, and EDX. We grew diamonds on Ir/ sapphire and Ir/MgO substrates.<br/>We found that Ir buffer layers had compressive stress, diamond layers had tensile stress. Ir buffer layers were concave and diamond layers were convex. However, the magnitude of compressive stress in Ir buffer on sapphire was much less than that on MgO, and the magnitude of tensile stress in diamond grown on Ir/sapphire was much less than that on Ir/MgO. This is a key to the success of a 2-inch diameter high-quality diamond wafer grown on Ir/sapphire.<br/>The (001) Ir buffer surface exhibits atomically flat terraces with atomic steps. However, after the BEN treatment, a ridged surface appears, and diamond island growth begins from the bottom of the ridges during the diamond CVD 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 &lt;010&gt; 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. These different growth processes on Ir/sapphire and Ir/MgO substrates lead to lower threading dislocation density and narrower XRC FWHM for the diamond grown on Ir/sapphire substrates.