Synthesis of Homogeneously {100}-Textured 3-Inch Free-Standing Diamond Wafer

A two-step growth process was developed to fabricate a 3-inch homogeneously {100}-textured free-standing diamond wafer by microwave plasma enhanced chemical vapor deposition (MPCVD). The sequential growth process is based on a change in the growth parameter α, which is given by the growth rates on {100} and {111} facets, α = 3·(V₁₀₀/V₁₁₁). Initial growth was executed with nitrogen addition, yielding an α value close to 3 for evolutionary selection of the (100) face, followed by cessation of nitrogen addition to yield a lower α value. A homogeneously grown {100}-textured diamond over an area of ca. 175 cm² with a thickness ≥ 0.8 mm was obtained after 196 h growth. The diamond growth rate was 4.0-5.5 µm/h, which is four times higher than the conventional growth of oriented diamond. This was substantiated by optical microscopy, Raman spectroscopy, and XRD analysis. The large crystal size of 210 ± 60 µm has been assigned to the second growth step, where growth is preferentially in the <111> direction. The homogeneous {100} texture and the large crystal size are conducive to achieving high thermal conductivity, as the in-plane thermal conductivity of the polycrystalline diamond wafer was increased from ca. 850 W/(mK) to 1125 W/(mK).