Heteroepitaxial diamond film deposition on KTaO3 substrates via single-crystal iridium buffer layers

Iridium (Ir) has recently been shown to be a superior buffer layer material for diamond heteroepitaxial growth on different substrates as it possesses chemical inertness and high melting point. This study reports the surface morphologies and microstructures of iridium films deposited on KTaO3 substrates by magnetron sputtering with sputtering powers ranging from 25 W to 100 W at a substrate temperature of ~850 °C. The Ir films were characterized by field-emission scanning electron microscope (FE-SEM) and X-ray diffraction (XRD). The results showed that the morphologies of Ir films turned out to be more homogeneous and more compact with the increase of sputtering power. In addition, single-crystal Ir films were obtained on all samples as identified by XRD measurements and the crystallographic orientations of the single-crystal Ir films changed from (111) to (100) textures with sputtering power increasing from 25 W to 100 W. The Ir thin film grown at 100 W presented a cube-on-cube-type orientation relationship with KTaO3(100) substrate and a mosaic spread of 0.53°. Then, a thin diamond film (~40-μm-thick) was deposited by microwave plasma chemical vapor deposition (MPCVD) on the Ir buffer layer. FE-SEM, XRD and Raman spectroscopy were used to characterize the heteroepitaxial diamond film. The results indicate that the diamond thin film shows a high degree of epitaxy on the KTaO3(100) substrate with the Ir buffer layer. The mosaicity of the diamond film were 0.42° (tilt) and 0.68° (twist), and the Raman full width at half maximum (FWHM) were typically in the range of 3.6–5.7 cm−1. [Display omitted] •Heteroepitaxial diamond films were successfully achieved on KTaO3(100) substrates via Ir buffer layers.•The tilt and twist for the 40-μm-thick diamond layer were 0.42° and 0.68°, respectively.•The change of crystallographic orientation of the Ir films was found with the increasing sputtering power.•The in-plane orientation relationship of Ir[010](100) || KTaO3[010](100) was confirmed.