Crystallinity of freestanding large undoped single crystal diamond plates produced using pre-ion-implanted substrates and lift-off processes

Crystallinity of freestanding large (size: ∼ 9 × 9 mm) undoped single crystal (SC) diamond films grown by plasma chemical vapor deposition (CVD) was investigated using optical transmission spectroscopy, polarized optical microscope, X-ray rocking curves, X-ray topographs and photoluminescence. The production of the freestanding film was performed by elimination of the substrates using a so-called “lift-off method” after the growth of a homoepitaxial thick-film on a pre-ion-implanted substrate. The remarkable optical absorption in the wavelength from ultraviolet to near-infrared region (220–2500 nm) was not seen, similarly to a high-pressure, high-temperature (HPHT) synthetic type-IIa diamond. The cross-nicol optical microscope image demonstrated that there are patchy white regions and many dotted patterns, originating from internal strain and threading dislocations, respectively, over the entire area of the sample. The dotted patterns, corresponding to threading dislocations observed in the cross-nicol image, were also observed in X-ray topographs. The full width at half maximum (FWHM) of the X-ray rocking curve was 19.8″. In photoluminescence spectra at room temperature, a strong sharp peak around 235 nm corresponding to the recombination emission of free exciton was observed, while there were no remarkable emission peaks related to various defects typically observed in the visible region.