The X-Ray Diffraction Method for Study of Growth Defects in CVD Diamond Single Crystals

Abstract

X-ray diffraction from Chemical Vapor Deposition (CVD) gem-quality colorless diamond single crystals, grown with nitrogen addition in methane –hydrogen plasma mixture, was studied by imaging plate area detector (IPD) giving pixel pattern. Growth defects are responsible for rising x-ray diffuse scattering beyond reciprocal lattice points (rlp), described in the framework of kinematical theory of X-ray diffraction. In the particular case of CVD diamond crystals grown epitaxially on (001) substrate, the additional scattering in the close vicinity of rpl’s was registered. This observation was possible because of the improved angular resolution of x-ray intensity measurements using imaging plate detector (IPD). The pronounced differences in scattering around 111 rlp’s for natural and CVD growth sector were demonstrated. Oscillation and stationary crystal methods allowed registration of diffraction spots that are different from natural diamond crystals. The diffraction patterns include features of short- and long-range atomic order. There are satellite reflections at the positions corresponding to the interatomic distances at 1.51 A and 1.57 A in the vicinity of 111 Bragg reflections, which are characteristic to 1.54 A of cubic diamond. The displacement disorder of atoms, understood as disturbance of lattice periodicity can be explained by hypothesis about linear defects running in and directions. Along twin line tetrahedra share edges. Hydrogen atoms are presumably incorporated along this linear twin to protect chemical bonding stability. Bragg reflections exhibit anisotropy and considerable broadening compared to the diffraction standards. The ratio of peak intensity of forbidden by the diamond space group symmetry 222 reflection to 111 reflection is larger than for natural crystal. Raman spectra from (001) CVD crystals fit well to the spectrum from nearly perfect natural diamond crystal. The X-ray scattering around Bragg reflection is characteristic for a given crystal and can be applied as a gem quality criterion for distinguishing among crystals of different origin, or different growth sectors or grown by different methods. The scattering around 111 CVD diamond reflection is the strongest among the rlp’s.