Nitrogen-doped CVD diamond: Nitrogen concentration, color and internal stress

Abstract

Single crystal CVD diamond has been grown on (100)-oriented CVD diamond seed in six layers to a total thickness of 4.3 mm, each layer being grown in gas with increasing concentration of nitrogen. The nitrogen doping efficiency, distribution of color and internal stress have been studied by SIMS, optical absorption, Raman spectroscopy and birefringence imaging. It is shown that nitrogen doping is very non-uniform. This non-uniformity is explained by the terraced growth of CVD diamond. The color of the nitrogen-doped diamond is grayish-brown with color intensity gradually increasing with nitrogen concentration. The absorption spectra are analyzed in terms of two continua representing brown and gray color components. The brown absorption continuum exponentially rises towards short wavelength. Its intensity correlates with the concentration of nitrogen C-defects. Small vacancy clusters are discussed as the defects responsible for the brown absorption continuum. The gray absorption continuum has weak and almost linear spectral dependence through the near infrared and visible spectral range. It is ascribed to carbon nanoclusters which may form in plasma and get trapped into growing diamond. It is suggested that Mie light scattering on the carbon nanoclusters substantially contributes to the gray absorption continuum and determines its weak spectral dependence. A Raman line at a wavenumber of 1550 cm −1 is described as a characteristic feature of the carbon nanoclusters. The striation pattern of brown/gray color follows the pattern of anomalous birefringence suggesting that the vacancy clusters and carbon inclusions are the main cause of internal stress in CVD diamond. A conclusion is made that high perfection of seed surface at microscale is not a required condition for growth of low-stress, low-inclusion single crystal CVD diamond. Crystallographic order at macroscale is more important requirement for the seed surface.

Luminescence of brown CVD diamond: 468 nm luminescence center

“…All samples studied in this research had intense brown striations similar to those reported in a number of publications and in our recent paper (e.g. [6,9]). In the images of the cross-sectionally cut plates, these striations are seen propagating either parallel to the growth surface, or tilted to an angle from 10 to 20°with respect to the growth surface (Figs.…”

“…Sample #305293 was grown on CVD seed in 6 layers with nitrogen addition gradually increasing from the first to the sixth layer. Detailed information on the growth conditions of this sample can be found in [9].…”

“…A suggestion was made that the vacancy clusters in natural diamonds are globular 3D nano-cavities while in CVD diamond they are preferentially 2D vacancy discs oriented along (111) and/or (110) planes [8]. In [9] it was argued that this difference is not necessarily the form, but the size. Much shorter growth time of CVD diamonds than natural diamonds can limit the diffusion of vacancies and, consequently, the vacancy clusters in CVD diamonds are expected to be smaller.…”

N+-ion implantation induced enhanced conductivity in polycrystalline and single crystal diamond

“…Similar report on 500 eV neon-ion bombardment on diamond (100) surface showed that no phase transformation took place from defective implanted layers to graphite even aer annealing. 77 Since one can not deny the possibility of formation of graphitic clusters or a very thin graphitic layer upon annealing, we conclude that complete graphitization of the implanted layer in SCD does not happen even at this high uence instead these are amorphous distorted sp 3 rich clusters which also has sp 2 bonding 32,78 where percolation occurs to form a conductive pathway with semi-metallic like conductivity.…”

Diamond with nitrogen: states, control, and applications

“…Experimentally, the intensity of the brown absorption continuum correlates well only with the concentration of nitrogen C-defects. Zaitsev et al [81] discussed that nitrogen doping contributed to the brown color not only for natural diamond but also synthetic counterpart. Furthermore, the vast majority of natural pink diamonds colored by the 550 nm absorption band are produced through deformation processes deep within the earth.…”