Nitrogen and hydrogen in thick diamond films grown by microwave plasma enhanced chemical vapor deposition at variable H2 flow rates

The presence and concentration of nitrogen and hydrogen impurities in thick diamond films grown by microwave plasma chemical vapor deposition at various ${\mathrm{H}}_{\mathrm{2}}$ gas flow rates, keeping a constant $[{\mathrm{CH}}_4\mathrm{]:[}{\mathrm{H}}_2\text{]=2.5\%}$ concentration ratio, have been determined by electron spin resonance and optical absorption spectroscopy. The relative concentration of both impurities, present as paramagnetic atomic species with different relaxation properties, has been found by ESR measurements to decrease exponentially with the increase in the ${\mathrm{H}}_{\mathrm{2}}$ gas flow rate. Moreover, the resulting values were proportional to the content of substitutional nitrogen and ${\mathrm{CH}}_x$ groups obtained from infrared and ultraviolet-visible optical absorption measurements, respectively. The decrease in the concentration of both impurities with an increase in the quality of the studied diamond films, early observed from high resolution electron microscopy studies on the same samples, strongly suggests that the incorporation of both impurities, as paramagnetic atomic species, is directly related to the concentration of the extended lattice defects.