Spectroscopic Analysis of Substitutional Nitrogen Concentration in Doped Diamond

Substitutional nitrogen plays a critical role in shaping the electronic and optical behavior of diamond, impacting its performance for quantum sensing and optoelectronic applications. Accurate quantification of these defects is essential for understanding material quality and optimizing growth conditions for synthetic diamond; however, their extremely deep donor level complicates electronic quantification, and mass spectroscopy methods do not distinguish between substitutional nitrogen and other forms of incorporation, such as clusters or nitrogen-vacancy (NV) centers. Developing a non-invasive method for quantifying substitutional nitrogen is particularly valuable for the QuOD Lab's ongoing investigations of deterministic multiphoton laser writing of NV centers. 

This project explores a spectroscopic approach for determining substitutional nitrogen concentrations using Fourier-transform infrared (FTIR) and UV-Vis spectroscopy. This method focuses on the prominent nitrogen-related absorption features in the infrared region, which are linked to substitutional nitrogen and related defect complexes. Python code was developed to process and deconvolve FTIR spectra using Gaussian peak profiles, applying baseline correction, thickness normalization, and iterative fitting routines. UV-Vis spectroscopy was used in parallel to identify similar potential defect-related features that support FTIR findings. These features were all compared with calibrations in the literature to determine the effect on the substitutional nitrogen concentration of varying growth conditions for the homoepitaxial deposition of single-crystal diamond by microwave plasma-enhanced chemical vapor deposition (MPECVD).