Spectral Characteristics of Nitrogen-Doped CVD Synthetic Diamonds and the Origin of Surface Blue Fluorescence

Abstract

In recent years, many studies have been published on CVD diamond growth, but the reason for the irregular blue surface fluorescence of CVD diamond under ultra-deep UV radiation (i.e., under DiamondView) is still unclear. Here, a batch of as-grown and LPHT-annealed CVD synthetic diamond samples from a Chinese company in Zhejiang were analyzed for the various spectral (infrared (IR), UV–visible absorption, Raman, and photoluminescence (PL)) characteristics to explore the origin of surface blue fluorescence. The results show that the samples are nitrogen-doped type IIa CVD synthetic diamonds. Spectral peaks of the earlier CVD products, e.g., 3123 cm−1 (NVH0) (IR absorption spectrum) and 596/597 nm (PL emission spectrum), are absent in these samples, while the peaks at 736.5/736.8 nm (SiV−) in the UV or PL spectra are less common. PL spectra and DiamondView fluorescence indicate that the samples have generally strong luminescence peaks at 637 nm in the NV− center, 575 nm in the NV0 center, and other luminescence peaks caused by nitrogen-related defects. The as-grown samples observed under DiamondView show orange-red fluorescence accompanied by striations due to step-flow growth, and blue fluorescence appears as irregular threads or bundles on the surface. The LPHT-annealed sample shows weaker fluorescence with localized patches of green fluorescence contributed by weak H3 centers. The micro-IR spectra suggest that the unique blue fluorescence in the CVD diamond may be related to the dislocations caused by sp3-CH2 due to the incomplete dehydrogenation of hydrocarbon groups in the raw material.