Defect transformations in nitrogen-doped CVD diamond during irradiation and annealing

Abstract

Nitrogen-doped CVD diamond treated with electron irradiation and subsequent annealing at temperatures from 860 to 1900 °C was studied using fluorescence imaging, optical absorption and photoluminescence. It was found that nitrogen impurity produces many optical centers active throughout the infrared and visible spectral ranges. The most prominent of them active in IR spectral range are the centers related to nitrogen–hydrogen complexes. They produce absorption lines at 2827, 2874, 2906, 2949, 2990, 3031, 3107, 3123 and 3310 cm−1. Two characteristic absorptions at wavenumbers 1293 cm−1 and 1341 cm−1 were tentatively ascribed to a modified form of nitrogen A-aggregates. In the visible and near IR spectral ranges, characteristic nitrogen-related centers have zero-phonon lines (ZPLs) at 457, 462, 489, 498, 722.5, 852.5, 865.5, 868.5, 908, 921.5 and 924.5 nm. Some of them, e.g. 457, 462 and 498 nm centers, are unique of CVD diamond. It has been confirmed that the brightest pink color of electron-irradiated nitrogen-doped CVD diamond is produced by annealing at temperatures about 1000 °C. Annealing at temperatures over 1600 °C destroys the irradiation-induced pink color. It was found that the center 489 nm is a major absorption feature in the visible spectral range of electron-irradiated, nitrogen-doped CVD diamond. Green color of electron-irradiated, nitrogen-doped CVD diamond is caused by combined absorption of GR1 center and 489 nm center. It has been confirmed that NV defects produced in CVD diamond during growth are very temperature stable. They survive heating at temperatures at least 2000 °C. In contrast, NV defects produced by irradiation may anneal out at temperatures as low as 1600 °C. This much lower thermal stability of the radiation-induced NV defects is the result of their interaction with other radiation defects produced in their vicinity. A conclusion has been made that in nitrogen-doped CVD diamonds nitrogen atoms may form clusters. These clusters are probably the origin of the broad band luminescence at wavelengths 360, 390, 535 and 720 nm and a strong broadening of ZPLs of many optical centers.