High-concentration diamond nitrogen vacancy color center fabricated by microwave plasma chemical vapor deposition and its properties
Authors: LIU Housheng , GUO Shifeng , CHEN Ming , ZHANG Guokai , GUO Chong , GAO Xuedong , YU Cui ,   Zhongnan Diamond Co., Ltd. of Yuxi Industries Group, Nanyang 473264, China,   The 13th Research Institute of China Electronics Technology Group Corporation, Shijiazhuang 050051, China,   National Key Laboratory of Solid-State Microware Devices and Circuits, Hebei Semiconductor Research Institute, Shijiazhuang 050051, China
Published: December 2024

Diamond nitrogen vacancy (NV) color centers have good stability at room temperature and long electron spin coherence time, and can be manipulated by lasers and microwaves, thereby becoming the most promising structure in the field of quantum detection. Within a certain range, the higher the concentration of NV color centers, the higher the sensitivity of detecting physical quantities is. Therefore, it is necessary to dope sufficient nitrogen atoms into diamond single crystals to form high-concentration NV color centers. In this study, diamond single crystals with different nitrogen content are prepared by microwave plasma chemical vapor deposition (MPCVD) to construct high-concentration NV color centers. By doping different amounts of nitrogen atoms into the precursor gas, many problems encountered during long-time growth of diamond single crystals under high nitrogen conditions are solved. Diamond single crystals with nitrogen content of about 0.205, 5, 8, 11, 15, 36, and 54 ppm (1 ppm = 10<sup>–6</sup>) are prepared. As the nitrogen content increases, the width of the step flow on the surface of the diamond single crystal gradually widens, eventually the step flow gradually disappears and the surface becomes smooth. Under the experimental conditions in this study, it is preliminarily determined that the average ratio of the nitrogen content in the precursor gas to the nitrogen atom content introduced into the diamond single crystal lattice is about 11. Fourier transform infrared spectroscopy shows that as the nitrogen content inside the CVD diamond single crystal increases, the density of vacancy defects also increases. Therefore, the color of CVD high nitrogen diamond single crystals ranges from light brown to brownish black. Compared with HPHT diamond single crystal, the CVD high nitrogen diamond single crystal has a weak intensity of absorption peak at 1130 cm<sup>–1</sup> and no absorption peak at 1280 cm<sup>–1</sup>. Three obvious nitrogen-related absorption peaks at 1371, 1353, and 1332 cm<sup>–1</sup> of the CVD diamond single crystal are displayed. Nitrogen atoms mainly exist in the form of aggregated nitrogen and single substitutional N<sup>+</sup> in diamond single crystals, rather than in the form of C-defect. The PL spectrum results show that defects such as vacancies inside the diamond single crystal with nitrogen content of 54 ppm are significantly increased after electron irradiation, leading to a remarkable increase in the concentration of NV color centers. The magnetic detection performance of the NV color center material after irradiation is verified, and the fluorescence intensity is uniformly distributed in the sample surface. The diamond single crystal with nitrogen content of 54 ppm has good microwave spin manipulation, and its longitudinal relaxation time is about 3.37 ms.