The influence of nitrogen and boron doping on the surface morphology, defects and crystallinity of large-area chemical vapor deposition grown single crystal diamond

Abstract

Large-area (∼15 mm × 15 mm) single crystal diamonds have been grown homoepitaxially on (100) oriented CVD diamond substrates by incorporating nitrogen (1–10 ppm) and boron (3 ppm) impurities. The nitrogen concentration (≤ 1 ppm) promotes the development of a new-diamond (200) phase during the growth of cubic (400) single crystal diamond. However, the crystal structure maintains four-fold azimuthal symmetry of the cubic diamond as confirmed by phi (ϕ)-scans through (111) reflections. The signature of the new-diamond phase decreases considerably with the addition of optimum nitrogen (10 ppm) and boron (3 ppm) concentrations. The optical and atomic force microscopy data demonstrate that the nitrogen addition in the feed gas is advantageous in microscopic smoothing of surface roughness and the suppression of hillocks or uneven growth. In addition, the diamond sample grown with 10 ppm nitrogen shows minimal random stress and dislocation density as estimated by the full width at half maximum of the Raman (1332 cm−1) and (400) x-ray diffraction peaks, respectively. The hydrogen content (2800–3000 cm−1) in the diamond sample was also found to decrease with an increase in nitrogen content, and it is completely suppressed at the optimum nitrogen level (∼10 ppm). The investigations demonstrate the critical role of nitrogen and boron concentrations in CVD growth of colorless single crystal diamonds for their optical, electronic, and gem applications.