Growth and characterization of large single crystal diamond grown by MPCVD with varying methane concentration

Large single-crystal diamond was synthesized in a 915 MHz Microwave Plasma-enhanced Chemical Vapor Deposition (MPCVD) reactor using sequential methane concentration steps (6.2% → 5.7% → 5.2%). The diamond was laser-sliced and scaife-polished to create optically flat cross-sections for depth-resolved investigation of gas-phase composition effects on growth dynamics and defect formation within a single 1.2 mm thick sample. Raman, FTIR, and photoluminescence spectroscopy reveal a systematic correlation between methane concentration and material properties: higher methane increases growth rate (8.8 µm/h at 6.2% vs. 7.8 µm/h at 5.2%) but simultaneously enhances compressive residual stress and promotes incorporation of hydrogen, nitrogen-vacancy (NV⁻, NV⁰), and silicon-vacancy (SiV⁻) centers. SiV⁻ intensity scales directly with methane concentration likely due to enhanced quartz erosion in reactor chamber. Critically, early-stage defects remain localized within their growth layer and do not propagate into subsequent diamond. This enables precision engineering of layered diamond structures with tailored defect and stress profiles at specific depths, which could be deployed for quantum sensing and photonic device applications. • Large single-crystal diamond grown by MPCVD with stepwise methane variation • Methane concentration directly influences growth rate and residual stress • Defect formation includes nitrogen- and silicon-vacancy centers within the crystal • Findings enable tailored diamond for sensing, electronics, and quantum technologies