Explore the growth mechanism of high-quality diamond under high average power density in the MPCVD reactor.

• A self-consistent multi-physics coupling model including microwave electromagnetic field, plasma field and fluid heat transfer field is established. • CH 4 -H 2 plasma characteristics from 18 to 100 W∙cm−3. • Kinetics of CH 4 -H 2 plasma chemical reaction at high average power density. • High-rate growth of high-quality Φ 60 mm diamond films at high average power density of 100 W∙cm−3. Investigating the mechanism behind the high-efficiency deposition of high-quality diamond has always been a prominent topic in related research. This paper investigates the CH 4 -H 2 plasma characteristics and related chemical reaction kinetics in the average power density range of 18–100 W·cm−3, which is a typical range for large-area diamond film deposition. The number densities of H, CH 3 and C 2 H 2 increase linearly with the average power density. C 2 H 2 is the main hydrocarbon in the discharge, and CH 3 is the main single-carbon hydrocarbon. The number density and radial uniformity of CH 3 and C 2 H 2 increase with the average power density, which is necessary for the high rate and uniform deposition of diamond films. The plasma's optical emission spectra indicate an acceleration in the C 2 production rate at high power density. The diamond film deposition experiment demonstrates the efficacy of high average power density in achieving high-quality diamond deposition at a high growth rate. [ABSTRACT FROM AUTHOR]