Homoepitaxial deposition of high-quality thick diamond films: effect of growth parameters

Owing to its exceptional properties, monocrystalline diamond is one possible interesting candidate for high-power electronic applications if a suitable and reproducible process allowing the deposition of high-quality thick films within a reasonable time is developed. In this paper, a Microwave Plasma-Assisted Chemical Vapour Deposition (MWPACVD) two-step process at high plasma density (microwave power 3200 W, pressure 220 mbar) has been successfully used on high-pressure high-temperature (HPHT) (100) substrates. It consisted in the etching of the diamond substrates with an O2/H2 plasma immediately followed by CVD diamond growth. Optimal growth conditions were determined leading to the synthesis of a 520-μm-thick high-quality single-crystal homoepitaxial layer at growth rate of 6 μm/h. This film exhibited a smooth surface with high optical clarity, and the photoluminescence (PL) spectrum was free from nitrogen- or silicon-related emission bands. Moreover, free exciton emission was clearly observed by cathodoluminescence (CL). Finally, the influence of small amounts of nitrogen was also investigated, which resulted in higher growth rate up to 33 μm/h and films as thick as 1.7 mm. The relatively good quality of these films was confirmed by several appropriate characterizations, including Raman, photoluminescence and cathodoluminesence. The use of this process opens the way to the synthesis of thick high-quality single-crystal specimens for high-power electronic applications.