Controlled boron content in lightly B-doped single crystal diamond films by variation of methane concentration

Obtaining desirable electrical properties from B-doped single crystal diamond (SCD) films hinges on precise control of boron incorporation into the crystal lattice structure. In this study, the impact of methane concentration during plasma deposition on boron incorporation of lightly B-doped SCD films is investigated. SCD layers are grown successively by microwave plasma enhanced chemical vapor deposition (CVD) at different methane-to-hydrogen concentrations (1%, 2%, and 3%), with residual boron atoms present in the CVD reactor. An increase in methane concentration leads to surface defects such as unepitaxial crystallites and pyramidal hillocks. The charge carrier mobility, electrical conductivity, and boron content of samples are evaluated and discussed. The temperature-dependent mobility is analyzed through. theoretical modeling, revealing dominant scattering mechanisms at different temperatures. At 300 K, the maximum hole mobility reached 1200 cm2/V·s for the 1% methane concentration sample, transitioning to hopping conduction at lower temperatures. An increase in boron-doping level with rising methane concentration is detected by Fourier transform infrared spectroscopy, cathodoluminescence spectroscopy, Hall effect, and X-ray photoelectron spectroscopy measurements. These findings highlight the potential of methane concentration in plasma feedgas to control boron concentration in CVD diamond and open avenues for crafting efficient high-power electronic applications using p-type SCD films.