In situ doping of epitaxial diamond with germanium by microwave plasma CVD in GeH4–CH4–H2 mixtures with optical emission spectroscopy monitoring

Abstract

We report the growth of Ge-doped homoepitaxial diamond films by microwave plasma CVD in GeH₄–CH₄–H₂ gas mixtures at moderate pressures (70–100 Torr). Optical emission spectroscopy was used to monitor Ge, H, and C₂ species in the plasma at different process parameters, and trends for intensities of those radicals, gas temperature, and excitation temperature, with variations of GeH₄ or CH₄ precursor concentrations, were investigated. The film deposited on (111)-oriented single crystal diamond substrates in a high growth rate regime revealed a strong emission of a germanium-vacancy (GeV) color center with a zero-phonon line at ≈604 nm wavelength in photoluminescence (PL) spectra, confirming the successful doping. The observed PL shift for the GeV defect is caused by stress in the films, as evidenced and quantified by Raman spectra. These results suggest that in situ doping with Ge using a GeH₄ precursor is a convenient method of controlling the formation of GeV centers in epitaxial diamond films for photonic applications.