The effect of gallium implantation on the optical properties of diamond

• We report the change in optical constants of diamond after implantation with Ga ions.
• First observation of decreasing the refractive index of implanted diamond is reported.
• Realization of diamond waveguides in which the active layer is intact is suggested.
• Possible role of the involved physical mechanisms is discussed.

Gallium focused-ion beam milling is a commonly used technique for sculpting diamond at the nano and micro scale. However even at fluences insufficient to cause sputtering, implanted gallium causes modification of the optical properties of the diamond substrate. We implanted 30 keV gallium ions at fluences from 1 × 1013 to 5 × 1014 Ga/cm2 and studied the effect on the optical properties via spectroscopic ellipsometry (SE), from 0.6 to 6.5 eV, obtaining the changes in refractive index and extinction coefficient in the implanted layer as a function of operating wavelength. Here, we report the first observation of decreased refractive index for a wide spectral range in low fluence implanted diamond. In addition, we observe non-monotonic response of the refractive index with fluence, which is in disagreement with proton studies, but accords with other heavy-ion implantation reports. Such discrepancies suggest that there are different mechanisms for refractive index modification for different species and that resulting optical properties are not solely a function of damage. Further comparisons with the white light reflectance and near infra-red transmittance measurements support the SE data.