Optical properties of single-crystal diamond MEMS: mitigating substrate interference

The precise characterization of bulk properties of thin homoepitaxial diamond layers with micrometer thickness is difficult due to the interference from the substrate. In this work, we utilized smart-cut method to fabricate single-crystal diamond (SCD) cantilevers or plates and transferred them to a foreign substrate (SiO2/Si). The mechanical resonance of the SCD cantilevers was characterized to confirm that the ion-implantation-induced damaged layer was nearly removed under the cantilever. Raman, photoluminescence (PL), and cathodoluminescence (CL) measurements were conducted on the transferred SCD cantilevers/plates and homoepitaxial layers on the substrate with and without ion implantation. As a result, it was found that both of the Raman spectral properties of the SCD layer on the ion-implanted regions and the freestanding SCD plates/cantilevers successfully avoid interference from the substrate. PL analysis showed no emission peaks attributable to nitrogen and other defects from the epilayers. Additionally, CL analysis from the freestanding cantilevers/plates disclosed the exciton emission at around 236 nm at room temperature. These results suggest the high crystal quality of the SCD cantilevers for MEMS applications.