Optical Analysis of p‐Type Surface Conductivity in Diamond with Slotted Photonic Crystals

2D slotted diamond‐based photonic crystals (PhCs) with Q factors up to 6500 are fabricated and optically characterized at 1550 nm in order to probe surface molecular modifications. This study focuses on the simplest surface modifications that can modify the diamond PhC optical properties, namely, hydrogenation and oxidation. Depending on the chemical surface termination, these diamond PhCs exhibit a strong modification of their spectral features. When the surface is tuned from oxidized to hydrogenated, a resonance wavelength shift of the cavity occurs and is accompanied by a decrease of the Q factor. Moreover, experimental evidence is given that this phenomenon is reversible, as the initial value of the Q factor is recovered when the surface is re‐oxidized. This is attributed to the subsurface conductive layer that is due to transfer doping in hydrogenated diamond and which is absent from oxidized diamond. Thanks to 3D finite differences in time domain (FDTD) simulations, an estimate of the effective refractive index of the surface conductive layer at 1.5 μm is given as a function of its thickness. This result highlights the high sensitivity of slotted diamond PhC and the importance of surface control for biosensing with diamond.