Kelvin Probe Characterization of Nanocrystalline Diamond Films with SiV Centers as Function of Thickness

Optically active color centers in diamonds have been intensively studied due to their potential in photonics, energy harvesting, biosensing, and quantum computing. Silicon vacancy (SiV) center offers an advantage of suitable emission wavelength and narrow zero-phonon line at room temperature. Measurement of surface potential and photovoltage can provide better understanding of the physics and control of SiV light emission, such as charge states and charging effects. Herein, optoelectronic properties of nanocrystalline diamond films with SiV centers at different layer thicknesses (10-200 nm, controlled by the growth time) under ambient conditions are studied. Time-dependent measurements are performed in the light-dark-light cycle. Positive photovoltage arises on samples with SiV layer thicknesses below 55 nm on both H- and O-terminated surfaces. Above 55 nm the photovoltage switches to negative. This layer thickness thus represents a halfway boundary between surface-controllable and bulk SiV centers dominant contribution. A band diagram scheme explaining the photovoltage switching mechanism is provided. Nanocrystalline diamond films with silicon vacancy (SiV) centers exhibit a change in work function and surface photovoltage including a switch of polarity with the increasing growth thicknesses (5-175 nm) for both H- and O-terminated surfaces. The SiV layer thickness of 32 or 20 nm, respectively, represents a halfway boundary between surface-controllable SiV centers and dominant bulk SiV contribution.image (c) 2023 WILEY-VCH GmbH