  The surface conductivity of hydrogen-terminated diamond is a topic of great
interest from both scientific and technological perspectives. This is primarily
due to the fact that the conductivity is exceptionally high without the need
for substitutional doping, thus enabling a wide range of electronic
applications. Although the conductivity is commonly explained by surface
transfer doping due to air-borne surface acceptors, there remains uncertainty
regarding the main determining factors that govern the degree of band bending
and hole density, which are crucial for the design of electronic devices. Here,
we elucidate the dominant factor influencing band bending by creating shallow
nitrogen-vacancy (NV) centers beneath the hydrogen-terminated diamond surface
through nitrogen ion implantation at varying fluences. We measured the
photoluminescence and optically detected magnetic resonance (ODMR) of the NV
centers, as well as the surface conductivity, as a function of the nitrogen
implantation fluence. The disappearance of the conductivity with increasing
nitrogen implantation fluence coincides with the appearance of
photoluminescence and ODMR signals from negatively charged NV centers. This
finding indicates that band bending is not exclusively determined by the
work-function difference between diamond and the surface acceptor material, but
by the finite density of surface acceptors. This work emphasizes the importance
of distinguishing work-function-difference-limited band bending and
surface-acceptor-density-limited band bending when modeling the surface
transfer doping, and provides useful insights for the development of devices
based on hydrogen-terminated diamond.
