Fermi level on hydrogen terminated diamond surfaces

Atomic force microscopy and Kelvin probe experiments are applied to characterize hydrogen terminated patterns contacted with gold and aluminum on (100) diamond surfaces. On hydrogen terminated diamond the work function of 4.9 eV is detected, with an accuracy of about 0.1 eV. Taking into account the negative electron affinity of $\text{−1.3\hspace{0.17em}}\mathrm{eV}$ and a band gap of 5.5 eV the Fermi energy is 0.7 eV deep in the valence band. Illumination of the sample results in a shift of the surface Fermi level by as much as 0.2 eV. This is attributed to a surface photovoltage effect.