Band bending, electronic affinity and density of states at several (100) surfaces of boron-doped homoepitaxial diamond thin films

Using ultraviolet and x-ray photoelectron spectroscopies, we investigate four types of the (100) surface of homoepitaxial diamond films, either doped with boron or undoped. We measure the position of the valence band maximum at the surface, the electronic affinity and the density of states. In p-type doped films, conductivity measurements indicate that the bulk Fermi level is pinned close to 0.4 eV above the valence band edge and subtracting this value from the valence band maximum at the surface permits us to derive the band bending. The different (100) surfaces of the p-type diamond samples are (i) hydrogenated with the 2 x I reconstruction (H-surface), (ii) free with the 2 x I reconstruction, and either (iii) post-oxygenated or (iv) oxygenated during the growth, both with the I x 1 reconstruction (O-surface). All these surfaces show a downward band bending, which implies hole depletion, ranging from 0.3 eV for the H-surface to 1.2 eV for the O-surface. Only the H-surface exhibits a negative electronic affinity (-0.9 eV) whereas the others display positive electronic affinities in the range 0.9-2.2 eV. Oxygen passivates the diamond surface, giving both very low conductivity and density of states in the bandgap, and increasing the band bending. These results, obtained in homoepitaxial diamond thin films, are shown to be relevant for implementing diamond-based electronic devices.