Photoelectron emission from nitrogen- and boron-doped diamond (100) surfaces

The nitrogen-doped (N-doped), type Ib, synthetic diamond (100) surface was investigated by means of X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). Photoelectron emission data from the boron-doped (B-doped) and the N-doped diamond (100) surfaces were compared and permitted the energy band diagrams for these differently terminated surfaces to be drawn. We observed emission from energy levels below the conduction band minimum up to the vacuum level and therefore succeed in evaluating the negative electron affinity (NEA) of the hydrogen-terminated diamond surfaces. Both the hydrogen-terminated N- and B-doped diamond (100) surfaces show NEA values of at least −0.2 and −1.0 eV, respectively, while the hydrogen-free surfaces show positive electron affinity. In contrast to the hydrogen-terminated B-doped (100) surface, UPS measurements on the hydrogen-terminated N-doped (100) surface do not reveal a high intensity NEA peak owing to the strong upward band bending. The high intensity NEA peak of B-doped diamond seems to be due to the downward band bending together with the reduced work function because of hydrogen termination. The work function increases for subsequent hydrogen desorption at higher annealing temperatures with associated loss of NEA. For the N-doped diamond (100) surface the work function behaves similarly but the observation of a NEA peak is absent because of the surface barrier formed by the upward band bending.