High temperature photoelectron emission and surface photovoltage in semiconducting diamond

A non-equilibrium photovoltage is generated in semiconducting diamond at above-ambient temperatures during x-ray and UV illumination that is sensitive to surface conductivity. The H-termination of a moderately doped p-type diamond (111) surface sustains a surface photovoltage up to 700K, while the clean (21) reconstructed surface is not as severely affected. The flat-band C 1s binding energy is determined from 300K measurement to be 283.87 eV. The true value for the H-terminated surface, determined from high temperature measurement, is (285.260.1) eV, corresponding to a valence band maximum lying 1.6 eV below the Fermi level. This is similar to that of the reconstructed (21) surface, although this surface shows a wider spread of binding energy between 285.2 and 285.4 eV. Photovoltage quantification and correction are enabled by real-time photoelectron spectroscopy applied during annealing cycles between 300K and 1200K. A model is presented that accounts for the measured surface photovoltage in terms of a temperature-dependent resistance. A large, high temperature photovoltage that is sensitive to surface conductivity and photon flux suggests a new way to use moderately B-doped diamond in voltage-based sensing devices.