P-Type Diamond Positive Surface Photo-Voltage

We report a large positive surface photo-voltage for lightly boron doped (p-type) diamond illuminated with 21.2 eV photons after exposing the surface to atomic hydrogen. We have recorded positive shifts well in excess of the band gap energy. Because the photo-voltage in most p-type materials is negative, we argue the observed positive shift indicates a lack of electron accumulation at the surface, as might be expected when the electron affinity is negative.