A series of heavily boron-doped polycrystalline diamond films was studied.
It was found that the electron affinity of the diamond surfaces increased w
ith increasing doping concentration and the Fermi level was pinned at simil
ar to 0.35 eV above the valence band maximum (VBM). After annealing at simi
lar to 500 degrees C, the electron affinity of all samples decreased and th
e Fermi level increased to 0.87 eV. These changes were concurrent with a de
crease in the concentration of both boron and oxygen, and an increase in th
at of BxOy relative to elemental boron on the diamond surfaces. A model was
proposed to explain the dependence of electron affinity on boron concentra
tion, and to explain other changes observed upon annealing.