Observation of surface charge screening and Fermi level pinning on a synthetic, boron-doped diamond

Spectroscopic current-voltage (1-v) curves taken with a scanning tunneling microscope on a synthetic, boron-doped diamond single crystal indicate that the diamond, boiled in acid and baked to 500 “C in vacuum, does not exhibit ideal Schottky characteristics. These 1-V curves taken in ultrahigh vacuum do not fit the traditional theory of thermionic emission; however, the deviation from ideal can be accounted for by charge screening at the diamond surface. At ambient pressure, the I-V curves have a sharp threshold voltage at 1.7 eV above the valence band edge indicating pinning of the Fermi energy. This measurement is in excellent agreement with the 4 band gap rule of Mead and Spitzer [Phys. Rev. 134, A713 ( 1964)].