OBSERVATION OF SURFACE-CHARGE SCREENING AND FERMI-LEVEL PINNING ON A SYNTHETIC, BORON-DOPED DIAMOND

Spectroscopic current-voltage (I-V) curves taken with a scanning tunne ling microscope on a synthetic, boron-doped diamond single crystal ind icate that the diamond, boiled in acid and baked to 500-degrees-C in v acuum, does not exhibit ideal Schottky characteristics. These I-V curv es taken in ultrahigh vacuum do not fit the traditional theory of ther mionic emission; however, the deviation from ideal can be accounted fo r 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 1/3 band gap rule of Mead and Spitzer [Phys. Rev. 134, A713 (1964)].