Electronic properties of H-terminated diamond in electrolyte solutions

The electronic properties of hydrogen-terminated single-crystalline chemical-vapor deposited diamond in electrolyte solutions between pH 2 and 12 have been characterized by cyclic voltammetry experiments and pH-sensitive measurements using ion-sensitive field-effect transistor structures. The data show the formation of surface conductivity in diamond if immersed into electrolytes. The drain-source conductivity is pH dependent, with about 66 mV/pH. Due to strong Coulomb repulsion between positive ions in the electrolyte (hydronium ions) and the H+-surface termination of diamond, an enlarged tunneling gap is established which prevents electronic interactions between the electrolyte and diamond. This gap is the "virtual gate insulator" of diamond ion-sensitive field-effect transistor structures, with an interface resistance of about 10(8) Omega. The application of potentials larger than the oxidation threshold of +0.7 V (pH 13) to +1.6 V (pH 1) gives rise to strong leakage currents and to partial surface oxidation. (c) 2006 American Institute of Physics.