Chemical and semiconducting properties of NO2-activated H-terminated diamond

• Published in: Diamond and related materials Vol. 84; pp. 86 - 94
• Main Authors: Geis, M.W., Fedynyshyn, T.H., Plaut, M.E., Wade, T.C., Wuorio, C.H., Vitale, S.A., Varghese, J.O., Grotjohn, T.A., Nemanich, R.J., Hollis, M.A.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.04.2018
• Subjects: Diamond; Hydrogen-termination; Molecular adsorption; Nitrogen dioxide; Molecular adsorption; Diamond; Nitrogen dioxide; Hydrogen-termination
• ISSN: 0925-9635; 1879-0062
• DOI: 10.1016/j.diamond.2018.03.002

The H-terminated surface of diamond when activated with NO2 produces a surface conduction layer that has been used to make field effect transistors (FETs). Previous reports have suggested that during NO2 exposure (NO2-activation), NO2− forms on the diamond surface and generates positive carriers (holes) in the diamond, making the diamond surface conductive. We report here on X-ray-photoelectron-spectroscopy (XPS) surface characterization of single crystal diamonds and on infrared absorption of diamond powder. After activation, XPS showed the presence of N atoms on the diamond surface, but infrared absorption found no evidence of NO2−, but instead NO3− is present on the diamond surface. Two wet chemistry techniques determined the concentration of NO3− per milligram of diamond powder. With the powder's surface area measured by the BET technique, the surface NO3− concentration was measured to be between 6.2 × 1013 and 8.2 × 1013 cm−2. This is in the same range as the carrier densities, 3 × 1013 to 9 × 1013 cm−2, determined by Hall mobility and surface conductivity measurements of single crystal diamonds. Using similar techniques, the concentration of NO2− was determined to be <1012 cm−2. Both the surface conductance and the surface H atoms are stable in dry nitrogen, with or without NO2-activation, but the surface conductance, the concentrations of H atoms both with and without activation and NO3− decrease when exposed to laboratory air over a period of hours to days. Infrared absorption measurements showed the reduction of surface NO3− and H atoms during laboratory air exposure, but gave no indication of what reactions are responsible for their loss in laboratory air. [Display omitted] •After NO2 exposure of H-terminated diamond, no NO2– is present on the diamond surface, but instead NO3–.•NO2 reacts with the diamond surface H atoms, reducing their concentration by >25 %.•NO3–concentration is approximately equal to the surface hole concentration.•Surface H and NO3– concentrations and surface conductance are stable in dry N2.•NO3– and H concentrations and surface conductance are decrease in laboratory air.