Influence of sulfur incorporation on field-emission properties of microcrystalline diamond thin films
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B.R. Weiner Department of Chemistry, University of Puerto Rico, San Juan, PO Box 23346, PR00931, Puerto Rico
G. Morell Department of Physical Sciences, University of Puerto Rico, San Juan, PO Box 23323, PR00931, Puerto Rico (Received 3 June 2003; accepted 25 August 2003)
Results are reported on the electron field emission properties of microcrystalline diamond thin films grown on molybdenum substrates by the sulfur (S)-assisted hot-filament chemical vapor deposition technique using methane (CH4), hydrogen sulfide (H2S), and hydrogen (H2) gas mixtures. Electron field-emission measurements revealed that the S-incorporated microcrystalline diamond thin films have substantially lower turn-on fields and steep rising currents as compared to those grown without sulfur. The field-emission properties for the S-incorporated films were also investigated systematically as a function of substrate temperature (TS). Lowest turn-on field achieved was observed at around 12.5 V/m for the samples grown at TS of 700 °C with 500 ppm H2S. To establish the property–structure correlation, we analyzed the films with multiple characterizations include scanning electron microscopy (SEM), atomic force microscopy (AFM), Raman spectroscopy (RS), and x-ray photoelectron spectroscopy (XPS) techniques. It was found that sulfur addition causes significant microstructural changes in microcrystalline diamond thin films. S-assisted films show smoother, coarse-grained surfaces (non-faceted) than those grown without it (well-faceted) and a relatively higher content of non-diamond carbon (primarily sp2-bonded C). RS and investigations on the morphology by SEM and AFM indicated the increase of sp2 C content with increasing TS followed by a morphological transition at 700 °C in the films. XPS investigations also showed the incorporation of S in the films up to a few atomic layers. It is believed that the electron-emission properties are governed by the sulfur incorporation during the chemical vapor deposition process. Although most of the S is expected to be electrically inactive, under the high doping conditions hereby used, it is shown rather indirectly through multiple characterizations that there may be some amount of S in donor states. Therefore the results are discussed in terms of the dual role of S whereby it induces the structural defects in the form of enhanced sp2 C content at the expense of diamond quality and a possibility of availability of conduction electrons. In fact the latter finding is supported through room temperature electrical conductivity measurements.
I. INTRODUCTION
Field-emission displays (FEDs) have the potential to be a low-cost, high-performance alternative to the currently dominant cathode ray tube and liquid-crystal display (LCD) technologies for flat panel display applications.1 One of the key issues in FEDs has been the
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J. Mater. Res., Vol. 18, No. 11, Nov 2003 Downloaded: 20
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