Enhanced field emission from nitrogen-doped amorphous diamond
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James C. Sung Kinik Company 64, Chung San Road, Ying-Kuo, Taipei-Hsien 239, Taiwan, Republic of China, and National Taipei University of Technology, Taipei, Taiwan 106, Republic of China
Kuei-Hsien Chen Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, Taiwan 106, Republic of China
Ding-Fwu Lii Department of Electrical Engineering, Cheng Shiu Institute of Technology, Kaohsiung County, Taiwan 833, Republic of China (Received 22 January 2003; accepted 9 April 2003)
Undoped and nitrogen-doped amorphous diamond were deposited on n-type Si(100) substrate by a cathodic arc process. By varying nitrogen partial pressure of the gas mixture in the range of 0 to 55.6%, up to 23 at.% of nitrogen was incorporated in amorphous diamond. The electron spectroscopy for chemical analysis, Raman, and atomic force microscopy measurements indicated that most nitrogen atoms replaced carbon atoms in the amorphous structure. The electron concentration, mobility, and its resistivity were determined by the measurement of Hall effect. With the increasing of nitrogen content, the resistivity curve is U-shaped with a local minimum. The electron emission current in vacuum was characterized based on the diode design. It was found that the electron emission was highly reproducible. This is in contrast to the high variability observed for carbon nanotubes. The lowest resistivity coating had the lowest “turn-on” electrical field of 0.7 V/m at the current density of 10 A/cm2.
I. INTRODUCTION
It has generally been accepted that carbon-based materials have great potential as prospective cold cathode materials in microelectronic devices and flat-panel display applications.1–3 These materials include diamond, nanodiamond, amorphous diamond, carbon nanofibers, tetrahedral amorphous carbon (ta-C) films, and random or oriented carbon nanotubes.4 –13 Microtips array or nanotips array of such materials can emit electric current at very low applied fields. The emission depends on various factors such as negative electron affinity, band gap, surface termination, nitrogen addition, depletion layers, and film thickness.5 However, the electron emission mechanisms for these materials are not well understood, although a number of hypotheses have been proposed. The negative electron affinity of diamond was believed to play an important role in determining fieldemission characteristics. But to obtain low-threshold emission, it is necessary to introduce a high concentration a)
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of donor atoms such as nitrogen atoms. The higher concentration of electrons will enhance the electrical conductivity of diamond so the supply of electrons for the emission is uninterrupted. Hence, it was reported that nitrogen could increase the electrical conductivity and electron emission of amorphous diamondlike carbon films.13–17 The field emission is typically described by the Fowler– Nordheim (F–N) equation,18–20 which correlates the emission-current density (J, in A/cm2) with the work functi
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