AVS 58th Annual International Symposium and Exhibition
    Electronic Materials and Processing Division Monday Sessions
       Session EM1-MoA

Paper EM1-MoA8
Novel Boron Carbide-Based Semiconducting Polymers for Enhanced Electronic Properties

Monday, October 31, 2011, 4:20 pm, Room 209

Session: Group III-Nitrides and Hybrid Devices
Presenter: Frank Pasquale, University of North Texas
Authors: F. Pasquale, University of North Texas
J. Kelber, University of North Texas
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We report the controlled modification of valence band electronic structure of semiconducting boron carbides with sharply narrowed band gap, by combination of 1,4 diaminobenzene (DAB) with orthocarboranes to form a novel boron-carbide based semiconducting film. Semiconducting boron carbide films (B10C2Hx) and related materials formed from crosslinking of carborane icosahedra are of rapidly increasing interest in neutron detection, nanoelectronics, spintronics, and even conventional CMOS ULSI applications. The ability to modify the material's electronic structure in a controlled manner is of obvious interest in all these areas. We report x-ray and ultraviolet photoelectron spectra (XPS, UPS), demonstrating that electron-induced cross-linking of carborane and DAB results in a novel semiconductor with a significantly enhanced valence band density of states near the Fermi level, resulting in a shift, as determined by UPS, in the valence band maximum from ~ 4.3 eV to ~ 1.7 eV below the Fermi level. Importantly, this effect is relatively insensitive to total film thickness and for DAB/orthocarborane atomic ratios (determined by XPS) ranging from 1:4 to 1:1. Films were formed by condensation and cross-linking of alternating layers of orthocarborane and DAB precursors under ultrahigh vacuum (UHV) conditions, allowing precise control of relative DAB and carborane concentrations. This procedure also yielded films of systematically varied DAB/carborane concentration and film thicknesses between 20 Å and 100 Å average thickness, as determined by attenuation of Cu(2p3/2 ) photoemission intensity from the substrate. The films exhibited shifts in the valence band spectra of ~ 0.2 eV to lower binding energies upon cross-linking, indicating a surface photovoltage effect, and the formation of a true p-type semiconducting film. The results demonstrate formation of a new semiconducting material based on carborane icosahedra but modified by the addition of an organic species. These data further indicate the potential for the development of a broad range of novel boron carbide-based polymers using carboranes and other organic additives, with film formation by a variety of methods, including photon or electron bombardment, or plasma-enhanced chemical vapor deposition.