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We have succeeded in the rf magnetron sputter deposition of high resistivity boron carbide (B1−xCx). This has been accomplished by the sputter depositing the boron carbide from a methane saturated boron carbide target. We show that the composition and optical band gap of the sputter deposited material are functions of the applied rf power. Furthermore, boron carbide/silicon heterojunction diodes fabricated via sputtering compare favorably with those fabricated from borane cage molecule sources using plasma enhanced chemical vapor deposition (PECVD).

We have grown nickel doped boron–carbon alloy films by the technique of plasma enhanced chemical vapor deposition. The source gas closo-1,2-dicarbadodecaborane (orthocarborane) was used to grow the boron–carbon alloy, while nickelocene [Ni(C5H5)2] was used as the dopant source for nickel. With sufficient levels of Ni doping, diodes with characteristic tunnel diode behavior can be fabricated. The doping of nickel transformed a B5C p-type material, relative to lightly doped n-type silicon, to a strongly n-type material. In order to gain insight into the shift of the Fermi level of the Ni-doped material, we have examined the changes in the electronic structure of sodium doped films of the precursor molecule orthocarborane which has an icosahedral structure similar to that of boron–carbon materials. The establishment of unoccupied states at the Fermi level with Na doping of the orthocarborane films is consistent with the transformation of the p-type B5C to an n-type material with Ni doping.

This dissertation summarizes the effects of doping of boron carbide materials. Hydrogen, nickel and phosphorus were doped into boron carbide. Boron carbide fabricated by plasma enhanced chemical vapor deposition (PECVD) contains hydrogen and reduction of the hydrogen content appears to reduce the band gap. The hydrogenated boron carbide was found to have very high resistivity $({\sim}10\sp7$ to $10\sp{10}\ \Omega$-cm). With the high resistivity form of the material, boron carbide (B$\sb5$C)/boron/silicon multilayer heterojunction devices were fabricated. Nickel doped boron carbide films were grown on n-Si(111) substrates to construct diodes and tunnel diodes. The source gas closo-1,2-dicarbadodecaborane (orthocarborane-$\rm C\sb2B\sb{10}H\sb{12})$ was used to grow the boron carbide, while nickelocene (Ni(C$\rm\sb5H\sb5)\sb2)$ was used to introduce nickel into the growing film. The doping of nickel transformed a rhombohedral B$\sb5$C material p-type, relative to lightly doped n-type silicon, to a strongly n-type material. In addition, it is possible to construct a p - n homojunction boron carbide (B$\sb5$C) diode. This homojunction diode exhibits excellent I - V characteristics not only at room temperature but also at higher temperatures (573 K). Moreover, with sufficient partial pressures of nickelocene in the plasma reactor, diodes with characteristic tunnel diode behavior can be made. These results suggest that Ni doping populates states in the gap which are pinned to one band edge (conduction band). From the gas phase of a sing!e source compound dimeric chloro-phospha(III) carborane $\rm((C\sb2B\sb{10}H\sb{10})\sb2(PCl)\sb2),$ phosphorus doped boron carbide films were made. Phosphorus doped B$\sb5$C materials increased the band gap from 0.9 eV to 2.6 eV.

We have nickel doped boron carbide grown by plasma enhanced chemical vapor deposition. The source gas closo-1,2-dicarbadodecaborane (ortho-carborane) was used to grow the boron carbide, while nickelocene [Ni(C5H5)2] was used to introduce nickel into the growing film. The doping of nickel transformed a p-type, B5C material, relative to lightly doped n-type silicon, to an n-type material. Both n-n heterojunction diodes and n-p heterojunction diodes were constructed, using as substrates n- and p-type Si(111), respectively. With sufficient partial pressures of nickelocene in the plasma reactor, diodes with characteristic tunnel diode behavior can be successfully fabricated.

We have succeeded in the fabrication of a boron–carbide/boron diode on an aluminum substrate, and a boron–carbide/boron junction field effect transistor. Our results suggest that with respect to the approximately 2 eV band gap pure boron material, 0.9 eV band gap boron–carbide (B5C) acts as a p-type material. Both boron and boron–carbide (B5C) thin films were fabricated from single source borane cage molecules using plasma enhanced chemical vapor deposition (PECVD). Epitaxial growth does not appear to be a requirement. ©1996 American Institute of Physics.

We have fabricated a B5C, boron-carbide/Si(111) heterojunction diode by the synchrotron radiation-induced decomposition of orthocarborane. This diode can be compared with similar boron-carbide/Si(111) heterojunction diodes fabricated by plasma enhanced chemical vapor deposition. The synchrotron radiation induced chemical vapor deposition is postulated to occur via the decomposition of weakly chemisorbed species and the results suggest that “real-time'' projection lithography (selective area deposition) of boron-carbide devices is possible.