Date of this Version
A dissertation presented to the faculty of the Graduate College at the University of Nebraska in partial fulfillment of requirements for the degree of Doctor of Philosophy
Major: Electrical Engineering
Under the supervision of Professor Natale Ianno
Lincoln, Nebraska, December 2023
This dissertation will show successful development and characterization of amorphous boron carbide-amorphous silicon heterojunction device with potential for neutron detection. The amorphous hydrogenated boron carbide (a-BC:H) has been extensively researched as a semiconductor for neutron voltaic device fabrication. Naturally occurring boron contains 19.8% of boron isotope B10 that has a high absorption cross section of thermal neutrons at lower energies, and boron carbide contains 14.7% of that B10 isotope. Therefore, as a semiconductor compound of boron a-BC:H has the ability to absorb radiation, generate charge carriers, and collect those carriers. Previous work on a-BC:H devices investigated the fabrication of homojunction, heterojunction and heteroisomeric devices from the polymeric precursors ortho-carborane (p-type) and meta-carborane (n-type) using plasma enhanced chemical vapor deposition (PECVD). However, the metal contact formation with a-BC:H has not been previously studied with respect to its possible effects on device performance. The metal/a-BC:H contact investigation was performed, producing contact resistance for an Ohmic contact formation of Ti on n-type a-BC:H. The resistivity of the n-type a-BC:H in the direction of the device current flow was also investigated. However, a metal that forms an Ohmic contact the p-type a-BC:H has not been identified. The p-type a-BC:H made from ortho-carborane has high resistivity and doping limitations, so p-type single crystal silicon with n-type a-BC:H grown from meta- carborane has been previously studied and shown to produce the most optimal device performance compared to different a-BC:H device structures. As single crystal silicon has well known electrical and material properties, with X-Ray Photoelectron Spectroscopy (XPS) and Spectroscopic Ellipsometry measurements, electronic properties at the heterojunction interface of a-BC:H/c-Si is obtained by calculating valence band offset. However, as single crystal silicon degrades over time due to radiation induced damage to its crystalline structure, p+ -type hydrogenated amorphous silicon (a-Si:H) is investigated as a potential layer in the formation of the a-BC:H heterojunction device. From the characterization of a-BC:H/c-Si and a-BC:H/a-Si:H devices, the a-BC:H/a-Si:H device shows potential in fabricating a novel neutron voltaic device.
Advisor: Natale Ianno