Amorphous Boron Carbide-Amorphous Silicon Heterojunction Devices

Authors

Vojislav Medic, University of Nebraska-LincolnFollow

First Advisor

Natale Ianno

Date of this Version

Fall 12-2023

Document Type

Article

Citation

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

Comments

Copyright 2023, Vojislav Medic

Abstract

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