Fabrication of a GaP Nanowire Betavoltaic Device Using Ni-63

Abstract

The functionality of a novel 3-dimensional betavoltaic battery design will be investigated to improve conversion efficiency over existing planar devices. A beta-emitting isotope of nickel, Ni-63, is embedded in the volume of empty space between self-assisted p-i-n junction gallium phosphide nanowires to improve the beta capture efficiency. Parameters such as nanowire pitch, diameter, and height will influence the efficiency and were investigated thoroughly. Material selection was performed based on the following considerations. Gallium phosphide is chosen to achieve a high open circuit voltage under beta exposure. Ni-63 has an optimal beta energy spectrum for a nanowire device and a half-life of 101 years for long term application. The majority of the work focused on the development of the fabrication process, particularly the radioactive source deposition. The method used for embedding the source was a citrate-based sol-gel which was spun onto the sample. This method was modified for this nanowire application and specific challenges to the process are outlined. Furthermore, the obstacles of working with radioactive materials will be discussed. The first nanowire-based betavoltaic device is reported to produce beta-generated current and achieved a beta conversion efficiency of 0.03%. Investigation of the junction was performed to provide future improvements to the efficiency. Additionally, simulated IV curves for a non-active sample exhibited a possible conversion efficiency of 1.92%.