Theoretical and experimental study of semiconducting iron disilicide and its applications to thin film solar cells

Abstract

Transition metal silicides have been studied extensively for many years due to their potential technological importance and applications. Recently, the semiconducting phase of iron disilicide (β-FeSi2) has received considerable attention due to its potential applications in optoelectronic and microelectronic areas. This is attributed to its direct bandgap of 0.86 eV that corresponds to ~1.5 µm of the optical fiber communication. In addition, β-FeSi2 is expected as a promising photovoltaic material with a theoretical conversion efficiency as high as 23% due to its ultrahigh optical absorption coefficient in the order of 105 cm-1 near the absorption edge. These properties, along with other features such as abundance of constituent elements, nearly lattice-matched to Si, and high thermal stability and oxidation resistance, have made β-FeSi2 one of the most attractive materials of choice for future generation thin film photovoltaic applications. In this work, both theoretical and experimental study of β-FeSi2 was explored. The theoretical study based on the first-principles calculations provides the fundamental understanding of various properties of β-FeSi2, including equilibrium crystal structure, bandgap properties, effects of native vacancy defects, and impurity doping in β-FeSi2. The experimental study involves the formation and structural, optical, and electrical characterization of sputtered and processed β-FeSi2 as well as eventual demonstration of semiconducting β-FeSi2-based heterojunction thin film solar cells on the Si platform.