Semiconducting ²-FeSi2 for high efficiency and low cost photovoltaics

The beta phase of iron disilicide, β-FeSi₂, behaves as a semiconductor and possesses three desirable material properties: direct band gap of around 0.87 eV, close lattice match with silicon (2-4% mismatch) and abundant availability of its constituent elements on the earth´s crust. Moreover, its high optical absorption coefficient (one to two orders of magnitude higher than silicon) makes it a promising next generation semiconductor for photovoltaics with high performance and low environmental burden. The purpose of this work is to examine fundamental properties of β-FeSi₂ material for application towards higher efficiency and low cost photovoltaics. Sputter deposition of Fe/Si multilayers was used to fabricate β-FeSi₂ films. Conversion of the multilayer films to β-FeSi₂ was accomplished by a thermal treatment under N₂ atmosphere. β-FeSi₂ films fabricated exhibited polycrystalline grains, with a direct energy band gap of 0.87 eV, an absorption coefficient in the order of 10⁵ cm^-1 and a residual carrier concentration due to electrons in the order of 10¹⁹ cm^-3. Results of characterization using x-ray photoelectron spectroscopy, x-ray diffraction, scanning electron microscopy, UV-VIS-IR spectrophotometer measurements and Hall effect measurements have been discussed.