Semiconducting ²-FeSi2 for high efficiency and low cost photovoltaics

摘要

The beta phase of iron disilicide, ²-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 ²-FeSi2 material for application towards higher efficiency and low cost photovoltaics. Sputter deposition of Fe/Si multilayers was used to fabricate ²-FeSi2 films. Conversion of the multilayer films to ²-FeSi2 was accomplished by a thermal treatment under N2 atmosphere. ²-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.