Dielectric function and band gap determination of single crystal CuFeS 2 using FTIR-VIS-UV spectroscopic ellipsometry

Abstract

Spectroscopic ellipsometry measurements were performed on antiferromagnetic semiconductor CuFeS 2 grown via molecular beam epitaxy. UV/Visible and IR ellipsometry data was merged and modeled to derive the dielectric function of CuFeS 2 from 30 meV to 4.5 eV. The CuFeS 2 samples were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM) and cross-section scanning electron microscopy (SEM) which gave the crystal quality, surface roughness and sample film thickness. A critical point analysis revealed a direct band gap of 0.76 eV, while modeling gives a carrier concentration of 8 ± 2 × 10 19 ~ cm −3 and an estimate of the indirect band gap of 0.5 eV. Optically active infrared phonons were observed at 319 cm −1 and 350 cm −1 with significant Raman active modes at 85.8 cm −1 , 265 cm −1 , 288 cm −1 , 318 cm −1 and 377 cm −1 . The fitted optical constants were then used to characterize the crystal quality and spatial uniformity.