Dielectric function and band gap determination of single crystal CuFeS2 using FTIR-VIS-UV spectroscopic ellipsometry

Abstract

Spectroscopic ellipsometry measurements were performed on antiferromagnetic semiconductor CuFeS2 grown via molecular beam epitaxy. UV/Visible and IR ellipsometry data was merged and modeled to derive the dielectric function of CuFeS2 from 30 meV to 4.5 eV. The CuFeS2 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 × 1019~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.