Detection of local vibrational modes induced by intrinsic defects in undoped BaSi2 light absorber layers using Raman spectroscopy

Abstract

We fabricate BaSi2 epitaxial films on Si(111) substrates by molecular beam epitaxy and investigate point defects inside the films using Raman spectroscopy with the help of first-principles calculation. Point defects such as Ba substituted for Si antisites, Si vacancies, and Si interstitials are considered as candidates for native point defects in BaSi2. Vibration analysis based on first-principles calculation suggests that local vibrational modes caused by these point defects appear at around 430, 480, and 560 cm−1, respectively, and are in good agreement with Raman peak positions. Comparing calculations with Raman spectra of the films formed with different Ba to Si deposition rate ratios RBa/RSi from 1.0 to 5.1, we conclude that the density of point defects reaches a minimum at RBa/RSi = 2.2. Furthermore, the position of Raman peaks at approximately 490 cm−1 shifts to a lower wavenumber, depending on RBa/RSi and thereby the density of point defects.