A spectroscopic ellipsometric investigation of new critical points of Zn1−xMnxS epilayers

Zn1−xMnxS epilayers were grown on GaAs (1 0 0) substrates by hot-wall epitaxy. X-ray diffraction (XRD) patterns revealed that all the epilayers have a zincblende structure. The optical properties were investigated using spectroscopic ellipsometry at 300 K from 3.0 to 8.5 eV. The obtained data were analyzed for determining the critical points of pseudodielectric function spectra, 〈ɛ(E)〉 = 〈ɛ1(E)〉 + i〈ɛ2(E)〉, such as E0, E0 + Δ0, and E1, and three E2 (Σ, Δ, Γ) structures at a lower Mn composition range. These critical points were determined by analytical line-shapes fitted to numerically calculated derivatives of their pseudodielectric functions. The observation of new peaks, as well as the shifting and broadening of the critical points of Zn1−xMnxS epilayers, were investigated as a function of Mn composition by ellipsometric measurements for the first time. The characteristics of the peaks changed with increasing Mn composition. In particular, four new peaks were observed between 4.0 and 8.0 eV for Zn1−xMnxS epilayers, and their characteristics were investigated in this study.