Optical spectra and energy band structure of single crystalline CuGaS₂and CuInS₂

Abstract

The reflection spectroscopy of chalcopyrite CuGaS2 and CuInS2 single crystals has been applied for light polarized perpendicular () and parallel () to the optical axis in the photon energy range between 1.5 and 6 eV at 77 K. By using the Kramers–Kronig relations, the spectral dependences of the real ε1 and imaginary ε2 components of the complex dielectric function ε(E) = ε1(E)+iε2(E) have been calculated for the investigated materials. As a result, the energy band structure of CuGaS2 and CuInS2 at photon energies higher than the fundamental band gap is derived from the analysis of the structures observed in ε(ω) spectra. Additionally, the spectral dependences of the complex refractive index, extinction coefficient and absorption coefficient s of CuGaS2 and CuInS2 single crystals are determined in the 1.5–6 eV photon energy range.

Electronic, optical and elastic properties of CuXS2 (X=Al, Ga, In) and AgGaS2 semiconductors from first‐principles calculations

“…The obtained equations of linear fits in Fig. 2 are as follows (in all equations V is the volume in nm 3 and B is the bulk modulus in GPa: for CuInS 2 : B=-442.3 + 172.5/V; for AgGaS 2 : B=-92.9 + 54.4/V; for CuAlS 2 : B=-488.9 + 163.6/V; for CuGaS 2 : B=-402.4 + 169.1/V. A similar analysis of dependence of the bulk modulus on pressure has been performed for the III-V [18] and for TlN, TlP, TlAs [19] compounds.…”

“…[2], energy band structure of CuGaS 2 and CuInS 2 was analyzed in Ref. [3]. Several examples of the first-principles calculations for some materials from this group also can be mentioned; in particular, the CuAlS 2 [4] and CuGaS 2 , AgGaS 2 band structures [5] were calculated.…”

Energy Generation: Solar Energy

“…Figures 2.9 and 2.10 [98] show calculations of the imaginary part of the macroscopic dielectric function for light polarized along the c-axis. The theoretical curves are also compared with the experimental data published in Levcenko et al [86] and Rife et al [128].…”

“…One should remember however that CIGS materials possess bound excitons [85][86][87][88], and that the TDDFT-LRC approach has proved to work better for systems with continuum excitons. That is why the only fully reliable approach in this case is the solution of the computationally demanding BSE or the use of a more sophisticated model kernel, which accurately describes the electron-hole pair dynamics [48,50,52,53].…”

“…The experimental dielectric functions of Alonso et al [99] were obtained with ellipsometry at room temperature, whereas the spectra of Levcenko et al [86] were …”