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The dielectric functions of Cu2ZnGeS4 bulk crystals grown by the Bridgman method were measured over the energy range 1.4 to 4.7 eV at room temperature using variable angle spectroscopic ellipsometry. The observed structures in the dielectric functions were adjusted using the Adachi's model and attributed to interband transitions E0, E1A, and E1B at Γ:(000), N(A):2π/a(0.5 0.5 0.5), and T(Z):2π/a(0 0 0.5) points of the first Brillouin zone, respectively. The model parameters (threshold energy, strength, and broadening) have been determined using the simulated annealing algorithm. The decrease in the first gap, E0, has been attributed to a higher Ge-S hybridization. The spectral dependence of the complex refractive index, the absorption coefficient, and the normal-incidence reflectivity were also derived. [ABSTRACT FROM AUTHOR]

Spectroscopic ellipsometry has been used to characterize the dielectric functions of bulk Cu(In1-xGax)5Se8 crystals. Spectra were measured at room temperature over the energy range 0.74–5.2 eV. The dielectric functions as well as the complex refractive index, the absorption coefficient, and the normal-incidence reflectivity have been modeled using a modification of the Adachi model. The results are in a good agreement with the experimental data over the entire range of photon energies. The model parameters (strength, threshold energy, and broadening) have been determined using the simulated annealing algorithm. The transition energies E0 and E1A are found to shift linearly to higher energies as the gallium content increases. [ABSTRACT FROM AUTHOR]

Using spectroscopic ellipsometry we investigated and analyzed the pseudo-optical constants of Cu2ZnSnSe4 bulk crystals, grown by the Bridgman method, over 0.8-4.5 eV photon energy range. The structures found in the spectra of the complex pseudodielectric functions were associated to E0, E1A, and E1B interband transitions and were analyzed in frame of the Adachi's model. The interband transition parameters such as strength, threshold energy, and broadening were evaluated by using the simulated annealing algorithm. In addition, the pseudo-complex refractive index, extinction coefficient, absorption coefficient, and normal-incidence reflectivity were derived over 0.8-4.5 eV photon energy range. [ABSTRACT FROM AUTHOR]

Abstract: A comparative study of chalcopyrite-related Cu2In7Se11.5 and CuIn5Se8 crystals by spectroscopic ellipsometry is presented. Their complex dielectric function ɛ(ω)= ɛ 1(ω)+ iɛ 2(ω) has been determined in the 0.8–4.7eV photon energy range. The spectral dependence of ɛ 1(ω) and ɛ 2(ω) as well as the complex refractive index, the absorption coefficient and the normal-incidence reflectivity for tetragonal Cu2In7Se11.5 and trigonal CuIn5Se8 crystals have been modelled using the Adachi''s model for interband transitions. The results are in a good agreement with the experimental data over the entire range of photon energies. The model parameters, including the energies corresponding to the lowest direct gap (E 0) and higher critical points (E 1A , E 1B ), have been determined using the simulated annealing algorithm. The results show that the tetragonal CuIn3Se5, the tetragonal Cu2In7Se11.5 and the trigonal CuIn5Se8 crystals belong to different phases of the Cu4In2n Se2+3n system, n =6, n =7 and n =10, respectively. [Copyright &y& Elsevier]

Abstract: We report the room temperature spectroscopic ellipsometry study of Cu2ZnGeSe4 and Cu2ZnSiSe4 crystals, grown by modified Bridgman technique. Optical measurements were performed in the range 1.2–4.6 eV. The spectral dependence of the complex pseudodielectric functions as well as pseudo- complex refractive index, extinction coefficient, absorption coefficient, and normal-incidence reflectivity of Cu2ZnGeSe4 and Cu2ZnSiSe4 crystals were derived. The observed structures in the optical spectra were analyzed by Adachi's model and attributed to the band edge transitions and higher lying interband transitions. The parameters such as strength, threshold energy, and broadening, corresponding to the E 0, E 1A and E 1B interband transitions, have been determined using the simulated annealing algorithm. [Copyright &y& Elsevier]