Dielectric functions and optical constants modeling for CuIn 3Se5 and CuIn5Se8

The complex dielectric functions, ε (ω) = ε1 (ω) +i ε2 (ω), of CuIn3Se5 and CuIn5Se8 crystals with different Cu contents have been determined in the 0.8-4.7 eV photon energy range by using spectroscopic ellipsometry. The spectral dependence of the real, ε1 (ω), and imaginary, ε2 (ω), parts of ε (ω), as well as the complex refractive index, the absorption coefficient, and the normal-incidence reflectivity, has been modeled by using a modification of Adachi's model. The results are in excellent agreement with the experimental data over the entire range of photon energies. The model parameters, including the energies corresponding to the lowest direct gap, E0, and to higher critical points, have been determined by using the simulated annealing algorithm. © 2008 American Institute of Physics.Peer Reviewe

Modeling the optical constants of Cu2 In4 Se 7 and Cu Ga3 Se5 crystals

Spectral dependence of the pseudodielectric function ε (E) = ε1 (E) +i ε2 (E) as well as of the complex refractive index, extinction coefficient, absorption coefficient, and normal-incidence reflectivity of Cu2 In4 Se7 and Cu Ga3 Se5 ordered vacancy compound crystals are modeled in the 0.8-4.4 eV photon energy range using a modification of Adachi's model [T. Kawashima J. Appl. Phys. 84, 5202 (1998)] for optical properties of semiconductors. Model parameters are determined using the acceptance- probability-controlled simulated annealing method. Excellent agreement with experimental data is obtained; the relative errors for the real ε1 and for imaginary ε2 part of the dielectric function are equal to 0.9%-1.5% and 3.2%-4.1% for the studied compounds. © 2007 American Institute of Physics.Peer Reviewe

Dielectric functions and fundamental band gaps of Cu2In 4Se7, CuGa3Se5 and CuGa 5Se8 crystals

Room temperature pseudodielectric function spectra ε(ω) ≤ ε1 (ω) + iε2(ω) of the ordered defects compounds Cu2In4Se7, CuGa 3Se5 and CuGa5Se8 have been measured by spectroscopic ellipsometry. The values of refractive index n and extinction coefficient k are given. The structures observed in ε(ω) spectra have been analysed using different methods, including fitting the numerically differentiated experimental spectrum (second derivative) to analytical line shapes. As a result, the energies corresponding to the fundamental gap (E 0) and higher critical points have been determined. A linear correlation of the fundamental gap values with Ga/Cu atomic ratio contents in CuGaxSey samples is deduced. © 2007 IOP Publishing Ltd.Financial support from the INTAS Program (Project 03-51-6314) Comunidad de Madrid (Project FOTOFLEX S-0505/ENE/0123) and from the Spanish Government MEC projects ENE 2004-07446-C02-01/ALT/ and MAT2003- 01490 is acknowledged.Peer Reviewe

Optical constants of Cu Ga5 Se8 crystals

Spectral dependence of the real ε1 (ω) and imaginary ε2 (ω) parts of the complex dielectric function, complex refractive index, absorption coefficient, and normal-incidence reflectivity of Cu Ga5 Se8 crystals with slightly different Cu contents are modeled using Adachi's model for interband transitions. The results are in good agreement with the experimental data over the entire range of photon energies. The model parameters are determined using the simulated annealing algorithm. © 2007 American Institute of Physics.Peer Reviewe

Optical characterization of CuIn3Se5, CuGa 3Se5 and CuGa5Se8 crystals by spectroscopic ellipsometry

The ellipsometric spectra of CuIn3Se5, CuGa 3Se5 and CuGa5Se8 ordered vacancy compounds (OVC) have been studied in the spectral range from 0.8 to 4.4 eV. The structures observed in the measured spectra were analyzed by fitting the second derivative of the experimental spectrum to analytical line shapes. The energies corresponding to different electronic transitions were determined. The lowest direct gap (E0) is characterized by 3-dimensional critical points, while higher energy structures are characterized by 2D critical points. Optical constants related to dielectric function, such as the complex refractive index n*(ω), extinction coefficient k(ω), absorption coefficient 0(ω), and normal-incidence reflectivity R(ω), of studied OVC were determined. © 2006 WILEY-VCH Verlag GmbH & Co. KGaA.Financial support from INTAS program (Project 03-51-6314) and from Spanish government MEC project ENE 2004-07446-C02-01/ALT/ are acknowledged.Peer Reviewe

Observation of local electron states linked to the quasi-Fermi level

We report on the observation of semiconductor local electron states linked to the quasi-Fermi level and, consequently, not characterized by the defined position in the energy spectrum which is familiar for shallow and deep impurities. This type of local electron states have been found in the doped narrow-gap semiconductor Pb1−xSnxTe(In). The binding energy of these states is less than 10 meV providing photoresponse at the wavelengths exceeding 100 μm

Magnetic-field-induced terahertz photogeneration in PbTe(Ga)

It has been shown that a magnetic field in PbTe(Ga) single crystals induces the appearance of a positive photoresponse in the terahertz spectral range. Nonequilibrium charge carriers are generated from states located against the background of the continuum of the conduction band near the quasi-Fermi level. The density of states on the quasi- Fermi level is a critical parameter responsible for the process of generation