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2Optical conductivity and plasma frequency of ZnImSe4 crystals
I.A. Mamedova1*, Z.A. Jahangirli1,2, E.G. Alizade1, T.G. Mammadov3, N.A. Abdullayev1,2
1-Institute of Physics Ministry of science and education. Azerbaijan, Baku, Azerbaijan 2- Baku State University, Baku, Azerbaijan
ZnIn2Se4 crystals have special properties, such as optical anisotropy, birefringence, significant nonlinear susceptibility coefficients, high photosensitivity, and bright luminescence, which makes them promising materials for optoelectronics and nonlinear optics. Using the spectral ellipsometry method, we experimentally determined the spectral dependences of the real and imaginary parts of the dielectric function and optical conductivity, refractive indices, extinction and other optical parameters of ZnIn2Se4 crystals. A comparative analysis of the obtained experimental data with theoretical calculations from the first principles was carried out. Ab initio calculations of electronic and optical properties were performed based on DFT using the full-potential linearized augmented plane waves (FP-LAPW) method implemented in the Wien2k code.
Figure 1 shows the experimentally determined optical conductivity data c=ci+ic2 (Fig. 1a), where <Ji=mso£2=2nkmsois the real part, and C2=weo(n2-k2) - is the imaginary part of the optical conductivity, as well as the theoretically calculated from first principles (Fig. 1b) real ci and imaginary part C2 of the optical conductivity for ZnIn2Se4 crystals. From the spectral dependence of the real parts of optical conductivity ci, the band gap of ZnIn2Se4 crystals is estimated.
Figure 1. (a) and (b) Spectral dependences of the real o and imaginary o2 parts of the optical conductivity of ZnIn2Se4 crystals, calculated from experimental data and from first principles, respectively. (c) - Dependency (n^k2) vs. A2 to determine the plasma frequency.
It is known that in the long-wave limit n2>>k2 the real part of the dielectric function si=n2-k2 is described by the relation [1]:
£•1 = £œ--7 = £œ--tt = ^œ — ^ , where plasma frequency rn p=e N/some* (1)
Here, e is the elementary charge, so is the dielectric constant, N is the charge carrier density, me* is the effective mass. From the dependence in Fig. 1c with linear approximation, £«=9.9, plasma frequency «p=3-1015 rad/s and N/me*=3.1-1057 m-3kg-1 are determined.
[1] S. Belgacem and R. Bennaceur, Propriétés optiques des couches minces de SnO2 et CuInS2 airless spray, Rev. Phys. Appl. (Paris) 25,
1245-1258 (1990).
