Compound CuIn3Se5 Research Articles

Effect of Annealing Process on the Structural, Morphological, Optical and Electrical Properties of the Ordered Vacancy Compound CuIn3Se5 Thin Films

Effect of Annealing Process on the Structural, Morphological, Optical and Electrical Properties of the Ordered Vacancy Compound CuIn3Se5 Thin Films

Structural characterization and optical constants of CuIn3Se5 vacuum and air annealed thin films

Milled powder of ordered defect compound (ODC) CuIn3Se5 phase was successfully synthesized via milling process. Thin films of CuIn3Se5 were deposited onto glass substrates at room temperature by thermal evaporation technique. The obtained layers were annealed in vacuum and air atmosphere. The structural and compositional properties of the powder were analyzed using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Powder XRD characterization, Rietveld analysis and chemical bounding confirm the tetragonal ordered defect compound phase formation with lattice constants a = 5.732 Å and c = 11.575 Å. Thin films were characterized by XRD, atomic force microscopy (AFM) and UV/Vis spectroscopy. Transmittance (T) and reflectance (R) spectra were measured in the spectral range of 300–1800 nm. The absorption coefficient α exhibits high values in the visible range and reaches a value of 105 cm−1. The band gap energy Eg of the annealed thin films is estimated to be approximately 1.75 eV. The refractive index n was estimated from transmittance data using Swanepoel's method. The refractive indices of the films as a function of wavelengths can be fitted with Cauchy dispersion equation. The oscillator energy E0, dispersion energy Ed, zero frequency refractive index n0, high frequency dielectric constant ε∞ and the carrier concentration per effective mass N/m∗ values were determined from the analysis of the experimental data using Wemple-DiDomenico and Spitzer-Fan models. We exploited the refractive index dispersion for the determination of the magneto-optical constant V, which characterizes the Faraday rotation. The nonlinear optical parameters namely nonlinear susceptibility χ(3), nonlinear refractive index and nonlinear absorption coefficient β are investigated for the first time for CuIn3Se5 material.

Enhanced thermoelectric performance of a chalcopyrite compound CuIn3Se5\u2212xTex (x\u2009=\u20090~0.5) through crystal structure engineering

In this work the chalcopyrite CuIn3Se5−xTex (x = 0~0.5) with space group through isoelectronic substitution of Te for Se have been prepared, and the crystal structure dilation has been observed with increasing Te content. This substitution allows the anion position displacement ∆u = 0.25-u to be zero at x ≈ 0.15. However, the material at x = 0.1 (∆u = 0.15 × 10−3), which is the critical Te content, presents the best thermoelectric (TE) performance with dimensionless figure of merit ZT = 0.4 at 930 K. As x value increases from 0.1, the quality factor B, which informs about how large a ZT can be expected for any given material, decreases, and the TE performance degrades gradually due to the reduction in nH and enhancement in κL. Combining with the ZTs from several chalcopyrite compounds, it is believable that the best thermoelectric performance can be achieved at a certain ∆u value (∆u ≠ 0) for a specific space group if their crystal structures can be engineered.

Dynamic electrical conduction in p-type CuIn3Se5

In this work, ac electrical conductivity measurements were studied for the first time in p type bulk ternary semiconductor compound CuIn3Se5. The dynamic electrical conductivity is analyzed in the frequency range 20 Hz to 1 MHz and temperature from 308 K to 500 K. The relaxation times for the grain and grain boundaries were studied from the second derivative of electric modulus versus frequency at various temperatures. The relaxation time is found to decrease with increasing temperature and to obey the Arrhenius relationship. The values of activation energies for conduction and relaxation times are obtained.

An ab-initio study of CuInSe2 based ordered defect compounds

We have used the Vienna ab-initio Simulation Package (VASP) to study the electronic and optical properties of ordered defect compounds (ODC's) CuIn5Se8 and CuIn3Se5. The supercells are generated with the parent chalcopyrite structure of CuInSe2. The defect pair (2VCu−+InCu2+) in CuInSe2 plays an important role in the electronic and optical properties of the ODC's are investigated. The band structure and density of states of ODC's are discussed in terms of the parent chalcopyrite compound CuInSe2. The calculated low defect formation energy explains the existence of the ODC's CuIn5Se8 and CuIn3Se5. The optical absorption peaks in the ε2(ω) are explained in the terms of band structure and density of states. The upper valence band of ODC is exclusively formed by the p-d hybridization of Cu-3d and Se-4p states. The obtained results are in good agreement with the available experimental data. The calculated threshold values for CuInSe2 and ODC's are underestimated.

Optical properties of films of the ternary compound CuIn3Se5

We have used the laser vaporization method to obtain films of the ternary compound CuIn3Se5 and have studied the composition and structure of the films obtained. We have determined the energy and nature of the optical transitions for the indicated compound from the transmission spectra in the region of the intrinsic absorption edge. We have calculated the valence-band crystal-field (ΔCF) and spin-orbit (ΔSO) splitting energies according to Hopfield’s quasicubic model for the ternary compound CuIn3Se5.

Photoconversion in n-ZnO:Al∕PdPc∕p-CuIn[sub 3]Se[sub 5] Structures

n-ZnO:Al/PdPc/p-CuIn3Se5 photosensitive structures have been proposed and fabricated for the first time by vacuum sublimation of palladium phthalocyanine on the surface of wafers of the ternary semiconductor compound CuIn3Se5 and by magnetron sputtering of n-ZnO:Al films on the surface of palladium phthalocyanine films. The current-voltage characteristics and spectra of the photoconversion quantum efficiency of the obtained structures are investigated. It is shown that these structures can be used as multiband white-light converters.

Investigations of the electrical properties in CuInSe2 and the related ordered vacancy compounds

The conductivity mechanisms in polycrystalline CuInSe2 and the ordered vacancy compounds CuIn3Se5, CuIn5Se8 and CuIn7Se12 were studied by low temperature conductivity measurements and room temperature Hall and photoconductivity measurements. The polycrystalline films were structurally, morphologically and compositionally characterized using x-ray diffraction, atomic force microscopy and energy dispersive analysis by x-rays, respectively. In general, the films showed Mott's variable range hopping conduction in the temperature range below 200 K while above 200 K thermally activated conductivity due to grain boundary effects and defect levels was observed. To investigate the reason for the metallic behaviour shown by Cu-rich films, the films were etched and the change in behaviour was studied.

Photoemission study and band alignment of the CuInSe2(001)/CdS heterojunction

The contact formation of thin-film epitaxial CuInSe2(001) with a physical-vapor-deposited CdS layer is presented in this work. Synchrotron-excited photoelectron spectroscopy was used for this investigation. The epitaxial CuInSe2 films contain a surface layer of reduced Cu stoichiometry similar to the ordered defect compound CuIn3Se5. A valence band offset of 0.79±0.15 eV has been determined for this heterojunction. The comparison to literature data indicates that neither surface orientation nor surface copper content have a major impact on the valence band offset of CuIn3Se5, respectively, CuInSe2 with CdS.

Electrical Properties of the Ordered Defect Compound CuIn3Se5

The electrical properties of n and p-type bulk samples of CuIn 3 Se 5 have been studied in the temperature range from 80 to 300 K. From the analysis of the temperature dependence of electron and hole concentrations in the activation regime above 110 K, the activation energy and the density of states effective mass of the charge carriers are estimated to be 36meV and 0.13m e for n-type samples, and 28 meV and 1.07m e for p-type samples, respectively. The relatively low value of the carrier concentration in n-Culn 3 Se 5 and the value in p-CuIn 3 Se 5 being of the same magnitude as in CuInSe 2 confirms that this compound is formed due to the presence of ordered arrays of electrically inactive donor-acceptor defect pairs (2 V Cu 1- + In Cu 2+ ). Below 110 K, the electrical conduction in the impurity band is due to nearest neighbor hopping mechanism. The relatively low magnitude of the electron mobility and its temperature dependence in the activation regime is explained by considering, in addition to the well-established scattering processes, a mechanism that involves the scattering of the charge carriers by ordered arrays of donor-acceptor defect pairs. At lower temperatures, the variation of the mobility is explained by taking into account the theoretical model for the thermally activated nearest neighbor hopping of the charge carriers between localized states in the impurity band.

Crystal Growth and Properties of the Compounds CuGa3Se5 and CuIn3Se5

CuIn 3 Se 5 and CuGa 3 Se 5 uniform single crystals 12 mm in diameter and 40 mm in length with the chalcopyrite-related structure were prepared by directed crystallization of the melt. The melting points of these compounds were defined by means of the differential thermal analysis (DTA). The lattice parameters a and c as well as the axial thermal expansion coefficients α a and α c were determined as a function of temperature in the range from 90 to 650 K by the X-ray diffraction method (XRD). It is found that for both the compounds the coefficients of expansion along the a-axis are larger than those along the c-axis over the entire temperature range studied.

Photoelectric Properties of the In/CuIn 3 Se 5 and In/CuGa 3 Se 5 Structures

Using the method of oriented crystallization of a melt (a vertical variant), we grew homogeneous single crystals of the ternary compounds CuIn3Se5 and CuGa3Se5. Photosensitive structures based on them were created for the first time, the spectral dependences of the relative quantum efficiency of the phototransformation of structures were investigated, and the energy gap width of the ternary compounds was determined. It is established that the CuIn3Se5 and CuGa3Se5 compounds are materials with direct interband transitions. We show that the structures created can be used as wide‐band photoconverters of natural radiation.

Urbach–Martienssen’s tail in the absorption spectra of the ordered vacancy compound CuIn3Se5

The presence of Urbach–Martienssen’s tail in the absorption coefficient spectra just below the fundamental absorption edge is observed in several samples of the ordered vacancy compound CuIn3Se5 at different temperatures below 300 K. An empirical relation that takes into account the effect of structural disorder and modification in the contribution of the thermal term, caused due to the deviation from the ideal stoichiometry 1:3:5, is proposed to explain the change of Urbach’s energy KT/σ with temperature. The phonon energy involved in the electron–phonon interaction, in the absence of structural disorder, is estimated to be around 23 meV.

Raman spectra of the ordered vacancy compounds CuIn3Se5 and CuGa3Se5

The optical vibrational modes of the ordered vacancy compounds CuIn3Se5 and CuGa3Se5 have been obtained by Raman spectra at various temperatures. The totally symmetric A1 mode appears around 155 and 167 cm−1 in CuIn3Se5 and CuGa3Se5, respectively. All the lines observed, except the B1 modes, present a reduction in their frequencies by about 10% as compared to the corresponding values in the CuInSe2 and CuGaSe2 chalcopyrites. This is due to the presence in these compounds of an array of vacancies occupying particular sites in the cation sublattice. These tend to relax the stretching forces thus reducing the vibrational frequencies.

Ordered vacancy compound CuIn3Se5 on GaAs (100): Epitaxial growth and characterization

Epitaxial growth of the ordered vacancy compound CuIn3Se5 has been achieved on GaAs (100) by molecular beam epitaxy from Cu2Se and In2Se3 sources. Electron probe microanalysis and x-ray diffraction have confirmed the composition for the 1-3-5 phase and that the films are single-crystal CuIn3Se5 (100). Transmission electron microscopy characterization of the material also showed it to be single crystalline. Structural defects in the layer consisted mainly of stacking faults. Photoluminescence measurements performed at 7.5 K indicate that the band gap is 1.28 eV. Raman spectra reveal a strong polarized peak at 152 cm−1, which is believed to arise from the totally symmetric vibration of the Se atoms in the lattice.

Epitaxial Growth and Characterization of the Ordered Vacancy Compound CuIn3Se5 on GaAs (100) Fabricated by Molecular Beam Epitaxy

ABSTRACTEpitaxial growth of the ordered vacancy compound (OVC) CuIn3Se5 has been achieved on GaAs (100) by molecular beam epitaxy (MBE) from Cu2Se and In2Se3 sources. Electron probe microanalysis and X-ray diffraction have confirmed the composition for the 1-3-5 OVC phase and that the film is single crystal Culn3Se5 (100). Transmission electron microscopy (TEM) characterization of the material also showed it to be single crystalline. Structural defects in the layer consisted mainly of stacking faults. Photoluminescence (PL) measurements performed at 7.5 K indicate that the bandgap is 1.28 eV. Raman spectra reveal a strong polarized peak at 152 cm−1, which is believed to arise from the totally symmetric vibration of the Se atoms in the lattice. Atomic force microscopy reveals faceting in a preferred (100) orientation.

Influence of Morphology and Structure of Cu/In Alloys on the Properties of CuInSe2

Thin CuInSe2 films were prepared by selenization of sputtered metal precursors. The surface morphology, phase composition and adhesion at the Mo/glass substrate of the ternary compound have been correlated to the structure of the precursor. Single phase, homogeneous, small grained (1 µm) CuInSe2 arises from precursors showing stable phases (Cu11In9 and In). An ordered vacancy compound (CuIn3Se5) is likely present in In-rich (In>27 at.%) films. Precursors with a high content of the metastable CuIn2 phase show a very poor adhesion to the substrate.