Defect Chalcopyrite Research Articles

Electron energy structure of defect chalcopyrite CdGa2Se4

The CdGa2Se4 compound, with a crystalline lattice of defect chalcopyrite, shows birefringence. However, in contrast to the similar CdGa2S4 compound, CdGa2Se4 has no experimentally observed isotropic points in the optical spectral range. In this study, the electron energy structure and optical spectra of CdGa2Se4 are calculated for three different experimentally obtained sets of crystalline parameters. Only one of these sets shows the absence of isotropic points.

Bulk Modulus and Electronic Band Structure of ZnGa2X4 (X = S,Se): a First-Principles Study

First-principles local density functional calculations are presented for the compounds ZnGa2X4 (X = S,Se). We investigate the bulk moduli and electronic band structures in a defect chalcopyrite structure. The lattice constants and internal parameters are optimized. The electronic structures are analysed with the help of total and partial density of states. The relation between the cohesive energy and the unit cell volume is obtained by fully relaxed structures. We derive the bulk modulus of ZnGa2X4 by fitting the Birch–Murnaghan's equation of state. The extended Cohen's empirical formula agrees well with our ab initio results.

Fabrication, Characterization and Optical Studies of Cu(In1-xGax)3Se5 Bulk Compounds

AbstractIn this paper we present the structural and optical properties of Cu(In1-xGax)3Se5 ternary and quaternary compounds crystals fabricated by horizontal Bridgman technique. The Cu(In1-xGax)3Se5 materials were characterized by Energy Dispersive Spectrometry (EDS), hot point probe method, X-ray diffraction, Photoluminescence (PL), and Optical response (Photoconductivity). The Cu(In1-xGax)3Se5 have an Ordered Vacancy Chalcopyrite-type structure with lattice constants varying as a function of the x composition. A good stœchiometry given by the EDS characterization method is well observed in our samples and its magnitude deviation Δy is slight; so, our samples present a nearly perfect stœchiometry (Δy = 0) [1]. X-Ray diffraction patterns show the presence of many preferential orientations according to the planes (112), (220) and (312) of all the samples [2]. Also, it shows a linear shifting of peaks towards the higher magnitudes of 2θ when the x composition increases. These compounds can be of stanite structure [3] or an Ordered Vacancy Chalcopyrite structure (OVC) [4] or Ordered Defect Chalcopyrite Structure (ODC). We observe a large shift of the main PL and optical response emission peak versus x composition. The band gap energy of Cu(In1-xGax)3Se5 compounds is found to vary from 1.23 eV to 1.85 eV as a function of x. [1] Migual A. Contreras, Holm Wiesner, Rick Mtson, John Tuttle, Kanna Ramanathan, Rommel Noufi, Mat. Res. Soc. Symp. Proc. Vol. 426 (1996) 243-254. [2] Ariswan, G. El Haj Moussa, M. Abdelali, F. Guastavino, C. Llinares, Solid State Communications 124 (2002) 391-396. [3] M. Suzuki, T. Uenoyama, T. Wada, T. Hanada, Y. Nakamura, Jpn. J. Appl. Phys. 36 L1139 (1997). [4] Kristjan Laes, Sergei Bereznev, A. Tverjanovich, E.N. Borisov, Tiit Varema, Olga Volobujeva , Andres Öpik. Thin Solid Films 517 (2009) 2286–2290.

Ordinary and extraordinary phonons and photons: Raman study of anisotropy effects in the polar modes ofMnGa2Se4

We present a spectroscopic study of optovibrational properties of ${\text{MnGa}}_{2}{\text{Se}}_{4}$, an ordered-vacancy compound with defect chalcopyrite structure and uniaxial optical behavior. Anisotropy affects the Raman spectrum of noncentrosymmetric media in two different ways: for nonpolar modes, birefringence produces a dephasing between ordinary and extraordinary waves that results in an apparent violation of selection rules. In polar modes, in addition, anisotropy affects phonon propagation, resulting in the phenomenon of directional dispersion. The Raman spectrum of ${\text{MnGa}}_{2}{\text{Se}}_{4}$ single crystals is measured onto three different crystallographic planes as a function of the polarization direction of incident and scattered light. Loudon equations are used to assign the symmetry and character of each mode. Two different regimes are found: For low-frequency modes, polarity is weaker than anisotropy effects and these modes show negligible directional dispersion. On the contrary, for high-frequency modes, anisotropy effects are negligible and these modes behave as quasicubic ones. By analyzing the intensities of the polar modes, information concerning the electron-phonon mechanisms involved in the activity of polar modes is obtained. The relative magnitude of electro-optic to deformation potential mechanisms participating in LO modes is derived.

Fermi resonance in the Raman spectrum of the Se-vacancy breathing mode ofMnGa2Se4

We present a Raman study of anharmonic phonon-lifetime broadening in $\mathrm{Mn}{\mathrm{Ga}}_{2}{\mathrm{Se}}_{4}$, an ordered-vacancy compound with defect chalcopyrite structure. Contrary to the well studied zinc-blende compounds, defect chalcopyrites present 13 Raman active phonons, which allow for the detection of anharmonic effects in phonons of symmetry other than ${\ensuremath{\Gamma}}_{15}$. In this work, we focus on the ${\ensuremath{\Gamma}}_{1}$ breathing mode of the Se tetrahedron around the vacancy, an intense characteristic feature of all OVCs, found at $135\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ in $\mathrm{Mn}{\mathrm{Ga}}_{2}{\mathrm{Se}}_{4}$. The temperature dependences of the energy, linewidth, and asymmetry of the breathing mode are explained as due to anharmonic coupling with a two-phonon continuum. Within that model, the fit of the spectrum as a function of temperature provides the evolution of the bare single- and two-phonon coupled excitations, as well as that of the coupling parameter. A residual linewidth of about $0.2\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$, not accounted for by the anharmonic decay model, is attributed to the Se isotope-mass fluctuation contribution.

Structural characterization and electrical properties of quaternary CdGaInSe 4 thin films

Stoichiometric bulk ingot material of the quaternary CdGaInSe 4 was prepared by direct fusion of the constituent elements in vacuum-sealed silica tubes. Nearly stoichiometric films could be deposited by thermal evaporation of the ingot material in 10 −3 Pa vacuum at a deposition rate 1.5 nm/s. Crystal structure investigation was carried out using X-ray diffractometry and transmission electron diffraction. Elemental composition was determined by means of energy-dispersive X-ray spectrometry. CdGaInSe 4 possesses a tetragonal defective chalcopyrite structure (space group I ¯ 4 ) with lattice parameters a=0.5665 nm and c=1.1221 nm. All the films exhibited n-type conduction and ohmic behaviour with metallic films of Au, Cd, In, Ag and Sb. However, in the case of Al a nonlinear behaviour occurs. Analysis of the temperature dependence of the dark conductivity in the range 130–470 K has revealed three operating conduction mechanisms; a variable range hopping conduction process dominating at low temperatures below 270 K, followed by a transport of the charge carriers across intercrystalline barriers and grain boundaries in the temperature range 270–353 K, and finally an extrinsic conduction above 353 K.

The influence of magnetic dilution in the Zn1−xMnxGa2Se4 series with 0.5<x⩽1

The Zn1−xMnxGa2Se4 system with 0.5<x<1, which represents a magnetic dilution of the tetragonal MnGa2Se4, retains the defective chalcopyrite structure of the parent compound. Neutron powder diffraction experiments and temperature dependent magnetic susceptibility measurements show that such dilution has a significant influence on the magnetic properties of the system. The distance between the closest magnetic atoms decreases from a to a∕2Å (where a is the lattice parameter and a≈5.6Å), making the Curie-Weiss temperature greater than the expected value. The magnetic dilution also decreases the internal distortion, so that the structure becomes closer to that of the ideal zinc-blende arrangement. Although MnGa2Se4 behaves as an antiferromagnet below TC=6.4±0.1K, the magnetic properties of Zn1−xMnxGa2Se4 with 0.5<x<1 suggest a glassy type behavior at low temperatures. This magnetic behavior is found to be compatible with the distribution of the Mn ions within the lattice and can be tuned by tailoring the concentration of magnetic ions. Surprisingly, the magnetically undiluted system corresponding to the Zn1−xMnxGa2Se4 0.5<x<1 series is not MnGa2Se4, a magnetic lattice with a body centered cubic symmetry, but a structure possessing a greater number of sites available to the magnetic ions.

The influence of pressure on the birefringence in semiconductor compounds ZnS, CuGaS2, and InPS4

AbstractUsing the modified method of augmented plane waves and the code WIEN2k the calculations of the electron band structure, densities of electron states, and imaginary part of dielectric response function were carried out for different polarization of the vector of electrical field εxx and εzz for the semiconductor compounds ZnS, CuGaS2, and InPS4. The calculations were performed both for undisturbed crystals and for distorted crystals due to the applied pressure. The compounds studied have the similar crystallographic structures: ZnS – sphalerite, CuGaS2 – chalcopyrite, and InPS4 – twice defective chalcopyrite. It is known, that in cubic ZnS there is no birefringence, whereas in CuGaS2 and InPS4 there is one. But CuGaS2 has so called isotropic point (where εxx = εzz) in the visible optical range, and InPS4 has no such point. Our calculations of εxx and εzz have shown that in ZnS under the pressure the isotropic points arise, but in InPS4 they do not exist. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

High pressure X-ray diffraction study of CdAl2Se4 and Raman study of AAl2Se4 (A=Hg, Zn) and CdAl2X4 (X=Se, S)

We report the results of an X-ray diffraction study of CdAl2Se4 and of Raman studies of HgAl2Se4 and ZnAl2Se4 at room temperature, and of CdAl2S4 and CdAl2Se4 at 80 K at high pressure. The ambient pressure phase of CdAl2Se4 is stable up to a pressure of 9.1 GPa above which a phase transition to a disordered rock salt phase is observed. A fit of the volume pressure data to a Birch–Murnaghan type equation of state yields a bulk modulus of 52.1 GPa. The relative volume change at the phase transition at ∼9 GPa is about 10%. The analysis of the Raman data of HgAl2Se4 and ZnAl2Se4 reveals a general trend observed for different defect chalcopyrite materials. The line widths of the Raman peaks change at intermediate pressures between 4 and 6 GPa as an indication of the pressure induced two stage order–disorder transition observed in these materials. In addition, we include results of a low temperature Raman study of CdAl2S4 and CdAl2Se4, which shows a very weak temperature dependence of the Raman-active phonon modes.

Effect of Cu/Al ratio on the properties of CuAlSe 2 thin films prepared by co-evaporation

Cu-rich, near-stoichiometric and Al-rich CuAlSe 2 thin films were deposited by elemental co-evaporation technique on glass substrates held at 673 K. Powder X-ray diffraction studies revealed that the Cu-rich CuAlSe 2 films contain Cu 2Se as second phase while near-stoichiometric and Al-rich CuAlSe 2 films are single phase. The Cu-rich and near-stoichiometric films are found to have chalcopyrite structure and the Al-rich films have defect chalcopyrite structure due to formation of ordered vacancy compound CuAl 2Se 3.5. The optical band gaps of Cu-rich, near-stoichiometric and Al-rich films determined from optical absorption studies are found to be 2.48 eV, 2.62 eV and 2.87 eV respectively. The electrical conductivity studies revealed that the Cu-rich and stoichiometric films are p-type and Al-rich films are n-type conducting. The resistivity of the films is found to increase with decrease in Cu/Al ratio.

Growth of ZnInGaS 4 by normal freezing method

The crystal structure and phase transition of ZnInGaS 4 were described. The ZnInGaS 4 had both a defect chalcopyrite and a layered structure below 920 °C, and only the layered structure ZnInGaS 4 existed between 920 and 1020 °C. The layered structure ZnInGaS 4 was grown using the normal freezing method. The bandgap of the layered structure ZnInGaS 4 was estimated to be approximately 2.6 eV and it is possibly a direct bandgap. This is a first step toward realizing the novel functions of ZnInGaS 4.

Optical phonon modes and structure of ZnGa 2Se 4 and ZnGa 2S 4

We present the infrared and Raman study of the optical phonon modes of the defective compounds ZnGa 2Se 4 and ZnGa 2S 4. Most of the A II B 2 III C 4 VI compounds have been found to crystallize in the thiogallate structure (defect chalcopyrite) with space group I 4 ¯ where all cations and vacancies are ordered. For some Zinc compounds a partially disordered cationic sublattice with various degrees of cation and vacancy statistical distribution, which lead to the higher symmetry I 4 ¯ 2 m (defect stannite), has been reported. For ZnGa 2Se 4 we have found three modes of A symmetry, showing Raman activity only. In addition, we have observed each five modes of B and E symmetry, showing infrared as well as Raman activity. The number of modes and their symmetry assignment, based on polarized measurements, clearly indicate space group I 4 ¯ for the investigated crystals of ZnGa 2Se 4. Regarding ZnGa 2S 4 we have found three modes exclusively showing Raman activity (2 A⊕1 B 1), and only eight modes showing infrared as well as Raman activity (3 B 2⊕5 E). The assignment of the modes has been derived by analyzing the spectral positions of the vibrational modes in comparison to a number of A II B 2 III C 4 VI compounds. From the number and symmetry assignment of the optical phonon modes we confirm that ZnGa 2S 4 most likely crystallizes in space group I 4 ¯ 2 m .

Optical properties of ZnHgGa4Se8 and ZnHgGa4Se8:Co2+ single crystals

[ <TEX>$ZnHgGa_4Se_8\;and\;ZnHgGa_4Se_8::Co^{2+}$</TEX> ] single crystals were grown by the Bridgman-Stockbarger method. The single crystals crystallized into a defect chalcopyrite structure. The optical energy band gap of the single crystals was investigated in the temperature range 11-300K. The optical energy band gap of the <TEX>$ZnHgGa_4Se_8:Co^{2+}$</TEX> single crystal was smaller than that of the <TEX>$ZnHgGa_4Se_8$</TEX> single crystal. The temperature dependence of the optical energy band gap of the single crystals was well fitted by the Varshni equqtion. The impurity optical absorption spectrum of the <TEX>$ZnHgGa_4Se_8:Co^{2+}$</TEX> single crystal was measured in the wavelength region 300-2300 m at 80 K. Impurity absorption peaks in the spectrum were analyzed within the framework of the crystal field theory and were attributed to the electron transitions between the energy levels of <TEX>$Co^{2+}$</TEX> sited in the Td symmetry point.

Raman selection rules in uniaxial media: The nonpolar modes ofMnGa2Se4

It is known that optically anisotropic media can change the polarization of light propagating inside them. As regards Raman spectroscopy, this affects the light intensity measured in different geometrical configurations and results in an apparent unfulfillment of selection rules. We present an experimental and theoretical study of such effects in the defect chalcopyrite semiconductor $\mathrm{Mn}{\mathrm{Ga}}_{2}{\mathrm{Se}}_{4}$. Optical anisotropy is taken into account by including in the calculation of Raman intensities the phase difference appearing between ordinary and extraordinary waves as they propagate, in uniaxial media, with different velocities. Birefringence can be obtained from Raman measurements provided that the distance run by the light is known.

Crystal Structure and Optical Properties of Defect-Chalcopyrite-Type MnGa2S4

The crystal structure of MnGa2S4 grown by the iodine transport method was refined by Rietveld analysis of its powder X-ray diffraction data, and it was confirmed to be the defect chalcopyrite structure. No emissions can be observed near the absorption edge region, but a red broad emission band having an asymmetric spectral shape with a low-energy tail is observed in the deep region at room temperature. The red broad emission band is considered to be due to the transition from the lowest excited state 4T1(4G) to the ground state 6A1(6S) of the Mn2+ ion, because five photoluminescence excitation bands corresponding to five optical absorption bands are assigned to transitions from the ground state 6A1(6S) to the excited states 4T1(4G), 4T2(4G), 4E(4G)+4A1(4G), 4T2(4D) and 4E(4D). The role of the Mn2+ ion with respect to the luminescence property of the defect-chalcopyrite-type MnGa2S4 is similar to its role with respect to the luminescence property of zinc-blend-type Mn-doped ZnS. This is reasonable because the Mn2+ ion is tetrahedrally coordinated by four S2- ions in both the defect-chalcopyrite-type MnGa2S4 and the zinc-blend-type Mn-doped ZnS.

Temperature dependence of the structural and optical properties of the amorphous-to-crystalline transition in CdGa2Se4 thin films

Nearly stoichiometric thin films of CdGa2Se4 were deposited, by conventional thermal evaporation of presynthesized ingot material, onto quartz and Corning glass substrates. The chemical composition of the samples was determined by means of energy-dispersive X-ray spectrometry. X-ray diffraction studies revealed that the as-deposited and annealed films at Ta = 473 and 573 K have an amorphous phase, while those annealed at Ta ≥ 673 K are crystalline with a single phase of a defective chalcopyrite structure similar to that of the synthesized material. The unit cell lattice parameters of both the synthesized material and the crystalline films were determined and compared with reported data. The optical constants (n, k) and the film thickness (t) of the films were determined from optical transmittance data using the Swanepoel method. The dispersion parameters were determined from an analysis of the refractive index. An analysis of the optical absorption spectra revealed a non-direct energy gap characterizing the amorphous films, while a direct energy gap characterized the crystalline films. The annealing temperature dependence of the corresponding energy gaps was found to fit a polynomial equation. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Absorption and photoluminescence studies of CdGa 2S 4:Cr

The potential of using ternary defect chalcopyrites as laser active materials is investigated by performing absorption, photoluminescence, and EPR studies of as-grown and vacuum annealed Cr-doped CdGa 2S 4. Although no consistent affect of annealing is observed, an increased concentration of Cr in the melt during growth is shown to broaden an absorption band at 1288 nm. Several of the absorption bands could be attributed to multiple charge states of Cr thought to be present in the crystal. A broad fluorescence was observed at visible wavelengths; however, no emission was detected in the middle-infrared region, contrary to expectation. The lack of infrared fluorescence may be attributed to an exchange interaction involving Cr impurities.

Electronic band structure of ordered vacancy defect chalcopyrite compounds with formulaII−III2−VI4

First-principles local-density-functional calculations are presented for the electronic band structures of the ordered vacancy defect chalcopyrites with formula $\mathrm{II}\ensuremath{-}{\mathrm{III}}_{2}\ensuremath{-}{\mathrm{VI}}_{4}$ for $\mathrm{II}=\mathrm{Zn},$ Cd, Hg, $\mathrm{III}=\mathrm{Al},$ Ga, In, and $\mathrm{VI}=\mathrm{S},$ Se, Te. Their relationship with the band structure of their parent chalcopyrite compounds $\mathrm{I}\ensuremath{-}\mathrm{III}\ensuremath{-}{\mathrm{VI}}_{2}$ with $\mathrm{I}=\mathrm{Cu},$ Ag, and their grand parent II-VI compounds is clarified. An empirical correction for the band gaps beyond local-density approximation is introduced and shown to give good agreement for cases where data are available. The chemical trends are discussed.

Antisite creation in ternary semiconductors by transmutation doping

Ternary semiconductors □AIIB2IIIC4VI with defect chalcopyrite structure offer the possibility to study various cation antisites in a single substance. We report on experiments aiming to position a B-atom, namely In, on the vacancy site, labelled B□. Radioactive 117Ag (T1/2=73s), decaying to 117Cd (T1/2=2.4h) and furthermore to 117In, was implanted into □CdGa2Se4 and incorporated at the vacancy-site by in situ thermal annealing. We have determined the lattice site of 117Cd(117In) by perturbed γ–γ angular correlation (PAC) spectroscopy as the Cd-site (117InCd) and not 117In□. This is explained with 117Cd being expelled from the vacancy-site due to the recoil following the nuclear decay of 117Ag. The displacement energy of Cd□ has been estimated to be smaller than 16eV.

Zone center wavenumbers of tetragonal AGa2X4 (A = Cd, Zn; X = S, Se)

AbstractA short‐range force constant model (SRFCM) was applied to investigate the phonons in AGa2X4 (A = Cd, Zn; X = S, Se) defect chalcopyrite compounds in the tetragonal phase. The calculation with six stretching and one bending force constants in the SRFCM agrees well with the observed Raman and infrared wavenumbers. In CdGa2X4, the nearest Ga—X interatomic force constants of its bonds were found to be stronger than the nearest Cd—X interatomic force constants, whereas in ZnGa2X4, the nearest Zn—X interatomic force constants of its bonds were found to be weaker than the nearest Zn—X interatomic force constants. The variation of interatomic force constants is discussed. The dominant force constants have nearly the same ratio when Se replaces S. Copyright © 2003 John Wiley &amp; Sons, Ltd.