Defect Chalcopyrite Research Articles

Effect of rare earth ions on the optical and electronic properties of defect chalcopyrite: Experimental and theoretical investigation

The present research is a systematic experimental and computational study focused on structural, electronic, and optical properties of ZnGa2S4 doped with neodymium rare earth ions for the first time. High-intensity, narrow-band luminescence peaks are observed in the visible and infrared regions by doping the matrix with Nd ions. These peaks in the background of the broadband spectrum are due to intercenter 4f-4f transitions of Nd3+ ions. The fact that the Raman peaks of the alloy crystal are more intense than that of the pure crystal confirms that the neodymium does not move freely in the lattice and occupies the place of defects. This confirms the results from our X-ray structural analysis. The crystal lattice parameters of the studied materials were determined as follows: a = 5.496 Å, c = 10.99 Å, c/a = 2. To explain the electronic, optical and magnetic properties, using ATK-DFT method, electronic energy band structure, density of states and optical spectrum for pure and doped with ZnGa2S4:Nd compound are computed and discussed. DFT result shows that impurity Nd leads to a decreased bandgap of ZnGa2S4 due to the hybridization of Nd-4d with S-3p orbital in the forbidden gap. The peaks in the optical spectrum are shifted toward the lower energy range for doped supercell.

Insights into the optoelectronic and thermoelectric properties of defect chalcopyrites XAl2Se4 (X = Zn, Cd, and Hg): A density functional theory approach

In the current study, we employed the full-potential linearized augmented plane wave plus local orbitals (FP-LAPW + lo) approach within the density functional theory (DFT) to investigate the physical properties of Defect Chalcopyrites XAl2Se4 (X = Zn, Cd, and Hg). Calculations yield precise structural and electronic parameters in good agreement with experimental data, revealing all three compounds as direct wide-bandgap semiconductors. The modified Becke-Johan potential (TB-mBJ) method accurately estimates energy gaps, which increase with decreasing lattice constants. The calculated values are 3.34 eV, 3.12 eV, and 2.30 eV for ZnAl2Se4, CdAl2Se4, and HgAl2Se4, respectively. The optical properties, including dielectric function and absorption coefficient, indicate potential applications in visible and ultraviolet optoelectronic devices. The high anisotropy of these materials further enhances their suitability for a range of linear and nonlinear optical applications. Moreover, ZnAl2Se4 exhibits the highest Seebeck coefficient at room temperature. The positive Seebeck coefficient confirmed the p-type behavior of the studied compounds. The highest observed power factor demonstrates optimal thermoelectric performance for these materials. High electrical conductivity values suggest their suitability as effective electrical conductors, especially at elevated temperatures. This study encourages further research into defect chalcopyrites for applications in optoelectronics and thermoelectric energy conversion.

Investigation of structural, electronic, mechanical, and thermoelectric properties of the defect chalcopyrite semiconductor ZnIn[formula omitted]Se[formula omitted] from density functional theory

In this study, the detailed structural, electronic, mechanical, and thermoelectric properties of ZnIn2Se4 defect chalcopyrite semiconductor are carried out using density functional theory & semi-classical Boltzmann transport theory. From the band structure analysis, the compound is confirmed to be a direct band gap semiconductor with a band gap of 1.20 eV. The presence of flat valence bands near the Fermi level indicates a higher effective mass of holes. From the elastic and mechanical properties, it has been found that the compound is mechanically stable and revealed to be ductile. The phonon dispersion study of the compounds shows that the compound is dynamically stable with no imaginary phonon modes. The electronic transport properties were studied within a temperature range of 300K to 900K as a function of chemical potential (μ), temperature(T), and carrier concentrations (n). The μ dependent electronic transport properties show enhanced values in the p-type doping region because of the cationic site vacancy. The dependency of electronic transport properties on n and T agrees well with Mott’s relation. The highest ZT is found to be 0.96 at 900K for a low carrier concentration of 1019cm−3. The phonon thermal conductivity of the compound is found to be 2.52 W/mK near room temperature and 0.84 W/mK at 900K using the Slack method. All these results support ZnIn2Se4, a defect chalcopyrite semiconductor, as a favorable candidate for thermoelectric applications.

Ordered-vacancy defect chalcopyrite ZnIn2Te4: A potential thermoelectric material with low lattice thermal conductivity

An effective route towards commercializing thermoelectric devices is to explore materials with high conversion efficiency. This study investigates the thermoelectric properties of ZnIn2Te4 with the combination of first-principles calculations, Boltzmann transport theory and the modified Debye Callaway model. This vacancy-ordered defect chalcopyrite shows a direct band gap of 1.37 eV, obtained by mBJ functional with spin orbit coupling. The positive phonon dispersion curves ensure the thermodynamical stability of the material. Moreover, strong acoustic-optical coupling, Grüneisen parameter, and moderate phonon group velocity yielded the low lattice thermal conductivity (kL) of 1.46 W m−1 K−1 at 900 K. Owing to this low kL, the optimum thermoelectric figure of merit of 0.90 and 0.98 is obtained for p and n-type ZnIn2Te4. These findings will open the way for the experimentalists to attempt for its experimental realization.

Optical absorption of defect chalcopyrite and defect stannite ZnGa2Se4 under high pressure

Optical absorption measurements at high pressure have been performed in two phases of the ordered-vacancy compound (OVC) ZnGa2Se4: defect stannite (DS) and defect chalcopyrite (DC). The direct bandgap energy of both phases exhibits a non-linear pressure dependence with a blueshift up to 10 GPa and a redshift at higher pressures. We discuss the different behavior of both phases in these two pressure ranges in relation to the pressure-induced order-disorder processes taking place at cation sites. Measurements performed in both phases on downstroke after increasing pressure to 22 GPa show that the direct bandgap energy of the recovered samples at room pressure was 0.35 eV smaller than that of the original samples. These results evidence that different disordered phases are formed on decreasing pressure, depending on the cation disorder already present in the original samples. In particular, we attribute the recovered samples from the original DC and DS phases to disordered CuAu (DCA) and disordered zincblende (DZ) phases, respectively. The decrease of the direct bandgap energy and its pressure coefficient on increasing disorder in the four measured phases are explained. In summary, this combined experimental and theoretical work on two phases (DC and DS) of the same compound has allowed us to show that the optical properties of both phases show a similar behavior under compression because irreversible pressure-induced order-disorder processes occur in all adamantine OVCs irrespective of the initial crystalline structure.

Optical and electronic properties of defect chalcopyrite ZnGa2Se4: Experimental and theoretical investigations

The optical properties of ZnGa2Se4 single crystals obtained by gas transport reaction have been systematically explored using ellipsometry measurements and first-principles calculations. Analysis of X-rays diffraction pattern showed that the compound has a single-phase and tetragonal structure (space group (I4‾2 m)). The determined and calculated lattice parameters are in good agreement with each other. Spectral dependence of optical parameters; real εr and imaginary εi parts of the pseudodielectric function, absorption and reflectivity coefficients were obtained from the analysis of ellipsometry measurements. Absorption coefficient–photon energy dependency revealed the existence of direct band gap transitions with an energy of 2.81eV. This result is very close to the band gap obtained from our theoretical calculation. To explore the origins of the interband optical transitions theoretical group analysis was carried out.

Insights into the Effects of RbF‐Post‐Deposition Treatments on the Absorber Surface of High Efficiency Cu(In,Ga)Se2 Solar Cells and Development of Analytical and Machine Learning Process Monitoring Methodologies Based on Combinatorial Analysis

AbstractThe latest record efficiencies of the Cu(In,Ga)Se2 (CIGSe) photovoltaic technology are driven by heavy alkali post‐deposition treatments (PDTs). Despite their positive effect, especially in the Voc of the devices, their underlying mechanisms are still under discussion. This work sheds light on this topic by performing a high statistics analysis on 620 high efficiency CIGSe solar cells submitted to four different PDT processes (different RbF source temperature) employing a combinatorial approach based on Raman and photoluminescence (PL) spectroscopies. This reveals with statistical confidence subtle differences in the spectroscopic data that relate to the redistribution of defects between the ordered vacancy compound (OVC) and the chalcopyrite phases at the absorber surface. In particular, there is an intertwined decrease of the OVC phase and increase of the so‐called “defective chalcopyrite phase.” Additionally, two industry‐compatible methodologies for the assessment of the RbF‐PDT process and prediction of the Voc of the final devices with a ±2% error and an efficacy of ≈95% are developed based on analytical and machine learning approaches. These results show that the combined Raman and PL spectroscopic techniques represent a powerful tool for the future development of the CIGSe technology at a research level and for more efficient industrial manufacturing.

Linear and Non-Linear Optical Characteristics of Defect Chalcopyrite Znin2te4 Thin Films for Opto-Electronic Device Applications

Linear and Non-Linear Optical Characteristics of Defect Chalcopyrite Znin2te4 Thin Films for Opto-Electronic Device Applications

Evaluation of defect formation in chalcopyrite compounds under Cu-poor conditions by advanced structural and vibrational analyses

Cu-poor compositions are key for obtaining high efficiency Cu(In,Ga)Se2 (CIGSe) devices. These conditions lead to Cu deficit accommodation mechanisms like the formation of Cu-related defects in the CIGSe crystal structure or of ordered vacancy compound. However, the origin of the benefits of Cu-poor compositions is still under discussion since these mechanisms are difficult to detect and characterize. In this work, a high precision Raman spectroscopy and X-ray diffraction analysis on a compositionally-graded CISe sample ([Cu]/[In] ratios from 0.48 to 1.03) allows us to shed light on this topic by reporting the detection of a “defective chalcopyrite phase” in the slightly Cu-poor compositional regime that may play a critical role, rather than other previously discussed mechanisms, on device performance. This phase is mainly characterized by the formation of a specific defect in the CISe structure which also contributes to appearance of a Raman peak at 230 cm−1. Finally, the analysis of high efficiency (> 18%) CIGSe solar cells and the extrapolation of the results on defect formation obtained for CISe, suggest a possible impact of the defective chalcopyrite phase on the open circuit voltage of the devices, and opens a possible way to further investigate and develop the chalcopyrite based technologies.

Experimental and theoretical study of the conduction mechanism and dielectric behavior of quaternary defect chalcopyrite CdInGaSe4 using adaptive neuro-fuzzy inference system (ANFIS) model

The first part is an experimental study of Ac. conduction and dielectric behavior of CdInGaSe4 defect chalcopyrite. CdInGaSe4 thin films were obtained by the thermal evaporation method. Measurements were investigated at temperatures (292.9–393.4 K), thicknesses (71–198 nm) and frequencies (100–1 MHz). The ac. conductivity σac.(ω) is temperature dependent and discussed by the correlated barrier hopping model CBH. Values of dielectric constant ε1(ω) and loss ε2(ω) are increased by temperature and decreased by frequency. The second part introduces estimation of ac conductivity and dielectric properties of CdInGaSe4 using adaptive neuro-fuzzy inference systems (ANFIS). Experimental data is used as inputs. Takagi-Sugeno type of ANFIS model is trained. The optimal networks are accomplished using MATLAB. ANFIS modeling outputs provide excellent results. Error values support the success of the modeling process. According to this research, the ANFIS technique is considered a successful tool to predict ac. conductivity and dielectric properties of CdInGaSe4.

Investigation of Mid-Infrared Broadband Second-Harmonic Generation in Non-Oxide Nonlinear Optic Crystals

The mid-infrared (mid-IR) continuum generation based on broadband second harmonic generation (SHG) (or difference frequency generation) is of great interest in a wide range of applications such as free space communications, environmental monitoring, thermal imaging, high-sensitivity metrology, gas sensing, and molecular fingerprint spectroscopy. The second-order nonlinear optic (NLO) crystals have been spotlighted as a material platform for converting the wavelengths of existing lasers into the mid-IR spectral region or for realizing tunable lasers. In particular, the spectral coverage could be extended to ~19 µm with non-oxide NLO crystals. In this paper, we theoretically and numerically investigated the broadband SHG properties of non-oxide mid-IR crystals in three categories: chalcopyrite semiconductors, defect chalcopyrite, and orthorhombic ternary chalcogenides. The technique is based on group velocity matching between interacting waves in addition to birefringent phase matching. We will describe broadband SHG characteristics in terms of beam propagation directions, spectral positions of resonance, effective nonlinearities, spatial walk-offs between interacting beams, and spectral bandwidths. The results will show that the spectral bandwidths of the fundamental wave allowed for broadband SHG to reach several hundreds of nm. The corresponding SH spectral range spans from 1758.58 to 4737.18 nm in the non-oxide crystals considered in this study. Such broadband SHG using short pulse trains can potentially be applied to frequency up-conversion imaging in the mid-IR region, in information transmission, and in nonlinear optical signal processing.

Pressure-induced band anticrossing in two adamantine ordered-vacancy compounds: CdGa2S4 and HgGa2S4

This paper reports a joint experimental and theoretical study of the electronic band structure of two ordered-vacancy compounds with defect-chalcopyrite structure: CdGa2S4 and HgGa2S4. High-pressure optical-absorption experiments (up to around 17 GPa) combined with first-principles electronic band-structure calculations provide compelling evidence of strong nonlinear pressure dependence of the bandgap in both compounds. The nonlinear pressure dependence is well accounted for by the band anticrossing model that was previously established mostly for selenides with defect chalcopyrite structure. Therefore, our results on two sulfides with defect chalcopyrite structure under compression provide definitive evidence that the nonlinear pressure dependence of the direct bandgap is a common feature of adamantine ordered-vacancy compounds and does not depend on the type of anion.

Preparation of Alloys and Investigation of Phase Equilibria in the CuFeS2−δ–CuGaS2 System

Alloys of the CuFeS2−δ-CuGaS2 system were synthesized by solid-state chemical reactions from the corresponding mixtures of powders of the CuFeS2−δ and CuGaS2 ternary compounds. Phase equilibria were investigated using x-ray powder diffraction (XRPD), differential thermal analysis (DTA), and scanning electron microscopy (SEM) combined with energy-dispersive x-ray spectroscopy (EDX). It was found that the T-x phase diagram of the (CuFeS2−δ)1−x-(CuGaS2)x system has a peritectic character with no solubility at room temperature in the composition range x = 0.34–0.94. The lack of complete solubility can be explained by the fact that the crystal structures of the starting ternary compounds CuFeS2−δ and CuGaS2 are different. Samples of the homogeneous chalcopyrite, having the chemical composition of CuFeS2−δ, possess deficiency of sulfur and exist in the defect chalcopyrite structure at room temperature, but the region of existence of the CuGaS2 compound includes the stoichiometric composition, and the samples crystallize in the ideal crystal structure of chalcopyrite.

High resolution structural refinement and band gap characterization of the defect chalcopyrites CuIn5Te8, AgIn5Te8 and AuIn5Te8

The AIn5Te8 compounds (A ​= ​Cu, Ag, Au), charge balanced defect chalcopyrites, are characterized. Synchrotron powder diffraction shows that the Cu and Ag analogs are tetragonal to high precision at room temperature, with classic 158 (I-III5-VI8) defect chalcopyrite structures in space group I4¯2m. These materials display ordered vacancies but disordered cations. The degree of cation intermixing is more significant in the Cu case than in the Ag case. In contrast, AuIn5Te8, a previously unreported 158 defect chalcopyrite, exhibits a tetragonal P4¯2c structure with disordered vacancies and cations, displaying poorer crystallinity than the other two materials. The direct optical band gaps (Eg), determined from UV–vis absorption measurements, are estimated to be 0.94, 0.99, and 0.77 ​eV, respectively. Comparison to the corresponding sulfides and selenides for 158 and standard 112 (I-III-VI2) type chalcopyrites is reported where the data are available.

The effect of galvanic interaction between chalcopyrite and pyrite on the surface chemistry and collector adsorption: Flotation and DFT study

An investigation on the surface properties and collector adsorption was conducted after the galvanic interaction of chalcopyrite and pyrite in the flotation system. The surface compositions were studied through the metal ion dissolution test and X-ray photoelectron spectroscopy (XPS) characterization. The galvanic effect on flotation behavior was examined by the flotation test of mineral mixtures; the collector adsorption on the defect chalcopyrite surfaces was analyzed by DFT calculation. The results showed that the addition of pyrite enhanced copper ion dissolution from the chalcopyrite surface significantly. Adsorption of copper ion on the pyrite surface was observed by XPS analysis. Chalcopyrite surface showed a higher oxidation degree after contacting with pyrite as polysulfide and elemental sulfur appeared. Mineral recovery from flotation tests showed the galvanic effect caused lower selectivity of chalcopyrite and pyrite with SBX as a collector. DFT study revealed that the metal-deficient chalcopyrite surface does not facilitate collector adsorption with high adsorption energy. Therefore, pyrite is galvanically protected while the oxidation dissolution of chalcopyrite is enhanced in their galvanic cell. Lower chalcopyrite recovery from mineral mixtures was obtained due to surface defection and weaken collector adsorption.

Electronic Structure of CO2 and CS2 Crystals

Density functional theory methods are used to study diamond-like crystals CO2 and CS2 with defect chalcopyrite structure (β-SiO2). Equilibrium crystal lattice parameters are determined, energy band spectra are calculated for these crystals and for their cation (C) and anion (O, S) sublattices. The formation of chemical bonding in the crystals is studied by analysing total and partial densities of states and distribution maps of differential and deformation charge densities of valence electrons.

Vibrational properties of CdGa2S4 at high pressure

Raman scattering measurements have been performed in cadmium digallium sulphide (CdGa2S4) with defect chalcopyrite structure up to 25 GPa in order to study its pressure-induced phase transitions. These measurements have been complemented and compared with lattice-dynamics ab initio calculations including the TO-LO splitting at high pressures in order to provide a better assignment of experimental Raman modes. In addition, experimental and theoretical Grüneisen parameters have been reported in order to calculate the molar heat capacity and thermal expansion coefficient of CdGa2S4. Our measurements provide evidence that CdGa2S4 undergoes an irreversible phase transition above 15 GPa to a Raman-inactive phase, likely with a disordered rock salt structure. Moreover, the Raman spectrum observed on downstroke from 25 GPa to 2 GPa has been attributed to a new phase, tentatively identified as a disordered zinc blende structure, that undergoes a reversible phase transition to the Raman-inactive phase above 10 GPa.

Elucidating linear and nonlinear optical properties of defect chalcopyrite compounds ZnX2Te4 (X=Al, Ga, In) from electronic transitions

We presented a theoretical study of electronic band structure of three compounds ZnAl2Te4, ZnGa2Te4 and ZnIn2Te4 using pseudo potential method within density functional theory. Calculated band structures show that all band gaps are direct with at Γ with values of 1.639eV for ZnAl2Te4, 1.026eV for ZnGa2Te4and 0.836eV ZnIn2Te4. The linear properties based on dielectric function and non-linear optical properties based on second harmonic generation (SHG) were computed. The origin of four critical points (peaks) determined from the second derivative of the imaginary part of the dielectric function is elucidated. The use of individual k-points and individual combination of valence and conduction bands dependent matrix of the dielectric function and the nonlinear optical susceptibility allowed to a precise determination of inter band optical transitions. Indeed, inter-band analysis shows the high intensity of non-linear effect compared to linear effect. Moreover, non-linear inter-band optical transitions involve lower valence bands and higher conduction bands.

First-principles study of phase transition, electronic, elastic and optical properties of defect chalcopyrite ZnGa2Te4 semiconductor under different pressures

The generalized gradient approximation (GGA) within the framework of density functional theory (DFT) has been used to investigate the phase transition, electronic, elastic and optical properties of ZnGa2Te4 defect chalcopyrite (DC) semiconductor at different pressures. At 18 GPa pressure, ZnGa2Te4 semiconductor has been found to undergo a structural phase transition from defect chalcopyrite (DC) to disordered rocksalt (DR) structure (phase). The calculated bandgap of DC structure at ambient pressure has been found to be 0.95 eV with direct in nature. The band structure of DR phase studied at 18 GPa pressure has been discussed through density of states. Pressure-dependent elastic stiffness coefficients (Cij), bulk modulus (B), shear modulus (G), Young modulus (E), Poisson's ratio (σ), B/G ratio and Zener anisotropy factor (A) have been calculated at 0, 10, 18 GPa pressures for DC phase and at 20, 25, 30 GPa pressures for DR phases. Further, optical properties such as dielectric function, refractive index, extinction coefficient, absorption coefficient, reflectivity and loss function have been estimated at 0, 10 and 18 GPa pressures for DC phase. The calculated parameters have been compared with the available experimental and theoretical values. A fairly good agreement has been obtained between them.

Structural, electronic, elastic and lattice dynamical properties of CdIn2Te4 under pressure from first principle

The first-principle calculations have been performed to study the pressure-induced effects on the structural, electronic, elastic and lattice dynamical properties of defect chalcopyrite CdIn2Te4. The optimized structural parameters are well consistent with the available experimental and theoretical data. The evolutions of energy gaps, elastic constants, elastic moduli, phonon dispersion spectra, and Raman scattering spectra, as well as zone-center phonon frequencies with pressure have been investigated in detail. Our results show that CdIn2Te4 has a direct bandgap and energy gaps decrease nonlinearly with pressure. A pressure-induced transition from brittle fracture to plastic flow exists, and DC-CdIn2Te4 is elastic anisotropy. Most Raman-active phonon frequencies have positive pressure dependence, the exception is for the E2 and B3 modes.