Chalcopyrite Semiconductors Research Articles

The first-principles study of electrical and thermoelectric properties of CuGaTe2 and CuInTe2

The thermoelectric material is a kind of new functional material, which can convert industrial waste heat and automobile exhaust into the available electric energy by the interaction of carriers. It is widely used in energy, environment, national defense and other fields. For the research of thermoelectric materials, it is the most important to improve the conversion efficiency now. Due to their unique structural properties, the ternary chalcopyrite semiconductors I-III-IV2 (I=Ag, Cu; III=Al, Ga, In; IV=S, Se, Te) display the better thermoelectric performances at high temperature. Many studies show that there are many ways to improve their performances. In order to optimize their thermoelectric efficiencies the structural, elastic and thermoelectric properties of CuGaTe2 and CuInTe2 are studied by employing the density function theory and semi-classical Boltzmann transport theory within the constant time approximation. The electronic band structures are calculated using the Tran-Blaha modified Becke-Johnson potential (MBJ-GGA) and the generalized gradient approximation (GGA). The calculated band gaps with MBJ-GGA of CuGaTe2and CuInTe2 are 0.86 and 0.56 eV, which are more accurate than the calculated values with GGA. The shear modulus, and Young's modulus and sound velocities are determined from the obtained elastic constants. The constant-volume heat capacity is estimated based on the quasi-harmonic Debye model. The calculated temperature dependence of heat capacity agrees very well with the experimental result. Below room temperature, the heat capacity increases quickly with the increasing of temperature. Above room temperature, the heat capacity approaches to the Dulong-Petit limit. In paper, we assume that the lattice thermal conductivities of CuGaTe2 and CuInTe2 are mainly from the phonon scattering. And the phonon scattering is dominated by Umklapp scattering. The calculated lattice thermal conductivities can fit the form kl = A/T-Bin the temperature range of 300-800 K. For CuGaTe2, A = 2869.96 and B = 2.86. The fitting result well approaches to the experimental values and other theoretical results. Based on the calculated band structures with mBJ-GGA potential, the transport properties of CuGaTe2 and CuInTe2 each as a function of chemical potential at various temperatures are investigated. The values of Seebeck coefficient S first increase and then decrease for n-type and p-type doping at low carrier concentrations, which are consistent with the previous results. Electrical conductivity divided by scattering time, i.e. / increases monotonically with chemical potential increasing. The power factor divided by scattering time, i.e. S2/ first increases and then decreases with chemical potential increasing. The magnitude of S2/ increases with temperature increasing. Besides, it is found that the value of S2/ for p-type doping is larger than that for n-type doping. These results show that optimizing the carrier concentration can improve their thermoelectric performances. In order to calculate the electrical conductivity, in this paper we estimate the scattering time from the experiments of Ref.[3]. The CuGaTe2 at 700 K possesses a figure of merit 0.63. These calculated results show that CuGaTe2 and CuInTe2 both are good thermoelectric materials with p-type doping.

Refractive Index and Electronic Polarizability of Ternary Chalcopyrite Semiconductors

Simple models are proposed for the calculation of refractive index n and electronic polarizability α of AI BIII C2VI and AII BIV C2V groups of chalcopyrite semiconductors from their energy gap data. The values of n and α for 2 compounds of AI BIII C2VI family and 12 compounds of AII BIV C2V family are calculated for the first time in this work. The proposed models are applicable for the whole range of energy gap materials. The calculated values are compared with the available experimental and reported values. A fairly good agreement between them is obtained.

Ab Initio Calculations and Experimental Properties of CuAl x Ga1−x Te2 for Photovoltaic Solar Cells

Nanostructured chalcopyrite CuAlxGa1−xTe2 (x = 0.25, 0.50, and 0.75) has been prepared by ball milling of Cu, Al, Ga, and Te precursors. Preliminary ab initio calculations of the main properties have been performed on the prototype chalcopyrite semiconductor CuAlGaTe2. The simulation method used is based on the density functional theory within the framework of pseudo-potentials and plane waves. Band Structure calculations suggest that CuAlGaTe2 is a direct bandgap semiconductor having a band gap = 1.35 eV. In the experimental part, x-ray diffraction analysis revealed the presence of (112), (220)/(204), (312)/(116), and (400) reflections for all the milled powders characteristic of the chalcopyrite structure. A shift in peaks towards a higher value of 2θ is observed with the increase in Al composition. With increasing Al content, it is found that the average crystallite size decreases whereas the bandgap energy increases from 1.34 eV to 1.51 eV. Compared with experimental data, calculated results by GGA–mBJ functional quantitatively agree with experimental data.

Electronic structure, chemical bonding and optical properties of the nonlinear optical crystal ZnGeP2 by first-principles calculations

Using the plane wave pseudopotential method within density-functional theory, we have theoretically investigated the structural, electronic, chemical bonding and optical properties of the chalcopyrite semiconductor ZnGeP2. It is found that ZnGeP2 has an indirect band gap of 1.222 eV. The covalent character of the bonds in ZnGeP2 crystal is verified by Mulliken population. By analyzing the optical properties including the dielectric function, refractive index, extinction coefficient, reflectivity spectrum and absorption coefficient, we indicate that ZnGeP2 is a promising mid-IR optical material, which is in good agreement with the available experimental results.

Cu2ZnSnS4 synthesized through a low-cost reflux method

Abstract The chalcopyrite semiconductors belonging to the I2-II-IV-VI4 class are emerging as promising absorber materials for photovoltaic applications. Among them, Cu2ZnSnS4 (CZTS) has been gaining importance due to its high absorption coefficient and optimum band-gap. To make CZTS an economically viable alternative, in this study, the CZTS powder has been synthesized via a low-cost, environment-friendly reflux method. In the current method, the salts of the respective metals were taken as initial precursors, and thiourea was used as a precursor for sulfur. The stoichiometric amounts of the precursors were taken in distilled water and the solution was refluxed for 8 h. The products were filtered and washed with distilled water and ethanol consecutively. Phase identification was done using powder X-ray diffraction (given by the reference pattern JCPDS card no. #00-026-0575) and Raman spectroscopy analysis (corresponding Raman shifts for CZTS: 288 and 338 cm-1). The band gap of the compound was calculated from the UV-visible spectroscopy and found to be 1.4 eV.

Effect of Na substitution on electronic and optical properties of CuInS2 chalcopyrite semiconductor

Electronic & optical properties of Na substituted CuNaIn2S4 chalcopyrite semiconductors are significantly modified due to Na substitution in the Cu deficient CuInS2 semiconductor. These properties are obtained form first principle calculation using density functional theory based tight binding Linear muffin tin orbital method. The presence of Na alters the structural distortion and enhances strengths of Cu d and S p hybridization in CuNaIn2S4. This effect reduces band gap, in agreement with experimental observations and modify other properties significantly. Calculations of optical matrix elements (OME) and joint density of states (JDOS) show that effects of Na substitution on optical properties come through p–d hybridization and structural distortion. OME contribution is prominent near band edge. Both systems show anisotropic optical properties.

Analysis of a data base of chalcopyrite semiconductors in 2 and 3 dimensions

The analysis of the data is currently, in the statisticians, the object of a true phenomenon of mode, characterized at the same time by the passion and the rejection. To determine the characteristics of a whole of data is obviously not an end in itself, but this lapse of memory is unfortunate because the type of data available always influences the direction of research. The factorial analysis in normalized principal components (PCA), is particularly adapted to the reduction of tables of measurements, where one generally works on a matrix of correlation between characters. In this article we will report our results of analysis into 2 and 3 dimensions of the molecular weight and energy of plasmon of semiconductor chalcopyrites by using what one call the datamining materials. All information was presented in the tables envisaged by an ACP method of the semiconductors etudies. L' analyzes factorial substitutes for primitive measurements of new variables or factors (which are linear combinations of the primitive variables) with the help of which it is thus possible to optimize the visualization of the data in a restricted number of figures.Large at the modo we present, the results related to the development of new approaches of Datamining, Analysis in principal components (ACP), of the data-processing techniques which were applied to semiconductors and combined with metals to predict new materials or ultra stable coatings

Investigations of the zero-field splitting with the local tilting angle τFe3+ for Fe3+ in ZnGeP2 crystal

The axial zero-field splitting parameter D for Fe3+ at Ge4+ site of ZnGeP2 chalcopyrite semiconductor is calculated using the method based on the dominant spin–orbit coupling mechanism. In the calculation, the impurity-induced local tilting angle of anion tetrahedron, which is much larger than the corresponding tilting angle in the host ZnGeP2 crystal, is applied. The results indicate the negative sign of D, whereas the magnitude of D is explained reasonably, and the large tilting angle is further confirmed for Fe3+ in ZnGeP2 crystal.

Revealing the optoelectronic and thermoelectric properties of the Zintl quaternary arsenides ACdGeAs2 (A = K, Rb)

Chalcopyrite semiconductors have attracted much attention due to their potential implications in photovoltaic and thermoelectric applications. First principle calculations were performed to investigate the electronic, optical and thermoelectric properties of the Zintl tetragonal phase ACdGeAs2 (A=K, Rb) using the full potential linear augmented plane wave method and the Engle–Vosko GGA (EV–GGA) approximation. The present compounds are found semiconductors with direct band gap and covalent bonding character. The optical transitions are investigated via the dielectric function (real and imaginary parts) along with other related optical constants including refractive index, reflectivity and energy-loss spectrum. Combining results from DFT and Boltzmann transport theory, we reported the thermoelectric properties such as the Seebeck’s coefficient, electrical and thermal conductivity, figure of merit and power factor as function of temperatures. The present chalcopyrite Zintl quaternary arsenides deserve to be explored for their potential applications as thermoelectric materials and for photovoltaic devices.

Ab‐initio study of ferromagnetism in Mn‐doped ZnSnAs2

AbstractThe electronic and magnetic properties of pure as well as Mn‐doped chalcopyrite semiconductor ZnSnAs2 were studied by the DFT+U ab initio method within the spin generalized gradient approximation. The band structure and DOS calculations resulted in a direct gap scenario for semiconducting ZnSnAs2. The energy gap of 0.34 eV occurs at the center of the Brillouin zone and linearly increases with increasing Mn concentration x at a rate of 2.05 eV for x < 0.03. The total energy calculations for a number of supercells showed that a ferromagnetic rather than antiferromagnetic ordering is favorable in Mn‐doped ZnSnAs2 when Mn replaced Sn. The energy deficient substitution of Zn by Mn led to the antiferromagnetic ordering. The magnetic moment per Mn atom, together with contribution of each atom into the total moment of ZnSnAs2: Mn was determined. The contributions from Mn and As are dominant but have opposite signs. Besides, the As atoms chemically bounded to Mn dopant were found to be most contributive. At last it was shown that the vacancies such as V(Zn), V(Sn), and V(As) affect the magnetic properties and may even strengthen the magnetization of Mn‐doped ZnSnAs2. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Quality CuInSe2 and Cu(In,Ga)Se2 thin films processed by single-step electrochemical deposition techniques

Ternary CuInSe2 and quaternary Cu(In,Ga)Se2 chalcopyrite semiconductor films with potential applications as solar absorbers were deposited by single-step electrochemical deposition (ECD) on molybdenum coated glass substrates. The films have been structurally characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM) combined with energy dispersive x-ray analysis (EDAX), x-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. Chalcopyrite phase formation was confirmed already in as-deposited films. The crystal structure of the films was further improved by thermal treatment. Element interdiffusion at the chalcopyrite/Mo/glass interface has been prevented by retaining moderate temperatures of deposition (70 °C) and subsequent annealing (300 °C). The SEM/EDAX analysis revealed the presence of CuxSe secondary phases on the surface of ternary films and almost stoichiometric growth of quaternary deposited on top of ternary films. The XRD and Raman analysis confirmed the high quality assessment of the films being almost equal to that of chalcopyrite selenide layers grown by physical vapor deposition at high temperatures (550–750 °C). The surface sensitive XPS analysis confirmed the absence of other impurities in the ECD processed films except from oxygen and carbon adsorbents by sample exposure to atmospheric air.

Effect of the Replacement of Some Indium Atoms with Aluminum Atoms on the Behaviour of p-CuInSe2 Thin Films and Schottky Diodes

As environmental and energy resource concerns have increased, greater stress has been placed on the development of renewable energy resources such as photovoltaic electric generators. Chalcopyrite semiconductors have gained prominence as solar cell fabrication materials due to its steady progress in conversion efficiencies. These have emerged as leading absorber semiconducting material for solar power generation purposes. CulnSe2 (CIS), a prominent member of the chalcopyrite family, has emerged as a promising material for high efficiency thin film solar cells. Due to its favorable electrical and optical properties, stability and inexpensive means of production that several recent advances have been made to improve its bandgap [Eg]. The bandgap of CIS has been tailored to match the desired portion of the Solar Spectrum by alloying the group III (Ga and Al) or group VI (S and Se) elements. An extensive research work has been carried out on Cu(In,Ga)Se2 [CIGS] and CuIn(S,Se)2 [CISS] alloy systems but the efficiency of these devices with Eg >1.3 eV is reduced due to degradation of the electronic properties of the absorber layer leading to losses in the fill-factor and the open-circuit voltage. The performance of thin film CIS based solar cells has alternatively been improved by the addition of Al in place of Ga to form CuInAlSe2(CIAS) absorber layers with changed bandgap to match the selective regions of the solar spectrum. Further, Ga is scarce and expensive material and can preferably be replaced by inexpensive and abundant Al. In the present investigation, behaviour of thin film CIAS to that of CIS as an absorber layer portion of the solar cells has been studied. Both the materials possessed tetragonal structure and found oriented towards < 112 > set of planes. The addition of ‘Al’ to CIS films caused reduction in the lattice imperfections’ which resulted in the improved cystallinity of the films. The grain size increased while microstrain and dislocation density decreased in CIAS. The films demonstrated decrease in the cohesive force between film and the substrate material. The optical analysis of the films revealed that the bandgaps and absorption coefficients increased on Al substitution and, thus, CIAS films have been found to be more suitable as an absorber layer in solar cells. The electrical measurements of the films showed that both CIS and CIAS films possessed p-type conductivity. Further, a significant improvement has been observed in the conductivity as well as mobility values in the CIAS films. The phenomenon has been attributed due to the reduction in the grain boundary scattering in the CIAS in comparison to CIS films. The Schottky Diodes of both the types of films were formed using Aluminum metals. The reverse biased leakage currents measured from the I-V/C-V characteristics of CIS were found to lower than that of CIAS films. The forward biased parameters such as ideality factors and series resistance decreased while barrier heights increased in the Al/p-CuIn0.81Al0.19Se2 Schottky Diodes. Further, the temperature dependence of the I-V/C-V characteristics of the undertaken CIAS diodes has been explained on the basis of barrier inhomogenities existing over the M-S interface. However, some deviations have been observed between the data generated on the basis of Gaussian Distribution Function for barrier inhomogenities to that obtained from the experimental studies of undertaken Schottky Diodes which indicated the existence of current component due to tunneling alongwith the thermionic emission of the charge carriers existing over the M-S interface.

A model for silver ion catalysis of chalcopyrite (CuFeS2) dissolution

Atmospheric leaching of chalcopyrite in sulfuric acid solutions is a slow process due to its passivation. Silver ions have been shown to catalyze this process and increase the oxidation rate. In this study the interaction between silver ions and chalcopyrite has been investigated in silver-containing sulfuric acid solutions. The silver concentration of the test solutions was between 0 and 10ppm. In situ Mott–Schottky analysis and X-ray photoelectron spectroscopy (XPS) were respectively applied to study chalcopyrite's semiconductor properties and silver diffusion into the chalcopyrite passive film. Results of the Mott–Schottky experiments showed that the addition of silver to the solution increases the apparent capacitance of the chalcopyrite passive film owing to changes in the semiconductor properties of the film. The measured capacitance was shown to be time dependent for the first 15min of the experiment (i.e. sample immersion in solution) and after this elapsed time the capacitance stayed constant. XPS results showed that silver atoms diffuse about 18nm below the chalcopyrite surface.A model is proposed for silver ion catalyzed chalcopyrite electro-dissolution. In this model it is assumed that silver cations adsorb to the electrode surface and form Ag2S. The formation of each Ag2S molecule on the surface requires the creation of a sulfur vacancy and a pair of holes in the passive film. The effect of both the sulfur vacancy and the pair of holes is an increase in the dissolution kinetics of chalcopyrite.

Influence of doping and solid solution formation on the thermoelectric properties of chalcopyrite semiconductors

We have investigated the influence of zinc doping on the thermoelectric properties of CuInTe2–CuGaTe2 solid solution alloys. Undoped end-member compounds display typical p-type semiconducting behavior, with a negative temperature coefficient of resistivity and large Seebeck coefficient. With zinc substituting for indium or gallium, the hole concentration is increased and the electrical transport behavior evolves into that of a degenerate semiconductor, with both electrical resistivity and Seebeck coefficient increasing with temperature up to the highest temperature measured. For undoped samples the thermoelectric power factor is maximized close to 750K, while in doped specimens the maximum occurs at much lower temperature. Substitution of gallium for indium induces significant phonon scattering and thermal conductivity reduction below 500K. The dimensionless figure of merit rises to above unity over a range of compositions in these chalcopyrite compounds, with optimized samples reaching a figure of merit of 1.3.

Nanorod Formation of Copper Indium (di) Selenide Nanorod Synthesize by Solvothermal Route

The compound belongs to I-III-VI2 group are promising material as an effective light-absorbing materials. Now a day, ternary chalcopyrite semiconductors, especially copper based I-III-VI2 semiconductors have attracted many investigators. They have several desirable features as absorbers in the thin film solar cells. In present work, copper indium (di) selenide have been prepared via solvothermal route. Several methods have been reported to prepare CuInSe2 nanostructures by solution route. In present work, tetragonal chalcopyrite copper indium (di) selenide nanorods has been synthesized by solvothermal method using ethylene diamine as a solvent. Structural analysis had been done by X-ray diffraction (XRD). The surface morphology of the as-grown nanorod has been studied using scanning electron microscopy. The bandgap of as grown nanorods is obtained from UV-Vis spectrum which will applicable to the solar cell devices.

Synthesis of Cu2NiSnS4 nanoparticles by hot injection method for photovoltaic applications

Quaternary chalcopyrite semiconductors are being considered as an attractive class of materials for thin film solar cells. The present study reports the synthesis of quaternary chalcopyrite Cu2NiSnS4 (CNTS) nanoparticles by hot injection method for the first time. The wurtzite structured CNTS nanoparticle formation was confirmed by X-ray diffraction (XRD). The nanoparticles were characterized by transmission electron microscopy (FEG-TEM), scanning electron microscopy (FEG-SEM) and energy dispersive spectroscopy (EDS). Light absorption in the visible region was confirmed with the help of UV–vis spectroscopy. Optical band gap as calculated from the absorption spectrum was found to be 1.38eV. Films prepared from the nanoparticle suspension displayed photoresponse behavior under illumination, suggesting the potential use of CNTS as an active layer in low-cost thin-film solar cells.

An insight into the mechanism of charge-transfer of hybrid polymer:ternary/quaternary chalcopyrite colloidal nanocrystals.

In this work, we have demonstrated the structural and optoelectronic properties of the surface of ternary/quaternary (CISe/CIGSe/CZTSe) chalcopyrite nanocrystallites passivated by tri-n-octylphosphine-oxide (TOPO) and tri-n-octylphosphine (TOP) and compared their charge transfer characteristics in the respective polymer: chalcopyrite nanocomposites by dispersing them in poly(3-hexylthiophene) polymer. It has been found that CZTSe nanocrystallites due to their high crystallinity and well-ordered 3-dimensional network in its pristine form exhibit a higher steric- and photo-stability, resistance against coagulation and homogeneity compared to the CISe and CIGSe counterparts. Moreover, CZTSe nanocrystallites display efficient photoluminescence quenching as evident from the high value of the Stern–Volmer quenching constant (KSV) and eventually higher charge transfer efficiency in their respective polymer P3HT:CZTSe composites. We modelled the dependency of the charge transfer from the donor and the charge separation mechanism across the donor–acceptor interface from the extent of crystallinity of the chalcopyrite semiconductors (CISe/CIGSe/CZTSe). Quaternary CZTSe chalcopyrites with their high crystallinity and controlled morphology in conjunction with regioregular P3HT polymer is an attractive candidate for hybrid solar cells applications.

The role of point defects in multinary chalcogenide compound semiconductors

The electronic properties of multinary chalcogenide compound semiconductors, like chalcopyrite type ternary Cu(In,Ga)Se2 and quaternary kesterite type Cu2ZnSnSe4, depend strongly on their intrinsic point defects. For instance it is generally believed that in CuInSe2 the copper vacancies (VCu) cause p-type conductivity, whereas copper on interstitial positions (Cui) or InCu anti-sites act as donors and promote a n-type character. These defects are resulting from deviations from the stoichiometric composition. In order to keep the charge balance in the non-stoichiometric compounds, only a number of cation substitution reactions are possible: for example the transition to Cu-poor CuInSe2 goes via the defect pair 2VCu+InCu, whereas the transition to Cu-poor and Zn-rich Cu2ZnSnSe4 goes via the substitution 2Cu+-&gt;ZnCu + VCu. The presentation will give a comparison of the role of cationic point defects in chalcopyrite and kesterite type compound semiconductors concerning the following features: (i) Phase stability: the chalcopyrite type structure is very flexible to hold defects and can adapt itself to substitutions. Beyond a given copper vacancy rate, a vacancy compound (for instance CuIn3Se5) is formed, thus avoiding the occurrence of binary secondary phases (like copper selenides). For kesterite type Cu2ZnSnSe4 the situation is different: due to the lower flexibility of the kesterite type structure and the absence of vacancy compounds, secondary phases, like ZnSe, occur when the compound becomes Cu-poor. (ii) Atomic disorder: The cationic point defects cause an atomic disorder on the short range level which also influences the electronic properties (for instance the bandgap energy). For instance in Cu(In,Ga)Se2 defects such as antisites or interstitials lead to variations in the local atomic arrangements and thus broaden the bond distance distribution due to static disorder. The discussion will be underlined by the experimental results of neutron diffraction [1], anomalous scattering of synchrotron X-rays [2] as well as X-ray absorption spectroscopy [3].

Linear properties of ternary chalcopyrite semiconductors

Linear properties of ternary chalcopyrite semiconductors have been studied. New relations based on plasma oscillations theory of solids have been proposed for calculation of homopolar, heteropolar and average energy gaps, dielectric constant and ionicity of A–C and B–C bonds in AIBIIIC2VI and AIIBIVC2V groups of semiconductors. The values of these parameters for 13 new chalcopyrites of AIIBIVC2V family have been calculated. The calculated values are compared with the available reported values and a fairly good agreement has been obtained.

Structural, electronic, optical, elastic and thermal properties of ZnXAs2 (X = Si and Ge) chalcopyrite semiconductors

We report first principles calculations of solid state properties of ZnSiAs2 and ZnGeAs2 chalcopyrite semiconductors. The structural properties are calculated using a Full Potential Linearized Augmented Plane Wave method (FP-LAPW) of the Density Functional Theory (DFT). A Generalized Gradient Approximation (GGA) scheme proposed by Wu and Cohen (WC) has been chosen to calculate electronic and optical properties. Optical features such as dielectric functions, refractive indices, extinction coefficient, optical reflectivity, absorption coefficients and optical conductivities were calculated for photon energies up to 30 eV. The elastic constants at equilibrium in tetragonal structure are also determined. Temperature effect on the volume, thermal expansion, heat capacity, Debye temperature, entropy, Gruneisen parameter and bulk modulus were calculated employing the quasi-harmonic Debye model at different temperatures and pressures and the silent results were interpreted. Finally using semi-empirical relation, we determined the hardness of the materials which attributed to different covalent bonding strengths.