Electronic structure theory of chalcopyrite alloys, interfaces, and ordered vacancy compounds (original) (raw)
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STRUCTURAL AND ELECTRONIC PROPERTIES OF CHALCOPYRITE SEMICONDUCTORS
This is to certify that the project thesis entitled " Structural and electronic properties of chalcopyrite semiconductor" being submitted by Bijayalaxmi Panda in partial fulfilment to the requirement of the one year project course (PH 592) of MSc Degree in physics of National Institute of Technology, Rourkela has been carried out under my supervision. The result incorporated in the thesis has been produced by using TB-LMTO codes.
AB INITIO MODELING OF OPTOELECTRONIC PROPERTIES OF CHALCOPYRITES AND OF THEIR POINT DEFECTS
Ab initio calculations have been instrumental in the understanding of important structural and chemical properties of Chalcopyrites, such as non stoichiometry, self compensation and stability. The benefit of such methods has been specially important as chalcopyrites are a very complex class of semiconductors, in which the interpretation of experiments is far from straightforward. The role of point defects in the electronic properties of chalcopyrites has been recognized long ago and challenging results have been presented using DFT calculations. Unfortunately, whereas DFT is well suited for ground state properties (structure, energy of formation, lattice vibrations), it is much less so when it comes to computing properties linked to excited states of the system (band gap, ionisation energies of defects, optical properties,..). These shortcomings have been addressed in different ways: either using semi-empirical electron-electron repulsion (LDA+U), or so called hybrid approaches (functionals combining "exact exchange" from Hartree-Fock and correlation from other sources) or even computationally intensive methods based on a Green's function description of the many body effects (GW approximation). GW calculations are often performed as "one-shot" corrections to self-consistent Kohn-Sham local density approximation calculations. This standard approach has been successful in many applications on solids. However, it has been shown that it fails for many compounds with d electrons, where only a self-consistent (SC) GW scheme allows to recover a good description of the quasi-particle energies.
First-principles calculation of the order-disorder transition in chalcopyrite semiconductors
Physical Review B, 1992
We describe the polymorphic order-disorder transition in the chalcopyrite-type semiconductor Cuo. slnosSe through a Monte Carlo simulation of a generalized Ising Hamiltonian whose interaction energies are determined from ab initio total-energy calculations. The calculated transition temperature (T, =1 l25+'20 K) compares well with experiment (T, =1083 K). Unlike the analogous ordering in isovalent III-V alloys, we find that the transition is dominated by electronic compensation between donor and acceptor states, leading to strong correlations in the disordered phase, and a decrease in the optical band gap upon disordering. Recent theory' and observations of spontaneous long-range order in isovalent III-V semiconductor alloys created interest in the theoretical implications on selforganization in random systems and in the technologically attractive possibility of changing the optical band gaps of random alloys at frxed composition through ordering. ' The relatively weak interactions between the isovalent atoms in such III-V alloys lead, however, to a small enthalpy difference between the disordered and ordered bulk phases (bH (0.5 kcal/mole), so the driving force for the transition is dominated by surface energetics. This leads to imperfect ordering and irreversibility that complicates the study of the transitions. There is, however, a large class of tetrahedrally bonded semiconductorsthe A 'B "'C '2 chalcopyrites"where the stronger interactions between the nonisovalent A'-B"' atoms (reflected in much larger latent heat BH of 2-3 kcal/mole) leads to reversible order-disorder transitions observable at conveniently higher temperatures even in bulk crystals. These ternary A'B"'C"'2 chalcopyrites (e.g., CuInSe2) undergo as a function of temperature a first-order phase transition between the high-temperature disordered zinc-blende-like (ZB) phase and the ordered chalcopyrite (CH) structure. Depending on the system, the disordering transition occurs in the temperature range" ' T,-800-1300 K, is accompanied by an abrupt disappearance of the zinc-blende-forbidden x-raydiffraction peaks, " a large (0.1-0.5 eV) reduction in the semiconducting band gaps' ' and marked changes in the short-range order seen in NMR studies. ' Since the disordered phase contains cross substitutions between nonisovalent A '-B"' atoms, it manifests donor-acceptor
AB-Initio Modeling of Intermediate Band Materials Based on Metal-Doped Chalcopyrite Compounds
2006 IEEE 4th World Conference on Photovoltaic Energy Conference, 2006
Results of quantum calculations in M-doped chalcopyrite Cu 4 MGa 3 S8 (with M=Ti, V, Cr or Mn) are evaluated. The purpose of this work is the quest of a compound which possesses an isolated narrow partiallyfilled electronic band sited into the host semiconductor bandgap. The aforementioned material could be useful for designing novel solar cells with very high efficiency. Density Functional Theory calculations in the spinpolarized GGA approach have been carried out in all cases for obtain band dispersion diagrams and densities of electronic states. For the systems having Cr and Ti as dopants, where the results reveal promising features, an advanced DFT+U formalism has been used to ascertain their properties with higher certainty. Finally, after having reasoned that Cu^iGasSs has the desired features, a prediction of its energetic feasibility has been formulated.
Structure modifications in chalcopyrite semiconductors
2000
The microstructure of epitaxial CuInS 2 , CuGaSe 2 and polycrystalline CuInS 2 ®lms was studied by transmission electron microscopy. We found that the vapour-phase epitaxy of CuInS 2 below the transition temperature T c results in ®lms with chalcopyrite and CuAu-like structures. The formation of CuAu-like ordered phases within the ®lms is independent of the substrate orientation, whereas the amount of CuAu-like ordered Cu and In atoms can be in¯uenced by the substrate orientation. The co-existence of chalcopyrite and CuAu-like ordering of the metal atoms was also found in polycrystalline CuInS 2 ®lms prepared by sulphurization of Cu/In metal precursor at a temperature below T c . In contrast, vapour-phase epitaxy of CuGaSe 2 below T c provides only ®lms with the chalcopyrite structure. The experimental ®nding is in good agreement with the results of ®rst-principle band-structure calculations. q 2000 Elsevier Science S.A. All rights reserved.
Phonons and electrons in chalcopyrite semiconductors
2012
In recent years the phonons and the electron phonon interaction of binary tetrahedral semiconductors have been profusely investigated by ab initio techniques and compared with experimental results. Of particular interest have been binary compounds in which the cations contain semi-core d-electrons (CuCl, CuI, AgI) which display anomalies related to the semi-core d-states (,).
Computational Study of Chalcopyrite Semiconductors and Their Non-Linear Optical Properties
2007
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On the role of order-disorder phenomena in chalcopyrite compounds
Materials Letters, 1989
Scarce attention has been paid to the thermodynamics of chalcopyrite compounds of the ABC1 family, where A = Ag, Cu; B = Al, Ga, In and C = S, Se, Te. This fact explains why many phenomena involved in growing, annealing and doping processes are not fully understood.
Solar Energy Materials and Solar Cells, 2010
Chalcopyrite Nanostructures Solar cells Nanostructured chalcopyrite compounds have recently been proposed as absorber materials for advanced photovoltaic devices. We have used photoreñectance (PR) to evalúate the impact of interdiffusion phenomena and the presence of native defects on the optoelectronic properties of such materials. Two model material systems have been analyzed: (i) thin layers of CuGaSe 2 (£ g =1.7 eV) and CuInSe 2 (1.0 eV) in a wide/low/wide bandgap stack that have been grown onto GaAs(0 0 1) substrates by metalorganic chemical vapor deposition (MOCVD); and (ii) thin In 2 S 3 samples (£ g =2.0 eV) containing small amounts of Cu that have been grown by co-evaporation (PVD) intending to form Cu x In y S z (£ g~1 .5 eV) nanoclusters into the In 2 S 3 matrix. The results have been analyzed according to the third-derivative functional form (TDFF). The valence band structure of selenide reference samples could be resolved and uneven interdiffusion of Ga and In in the layer stack could be inferred from the shift of PR-signatures. Hints of electronic confinement associated to the transitions at the low-gap región have been found in the selenide layer stack. Regarding the sulphide system, In 2 S 3 is characterized by the presence of native deep states, as revealed by PR. The defect structure of the compound undergoes changes when incorporating Cu and no conclusive result about the presence of ternary clusters of a distinct phase could be drawn. Interdiffusion phenomena and the presence of native defects in chalcopyrites and related compounds will determine their potential use in advanced photovoltaic devices based on nanostructures. (D. Fuertes Marrón). energy range of zero density of states, as originally proposed by Luque and Martí . The device is completed with two emitters that selectively extract electrons and holes at either side of the absorber. In this way, three absorption onsets are expected at photon energies corresponding to transitions from the valence band to the intermedíate band, from the intermedíate to the conduction band, and from the valence to the conduction band, leading to an increase of the generated photocurrent. The proper use of the emitters and the isolation of the intermedíate band material from the contacts ensure that the expected voltage delivered by the device will be limited by the main gap of the material and not by any of the sub-bandgaps associated to the intermedíate band. The overall balance is an increased efficiency of energy conversión .