Search

In the present study we explore the structural, electronic and thermoelectric properties of IV-VI semiconductors using first principle calculations based on the density functional theory. Generalized gradient approximation (GGA-PBEsol) is used as an exchange-correlation functional for the structural properties of the different crystal phases of these semiconductors. The compounds SnS, SnSe, GeS and GeSe favor orthorhombic structure, lead chalcogenides (PbS, PbSe and PbTe) are stable in the cubic rocksalt structure, while SnS 2 and SnSe 2 exist in hexagonal structure. For band structures additional to GGA, modified Becke and Johnson (mBJ) exchange potential is used. These compounds are narrow band gap semiconductors in the energy range 0.2–2.8 eV. These binary IV-VI chalcogenides have direct band gap nature in cubic crystals while indirect in the orthorhombic phases. The post-DFT (BoltzTraP) calculations are performed to estimate Seebeck coefficient, electric and thermal conductivities, power factor and figure of merit of these compounds to check their applicability in thermoelectric devices. Spin orbit coupling effect influences the electronic and thermoelectric properties of these compounds due to the large size of the constituent elements. Further, the total thermal conductivity is computed using ad-hoc calculation with the experimental results. The calculated values of figure of merit for PbS, PbSe, PbTe and SnTe are in the range 0.68–0.77 at room temperature. [ABSTRACT FROM AUTHOR]

We have performed ab-initio calculations for the structural, electronic, optical, elastic and thermal properties of the copper gallium chalcopyrite (CuGaSe 2 ). The Full Potential Linearized Augmented Plane Wave (FP-LAPW) method is used to find the equilibrium structural parameters and to compute the full elastic tensors. We have reported electronic and optical properties with the recently developed density functional of Tran and Blaha. Furthermore, optical features such as dielectric functions, refractive indices, extinction coefficient, optical reflectivity, absorption coefficients, optical conductivities, are calculated for photon energies up to 30 eV. The thermodynamical properties such as thermal expansion, heat capacity, Debye temperature, entropy and Grüneisen parameter, bulk modulus and hardness are calculated employing the quasi-harmonic Debye model at different temperatures (0–1200 K) and pressures (0–8 GPa) and the silent results are interpreted. To check the potentiality of CuGaSe 2 as future solar cell material, device modeling and simulation studies have been carried out with a variety of buffer layers over CuGaSe 2 absorption layer. The band diagram and J / V curves are analyzed and device performance parameters i.e. efficiency, open circuit voltage, short circuit current, quantum efficiency are calculated for CdS, ZnS and ZnSe buffer layers. Simulation results for CuGaSe 2 thin layer solar cell show the maximum efficiency (15.8%) with ZnSe as the buffer layer. Most of the investigated parameters are reported for the first time. [ABSTRACT FROM AUTHOR]

First-principles calculations are performed to study the structural, electronic and thermodynamic properties of technologically important Cd 1− x Be x Se ternary alloys using the full potential-linearized augmented plane wave method within the density functional theory. We use both PBE and Engel–Vosko generalized gradient approximations of the exchange-correlation energy that are based on the optimization of total energy and corresponding potential, respectively. The ground-state properties are determined for CdSe, BeSe and their mixed crystals at various concentrations ( x =0.25, 0.5, and 0.75). Deviation of the lattice parameter from Vegard׳s law and the bulk modulus from the linear concentration dependence was observed. Using the approach of Zunger and co-workers, the microscopic origins of the band-gap bowing parameter have been explained. Through the quasi-harmonic Debye model, in which the phononic effects are considered, we have determined the thermal properties of the Cd 1− x Be x Se alloy such as the Debye temperature and heat capacities. [ABSTRACT FROM AUTHOR]

Cadmium sulfide (CdS) micro/nanocrystalline structures were fabricated by thermal evaporation in the absence of a catalyst on ITO-coated glass and Si(100) substrates. The samples prepared at 520 °C showed two structures of CdS: nanowires (NWs) and necklace-like microstructures grown on Si(111) and ITO substrates, respectively. The crystalline structures of the grown CdS necklace-like microstructures and NWs were studied using XRD analysis. The CdS necklaces and NWs structures were formed with hexagonal (wurtzite) structure. Two emission bands (green and red) were observed in the photoluminescence spectra of the prepared samples. The green PL emission in both structures showed a strong blue-shift compared with the optical band gap of CdS. Raman spectra of the grown CdS micro/nanocrystalline structures show redshift in the fundamental (1LO) and overtone (2LO) peaks location compared with Raman bands of bulk CdS. [ABSTRACT FROM AUTHOR]

Abstract: The results of kinetic investigation of silver sulfide (Ag2S) phase transformations–monoclinic (α) to body-centered-cubic (β) and body-centered-cubic to face-centered-cubic (γ) crystal form – are presented in this paper. Measured data obtained by thermal analysis under non-isothermal conditions were used for kinetic analysis. The activation energy for investigated phase transformation process was determined according to the methods by Kissinger and Ozawa. [Copyright &y& Elsevier]