Polycrystalline cadmium selenide, CdSe, thin films were prepared by chemical bath deposition (CBD) technique. The films were deposited using cadmium chloride as a Cd+2 ion source, and sodium selenosulphite as a Se-2 ion source. Annealing the films in air for 10 minutes at 100 0C-350 0C affected the grain growth. The annealed films were returned to room temperature either by quenching or slow cooling. The energy band gap (Eg) decreased with increasing thicknesses and substrate temperatures. Value of Eg calculated from UV/visible absorption spectra ranged between 2 and 1.83 eV. The used film thickness was ~10μm. Annealing and rate of cooling that present the best photoluminescence (PL), photo and dark currents for the film electrodes are discussed here. Covering CdSe thin films with metalloporphyrine complex, embedded inside polymeric polysiloxane matrices, enhanced the electrode efficiency and stability. The deposited films were investigated by optical PL and UV absorption spectra.
Monday, January 18, 2010
FP-LAPW CALCULATIONS OF THE STRUCTURAL PHASE TRANSFORMATIONS OF ZnSe AND ZnS UNDER HIGH PRESSURE
ABSTRACT FP-LAPW CALCULATIONS OF THE STRUCTURAL PHASE TRANSFORMATIONS OF ZnSe AND ZnS UNDER HIGH PRESSURE At present, calculations of ground–state energy of II–VI and III–V compounds are computed relatively slowly and expensively, even on supercomputers. Thus, an efficient, inexpensive and accurate method of calculations is very important. The Full-Potential Linearized Augmented Plane-Wave (FP-LAPW) method have been used to investigate the structural phase transformations of ZnS and ZnSe under high-pressure. In these calculations, the local density approximation (LDA) for the exchange-correlation potential have been used. Equations of states (EOS's) of the zinc-blende (ZB), rock-salt (RS), cinnabar and simple cubic-16 (SC16) of the ZnS and ZnSe have been calculated. From these EOS's, the structural phase transformations of both ZnS and ZnSe under high pressure were investigated by treating the 3d-electrons of Zn and Se as valence states. Moreover, the structural properties and the electronic structures of the ZB, RS, cinnabar and SC16 phases of ZnS and ZnSe have also been calculated. The most important results are: (1) our calculations agree very well with the available experimental data and the other theoretical calculations. (2) the relaxation of the internal parameters of the (ZnS and ZnSe) in cinnabar and SC16 structures have important effects on its calculated equation of state. (3) the ZB and RS forms of ZnS are found to be semiconductors up to the transition pressure. (4) the ZB form of ZnSe is found to be semiconductor while the RS of ZnSe is found to be semimetal with narrow energy band-gap of 0.5eV. (5) the cinnabar and SC16 structures of ZnS and ZnSe which lies between ZB and RS are expected to be semiconductors. (6) SC16 is a stable phase and relatively more stable than RS and cinnabar phases for ZnS and ZnSe.
Ga1−xMnxN Magnetic Semiconductors: First-Principles Study
Abstract
We present the results of First-Principles calculations of the magnetic semiconductors for systems taking the concentrations (0.0,0.125, 0.25, 0.50, 0.75 , 1.00) in the Zinc-blende Structure (ZB-Structure), using a self-consistent full-potential linearized augmented plane-wave (FP-LAPW) method implemented by the WIEN2K package. The local spin density approximation (LSDA) as well as the generalized gradient approximation (GGA) are used to treat the exchange correlation potential, and taking into account spin polarization.
In order to design new or employ the existing diluted magnetic semiconductor materials, the underlying mechanisms of magnetism must be understood. The total energy versus lattice constant is obtained using the spin density functional theory (DFT). It is found that the equilibrium lattice parameters strongly depend on the concentration of the Mn-dopant (x ). Also we found that the energy band gaps ( ) for these systems depend on (x ), in other words the energy band gap decreases by increasing the Mn concentration.
We mainly studied the Bulk parameters of our system, band structures, and magnetic properties. We made numerical investigations of the structural, magnetic properties for simple cases under pressure, in other part of our results we report an analysis of structures, magnetic properties of the , i.e GaN doped with Mn, with different concentrations, 0.125, 0.25, 0.5, 0.75 and so for major, minor compounds (GaN, MnN).