Thermal property of binary tetrahedral semiconductors

In this paper we present an expression relating the lattice thermal expansion coefficient α_L (10⁻⁶ K⁻¹) for the A^IIIB^V and A^IIB^VI semiconductors with the product of ionic charges (Z₁Z₂), melting temperature (T_m) and nearest neighbor distance d (Å). The lattice thermal expansion coefficient of these compounds exhibit a linear relationship when plotted on a log–log scale against the melting temperature (T_m), but fall on different straight lines according to the ionic charge product of the compounds. A good agreement has been found between the experimental and calculated values of the lattice thermal expansion coefficient for A^IIIB^V and A^IIB^VI semiconductors.     

Optical properties of donor electrons in semimagnetic semiconductors

The cross section of the spin-flip Raman scattering and the absorption coefficient of the electric-dipole spin-resonance of donor electrons in Cd_1?x Mn_xSe are calculated. The exchange induced spin-splitting of a donor level is described taking into account three sources of a local magnetization: external magnetic field, thermodynamical fluctuations of magnetization and molecular field of the donor electron (bound magnetic polaron). The theory takes into account the selection rules appropriate for the hexagonal CdMnSe. The role played by fluctuations of composition is considered. It is suggested that a spin-flip line is inhomogeneously broadened by thermodynamical fluctuations of magnetization and additionally, in high fields, by fluctuations of the composition.     

Birefringence of optically uni-axial ternary semiconductors

Refractive indices and birefringences for some representative uni-axial crystals such as II- SiP₂ and II- GeP₂ have been determined over a wide range of wavelengths by the use of first-principles electronic structure calculations. First, the calculated refractive indices are fitted usually by a generalized Sellmeier equation which consists of several oscillation terms involve in its parameters more direct information about material such as electronic transitions or resonance wavelengths. Then, in contrast to all other semiconductors under discussion our spectra show a negative birefringence for CdSiP₂ in agreement with the experimental data, and they exhibit a considerable dispersion near the band gap.     

Magnetic properties of Ni/NiO nanocomposites synthesized by one step solution combustion method

Ni/NiO nanocomposites were synthesized using solution combustion method and characterized with X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDAX) and carbon, hydrogen, nitrogen (CHN) analyser. The Ni or NiO content in Ni/NiO nanocomposites vary with the quantity of HNO₃ used for the synthesis. Magnetic coercivity (H_c) of Ni/NiO nanocomposites is found to be 413 Oe which can be used in magnetic applications. A feeble exchange bias of 7 Oe is seen from the NiO rich Ni/NiO.     

Magnetic and optical properties of self-organized InMnAs quantum dots

Ten layers of self-assembled InMnAs quantum dots with InGaAs barrier were grown on high resistivity (1 0 0) p-type GaAs substrates by molecular beam epitaxy (MBE). The presence of ferromagnetic structure was confirmed in the InMnAs diluted magnetic quantum dots. The ten layers of self-assembled InMnAs quantum dots were found to be semiconducting, and have ferromagnetic ordering with a Curie temperature, T_C=80 K. It is likely that the ferromagnetic exchange coupling of sample with T_C=80 K is hole mediated resulting in Mn substituting In and is due to the bound magnetic polarons co-existing in the system. PL emission spectra of InMnAs samples grown at temperature of 275, 260 and 240 °C show that the interband transition peak centered at 1.31 eV coming from the InMnAs quantum dot blueshifts because of the strong confinement effects with increasing growth temperature.     

Self-assembly of Sb2O3 nanowires into microspheres: Synthesis and characterization

Sb₂O₃ nanowires with diameters of ∼233 nm and microspheres assembled by these nanowires were successfully synthesized by a simple poly-(vinylpyrrolidone) (PVP) assisted hydrothermal method. The morphologies, nano/microstructures and optical properties of the as-grown nanowires and microspheres were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and UV-vis diffuse reflection spectrum. It has been found that the experimental parameters, such as mineralizers, played crucial roles in the morphological control of Sb₂O₃ nanowires. The possible growth mechanism of microspheres has been proposed.     

Temperature and pressure behaviour of narrow-gap semiconductors including galena

The structural high pressure and temperature investigation of narrow-gap semiconductors (lead chalcogenides) has been performed in the present article. A realistic approach for room temperature and high temperature study of narrow-gap semiconductors has been used. It is examined that the present compounds are more stable in NaCl-phase and they transform to CsCl-phase at high pressure. In the present article, the phase transition pressures and volume collapses of lead chalcogenides have been investigated at room and high temperatures. Phase transition pressures have been reported at high temperature range from 0 to 1200 K. Elastic and anharmonic constants have also been reported at room temperature. A structural study of the narrow-gap semiconductors have been carried out using the realistic model including temperature effect. The temperature and pressure behaviour of elastic constants for the present compounds have also been discussed. Furthermore, various mechanical and thermo dynamical properties like modulus of elasticity, Debye temperatures etc. are also presented.     

Model of magnetic anisotropy in disordered semimagnetic semiconductors

We propose a model explaining the origin of cubic magnetic anisotropy in disordered semiconductor. We show that the magnetic anisotropy changes with the position of the Fermi energy in the valence band and the level of disorder in the crystal. The method is applied to Pb_1−x−ySn_yMn_xTe and Sn_1−xMn_xTe ferromagnetic semiconductor crystals.     

Excitonic effects in core-excitation spectra of semiconductors

Computer simulations of a model glass-forming system are presented, which study the correlation between the dynamics in real space and the topography of the potential energy landscape. This analysis clearly reveals that in the supercooled regime the dynamics is strongly influenced by the presence of deep valleys in the energy landscape, corresponding to long-lived metastable amorphous states. We explicitly relate nonexponential relaxation effects and dynamic heterogeneities to these metastable states and thus to the specific topography of the energy landscape.     

Optical properties of the filled tetrahedral semiconductors LiZnX (X=N, P, and As)

We present first principles calculations of the electronic and the optical properties of the filled tetrahedral compounds LiZnN, LiZnP, and LiZnAs performed with the full potential linearized augmented plane wave method within the local density approximation. The origin of the small gap of LiZnN is attributed to the strong p-d coupling in this compound. The assignments of the structures in the optical spectra and band structure transitions are discussed in detail. The predicted values of the dielectric constants for LiZnP and LiZnAs are close to those of the binary compounds GaP and GaAs, respectively.     

Galvanomagnetic properties of Hg1−x MnxTe1−y Sey semimagnetic semiconductors

The galvanomagnetic properties of single crystals of the semimagnetic semiconductors Hg_1−x Mn_xTe_1−y Se_y with 0.01<y<0.1 and x=0.05 and 0.14 in the temperature range 4.2–300 K are investigated. The features of the temperature dependence of the Hall coefficient R _H and the complicated behavior of R _H in a magnetic field are attributed quantitatively to the existence of three groups of current carriers, viz., electrons and two types of holes, for which the temperature dependences of the densities and mobilities are obtained. A transition from p-type to n-type conductivity is observed as the Se content is increased, and the negative magnetoresistance simultaneously gives way to positive magnetoresistance. Zh. éksp. Teor. Fiz. 112, 1809–1815 (November 1997)     

Interface modification and trap-type transformation in Al-doped CdO/Si-nanowire arrays/p-type Si devices by nanowire surface passivation

The present work reports the fabrication and detailed electrical properties of Al-doped CdO/Si-nanowire (SiNW) arrays/p-type Si Schottky diodes with and without SiNW surface passivation. It is shown that the interfacial trap states influence the electronic conduction through the device. The experimental results demonstrate that the effects of the dangling bonds at the SiNW surface and Si vacancies at the SiO_x/SiNW interface which can be changed by the Si–O bonding on the energy barrier lowering and the charge transport property. The induced dominance transformation from electron traps to hole traps in the SiNWs by controlling the passivation treatment time is found in this study.     

Effects of an electric field on the electronic and optical properties of zigzag boron nitride nanotubes

We have investigated the electro-optical properties of zigzag BNNTs, under an external electric field, using the tight binding approximation. It is found that an electric field modifies the band structure and splits the band degeneracy. Also the large electric strength leads to coupling the neighbor subbands which these effects reflect in the DOS and JDOS spectrum. It has been shown that, unlike CNTs, the band gap of BNNTs can be reduced linearly by applying a transverse external electric field. Also we show that the larger diameter tubes are more sensitive than small ones. The semiconducting metallic transition can be achieved through increasing the applied fields. The number and position of peaks in the JDOS spectrum are dependent on electric field strength. It is found that at a high electric field, the two lowest subbands are oscillatory with multiple nodes at the Fermi level.     

Structural and elastic properties of the filled tetrahedral semiconductors LiZnX (X=N, P, and As)

We report on first-principles study of the structural and elastic properties of the Nowotny-Juza filled tetrahedral compounds LiZnX (X=N, P, As) using the full-potential linearized augmented plane wave method within the local density approximations. Our results indicate that the energetically favourable α-LiZnX materials are slightly softer than their binary analogous GaX and the sound speeds are quantitatively similar for LiZnAs and GaAs.     

Fabrication, study of optical properties and structure of most stable (CdP2)n nanoclusters

CdP₂ nanoclusters were fabricated by incorporation into pores of zeolite Na–X and by laser ablation. Absorption and photoluminescence (PL) spectra of CdP₂ nanoclusters in zeolite were measured at the temperatures of 4.2, 77 and 293 K. Both absorption and PL spectra consist of two bands blue shifted with respect to bulk crystal. We performed the calculations aimed to find the most stable clusters in the size region up to size of the zeolite Na–X supercage. The most stable clusters are (CdP₂)₆ and (CdP₂)₈ with binding energies of 9.30 and 10.10 eV per (CdP₂)₁ formula unit, respectively. Therefore, we attributed two bands observed in absorption and PL spectra to these stable clusters. The Raman spectrum of CdP₂ clusters in zeolite was explained to be originated from (CdP₂)₆ and (CdP₂)₈ clusters as well. The PL spectrum of CdP₂ clusters produced by laser ablation consists of the asymmetric band with low-energy tail that has been attributed to emission of both (CdP₂)₈ cluster and CdP₂ microcrystals.     

The effect of the Bi source on optical properties of Bi2Te3 nanostructures

nanostructures were synthesized by using different Bi sources via a simple solvothermal process, in which and BiCl₃ were used as the Bi sources. Optical properties of nanostructures prepared with and BiCl₃ as the Bi sources were investigated by micro-Raman spectroscopy. The Raman scattering spectrum of hexagonal nanoplates prepared by using as the Bi source shows that the infrared (IR) active mode A_1u, which must be odd parity and is Raman forbidden for bulk crystal due to its inversion symmetry, is greatly activated and shows up clearly in the Raman scattering spectrum. We attribute the appearance of the infrared active A_1u mode in the Raman spectrum to crystal symmetry breaking of hexagonal nanoplates. However, the Raman scattering spectrum of nanostructures with irregular shape prepared by using as the Bi source only exhibits the two characteristic Raman modes of crystals. Micro-Raman measurements on nanostructures with different morphologies offer us a potential way to tailor optical properties of nanostructures by controlling the morphologies of the nanostructures, which is very important for practical applications of nanostructures in thermoelectric devices.     

Elastic properties of metastable crystalline and amorphous gasb-ge semiconductors synthesized under high pressure

We present the systematic study of the elastic shear G and bulk B moduli in amorphous and crystalline metastable ternary solid solutions (GaSb)_1?x Ge_2x . It is found that the moduli of crystalline phases initially decrease with Ge concentration, falling down to minimum values at 20-30% Ge. The minimal values of elastic moduli for amorphous samples are observed at 50-60% Ge. Elastic softness of crystalline solid solutions is assumed to be related to the increase of chemical disorder and, consequently, of static (non-thermal) geometrical disorder in positions of atoms. An additional topological disorder in amorphous solid solutions leads to additional elastic softening.     

Self-assembly of doped semiconductor nanocrystals leading to the formation of highly luminescent nanorods

Meso-scale self-assembly of doped semiconductor nanocrystals leading to the formation of monocrystalline nanorods showing enhanced photo- and electro-luminescence properties are reported. Polycrystalline ZnS: Cu⁺-Al³⁺ nanoparticles of zinc-blended (cubic) structure with an average size of ∼4 nm were aggregated in aqueous solution and grown into nanorods of length ∼400 nm and aspect ratio ∼12. Transmission electron microscope (TEM) images indicate crystal growth mechanisms involving particle-to-particle oriented-attachment assisted by sulphur-sulphur catenation leading to covalent-linkage. The nanorods exhibit self-assembly dependant luminescence properties such as quenching of the lattice defect-related emissions accompanied by enhancement of dopant-related emission, efficient low-voltage electroluminescence (EL) and super-linear voltage-brightness EL characteristics. This study demonstrates the technological importance of aggregation based self-assembly in doped semiconductor nanosystems.     

Effect of the dangling bond on the electronic and magnetic properties of BN nanoribbon

The effect of the dangling bond on the electronic and magnetic properties of BN nanoribbon with zigzag edge (ZBNNR) and armchair edge (ABNNR) have been studied using the first-principles projector-augmented wave (PAW) potential within the density function theory (DFT) framework. Though ZBNNR or ABNNR with H atom terminated at both edges is nonmagnetic semiconductor, the dangling bond induces magnetism for the ZBNNR with bare N edge, bare B edge, bare N and B edges, the ABNNR with bare N edge and bare B edge. However, the ABNNR with bare N and B edges is still nonmagnetic semiconductor due to the strong coupling of the dangling bonds of dimeric N and B atoms at the same edge. The magnetic moment of ZBNNR with bare N(B) edge is nearly half the magnetic moment of ABNNR with bare N(B) edge. Such a half relationship is also existed in the number of the dangling bond states appeared around the Fermi level in the band structures. Furthermore, the dangling bond states also cause both ZBNNR and ABNNR with bare N edge a transition from semiconducting to half-metallic and thus a completely (100%) spin-polarization, while cause both ZBNNR and ABNNR with bare B edge as well as ABNNR with bare N and B edges only a decrease in their band gap.