Electrical transport properties of copper-doped tellurium films

Polycrystalline films of copper-doped tellurium were grown by co-evaporating copper and tellurium from separate boats. Measurements were made of the electrical transport properties of these films. It was observed that the addition of copper decreases the activation energies of both the conductivity and the mobility. The low temperature conduction data were interpreted on the basis of a variable range hopping mechanism while the high temperature data indicate the dominance of the grain boundary scattering mechanism.     

Optical properties of (1-x-y)B2O3-xLi2O-yMCI2 (M=Cd, Zn) glasses

Optical absorption and transmission spectra of (1-x-y)B₂O₃-xLi₂O-yMCI₂ (M=Cd, Zn) glasses of varying compositions were recorded in the UV-visible region. From the spectra, various optical parameters such as optical energy gap (E _opt), refractive index (n), optical dielectric constant (ɛ′), width of the tail of localized states in the forbidden gap (ΔE), ratio of carrier concentration to the effective mass (N/m*) and the constantB were evaluated. The effects of composition of glasses on these parameters are discussed.     

4.6 Some optical properties of thin Cd3As2 films

The transmission of vacuum deposited Cd₃As₂ films has been measured in the spectral range 0.6–15 ωm. The absorption coefficient α has been calculated from the data for crystalline films obtained at substrate temperature T_s = 440 K and also for amorphous films obtained on substrates at T_s = 300?393 K. The position of the low-energy absorption edge in the spectral range 0.1–0.3 eV is discussed and the value Δ_g^opt = 0.06 eV for indirect transion Γ → Γ₁₅ is obtained for crystalline films. For amorphous films, a shift of the minimum absorption edge to $\text{Δ}\text{E}{}_{\mathrm{g}}{}^{\mathrm{opt}}\text{? 0.4?0.5}\text{eV}$ was observed. For higher energies two direct transitions have been established: the first at E₁ = 0.9 eV in the photon energy range 0.9–1.2 eV.and the second at E₂ = 1.2?1.3 eV in the photon energy range 1.3?1.6 eV. The last value is in good agreement with the value calculated by Lin Chung and with reflectivity data; it corresponds to the transition Γ₁₅ → X₁ in the hypothetical band model of Lin Chung. Differences in the reflective index values for crystalline and amorphous Cd₃ As₂ are also discussed.     

The g-factor of conduction electrons in Cd3P2 at low temperatures

The g-factor of conduction electrons in Cd₃P₂ at low temperatures is calculated as a function of carrier concentration, taking into account the InSb-like electronic energy-band structure of this material. In the case of typical samples with 10¹⁷, 5 × 10¹⁷, and 10¹⁸ electrons per cm³, we have determined the values of the magnetic field at which the extrema in the Shubnikov-de Haas and/or de Haas-van Alphen oscillations should occur, and suggested the experimental conditions under which effects due to spin splitting may be observed.On leave of absence from Centre de Recherches sur les Très Basses Températures, CNRS, and Service Basses Températures, Centre d'Etudes Nucléaires, Grenoble, France.     

On the preparation,growth and properties of Cd3As2

A new general method for the preparation of compounds having volatile components, and its application to the preparation of Cd₃As₂, is described. The pulling of Cd₃As₂ by liquid encapsulation, using firstly a new encapsulant to clean the melt, and secondly a modified B₂O₃ encapsulant for pulling, is reported. Electrical properties of pulled Cd₃As₂ are given.The effects of annealing on the optical transmission of evaporated Cd₃As₂ films are described, and the energy gap suggested by optical transmission and photoconduction are briefly discussed.     

Optical properties of Ca3TaGa3Si2O14 single crystal

The interference patterns of polarized light are measured by polarizing microscopy. The specific rotation ρ of Ca₃TaGa₃Si₂O₁₄ (CTGS) piezoelectric single crystal is determined from 200 to 850 nm by measuring the optical transmission between parallel polarizers in <001> direction. It is shown that Ca₃TaGa₃Si₂O₁₄ has quite large a value of ρ which is a little smaller than that of Ca₃NbGa₃Si₂O₁₄ (CNGS).     

The growth and electrical properties of single crystal Cd3As2 platelets

Single crystal platelets of Cd₃As₂ having carrier concentrations less than 10²⁴ m⁻³ have been grown from the vapour in the presence of argon gas and excess cadmium vapour. It is shown that the resistivity and Hall data is consistent with a band model in which there is a direct band-gap atk=0 of approximately 0.38 eV and an indirect zero band-gap. It is suggested that the large electron carrier concentrations usually present in Cd₃As₂ result from anti-structure disorder.     

Optical properties of a correlated electron system:V 2 O 3

The optical spectrum of V₂O₃ is found to resemble a Hubbard model system as described in an infinite-dimensional approximation. Assuming the validity of this comparison, we parameterize the effective Coulomb repulsive energy, the bandwith, and the mass enhancement. We suggest implicitly that these results should be compared with the cuprate and heavy Fermion superconductors.     

Electrical and gas sensing properties of self-aligned copper-doped zinc oxide nanoparticles

Electrical and gas sensing properties of nanocrystalline ZnO:Cu, having Cu X wt% (X = 0.0, 0.5, 1.0, and 1.5) in ZnO, in the form of pellet were investigated. Copper chloride and zinc acetate were used as precursors along with oxalic acid as a precipitating reagent in methanol. Material characterization was done by X-ray diffraction (XRD), scanning electron microscopy (SEM), field emission scanning electron microscopy (FE-SEM) and inductive coupled plasma with optical emission spectrometry (ICP-OES). FE-SEM showed the self-aligned Cu-doped ZnO nano-clusters with particles in the range of 40-45 nm. The doping of 0.5% of copper changes the electrical conductivity by an order of magnitude whereas the temperature coefficient of resistance (TCR) reduces with increase in copper wt% in ZnO. The material has shown an excellent sensitivity for the H₂, LPG and CO gases with limited temperature selectivity through the optimized operating temperature of 130, 190 and 220 °C for H₂, LPG and CO gases, respectively at 625 ppm gas concentration. The %SF was observed to be 1460 for H₂ at 1% Cu doping whereas the 0.5% Cu doping offered %SF of 950 and 520 for CO and LPG, respectively. The response and recovery time was found to be 6 to 8 s and 16 s, respectively.     

Structural and optical properties of Zn3P2 thin films

Conditions have been developed for the deposition of a stoichiometric thin film of zinc phosphide (Zn₃P₂) using electron beam evaporation. Structural properties of as-deposited and annealed thin films of zinc phosphide have been studied using electron and X-ray diffraction. The as-deposited film is non-crystalline, structural ordering starts on annealing at 200° C and the film becomes crystalline at 300° C with the structure matching that of the bulk material. Optical absorption has been investigated over the range 1 to 3 eV with emphasis on the region of interband absorption. The thin film absorption edge is found to be exponential for lower values of absorption coefficient. Analysis of thin film data showed that Zn₃P₂ is a direct-band-gap material. On annealing there is a shift in the band edge towards higher energy. NCL Communication No. 3571.     

Preparation and characterisation of Cd3P2, a II–V group compound semiconductor

Cadmium phosphide (α-Cd₃P₂) a II₃–V₂ compound semiconductor has been prepared by C/H₂ reduction of cadmium phosphate. The reduction process is conducted at 550°C allowing the reaction to continue for 4 to 5 hr. The material always gets deposited on the walls of the quartz tube at different zones, which after analysis is found to contain, depending upon the location of the zone, Cd₃P₂, CdP₂ and other cadmium rich phosphides. The resistivity of the pressed samples are of the order of 3 × 10⁻⁴Θ-cm. Optical absorption spectra of thin films, obtained by thermal evaporation on glass substrates, have exhibited broad bands around 620 nm.     

Optical properties of CulnSe2 thin films

The optical constants of vacuum-deposited CulnSe₂ films were determined from the measured transmittance and reflectance at normal incidence of light in the wavelength range 500 to 2000 nm. The analysis of the experimental points of the absorption coefficient revealed the existence of two optical transition processes: an allowed direct transition withE _g=1.03±0.01 eV and a forbidden direct transition withE _f=1.254±0.001 eV. The optical constants of the films were independent of the substrate temperature.On leave to the Kingdom of Saudi Arabia.     

Optical properties of evaporated PbSnS3 thin films

PbSnS3 is a ternary sulfide semiconductor material which has been relatively little studied in the literature. Thin films of this material were deposited on glass substrates by a thermal evaporation process and their optical properties investigated. The optical parameters were determined from the analysis of measured transmission spectra, at normal incidence, from 400–1500 nm, at room temperature. The fundamental absorption edge is placed at 1.04±0.05 eV and is forbidden in nature. Other absorption edges are obtained at 1.44 and 1.55±0.05 eV, with a nearby direct one at 1.68±0.05 eV. The peaks at 1.44 and 1.55 eV have been independently confirmed by the spectral photocurrent response of the films. © 1998 Kluwer Academic Publishers