Preparation and electrical conductivity of Pb2Ru2O6.5 crystals

Single crystals of Pb₂Ru₂O_6.5 have been grown by flux method from a mixture of lead oxides. The electrical conductivity of the crystals is of a metallic type, major current carriers being holes.     

Connection between electrical and deformation characteristics of PbS crystals

The influence of plastic deformation on temperature dependence of carrier concentration n and mobility μ in PbS crystals has been studied. Comparison of the results obtained with selective etching patterns from original and deformed crystals makes it possible to conclude that during the plastic deformation there takes place a dissolution of precipitates by passing of dislocations through them. As a results, rows of point defects appear along the path of dislocation movement which may be the cause of a change in n and μ due to deformation. A change in the electron scattering mechanism below 110 K has been discovered.     

Structural characteristics and second harmonic generation in l-threonine crystals

l-threonine, an organic material with interesting non-linear optical properties, has been grown in solution and characterized by X-ray diffraction, FT infrared spectral, Raman spectral, UV VIS spectral and thermal techniques. The structural and spectral characteristics show that strong hydrogen bonds appearing in l-threonine have an influence on the stabilization of the crystal structure. The main contributions to the second harmonic generation in threonine results from the hydrogen bond and also from the vibrational part due to very intense IR bands of the hydrogen bond vibrations. The OH and NH involved in strong hydrogen bonds are responsible for the higher thermal stability of l-threonine compared to other organic non-linear optical materials. l-threonine is thermally stable up to 270 °C.     

Structural and electrical characteristics of InGaAsN layers grown by LPE

Crystallographic and transport properties of nominally undoped and Sn-doped InGaAsN layers grown by low-temperature LPE have been studied and related to the growth conditions.In the case of lattice matching, flat and uniform mirror-like layers of 8–10 μm in thickness are obtained. The compositions of the layers under study have been determined by combination of X-ray microanalysis and X-ray diffraction methods to be In_0.035Ga_0.065As_0.086N_0.014. The lattice mismatch between layer and substrate Δa_l/a_s calculated from X-ray diffraction curves is less than?7×10^?4 for all samples. The layers grown at lower epitaxy temperatures exhibit the highest crystalline quality, better lattice match and better homogeneity. This is in good agreement with the results of morphological study by atomic force microscopy which show root mean-square surface roughness of 0.18 nm for the best layers.CV and Hall measurements reveal that intentionally undoped InGaAsN layers are n-type with free carrier concentration about one order of magnitude higher in comparison to layers not containing nitrogen and high electron mobility values over 2000 cm²/Vs. A dramatic reduction in the free carrier concentration and slightly increase in mobility are observed for Sn-doped InGaAsN layers.     

Chemical lap polishing of PbTe and Pb1−xSnxTe crystals

Chemical lap polishing of PbTe and Pb_1−xSn_x Te crystals is investigated. A mixture of potassium hexacyanoferrate (III), sodium hydroxide, glycerol and water is used as a polish. The effect of various parameters of the process on the quality of the surface and on the rate of material removal is studied. The quality of the surface is strongly is strongly affected by the composition of the polish. The roughness increases with rising sodium hydroxide concentration but decreases with rising glycerol concentration. If the molar ratio of sodium hydroxide and potassium hexacyanoferrate (III) exceeds the value 0.5 etch figures are formed. The rate of material removal largely depends on the velocity of the relative movement between specimen and cloth, the rate of supply of polishing solution and on the concentration of sodium hydroxide.     

Structural characteristics of the boron nitride sphalerite modification synthesized in a shock wave

Crystallography Reports - The real structure of ultradispersed powders of sphalerite boron nitride synthesized under shock compression has been studied by X-ray diffraction. The lattice microstrain...     

Structural,electrical and optical properties of Ge implanted GaSe single crystals grown by Bridgman technique

Structural, optical and electrical properties of Ge implanted GaSe single crystal have been studied by means of X‐Ray Diffraction (XRD), temperature dependent conductivity and photoconductivity (PC) measurements for different annealing temperatures. It was observed that upon implanting GaSe with Ge and applying annealing process, the resistivity is reduced from 2.1 × 10⁹ to 6.5 × 10⁵ Ω‐cm. From the temperature dependent conductivities, the activation energies have been found to be 4, 34, and 314 meV for as‐grown, 36 and 472 meV for as‐implanted and 39 and 647 meV for implanted and annealed GaSe single crystals at 500°C. Calculated activation energies from the conductivity measurements indicated that the transport mechanisms are dominated by thermal excitation at different temperature intervals in the implanted and unimplanted samples. By measuring photoconductivity (PC) measurement as a function of temperature and illumination intensity, the relation between photocurrent (I_PC) and illumination intensity (Φ) was studied and it was observed that the relation obeys the power law, I_PC αΦⁿ with n between 1 and 2, which is indication of behaving as a supralinear character and existing continuous distribution of localized states in the band gap. As a result of transmission measurements, it was observed that there is almost no considerable change in optical band gap of samples with increasing annealing temperatures for as‐grown GaSe; however, a slight shift of optical band gap toward higher energies for Ge‐implanted sample was observed with increasing annealing temperatures. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Absorption and electrical conductivity of CaMoO4 crystals

The electrical conductivity σ of CaMoO₄ crystals was investigated between room temperature and 850°C. The mobility v_v and the diffusion coefficient D_v of the O⁻ ion vacancies have been derived from σ: v_vT = 3300 exp (−1.52 eV/kT) cm² K/Vs, D_v = (0.1…1) × exp (−1.52 eV/kT) cm²/s. An absorption occuring in crystals which are reduced or X-irradiated at low temperatures is dichroitic and caused by Mo⁵⁺ ions. For measurement in c direction the oscillator strength of the 680 nm absorption band is found to be about 0.1.     

Bulk crystals of PbTe synthesized by the iodide method

Bulk crystals have been prepared for the first time from PbTe synthesized by low-temperature iodide method. Their basic structural, physico-chemical and electrical parameters as a result of certain technology conditions have been investigated.     

Stoichiometric dependence of electrical characteristics in WSSe single crystals grown by direct and chemical vapour transport techniques

Single crystals of tungsten sulphoselenide (WSSe) have been grown by both direct and chemical vapour transport techniques. The crystals have been subjected to Hall effect and resistivity measurements for their electrical characterization. The observed differences in the electrical resistivity, type of conduction, and activation energy have been attributed to the stoichiometric differences between the crystals grown by the two techniques. The crystals grown by chemical vapour transport technique with iodine as the transport agent have been found to be more stoichiometric.     

Growth,structure, electrical and optical properties of transition metal chalcogenide crystals synthesized by improved chemical vapor transport technique for semiconductor technologies

Low dimensional structures, including bulk crystals, thin films, nanowires and nanotubes, have received remarkable attention due to their novel functionality and potential applications in various areas of optics, electronics, photonics, and sensing devices and photovoltaic field. Recently, remarkable progress and modification have been achieved in the synthesis process of crystalline material by vapor transport technique. In this review, we introduce an improved concept of the closed tube Chemical Vapor Transport (CVT) technique for the single crystal growth of ZrSTe, TiSTe and TiSeTe. A modified reverse temperature profile has reported the growth of ZrSTe, TiSTe and TiSeTe results show the good crystalline quality of synthesized materials. The single-crystal X-ray diffraction data reveals all three samples have trigonal unit cell structure with a space group of P31. The Semiconducting behavior of grown crystals of ZrSTe, TiSTe and TiSeTe was verified by two probe resistivity measurements, Hall Effect measurements and optical absorption at room temperature in the spectral range of 200 nm - 2200 nm. In this review, we highlight the recent progress in the transition of metal chalcogenides for their advanced application in solar energy conversion, thin-film electronics, optoelectronic devices and quantum communication devices. Moreover, different experimental challenges within the described growth technique are probed. Additionally, a survey was done for the possible enhancement of Transition Metal Chalcogenide (TMC) crystalline materials grown by the Chemical Vapor Transport technique based on various growth parameters.     

Optical and electrical properties of Be doped GaN bulk crystals

Highly resistive GaN : Be was obtained by means of synthesis of Ga+Be with atomic nitrogen under high nitrogen pressure. Activation energy of resistivity is about 1.5 eV. This material exhibits features very different from those observed in highly resistive bulk GaN : Mg. Up to 300 K strong yellow band dominates photoluminescence spectrum in resistive GaN : Be crystals. Positron annihilation studies point to the presence of gallium vacancies, V_Ga. In highly resistive GaN:Mg neither yellow band with considerable intensity, nor detectable concentration of V_Ga was found. We also discuss the puzzling findings in highly resistive bulk GaN : Be of morphological features typical for highly conducting bulk n-GaN material.     

Growth of PBI2 single crystals from stoichiometric and Pb excess melts

We have successfully grown high-purity and -quality PbI₂ single crystals by the vertical Bridgman method. The rocking curves of four-crystal X-ray diffraction (XRD) show 120 arcsec in full-width at half-maximum (FWHM). The photoluminescence (PL) spectra at 7.8 K show the resolved intensive exciton emission line and the weak DAP emission band. The deep-level emissions are not observed. The measurement of the electrical and radiographic properties show that Leadiodide (PbI₂) single crystal has a resistivity of 5×10¹⁰ Ω cm and imager lag is 8 s, respectively. In order to improve the controllability of crystal growth, PbI₂ single crystals were also grown from a lead (Pb) excess PbI₂ source. The experimental results show very good reproducibility. In addition, the growth models of crystal are proposed, and the growth mechanism is discussed.     

Structural and electrical properties of vapour phase grown Cd1 − xFexTe single crystals

Cd_1 − xFe_xTe single crystals were prepared by vapour phase growth method in the composition range of 0 ≤ x ≤ 0.03. Chemical analysis, surface morphology, structural investigations and electrical properties were carried out by EDAX, SEM, XRD, TEM and transport technique, respectively. Microscopic variations between the target and actual compositions were noticed. Morphology studies revealed that dislocation aided growth is active in the present crystals. TEM and XRD studies confirmed that the samples of all compositions crystallized in zinc blende structure, and the lattice parameters varied almost linearly decreases with Fe content. At room temperature, the resistivity of the Cd_1 − xFe_xTe crystals of all compositions (x = 0.01, 0.015, 0.02, 0.025 and 0.03) lies in the range of 3.5-6.5 M Ω, the activation energies lie in the range of 63-133 meV, and the samples were show the ‘p’ type conductivity.     

Photoelectronic and electrical properties of CuIn5S8 single crystals

To identify the impurity levels in CuIn₅S₈ single crystals, the dark electrical conductivity and photoconductivity measurements were carried out in the temperature range of 50–460 K. The data reflect the intrinsic and extrinsic nature of the crystals above and below 300 K, respectively. Energy band gaps of 1.35 and 1.31 eV at 0 K and 300 K, were defined from the dark conductivity measurements and the photocurrent spectra, respectively. The dark and photoconductivity data in the extrinsic temperature region reflect the existence of two independent donor energy levels located at 130 and 16 meV. The photocurrent‐illumination intensity dependence (F) follows the law I_phαF^γ, with γ being 1.0, 0.5 and 1.0 at low, moderate and high intensities indicating the domination of monomolecular, bimolecular and strong recombination at the surface, respectively. In the intrinsic region and in the temperature region where the shallow donor energy level 16 meV is dominant, the free electron life time, τ_n, is found to be constant with increasing F. In the temperature region 140 K < T < 210 K, the free electron life time increases with increasing illumination intensity showing the supralinear character. Below 140 K, τ_n decrease with decreasing illumination intensity. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Studies on electrical conduction behavior of La1‐3xCaxBaxSrxMnO3 synthesized by chemical route

In the manganite La_1‐xM_xMnO₃ (M = Ca, Ba, Sr) the doping concentration introduces a mixed valency (Mn³⁺, Mn⁴⁺) which governs the magnetic and electrical properties of the compound. The perovskite oxides La_1‐3xCa_xBa_xSr_xMnO₃ (x = 0.00, 0.05, 0.10) were prepared by chemical method. Single‐phase formation is confirmed by XRD studies. The electrical behavior of compositions with x = 0.00, 0.05 and 0.10 in the system La_1‐3xCa_xBa_xSr_xMnO₃ was studied in the temperature range 300‐420 K. It is observed that conductivity decreases with increasing temperature as well as dopants concentration. Metallic behavior of these compositions decreases with increasing dopants concentration (x). The microstructures of these samples have been characterized using scanning electron microscopy (SEM). (© 2007 WILEY ‐VCH Verlag GmbH & Co. KGaA, Weinheim)