Some Physical Properties of Ga2Se Single Crystals

Measurements of the electrical conductivity, Hall effect, thermnoelectric power were carried out in a wide temperature range (from about 170 to 475 K) for Ga₂Se compound grown in single crystalline form. The present investigation revealed unusual observations in the Hall effect and the scattering mechanisms of the charge carriers indicating that Ga₂Se is not a simple semiconductor. Also it showed that Ga₂Se has a relatively high value of the thermoelectric power. A lot of physical parameters were deduced in the present study.     

Electronic Transport Properties of Thallium Sesquiselenide Single Crystals

Electronic transport measurements were made on single crystal samples of Tl₂Se₃. The crystals were prepared by a special design based on Bridgman technique. The influence of temperature on the electrical conductivity, Hall effect, Hall mobility and the carrier concentration was investigated in the temperature range 200–400 K. The energy gap as well as the ionization energy were calculated. The scattering mechanism of the charge carrier was discussed in the same temperature range.     

Transport Properties of TlInSe2 Single Crystals

Single crystals of TlInSe₂ were prepared by a special modified Bridgman technique. The influence of temperature on the electrical conductivity, Hall effect, Hall mobility, and the carrier concentration was investigated in the temperature range 190–625 K. The energy gap of conduction was calculated. The scattering mechanism of the charge carrier was discussed in the same temperature range. Beside this, the thermoelectric power was measured in a temperature range extending from 190 up to 485 K.     

Effect of indium intercalation on various properties of MoSe2 single crystals

Indium intercalated MoSe₂ single crystals i.e. In_xMoSe₂ (0 ≤ x ≤ 1) are grown by direct vapour transport technique. These crystals are structurally characterized by X‐ray diffraction, by determining their lattice parameters ‘a’ and ‘c’ and X‐ray density. The Hall effect and thermoelectric power measurements shows that In_xMoSe₂ (0 ≤ x ≤ 1) are p‐type in nature. The direct and indirect band gap measurements are also undertaken on these semiconducting materials. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and Characterization of Single Crystals of the Ternary Compound TlGaTe2

The electrical conductivity and the Hall effect for TlGaTe₂ crystals have been measured over a wide temperature range. The crystal used for our study was grown by the Bridgman technique and possessed p-type conductivity. The energy gap has been found to be 0.84 eV, whereas the ionization energy has the value 0.25 eV. The variation of the Hall mobility as well as the carrier concentration with temperature was investigated. The scattering mechanism of the carrier in the whole temperature range of investigation was checked.     

Electron‐phonon short‐range interactions mobility and p‐ to n‐type conversion in TlGaS2 crystals

The conductivity type conversion from p ‐ to n ‐type at a critical temperature of 315 K in TlGaS₂ crystals is observed through the Hall effect measurements in the temperature range of 200–350 K. The analysis of the temperature‐dependent electrical resistivity, Hall coefficient and carrier concentration data reveals the extrinsic type of conduction with donor impurity levels that behave as acceptor levels when are empty. The data analysis allowed the calculation of hole and electron effective masses of 0.36m ₀ and 0.23m ₀, respectively. In addition, the temperature‐dependent Hall mobility is found to decrease with temperature following a logarithmic slope of ∼1.6. The Hall mobility in the n ‐region is limited by the electron‐phonon short‐range interactions scattering with an electron‐phonon coupling constant of 0.21. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Investigation of Thermoelectric Power of Ga2Se3 Monocrystals

Single crystals of Ga₂Se₃ were prepared by a technique based on the Bridgman method. Thermoelectric power was investigated in the temperature range 160–525 K. From this investigation many physical parameters such as effective masses of charge carriers, carrier mobilities, diffusion length, diffusion coefficient, and the relaxation time for both majority and minority carriers were estimated. In conjunction with the electrical conductivity and the charge carrier concentration, the thermoelectric power is discussed.     

Carrier Scattering Mechanisms in GaS0.5Se0.5 Layered Crystals

Systematic dark electrical resistivity and Hall mobility measurements have been carried out in the temperature range 150‐400 K on n‐type GaS_0.5Se_0.5 layered crystals. The analysis of temperature dependent electrical resistivity and carrier concentration reveals the extrinsic type of conduction with a donor impurity level located at 0.44 eV, donor and acceptor concentrations of 3.4 ×10¹⁷ and 4.1×10¹⁶ cm^‐3, respectively, and an electron effective mass of 0.41 m₀. The Hall mobility is limited by the electron‐phonon short‐range interactions scattering at high temperatures combined with the ionized impurity scattering at low temperatures. The electron‐phonon short‐range interactions scattering mobility analysis reveals an electron‐phonon coupling constant of 0.25 and conduction band deformation potential of 5.57 eV/Å.     

Electrical Properties of CuIn3Se5 Bulk Crystal at Low Temperature

CuIn₃Se₅ crystals were grown from the melt containing stoichiometric quantities of the elements of at least 5 N purity. The structure was analyzed by X‐ray powder diffraction, and shows mainly a tetragonal single phase. The chemical composition was determined by EDAX and Total X‐Ray Fluorescence (TXRF). The conductivity and the Hall effect have been measured in the temperature range from 10 to 300 K. The polar optical scattering was found to dominate at low temperatures, while in the high temperature region ionized impurity scattering mechanism was observed.     

Electrical conductivity of Cs<Subscript>2</Subscript>CuCl<Subscript>4</Subscript> crystals

The electrical conductivity of Cs₂CuCl₄ single crystals, synthesized by crystallization from aqueous solutions in the CsCl–CuCl₂–H₂O system, has been investigated. The temperature dependence of the electrical conductivity of crystals in a temperature range of 338–584 K exhibits no anomalies. The electrical transfer activation enthalpy is ΔH_σ = 0.72 ± 0.05 eV and the conductivity is σ = 3 × 10^–4 S/cm at 584 K. The most likely carriers in Cs₂CuCl₄ are Cs⁺ cations, which transfer electric charge according to the vacancy mechanism.     

Sb2Te3 Single Crystals Doped with Chromium Atoms

Chromium-doped Sb₂Te₃ single crystals were prepared from elements of semiconductor purity using a modified Bridgman method. The samples of these crystals were characterized by means of X-ray diffraction analysis, measurements of the reflectivity in the plasma resonance frequency range ω_p, of the Hall constant R_H and electrical conductivity σ. It was found that the incorporation of Cr atoms into the Sb₂Te₃ crystal lattice reduces the volume of the unit cell, whereas the values of ω_p and R_H (i.e. the concentration of holes) remain unaltered and the values of σ decrease with increasing chromium content. This effect is qualitatively explained by an interaction of incorporated Cr atoms with antisite defects of Sb₂Te₃ crystal lattice. The In (R_Hσ) vs. In T dependences show that the dominant mechanism of scattering of free charge carriers in the studied crystals is the scattering by acoustic phonons; the presence of chromium atoms increases the scattering rate by ionized impurities.     

Carrier Transport Properties of InS Single Crystals

The electrical resistivity and Hall effect of indium sulfide single crystals are measured in the temperature range from 25 to 350 K. The donor energy levels located at 500, 40 and 10 meV below the conduction band are identified from both measurements. The data analysis of the temperature‐dependent Hall effect measurements revealed a carrier effective mass of 0.95 m₀, a carrier compensation ratio of 0.9 and an acoustic deformation potential of 6 eV. The Hall mobility data are analyzed assuming the carrier scattering by acoustic and polar optical phonons, and ionized impurities.     

Investigation of carrier scattering mechanisms in TlInS2 single crystals by Hall effect measurements

TlInS₂ single crystals are studied through the conductivity and Hall effect measurements in the temperature regions of 100‐400 and 170‐400 K, respectively. An anomalous behavior of Hall voltage, which changes sign below 315 K, is interpreted through the existence of deep donor impurity levels that behave as acceptor levels when are empty. The hole and electron mobility are limited by the hole‐ and electron‐phonon short range interactions scattering above and below 315 K, respectively. An energy level of 35 meV and a set of donor energy levels located at 360, 280, 220 and 170/152 meV are determined from the temperature dependencies of the carrier concentration and conductivity. A hole, electron, hole‐electron pair effective masses of 0.24 m_o, 0.14 m_o and 0.09 m_o and hole‐ and electron‐phonon coupling constants of 0.50 and 0.64, respectively, are obtained from the Hall effect measurements. The theoretical fit of the Hall coefficient reveals a hole to electron mobility ratio of 0.8. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Electrical Conductivity and Thermal Dehydration Studies of Mixed Single Crystals of BaCu(C2O4)2 · 6 H2O,Ba1–xCuxC2O4 · 4 H2O and Ba1–2x(NH4)2xC2O4 · 4 H2O

The measurement of electrical conductivity for the investigation of the number of water molecules present in the mixed crystals of barium copper oxalate and barium ammonium oxalate lattice have been carried out in the temperature range 30 to 450 °C. The dehydration temperature and the number of water molecules removed out of the structure at a particular temperature is estimated from the sharp increase in conductivity at these points. The almost steep increase of conductivity is attributed to the increase in the number of mobile charge carriers H⁺ and OH^– ions generated from the escaping water molecules. The study of electrical conductivity in association with the thermal behaviour has been used to understand the mechanism of conduction.     

Influence of photonic excitations on the electrical parameters of TlInS2 crystals

The photo‐excitation effect on the current transport mechanism in TlInS₂ crystals has been studied by means of dark and illuminated conductivity measurements. The temperature‐dependent electrical conductivity analysis in the temperature region of 110‐340 K revealed the domination of the thermionic emission and the thermally assisted variable range hopping (VRH) of charge carriers above and below 160 K, respectively. Above 160 K, the conductivity activation energies in the dark are found to be 0.28 and 0.15 eV in the temperature regions of 340‐240 K and 230‐160 K, respectively. In the temperature region of 110‐150 K, the dark variable range hopping analysis revealed a density of localized states of 1.99×10²² cm^–3eV^–1, an average hopping distance of 0.53 nm and an average hopping energy of 79.65 meV. When the sample was photo‐excited, the values of the conductivity activation energies, the density of localized states near the Fermi level and the average hopping energy were observed to decrease sharply with increasing illumination intensity. On the other hand, the average hopping distance increased with rising illumination intensity. Such behaviours were attributed to the Fermi level shift and/or trap density reduction by electron‐hole recombination. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Semiconducting Properties of TI2Te3 Single Crystals

Electrical conductivity and Hall effect measurements were performed on single crystals of TI₂Te₃ to have the general semiconducting behaviour of this compound. The measurements were done at the temperature range 160–350 K. All crystals were found to be of p-type conductivity. The values of the Hall coefficient and the electrical conductivity at room temperature were 1.59 × 10³ cm³/coul and 3.2 × 10⁻² ω⁻¹ cm⁻¹, respectively. The hole concentration at the same temperature was driven as 39.31 × 10¹¹ cm⁻³. The energy gap was found to be 0.7 eV where the depth of impurity centers was 0.45 eV. The temperature dependence of the mobility is discussed.     

On a Hypothesis on the Molecule Vacancies in PbTe

The temperature dependence of the current carriers mobility in SnTe(I) and PbTe (I) synthesized in presence of SnI₂ or PbI₂ respectively was studied. An experimental formula was established, showing that current carriers scattering in SnTe(I) is due to vacancies at constant Hall coefficient. For PbTe (I) crystallized from tellurium solution by traveling heater method the mobility is high (between 2.10⁴ and 4.10⁴ cm²/Vs) and the Hall coefficient is constant within the interval 77 K–450 K. Only within 77 K–160 K interval the current carriers scattering is due to vacancies. A hypothesis is proposed based on the presence of molecular vacancies (V_pbTe). These vacancies do not change electron gas concentration but do change the carriers mobility. Specimens with a negligibly low lead atoms vacancies Concentration were investigated. An empirical expression is established which shows that their mobility depends on molecular vacancies concentration and explains observed weak temperature influence upon carriers mobility. These results are obtained only from Hall coefficient and electric conductivity measurements within the 77 K–160 K temperature interval.     

Thermoelectrical properties of In1‐xGaxAs and InAs crystals irradiated with fast electrons

The thermoelectric power in In_1‐xGa_xAs (x = 0,01;0,04) solid solutions and InAs crystals irradiated with fast electrons by the energy of 6 MeV and dose of 10¹⁶‐ 2 x 10¹⁷ el/cm^‐2 on the interval 80‐400 K have been investigated. It is revealed that in the all crystals the value of the thermoelectric power is decreased under irradiation that resulted from the growth of the free electron concentration to form radiation induced defects of the donor type. It has been determined that in the initial InAs after irradiation, the charge carriers scatter on optical phonons and in In_1‐xGa_xAs solid solutions they do on optical phonons and ionized impurities. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and morphology of the single crystals of thermoelectric oxide material NaxCoO2

We have grown single crystals of recently discovered thermoelectric oxide material Na_xCoO₂ using NaCl flux. Crystals of sizes upto 1.5 x 1.5 x 1.5 mm³ having different morphological habits were reproducibly grown. The atomic force microscopic studies show that along c‐axis crystals grow via 2D layer‐by‐layer mechanism. The X‐ray diffraction analyses show that grown crystals are rich in Na content as compared to the starting charge indicating that NaCl flux also acts as a source of Na. The resistivity of the crystals exhibited a linear temperature dependence in the region between 30 and 300 K. © 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim     

On the conduction mechanism and thermoelectric phenomena in In6S7 layer crystals

In the present paper, measurements of the electrical conductivity and Hall coefficient on single crystal of In₆S₇, grown by a new crystal growth technique, were done. The crystal was found to be of n-type conductivity. The low conductivity sample showed as the most striking feature an exponential increase of the Hall mobility with temperature. This effect was explained by assuming a mixed conduction and different scattering mechanisms for electrons and holes in the same temperature range. Also we have made thermoelectric power measurements to support this assumption. An energy gap of 0.64 eV was found.