Photoconductivity of Se85−xTe15Hgx thin films

The photoconductive properties such as dark conductivity, steady state and transient characteristics of a-Se_85−xTe₁₅Hg_x thin films, prepared by thermal vacuum evaporation technique have been studied in the temperature range 312–380 K. Analysis of data shows that the activation energy of dark current is greater as compared to the activation energy of photocurrent. The activation energy increases at higher concentration of Hg which shows that the defect density of states decreases. Analysis of intensity dependent photoconductivity shows that the bimolecular recombination is predominant. The transient photoconductivity shows that the carrier lifetime decreases with the increase in Hg concentration and increases at higher concentration of Hg. This decrease is due to the transition trapping process. Further the photosensitivity and carrier lifetime increases at higher concentration of Hg which also confirms that the density of defect states decreases.     

Photoconductivity and electrical properties of epitaxial Pb1 − xCdxSe films

Photosensitive monocrystalline films Pb_{1 − x}Cd_xSe (x⩽ 0.03) of low carrier concentration (n = 0.3 ÷ 4 × 10¹⁷ cm⁻³ have been grown by hot wall epitaxy method on cleaved (111)BaF₂ or (100)KCl substrates.Photoconductive thresholds determined by spectral response measurements (at temperatures 4.2, 77 and 300 K) were in good agreement with the fundamental absorption edges and showed a large increase in the energy gap E_g with Cd content. Photoconductivity in the impurity range (hv < E_g) was observed.The temperature dependence of the Hall coefficient and the mobility between 4.2 and 300 K have been studied. Temperature freeze out of the free carriers was observed.Discussion of the carrier scattering mechanisms and impurity photoconductivity phenomena is presented.     

Synthesis, structure, and magnetic properties of anion-substituted manganese chalcogenides

The anion-substituted solid solutions of the MnSe_{1 t x} Te _x system have been synthesized. The crystal structure and magnetic properties of the synthesized solid solutions have been investigated. It has been shown that, in the concentration range 0 ?? x ?? 0.4, the solid solutions have a face-centered cubic structure. It has been revealed that an increase in the concentration of the substituting element in the MnSe_{1 ? x} Te _x system leads to an increase in the coefficient of thermal expansion of the sample. The investigation of the magnetic properties has been carried out at temperatures in the range 80 K < T < 1000 K in a magnetic field up to 8.6 kOe. It has been experimentally found that the type of antiferromagnetic order (the second type of ordering) remains unchanged over the entire concentration range up to x = 0.4 and that the paramagnetic Curie temperature and the Néel temperature decrease within the limits of 20%. Theoretical calculations have been performed using the Monte Carlo method, and the model of nanoclusters with an uncompensated antiferromagnetic moment has been proposed.     

Effect of Pb on the electrical properties of a-Ge20Se80 glasses

The present paper reports the effect of Pb impurity (low ∼2 at% and high ∼10 at%) on the ac conductivity (σ_ac) of a-Ge₂₀Se₈₀ glass. Frequency-dependent ac conductance and capacitance of the samples over a frequency range ∼100 Hz to 50 kHz have been taken in the temperature range ∼268 to 358 K. At frequency 2 kHz and temperature 298 K, the value of σ_ac increases at low as well as at higher concentration of Pb. σ_ac is proportional to ω^s for undoped and doped samples. The value of frequency exponent (s) decreases as the temperature increases. The static permittivity (ε_s) increases at both Pb concentrations. These results have been explained on the basis of some structural changes at low and higher concentration of Pb impurity.     

Investigation of magnetic phase transitions in dilute copper ferrites

Mössbauer spectra of copper ferrites CuGa _x Al_2x Fe_{2 ? 3x} O₄ (x = 0.3, 0.4, 0.5) have been measured at temperatures in the range from 90 to 295 K. The degree of disturbance of long-range magnetic order has been determined as a function of the temperature. The Curie temperature has been found for the composition with x = 0.5, and the dependence of the Curie temperature on the concentration of the nonmagnetic impurity has been constructed.     

Electrophysical parameters of <Emphasis Type="Italic">c</Emphasis>-oriented Bi<Subscript>2</Subscript>Te<Subscript>3</Subscript> films with a low concentration of antistructural defects

Epitaxial c-oriented Bi₂Te₃ films 1.2 μm in thickness are grown by the hot wall method for a low supersaturation of the vapor phase over the surface of mica substrates. The hexagonal unit cell parameters a = 4.386 Å and c = 30.452 Å of the grown films almost coincide with the corresponding parameters of stoichiometric bulk Bi₂Te₃ crystals. At T = 100 K, the Hall concentration of electrons in the films is on the order of 8 × 10¹⁸ cm^?3, while the highest values of the thermoelectric coefficient (α ≈ 280 μV K^?1) are observed at temperatures on the order of 260 K. Under impurity conduction conditions, conductivity σ of the films increases upon cooling in inverse proportion to the squared temperature. In the temperature range 100–200 K, thermoelectric power parameter α²σ of Bi₂Te₃ films has values of 80–90 μW cm^?1 K^?2.     

Investigation of a.c. conductivity measurements in a-Se80Te20 and a-Se80Te10M10 (M = Cd, in, Sb) alloys using correlated barrier hopping model

The a.c. conductivity of a-Se₈₀Te₂₀ and a-Se₈₀Te₁₀M₁₀ (M = Cd, In, Sb) alloys has been investigated as a function of temperature in the range from 280 to 330 K and frequency in the range from 10² to 10⁴ Hz. The experimental results indicate that a.c. conductivity σ_ac is proportional to ω^s where s < 1 and decreases with increasing temperature. The results obtained are discussed in terms of the correlated barrier hopping (CBH) model. An agreement between experimental and theoretical results suggests that the a.c. conductivity behavior of a-Se₈₀Te₂₀ and a-Se₈₀Te₁₀M₁₀ (M = Cd, In, Sb) system can be successfully explained by CBH model. The contribution of single polaron and bipolaron hopping to a.c. conductivity in present alloys is also studied.     

Influence of silver on the galvanomagnetic properties and energy spectrum of mixed (Bi1− x Sbx)2Te3 crystals

An investigation is made of the temperature dependences of the resistivity in the range 4.2–300 K, the Hall effect, and the Shubnikov-de Haas effect in magnetic fields up to 40 T in (Bi_{1? x} Sb_x)₂Te₃Ag_y single crystals (0 ≤ x ≤ 0.75). Doping (Bi_{1? x} Sb_x)₂Te₃ crystals with silver showed that in Sb₂Te₃ and (Bi_{1? x} Sb_x)₂Te₃ crystals unlike Bi₂Te₃ silver exhibits acceptor properties. The angular and concentration dependences of the Shubnikov-de Haas effect were studied in (Bi_{1? x} Sb_x)₂Te₃Ag_y. It was established that the anisotropy of the ellipsoids of the upper valence band in Bi_0.5Sb_1.5Te₃ remains unchanged as a result of silver doping.     

Photoconductivity in amorphous thin films of Ge22Se78−xBix

Temperature and intensity dependence of photoconductivity is studied in amorphous thin films of Ge₂₂Se_78−x Bi_x with x = 0, 2 and 10. Transient photoconductivity measurements have also been made on the same samples. Our results show that photosensitivity decreases as Bi concentration is increased from x = 0 to x = 2. However, at high concentration of Bi(x = 10), photosensitivity again increases. Transient photoconductivity also show a different behaviour at low and high concentration of Bi. Results have been explained in terms of defect states produced due to Bi incorporation in GeSe system.     

Transport coefficients and defect structure of Sb2−xAgxTe3 single crystals

Incorporation of Ag in the crystal lattice of Sb₂Te₃ creates structural defects that have a strong influence on the transport properties. Single crystals of Sb_2−xAg_xTe₃ (x=0.0; 0.014; 0.018 and 0.022) were characterized by measurements of the temperature dependence of the electrical resistivity, Hall coefficient, Seebeck coefficient and thermal conductivity in the temperature range of 5-300 K. With an increasing content of Ag the electrical resistance, the Hall coefficient and the Seebeck coefficient all decrease. This implies that the incorporation of Ag atoms in the Sb₂Te₃ crystal structure results in an increasing concentration of holes. However, the doping efficiency of Ag appears to be only about 50% of the expected value. We explain this discrepancy by a model based on the interaction of Ag impurity with the native defects in the Sb_2−xAg_xTe₃ crystal lattice. Defects have a particularly strong influence on the thermal conductivity. We analyze the temperature dependence of the lattice thermal conductivity in the context of the Debye model. Of the various phonon scattering contributions, the dominant influence of Ag incorporation in the crystal lattice of Sb₂Te₃ is revealed to be point-defect scattering where both the mass defect and elastic strain play a pivotal role.     

An analysis of the thermoelectric efficiency of n-(Bi,Sb)2(Te,Se,S)3 solid solutions within an isotropic scattering model

A study is reported on the thermoelectric properties of n-type solid solutions Bi₂Te_3?y Se_y (y=0.12, 0.3, 0.36), Bi_2?x Sb_xTe_3?y Se_y (x=0.08, 0.12; y=0.24, 0.36), and Bi₂Te_3?z S_z (z=0.12, 0.21) as functions of carrier concentration within the 80-to 300-K range. It has been established that the highest thermoelectric efficiency Z is observed in the Bi₂Te_3?y Se_y (y=0.3) solid solution containing excess Te at optimum carrier concentrations (0.35×10¹⁹ cm^?3) and at temperatures from 80 to 250 K. The increase in Z in the Bi₂Te_3?y Se_y solid solution compared with Bi_2?x Sb_xTe_3?y Se_y and Bi₂Te_3?z S_z is accounted for by the high mobility μ₀, an increase in the effective mass m/m ₀ with decreasing temperature, the low lattice heat conductivity κ_L, and the weak anisotropy of the constant-energy surface in a model assuming isotropic carrier scattering.     

Influence of frequency, temperature and composition on electrical properties of polycrystalline Co0.5CdxFe2.5−xO4 ferrites

Polycrystalline ferrites with general formula Co_0.5Cd_xFe_2.5−xO₄ (0.0?x?0.5) were prepared by sol-gel method. The dielectric properties ε′, ε″, loss tangent tan δ and ac conductivity σ_ac have been studied as a function of frequency, temperature and composition. The experimental results indicate that ε′, ε″, tan δ and σ_ac decrease as the frequency increases; whereas they increase as the temperature increases. These parameters are found to increase by increasing the concentration of Cd content up to x=0.2, after which they start to decrease with further increase in concentration of Cd ion. The dielectric properties and ac conductivity in studied samples have been explained on the basis of space charge polarization according to Maxwell and Wagner's two-layer model and the hoping between adjacent Fe²⁺ and Fe³⁺ as well as the hole hopping between Co³⁺and Co²⁺ ions at B-sites. The values of activation energies E_f for conduction process are determined from Arrhenius plots, and the variations in these activation energies as a function of Cd content are discussed. The complex impedance analysis is used to separate the grain and grain boundary of the system Co_0.5Cd_xFe_2.5−xO₄. The variations of both grain boundary and grain resistances with temperature and composition are evaluated in the frequency range 42 Hz-5 MHz.     

Photoconduction in amorphous thin films of Se90Sb10-xAgx glassy alloys

The present paper reports the steady state photoconductivity and photosensitivity response of thermally evaporated amorphous thin films of Se₉₀Sb_10-xAg_x(x = 2, 4, 6, 8, 10). Temperature dependence of dark conductivity is studied and activation energy is calculated for different samples. Temperature dependence of photoconductivity is also studied at different intensities. From temperature dependence of photoconductivity activation energy is computed at different intensities which are found to vary from 0.26 to 0.47 eV. Intensity dependence of photoconductivity has also been studied at different temperatures. These curves are plotted on logarithmic scale and found to be straight lines which show that photoconductivity follows a power law with intensity. Composition dependence of dark conductivity, activation energy of DC conduction and photosensitivity show that these parameters are highly. composition dependent and show a discontinuity at a particular composition when Ag concentration becomes 6 at. %. This is explained in terms of transition from floppy state to mechanically stabilized state at this composition.     

On the nature of a lattice vibrational mode at a frequency of 135 cm−1 in Hg1 − x Cd x Te alloys

The vibrational spectrum of a cadmium impurity atom in the HgTe crystal has been calculated using the microscopic theory of lattice dynamics in the approximation of a low impurity concentration. Within this theory, the behavior of the local and quasi-local modes induced upon substitution of the lighter Cd atom for the Hg atom in the region of the zero or very low one-phonon density of states in the HgTe crystal has been considered. It has been found that, apart from the local mode at a frequency of 155 cm^?1, the calculated vibrational spectra exhibit a weak (but clearly pronounced) feature at a frequency of 134 cm^?1, which coincides with the experimentally observed vibrational mode (the “minicluster” mode) at a frequency of 135 cm^?1 in the Hg_{1 ? x} Cd _x Te (x = 0.2–0.3) alloys at 80 K.     

Solid solutions of CdSn(As1−xPx)2 and their properties

We have grown single crystals of CdSn(As_1–xP_x)₂ solid solutions over the entire range of x. On the basis of the temperature dependence of the Hall coefficient and the Hall mobility, we conclude that there is a mixed carrier scattering mechanism in all of these solid solutions, over the entire temperature range from 100 to 500 K, involving both impurity ions and thermal lattice phonons. IR absorption and photoconductivity spectra show that the band gap in the solid solutions varies linearly with composition. We conclude that crystals in the range 0.5相似文献   

Far-infrared detection with Hg1−xCdxTe

We report detection in liquid He cooled n−Hg_1−xCd_xCd_xTe at wavelengths between 140 and 1200 μm. With the mole fraction, x, of Cd <0.4m the alloy behaves as an electron bolometer with similar detectivity, but much improved bandwidth, compared with n-InSb. With x > 0.48 the detection process is extrinsic photoconductivity with an energy gap of a few meV. Lattice absorption severely limits detection in the wavelength range 220–340 μm.     

Effect of bond polarity in Sb2Te3−x Se x single crystals

Sb₂Te_3?x Se _x (x=0·00?1·25) single crystals were prepared from 5N purity elements using a modified Bridgman method. Measurements of the reflectivity spectra in the plasma resonance frequency range, Hall constantR _H(B∥c) and electrical conductivityσ _⊥C were carried out on these samples at room temperature. With increasing selenium content a shift of the reflectivity minimum towards longer wavelengths was observed as well as an increase of the Hall constant and a decrease of the electrical conductivity — the incorporation of Se atoms into the Sb₂Te₃ crystal lattice results obviously in a decrease in the concentration of free carriers. This effect is accounted for by a change in the polarity of bonds in the Sb₂Te₃ crystal lattice, due to the formation of Se _Te ^x substitutional defects.     

Short-Range order of TlIn<Subscript>1–<Emphasis Type="Italic">x</Emphasis></Subscript>Sn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Te<Subscript>2</Subscript> thin films

The formation of the short-range order structure of amorphous nanometer-thick TlIn_1–x Sn _x Te₂ films (х = 0.02–0.09) obtained via vacuum deposition onto substrates of fresh KCl and KJ chips and celluloid at a temperature below Т = 213 K is studied by high-energy electron diffraction. Both freshly deposited films and films held in vacuum (10^–2 Pa) at room temperature in darkness for several months are studied. The effect of the tin concentration on the interatomic distances, the coordination numbers, and the time of amorphous phase stability of TlIn_1–x Sn _x Te₂ films due to a great spread in bond lengths and bond angles is established.     

Ferromagnetism in a new dilute magnetic semiconductor Sb<Subscript>2−<Emphasis Type="Italic">x</Emphasis></Subscript>Cr<Subscript>x</Subscript>Te<Subscript>3</Subscript>

Magnetic and galvanomagnetic properties of single crystals of a new dilute magnetic semiconductor p-Sb_2?xCr_xTe₃ (x = 0, 0.0115, 0.0215) are investigated in a temperature range of 1.7–300 K. A ferromagnetic phase with a Curie temperature of T_C ≈ 5.8 (x = 0.0215) and 2.0 K (x = 0.0115) is detected. The easy magnetization axis is parallel to the C₃ crystallographic axis. Analysis of the Shubnikov-de Haas effect observed in these crystals in strong magnetic fields leads to the conclusion that the hole concentration decreases as a result of doping with Cr. Negative magnetoresistance and the anomalous Hall effect are observed in Cr-doped samples at liquid helium temperature.