Theory Of Hopping Conductivity Research Articles

Electrical conductivity of tungsten doped vanadium dioxide obtained by the sol–gel technique

Thin films of tungsten-doped and pure vanadium dioxide with a metal–insulator transition are prepared by a sol–gel method. The films are characterized by X-ray diffraction, and electrical conductivity is measured in a temperature range from 50 to 380K. It is shown that the conductivity of the films varies with temperature as σ~exp(aT−b/T). The experimental results are discussed from the viewpoint of the small polaron hopping conduction theory taking into account the influence of thermal lattice vibrations onto the resonance integral. The values of the activation energy and polaron radius are found. It is shown that doping with tungsten affects severely onto the electrical properties of vanadium dioxide.

Electrical conductivity of vanadium dioxide switching channel

The electrical conductivity of the switching channel of vanadium dioxide thin-film sandwich structures is studied over a wide temperature range (15-300 K). It is shown that the electrical resistance of the channel varies with temperature as R~exp(aT-b/T) in the high-temperature region (above 70 K). The experimental results are discussed from the viewpoint of the small polaron hopping conduction theory which takes into account the influence of thermal lattice vibrations onto the resonance integral.

Variable Range Hopping Conduction in Neutron-Transmutation-Doped70Ge:Ga

Variable range hopping conduction in neutron-transmutation-doped, isotopically enriched 70Ge:Ga samples for the temperature range T = 20 to 250 mK has been studied in the critical regime for the metal–insulator transition. Eighteen samples investigated had Ga concentrations in the range N = 0.942Nc to 0.998Nc, where Nc is the critical Ga concentration for the metal–insulator transition. The low temperature resistivities ρ of all samples obey the variable range hopping conduction theory of Efros-Shklovskii type with an appropriate temperature dependence in the pre-factor; ρ = ρ0T–1/3 exp (T0/T)1/2. The critical exponent α of T0 as a function of N has been determined using the form T0 ∝ (1 — N/Nc)α. A clear crossover of α from α ≈︂ 1 to 3.5 has been observed at N ≈︂ 0.99Nc. The excitation of holes from the lower- to upper-Hubbard bands is the dominant conduction mechanism in the α ≈︂ 1 region, while the standard variable range hopping of holes from occupied to empty Ga sites takes place in the very vicinity of the transition where α ≈︂ 3.5. The important role of the doping compensation is proposed in connection with the critical behavior of the electrical conductivity.

Thermal annealing effect on low temperature molecular beam epitaxy grown GaAs: Arsenic precipitation and the change of resistivity

The post-growth annealing effects on the electrical properties of low temperature (LT-) GaAs grown by molecular beam epitaxy have been investigated. It was found that the resistivity of the LT-GaAs layer increased exponentially with annealing temperature TA, resulting in an activation energy of 2.1 eV. This activation energy is related to the activation energy of arsenic precipitation. Based on hopping conduction theory, an As cluster density NT, has been estimated from the resistivities of the LT-GaAs layers. The change of density of arsenic clusters with TA, was found to be of the form NT=NT0 exp(−T/T0), in agreement with values obtained by transmission electron microscopy measurements. The breakdown voltage of the LT-GaAs layer remained almost unchanged as TA was increased up to 650 °C, but the breakdown characteristic became soft. The formation of As clusters is held responsible for the soft breakdown of the LT-GaAs layer after annealing.

Dc electrical conductivity of tellurite phosphate glasses

The dc electrical conductivity of the ternary glasses [81 mol, TeO2-19 mol P2O5]0.95 [RnOm]0.05 (R=La, Ce, Pr, Nd, Sm, and Yb) have been measured in the temperature range 50–300 °C. The electrical conductivity data have been examined and discussed on the basis of small polaron hopping conduction theory for the purpose of determining why rare earth containing tellurite glasses show lower electrical conductivity than the undoped glass. The values of the activation energies were in the range 0.84–1.04 eV depending upon the kind of the rare-earth ion. It is concluded that the lower dc electrical conductivity of these rare earth containing tellurite phosphate glasses is predominantly due to a higher activation energy.

Electronic conduction in Fe 2O 3TeO 2P 2O 5 glasses: an explication for high conductivity of iron-containing tellurite glasses

The electrical conductivity of ternary Fe 2O 3TeO 2P 2O 5 glasses has been examined and discussed on the basis of the small polaron hopping conduction theory for the purpose of determining why iron-containing tellurite glasses show higher electrical conductivity than other iron-containing phosphate and borate glasses. The tunneling factor of the hopping electron for the TeO 2-rich glass does not differ from that of the P 2O 5-rich glass, indicating that the pre-exponential factor is not important for elucidating the high electrical conductivity of the tellurite glass. The activation energy for electrical conduction of the TeO 2-rich glass is much lower than that of the P 2O 5-rich glass and its variation with the composition corresponds to the variation of the electrical conductivity. It is concluded that the higher electrical conductivity of the iron-containing tellurite glass is predominantly brought about by the lower activation energy.

Charge storage in pure and titanium dioxide doped polyarylate, and conduction in pure polyarylate

Charge storage of cast, pure and titanium dioxide doped amorphous polyarylate films was studied using thermally stimulated charge decay and thermally stimulated currents (TSC). Optimum storage was obtained by corona charging at 180°C, using 10 wt% titanium dioxide. A half value charge decay temperature ( T 1 2 ) of 180°C at 30% R.H. was then obtained. This value is 54°C higher than the T 1 2 of 126°C obtained for room temperature charging. Pure polyarylate charged at 180°C had a T 1 2 of 126°C, the same as that for room temperature charging. Both dopant-matrix boundaries and/ or additives themselves may act as deep traps. Steady state current-field ( F) curves of pure polyarylate follow a sinh law in F/ kT in the temperatuer range 87–143°C, favouring carrier hopping as the conduction mechanism. An activation energy of 1.1 eV was obtained from thermally stimulated polarization currents, and agreed with that obtained from a hopping conduction theory.

Alternative generalized master equation approach to the dc phonon-assisted hopping

As the momentum operator has no diagonal elements between localized states, the hopping conduction theory should be formulated in terms of the linear response of the site-off-diagonal elements of the single-electron density matrix to an external field. A theory of this kind, starting from generalized master equations and yielding the dc phonon-assisted hopping conductivity and thermopower is formulated. This is an alternative to the usual approach treating the current conduction via a time-derivative of the electric dipole momentum.

Debye Temperature and Electrical Conduction of Fe2O3‐CaO‐SiO2 Glasses

The electrical conductivity of iron‐containing silica glasses was measured from 80 to 350 K. The conductivity data were analyzed based on the hopping conduction theory. The hopping binding energy (Wp) and disorder energy WD) were calculated from the activation energy at high and low temperatures. The disorder energy obtained was much lower than reported for FeO‐P2O5 glasses, but similar to that for vandium‐containing glasses.

Investigation of shallow radiation defect levels produced in Ge by fast-neutron irradiation

The electronic properties of Ge crystals irradiated with fast reactor neutrons are studied in the temperature range 1.7 to 300 K. Sb-, As- and Ga-doped Ge are used as original material. It is found that the activation energy of shallow radiation defect levels is 16 meV in the case of low concentration and compensation. Some deepening of the Fermi level at a degree of compensation ≈ 0.4 is observed which increases the activation energy of the (Ev + 0.016) eV level. Hopping conductivity between shallow radiation defect levels, (Ev + 0.016) eV, is studied. The conclusion is made that the theory based on the percolation model can be used for accounting for hopping conductivity between these levels. The experimental dependence of the extrapolated resistivity Q3 on the defect concentration is in agreement with the hopping conduction theory if the Bohr radius of the defect is assumed to be close to 40 Å. [Russian Text Ignored].