Two-carrier transition in radiative recombination of two-dimensional electrons in GaAs/AlGaAs

We observed photoluminescence (PL) and photoluminescence excitation (PLE) spectra due to shake-up processes of recombination of two-dimensional electrons and free excitons in a modulation-doped GaAs quantum well at He temperatures. One of the processes is that when an electron recombines with a hole, another electron is excited from the conduction band in GaAs to that in AlGaAs. The other process is that a hole is excited from an acceptor level or the valence band in GaAs to the valence band in AlGaAs during recombination. The electron process is observed in both PL and PLE spectra while the hole process only in the PL spectra. The excitation-intensity dependence of the peak intensity of hole-excited PL is almost quadratic, indicating three-carrier process in the shake-up process. The band offsets of the conduction and valence bands are estimated to be 220 and 146 meV, respectively.     

Space-charge conduction

Electric currents in solids are usually associated with the presence of electrons which are free to move under the influence of a field. In most cases these free current carriers exist in the charge neutral material. In this article the introduction of excess charge is discussed and it is shown how such charge can carry a current. The use of space-charge conduction as a tool in the study of defects and surfaces is discussed. The simultaneous injection of positive and negative charge at opposite electrodes is also considered. The bearing of space-charge conduction on device technology is reviewed.     

Hopping conduction in amorphous semiconductors

It is suggested that conduction in localized states at the band edge of an amorphous semiconductor occurs by variable-range hopping. The hopping length is then typically ten times larger than the average interatomic separation and increases with decreasing temperature. The hopping energy is several times smaller than Arrhenius plots of the mobility would indicate.     

Electrical conduction in copper vanadate

A.C. and d.c. electrical conductivities, thermoelectric power and dielectric constant of copper vanadate (CuV₂O₆) have been measured in the temperature range 300–1000 K in order to discuss the electrical conduction in the compound. The extrinsic conduction, which takes place below 500 K, has been explained by small polaron hopping mechanism while intrinsic conduction, which takes place above 500 K, has been explained by large polaron band mechanism in view of the values of activation energy and charge carrier mobility in the temperature ranges 300–500 K and 500–1000 K.     

Hopping conduction in iodine-doped polystyrene

This paper discusses electromigration in iodine-doped polystyrene in the temperature interval from 300 to 400 K. It is shown that, because of impurities capable of forming charge-transfer complexes with the macromolecules of the polymer, electrical conduction occurs by a hopping mechanism. Fiz. Tverd. Tela (St. Petersburg) 39, 951–952 (May 1997)     

Hopping conduction in modulated superionics

The dynamics of a lattice gas model within a hopping limit in the presence of a structure modulation is studied. It is found that above a given critical value U_c of the modulating potential extra modes due to oscillations of the occupation numbers appear. In particular, it is shown that in the case of superionic conductors these are responsibilities for the peculiar dispersion of the microwave conductivity.     

Hopping conduction in EuS polycrystals

The dependences of the electrical conductivity of europium monosulfide (EuS) polycrystals on temperature in the range 150–400 K and pressures to 620 MPa have been studied. It is shown that the electrotransfer is mainly performed due to a hopping mechanism.     

One-dimensional conduction in charge-density-wave nanowires

We report a systematic study of the transport properties of coupled one-dimensional metallic chains as a function of the number of parallel chains. When the number of parallel chains is less than 2000, the transport properties show power-law behavior on temperature and voltage, characteristic for one-dimensional systems.     

Steady-state conduction in self-similar billiards

The self-similar Lorentz billiard channel is a spatially extended deterministic dynamical system which consists of an infinite one-dimensional sequence of cells whose sizes increase monotonically according to their indices. This special geometry induces a nonequilibrium stationary state with particles flowing steadily from the small to the large scales. The corresponding invariant measure has fractal properties reflected by the phase-space contraction rate of the dynamics restricted to a single cell with appropriate boundary conditions. In the near-equilibrium limit, we find numerical agreement between this quantity and the entropy production rate as specified by thermodynamics.     

Two-band conduction in TiO2

The contribution of electrons and holes to the electrical conduction of titanium dioxide TiO₂ in the Si/TiO₂/Al structure is determined in experiments on the injection of minority carriers from n-type and p-type silicon layers. It is established that both electrons and holes contribute to electrical conduction of the titanium dioxide layer in the Si/TiO₂/Al structure; i.e., the electrical conduction of titanium dioxide has a two-band nature.     

Mixed conduction in Cr-doped GaAs

Hall-effect and magnetoresistance measurements have been carried out in GaAs : Cr as functions of magnetic field strength (B = 0–18kG) and temperature (T = 125–420°K). Independent solutions for the mobilities, μ_n and μ_p, and the carrier concentrations, n and p, are obtained from the basic mixed-conductivity equations. These quantities, as well as the intrinsic carrier concentration, n_i are then calculated as a function of temperature for one sample, and subsequent analysis yields the following values in the range T = 360–420°K: an acceptor (presumably Cr) energy E_A = 0.69±0.02eV (from the valence band); the bandgap energy E_g = E_g0 + αT, with E_go = 1.48±0.02eV, $\text{α ? 3.2 × 10}{}^{\mathrm{?4}}\text{eV}\text{°}\text{K}$; $\text{μ}{}_{\mathrm{n}}\text{= 2700± 100}\text{cm}{}^2\text{V}\text{sec}$, decreasing slightly with temperature; = 350± 50 $\text{cm}{}^2\text{V sec}$; and an acceptor-to-donor concentration ratio, itN_A/N_D?8. The electron mobility appears to be limited by neutral impurity scattering, with N_A ? 2 × 10¹⁶cm^?3. Several other samples were also investigated but as a function of temperature only (at B = 0). At room temperature both positive (p-type) and negative (n-type) Hall coefficients were observed.     

Mixed anionic conduction in PbFCl

We have measured transference numbers of fluoride ions and chloride ions in undoped and doped samples of PbFCl. The results indicate pure anionic conduction. The electrical conductivity of doped single crystals support the assumption that the thermal defects in PbFCl are of the Schottky-type. The defect chemistry of PbFCl involved is described.     

Hopping conduction in semiconductor films

The topological picture of the infinite cluster near the percolation threshold is used to predict the exponential dependence of the planar hopping conduction on the thickness of the moderately thin films.     

Electrical conduction in manganese tungstate

The a.c. and d.c. electrical conductivity and thermoelectric power of a single crystal of MnWO₄ are reported in the temperature range 300–1200 K. It has been found that the dominant charge carriers are holes over the entire temperature range studied. A break in the log σ-($\text{1}\text{T}$) curve occurs around 600 K. The activation energies below and above this break temperature have been estimated as 0.53 and 0.57 eV. The charge carrier mobilities have also been estimated. The data have been analysed using the polaronic concept of electrical conduction.     

Model for heat conduction in nanofluids

A comprehensive model has been proposed to account for the large enhancement of thermal conductivity in nanofluids and its strong temperature dependence, which the classical Maxwellian theory has been unable to explain. The dependence of thermal conductivity on particle size, concentration, and temperature has been taken care of simultaneously in our treatment. While the geometrical effect of an increase in surface area with a decrease in particle size, rationalized using a stationary particle model, accounts for the conductivity enhancement, a moving particle model developed from the Stokes-Einstein formula explains the temperature effect. Predictions from the combined model agree with the experimentally observed values of conductivity enhancement of nanofluids.     

Hopping conduction in disordered carbon nanotubes

We report electrical transport measurements on individual disordered multiwalled carbon nanotubes, grown catalytically in a nanoporous anodic aluminum oxide template. In both as-grown and annealed types of nanotubes, the low-field conductance shows an exp[−(T₀/T)^1/2] dependence on temperature T, suggesting that hopping conduction is the dominant transport mechanism, albeit with different disorder-related coefficients T₀. The electric field dependence of low-temperature conductance behaves as exp[−(ξ₀/ξ)^1/2] at high electric field ξ at sufficiently low T. Finally, both annealed and unannealed nanotubes exhibit weak positive magnetoresistance at . Comparison with theory indicates that our data are best explained by Coulomb-gap variable-range hopping conduction and permits the extraction of disorder-dependent localization length and dielectric constant.     

Electrical conduction in ordered defect compounds

A comparative study of the temperature dependence of electrical resistivity, carrier concentration and carrier mobility of the Ordered Defect Compounds (ODCs) CuIn₃Se₅, CuIn₃Te₅, and CuIn₅Te₈ with their corresponding normal 1:1:2 phase is reported. Relatively lower carrier concentration and higher activation energy observed in ODCs is explained on the basis that shallow acceptor or donor levels observed in 1:1:2 phase are partially annihilated in these compounds due to attractive interaction between V_Cu⁻¹ and In_Cu⁺² defect pair. In the activation regime, the mobility is explained by taking into account a scattering mechanism of the charge carriers with donor–acceptor defect pairs. The electrical data at lower temperatures is explained with the existing theoretical expression for the nearest neighbor hopping conduction mechanism.