Nonequilibrium Current Carriers Research Articles

The investigation of the kinetics of the losses of nonequilibrium current carriers in Cu-=SUB=-2-delta-=/SUB=-NiSnS-=SUB=-4-=/SUB=- (0≤delta≤0.2) quaternary copper compounds

By solid-phase synthesis from elemental Cu, Ni, Sn, and S samples Cu2-deltaNiSnS4 (0≤delta≤0.2) was prepared. The parameters of their crystal lattice have been refined. The lifetimes of photogenerated current carriers in Cu2-deltaNiSnS4 were estimated for the first time by the contactless time-resolved microwave photoconductivity method. This times turned out to be tau~7 ns, which is comparable with the literature data for the times in kesterites CZTS. Herewith, in kinetics of loses of photogenerated cureent carriers is observed predominance of bimolecular recombination processes over capture processes. Keywords: Cu2-deltaNiSnS4, onequilibrium current carriers, lifetimes, kinetics.

Электрофизические и фотоэлектрические характеристики трехбарьерной фотодиодной GaAs-структуры

The work is devoted to the study of physical features of electronic processes taking place in the space charge region and in the base region of arsenide-gallium three-barrier photodiode structures with the effect of locking two adjacent transitions. The structures have high photosensitivity in the «impurity» region of the spectrum at both inclusion polarities. The obtained results suggest that such structures can be used in optical communication systems. The study allowed showing that a three-barrier photodiode m1—p-GaAs—n-GaAs—m2-structure with a high quantum efficiency can exceed 8 times the photosensitivity of a photodiode as compared to a photodiode with a single p—n junction. In the m1—p-GaAs—n-GaAs—m2 photodiode structure, the maximum photosensitivity is achieved in the impurity region of the spectrum (above 1.0 µm) when excitation of nonequilibrium current carriers through the barrier to the semiconductor, in contrast to the intrinsic spectral region (0.86 µm). It has been shown experimentally that the photosensitivity of the structure in the direct-displacement mode of the p-n junction is larger, compared with the locking mode, and the maximum photosensitivity is achieved in the impurity region of the spectrum. That is, the impurity levels of oxygen present in the base region take part in the separation of the photocarriers. The dependence of the current on the voltage is described by a power function with an exponent of 0.5 corresponding to the generation-recombination process in the space-charge region of the p-n junction.

Optical Properties of Boron-Doped Gallium Selenide

The electronic-absorption and luminescence spectra and the kinetics of relaxation of photocurrent in GaSe single crystals and thin films doped with boron atoms are experimentally investigated. Crystals are doped either in the course of synthesis or upon growing single crystals by the Bridgman method. Thin GaSe films are obtained by thermal evaporation of the compound preliminarily doped with boron. An absorption band with the maximum at λ = 925 nm, which is attributed to boron contaminations, is revealed from the comparison of the electronic-absorption spectra of a GaSe crystal and thin films doped with boron. When the crystals are excited with Nd:YAG laser pulses of a duration of 12 ns, it is established that recombination of nonequilibrium current carriers in pure crystals occurs through rapid and slow recombination channels and in crystals doped with boron only through rapid channels. In the region near λ = 932 nm, photoluminescence is observed in the crystals doped with boron, and its half-bandwidth is 15 A.

Effect of Circular p-n Junction Curvature on the Diode Current Density

The influence of the circular geometry of a p-n junction built into a nanowire or a nanorod, on the radial diode current density is investigated. While the current density from the core to the shell proves to be larger than that in a planar diode at the same values of the parameters, the density of the diode current from the shell to the core, on the contrary, proves to be smaller. A dependence of the effect on the core and the shell radii has been demonstrated. The nature of the effect is explained on the basis of radial distributions of the nonequilibrium current carriers.

Two-dimensional model of a strip detector with two tunnel junctions

The article describes a two-dimensional model of a strip X-ray detector with a superconducting absorbing strip and two tunnel junctions at its ends, The motion of nonequilibrium current carriers (quasiparticles) is considered in the framework of a diffusion equation with boundary conditions of third kind. The detector signals Q l and Q r and the spectral line shape are computed as a function of the strip size, quasiparticle capture efficiency in the tunnel junction, the quasiparticle loss parameter on the absorber lateral boundaries, and the quasiparticle recombination parameter R. Analytical solutions for the detector signals Q l and Q r are derived for the case R?=?0 . Numerical calculations are generally used. When boundary and recombination losses are allowed for, the detector signals turn out to depend on the photon absorption coordinate in the transverse direction. This broadens and distorts the spectral line shape.

Negative photoconductivity of ferrocenyl-containing oligomer films with a merocyanine dye

The effect of negative photoconductivity of ferrocenyl-containing oligomer films doped with a merocyanine dye based on ferrocene and tetranitrofluorene has been found. The decrease in the conductivity current and its recovery after switching off light are in agreement with the decrease and the recovery of the dielectric loss tangent in the films studied. The phenomenological model is suggested in which the buildup of space charge from nonequilibrium current carriers and its effect on electric conductivity of the films are taken into account. It is supposed that energetic traps for nonequilibrium charge carriers are formed due to proximity of the ferrocenyl fragments in the oligomer and a long distance between its end groups.

Localization of nonequilibrium current carriers close to Cr ions in ZnSe:Cr single crystals

The photoluminescence (PL) of Cr-doped ZnSe single crystals is investigated in a temperature interval from 83 up to 297 K and in a wavelengths region from 440 up to 2700 nm. The doping was carried out during a high-temperature annealing of ZnSe crystals in CrSe vapors and in chrome chlorides medium. It is revealed that the doping results in an appearance of both luminescence bands located at 0.54, 0.97, and 2.15 μm and edge luminescence bands located at 454, 457, and 460 nm at 83 K. It is shown that the PL bands located at 457 and 460 nm are caused by the radiative recombination with the participation of holes located on hydrogen-like orbits close to Cr + centers, having a binding energy of 99 meV. The excitons bound with centers responsible for the radiation located at 0.54 μm and having a binding energy of 65–68 meV are considered. The energy of a lattice relaxation at recharge of centers responsible for green radiation is estimated and equals 40–170 meV.

Pulse-Height Defect of48Ca Ions in an Ion-Implanted Silicon Detector

The results of studying the pulse-height defect (PHD) of 48Ca ions in an ion-implanted silicon detector in the energy range 110 to 223 MeV are presented. The energy dependences of the total PHD, its recombination component, and the relative recombination energy losses are obtained. The dependences of the measured ion energies and PHD on the electric field strength are also obtained. The results are discussed on the basis of a recombination model that takes into consideration the spread of nonequilibrium current carriers due to ambipolar diffusion during the plasma time.

Photoluminescent discovery of the impurity–band non-equilibrium current carriers condensation in Ge : Sb

Kinetics and magnetic-field investigations of photoluminescent spectra at temperatures between 0.5 and 4.2 K in moderately heavily doped Ge : Sb ( n D∼10 16–10 17 cm −3, below the Mott transition n c=10 17 cm −3) revealed strong changes in the phase diagram of non-equilibrium current carriers compared to the case of pure or lightly doped Ge. The data show that due to the presence of narrow impurity bands at such doping concentrations the non-equilibrium impurity-band current carriers (D −) and free holes (h) condense into the D −H liquid surrounded by the gas phase of D −H-plasma.

Low-temperature anomalies exhibited by the photoelectromagnetic effect in p-type CdxHg1−x Te

When p-type crystals of CdxHg1−xTe (x=0.20–0.30) are placed in a magnetic field in the temperature range where holes freeze out onto acceptor states (T<30 K), the current associated with the photoelectromagnetic effect (PEME) is found to exhibit sign changes. It is shown that the reason for this anomalous behavior of the PEME is the changing ratio of concentrations of equilibrium and nonequilibrium current carriers. The theoretical model derived here, which takes into account the dependence of the effective ambipolar diffusion length on this concentration ratio, gives a good description of the PEME anomalies observed in experiment.

Interfacial recombination of current carriers: influence on magnetoconcentration effect in semiconductor heterostructure

This paper investigates theoretically the magnetoconcentration effect in an abrupt heterostructure on the basis of non-degenerate semiconductors with an intrinsic conductivity in the case when a recombination of non-equilibrium current carriers occurs at the heterostructure interface. The influence of the interfacial recombination velocity on the current-voltage characteristics of the heterostructure is analysed.

Traveling helical wave amplifier for superhigh frequencies on the base of a semiconductor containing deep impurity levels

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Recombination of nonequilibrium current carriers in n-InAs1?x?ySbxPy

The stationary photoconductivity, the photomagnetic effect, and the relaxation kinetics of photoconductivity in n-InAs1−x−ySbxPy crystals (x=0.06, y=0.11) with n0 = 8·1015 and 3·1016 cm−3 were measured and the lifetimes of nonequilibrium current carriers in the temperature interval T=78–295 K were determined. The possible mechanisms of recombination, which limit the lifetimes (radiative τR, Auger recombination τA, and recombination through centers with Ef=0.13 eV), which, as is demonstrated, are determined by interband recombination processes with τRA = τRτA/(τR + τA), are calculated theoretically. The contribution of the 0.13 eV recombination centers can be significant when n0≤1014 cm−3.

Defect formation in solids by decay of electronic excitations

We consider a new type of nonradiative transitions in nonmetallic solids. The transitions are not accompanied by heat release but by large (compared with interatomic distances) displacements of individual atoms. These instabilities (electrostatic, vibronic, structural), which lead to formation of defects in solid crystals and glasses, are classified. We describe defect-formation processes both in ionic crystals upon decay of self-trapping excitons, and in semiconductors following multiple ionization of atoms near pre-existing charged impurity centers. The mechanisms whereby complex defects are restructured in semiconductors when nonequilibrium current carriers are introduced and when electrons and holes recombine are discussed. The role of current carriers in thermal production of defects is considered. The mechanism of formation of peculiar defects in glassy semiconductors is discussed.

Trapping of nonequilibrium current carriers in plastically deformed germanium

Trapping of nonequilibrium current carriers in plastically deformed germanium