Features Of Photoconductivity Research Articles

Room-temperature photoconductivity in superconducting tungsten meander wires

At room temperature, the FIB fabricated tungsten meander wire shows positive photoconductivity features through the generation of extra charge carriers by absorbing photons of required energy from the illuminated 532 nm wavelength laser light.

Features of photoconductivity and luminescence of CdS thin films and Cd-=SUB=-1-x-=/SUB=-Zn-=SUB=-x-=/SUB=-S solid solutions under laser excitation

The features of photoconductivity and luminescence of CdS thin films and Cd1-xZnxS solid solutions obtained by chemical pulverization with subsequent pyrolysis under laser excitation have been studied experimentally. Pulsed liquid (473-547 nm) and nitrogen (337 nm) lasers were used as a radiation source. An experimental study was made of the photoconductivity and photoluminescence spectra of Cd1-xZnxS thin films depending on the composition x at different excitation intensities and the relaxation curves of nonequilibrium photoconductivity. It is shown that the observed features in the photoconductivity and photoluminescence spectra of Cd1-xZnxS thin films are due to direct band-to-band transitions. Amplification of light is observed at high intensities of optical excitation in thin CdS films. Keywords: Thin films CdS, Cd1-xZnxS, laser, photoconductivity spectra, photoluminescence

Особенности фотопроводимости и люминесценции тонких пленок CdS и твердых растворов Cd-=SUB=-1-x-=/SUB=-Zn-=SUB=-x-=/SUB=-S при лазерном возбуждении

Abstract. The features of photoconductivity and luminescence of CdS thin films and Cd1-хZnxS solid solutions obtained by chemical pulverization with subsequent pyrolysis under laser excitation have been studied experimentally. Pulsed liquid (473 - 547) nm and nitrogen (337 nm) lasers were used as a radiation source. An experimental study was made of the photoconductivity and photoluminescence spectra of Cd1-хZnxS thin films depending on the composition х at different excitation intensities and the relaxation curves of nonequilibrium photoconductivity. It is shown that the observed features in the photoconductivity and photoluminescence spectra of Cd1-хZnxS thin films are due to direct band-to-band transitions. Amplification of light is observed at high intensities of optical excitation in thin CdS films.

Features of the photoconductivity of the quasi-one-dimensional compound TiS3

Problem formulating. The features of linear and nonlinear conductivity, magnetic conductivity, thermopower, and the Hall effect observed on TiS3 whiskers indicate phase transitions to a state of CDW in this compound, but there is no direct evidence yet. The study of photoconductivity would allow us to learn more about the nature of these phase transitions. Goal. Study of the effect of radiation in the range from near-IR to near-UV on the conductivity of single-crystal TiS3 whiskers at 4.2 <T<300 K and search for features of photoconductivity in the temperature range of the suggested phase transitions. Result. Features of the photoconductivity of TiS3 at temperatures of 50 K and 15 K, at which the −dlnσ/d(1/T) maxima were previously observed, are found. A decrease in photoconductivity at these temperatures indicates a change in the electronic spectrum, which may be associated with the formation of CDW. Practical meaning. In the case of developing TiS3-based photosensors, it is important to study the photoconductivity in a wide temperature range.

Recombination and long-term relaxation of photoconductivity in p+–p–p− structures of CdxHg1-xTe (0.24 ≤ x ≤ 0.29)

The paper presents the results of a study of the photoconductivity of p+−p−p− structures of CdxHg1–xTe (0.24 ≤ x ≤ 0.29) single crystals obtained by thermal diffusion of copper at T = 130°C. The long-term relaxation (LR) of photoconductivity with a duration of up to 10 ms in the presence of a thermal background of intensity Φ = 1016−1017 cm−2·s−1 is observed for the first time in narrow-gap materials in the T = 77–150 K range. Recombination, diffusion-drift processes in the sample are analyzed, which cause LR and spectral features of photoconductivity. The obtained structures are promising for the development of various highly sensitive IR detectors with an elevated operating temperature.

Photoconductivity and nonlinear optical features of novel AgxGaxGe1-xSe2 crystals

Complex studies of photoconductivity, two-photon absorption (TPA) and third harmonic generation (THG) were performed for three principal representatives of chalcogenide crystals. Comparison of carrier transport kinetics and third order nonlinear optical properties was performed and the principal role of the anionic co-ordination is discussed. Specific features of photoconductivity in synthesized crystals show that the relaxation kinetics of photoconductivity can be determined by the existence of at least two types of relaxation processes: slow and quick. The control of the relaxation processes for s- and r-centres was carried out by temperature dependences of t-levels relaxation photoconductivity. The maximum THG is observed for the sample AgGaGe5Se12. The less THG exists for the sample AgGaGe3Se8 and the lowest for the AgGaGe4Se10.

Specific features of photoconductivity and photoinduced piezoelectricity in AgGaGe3Se8 doped crystals

In this work, complex photoconductivity and photo-induced piezoelectricity studies were performed for the AgGaGe3Se8 single crystals doped by In, Sn and Cu with content 5% in weighting units. The principal role of the intrinsic cationic and anionic defects is demonstrated. The photoconductivity and optical absorption spectra show substantial changes of effective energy gap and steepness of absorption edge. The role of optical transitions between the localized states in the presence of Sn, Cu, In impurities is explored. Piezoelectric studies under external laser illumination have shown significant role of dopants on the piezoelectric constants values and their anisotropy. Clear photo-induced jumps were discovered. The discussion is performed within the framework of crystallochemistry analysis and quantum chemical evaluations. Possibility of production of optically operated piezoelectric triggers is proposed.

Terahertz detection of magnetic field-driven topological phase transition in HgTe-based transistors

We report on terahertz photoconductivity under magnetic field up to 16 T of field effect transistor based on HgTe quantum well (QW) with an inverted band structure. We observe pronounced cyclotron resonance and Shubnikov-de Haas-like oscillations, indicating a high mobility electron gas in the transistor channel. We discover that nonlinearity of the transistor channel allows for observation of characteristic features in photoconductivity at critical magnetic field corresponding to the phase transition between topological quantum spin Hall and trivial quantum Hall states in HgTe QW. Our results pave the way towards terahertz topological field effect transistors.

Features in the impurity photoconductivity spectra of n-GaAs and n-InP at energies multiple of the optical phonon energy

We report the experimentally revealed peculiarities in the impurity photoconductivity spectra of bulk n-GaAs and n-InP samples doped with shallow impurities. These features are essentially the photoconductivity steps at the photoexcitation quanta energies near (2, 3, 4, 5) · ℏωLO, where ℏωLO is the energy of the longitudinal optical phonon. A theoretical description of the observed peculiarities is proposed. It is shown that the photoconductivity features are determined by the energy dependence of the rate of electron energy relaxation.

Specific features of photoconductivity in a polymer composite with a heterometallic Copper(II)/Vanadium(V) complex

The dark conductivity and the photoconductive properties of polymer film composites based on polyvinyl butyral doped with various amounts of the heterometallic complex (H3O)2(H2en)[Cu(en)2(H2O)2][V10O28] · 3H2O (where en is ethylenediamine) have been studied. It has been found that the activation energy of photocurrent in the films increases with an increase in applied electric field strength. An increase in the applied electric field strength has been assumed to result in the release of charge carriers from deeper energy traps that can occur in the heterometallic complex.

Photoconductivity of silicon with nanoclusters of manganese atoms

In this work, specific features of photoconductivity of silicon with multicharge nanoclusters of manganese atoms are investigated. It is shown that for such samples, anomalously high impurity photoconductivity is observed in the spectral region λ = 1.8–3 μm. It is also shown that such samples possess giant residual photoconductivity.

Relaxation process features of photoconductivity in p-i-n structures

Relaxation process features of photoconductivity in p-i-n structures

Specific features of the photoconductivity of polymer film composites containing a heterometallic iron(II)/zinc(II) complex

The specific features of electric conductivity and photoconductivity in films of composites based on poly(vinyl alcohol) doped with the complex [Fe(bipy)3][Zn(NCS)4] (where bipy is 2,2′-bipyridyl) and the effect of magnetic field on these properties were studied. It was found that photocurrent decreases with an increase in the magnetic field strength up to 5.5 kOe. It was assumed that the photoconductivity of these composites and its dependence on magnetic field are affected by paramagnetic iron(III) complex particles produced as a result of internal photoelectric effect. The effect of magnetic field on the photoconductivity is associated with the spin-dependent recombination of photogenerated charge pairs.

Structural Phase Transition and Photo-Charge Carrier Transport in SrTiO3

The effect of the antiferrodistorsive phase transition observed at ∼ 105 K on the photo-carriers transport and band structure of nominally pure SrTiO3 single crystals was investigated. Simultaneously the ab-initio analysis based on the DFT-HF hybrid approach was performed in order to elucidate the atomic and electronic structure changes. It was found that the structural transition play a minor role in photo-charge transport. However, in highly resistive specimens at low UV-light intensities or under visible-light, 514 nm excitation, weak photoconductivity features are observed in the transition region. Besides, in this region the temperature maximum was found for the photoconductivity spectra. Experimental results are discussed and agree well with theoretical predictions.

Specific features of photoconductivity in thin n-PbTe:Ga epilayers

Photoconductivity and transient processes in thin (0.2–0.3 µm) n-PbTe:Ga epilayers were studied. The films were grown by the hot-wall technique on BaF2 〈111〉 substrates. Photoelectric properties of the samples were investigated in the temperature range from 4.2 to 300 K. A GaAs light-emitting diode and miniature incandescent lamp were used as sources of pulsed and continuous infrared radiation, respectively. The most important characteristic of the films is the very wide temperature range of photosensitivity. At an illumination power density of 10−5 to 10−4 W/cm2, the temperature at which the films become photosensitive TC is as high as 150 K, which exceeds TC for thicker films (2–3 µm) and high-resistivity single crystals of n-PbTe:Ga by 40 and 70 K, respectively. An analysis of the transient behavior of photoconductivity shows that photoexcited carriers are uniformly distributed over the volume of the thin films. A barrier for recombination of nonequilibrium charge carriers was estimated for slow relaxation processes.

Influence of Ionic Forms of Polymethine Dyes on the Photoconductivity of Doped Films of Poly-N-Epoxypropylcarbazole

The features of photoconductivity of the films of poly-N-epoxypropylcarbazole doped with cationic, squarylium and merocyanine dyes are investigated. Under temperature growth starting from room the photoconductivity of the films with cationic and squarylium dyes increases more strongly as compared to the similar films with merocyanine. It was explained by a destruction of structural traps close to electrically charged fragments of dyes. In contrast to the films of the first two types, the photoconductivity of the films with merocyanine dye depends sublinearly on incident light intensity due to an effective bimolecular charges recombination.

Characteristics of photoconductivity in As-Sb-Se glasses

Characteristic features of photoconductivity in As x Sb15Se85−x and AsxSb10Se90−x bulk glass systems have been measured and reported. Both a.c and d.c techniques have been employed for the measurements. The temperature dependence of photoconductivity has been analysed in terms of the ABFH model and both systems are found to exhibit type I photoconductivity. Photoconductivity shows a clear change in slope corresponding to the stoichiometric composition in both the systems. The composition dependence of photoconductivity is explained on the basis of chemically ordered covalent network (COCN) model. Photoconductivity response time of the two systems have been determined from frequency-resolved photocurrent (FRPC) measurements. Variation of response time with composition exhibits a clear change in slope at the stoichiometric composition in both the systems.

New features of photoconductivity in fullerene doped conducting polymer

Summary form only given. Dynamics of enhanced photoconductivity in fullerene (C60, C70, etc.) doped conducting polymers such as poly(3-alkylthiophene) and poly(2,5-dialkoxy phenylenevinylene) upon irradiation of light pulse and its decaying characteristics have been studied in detail. New features have been found in the decaying behaviour depending on pulse width, wave length, concentration of fullerene, temperature and molecular structure of conducting polymer, which have been explained by taking dynamics of excitons, polaron/bipolarons in both conducting polymer and fullerene into consideration.

Dislocations as Traps for Holes in Germanium

AbstractA further development of the barrier model of recombination at dislocations is presented. It is shown that in spite of the tunnel effect, the barrier height is the main factor limiting the capture rate of electrons down to about 180 °K. Some features of photoconductivity in crystals with dislocations and their temperature‐dependences, are discussed (such as the lux‐ampere characteristics, and the relaxation of the photocurrent). It is shown how the density of dislocations and the position of the dislocation acceptor level can be estimated from experimental data.