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Optical properties of green emission Ga_0.80In_0.20N/GaN multi-quantum well and light emitting diode have been investigated by using photoluminescence, cathodoluminescence, electroluminescence, and photoconductivity. The temperature dependent photoluminescence and cathodoluminescence studies show three emission bands including GaInN/GaN quantum well emission centered at 2.38 eV (~ 520 nm). The activation energy of the non-radiative recombination centers was found to be ~ 60 meV. The comparison of photoconductivity with luminescence spectroscopy revealed that optical properties of quantum well layers are strongly affected by the quantum-confined Stark effect.

Doping of the lead telluride and related alloys with the group III impurities results in the appearance of unique physical features of the material, such as persistent photoresponse, enhanced responsive quantum efficiency (up to 100 photoelectrons/incident photon), radiation hardness and many others. We review physical principles of operation of the photodetecting devices based on the group III doped IV–VI including possibilities of fast quenching of the persistent photoresponse, construction of a focal-plane array, new readout technique, and others. Comparison of performance of the state of the art Ge(Ga) and Si(Sb) photodetectors with their lead telluride based analogs shows that the responsivity of PbSnTe(In) photodetectors is by several orders of magnitude higher. High photoresponse is detected at the wavelength of 241 μm in PbSnTe(In), and it is possible that the photoconductivity spectrum covers all the submillimeter wavelength range.

Recent results on nonequilibrium magnetotransport of electrons in irradiated quantum Hall systems are reviewed. The phenomena discussed include integer and fractional microwave-induced resistance oscillations as well as quantum magnetooscillations in DC and AC conductivity and in local compressibility of a 2D electron gas.

We study magnetoresistivity oscillations induced by microwave radiation or acoustic phonons in high-mobility two-dimensional electron systems subject to dc electric field. In microwave-irradiated samples the response is governed by combined electron transitions, composed of microwave absorption and scattering off impurities. In non-irradiated samples, acoustic phonon resonances are tuned by dc electric field. Here, we show that in both experiments scattering off impurities without microwave or phonon absorption plays an important role and might even dominate the response.

The research results of photoelectric, optical and recombination properties of neutron transmutation doped (NTD) semiconductor solid alloys Si_1-xGe_x(x = 0.008–0.112) are presented in spectral range 0.8–10.6 μm. It is shown that these properties of NTD Si_1-xGe_x are determined by creation of transmutation impurities of Se and Ga as well as by variation of Ge content and compensation. The theoretical and applied aspects of the NTD Si_1-xGe_x have been also considered.

In the development of most phenomenological models used to explain the infrared excited luminescence, a major assumption is usually made in the degree of freedom the excited charge has. One of the two extremes is normally assumed: charge is free to move anywhere over the whole crystal, or it is confined close to the trap and the centers immediately adjacent to it. Determining which of these extremes is more reasonable is difficult to do on the basis of the temporal behavior of the luminescence intensity alone. However, this assumption has important consequences for the understanding of the dynamics of the luminescence process because of the difference in the number of recombination and trapping centers available to the excited charge. Additional experimental evidence was thus sought on this aspect of charge movement. One such experiment is the detection of photoconductivity in which an electrical current is measured during optical excitation or shortly there-after. In this paper, the details of photoconductivity experiments on K crystal are presented.

Photoconductivity measurements were inconclusive as to whether or not there was a current flowing during the 850 nm excitation of a feldspar sample. However, there was a clear current when exciting the same sample with 515 nm light, but there was a complex relationship between the magnitude of the current and the number of emission photons counted. A model was developed to explain the photoconductivity results where electrons migrate through the conduction band aided by thermal excitation and tunneling.

Photoconductivity characteristic of undoped and gadolinium (Gd)/dysprosium (Dy) co-doped layered $p$-GaSe semiconductor has been experimentally investigated. A model is proposed to explain the obtained results. The creating possibility of multi-band photo-detectors with stable and reproducible parameters is shown and characteristics based on single crystals of $p$-GaSe are activated with mentioned rare-earth ions with concentration of $10^{-2}÷10^{-1}$ at.%.

Log Q versus log I_ph characteristics and laser enhanced mobility in the case of ZnS have been studied using a XeCl laser. The comparison of results in this case with multiphoton photoconductivity of other materials indicates two photon excitation from a lower valance band, wherefrom one-photon excitation is forbidden but two-photon excitation is allowed. Since the band-gap of ZnS is smaller than the photon energy of the XeCl laser, the result seems to be interesting.

The temperature dependence of photoinduced anisotropy in the photoconductivity of As₂Se₃ and Sb₂S₃ thin films was investigated, in the interval between -50 and 70°C. Our results demonstrate that for both As₂Se₃ and Sb₂S₃ thin films, the anisotropy percentage falls with increasing temperature. We surmise that the aligning effect of the linearly polarized light was diluted with increasing temperature, because the latter induces similar mechanisms to those induced by polarized light, but in an isotropic fashion.

Laser enhanced mobility in the case of PbI₂ single crystal has been investigated on the basis of the experimental results of photoconductivity measurements using high power Nd:YAG laser. Its dependence on energy area density/photon density and charge carrier concentration has been studied. The obtained results of PbI₂ have been compared with that of CdI₂ and ZnS crystals studied under similar experimental conditions. The laser enhanced mobility has also been compared with the theoretical study in the case of GaAs crystal using CO₂ laser.

In this paper, S-doped vanadium oxide thin films with doping levels up to 40 at.% are prepared via spray pyrolysis method on glass substrates, and the effect of S-doping on the structural and photoconductivity related properties of $\beta$-V₂O₅ thin films is studied. The results show that most of the films have been grown in the tetragonal $\beta$-V₂O₅ phase structure with the preferred orientation along [200]. With increasing the doping level, the samples tend to be amorphous. The structure of the samples reveals to be nanobelt-shaped whose width decreases from nearly 100 nm to 40 nm with S concentration. The photoconductivity measurements show that by increasing the S-doping level, the photosensitivity increases, which is due to the prolonged electron’s lifetime as a result of enhanced defect states acting as trap levels.

In this paper, the distribution of the charge trap levels in polyimide (PI) films was investigated by using photo-stimulated discharge (PSD) technique, which was to explore the effect of photoconductivity on photo-stimulated discharge current. The PSD spectra show that the photo-stimulated discharge current of the PI films is mainly distributed in the range of 649–320 nm, but there are two significant current peaks when the wavelength is 300 nm and 244 nm, respectively. By studying the reason of generating two current peaks, it is concluded that the two current peaks are not generated by trapped charge de-trapping but generated by photoconductivity of charge-transfer complex in the PI films. According to the research, it is concluded that the trap levels in PI films are mainly distributed in the range of 1.92 eV–3.88 eV.

In this work, we consider the results of studying the spectral distribution, the temperature dependence of photoconductivity, and the dependence of the spectral distribution of photoconductivity on the applied electric field of doped with rare earth elements GaTe single crystals in the temperature range of 30–300 K. As the temperature decreases to 30 K, the impurity peaks disappear, and the intense maximum shifts to the short wavelength region. The increase in impurity photoconductivity with increasing temperature is due to the thermooptical filling of acceptor levels with electrons and their further transition to the conduction band under the action of illumination. Such a temperature dependence of the photoconductivity is explained by the presence of acceptor levels in the band gap.

The n-type conductivity nitrogen-doped amorphous carbon (n-C) films have been grown by surface wave microwave chemical vapor deposition (SWP-CVD) on plastic and quartz substrates. The bonding, electrical and photovoltaic properties have been studied. The Tauc plot of UV-Visible measurement have shown that n-C films deposited on plastic have smaller optical band gaps compared to the films grown on quartz substrate at the same parameters. Temperature dependence and photoresponse measurements also have shown that the properties of n-C thin films deposited on plastic have higher photoelectrical response. Our experimental results have shown that the flexible polytetrafluoroethene plastic substrate is a reliable candidate for future photovoltaic applications.

Zn–In–Se thin films were fabricated on the ultrasonically cleaned glass substrates masked with clover-shaped geometry by thermal evaporation of its elemental sources. Temperature-dependent conductivity characteristics of the films were investigated under dark and illuminated conditions. The semiconductor type of the films was found as n-type by thermal probe test. According to the van der Pauw technique, the dark electrical conductivity analyses showed that the variations of conductivity of unannealed and annealed at $300^{\circ }$C samples are in exponential dependence of temperature. These conductivity profiles were found to be dominated by the thermionic emission at high temperature region whereas their behaviors at low temperatures were modeled by hopping theory. On the contrary, as a result of the further annealing temperatures, the surface of the samples showed semi-metallic characteristics with deviating from expected Arrhenius behavior. In addition, the temperature-dependent photoconductivity of the films was analyzed under different illumination intensities and the results were explained by the supra-linear characteristic based on the two-center recombination model.

An organic nonlinear optical (NLO) single crystal of L-methioninium picrate (LMP) has been grown by slow evaporation solution technique (SEST) at a constant temperature of $40^{\circ }$C. Formation of nucleation and growth kinetics of the crystal were observed using an optical microscope for different durations and it was found that the shape of nucleation is similar to the grown large size single crystals of the same material. The characterization techniques such as powder X-ray diffraction (PXRD) analysis, UV–Vis NIR, Vickers microhardness, piezoelectric d${}_{33}$ coefficient, photoconductivity and etching studies have been performed. The crystal system and lattice parameters of the grown crystal were determined by PXRD analysis. The spectroscopic properties of the synthesized compound were confirmed by Fourier transform infrared (FTIR) analysis. The UV–Vis NIR analysis was performed on the grown single crystal to find the optical absorption in the entire visible region. Attempts have been made to investigate the mechanical properties of LMP crystal using Vickers diamond pyramid indenter. In addition piezoelectric, photoconductivity and etching studies were carried out to study the d${}_{33}$ coefficient, photoconducting nature and surface properties respectively.

The effect of annealing on the structural and the magnetic properties of GaN implanted with Gd is investigated. The wavelength dependence of the photoconductivity of Gd:GaN layers doped in situ is also studied. These results show that Gd incorporation produces defects not only in implanted samples, but also in Gd:GaN layers doped in situ. A clear correlation between the saturation magnetization and the defect density is observed in implanted samples. A model has been proposed to explain the effects of colossal magnetic moment per Gd ion and associated ferromagnetism observed in this system in terms of the formation of giant defect cluster around each Gd ion.

Photoconductive and photovoltaic properties of film composites based on poly-$N$-epoxypropylcarbazole doped with a derivative of nickel dithiolene are investigated. These composites possess a hole-type photoconductivity. The internal photoeffect is attributed to the photogeneration of charge carriers from the metal complex and the hole transport through the donor fragments of the polymer matrix.

The photoconductivities of a series of novel polyacetylene derivatives (PAs) serving as charge generation materials in the single-layered photoreceptors were investigated using photoinduced xerographic discharge technique. It was found that the substitution can improve the photosensitivity of PAs by increasing the conjugation of π electrons. When the substituent is itself photoconductive, the photoconductivity becomes even higher. It can be concluded from cyclic voltammetry that when the HOMO level of the polymer is closer to that of the charge transport material, the photoconduction performance will be better.

Metallophthalocyanine complexes and related compounds play an important role in many advanced applications and modern technologies mostly by virtue of their characteristic optical absorption and high chemical stability. As a class of materials made well-known by their vivid and fast colors, it is expected that metallophthalocyanines and analogues, e.g. naphthalocyanines, are going to keep their role with the increasing use of natural and artificial light in the technologies of the future. In the present review some relevant properties of phthalocyanines and related macrocycles for technological applications are analyzed. In particular the electrical conductivity and photoconductivity as well as some nonlinear optical properties (mostly optical limiting), of phthalocyanines and related compounds are discussed.