Photoelectronic and electrical properties of CuIn5S8 single crystals

To identify the impurity levels in CuIn₅S₈ single crystals, the dark electrical conductivity and photoconductivity measurements were carried out in the temperature range of 50–460 K. The data reflect the intrinsic and extrinsic nature of the crystals above and below 300 K, respectively. Energy band gaps of 1.35 and 1.31 eV at 0 K and 300 K, were defined from the dark conductivity measurements and the photocurrent spectra, respectively. The dark and photoconductivity data in the extrinsic temperature region reflect the existence of two independent donor energy levels located at 130 and 16 meV. The photocurrent‐illumination intensity dependence (F) follows the law I_phαF^γ, with γ being 1.0, 0.5 and 1.0 at low, moderate and high intensities indicating the domination of monomolecular, bimolecular and strong recombination at the surface, respectively. In the intrinsic region and in the temperature region where the shallow donor energy level 16 meV is dominant, the free electron life time, τ_n, is found to be constant with increasing F. In the temperature region 140 K < T < 210 K, the free electron life time increases with increasing illumination intensity showing the supralinear character. Below 140 K, τ_n decrease with decreasing illumination intensity. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structural,electrical and optical properties of Ge implanted GaSe single crystals grown by Bridgman technique

Structural, optical and electrical properties of Ge implanted GaSe single crystal have been studied by means of X‐Ray Diffraction (XRD), temperature dependent conductivity and photoconductivity (PC) measurements for different annealing temperatures. It was observed that upon implanting GaSe with Ge and applying annealing process, the resistivity is reduced from 2.1 × 10⁹ to 6.5 × 10⁵ Ω‐cm. From the temperature dependent conductivities, the activation energies have been found to be 4, 34, and 314 meV for as‐grown, 36 and 472 meV for as‐implanted and 39 and 647 meV for implanted and annealed GaSe single crystals at 500°C. Calculated activation energies from the conductivity measurements indicated that the transport mechanisms are dominated by thermal excitation at different temperature intervals in the implanted and unimplanted samples. By measuring photoconductivity (PC) measurement as a function of temperature and illumination intensity, the relation between photocurrent (I_PC) and illumination intensity (Φ) was studied and it was observed that the relation obeys the power law, I_PC αΦⁿ with n between 1 and 2, which is indication of behaving as a supralinear character and existing continuous distribution of localized states in the band gap. As a result of transmission measurements, it was observed that there is almost no considerable change in optical band gap of samples with increasing annealing temperatures for as‐grown GaSe; however, a slight shift of optical band gap toward higher energies for Ge‐implanted sample was observed with increasing annealing temperatures. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Annealing effect on electrical and photoconductive properties of Si implanted GaSe single crystal

GaSe single crystals grown by Bridgman method have been doped by ion implantation technique. The samples were bombarded in the direction parallel to c‐axis by Si ion beam of about 100 keV to doses of 1 × 10¹⁶ ions/cm² at room temperature. The effects of Si implantation with annealing at 500 and 600 °C on the electrical properties have been studied by measuring the temperature dependent conductivity and photoconductivity under different illumination intensities in the temperature range of 100–320 K. It is observed that Si implantation increases the room temperature conductivity 10⁻⁷ to 10⁻³ (Ω‐cm)⁻¹ depending on the post annealing temperature. The analysis of temperature dependent conductivity shows that at high temperature region above 200 K, the transport mechanism is dominated by thermal excitation in the doped and undoped GaSe samples. At lower temperatures, the conduction of carriers is dominated by variable range hopping mechanism in the implanted samples. Annealing of the samples at and above 600 °C weakens the temperature dependence of the conductivity and photoconductivity. This indicates that annealing of the implanted samples activates Si‐atoms and increases structural deformations and stacking faults. The same behavior was observed from photoconductivity measurements. Hence, photocurrent‐illumination intensity dependence in the implanted samples obeys the power low I_pc ∝ Φⁿ with n between 1 and 2 which is an indication of continuous distribution of localized states in the band gap. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Photoconductivity in Tl4S3 layered single crystals

Photoconductivity measurements are carried out in this work for single crystals of Tl₄S₃ compound by using both pulsed excitation (a.c) and steady state (a.c) methods in order to elucidate the nature of photoconductivity (PC) in this compound. Results are reported in the temperature range from 77 to 300 K, excitation intensity range from 1800 to 3300 Lux, applied voltage range from 8 to 14 V, and wavelength range from 840 to 1450 nm. Both of the ac‐photoconductivity (ac‐PC) and the spectral distribution of the photocurrent are studied at different values of light intensity, applied voltage and temperature. Dependencies of carrier lifetime on light intensity, applied voltage and temperature are also investigated as results of the ac‐PC measurements. By using the results of the dc‐photoconductivity (dc‐PC) measurements, the temperature dependence of the energy gap width is described. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Improvement of the electrical properties of Se3Te1 thin films by In additions

The electronic and photoconductivity properties of semiconducting chalcogenide glasses have been largely stimulated by attractive micro-electronic device applications. The present paper aims to study the effect of In additions on the steady state and transient photoconductivity of amorphous In_x(Se₃Te₁)_100 ? x (0 ≤ x ≤ 10 at.%) chalcogenide films. It was found that, the Indium additions lead to the decrease of both the activation energies (ΔE_dc in the dark and ΔE_ph for the photoelectrical conduction) and the optical band gap E_g that improved the electrical properties of these films. The photoconductivity increases while photosensitivity changes from 8.73 to 7.18 with the increase of In content. The exponential dependence of photocurrent on the light intensity suggests that, the recombination mechanism in these films is due to bimolecular recombination. The transient photoconductivity measurements stated that, the carrier lifetime decreased by the increase of the light intensity and In content. The obtained results were discussed in terms of the width of localized states (Mott and Davis model) and the chemical-bond approach.     

Crystal data and some physical properties of Tl2InGaTe4 crystals

The room temperature crystal data, Debye temperature, dark and photoelectrical properties of the Bridgman method grown Tl₂InGaTe₄ crystals are reported for the first time. The X‐ray diffraction technique has revealed that Tl₂InGaTe₄ is a single phase crystal of tetragonal body‐centered structure belonging to the space group. A Debye temperature of 124 K is calculated from the results of the X‐ray data. The current‐voltage measurements have shown the existence of the switching property of the crystals at a critical voltage of 80 V. The dark electrical resistivity and Hall effect measurements indicated the n ‐type conduction with an electrical resistivity, electron density and Hall mobility of 2.49×10³ Ω cm, 4.76×10¹² cm^–3 and 527 cm²V^–1s^–1, respectively. The photosensitivity measurements on the crystal revealed that, the variation of photocurrent with illumination intensity is linear, indicating the domination of monomolecular recombination at room temperature. Moreover, the spectral distribution of the photocurrent allowed the determination of the energy band gap of the crystal studied as 0.88 eV. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Electrical and photoelectrical properties of chalcopyrite n-AgInS2 crystals

The chalcopyrite n-type crystals have been grown from AgInS₂ material having stoichiomtric Ag excess. The temperature dependence of the Hall effect in these crystals have been studied. The ionization energies of donors have been determined. The dependence of the photoconduction on the photon energy, the light intensity and the temperature in the n-AgInS₂ crystals have been measured. The recombination model of photoconductor with one class of recombination centres has been proposed for explanation of the photoelectrical results.     

Phase diagram and single crystal growth of the CuInSe2xS2(1−x) solid solutions

The phase diagram of the CuInSe₂-CuInS₂ system is plotted using DTA and the solidus and liquidus lines by the approximation of the theory of regular and ideal solutions are calculated. The single crystals of the CuInSe_2xS_2(1−x) solid solutions are first grown by chemical transport.     

Enhanced persistent photoconduction in CuInS2–ZnIn2S4 alloys single crystals and processes of its relaxation

ABSTRACT

Photoelectrical response in CuInS₂–ZnIn₂S₄ alloys single crystals was analysed in the low temperature region from 30 K up to 100 K. The molar ratio of ZnIn₂S₄ in the alloys was varied in the range 0 mol%?16 mol%. The crystals with up to 12 mol% were the single-crystalline, meanwhile those with 16 mol% were the two phase ones. We have analysed spectral distribution of their photocurrent at different temperatures and the following relaxation towards the stationary values. The photo-induced photoconductivity phenomena were identified. Moreover the long-lasting relaxations with characteristic times exceeding 1.5×10³ sec were observed at lowest temperatures. They used to shorten exponentially with increasing temperature showing thermally activated behaviour. The main parameters of the photoconductivity kinetics and their temperature dependencies were determined. The observed behaviour was explained by the slow multicenter recombination due to the combined effect of different trapping and recombination centers. The effects of both – “fast” and “slow” recombination centers were taken into account.     

Second-order nonlinear susceptibilities of the crystals of some metal tartrates

The relative (with respect to a powder potassium dihydrophosphate crystal) effective second-order nonlinear susceptibilities have been measured for gel-grown single crystals of some tartrates with the general formula MeC₄H₄O₆ · nH₂O on powder samples upon the excitation of the second harmonic of laser radiation with a wavelength of 1.064 μm. The unit-cell parameters and the symmetry space groups have been determined for the single crystals under study.     

Long-lifetime photoconductivity in Cz n- and p-Si

Long-lifetime photoconductivity is observed in Czochralski-grown oxygen-rich heattreated n- and p-type silicon crystals. It appears due to a slow electron (in Cz n-Si) and hole (in Cz p-Si) recombination via two kinds of oxygen-induced recombination centres. Dependences of the long-lifetime photoconductivity on the oxygen content, excitation intensity and temperature are presented. Possible models to explain an appearance of the long-lifetime photoconductivity in Cz n- and p-Si are discussed. The data presented are important for understanding the long-time photoeffects in semiconductors and for elucidating the origin and structure of oxygen-induced recombination centres in silicon.     

Effect of lead additive on photoconductive properties of Se–Te chalcogenide films

Steady state and transient characteristics of photoconductivity have been studied in amorphous thin films of Se₈₅Te_15−xPb_x (x = 0, 2, 4 and 6). The studies of temperature dependence of photoconductivity show that photoconduction is a thermally activated process. The value of activation energy of photoconduction is, however, smaller as compared to activation energy in dark. The results of intensity dependence of steady state photoconductivity indicate that bimolecular recombination is predominant in these materials. The Se₈₅Te_15−xPb_x is found highly composition dependent as lead impurity drastically changes the conduction parameters. The incorporation of Pb impurity is found to affect the transient photoconductivity properties drastically. A spike is observed in the rise curve of photocurrent in undoped a-Se₈₅Te₁₅, which disappears in Pb doped samples. The lead incorporation is found to delay the onset time of recombination in the rise and decay of photocurrent which is attributed to the trapping of charge carriers in deep localized states produced by lead impurity. The photocurrent rise and decay is explained by the trap-controlled recombination model proposed by Iovu et al. and the dispersion parameter α of localized state energy distribution is determined from the experimental results.     

Photoconductivity of vitreous chalcogenides chemically modified by bismuth

Photoconductive properties, such as the spectral response and the excitation intensity and temperature dependences were investigated in the Ge₂₀Bi_xSe_80?x (X=0?13) system, which shows n-type conduction for $\text{× ≧9}$. The increase in Bi content caused the increase in photoconductivity, accompanied by the change of conduction type from p to n. It was found that the recombination processes of photocarriers were monomolecular and bimolecular in low and high excitation intensity regions, respectively, the processes being affected by localized states in the mobility gap. Relatively large activation energies for photoconduction were obtained in n-type samples.     

Electrical conductivity and photoconductivity of As2S3PbS glasses

Measurements of dc electrical conductivity and photoconductivity of various glassy compositions (x = 0.1?0.625) in (As₂S₃)_1?x(PbS)_x have been made. Experimental results of the temperature dependence of dc conductivity from room temperature to 200°C (which includes the glass transition temperature) are reported. All the compositions exhibit intrinsic conduction in the measured temperature range. Thermal activation energy, glass transition temperature and σ₀ for the compositions studied, were determined from the experimental data. The low value of $\text{σ}{}_0\text{(10?10}{}^{\mathrm{?2}}\text{Ω}{}^{\mathrm{?1}}\text{cm}{}^{\mathrm{?1}}$) in these semiconducting glasses is attributed to the greater participation of localized states in the conduction process.In the measurements of photoconductivity, the variation of photocurrent with temperature, photon energy, light intensity and electric field is observed. The recombination model has been involved to explain the results of photoconductivity. Both electrical and photoconductivity data support the presence of higher density of localized states in the x = 0.1 composition than in others.     

Temperature and excitation intensity tuned photoluminescence in Tl4GaIn3S8 layered single crystals

Photoluminescence spectra of Tl₄GaIn₃S₈ layered crystals grown by Bridgman method have been studied in the wavelength region of 500–780 nm and in the temperature range of 26–130 K with extrinsic excitation source (λ_exc = 532 nm), and at T = 26 K with intrinsic excitation source (λ_exc = 406 nm). Three emission bands A, B and C centered at 514 nm (2.41 eV), 588 nm (2.11 eV) and 686 nm (1.81 eV), respectively, were observed for extrinsic excitation process. Variations in emission spectra have been studied as a function of excitation laser intensity in the 0.9‐183.0 mW cm^–2 range for extrinsic excitation at T = 26 and 50 K. Radiative transitions from the donor levels located at 0.03 and 0.01 eV below the bottom of the conduction band to the acceptor levels located at 0.81 and 0.19 eV above the top of the valence band were proposed to be responsible for the observed A‐ and C‐bands. The anomalous temperature dependence of the B‐band peak energy was explained by configurational coordinate model. From X‐ray powder diffraction and energy dispersive spectroscopic analysis, the monoclinic unit cell parameters and compositional parameters of Tl₄GaIn₃S₈ crystals were determined, respectively. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Some Physicochemical Parameters of Saturated Ternary Solutions of Systems with Mixed Crystals in their Solid Phase

The measurements of density (ϱ), viscosity (η) and hydration number (n_h) of saturated solutions of ternary systems KCl KBr H₂O, K₂SO₄ (NH₄)₂SO₄ H₂O and KNO₃ NH₄NO₃ H₂O with mixed crystals in the solid phase have been conducted. It has been confirmed, that the occurence of the extremes on the curves of dependence of the properties (ϱ, η, n_h) on the composition of saturated solution may be the base for the supposition that beside mixed crystals the double salts have also been formed in the solid phase of a given system.     

Light Intensity Variation Studies of MoS2/Electrolyte Interface

Photoelectrochemical characterization of natural and synthetic molybdenum disulphide prepared by direct vapour transport technique have been carried out. The quality of the MoS₂/electrolyte junction for photovoltatic applications was assessed examining the effect of varying light intensity on current voltage behaviour. For measurements at low intensity a broad light source was used. The ideality factor (n) was determined for these junctions by modelling the MoS₂/electrolyte junction in terms of a Schottky barrier. The effect of intensity in the efficiency of the PEC solar cells has also been studied in detail. All the observations have been described and the implications have been discussed.     

Strength of Crystals of Small Dimensions and their Triboluminescence

Stress-dependence of triboluminescence (TBL) in uranyl nitrate, tartaric acid and other nine crystals has been studied with the help of a new technique of crushing the crystals. As the appearance of TBL needs the creation of new surfaces in a crystal, the minimum stress at which TBL appears has been taken to be the fracture-strength of the crystal. The value of the fracture-strength and stress coefficient of binding energy determined from TBL measurements are found to be of correct order. It has been found that the rate of rise of TBL intensity with stress is higher for those crystals which have less value of the fracture-strength. The fracture strength (σ_f) is found to be higher for those crystals which have less value of stress coefficient of binding energy (β) and the product of σ_f and β is higher for those crystals which have higher melting point. It has been shown that the rate of rise of TBL intensity with stress decreases at higher values of stress due to strain hardening in the crystals.     

Die Phasenübergänge und die Störstellenphotoleitung von Sb2S3

The influence of the Sb₂S₃ single crystals growing conditions on the mikrowave dielectric permittivity and the photoconductivity has been investigated. An improper photoconductivity arises on the ferroelectric plane (001) in the crystals with a high dielectric permittivity.     

Electrical properties of a-Ge-Se-In thin films

Steady state and transient photoconductivity has been measured on Ge₂₀Se_80−xIn_x (x = 0, 5, 10, 15, 20) vacuum evaporated thin films. Study of temperature dependent dark conductivity σ_d and photoconductivity σ_ph measurements in the temperature range 303-375 K, shows that the conduction in this glass is through an activated process having single activation energy. The activation energy value of photoconduction is smaller in comparison to activation energy in dark. The photosensitivity shows a maximum value at 10 at.% of In concentration. This is attributed to the decrease in the density of defect states of Ge-Se alloy with increase of In content. The results of intensity dependent steady state photoconductivity σ_ph follow a power law with intensity (F), i.e. σ_ph α F^γ where the value of power γ lies between 0.5 and 1.0, suggesting bimolecular recombination. Rise and decay of photocurrent for different concentration of In shows that photocurrent rises monotonically to the steady state value and the decay of photocurrent is also very fast. An attempt has been made to explain the results on the basis of defects and density of states.