Photoconductivity Studies Research Articles

Effect of Nd doping on structural and opto-electronic properties of CdO thin films fabricated by a perfume atomizer spray method

A perfume atomizer-assisted spray pyrolysis method was employed to fabricate undoped and neodymium (Nd)-doped cadmium oxide (CdO) thin films. X-ray diffraction results reveal that all the films are polycrystalline with a cubic structure with a preferential orientation along the (200) direction. Scherrer’s formula was used to calculate the crystallite size of Nd-doped CdO films. Energy dispersive spectroscopy results show that Cd, Nd and O elements are present in Nd-doped CdO thin films. The optical absorption of the doped films is increased along with increasing Nd-doping level. The prepared CdO thin films have a high absorption coefficient in the visible region and the optical band gap is decreased on increasing Nd doping content. The electrical carrier concentration (n) of the deposited films is increased with increasing Nd doping concentration. Photoconductivity studies of a nanostructured Al/Nd–n-CdO/p-Si/Al device showed a non-linear electric characteristics indicating diode-like behaviour. Prepared Nd:CdO films could increase the photo-sensing effect of this n-CdO/p-Si heterostructure. These Nd-doped CdO thin films may open a new avenue for photodiode application in near future.

Crystal growth and characterization of γ-glycine grown from AgSO4 for nonlinear optical applications

In the present work 0.1–0.5 M proportions of silver sulphate (AgSO4) added glycine single crystals were grown by slow solvent evaporation method. The Powder XRD study confirms that the grown crystals have γ-glycine crystal structure and it crystallizes into a hexagonal structure with a non-centrosymmetric space group of P31. The dielectric constant and dielectric loss of grown crystal was carried out as a function of frequency and the results were discussed. The positive photoconducting nature of the grown crystals was studied by the photoconductivity study. Second harmonic generation (SHG) efficiency of the grown γ-glycine crystal was assessed by using Nd: YAG laser. The results confirms that the grown crystals have higher efficiency compared to the reference (KDP) crystal.

Plasmon (Al) Impregnated Sno2/Tio2 and Zno/Tio2 Nanocomposites as Efficient Photoelectrodes for Dsscs – a Relative Analysis

We report herein a relative analysis of plasmon (Al) impregnated SnO2/TiO2 and ZnO/TiO2 nanocomposite systems synthesized using sol-gel method. The properties of the Al-SnO2/TiO2 and Al-ZnO/TiO2 have been studied using various characterisation techniques such as XRD, EDAX, FESEM, UV-DRS, and Photoconductivity techniques. The elemental composition and phase structures of the as-synthesized Al-SnO2/TiO2 and Al-ZnO/TiO2 nanocomposites were investigated using Energy Dispersive X-Ray (EDAX) and X-Ray Diffraction (XRD), which showed high degree of purity and crystallinity respectively. The crystallite sizes estimated with Scherrer’s formula were about 24 and 22 nm respectively. The FESEM images revealed that, both the samples were mesoporous in nature. The optical properties of both Al-SnO2/TiO2 and Al-ZnO/TiO2 samples exhibited strong absorption and diffused reflectance which suggested the possibility of the samples being used as photoelectrodes and the band gap value was found to be 3.38 eV and 3.07 eV using Kubelka-Munk plot. The photoconductivity studies suggested that Al-SnO2/TiO2 showed higher photo current values in reference to the Al-ZnO/TiO2 nanocomposite. Upon overall comparison, it is concluded that the Al doped SnO2/TiO2 exhibited enhanced characteristics over that of Al-ZnO/TiO2 nanocomposite and hence could be applied as efficient photoelectrodes for DSSCs.

F-T Raman, Microhardness and Photoconductivity study of Zinc Sulphate doped L-Threonine dihydrogen phosphate Single Crystal

F-T Raman, Microhardness and Photoconductivity study of Zinc Sulphate doped L-Threonine dihydrogen phosphate Single Crystal

Engineering Interface-Dependent Photoconductivity in Ge2Sb2Te5 Nanoscale Devices.

Phase-change materials are increasingly being explored for photonics applications, ranging from high-resolution displays to artificial retinas. Surprisingly, our understanding of the underlying mechanism of light-matter interaction in these materials has been limited to photothermal crystallization because of its relevance in applications such as rewritable optical discs. Here, we report a photoconductivity study of nanoscale thin films of phase-change materials. We identify strong photoconductive behavior in phase-change materials, which we show to be a complex interplay of three independent mechanisms: photoconductive, photoinduced crystallization, and photoinduced thermoelectric effects. We find that these effects also congruously contribute to a substantial photovoltaic effect, even in notionally symmetric devices. Notably, we show that device engineering plays a decisive role in determining the dominant mechanism; the contribution of the photothermal effects to the extractable photocurrent can be reduced to <0.4% by varying the electrodes and device geometry. We then show that the contribution of these individual effects to the photoresponse is phase-dependent with the amorphous state being more photoactive than the crystalline state and that a reversible change occurs in the charge transport from thermionic to tunnelling during phase transformation. Finally, we demonstrate photodetectors with an order of magnitude tunability in photodetection responsivity and bandwidth using these materials. Our results provide insights to the photophysics of phase-change materials and highlight their potential in future optoelectronics.

Oxygen vacancy induced photoconductivity enhancement in Bi1-xCaxFeO3-δ nanoparticle ceramics: A combined experimental and theoretical study

Based on experimental and density functional studies, we show that tailoring of oxygen vacancies (OV) leads to large scale enhancement of photoconductivity in BiFeO3 (BFO). The OV concentration is increased by substituting an aliovalent cation Ca2+ at Bi3+ sites in the BFO structure. Furthermore, the OV concentration at the disordered grain boundaries can be increased by reducing the particle size. Photoconductivity studies carried out on spark plasma sintered Bi1-xCaxFeO3-δ ceramics show four orders of enhancement for x = 0.1. Temperature dependent Nyquist plots depict a clear decrease in impedance with increasing Ca2+ concentration which signifies the role of OV. A significant reduction in photoconductivity by 2 to 4 orders and a large increase in impedance of the air-annealed (AA) nanocrystalline ceramics suggest that OV at the grain boundaries primarily control the photocurrent. In fact, activation energy for AA samples (0.5 to 1.4 eV) is larger than the as-prepared (AP) samples (0.1 to 0.5 eV). Therefore, the room temperature J-V characteristics under 1 sun illumination show 2–4 orders more current density for AP samples. Density-functional calculations reveal that, while the defect states due to bulk OV are nearly flat, degenerate, and discrete, the defect states due to surface OV are non-degenerate and interact with the surface dangling states to become dispersive. With large vacancy concentration, they form a defect band that enables a continuous transition of charge carriers leading to significant enhancement in the photoconductivity. These studies reveal the importance of tailoring the microstructural features as well as the composition-tailored properties to achieve large short circuit current in perovskite oxide based solar cells.

Method of Increasing Photosensitivity of Silicon Power Planes for Solar Energy

The solubilities of sulfur are determined by neutron activation analysis and silicon compensation by sulfur with different concentrations of the initial boron. It is shown that the sulfur solubility at a silicon doping temperature of 1250°C is ~1.8 × 1016 cm–3. Joint analysis of the results of studies of photoconductivity (PC) spectra, both in combined illumination with integral and infrared (IR) light and after the integral light is switched off, and the results of a study of the isothermal relaxation spectra of the capacity (DLTS) of Si❬S❭ crystals manufactured at different pressures of the diffusant vapor been established that single sulfur centers in silicon create two deep levels of ES – 0.12 and ES – 0.18 eV. All of the remaining energy levels of ES – 0.27 and ES – 0.53 eV are related to the quasi-molecules S2 and S4, respectively.

Studies on the photoelectric properties of crosslinked-poly(acrylamide co-acrylic acid) for photo detector applications

Abstract The co-polymer, polyacrylamide co-acrylic acid-P(AM-AA) was prepared by chemical polymerization of acrylamide with acrylic acid in presence of methylene bisacrylamide as a crosslinker. The copolymer was analyzed using FTIR, XRD and DTA. The I-V characteristics of the copolymer were studied and proved that the recombination process is dependent on the presence of traps distributed in the energy gap. The results showed that the traps contribute significantly in the increased photosensitivity of the co-polymer. The behaviors of both dark and photoconductivity with temperature showed linear relations at different light intensities and proved an activated conduction with single activation energy. The activation energy (Ea) at different light intensity was found to follow Meyer Neldel rule (MN rule) and the intercept σo (pre factor) as well. The characteristic energy of exponential traps was found to be within 0.0134–0.009 eV, at different light intensities. The transient photoconductivity studies on the co-polymer confirmed the presence of traps. Where, the high photosensitivity and the presence of traps may contribute to the development of the improved performance of photo detectors.

Growth and characterization of γ-glycine single crystals for photonics and optoelectronic device applications

In this present work, MnSO4-added glycine single crystals were grown by slow solvent evaporation method. Powder XRD study confirms that the crystals grown in γ-phase and it crystallizes in hexagonal structure with a space group of P31. Differential Scanning Calorimetry study revealed that the thermal characteristics of the grown polymorph. The dielectric constant and dielectric loss of grown crystal was carried out as a function of frequency and the results were discussed. The positive photoconducting nature of the grown crystals was studied by photoconductivity study. Non-Linear Optical (NLO) productivity of grown γ-glycine crystal was measured by using Nd: YAG laser. It was found to be 1.67 times higher than that of a reference (KDP).

Low temperature photoconductivity of few layer p-type tungsten diselenide (WSe2) field-effect transistors (FETs)

We report on the low-temperature photoconductive properties of few layer p-type tungsten diselenide (WSe2) field-effect transistors (FETs) synthesized using the chemical vapor transport method. Photoconductivity measurements show that these FETs display room temperature photo-responsivities of ∼7 mAW−1 when illuminated with a laser of wavelength λ = 658 nm with a power of 38 nW. The photo-responsivities of these FETs showed orders of magnitude improvement (up to ∼1.1 AW−1 with external quantum efficiencies reaching as high as ∼188%) upon application of a gate voltage (VG = −60 V). A temperature dependent (100 K < T < 300 K) photoconductivity study reveals a weak temperature dependence of responsivity for these WSe2 phototransistors. We demonstrate that it is possible to obtain stable photo-responsivities of ∼0.76 ± 0.2 AW−1 (with applied VG = −60 V), at low temperatures in these FETs. These findings indicate the possibility of developing WSe2-based FETs for highly robust, efficient, and swift photodetectors with a potential for optoelectronic applications over a broad range of temperatures.

Growth, structural, optical, thermal and dielectric properties of l-glutamic acid hydrochloride crystal for optoelectronic device applications

A single crystal of l-glutamic acid hydrochloride was successfully grown by slow evaporation method. The grown crystal was analyzed for structural, optical and thermal studies. The powder XRD studies were applied to analyze the lattice parameter of the grown crystals. The optical band gap of the grown crystal was effectuate by UV–Vis spectroscopy. The thermal strength of the grown crystals was observed by Differential Scanning Calorimetry studies. The dielectric study carried out determined the dielectric constant and dielectric loss decreases with a higher frequency at various temperatures. The photoconductivity study contributed its positive photo conducting nature. The second harmonic generation (SHG) for the grown crystal was confirmed by Nd: YAG laser Kurtz Perry technique and the efficiency of the grown crystal was evaluated with KDP crystal.

Tailoring sub-bandgap of CuGaS2 thin film via chromium doping by facile chemical spray pyrolysis technique

Tailoring sub-bandgaps using intermediate states or bands with wide bandgap semiconductors is a promising and novel technique for the application in high efficiency solar cells. Pure and chromium (Cr) doped chalcopyrite CuGaS2 (CGS) thin films were prepared by facile chemical spray pyrolysis technique and annealed in vacuum, nitrogen and argon atmospheres. Structural characterization confirmed that the prepared films are in tetragonal chalcopyrite structure with polycrystalline nature. No secondary phases were present in both pure and Cr doped CGS thin films. Presence of Cr ions was confirmed by X-ray photoelectron spectroscopy and energy dispersive analysis of X-rays analyses. The optical direct and sub band gap of pristine and Cr doped CGS thin films were measured from UV absorption data. It was revealed that the pure CGS film has a band gap of 2.40 eV sub-band gap values were observed at 2.25 and 2.15 eV for 1 and 2 wt% of Cr doping, respectively. These gaps can be ascribed to the formation of intermediate bands due to hybridization of Cr d-states into the host electronic structure. Meanwhile, photoconductivity study demonstrated the photo-electric activity of the intermediate bands in the Cr doped thin films.

Growth and characterization study of α and β polymorphs of l-glutamic acid single crystals in the presence of ammonium sulphate

In this work, l-glutamic acid polymorphs of β and α crystal were grown by the slow evaporation method by using additives of ammonium sulphate. The selective additive ammonium sulphate was added at different concentrations to study the l-glutamic acid polymorphs. It creates that at a level of 0.04 g/100 ml, the additive contributed to the crystallization of l-glutamic acid in α-form, and this additive exhibited an inhibitory action on the transition of α crystal to β crystals. The lower concentration of ammonium sulphate provides β polymorph whereas the higher concentration of ammonium sulphate provides α polymorph crystal. Structural confirmation of the grown polymorph was executed by powder X-ray diffraction study. UV–Vis-NIR spectral analysis the optical transparency of grown crystals. The powder second harmonic conversion efficiency of grown crystal was determined by using Kurtz and Perry powder technique and the efficiency compared to standard inorganic material potassium dihydrogen phosphate. The dielectric properties of dielectric constant and dielectric loss of grown crystal have been measured as a function of frequency and temperature. The photoconductivity study contributed its positive photo conducting nature. In vitro antimicrobial activity of grown crystals was analyzed against gram positive and negative bacteria’s carried out by disk diffusion process and created that the crystal proves superior inhibition against various bacteria’s strains.

Synthesis, growth, structure, optical, mechanical, and electrical properties of an Inorganic new nonlinear optical crystal: sodium manganese tetra chloride (SMTC)

A new inorganic nonlinear optical single crystal of sodium manganese tetra chloride (SMTC) has been successfully grown form aqueous solution by the slow evaporation technique at room temperature. The crystals obtained by the above technique were subjected to different characterization analysis. The crystalline nature of the grown crystal of SMTC was analyzed by powder X-ray diffraction. Single crystal X-ray diffraction study reveals that the crystal belongs to orthorhombic system with non-centrosymmetric space group Pbam. Optical transmission study on SMTC crystal shows high transmittance in the entire UV–Vis region and the lower cutoff wavelength is found to be 240 nm. The mechanical strength of the grown crystal was estimated by Vicker’smicrohardness test. The second harmonic generation (SHG) efficiency of the crystal was measured by Kurtz’s powder technique infers that the crystal has nonlinear optical (NLO) efficiency 1.32 times that of KDP.The dielectric constant and dielectric loss of the compound were measured at different temperature with varying frequencies. Photoconductivity study confirms that the title compound possesses a negative photoconducting nature. Growth mechanism and surface features of the as grown crystals were analyzed by chemical etching analyzing.

Third order nonlinear optical, luminescence and electrical properties of ʟ-phenylalanine ʟ-phenylalaninium bromide bulk crystals

Optical quality ʟ-phenylalanine ʟ-phenylalaninium bromide (LPLPB) bulk crystals were grown by slow evaporation technique. The third order nonlinear refractive index and nonlinear absorption coefficient of the grown crystal were measured by Z-scan studies. The third order nonlinear susceptibility was found to be 1.8792 х 10−4 esu which is fairly higher than the other compounds. The Photoluminescence spectra reveal the emission bands for LPLPB crystals. The Photoconductivity studies were employed to determine the dependence of photocurrent on the applied electric field. Negative photoconductivity was exhibited by the sample. The d. c. conductivity of the grown crystal was measured by the complex impedance analysis wherein the obtained plot in the form of semicircle finds application in Debye relaxation for materials having large dc conductivity.

Growth, Hirshfeld surfaces, spectral, quantum chemical calculations, photoconductivity and chemical etching analyses of nonlinear optical p-toluidine p-toluenesulfonate single crystal.

A single crystal of p-toluidine p-toluenesulfonate (PTPT) has been grown by slow evaporation solution technique (SEST) at room temperature. Single crystal X-ray analysis confirms that grown crystal belongs to the monoclinic structure with space group P21. Intermolecular interactions and fingerprint plots of PTPT molecules are executed by Hirshfeld surface analysis. It was found that H···H (44.2%) contacts have maximum intermolecular interactions contributions in the total Hirshfeld surface area. The characteristic absorption band occurs at below 290 nm. The functional groups were identified using FTIR and FT-Raman analyses and compared with theoretical values. The title molecule contains fourteen CH bonds and three OH bonds. The calculated HOMO and LUMO energy values are -6.125 eV and -1.157 eV, respectively. The chemical potential (μ) and electronegativity (χ) values are estimated to be -3.4938 eV and 3.4938 eV, respectively. The strongest negative hyperconjugation occurs due to the charge transfer from the occupied orbital (σ) to the unoccupied orbital (π*) which is calculated for the σ(N20-C21) → π*(N20-O18). The green and red lines in the total density of states (TDOS) spectrum indicate the occupied orbital and virtual orbital levels, respectively. Photoconductivity studies have been done for the grown crystal. It is observed that the dark current is greater than photocurrent. It shows negative photoconductivity nature of PTPT crystal. The etching analysis was executed on (001) plane of PTPT crystal. It has rectangular shape etch pits patterns.

Photophysical and photoconductive aspects of donor-acceptor low band gap conjugated copolymer

This article presents the photophysical and photoconductive properties of a newly synthesized low band gap Donor-Acceptor conjugated poly (benzothiadiazole-triphenylamine) co-polymer labelled as P(BTZ-TPA) in which 2,1,3 benzothiadiazole (BTZ) act as the electron deficient moiety and triphenylamine (TPA) is used as donor moiety. Photophysical properties of this synthesized polymer were analyzed by recording steady state absorption and emission spectra of dilute solution and thin films respectively. In addition to this, solvatochromic experiments were carried out using a binary mixture consisting of toluene and acetonitrile to understand the solvent dependence on the ground state and excited states of this polymer. The optical characterization revealed high degree of intramolecular charge transfer through the polymer backbone. The P(BTZ-TPA) thin films exhibit good fluorescence emission with emission peak around 615 nm. Quantum yield of the fluorescence emission is measured in relative method. Also, fluorescence decay parameters were examined using time correlated single-photon counting (TCSPC) technique. Carrier generation and transport of the generated carriers upon photo excitation is studied in pristine polymer films as well as in P(BTZ-TPA):PCBM blend films, by performing photoconductivity studies using broad spectral source and lasers of wavelengths 488 nm and 632 nm. P(BTZ-TPA) thin films exhibited good photoresponse over the entire visible region, with promising internal photocurrent efficiency. Quenching of fluorescence is observed in PCBM blend films. This drastic quenching of fluorescence emission is assigned to the charge transfer interaction between co-polymer and PCBM, and is confirmed by substantial increment in photoconductivity of the blend films. An internal photocurrent efficiency of 17.4% was obtained in the blend films for a biasing field of 10V/μm.

Optical, photoconductivity and dielectric studies of zinc sulphate added glycine crystal for photonics applications

In present studies, we have successfully grown γ-glycine single crystal in the presence of ZnSO4 as an additive by using slow solvent evaporation method. Powder X-ray Diffraction study confirms crystal grown in γ-phase and it crystallizes into a hexagonal structure with a space group of P31. UV–vis transmittance spectra was recorded for the sample to analyse the optical transparency in visible and near infrared region (NIR). In Kurtz-Perry powder test, SHG efficiency of the grown ZnSO4 added glycine crystal is found to be 3.18 times higher than reference KDP crystal. The dielectric constant and dielectric loss of ZnSO4 added glycine crystal was carried out as a function of temperature by varying the frequency and the obtained results were discussed. The photoconductivity study confirms the positive photoconducting nature of grown ZnSO4 added glycine crystal.

Relative Analysis of Plasmonic Impact of Silver and Aluminium Nanoparticles on SnO2 Nanoparticles for Photovoltaic Applications

The present study reports Ag and Al plasmon doped SnO2 nanoparticles synthesized by a facile sol–gel route for photovoltaic applications. The crystallite and particle size of the samples detected from X-ray Diffraction (XRD) and Field Emission Scanning Electron Microscope (FE-SEM) studies depict that the Ag and Al doped SnO2 nanoparticles possessed declined sizes due to the effect of plasmons. Ultra Violet Diffuse Reflectance Spectroscopy (UV-DRS) technique deduced the optical behaviour of the samples enriched with Surface Plasmon Resonance effect in the doped SnO2 nanoparticles. Surface properties from Brunauer Emmett Teller (BET) studies revealed an enhancement of surface area in the Ag doped SnO2 nanoparticles. Field-dependent dark and photoconductivity studies of the samples revealed significant rise in the photo conducting nature of Ag and Al doped SnO2 nanoparticles. An overall relative analysis suggests that the Ag and Al plasmon doped SnO2 nanoparticles attributed with outstanding opto-electrical and surface properties, could serve as promising materials for photovoltaic applications especially in solar cells.

Photocatalytic degradation and antimicrobial activity of transition metal doped mesoporous ZnS nanoparticles

Latterly the development and application of photocatalysts to decompose or convert pollutants into organic fuels is one of the urgent issues. In the present work Fe3+, Mn2+ and Y3+ doped ZnS nanoparticles are prepared by using chemical co-precipitation method with equal amount of 5 wt% dopant. Their photocatalytic activity is evaluated by the degradation of Turquoise Blue H5G (used as model pollutant) in aqueous solution under sunlight. The descending order of photocatalytic degradation efficiency under solar light is as follows: ZnS: Fe > ZnS: Mn > ZnS > ZnS: Y. Adsorption–desorption results show that applying the co-precipitation synthesizing method in the aqueous atmosphere will cause a mesoporous structure. The obtained specific surface area of the synthesized ZnS and doped ZnS nanoparticles varies from 12.6 to 55 m2 g−1. TOC measurements confirm the mineralization of the photocatalyst. Photostability of the mesoporous doped ZnS nanoparticles regarding Zn leaching was evaluated. The photocurrent generation of the samples is confirming by using photoconductivity studies. Antimicrobial activities of the synthesized nanoparticles are tested for its efficiency. This is the first ever report on photocatalytic degradation of Turquoise Blue H5G by mesoporous ZnS and doped mesoporous ZnS nanoparticles.