Photoconductivity Studies Research Articles

Intrinsic Photoconductivity of Few-layered ZrS2 Phototransistors via Multiterminal Measurements

We report intrinsic photoconductivity studies on one of the least examinedlayered compounds, ZrS2.Few-atomic layer ZrS2 field-effect transistorswere fabricated on the Si/SiO2 substrate and photoconductivity measurements were performed using both two- and four-terminal configurationsunder the illumination of 532 nm laser source. We measured photocurrentas a function of the incident optical power at several source-drain (bias)voltages. We observe a significantly large photoconductivity when measured in the multiterminal (four-terminal) configuration compared to thatin the two-terminal configuration. For an incident optical power of 90nW, the estimated photosensitivity and the external quantum efficiency(EQE) measured in two-terminal configuration are 0.5 A/W and 120%,respectively, under a bias voltage of 650 mV. Under the same conditions,the four-terminal measurements result in much higher values for both thephotoresponsivity (R) and EQE to 6 A/W and 1400%, respectively. Thissignificant improvement in photoresponsivity and EQE in the four-terminal configuration may have been influenced by the reduction of contactresistance at the metal-semiconductor interface, which greatly impacts thecarrier mobility of low conducting materials. This suggests that photoconductivity measurements performed through the two-terminal configurationin previous studies on ZrS2 and other 2D materials have severely underestimated the true intrinsic properties of transition metal dichalcogenides andtheir remarkable potential for optoelectronic applications.

Crystal growth, optical, thermal, laser damage threshold, photoconductivity and third-order nonlinear optical studies of KCl doped sulphamic acid single crystals

Good quality of pure and 1 mol% KCl doped sulphamic acid (SA) single crystal was grown by the solvent evaporation technique. The grown crystals belong to an orthorhombic structure. The peak present in the frequency region between 2870 and 3137 cm−1 is owing to NH3+ stretching vibration. The addition of dopant enhances the transmittance and mechanical strength of the SA crystal. The intense emission bands are obtained at 335 and 424 nm for pure and 337 and 468 nm for 1 mol% KCl doped SA crystal, respectively. The first decomposition point observed at 229 °C and 232 °C for pure and doped SA crystals, respectively. Laser damage threshold resistant of the crystals is 57, 89 and 132 mJ for KDP, pure and 1 mol% KCl doped SA crystals, respectively. The negative photoconductivity nature of title crystals was confirmed by photoconductivity studies. The third-order nonlinear optical (TONLO) susceptibility (χ3) of the pure and doped crystal is 5.004 × 10−10 esu and 7.848 × 10−10 esu, respectively. All the results show that the grown crystals have good transmittance, high LDT, mechanical, thermal and large susceptibility values. So, the title crystals are potential material for NLO applications.

Anisotropy of Excitons in Two-Dimensional Perovskite Crystals.

Two-dimensional (2D) perovskites show great potential for optoelectronic applications due to their bandgap tunability, extremely large excition binding energy, and large crystal anisotropy compared with their three-dimensional counterparts. To fully explore exciton-based applications and improve their performance, it is essential to understand the exciton behavior in 2D perovskites. Here, we investigate exciton anisotropy within the crystallographic plane and cross plane of (C4H9NH3)2PbI4 2D perovskite crystals by polarization-resolved photoluminescence, reflection, and photoconductivity studies. We observe a polarization-dependent emission evolution and an enhanced self-trapped exciton emission with an oblique incident excitation from the cross plane. Furthermore, the anisotropy of excitons in (C4H9NH3)2PbI4 2D perovskite crystals is identified by polarization-resolved photoluminescence and photoconductivity measurement, and a completely opposite polarization-dependent behavior was observed for free excitons and self-trapped excitons. We attribute this different anisotropy to the existence of out-of-plane excitons and different optical selection rule for free excitons and self-trapped excitons. Our findings will shed light on designing and improving the performance of exciton-based optoelectronic devices in 2D perovskites.

Growth, spectroscopic, electrical and mechanical studies on hexamethylenetetramine succinate crystal: a new third harmonic generation material

Abstract Hexamethylenetetramine succinate was synthesized and good quality single crystals with the size of 14 mm × 6 mm × 4 mm were grown by the slow evaporation solution growth technique at room temperature. The single crystal XRD revealed that the grown crystal belongs to the monoclinic system with the space group of P21/c. The presence of functional groups in the crystal was identified using FT-IR technique. The optical behavior was examined through UV-Vis-NIR studies. The photoconductivity study exhibited the positive photoconductivity nature of the grown crystal. Microhardness studies revealed the soft nature of the crystal. The nonlinear refractive index (n2), nonlinear absorption coefficient (β) and third order nonlinear optical susceptibility χ(3) of the crystals were measured by Z-scan studies.

Photoconductivity study of spray pyrolized pure and Cu-modified SrTiO3 thin films

The SrTiO3 (STO) and Cu-STO nanostructured thin films were prepared using the spray pyrolysis technique. So prepared films were characterized for structural, electrical and optical and photoconductivity properties. The FE-SEM showed with inhomogeneous grain growth. Scherrer formula used to calculate particle size. The band gap, activation energies are estimated. AFM results were analyzed to estimate roughness. Absorbance and band gaps are calculated. The tungsten 100 W bulb was used to irradiate the films. The nature of I-V characteristics of the films changes with the ranges of applied bias. The effect of electric field and intensity relies photoconductivity of the films. The photo generated current Ip and dark current Id varies according to the power law I α Vm with the applied field and intensity of illumination, due to the defect related mechanism including both recombination centres and traps. The variation in linearity is attributed to flow of trap limited as well as space charge limited current inside the material. Doping of Cu led to the introduction of a high concentration of oxygen vacancies on the surface of the STO lattice. Consequently, to maintain the regional charge balance of STO, Cu2+ could be substituted for Sr2+. Moreover, oxygen vacancies induced localized states into the band gap of the modified STO and acted as photoinduced charge traps, thus promoting the photoconductivity process. The photoconductivity of Cu modified films was found to be more than that of pure STO thin films. This study will have significant impact on the use of Cu-STO in optoelectronics devices.

Investigations on growth and characterization of glycine potassium iodide for non liner optical applications

Glycine Potassium Iodide (GPI) crystals have been grown using slow evaporation solution technique at room temperature. The functional groups and vibrational frequencies were identified using FTIR spectral analysis. The cell parameters were determined from single crystal X-ray diffraction analysis. The optical transmittance window and lower cutoff wavelength have been identified by UV-absorption spectrum analysis. The second harmonic generation (SHG) efficiency measurement was carried out by powder Kurtz method. The photoconductivity study confirms the positive photo conducting nature of grown crystal. The characterization studies have confirmed that the grown crystal is suitable for Non linear optical applications.

Photoconduction in CuO

With the global surge in the research on perovskite halides as cost effective alternative Silicon solar cells, it is necessary to find the replacement of very expensive hole transport materials (HTM). Copper oxide (CuO) is one of the inorganic binary compound and much cheaper than the organic HTMs. In this work, light absorption behaviour and photoconductivity of CuO are examined. The band gap and Urbach energy is estimated using UV-visible absorbance spectrum. The photo-conduction study of the CuO is carried in 1.5AM-G solar light.

Biofriendly and competent domestic microwave assisted method for the synthesis of ZnO nanoparticles from the extract of Azadirachta indica leaves

ZnO nanoparticles are successfully prepared via eco-friendly synthesis using Azadirachta indica leaves extract with microwave assisted solvothermal method using a domestic microwave oven. The structure of green synthesized ZnO NPs and lattice parameters were confirmed using powder X-ray diffraction. Scanning electron microscopy and energy dispersive X-ray analysis exhibit the morphology and elemental analysis of the green synthesized ZnO NPs. The photoconductivity study reveals the positive photoconductive nature of ZnO nanoparticles.

Band engineering via grain boundary defect states for large scale tuning of photoconductivity in Bi1−xCaxFe1−yTiyO3−δ

Spark plasma sintered Bi1−xCaxFe1−yTiyO3−δ (BCFTO) (x = y = 0.05 and 0.1) nanoparticle ceramics are studied for photoconductivity properties. As-prepared (AP) BCFTO hosts a large concentration of grain boundary (GB) oxygen vacancies (OV), whereas air annealed (AA) BCFTO have significantly suppressed GB OV. X-ray absorption near edge spectroscopy study confirms that Fe and Ti remain in 3+ and 4+ oxidation states, respectively. Thus, lattice OV created when only Ca2+ is substituted in BiFeO3 are charge compensated in Ca and Ti codoped BiFeO3. This ascertains that BCFTO is devoid of lattice OV. Photoconductivity studies show four orders of more photocurrent arising from GB OV contributions in BCFTO-AP compared to that in BCFTO-AA samples. A large increase in the activation energy for the AA samples (0.4 eV to 1.6 eV) compared to that for the AP samples (0.06 eV to 0.5 eV) is obtained from ln ω vs 1/T Arrhenius plots. This further substantiates the suppression of GB OV resulting in poor photoconductivity. Diffuse band edges observed in Kubelka-Munk plots of BCFTO-AP samples are a consequence of OV defect states occupying the bulk bandgap. In the absence of OV defect states, band edge becomes sharper. Density functional theory (DFT) calculations further support the experimental observations. DFT study shows that the presence of Ca and Ti does not enhance the photocurrent as these codopants do not produce mid-bandgap states. The mid-bandgap defect states are attributed only to the unsaturated bonds and OV at the GB in BCFTO. These studies manifest a critical role of OV residing at the GB in tuning the photoconductivity and, hence, the photoresponse of BCFTO.

Positive and negative photoconductivity in sprayed β-In2S3 thin films

In2S3 indium sulfide thin films were deposited on glass substrates by chemical reactive pulverization in liquid phase at substrate temperature of 300 °C. The layers obtained were characterized by x-ray diffraction (XRD), Raman spectroscopy, spectrophotometry and photoluminescence (PL). In this work, photoconductivity study was conducted using white light source (halogen lamp) and red laser source (λ = 655 nm). This study shows that the photocurrent follows power law with the change of white light irradiance and linear law as function of the bias voltage. The traps energy depths were estimated from photocurrent decay. However, when the bias voltage is shifted to low values, the In2S3 material reveals negative photoconductivity. An interpretation of this behavior was also proposed.

Hydrothermal synthesis of ZnO–CdS nanocomposites: Structural, optical and electrical behavior

ZnO–CdS nanocomposites with three different molar ratios of 25:75, 50:50 and 75:25 were synthesized by simple hydrothermal technique. Powder X-ray diffraction patterns confirmed the phase formation of ZnO and CdS in ZnO–CdS nanocomposites. The calculated crystallite size was found in the range of 33–38 nm and 15–21 nm for ZnO and CdS respectively. HRSEM images revealed flake-like morphology for all samples. Energy dispersive X-ray spectra confirmed the presence of all the elements. The estimated optical bandgap was found in the range of 3.71–3.35 eV. IR spectra confirmed the formation of stretching vibration in ZnO and CdS. Dielectric analysis was performed in order to study Ac conductivity, dielectric constant and dielectric loss. Photoconductivity studies revealed that ZnO–CdS nanocomposites material exhibited sound photo-response characteristics.

Importance of cesium carbonate additives in the nucleation and growth of α- and γ-glycine single crystals

In the present work, successful growth of α- and γ-glycine single crystals using cesium carbonate (Cs2CO3) as an additive has been reported. The powder XRD study confirms that the grown 0.2 M cesium carbonate added glycine crystal has α-glycine crystal morphology and it crystallized in a monoclinic crystal structure with a space group of P21/n. In a similar manner, the PXRD patterns recorded for 0.4, 0.6, 0.8 and 1 M concentrations of cesium carbonate added glycine crystals and the obtained PXRD patterns authenticated that the harvested grown crystals belong to hexagonal crystal system with space group P31. The variation of dielectric constant and dielectric loss for the γ-glycine single crystal was carried out as a function of frequency and the results were discussed in detail. The transmittance spectrum shows that the grown α- and γ-glycine crystals had an extensive optical transparency window in the entire spectrum especially in visible region. The band gap varies from 4.59 to 6.01eV. The positive photoconducting nature of the grown γ-glycine single crystal in the presence of cesium carbonate was studied by the photoconductivity study. The second harmonic generation (SHG) for the prepared γ-glycine single crystals was studied by using Kurtz and Perry powder technique with Nd-YAG laser. The result shows that the prepared γ-glycine single crystals exhibit enhanced second harmonic conversion efficiency and it proves that these crystals are an alternate to KDP crystal in optoelectronic devices and NLO applications.

Structural, optical and photoconductivity studies of ZnO bicones synthesized by seed-mediated method

ZnO bicones (BC) have been synthesized by a seed-mediated method using polyethylene glycol (PEG) and triethylamine (TEA). As-synthesized ZnO BC has been characterized by X-ray diffraction method (XRD), UV–visible absorption spectroscopy, Photoluminescence spectroscopy (PL), Fourier Transform Infrared (FTIR) spectroscopy, Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and Time-dependent Photoconductivity study. XRD pattern of ZnO BC shows hexagonal wurtzite phase structure. The UV–visible absorption spectrum of ZnO BC shows two absorption band edges at 302 nm and 370 nm due to its diameter and length. The PL spectrum of ZnO BC shows rich zinc interstitial defects due to the presence of an intense peak at 423 nm. The FTIR spectrum of ZnO BC confirms the presence of TEA and PEG. SEM and TEM images of ZnO nanostructures confirm the bicones structure as well as the size of the ZnO BC. Photoconductivity study shows that the time-dependent rise and decay curves of ZnO BC has very high photosensitivity in vacuum medium compared to its air medium due to the presence of hydrocarbon functional groups and oxygen deficiency atmosphere.

Experimental and quantum chemical studies on SHG, Z-scan and optical limiting investigation of 2-amino-5-bromopyridinium trifluoroacetate single crystal for optoelectronic applications

The 2-amino-5-bromopyridinium trifluoroacetate (2A5BPTFA) crystal has been successfully grown by solvent slow evaporation technique. The grown crystal is found to non-centrosymmetric space group Pna21 with orthorhombic crystal system, which has been confirmed from single crystal X-ray diffraction analysis. The crystalline nature of the 2A5BPTFA is supported by powder X-ray diffraction technique. The molecular structure and different functional groups in 2A5BPTFA were confirmed by 1H, 13C NMR and FTIR spectral analyses. The intermolecular charge transfer that occurs in 2A5BPTFA molecule due to the presence of N–H⋯O and C–H⋯O hydrogen bondings have been studied by Hirshfeld surface analysis. From the UV–Vis absorption and photoluminescence spectra, the lower cutoff wavelength and emission peak are found to be 364 nm and 392 nm, respectively. In addition, the optical band gap of grown crystal has been calculated as 3.47 eV. Powder second harmonic generation efficiency of the crystal is observed to be 2.44 times greater than that of potassium dihydrogen phosphate. A positive photoconducting nature and low dielectric constant values have been obtained from photoconductivity and dielectric studies. From the Z-scan study reveals the self-defocusing nature of the grown crystal. Optical limiting study shows the optical limiting response of 2A5BPTFA crystal. In addition, the intermolecular charge transfer interactions and existence of N–H⋯O hydrogen bonding of the 2A5BPTFA have been confirmed by density functional theory methods and are discussed in detail.

Effect of NaCl on the properties of sulphamic acid single crystals

Single crystals of pure and NaCl doped sulphamic acid (SA) were grown by slow evaporation method at room temperature. The lattice parameters and structure were determined by using single crystal and powder X-ray diffraction analyses. The presence of dopant in the SA lattice was affirmed by EDAX analysis. UV-Vis spectra show maximum transmittance in the visible region. The band gap energies were found to be 6.06 eV and 5.70 eV for pure and NaCl doped SA crystals respectively. From the PL specta the emission were observed at 335 and 424 nm for pure and 340 and 428 nm for doped SA crystal. The thermal stability of the grown crystals were analyzed by thermogravimetric and differential thermal analysis (TGA/DTA) and revealed that the grown crystals were thermally stable up to 331 ̊C and 334 ̊C for pure and NaCl doped SA. Vickers microhardness study reveals that the hardness of the crystals is increase with increasing load. The photoconductivity study shows that the grown crystals are negative photoconductive nature. The Laser Damage Threshold (LDT) indicates the grown crystals have good resistance to laser radiation than a standard Potassium dihydrogen phosphate (KDP) crystal. The Z-scan technique was employed to determine the nonlinear refractive index, nonlinear optical absorption and third order nonlinear optical (TONLO) susceptibility of the grown crystals using He–Ne laser.

Experimental Study of Different Vanadium Dopant Concentrations in ZnO Nanorods for a Low Frequency Piezoelectric Accelerometer

Nano-electro-mechanical systems accelerometers using undoped (Z) and 1 wt.%, 3 wt.% and 5 wt.% of Vanadium doped (ZV1, ZV3 and ZV5) Zinc Oxide (active layer) nanorods are fabricated. A low temperature assisted hydrothermal method was used to grow nanorods on Fluorine-doped Tin Oxide substrates. The complete accelerometer device architecture includes formation of a p-n junction by depositing poly (3,4-ethylene dioxythiophene) polystyrene sulfonate (p-type layer) on V doped and undoped active layers (n-type layer) with silver as top electrode. The structural analysis revealed the (002) plane c-axis orientation of 1 D nanorods grown. A field emission scanning electron microscope with energy dispersive x-ray spectroscopy showed changes in the morphology in the undoped and doped devices. Optical analysis showed a band gap decrease from 3.15 eV (Z) to 2.92 eV (ZV5). Photoconductivity study proved the formation of a p-n junction between the p-type and active layer in all the fabricated piezoelectric accelerometers. The Nyquist plots obtained using impedance analysis depicted the presence of RC circuit in all the fabricated accelerometers. A less internal resistance of 1.26 kΩ and RC time constant of 0.032 ms for ZV5 showed an improved piezoelectric property due to 5 wt.% of V doping compared to other fabricated accelerometers. The highest sensitivity of 3.528 V/g was acquired for ZV5 with maximum output voltages of 2.30 V and 2.9 V at 9 Hz resonant frequency and 1 g acceleration, respectively. An improvement of 77.28% sensitivity in ZV5 was observed compared to that of Z.

Synthesis of silver-loaded ZnO nanorods and their enhanced photocatalytic activity and photoconductivity study.

Herein, we synthesized ZnO nanorods using a solvothermal reaction technique at 200 °C for 24 h, and the prepared ZnO nanorods were decorated with silver (Ag) nanoparticles to enhance their photocatalytic activity. The Ag nanoparticles were photochemically deposited on the ZnO rods with varying molar concentrations (from 0.5 to 10 mol%), and their various physicochemical properties were studied. The prepared material was characterised using different spectroscopic techniques. XRD revealed the formation of a highly crystalline hexagonal phase of ZnO. For a higher silver loading (>5 mol%), separate peaks corresponding to cubic silver were observed in the XRD pattern. The photoluminescence spectra of the Ag/ZnO nanostructures show two distinct peaks at 390 and 500 nm; interestingly, the PL intensity of the ZnO emission peak at 500 nm decreases with an increase in the silver concentration. The diffuse reflectance spectra of Ag/ZnO indicate absorbance at 380 nm due to ZnO and a slight hump at 440 nm that corresponds to silver nanoparticles. The FE-SEM and TEM analysis indicates the formation of a hexagonal rod-like morphology, with the lengths of the rods ranging from around 50 to 200 nm and a diameter of around 30 nm. TEM also confirms the presence of Ag nanoparticles with sizes in the range of 20 to 30 nm on the surface of the ZnO nanorods. The photocatalytic activity of the Ag/ZnO nanostructures was evaluated by following the degradation of methylene blue (MB) dye under a 400 W mercury vapour lamp. ZnO with 10 mol% Ag loading shows the highest photocatalytic activity as compared to the 0.5, 1 & 5 mol% Ag-ZnO catalysts. The observed apparent rate constant for the photocatalytic MB degradation using 10 mol% Ag-ZnO (Kapp = 6.01 × 10-2 min-1) was six times that of pure ZnO (Kapp = 1.09 × 10-2 min-1). A gradual increase in the photocatalytic activity of Ag/ZnO was observed with an increase in the silver concentration. The photocurrent response of the prepared Ag-ZnO nanostructures was examined by a photoconductivity study. Moreover, the photocatalytic performance of the sample was correlated with the photoconductivity of the samples. The photoconductivity of the samples was stable, and the photoconductivity of 10 mol% Ag-ZnO was almost 20 times that of pure ZnO, resulting in a higher photocatalytic activity.

Investigations on physiochemical and third-order nonlinear optical studies on quinolinium based organic crystal

Newly identified organic single crystals of 8-hydroyquinolinium 2-chloro 4-nitrobenzoate (HQ2ClNB) were grown by the slow evaporation solution growth technique (SEST) using methanol as a solvent. It crystallizes in monoclinic crystal system with a space group of P21/c. Crystalline nature and phases were confirmed by powder X-ray diffraction (XRD). The existence of various functional groups in the molecule was identified using the Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) technique. Optical transmission window and lower cut-off wavelength of the HQ2ClNB crystal have been evaluated by UV–Visible–NIR studies. Dielectric and photoconductivity studies were recorded. Third-order nonlinear optical susceptibility [Formula: see text] of the crystals were evaluated by [Formula: see text]-scan studies.

A new organic nonlinear optical material: L-asparagine cetrimonium bromide single crystal for photonic applications

Abstract The new organic nonlinear optical material, L-Asparagine Cetrimonium Bromide (LACB) was synthesized by using slow evaporation method at ambient conduction. The crystallographic data was analyzed by single crystal X-ray diffraction (XRD) and crystalline perfection was studied under high resolution powder X-ray diffraction technique. The functional groups were found out by FT-IR spectroscopy and various optical parameters were performed by using UV–Vis NIR spectroscopy. In fluorescence spectrum the sharp emission peak was observed at 529 nm it reveals the green emission. The second harmonic generation efficiency was determined by the Kurtz powder method using Nd-YAG laser. The laser induced damage threshold value was found to be higher than most of the reported organic single crystals. The dielectric permittivity and dielectric loss were analyzed as a function of frequency. The photoconductivity study implies that the grown crystal has positive photoconductive nature. Different mechanical properties were analyzed by Vickers microhardness test.

Enhanced photocatalytic activity of Fe3O4/SnO2 magnetic nanocomposite for the degradation of organic dye

Composite photocatalysts composed of semiconductor and magnetic matters are of great concern due to their excellent catalytic and recyclable performances. In this work, hydrothermal synthesis technique was employed to prepare magnetic Fe3O4/SnO2 nanocomposites (FS1, FS2, and FS3) of different molar ratios. The nanocomposites material was characterized by powder X-ray diffraction (XRD), high resolution scanning electron microscopy (HRSEM), energy-dispersive X-ray spectroscopy (EDS) and UV–vis diffuse reflectance spectroscopy (UV–vis DRS), Vibrating sample magnetometer (VSM) analysis. The SnO2 optical absorption was extended into visible region after coupling with Fe3O4. The magnetic features of Fe3O4/SnO2 nanocomposites offer simply separable method for reusability of the material in photocatalytic application. The catalytic activity of as prepared magnetically separable nanocomposites was inspected based on photodegradation of crystal violet as model organic pollutant. The extent of variation of field-dependent photo and dark current of the samples were determined from photoconductivity studies. The photoconductivity studies revealed the ohmic nature of the samples with a linear increase in both dark and photocurrent with a corresponding increase with increase in the applied field. The nanocomposite FS1 depicted good photocatalytic activity due to enlarged photoresponsive range and increase in charge separation rate. From the results, we suggest an attractive physical property and an efficient and a recyclable nanocomposite catalyst active under UV light irradiation for use in wastewater treatment to control water pollution.