Arka Dey

Investigation of charge transport properties in less defective nanostructured ZnO based Schottky diode

In this report the synthesis of novel zinc oxide (ZnO) with a lower defect density and its effect on the Al/ZnO Schottky junction has been demonstrated. The defect density was estimated by positron annihilation lifetime measurement which ensures the materials superiority (i.e. free from point defects or any type of vacancies) over the earlier reported results. The thin film device of synthesized ZnO was fabricated on an ITO coated glass substrate. As the front contact was made by aluminium, the characteristic I–V produced rectifying Schottky behavior. The underlying charge transport mechanism through a metal–semiconductor (i.e. Al/ZnO) junction was analyzed on the basis of thermoionic emission theory to find out the quality of the fabricated device. In this regard we have studied the charge transport mechanism by measuring the density of states (DOS) at the Fermi level, mobility-lifetime product and diffusion length.

One step hydrothermal synthesis of a rGO–TiO2 nanocomposite and its application on a Schottky diode: improvement in device performance and transport properties

The presence of a Schottky barrier (SB) at a metal–semiconductor (MS) interface is of paramount importance to numerous application fields. In this report, we demonstrate the performance comparison of Schottky diodes fabricated with TiO2 and rGO–TiO2 nanocomposites, in contact with aluminium. From forward I–V characteristics, important diode parameters i.e. rectification ratio, ideality factor, series resistance and barrier height were obtained. A photoresponse comparison of the diodes has also been performed. It was found that the rGO–TiO2 based junction showed improved performance. The rectification ratio increased by ∼94% and the barrier height was lowered by ∼10%, under dark conditions. For better realization of the junction, here we provide insight into the carrier transport properties with the help of space charge limited current (SCLC) theory. After introducing graphene, the carrier mobility and carrier concentration increased by 64% and 21% respectively, while the diffusion length is found to be improved by 13.4%. These results illustrate that rGO incorporation has led to a much improved carrier transport and electron hole separation. Due to greater light absorption, the improvement in diode parameters and transport properties were even better when the device was subjected to irradiation.

Novel CuFeS2 pellet behaves like a portable signal transporting network: studies of immittance

A novel synthesis of CuFeS2 nanoparticles has been demonstrated here. This is the first time we have thoroughly investigated the frequency dependent dielectric behavior of iron-chalcopyrite (CuFeS2) pellets (with σd.c. = 47.27 × 10−9 S cm−1). The room temperature a.c. conductivity of the material has also been investigated in the frequency range 200 Hz–2 MHz. Frequency dependent impedance analysis of the material indicates the charging and discharging behavior of the capacitor. Throughout this report we have analyzed the frequency dependent complex impedance, electric modulus and the loss tangent of the CuFeS2 pallet as series and parallel combinations of capacitors and resistors.

Two isostructural linear coordination polymers: the size of the metal ion impacts the electrical conductivity

Two new one-dimensional coordination polymers (1D CPs) {[Zn(adc)(4-spy)2(H2O)2]}n (1), and {[Cd(adc)(4-spy)2(H2O)2]}n (2) (H2adc = acetylenedicarboxylic acid and 4-spy = 4-styrylpyridine), have been synthesized and well characterized. Single crystal X-ray diffraction data exhibit that compounds 1 and 2 are isostructural and undergo hydrogen bonding and C–H⋯π interactions to construct 3D supramolecular architectures. Electrical characterization reveals that both compounds show substantive electrical conductivity and exhibit Schottky diode nature. However, compound 2 has a higher mobility and higher conductivity compared to 1. The estimated values of effective carrier mobility, transit time, carrier concentration and diffusion length demonstrate that the charge transport properties have been improved for 2. Therefore, compound 2 has better performance in the fabrication of electronic devices.

Multifunctional mixed ligand metal organic frameworks: X-ray structure, adsorption, luminescence and electrical conductivity with theoretical correlation

Two new mixed ligand metal–organic frameworks of Zn(II) with disodium 5-hydroxyisophthalate and 4,4′-azobispyridine (azbpy) ligands, {[Zn(azbpy)(HO-1,3-bdc)(H2O)]·(azbpy)}n (1) and {[Zn(azbpy)0.5(HO-1,3-bdc)(C2H5OH)]·(H2O)}n (2) have been synthesized by changing the reaction medium (methanol to ethanol) and structurally characterized by elemental analysis, IR, PXRD, TG and single crystal X-ray diffraction. Compound 1 exhibits a 2D sheet network structure with free azbpy ligands in its void space, and is stabilized by π–π and C–H⋯π interactions, whereas 2 has a 2D layered architecture with lattice water molecules in its void space. Compound 2 has a flexible structure and shows gated adsorption (gas and solvent) behavior, while framework 1 is nonporous. These two MOFs exhibit remarkable electrical conductivity values at room temperature and their comparison is discussed carefully. Theoretical calculations suggest that both the compounds are p-type semiconductors and correlate the structure–property relationship. Schottky barrier diode electronic devices have been fabricated by using these two semiconductor materials with aluminium (Al) and indium tin oxide (ITO) in sandwich configuration, ITO/MOF-1 or 2/Al, and both the devices exhibit sound rectification behavior. The photoluminescent properties of both the compounds in the solid state are also investigated in detail.

Cu(II)-Based binuclear compound for the application of photosensitive electronic devices

In this study, an acetylenedicarboxylate based binuclear Cu(II) compound [Cu2(adc)(4-pic)6(H2O)4][ClO4]2 (1) (H2adc = acetylenedicarboxylic acid and 4-pic = 4-picolene) has been synthesized and well characterized using elemental analysis, infrared (IR) spectra, thermogravimetric analysis (TGA), powder X-ray diffraction (PXRD) patterns and single crystal X-ray diffraction (SCXRD) techniques. The binuclear compound undergoes hydrogen bonding interactions to form a 1D hydrogen bonded aggregate, which further undergoes extensive edge-to-face C–H⋯π interactions to form a 3D supramolecular motif. The current conductivity of compound 1 was recorded under dark and illuminated conditions. Interestingly, the measured I–V characteristics of the synthesized material in the dark and under the illumination of incident light exhibit a highly non-linear rectifying behavior signifying a Schottky diode nature. Furthermore, the enhancement of values of the electrical parameters after exposure to illumination of incident radiation indicates the light sensing behaviour of the material. Therefore, the material can be used as a promising candidate in photosensitive electronic devices.

Positron Annihilation Spectroscopic Investigation on the Origin of Temperature-Dependent Electrical Response in Methylammonium Lead Iodide Perovskite

Organic-inorganic hybrid perovskite has appeared as one of the leading materials for realizing solution-based high-performing optoelectronic devices. The charge transport properties in this class of material are quite intriguing and still need to be carefully investigated. The temperature-dependent electrical property of methylammonium lead iodide (CH3NH3PbI3) has been investigated by employing positron annihilation spectroscopy (PAS), which unambiguously reveals the gradual formation of open volume defects with the enhancement in temperature. The high-temperature ionic conductivity is due to the generation of both cationic (CH3NH3+) and anionic (I-) vacancies, possibly because of the elimination of methylammonium iodide (CH3NH3I) as identified from the coincidence Doppler broadening (CDB) of the positron annihilation spectroscopy. Further, the evolution of temperature-dependent defect density and corresponding electrical responses has been correlated with the structural phase transitions of CH3NH3PbI3. This is the first ever report of temperature-dependent PAS measurement on hybrid lead halide perovskites to understand the nature and the origin of its electrical characteristics arising due to the variation in temperature.

Application Possibility of Mn 0.04 Cu 0.05 Zn 0.91 O in Electronic and Magnetic Devices

In this literature, we have investigated the magnetic properties and Schottky device-based charge transport properties of hydrothermally derived Mn0.04Cu0.05Zn0.91O nanorod. The doping of 3-D transitional metals, Mn and Cu, within ZnO makes it potentially applicable in spin-based electronics, whereas its temperature-dependent conductivity (of the order of 10−3 in C.G.S.) makes it suitable for semiconductor-based devices. The observation of intrinsic ferromagnetism of the synthesized composite and its variation of magnetization with magnetic field and temperature exhibited the suitability of spin-based electronic application. To check the applicability in optoelectronic devices, metal–semiconductor (Al/Mn0.04Cu0.05Zn0.91O) junction was fabricated and analyzed. The current–voltage characteristic represented the rectifying behavior of the junction with on/off current ratio 4.3 at ±1 V in dark and potential barrier height 0.61 eV. The significant change in rectification due to the influence of incident radiation makes this material suitable for photosensing electronic device application.

Temperature dependent performance of Al/ZnCdS Schottky diode and charge transport analysis

Here we report the temperature dependent behaviour of Al/ZnCdS interface. In this regard, ZnCdS nanocomposite was synthesized by hydrothermal technique. Detailed study of schottky parameters including rectification ratio, ideality factor, series resistance and barrier height was performed. We explored the underlying charge transport phenomena through the Metal-semiconductor (MS) interface with the help of space charge limited current(SCLC) theory. A compartive analysis of carrier mobility and diffusion length was done.

Development of large area nanostructured silicon-hydrogen alloy material with improved stability for solar cell application by argon dilution method

Here we have presented the results of large area (30 × 30 cm2) silicon-hydrogen alloy material and solar cell by argon dilution method. As an alternative to hydrogen dilution, argon dilution method has been applied to develop single junction solar cell with appreciable stability. Optimization of deposition conditions revealed that 95% argon dilution gives a nanostructured material with improved transport property and less light induced degradation. The minority carrier diffusion length (Ld) and mobility-lifetime (μτ) product of the material with 95% argon dilution degrades least after light soaking. Also the density of states (DOS) below conduction level reveals that this material is less defective. Solar cell with this argon diluted material has been fabricated with all the layers deposited by argon dilution method. Finally we have compared the argon diluted solar cell results with the optimized hydrogen diluted solar cell. Light soaking study proves that it is possible to develop stable solar cell on large area by argon dilution method and that the degradation of argon diluted solar cell is less than that of hydrogen diluted one.