Mrinmay Das

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.

Synthesis of rGO–Zn0.8Cd0.2S via in situ reduction of GO for the realization of a Schottky diode with low barrier height and highly enhanced photoresponsivity

A metal–semiconductor interface is an integral part of numerous electronic devices such as Schottky barrier diodes (SBDs). On the other hand, ever since graphene was isolated, there has been an impressive growth in the application of graphene to electronic devices. In this study, we present the synthesis of a reduced graphene oxide–zinc cadmium sulfide (rGO–Zn0.8Cd0.2S) composite via an in situ reduction of graphene oxide. Such a composite was applied to the fabrication of a Al/rGO–Zn0.8Cd0.2S SBD, and its performance was compared with the Al/Zn0.8Cd0.2S SBD. After current–voltage (I–V) measurements in the dark and under illumination, important diode parameters were obtained from the (I–V) characteristic curves. Due to the incorporation of graphene, the photoresponse of the Al/rGO–Zn0.8Cd0.2S SBD was enormously enhanced by 448% compared to its counterpart without rGO. Furthermore, the detectivity also increased significantly by 2 order of a magnitude. Moreover, a considerably lower barrier height of 0.16 eV was achieved with rGO–Zn0.8Cd0.2S compared to Zn0.8Cd0.2S (0.28 eV). The superior performance for the rGO–Zn0.8Cd0.2S-based SBD was analyzed and explained by the space charge limited current (SCLC) theory, which confirmed that the charge transfer kinetics improved vastly due to the incorporation of rGO. Notably, there was an exceptional 300% increase in the effective carrier mobility for rGO–Zn0.8Cd0.2S. The SCLC analysis of the charge transfer kinetics was also verified by photoluminescence and electrochemical impedance spectroscopy. These results demonstrated the beneficial impact of graphene on a Zn0.8Cd0.2S-based diode. Indeed, the rGO–Zn0.8Cd0.2S diode exhibited an impressive performance, with a considerably lower barrier height, highly enhanced photoresponsivity and detectivity. Overall, our extensive study reveals that rGO–Zn0.8Cd0.2S exhibits a great potential in the design of multifunctional optoelectronic devices.

Redox-active and semi-conducting donor–acceptor conjugated microporous polymers as metal-free ORR catalysts

Metal-free pristine conjugated microporous polymers (CMPs) catalyzing electrochemical oxygen reduction reaction (ORR) are still rare. We therefore put forward a design strategy to fabricate electrochemically active CMPs by linking donor nodes and acceptor spacers. The two new CMPs have been structurally well characterized and show semi-conduction and redox-activity. As a proof of concept, we show that both the CMPs have appreciable ORR activity and catalytic stability over time. Further, DFT calculations reveal the origin of the semi-conducting property and also the mode of oxygen binding to the catalytic centres. This work shows the potential application of pristine metal-free CMPs in energy conversion processes.

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.

Charge transport mechanism analysis of Al/CdS:Sr2+/ITO device under dark and light

In this study, we have synthesized CdS:Sr2+ by hydrothermal technique. Material property has been studied by X-ray diffraction (XRD), Scanning electron microscope (SEM) and UV-vis absorption spectroscopy. XRD data revealed that there are mixed phases of CdS and SrS in the synthesized sample. The optical band gap of the material was estimated as 3.15 eV from UV-vis data. The synthesized material has been applied in metal-semiconductor device and transport properties have been analyzed by measuring current–voltage characteristics under dark and light conditions at room temperature. Variation in different device parameters like ideality factor, barrier height and series resistance of Al/CdS:Sr2+/ITO device were analyzed by using Cheung’s function.