Space Charge Limited Current Theory Research Articles

Improvement of charge kinetics of MoS2 nano-petal based Schottky device by incorporation of W: A comparative study of structural, optical, and electrical properties

Molybdenum Tungsten Di-Sulphide is a semiconducting alloy of different TMD (transition metal dichalcogenide) materials that has enormous tunable structural, optical, and electrical attributes. In this research, we have performed the hydrothermal synthesization of Mo1-xWxS2 nanocomposites with different molar concentration of tungsten (i.e. x = 0, 0.1, 0.2, 0.3) and fabricated Al/Mo1-xWxS2/ITO structured Schottky Barrier diodes. Characterization of their structural, optical, and charge transport attributes are compared. In this alloy formation, the amount of W (tungsten) concentration has a great impact on the particle size of composites. The transportation of charges via the metal-semiconductor junction is the basis for the superiority of thin film semiconductor devices like the Schottky diode. The diode parameters as well as charge transfer characteristics were analyzed by Impedance Spectroscopy and the theory of SCLC (space charge limited current). The calculated mobility and transit time for the Mo0.8W0.2S2 device are 5.65 × 10−4 m2 V−1 s−1 and 1.59 ns respectively. These results are better than the rest of the devices. Dramatic conductivity enhancement for the Mo0.8W0.2S2-based Schottky device is observed. As a result, this work not only investigates Al/MoWS2 interface in detail but also explains the faster and better charge transport of the Mo0.8W0.2S2-based device from a structural perspective.

Charging and Discharging Current Characteristics of Polypropylene Film under Varied Electric Fields

Charging and discharging current behavior under high DC electric field in polypropylene (PP) film is closely related to the charge transport and accumulation process, which has an important effect on the electrical insulating properties of PP. In this paper, the dependence of the charging and discharging current of polypropylene films on time and electric field has been comprehensively studied. The results showed that the transient and steady current values of the charging and discharging process increase with the increase of electric field. Dependence of the charging current on the electric field conformed well to the space charge limited current (SCLC) theory with a transition electric field of 270 kV/mm, at which the charge transport changed from ohmic conduction to SCLC conduction. The carrier mobility derived from the discharging current became significantly smaller with increase of the charging electric field. The charge accumulation after discharging was derived from the integration of the difference of the charging and discharging current and it showed an increase with the electric field and increased sharply above a certain threshold electric field (the same as the transition electric field in SCLC theory). It was proved that the conduction current and charge accumulation evolution and dependence on the electric field were mainly determined by the balance between the electrode charge injection process and the bulk conduction process.

Investigation of electrical and photovoltaic properties of Au/n-Si Schottky diode with BOD-Z-EN interlayer

4,4-Difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) based BOD-Z-EN compound was used as an interfacial organic layer to fabrication of Au/BOD-Z-EN/n-Si/In diode. The electrical parameters of Au/BOD-Z-EN/n-Si/In diode such as ideality factor (n), barrier height (Φb) and series resistance (Rs) have been investigated through current–voltage (I–V) studies at dark and under various illumination intensities to understand the effect of interlayer on the device properties. The values found for the n varied from 2.33 to 1.55 and the Φb ranged from 0.86 to 0.90 eV as the illumination condition changed from dark to 100 mW/cm2. Series resistance (Rs) values calculated using Cheung’s method were found to decrease with increasing illumination level. The forward bias I–V characteristics of the diode were explained by the space charge limited current theory. The main photovoltaic parameters such as open circuit voltage (Voc), short circuit current density (Jsc) and fill factor (FF) were determined for various light intensity. The Au/BOD-Z-EN/n-Si/In diode exhibits a photovoltaic behavior with a Voc of 150 mV and Jsc of 10 µA/cm2 under 100 mw/cm2. In addition, photosensitivity and photoresponsivity properties of the diode were determined. All these results indicate that Au/BOD-Z-EN/n-Si/In device can be used as photosensor in optoelectronic applications.

The Simultaneous Evolution of Space Charge and Conduction Current in LDPE

The development of a system to measure simultaneously the current and space charge in a dielectric is described. The results obtained for low density polyethylene samples show that the relationship between space charge accumulation and the time-dependent current is not straightforward. In accord with previous work on space charge limited currents, the transient currents initially decreased, but after a while an increment or peak appeared. Additionally, the generation and extraction of space charge packets caused an impulse-like current peak such as previously observed. By comparing the electric field and current at the anode, it was found that the increment and the peak of the anode current are determined by injected negative carriers reaching the anode rather than the increase of electric field at the anode. It is shown that the dynamical evolution of the current can be divided into three stages similar to transient space charge limited current theory.

Improved device performance of rod like ZnO in a Schottky type photosensor compared to particle like ZnO: Analysis of charge transport

In this work, we report two different synthesis process of semiconducting ZnO which modifies the morphology of the ZnO materials and its impact in photosensing Schottky diode. Hydrothermal and co-precipitation method were used to synthesize ZnO which gave rise to rod like (ZnO HT) and particle like ZnO (ZnO COP), respectively. From UV–Vis analysis, ZnO HT exhibited greater optical absorption. Al/ZnO (HT and COP)/ITO Schottky diodes were fabricated and the photoresponse as well as diode parameters were investigated by current-voltage and capacitance voltage measurements. Then charge transport properties were determined by space charge limited current theory and impedance spectroscopy. The results showed that the ZnO HT based SBD delivered a responsivity of 0.144 A/W which is 121% higher than the responsivity showed by ZnO COP based SBD (0.065 A/W). The specific detectivity of ZnO HT was measured at 7.54 × 109 Jones, a noticeable improvement from the 4.10 × 109 Jones of ZnO COP. The carrier mobility, lifetime and diffusion length of the ZnO HT based device were found to be 0.0014 cm2 V−1s−1, 72.35 μs and 72.37 μm respectively which are again superior to its counterpart. The faster and better charge transport is facilitated by the rod like morphology of the former. The study demonstrates improved device performance of rod like ZnO based Schottky diode and provides detail analysis of the Al/ZnO interface which can be beneficial for future research on metal-semiconductor junction.

Investigation of conduction kinetics in Al/CuInSe2 Schottky device utilizing impedance spectroscopy (IS) measurement and study of its photosensing behaviour

Copper Indium Selenide (CuInSe2) has been synthesized by solvothermal synthesis method. The Schottky diode (SD) has been fabricated by using the material and the interface characteristics of Al/CuInSe2/ITO have been investigated with the help of ac impedance spectroscopy (IS) analysis (under dark condition) and dc current-voltage (I–V) measurements (under both dark and photo condition). IS is a very important and powerful technique to investigate and analyze the impedance at the boundary regions of SDs. Ac impedance spectra of Al/CuInSe2 SD have been recorded in the wide range of frequency from 40 Hz to 20 MHz during dc bias scanning from −0.5 V to 0.5 V under dark condition. From forward I–V characteristics, important parameters such as ideality factor (η), photosensitivity, barrier height (Φb), series resistance (RS) of SD were obtained under dark and photo condition. The photosensitivity of the Al/CuInSe2 SD was found to be 3.36. For better realization of charge transport phenomena through the MS junction, space charge limited current (SCLC) theory has been employed. The effective mobility of the carrier is evaluated in dark and photo condition as 0.42 × 10−3 m2V−1s−1 and 2.11 × 10−3 m2V−1s−1 respectively. It has been observed that the mobility is improved 5 times under illumination compared to the dark condition.

Improved charge transport properties of graphene incorporated tin oxide based Schottky diode over pure one

Graphene and its nanocomposites with different semiconductor materials have attracted significant research interest in the last decade due to their improved performance in various fields. In this report, SnO2 and a reduced graphene oxide (rGO)-SnO2 composite is synthesized via hydrothermal method. Structural, optical and electrical characterization of the material is performed. Incorporation of rGO increases the light absorption and reduces the band gap of SnO2. Schottky barrier formation at metal-semiconductor junction is important for various applications. Here, we describe the performance of SnO2 and rGO-SnO2 based Schottky diode. Important diode parameters like rectification ratio, ideality factor, barrier height and series resistances are calculated from forward Current density-voltage (J-V) characteristics. rGO-SnO2 shows much better performance compared to SnO2. Analysis of Photoresponse behavior reveals that rGO-SnO2 shows photosensitivity of about 9.95 which is higher than that of SnO2 (2.42). After incorporation of rGO, other diode parameters and transport properties were also improved. To gain better insight on charge transport properties, space charge limited current theory has been utilized. In rGO-SnO2, carrier mobility is increased by 62% compared to SnO2, implying that rGO-SnO2 has better charge transport due to enhanced electron hole separation which is attribute to the presence of graphene.

Electrical and photocatalytic properties of composites of manganese and titanium oxides

In this study, mesoporous manganese oxide-titanium dioxide (Mn2O3/TiO2) nanocomposites have been synthesized following sol-gel method. Different molar ratios of Mn/Ti were evaluated and MT2 (5:1) showed the best photoactivity as well as carrier transport properties. The Langmuir–Hinshelwood model was delineated to calculate the reaction rate which was found to be highest for MT2 (min-1). Several parameters including pore size distribution, pore volume, adsorption isotherms have been analyzed as per Brunauer–Emmett–Teller (BET) method. That was attributed to the high surface area (121.81 m2/g). The space charge limited current (SCLC) theory was employed to calculate the mobility and transit time. MT2 showed the highest carrier mobility (326×10–7 m2 V-1s-1) and lowest transit time (0.08×10–5 s) which are desirable for efficient photoactivity.

Modelling the photocatalytic behaviour of p-n nickel-titanium oxide nanocomposite

NiO-TiO2 (TN) nanocomposite is synthesized from an assembly of p-type nickel oxide (NiO) and n-type titanium oxide (TiO2) in an ultrasound assisted operation. Transmission electron microscopy (TEM) demonstrates the existence of hexagonal particles in the nanocomposite. Dynamic light scattering (DLS) measurements show stable TN nanoparticles (NPs) at a negative zeta potential (−18.5 ± 0.8 mV). The nanocomposite is tested for its catalytic activity towards degrading malachite green (MG), a known water toxicant and methylene blue (MB) under ultraviolet (UV) irradiation. Response surface methodology (RSM) is employed to optimise the influence of significant variables such as initial dye concentration, catalyst dose and time. Their mutual interactions are mapped by response surface and contour plots and correlated with degradation process by a designed model. The best photocatalytic efficiency (87%) is observed at an optimised concentration of 5 ppm dye with 10 ppm catalyst. The presence of inorganic ions and organic matter hardly affected the aggregate size of TN but caused a decline in photoactivity. The catalyst is found effective even in real water system (Hooghly River). A (Fluorine doped tin oxide) FTO/TN/Al heterojunction is fabricated. TN showed enhanced carrier mobility (1.03.10−4 m2V-1s-1) and low transit time (1.76.10-6 s) evaluated using space charge limited current (SCLC) theory. The nanocomposite appears suitable for energy preservation and environmental applications.

Sonochemical synthesis of nanospherical TiO2 within graphene oxide nanosheets and its application as a photocatalyst and a Schottky diode

The hybrid of graphene oxide (GO) nanosheets with well embedded nanospherical TiO2 was prepared through mechanical mixing using ultrasound. This modified TiO2-GO (TGO) composite exhibits reduced recombination of charge carriers. Benefiting from unique morphology and surface area (92 m2g−1), the TGO composite showed remarkable catalytic activity for the photodegradation of congo red (CR) and methyl orange (MO). The rate constant values were 0.0652 min−1 (pseudo first order) for CR (5 ppm) and 0.0631 min−1 for MO (5 ppm). The stability and aggregation behavior of TGO was examined using the dynamic light scattering (DLS) technique. The key parameter affecting photocatalytic performance is electron-hole separation. To illustrate this issue, a Schottky diode has been fabricated with TGO composite, in contact with aluminium. Important diode parameters i.e. ideality factor, series resistance, barrier height have been estimated from forward current-voltage (I-V) characteristics. Space charge limited current (SCLC) theory was employed to provide insight into the carrier transport properties of TGO and enhanced carrier mobility (2.11.10−6 m2V−1s−1) and low transit time (0.237.10−6 s) under illumination was obtained. The composite appears suitable for energy and photocatalytic applications.

Optimization of electrical and photovoltaic properties of Au-BiFeO<sub>3</sub> nanocomposite films

Ferroelectric films, are an important class of photoelectric functional material, which possess the following characteristics: the breaking of their symmetry can lead to self-polarization and this polarization state can be regulated by external stimuli. The photovoltaic properties of ferroelectric films have been extensively investigated due to their potential applications in the field of photodetection, energy conversion harvesting and nonvolatile storage. In view of the small photocurrent density and the degradation of photovoltaic property caused by the depolarization effect in ferroelectric films, it is necessary to explore an approach to improving the self-polarization phenomenon and regulating the conduction mechanism to further optimize their photovoltaic properties. Here in this work, BiFeO<sub>3</sub> (BFO) films dispersed with Au nanoparticles are deposited on FTO glass substrates by the sol-gel method to obtain the Au-BFO nanocomposite films. Moreover, the relationships between Au content (0 mol%, 0.25 mol%, 0.5 mol%, 1 mol% and 3 mol%) and microstructure, electrical and photovoltaic properties of Au-BFO nanocomposite films are investigated to determine the optimal Au content. Piezoresponse force microscopy studies show that the Au-BFO nanocomposite film with 0.5 mol% Au has the strong self-polarization phenomenon. With the increase of Au content, the conduction mechanism of the Au-BFO nanocomposite films is described by the space-charge limited current theory but not the Schottky emission model any more. The photovoltaic properties of the Au-BFO nanocomposite films first increase and then decrease. When Au content is 0.5 mol%, the Au-BFO nanocomposite film has the best photovoltaic property. The open-circuit voltage and short-circuit photocurrent density of the Au-BFO nanocomposite film with 0.5 mol% Au increase nearly 3 and 5 times counterparts of the BFO film, respectively. The photovoltaic effects of Au-BFO nanocomposite films are improved mainly by regulating the self-polarization phenomenon and conduction mechanism. This study demonstrates the merits of BFO films dispersed with Au nanoparticles, specifically, the photovoltaic properties of Au-BFO nanocomposite films are further optimized. In this work, we propose a simple and effective method to regulate the electrical and photovoltaic properties of ferroelectric films, which provides a new perspective for further understanding the photovoltaic effects of ferroelectric films.

Improvement of memristive properties in CuO films with a seed Cu layer

We have prepared CuO-based structures including Au/CuO/Pt and Au/CuO/Cu/Pt films and studied the memristive characteristics of the two samples. Current-voltage curves of the samples suggest that both CuO-based films are typical memristive devices, showing conventional pinched hysteresis loops. Furthermore, the presented Au/CuO/Cu/Pt structure with a seed Cu layer between CuO and bottom electrodes Pt demonstrates more typical memristive and better retention characteristics than Au/CuO/Pt. In order to explore the conducting mechanism for improved memristive properties, the electric transport characteristics of the device are analyzed using a space charge limited current and charge trap defect theory.

The carrier transport properties and photodegradation ability of low temperature synthesized phase pure rutile titanium oxide nanostructured materials

Abstract In this study, we report synthesis of pure rutile phase titanium oxide (TiO2) nanoparticles (NPs) at a considerably low temperature with particle size ca. 20 nm (from TEM). The sample showed mesoporous nature as per Brunauer- Emmett- Teller (BET) method with a surface area of 211.7 m2 g−1and band gap 2.94 eV stretching into the visible portion of the electromagnetic spectrum. Two Indium tin oxide (ITO)/TiO2 (rutile and commercial)/Aluminium (Al) based heterojunctions were fabricated and carrier transport properties evaluated with the help of space charge limited current (SCLC) theory. The values of mobility and transit time for rutile were 7.44 × 10−7 m2V−1s−1and 9.52 × 10−5 s respectively and were found to be enhanced on illumination in comparison to commercial TiO2. Rutile exhibited a higher photosensitivity of 5.48 which predict photo-switching nano device applicability. Impedance analysis showed stable and enhanced photocurrent response. The degradation ability of rutile for malachite green oxalate (MG), a hazardous dye, was also checked and found to be 97.54% in 3 h being comparable to commercial TiO2 when irradiated with a definite dose of ultraviolet (Uv) radiation (1.035 × 10−15 Jsm2). The Langmuir- Hinshelwood model was delineated to calculate the reaction rate which was higher for rutile (0.0183 min−1). Lower electron hole pair (EHP) recombination was proved for rutile by photoluminescence (PL) measurements.

Memory capacitance behavior at single resistance state in memristor and multi-state characteristic

With the advent of the information age, big data put forward higher requirements for capacity of storage devices. Compared with the method of reducing the size of the device to enhance the integration level, the high density storage of increasing the memory state of the single device will be very beneficial to solving the problem. In this work, we propose an idea of two-parameter and multi-state memory device involved in both resistance and capacitance operation levels. At first, a new donor-acceptor (D-A)-type copolymer is designed and synthesized. Then, the memory device of Al/copolymer/ITO structure is fabricated, and the current-voltage (<i>I-V</i>) and capacitance-voltage (<i>C-V</i>) curves are measured by a KEITHLEY 4200 semiconductor characterization system. The device not only displays the obvious memory resistance characteristics, but also has the memory capacitance behavior in single resistance state, which results in two resistance states and four capacitance states, so that the device has the capability of two-parameter and multi-state memory. In addition, the device shows more capacitance states after the switching behavior has been modulated by the voltage amplitude, which provides an effective method to control the memory states. In order to study the conductive mechanism of the device, we test the relationship between resistance and temperature. It is found that the resistance decreases with the increase of temperature, indicating that the device has the obvious semiconductor properties. Furthermore, the fitting results of <i>I-V</i> data show that the mechanism of resistance switching is in good consistence with the classical trap-controlled space charge limited current theory. The capacitance switching in single resistance state is closely related to the polarization characteristic of D-A structure in the copolymer film. The polarization force microscopy phase image shows that the copolymer film has obvious polarization and depolarization characteristics under the external electric field. Based on the polarization characteristics of copolymer, the correlation between memory resistance and memory capacitance is established by introducing a polarization operator of molecules, and the matrix model describing the two-parameter and multi-state memory characteristics is given. The above results show that the multi-state memory characteristics will store more information than 2-bits mode in a single cell, which will provide a reference for improving the storage density of information.

Enhanced charge transport properties of rGO-TiO2 based Schottky diode by tuning graphene content

Here we report the fabrication of Al/rGO-TiO2 Schottky barrier diodes (SBD) and the effect of graphene content on charge transport properties. The SBDs showed better performance after graphene incorporation and the best result was obtained for 5% rGO. We employed space charge limited current (SCLC) theory to estimate the carrier mobility, carrier concentration and diffusion length. For 5% rGO, we achieved a carrier mobility of 0.065 cm2V-1s-1, which is almost a 15 fold increase on pure TiO2 and the diffusion length improved by 35%. The study demonstrates improved charge transport by tuning rGO content, which can be beneficial for device applications.

Supramolecular Assembly of a Zn(II)-Based 1D Coordination Polymer through Hydrogen Bonding and π···π Interactions: Crystal Structure and Device Applications.

A new mixed-ligand divalent one-dimensional coordination polymer (1D CP) [Zn(adc)(4-nvp)2(H2O)2]n, (1) [H2adc = acetylenedicarboxylic acid and 4-nvp = 4-(1-naphthylvinyl)pyridine] has been synthesized and well characterized by elemental analysis, infrared spectrum, single-crystal X-ray crystallography, powder X-ray diffraction pattern, and thermogravimetric analysis. The compound 1 constructs a 3D supramolecular network by the combination of hydrogen bonding, C–H···π, and π···π interactions. Interestingly, the material shows Schottky behavior which is exclusively analyzed with the help of thermionic emission and space charge-limited current theory. In addition, the Schottky barrier diode parameters for compound 1 demonstrate better device performance after light soaking. Hence, the compound has applicability in the fabrication of optoelectronic devices.

Performance analysis of Fe-doped calcium copper titanate quadruple perovskite in optoelectronic device

We report here the synthesis of nanosized (50–55 nm) Fe-doped calcium copper titanate CaCu2.5Ti3.5FeO12 quadruple perovskite semiconductor by a two-step synthetic protocol involving citrate combustion for precursor synthesis followed by its calcination at different temperatures for the synthesis of the target materials. Materials were applied in thin film metal-semiconductor (MS) junction based Schottky Barrier Diodes (SBDs). The non-linear current-voltage characteristics indicate successful application of the materials in optoelectronic device. The device performance of the fabricated SBDs are analyzed by employing the thermionic emission (TE) theory and the space charge limited current (SCLC) theory followed by a schematic band structure.

Analysis of interfaces in Bornite (Cu5FeS4) fabricated Schottky diode using impedance spectroscopy method and its photosensitive behavior

In this report, we have synthesized Bornite (Cu5FeS4) material by hydrothermal synthesis technique. The interface characteristics of Al/Cu5FeS4/FTO Schottky barrier diode (SBD) are investigated by using ac impedance spectroscopy (IS) analysis (under dark condition) and dc current-voltage (I–V) measurements (under dark and light both condition). IS is a powerful tool to identify the interface regions of SBDs. Ac impedance spectra of Al/Cu5FeS4 SBD are recorded in the frequency range 40 Hz-20 MHz during dc bias scanning from -0.6 V to 0.6 V under dark condition. The diode parameter including ideality factor and barrier height is calculated from the conventional I–V measurement based on thermionic emission (TE) theory. Space charge limited current (SCLC) theory has been employed to further exemplify the improved performance of Cu5FeS4 based SBD, which points out that the carrier mobility is enhanced ∼2-fold after irradiation of light.

Asymmetric resistive switching behaviour in a Au/a-C:Co/Au planar structure

Using a simple fields induced mass motion method, Au/a-C:Co/Au planar structures with micro-gap Au electrodes were fabricated. Asymmetric current-voltage characteristics and resistive switching behaviours were observed in these cells. Reliable performance, with a reasonable ON/OFF ratio of >4, stable endurance of >200 cycles, and good retention of >105 s, were achieved at the read voltage of −3.6 V. Space charge limited current (SCLC) theory with an asymmetric potential barrier caused by different densities of traps was proposed to explain the asymmetric resistive switching behaviour.

Effects of interface modification on electrical and optoelectronic properties of p-type CuAlO2/n-type Si heterojunction devices

The effect of interface modification on the electrical properties of heterojunction diodes based on the p-type CuAlO2 and n-type Si is investigated. Compared with the CuAlO2/Si device without H2O2 treatment, the CuAlO2/Si device with H2O2 treatment exhibits a better rectification behavior. The forward-bias current–voltage characteristics can be explained on the basis of the space charge limited current theory for CuAlO2/Si device without H2O2 treatment. However, the thermionic emission model is the dominant process in this fabricated CuAlO2/Si device with H2O2 treatment. The enhanced device performance is mainly the result of the formation of Si–O bonds that serves to reduce the number of interface states. The effect of H2O2 treatment on the sensitivity to solar irradiation and the response time for CuAlO2/Si devices is also studied. An increase in the values of photocurrent and photosensitivity is attributed to the rectification performance improvement that results from interface passivation.