Temperature Dependence Of Capacitance Research Articles

Understanding the trap-induced frequency dispersion in the C–V curve of AlGaN/GaN hetero-structure

This article investigates the trapping mechanism in AlGaN/GaN heterostructure. For our study, the traps within the AlGaN layer are introduced at the interface and near the interface of AlGaN/GaN, in the SILVACO TCAD tool. Frequency-dependent capacitance-Voltage (CVF) curves are obtained to study the impact of traps on device performance. From the CVF curve, it is found that the existence of interface traps introduces a shift in capacitance along the gate voltage axis. These traps introduce the threshold voltage ( VTH ) shift. Furthermore, a detailed study of near-interface traps (NITs) is done based on tunneling mechanisms. For our investigation, the NITs are positioned at 0.5 nm, 1 nm, and 1.5 nm away from the AlGaN/GaN interface. The response of the NITs reduces the capacitance value in the accumulation region. The response of the NITs is explained through the capacitance charge model and border trap model. For NITs placed 0.5 nm away from the interface, the frequency dispersion in the accumulation region becomes evident. On the contrary, the dispersion reduces significantly, as the NITs goes deeper upto 1.5 nm. The results indicate that the NITs nearer to the interface respond to high frequencies. Further, the temperature dependent capacitance–voltage analysis is done for both interface and NITs, to understand the effect of temperature on frequency dispersion.

Characterization of a Heterojunction Silicon Solar Cell by Means of Impedance Spectroscopy.

Impedance spectroscopy provides relevant knowledge on the recombination and extraction of photogenerated charge carriers in various types of photovoltaic devices. In particular, this method is of great benefit to the study of crystalline silicon (c-Si)-based solar cells, a market-dominating commercial technology, for example, in terms of the comparison of various types of c-Si devices. This study investigates the dark and light electrophysical characteristics of a heterojunction silicon solar cell fabricated using plasma-enhanced chemical vapor deposition. The measurements are performed at various applied biases, enabling the determination of complex resistance, characteristic time, capacitive response and impurity concentration within the semiconductor junction and to correlate them with the device performance. In addition, the impedance spectra of the studied cell were investigated as a function of temperature. Studies of the frequency and temperature dependences of capacitance do not reveal a significant presence of thermally activated centers of free carrier capture, concomitant with a very small value of the activation energy extracted from an Arrhenius-type analysis. This leads to a conclusion that these centers are likely not impactful on the device operation and efficiency.

Temperature-dependent differential capacitance of an ionic liquid-graphene-based supercapacitor.

One of the critical factors affecting the performance of supercapacitors is thermal management. The design of supercapacitors that operate across a broad temperature range and at high charge/discharge rates necessitates understanding the correlation of the molecular characteristics of the device (such as interfacial structure and inter-ionic and ion-electrode interactions) with its macroscopic properties. In this study, we use molecular dynamics (MD) simulations to investigate the influence of Joule heating on the structure and dynamics of the ionic liquid (IL)/graphite-based supercapacitors. The temperature-dependent electrical double layer (EDL) and differential capacitance-potential (CD-V) curves of two different ([Bmim][BF4] and [Bmim][PF6]) IL-graphene pairs were studied under various thermal gradients. For the [Bmim][BF4] system, the differential capacitance curves transition from 'U' to bell shape under an applied thermal gradient (∇T) in the range from 3.3 K nm-1 to 16.7 K nm-1. Whereas in [Bmim][PF6], we find a positive dependence of differential capacitance with ∇T with a U-shaped CD-V curve. We examine changes in the EDL structure and screening potential (ϕ(z)) as a function of ∇T and correlate them with the trends observed in the CD-V curve. The identified correlation between the interfacial charge density and differential capacitance with thermal gradient would be helpful for the molecular design of the IL-electrode interface in supercapacitors or other chemical engineering applications.

Temperature-driven enhancement in pseudocapacitive charge storage of Sn-doped WO3 nanoflowers and its high-performance quasi-solid-state asymmetric supercapacitor

The substitution of another metal cations in the WO3 matrix enhances their electrochemical performance due to the synergistic effect. In this report, Sn-doped WO3 nanoflowers are synthesized via a facile single-step hydrothermal method. Further, the temperature-dependent pseudocapacitive behavior of Sn-doped WO3 nanoflowers is investigated for quasi-solid state asymmetric supercapacitors (QSSAC). The electrochemical study reveals that the specific capacitance values of WO3 increase from 72 F g−1 to 138 F g−1 (Sn-doped WO3) at 1 A g−1. The temperature-dependent specific capacitance values of Sn-doped WO3 nanoflowers demonstrating six times enhancement with rising temperature, from 109 F g−1, 139 F g−1, 194 F g−1, 301 F g−1, to 603 F g−1 at 10 °C, 20 °C, 30 °C, 40 °C, to 50 °C respectively. Furthermore, the QSSAC exhibits better stability of 97.51 % up to 2500th cycles with an energy density of 8 W h kg−1 and a power density of 6400 W kg−1, attributed to enhanced conductivity, large diffusion capability, and high strength with multiple redox active sites. The experimental results emphasize the promising electrochemical features of the Sn-doped WO3 matrix, which is an effective approach for electrode materials development.

Temperature and frequency dependent dielectric capacitance and polarization performances of low dimensional perovskite based manganese stannate

Manganese stannate perovskite nanoparticles were synthesized by applying a complexation mediated approach. Rietveld refinement of the XRD data exhibited orthorhombic structure with space group of Pnma. The structure included eightfold coordinated Mn2+ cation, surrounded by eight O2− anions and formed MnO8 polyhedra unit. Each polyhedra unit interconnected through the corner-sharing SnO6 octahedra with the formation of a cage-like network. The temperature and frequency dependent dielectric performances of manganese stannate were measured in the form of a device, which exhibited maximum dielectric constant value ~ 3445. The high dielectric constant value was originated due to the contribution of space charge polarization and orientation polarization of dipoles within the measured frequency ranges. Temperature and frequency dependent AC-conduction mechanism of the manganese stannate-based device involved both overlapping large polarons and non-overlapping small polarons. Electric field-dependent of polarization hysteresis loop of the device exhibited the maximum polarization value 1.5 µC/cm2 under the electric field of 3 kV/mm. Under the applied field of 2 kV/mm, the device exhibited a fatigue-free polarization with a maximum value of 0.92 µC/cm2, sustained for 103 cycles under ambient temperature condition.

Temperature dependence of capacitance–voltage characteristics of germanium telluride thin films

Temperature-dependent capacitance–voltage and conductance–voltage measurements of 200-nm-thick germanium telluride (GeTe) thin films deposited via direct current magnetron sputtering were investigated. Measurements were performed across a temperature range of 27–357 °C, with a sweep of voltage values from −20 to +20 V at an operating frequency of 1 MHz. An amorphous–crystalline transition temperature (Tc) of 197 °C was found. Below Tc, the GeTe films were highly resistive, and their capacitance was insensitive to the applied bias voltage and temperature. Above Tc, the capacitance showed strong dependence on temperature, owing to the triggering of GeTe crystallization incorporating nucleation and growth processes. Applied bias voltage did not show a profound impact on the GeTe capacitance even after crystallization, but it had an observable impact on the film conductance beyond 250 °C. Moreover, the GeTe thin film capacitance increased by a factor of 13 upon crystallization. Hall-effect measurements revealed that the film conductivity increased upon crystallization, as did the hole concentration and mobility. Cross-sectional transmission electron microscopy demonstrated that the GeTe thin films crystallize via a nucleation-dominated crystallization mechanism.

Synthesis of nickel nanoparticles-deposited strontium titanate nanocubes (Ni-STO) and heterojunction electrical applications over a wide temperature range

In the present study, the structural properties of nickel nanoparticles-deposited strontium titanate nanocubes (Ni-STO) were examined by taking XRD, ICP-MS, TEM and SEM images. Temperature-dependent capacitance–voltage (C-V) and current–voltage (I-V) measurements were made for the electrical characterization of the Ni/Ni-STO/n-Si heterojunction devices produced. As the temperature increases from 80 K to 400 K, the ideality factor (n) decreases from 2.30 to 1.02 while barrier height (BH) increases from 0.27 eV to 0.80 eV. In the heterojunction device between Ni-STO and n-type Si, electrons can be captured at the Schottky barrier interface and recombinations can be reduced. Devices produced with Ni-STO material had a positive effect on performance compared to the devices produced with STO in previous studies. The electrical parameters obtained give compatible results as a function of temperature. Metal deposited STOs are potential candidates for temperature-dependent sensors and electrical devices.

Analysis of grain orientation and defects in Sb2Se3 solar cells fabricated by close-spaced sublimation

The performance of a superstrate TiO2/Sb2Se3 solar cell, fabricated by close-spaced sublimation technique (CSS), was improved after the deployment of a seed layer. The seed layer caused columnar Sb2Se3 film growth with texture coefficient analysis (TC) showing increased presence of crystal planes, which are inclined towards the [001] crystal direction. Given the highly anisotropic properties of Sb2Se3, preferential growth of (Sb4Se6)n ribbons along the [001] direction is best suited for effective charge collection. Hence, grain orientation of Sb2Se3 films was studied more closely via measurement of pole figures by XRD and orientation distribution maps by electron backscatter diffraction (EBSD). Although the measurements did not reveal strong preferred orientation, it was observed that the columnar Sb2Se3 growth enhanced texture along the [001] direction. Temperature-dependent admittance spectroscopy (TAS) and capacitance–voltage (CV) profiling were performed on the seed-assisted TiO2/Sb2Se3 solar cell to evaluate carrier density and deep defects in the Sb2Se3 absorber. TAS study revealed a deep defect with activation energy of 0.39 eV. CV profiles indicated that the density of defects could be as high as 1017 cm−3, which needs to be addressed by post-deposition treatments.

Mechanistic origin and unlocking of negative capacitance in perovskites solar cells

SummaryWe have unlocked the mechanistic behavior of negative capacitance in perovskite solar cells (PSCs) by analyzing impedance spectra at variable photovoltage and applied bias, temperature-dependent capacitance versus frequency (C-f) spectra, and current-voltage (J-V) characteristics. We noted that p-i-n type PSCs having PEDOT:PSS or PTAA as hole transport layer display negative capacitance feature at low and intermediate frequencies. The activation energies (Ea) for the observance of negative capacitance were found to be in a similar order of magnitude required for the ionic migration. Moreover, the kinetic relaxation time (τkin) estimated to be in the same order of magnitude required to activate the halide ion migration. Our investigation suggests that the primary reason for the appearance of negative capacitance in PSCs with a p-i-n configuration is associated with the migration of halide ions and vacancies in the perovskite layers.

Electro-Optical Properties of Sputtered Calcium Lead Titanate Thin Films for Pyroelectric Detection.

We report the deposition and characterization of calcium lead titanate (PCT) thin films for pyroelectric detectors. PCT films of thicknesses ranging from ~250 to 400 nm were deposited on both silicon and Si/SiN/Ti/Au substrates at 13 mTorr pressure by 200W radio frequency sputtering in an Ar + O2 environment. Substrates were kept at variable temperatures during the deposition. The PCT films were annealed at various temperatures in an O2 environment for 15 min. X-ray diffraction results confirm the polycrystalline nature of these films. Energy dispersive spectroscopy function of scanning electron microscope showed that the films are stoichiometric (Ca0.43Pb0.57) TiO3 (Ca/Ti = 0.5, Pb/Ti = 0.66). Temperature dependence of capacitance, pyroelectric current, and pyroelectric coefficient was investigated for different PCT films. Our results show that films deposited at 550 °C and 600 °C demonstrate better quality and larger values of the pyroelectric coefficient. On the other hand, the capacitance fabricated on the PCT films at 550 °C showed the highest value of pyroelectric current and pyroelectric coefficient which were 14 pA and at 30 °C was ~2 µC/m2K respectively at a higher temperature. In addition, we used density functional theory to determine the atomic and band structure, real and imaginary parts of dielectric constant and refractive index, and absorption and reflection constants with energy.

On the studies of capacitance–voltage and impedance spectroscopy of an Ni/(GO-Fe3O4)/n-Si heterojunction device over a wide temperature range

The purpose of this work is to fabricate a Ni/GO-Fe3O4/n-Si heterojunction device using Mott-Schottky plots and to study the capacitance–voltage/conductance/series resistance characteristics of the device as a function of temperature. We analyzed temperature dependent capacitance–voltage measurements for the Ni/GO-Fe3O4/n-Si device in the temperature range from 80 to 360 K. Temperature dependent electrical measurements have been performed at a fixed frequency of 500 kHz and frequency dependent ones have been carried out at room temperature. In the reverse bias capacitance–voltage characteristics figure, it has been determined that the barrier height is 1.73 eV (80 K) and 1.50 eV (360 K) with 20 K steps. The impedance analysis measurements have been performed in the reverse and forward biases. The experimental results have shown that the values of capacitance, conductance, interface states and series resistance Rs depend on both bias voltage and temperature.

A COMPREHENSIVE DETERMINING OF CAPACITANCE -VOLTAGE PARAMETERS OF ELECTRONIC DEVICES WITH METAL AND p-Si JUNCTION

Al-p-Si-Al structures were fabricated and temperature dependent capacitance versus voltage measurements were performed in this study. The Al contacts were grown by the sputtering method and then capacitance-voltage characteristics of the devices were performed with forward and reverse biases. According to this measurements, the C-2 –V plots were conducted. With the help of those calculation, the barrier height vs temperature (ΦCV – T), the carrier concentration vs temperature (NA – T) and the depletion width vs temperature (w – T) graphs were plotted. In conclusion, it has been seen that the ΦCV and w decreased, and NA almost remained constant with increasing temperature.

Improvement in Sensing Characteristics of Silicon Microstructure based MEMS Capacitive Sensor for Automotive Applications

Capacitive pressure sensors have become a reasonable choice due to their low power consumption, energy efficiency, and robustness. In this paper, a thorough investigation of MEMS based capacitive pressure sensor with square diaphragm has been carried out. A comparative study of the diaphragm displacement and capacitance as a function of external pressure and temperature has been done by using various diaphragm materials such as Si, Poly Si, Si3N4 and 3C-SiC. The performance analysis of the device was envisaged with and without packaging stress by measuring various parameters. The simulation results are emphasized on the change in capacitance at different die bonding temperatures. Temperature dependence of capacitance at varying ambient pressure has also been realized. The present work will facilitate researchers for choosing a selective material for automotive applications.

Temperature dependence of differential capacitance in the electric double layer.Symmetric valency 1:1 electrolytes.

The differential capacitance of an electric double layer formed by an aqueous solution of KNO3 on a glassy carbon electrode is measured by impedance analysis at constant frequency. Results are obtained at electrolyte concentrations of 0.1 mol/dm3, 0.5 mol/dm3, and 1.0 mol/dm3, and at a series of temperatures, viz., 288 K, 298 K, 308 K, 318 K, and 328 K. The differential capacitance envelopes reveal a rich, complex pattern of maxima, minima, and local minima, whose magnitude and position change with a change in solution concentration. At the two lower concentrations, the temperature dependence of the capacitance, for example, at zero electrode potential, shows an alternating positive-negative behavior, while at the highest concentration of 1.0 mol/dm3, the slope of the differential capacitance-electrode potential curve is always positive. The experimental results are supplemented by a numerical grand canonical Monte Carlo simulation study of a restricted primitive model double layer but with an off-center cationic charge achieved by displacing the charge center from the ion sphere center toward its surface. The simulations, performed at the electrolyte concentration of 1.0 mol/dm3 and constant cation charge center displacement, and at varying electrode potentials and temperatures, show, in general, a negative temperature dependence of the differential capacitance. However, this temperature dependence can also be positive for a negative electrode charge and for a sufficiently large gradient of the cation charge center displacement with temperature. This feature is seen to be associated with an increase in the entropy of formation of the double layer.

Capacitance Properties in Ba0.3Sr0.7Zr0.18Ti0.82O3 Thin Films on Silicon Substrate for Thin Film Capacitor Applications

Crystalline Ba0.3Sr0.7Zr0.18Ti0.82O3 (BSZT) thin film was grown on Pt(111)/Ti/SiO2/Si substrate using radio frequency (RF) magnetron sputtering. Based on our best knowledge, there are few reports in the literature to prepare the perovskite BSZT thin films, especially using the RF magnetron sputtering method. The microstructure of the thin films was characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM), and capacitance properties, such as capacitance density, leakage behavior, and the temperature dependence of capacitance were investigated experimentally. The prepared perovskite BSZT film showed a low leakage current density of 7.65 × 10−7 A/cm2 at 60 V, and large breakdown strength of 4 MV/cm. In addition, the prepared BSZT thin film capacitor not only exhibits an almost linear and acceptable change (ΔC/C ~13.6%) of capacitance from room temperature to 180 °C but also a large capacitance density of 1.7 nF/mm2 at 100 kHz, which show great potential for coupling and decoupling applications.

Electrical characteristics of atomic layer deposited Au/Ti/HfO2/n-GaAs MIS diodes in the wide temperature range

Au/Ti/HfO2/n-GaAs MIS (metal/insulating layer/semiconductor) diodes were fabricated by atomic layer deposition technique and their electrical properties were investigated in detail by the help of current–voltage (I–V) and admittance measurements in the temperature range of 60–320 K. Together with the surface morphology analysis on the HfO2 thin-film layer, main electrical parameters such as series resistance (Rs), zero bias barrier height (ΦBo), ideality factor (n), impedance (Z) and phase angle were determined and effects of temperature on these parameters of the MIS diodes were discussed. The evaluation of I–V data exhibits a decrease in Rs and ΦBo, however an increase in n, with a decrease in temperature. Temperature-dependent conductance (G) and capacitance (C) characteristics of the MIS diode were investigated at 1000 kHz in the voltage interval in between − 3 and 2 V. G and C values were found in a direct relation with the change in temperature. On the other hand, Z values showed an inverse proportionality with temperature. The phase angle versus voltage plots were evaluated at different temperatures (60–320 K) at 1000 kHz and the obtained results indicated that the device behaves more capacitive in the voltage range of − 3 V and about 0.4 V for all temperature, and phase angle decreases with increasing temperature from 0.4 to 1.6 V. In addition, the interface state density (Dit), the effective oxide charge density (Qeff) and effective number of charges per unit area (Neff) of the fabricated diodes were investigated over temperature range 60–320 K in which these values were found in a decreasing trend with increasing temperature.

Dielectric relaxation and magnetodielectric response of mesoporous terbium manganate nanopaticles

We report here the investigation on dielectric response, charge transport mechanism and magnetocapacitance of mesoporous perovskite Terbium Manganate (TMO) nanoparticles. TMO NPs possess relatively high specific surface area (20.9 m2 g−1) than that of general perovskite-type metal oxides. To study the dielectric/magnetodielectric response in TMO material, a capacitive system is fabricated. Impedence spectroscopy shows electrically heterogeneous nature of the material. Due to the existence of inhomogeneity at electrode-TMO interface, ideality factor is larger than unity. Various Schottky diode electrical parameters are obtained here from temperature dependent capacitance–voltage (C–V) measurements. The function of Au/TMO/Au Schottky diode system is well explained from current–voltage (I–V) characteristics study. Ferroelectric-like hysteretic behaviour is observed at and above room temperature from non-ferroelectric TMO. Presence of defect states at TMO interface layer dominates the charge conduction phenomenon. Negative magnetodielectric effect arises in heterogeneous TMO sample due to the effect of magnetic field on Maxwell–Wagner space charge at the interface. The thermionic current–voltage (I–V) characteristics of the Au/TMO/Au Schottky diode have been measured within the voltage range ± 40 V. Ferroelectric type hysteretic behaviour is observed in non-ferroelectric TMO sample.

Influence of Charge Transport Layers on Capacitance Measured in Halide Perovskite Solar Cells

Summary Capacitance-based techniques have been used to measure the electrical properties of halide perovskite solar cells (PSCs) such as defect activation energy and density, carrier concentration, and dielectric constant, which provide key information for evaluating the device performance. Here, we show that capacitance-based techniques cannot be used to reliably analyze the properties of defects in the perovskite layer or at its interface, because the high-frequency capacitance signature is due to the response of charge carriers in the hole-transport layer (HTL). For HTL-free PSCs, high-frequency capacitance can be considered as the geometric capacitance for analyzing the dielectric constant of the perovskite layer because there is no trapping and de-trapping of charge carriers in the perovskite layer. We further find that the low-frequency capacitance signature can be used to calculate the activation energy of the ionic conductivity of the perovskite layer, but the overlapping effects with charge transport materials must be avoided.

Facet-Dependent Surface Trap States and Carrier Lifetimes of Silicon.

The facet-dependent electrical conductivity properties of silicon wafers result from significant band structure differences and variations in bond length, bond geometry, and frontier orbital electron distribution between the metal-like and semiconducting planes of silicon. To further understand the emergence of conductivity facet effects, electrochemical impedance measurements were conducted on intrinsic Si {100}, {110}, and {111} wafers. The attempt-to-escape frequency, obtained from temperature-dependent capacitance versus applied frequency curves, and other parameters derived from typical semiconductor property measurements were used to construct a diagram of the trap energy level (Et) and the amount of trap states Nt(Et). The trap states are located 0.61-0.72 eV above the silicon conduction band. Compared to {100} and {110} wafers, Si {111} wafer shows far less densities of trap states over the range of -0.2 to 2 V. Since these trap states inhibit direct electron excitation to the conduction band, the {111} wafer having much fewer trap states presents the best electrical conductivity property. Impedance data also provide facet-specific carrier lifetimes. The {111} surface gives consistently the lowest carrier lifetime, which reflects its high electrical conductivity. Lastly, ultraviolet photoelectron spectra and diffuse reflectance spectra were taken to obtain Schottky barriers between Ag and contacting Si wafers. The most conductive {111} surface presenting the largest Schottky barrier means the degrees of surface band bending used to explain facet-dependent electrical behaviors cannot be reliably attained this way.

Quantifying mobile ions and electronic defects in perovskite-based devices with temperature-dependent capacitance measurements: Frequency vs time domain.

Perovskites have proven to be a promising candidate for highly efficient solar cells, light-emitting diodes, and x-ray detectors, overcoming limitations of inorganic semiconductors. However, they are notoriously unstable. The main reason for this instability is the migration of mobile ions through the device during operation as they are mixed ionic-electronic conductors. Here, we show how measuring the capacitance in both the frequency and the time domain can be used to study ionic dynamics within perovskite-based devices, quantifying activation energy, diffusion coefficient, sign of charge, concentration, and the length of the ionic double layer in the vicinity of the interfaces. Measuring the transient of the capacitance furthermore allows for distinguishing between ionic and electronic effects.