Admittance Spectroscopy Technique Research Articles

Structural, electrical properties and complex impedance analysis of Pr0.67Ba0.22Sr0.11Mn1−xTixO3 perovskites

The Pr0.67Ba0.22Sr0.11Mn1−xTixO3 (x = 0.05 and 0.075) manganites are synthesized using solid-state reaction route. All XRD patterns with narrow and intense diffraction peaks reveal that the samples are well crystallized. For electrical properties we measure the conductivity versus temperature (80–400 K) and frequencies (40 Hz–10 MHz). These measurements were made by admittance spectroscopy technique. The effect of titanium doping on the electrical properties of our compounds appears by semiconductor behavior. The variation of DC-conductivity with temperature presents two metal–semiconductor transitions. The first transition TMS bound by Mn3+/Mn4+ ratio but the second transition TSM depends to an extrinsic effect of grain boundaries. It was observed also that the conductivity decreases with titanium concentration, such behavior is associated to a reduction of double-exchange mechanism. The conduction mechanism is explained by thermally activated hopping of small polaron at high temperature range. The activation energy was evaluated of about Ea = 30 m eV for x = 0.05 and Ea = 61 meV for x = 0.075. The total conductance spectrum of Pr0.67Ba0.22Sr0.11Mn0.925Ti0.075O3 compound is well described by the Jonscher power law: $$G\left(w\right)={G}_{dc }+A{\omega }^{n}$$ . Impedance study for the sample with x = 0.075 indicates the presence tow metal–semiconductor transitions and a non-Debye relaxation phenomenon related to a grain and grain boundary medium. Also, the modulation of the material by an electrical equivalent circuit show high values of grain boundary medium capacity.

Detailed Consideration of Electrical and Dielectric Properties of Au/Ni/n-Si MS Structure in a Wide Frequency Range

In the presented study, the electrical and dielectric properties of Au/Ni/n–Si MS structure are examined in detail by performing frequency–dependent admittance spectroscopy technique over a wide frequency range (3 kHz–1 MHz). Dielectric constant, dielectric loss, dielectric loss tangent, real modulus, imaginary modulus, and electrical conductivity of the structures are calculated by evaluating the results obtained from admittance spectroscopy. The experimental data received in the wide frequency range is examined in three different frequency ranges as low (3–10 kHz), medium (20–100 kHz) and high (0.2–1 MHz) to a more detailed examination and a better understanding of electrical and dielectric properties. The dielectric loss tangent, real modulus and imaginary modulus values increase with increasing frequency, while dielectric constant and dielectric loss values decrease with increasing frequency. The electric modulus values increase with the increasing frequency is ascribed by the dipoles and the polarize electrons’ dielectric relaxation. In addition, despite the change of electrical conductivity values are constant in the low frequency and middle frequency regions, it decreases as the frequency increases in the high–frequency region. For all parameters, the frequency–dependent behavior of the structure is specifically studied at 2 V. It is concluded within the present study that Si–based MS structures created by integrating Au/Ni have the potential to be used especially in innovative and applicable electronic and optoelectronic devices such as rectifiers and switchers.

Electrical characterization of low temperature plasma epitaxial Si grown on highly doped Si substrates

Epitaxial silicon layers were grown on highly doped c-Si substrates using the plasma-enhanced chemical vapour deposition process (PECVD) at low temperature (175 °C). The transport and defect-related properties of these epi-Si layers were characterized by current density-voltage (J–V) and capacitance–voltage (C–V) techniques. The results show that the epi-Si layers exhibit a non-intentional n-type doping with a low apparent doping density of about 2 × 1015 cm−3. The admittance spectroscopy technique is used to investigate the presence of deep-level defects in the structure. An energy level at 0.2 eV below the conduction band has been found with a density in the range of 1015 cm−3 which may explain the observed apparent doping profile.

Dielectric, modulus and conductivity studies of Au/PVP/n-Si (MPS) structure in the wide range of frequency and voltage at room temperature

Both the real-imaginary components of complex dielectric permittivity and electric modulus, and ac conductivity of Au/PVP/n-Si (MPS) structures were analyzed by admittance spectroscopy technique between 1 and 500 kHz, − 3 and 5 V. The polyvinylpyrrolidone (PVP) polymer layer was deposited on n-Si wafer by spin-coating technique. The e′, e″, M′, M″ and σac values were calculated from the admittance measurements and they are quite function of frequency and voltage due to a special distribution of surface states at PVP/n-Si interface, interfacial/dipole polarizations at low frequencies. While the e′ and e″ values decrease as frequency increases, the σac, M′ and M″ increase. The ln(σac) vs ln(ω) plot for 3V has two linear region between 1 and 20 kHz, 30 and 500 kHz frequencies, respectively. The obtained 0.033 slope value for low-frequencies which corresponding to dc conductivity and it is almost independent of frequency, but it obtained 0.46 for high-frequencies which corresponding ac conductivity and is strong function of frequency due to the increase eddy current. As a result, the prepared MPS structure can be used as charges/energy storage device due to the dielectric property of the PVP polymer layer.

Improvement of Ga distribution with Sb incorporation for two-step low-temperature processing of CIGSe thin film solar cells

In this study, the application of Sb incorporation for low-temperature (≤ 450 °C) processing of Cu(In,Ga)Se2 (CIGSe) solar cells is explored. At low reaction temperature, most Ga remains at the back of the film adjacent to the Mo back contact. We observed that the incorporated Sb enhanced grain size and improved device performance compared with similarly processed CIGSe films made without Sb. From the energy-dispersive spectroscopy analysis and secondary ion mass spectrometry results, it was determined that elemental Ga accumulation at the back of the reacted film after the two-step selenization process was significantly alleviated owing to Sb incorporation. Significant Sb-induced grain size enhancement was confirmed using cross-sectional scanning electron microscopy. The electronic and optical properties of the Sb incorporated CIGSe films were examined with admittance spectroscopy and fluorescence lifetime imaging techniques.

Carrier transport properties in a thin-film Cu2ZnSnSe4 solar cell

We report the measurement of majority carrier concentration, depletion width, mobility, and resistivity in a thin-film based Cu2ZnSnSe4 (CZTSe) photovoltaic device. The carrier transport properties were measured using coordinated admittance spectroscopy and capacitance-voltage technique. The bias dependence of the modified dielectric relaxation in the absorber of the CZTSe solar cell was investigated to extract the mobility and resistivity. Hall measurement was also performed at room temperature for the verification of carrier concentration, resistivity, and mobility. The temperature dependent resistivity and mobility exhibit thermally activated behaviors characterized by a thermal activation energy ≈ 60 meV. The positive temperature dependence of the mobility indicates a carrier-transport impeding effect caused by the band-edge fluctuation in poly-crystalline CZTSe, whose magnitude is measurable by the aforementioned activation energy.

The effects of doping type on structural and electrical properties of silicon nanocrystals layers grown by plasma enhanced chemical vapor deposition

The purpose of this paper is to compare the influence of boron and phosphor doping on the optical, structural and electrical properties of hydrogenated amorphous silicon (a-Si:H) thin films elaborated at low radiofrequency power and low hydrogen dilution. Structural properties of deposited films were investigated by scanning electron microscopy (SEM), grazing incidence X-ray diffraction (GI-XRD) and Raman spectroscopy. The SEM analysis shows that the best homogeneity is observed in the layer doped with low diborane flow rate. Reflectance, XRD and Raman measurements show that the doping of thin films induces the formation of nanocrystallites (nc-Si) embedded in the amorphous matrix with higher density in the phosphorus-doped layers compared to those of boron-doped one. The temperature dependent electrical properties of Au/a-Si:H Schottky diodes were investigated using current–voltage characteristics (I–V), admittance spectroscopy technique and capacitance–voltage characteristics [C(V)] in the temperature range of 100–400 K. From the I–V analyses based on thermionic emission (TE) theory we notice the heterogeneity of the barrier height of the Schottky diodes. From the electrical conductivity measurements, we plotted the evolution of the logarithm of the conductivity σ·T as a function of 1000/T. Activation energies \({\text{E}}_{{\text{a}}}^{{{\text{Low}}}}\) and \({\text{E}}_{{\text{a}}}^{{{\text{High}}}}\) of the samples in low and high temperature ranges respectively are estimated. The decrease of \({\text{E}}_{{\text{a}}}^{{{\text{Low}}}}\) with increasing boron flow rate is attributed to an increase in the density of the traps in the band gap of silicon. On the other hand, we found that \({\text{E}}_{{\text{a}}}^{{{\text{High}}}}\)increases when the flow rate of boron increases and decreases when the flow rate of phosphorus increases. We attributed these behaviors to the increase in the crystallinity of the n-type layers and to the presence of a deep defect in the p-type layers. C−2(V) plots show the presence of two linear regions. We found that the response of the nanocrystalline phase becomes more pronounced at high doping flow rate. Optical, structural and electrical measurements confirmed that the type and the density of doping are important parameters that influence the electrical properties of nc-Si:H Schottky diodes.

Investigation of structural, electrical and dielctrical properties of Pr0.67Ba0.22Sr0.11Mn1−xFexO3 (0 ≤ x ≤ 0.2) perovskite

In the present work, we have studied the structural, electrical and dielectrical properties of Pr0.67Ba0.22Sr0.11Mn1−xFexO3 (0 ≤ x ≤ 0.2) materials prepared through the solid state reaction. This study has been performed using admittance spectroscopy technique over a wide range of temperatures (80–340 K) and frequencies (40 Hz–10 MHz). The variation of conductivity with temperature shows a metal–semiconductor transition for x = 0 and 0.05. A semiconductor behavior is noticed for the others compositions. The transition temperature TMS was found to be about 220 and 90 K for samples with x = 0 and 0.05, respectively. It is also found that the conductivity decreases with Fe concentration, such behavior is related to a reduction of double exchange mechanism. The conduction mechanism is described by thermally activated hopping of small polaron. The activation energy of such process is sensitive to the iron concentration. This energy increases with increasing Fe content from Ea = 22 meV for x = 0 to Ea = 67 meV for x = 0.20. The dielectric permittivity as function of the temperature is characterized by the appearance of dielectric transition which is described by the Curie–Weiss law. The dielectric transition temperature Td change with the iron concentration and it is found to be 100, 170, 140 and 180 K for x = 0.05, 0.10, 0.15 and 0.20, respectively.

Study of MgCl2 activation treatment on the defects of CdTe solar cells by capacitance-voltage, drive level capacitance profiling and admittance spectroscopy techniques

CdTe solar cells have recently reached its highest conversion efficiencies, comparable to CuInGaSe2 and Si devices. One of the key factors for the success of these devices is the so-called “activation” treatment, which typically consists in depositing a CdCl2 film on the CdTe absorber layer and in a subsequent annealing in air or nitrogen atmosphere. Nevertheless CdCl2 is a carcinogenic and water-soluble compound; for this reason recent studies have found MgCl2 as a good alternative.In this work we have studied devices (exceeding 14% efficiency) prepared by low-substrate temperature CdTe deposition and activated with MgCl2 treatment (applied by wet deposition). The devices were characterized by means of current-voltage, capacitance-voltage, drive level capacitance profiling and admittance spectroscopy techniques. Carrier concentration and also concentration and distribution of shallow and deep defects are presented and compared with data obtained from analogous devices but activated with the standard CdCl2. Despite CdTe layers treated with the two different processes exhibit similar structural properties, the distribution of deep and shallow defects results to be different and moreover admittance spectroscopy technique reveals the presence of different defects, at 344 and 358meV, which are present only in MgCl2 treatment case.

Effect of exceeding the concentration limit of solubility of silver in perovskites on the dielectric and electric properties of half doped lanthanum–calcium manganite

Dielectric and electric properties of La0.5Ca0.2Ag0.3MnO3 (LCMO–Ag) manganite have been investigated using admittance spectroscopy technique. AC conductivity analysis shows that the conductivity verifies the Jonscher universal power law. The deduced exponent ‘s’ values prove that hopping model is the dominating mechanism in the material. From dc-electrical resistivity study, conduction process is found to be dominated by thermally activated small polaron hopping (SPH) mechanism. Complex impedance analysis (CIA) indicates the presence of relaxation phenomenon and allows to modelize the sample in terms of an electrical equivalent circuit. Also, impedance study confirms the contribution of grain boundary in the electrical properties. Dielectric studies indicate that the La0.5Ca0.2Ag0.3MnO3 compound has a Debye-like relaxation. The temperature dependence of permittivity is well fitted by the modified Curie–Weiss law. It is found that dielectric permittivity behavior and the estimated relaxation parameter value (γ≈2), support the evidence of the relaxor nature of La0.5Ca0.2Ag0.3MnO3 material. The high dielectric constant and the low loss tangent indicate the material is promising for tunable capacitor applications.

Electrical Conductivity and Complex Impedance Analysis of Ba2CrMo0.8W0.2O6 Double Perovskite

Electrical properties of Ba 2CrMo0.8W0.2O6 double perovskite were investigated using admittance spectroscopy technique. According to impedance analysis, the material was modeled by an electrical equivalent circuit. Such analysis proves the presence of relaxation phenomenon in the compound. We also found that ac conductivity follows the Jonscher universal power law. Conduction process is found to be dominated by the thermally activated small polaron (SPH). The activation energy values, inferred from dc conductivity and from the temperature dependence of relaxation time, are closed to each other. Such result indicates that conduction process and relaxation phenomenon are related to the same defect.

Influence of Al substitution on physical properties of Pr0.67Sr0.33Mn1−x Al x O3 manganites

We have investigated the effect of Al doping on physical properties of \({\rm Pr}_{0.67}^{3+}{\rm Sr}_{0.33}^{2+}{\rm Mn}_{0.67-x}^{3+}{\rm Al}_{x}^{3+}{\rm Mn}_{0.33}^{4+}{\rm O}_{3}^{2-}\) manganites synthesized using the solid-state reaction method at high temperature. Rietveld refinement of XRD patterns revealed that all samples crystallize in an orthorhombic structure with Pnma space group. Magnetization measurements show that all samples exhibit a paramagnetic–ferromagnetic phase transition at the Curie temperature TC which decreases from 282 to 240 K when increasing Al content from x = 0.025 to 0.1, respectively. Electrical properties of samples have been investigated using admittance spectroscopy technique in 102–106 Hz and 100–320 K, frequency and temperature ranges, respectively. All samples exhibit a metallic behavior below the metal–semiconductor transition temperature (TM–Sc) and a semiconductor behavior above TM–Sc. The total conductance curves for our samples are found to obey Jonscher power law (G(ω) = Gdc + Aωn). The activation energy (Ea) increases with increasing Al content from 34.44 meV for x = 0.025 to 43.18 meV for x = 0.1. From AC conductance study, we deduced the binding energy (Wm) at 100 K. Its values decrease with Al content increases.

Characterization of deep level defects present in mono-like, quasi-mono and multicrystalline silicon solar substrates

Defects on mono-like (ml-Si), quasi-mono (qm-Si) and multicrystalline silicon solar cell substrates are studied in depth. Using the thermal admittance spectroscopy technique we found a single deep level with an activation energy between 213 and 224 meV and a capture cross section in the order of 10−15−10−14 cm2, in the case of ml-Si samples. The 271, 291 and 373 meV levels were found in qm-Si samples. The first one is associated with a capture cross section in the order of 10−16 cm2, the second one in the order of 10−14, while the third one is associated, for the same magnitude, with a value in the order of 10−12 cm2. Multicrystalline samples showed two tendencies in the Arrhenius plot fit associated with a deep level in each one. The activation energy of the first one ranges from 336 meV to 342 meV, and the capture cross sections are in the order of 10−13−10−11 cm2. The values obtained for the second one are 251 and 171 meV, with the capture cross section values in the order of 10−15 and 10−18 cm2, respectively. The nature of these defects is probably due to iron-based impurities in different complexes. Segregation into extended defects of Fei or Fei-V is the most probable cause of the deep levels with higher capture cross section value. Punctual complexes such as Fei or Fei-V2 are probably the reason for the deep levels with lower capture cross section value.

Acoustic, electrochemical and microscopic characterization of interaction of Arthrospira platensis biofilm and heavy metal ions

This study examines a biofilm of Arthrospira platensis and its interactions with cadmium and mercury, using electrochemical admittance spectroscopy technique combined with highly sensitive Love wave platform for the real-time detection in liquid medium. Spirulina cells were immobilized via multilayers of polyelectrolyte (PEM) on Si/SiO2 surface of both transducers and characterized using atomic force microscopy (AFM). Scanning electron microscopy (SEM) cell images revealed a first defense mechanism against cadmium at 10−12M and it immediately takes place after 4s from injection. The cyanobacteria biofilm becomes more conductive, due to an increase of polyphosphate bodies. An increase of density induces a decrease of frequency. Response time τ90% of the biofilm toward Cd2+ was between 6 and 8min, while it did not exceed a few seconds toward Hg2+ at 10−12M. However, the initial rapid stage of mercury adsorption took 40s to reach the saturated stage. Once external sorption reached the saturated stage, internal mercury uptake began; cations were transported across the cell membrane into the cytoplasm and a beta-HgS precipitation took place, inducing conductivity biofilm decrease, and generating an increase of density, and thus a frequency decrease. SEM images revealed the beginning cell damage at 10−06M of cadmium and mercury.

Trap levels in the atomic layer deposition-ZnO/GaN heterojunction—Thermal admittance spectroscopy studies

In this work, a n-ZnO/p-GaN heterojunction is analyzed using admittance spectroscopy techniques. Capacitance transient measurements performed at 10 kHz reveal four majority-carrier deep levels, the most important one located at approximately 0.57 eV below the ZnO conduction band (CB) edge with a density about two orders of magnitude below the doping level (NT = 4 × 1015 cm−3). The others, located at 0.20 eV, 0.65 eV, and 0.73 eV, are about three orders of magnitude below the doping level (NT = 4–9 × 1014 cm−3).

Effects of iron concentrations on the electrical properties of La0.67Ba0.33Mn1−xFexO3

• Introducing iron in LBMO system decreases electrical conductance. • The material turns from metallic into semi-insulating behavior when increasing Fe concentration. • The value x = 0.10 represents the limit of Fe concentrations which destroys metallic-insulating transition. • Under polarization, the conductance of the material increases and activation energy decreases for all Fe concentrations. In order to study the electrical properties of the samples La 0.67 Ba 0.33 Mn 1− x Fe x O 3 , transport measurements have been performed on this compound using admittance spectroscopy technique. For all temperatures the DC conductance decreases when increasing Fe content and x = 0.10 represents the limit value of Fe concentration which destroys metallic-insulating transition. From DC conductance study, electronic conduction is found to be dominated by thermally activated hopping. Activation energy is deduced from the variation of conductance with temperature. This energy increases with increasing Fe content from E a = 27 meV for x = 0 to E a = 154 meV for x = 0.20. The AC conductance spectrum is found to obey Jonscher universal power law. The exponent “ n ” changes with Fe concentration ( n ≈ 1 for x = 0.20 and n = 0 for x = 0). This indicates that the material evolves from metallic to semi-insulating behavior when increasing Fe content. Under polarization, the conductance of the material increases and activation energy decreases for all Fe concentrations.

Effect of Polymer Crystallinity in P3HT:PCBM Solar Cells on Band Gap Trap States and Apparent Recombination Order

AbstractThe non‐geminate recombination of charge carriers in polymer‐fullerene solar cells has been modeled in the last few years with a trap‐assisted recombination model, which states that the apparent recombination order depends on the concentration of trapped charges tailing into the band gap. Higher concentrations of trapped charges lead to higher apparent recombination orders. In this work, the mass fractionfof highly crystalline nanofibrillar P3HT to the total P3HT content in P3HT:PCBM solar cells is consistently varied, controlling the temperature of a nanofibers‐P3HT casting dispersion. A systematic study of the apparent recombination order, measured with a transient photovoltage technique, as a function offis presented. A correlation is shown between the apparent recombination order, the P3HT crystallinity, and the trap concentration in the band gap measured with an admittance spectroscopy technique.

Electrical properties of MBE grown Si3N4–cubic GaN MIS structures

AbstractIn this work we report on the electrical characterization of non‐polar cubic GaN metal‐insulator‐semiconductor (MIS) structures. Si3N4 layers were deposited in‐situ on top of cubic GaN grown on 3C‐SiC (001) substrates. The electric characteristics of the MIS structures are measured by capacitance and admittance spectroscopy techniques. From the hysteresis in the capacitance‐voltage curves and the peak height of the conductance Gp –ω frequency curves the interface state densities are calculated.We find interface traps about 0.3 eV below the conduction band. The density of these traps is Dit = 2.5x1011 cm‐2eV‐1. This is one order of magnitude lower than in MIS structures with a Si3N4 insulator produced by plasma enhanced vapour deposition and two orders of magnitude lower than in MIS structures on c‐GaN with SiO2 as insulator (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Low interface trapped charge density in MBE in situ grown Si3N4 cubic GaN MIS structures

In this work we report on the electrical characterization of nonpolar cubic GaN metal–insulator–semiconductor (MIS) structures. Si3N4 layers were deposited in situ on top of cubic GaN grown on 3C–SiC (0 0 1) substrates. The electric characteristics of the MIS structures are determined by current–voltage measurements and by capacitance and admittance spectroscopy techniques. Time-of-flight secondary ion mass spectroscopy (TOF-SIMS) was used to investigate the composition of our samples. From the flat band voltage in the MIS capacitors and a detailed band diagram analysis, the conduction band discontinuity of Si3N4 and cubic GaN was evaluated 1.17 eV, which is slightly lower than reported for hexagonal GaN. By admittance spectroscopy interface state densities are calculated. Current–voltage characteristics were used to evaluate the influence of the substrate temperature on the insulating properties of the MIS structures. The energetic position of the interface traps was found to be about 0.3 eV below the conduction band of cubic GaN. The density of these traps is 2.5 × 1011 cm−2 eV−1. We find a conductivity minimum in the MIS structure grown at 600 °C.

Influence of Ga content on defects in CuIn xGa 1 − x Se 2 based solar cell absorbers investigated by sub gap modulated photocurrent and admittance spectroscopy

In this work, we investigate the influence of gallium content on the defects properties of co-evaporated CuIn xGa 1 − x Se 2 by sub gap modulated photocurrent spectroscopy and admittance spectroscopy techniques. A series of CuIn xGa 1 − x Se 2 based solar cells with different gallium content in the range from 0% to 33%, and with the same CdS buffer layer have been investigated. On one hand, photocurrent spectroscopy results show 2 types of defects named D1 and D2, and on the other hand, admittance spectroscopy results exhibit only one type of defect. I–V curves show that one of the two defects probed by photocurrent is responsible of the dominant recombination mechanisms next to the heterointerface, between the absorber and the buffer layers. Moreover, I–V curves under AM 1.5 conditions show that the cell with no probed D2 defect presents the best photovoltaic performances.