Activation Energy Of Carriers Research Articles

Ionic conductivity studies on PEMA/PVC-NH<SUB align="right">4I polymer electrolytes

Polymer electrolyte of poly(ethyl methacrylate) and polyvinyl chloride blend containing various weight percentages of ammonium iodide salt were prepared via solution casting technique employing tetrahydrofurane as the solvent. The conductivity values of the electrolytes were determined via impedance spectroscopy. The conductivity of the electrolytes is observed to increase with increasing salt concentration and the highest conductivity obtained is in the order of 10–6 S cm–1 at salt concentration of 40 wt %. In order to understand the conductivity behaviour, X-ray diffraction, temperature dependence of conductivity and dielectric studies were done. The results show that the conductivity is influenced by the fraction of amorphous region, activation energy and migration of charge carriers in the system.

Time-resolved and temperature-dependent photoluminescence studies on CdTe/ZnTe quantum dots with different ZnTe capping layer thicknesses

We investigate the effects of the capping layer thickness on the optical properties of CdTe/ZnTe quantum dots (QDs). The time-resolved photoluminescence (PL) measurements used to study the carrier dynamics show a shorter decay time for CdTe/ZnTe QDs with decreasing thickness of the ZnTe cap layer due to an increase in the nonradiative surface recombination rate. The activation energy of the electrons confined in the CdTe/ZnTe QDs, as obtained from the temperature-dependent PL spectra, decreases with the thickness of the ZnTe cap layer. These results indicate that the carrier dynamics and activation energy of CdTe/ZnTe QDs are affected by the thickness of the ZnTe cap layer.

Investigation of Reverse Leakage Characteristics of InGaN/GaN Light-Emitting Diodes on Silicon

We investigate the reverse leakage characteristics of InGaN/GaN multiple-quantum-well light-emitting diodes (LEDs) grown on Si (111) substrate by metal-organic chemical vapor deposition. The reverse leakage characteristics of InGaN/GaN LED on silicon are measured as low as ~10 nA at -5 V and -10 μA at -15 V. Temperature-dependent current-voltage ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> - <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> ) measurements of LED devices reveal that the reverse leakage current mechanism is mainly attributed to the field-enhanced thermionic emission, also known as Poole-Frenkel emission, of carriers from deep centers within the space charge region up to ~ -18 V. The analysis of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> - <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> - <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> curve yields the calculation of the coefficient of the Poole-Frenkel effect (1.12 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> eV·V <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1/2</sup> ·cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> ) and activation energies of carriers (~214 meV at -5 V). With further increase of reverse bias, up to -40 V, LED devices exhibit the onset of space-charge-limited leakage current mechanism without any local breakdown.

Influence of the composition on electrical properties of low-temperature ionic conductors in the Cu1 − x Ag x GeAsSe3 system

The chalcogenides Cu1 − xAgxGeAsSe3 (x = 0.5, 0.8, 0.9) have been synthesized and their electrical properties have been studied at low temperatures. Compounds of this type are electron-ionic conductors with a mixed character of conduction. It has been shown that the substitution of copper atoms for a part of silver atoms in the AgGeAsSe3 compound leads to a decrease in the total conductivity, a decrease in the fraction of ionic component of the conductivity, a significant increase in the polarization times, an increase in the temperature of the onset of a noticeable contribution (as compared to the electron contribution) of the ionic transport, and a decrease in the activation energy of carriers.

Carrier dynamics and activation energy of CdTe/ZnTe nanostructures with different CdTe thicknesses

We investigate the dimensional transition and optical properties of CdTe/ZnTe nanostructures with various CdTe thicknesses. The excitonic peak corresponding to the transitions from the ground electronic sub-band to the ground heavy-hole band in CdTe/ZnTe nanostructures shows different redshifts with increasing CdTe thickness due to variations in the dimensions of CdTe/ZnTe nanostructures. Time-resolved photoluminescence (PL) measurements used to study the carrier dynamics show that the decay time of 4.0 monolayer (ML) CdTe/ZnTe nanostructures is longer than that of CdTe/ZnTe nanostructures with different CdTe thicknesses. The activation energy of electrons confined in 4.0 ML CdTe/ZnTe nanostructures, as obtained from the temperature-dependent PL spectra, is higher than that of electrons confined in CdTe/ZnTe nanostructures with different CdTe thicknesses. These results indicate that the carrier dynamics and activation energy of CdTe/ZnTe nanostructures are affected by the thickness and dimensions of CdTe/ZnTe nanostructures.

Hot-wire chemical vapor deposition and characterization of p-type nanocrystalline Si films for thin film photovoltaic applications

P-type nanocrystalline Si (p-nc-Si) films were deposited by hot-wire chemical vapor deposition (HWCVD) system using SiH4, B2H6, and H2 as reactants. The effect of H2 flow rate on the material properties of p-nc-Si films were investigated using Raman spectroscopy, X-ray diffractormeter, ultraviolet–visible-near infrared spectrophotometer, Fourier transform infrared spectroscopy, field emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM). Moreover, the electrical properties, such as carrier concentration, activation energy, dark conductivity, and Hall mobility, of p-nc-Si films were also measured. It was found that H2 flow rate played an important role in forming of p-nc-Si, decreasing the deposition rate, and increasing the crystallinity of p-nc-Si films. FESEM and TEM micrographs also showed the enhancement of crystallinity with adding H2 flow rate. Furthermore, the change of microstructure at various H2 flow rates was found to affect the electrical properties of p-nc-Si films. Details of the growth mechanism in p-nc-Si films will be discussed also. Moreover, the optimum p-nc-Si film was used as window layer in n-type crystalline Si heterojunction (HJ) solar cell. After the deposition parameters were optimized, the Si HJ solar cell with the open-circuit voltage of 0.58V, short-circuit current density of 33.46mA/cm2, fill factor of 64.44%, and the conversion efficiency of 12.5% could be obtained.

AC electrical properties of FeIn2S4

The frequency and temperature dependences of the ac capacitance and resistivity of FeIn2S4 semiconductors are studied. Resonances are observed at certain temperatures in the frequency range (2.5–5.0) × 105 Hz. The permittivity of the crystals and the activation energy of charge carriers are determined. It is found that electrical conduction in the given temperature interval is governed by an activation mechanism. The activation energy is frequency-dependent, because the relaxation time of barrier layers decreases with rising frequency.

Carrier dynamics and activation energy of CdTe quantum dots in a CdxZn1−xTe quantum well

We investigate the optical properties of CdTe quantum dots (QDs) in a Cd0.3Zn0.7Te quantum well (QW) grown on GaAs (100) substrates. Carrier dynamics of CdTe/ZnTe QDs and quantum dots-in-a-well (DWELL) structure is studied using time-resolved photoluminescence (PL) measurements, which show the longer exciton lifetime of the DWELL structure. The activation energy of the electrons confined in the DWELL structure, as obtained from the temperature-dependent PL spectra, was also higher than that of electrons confined in the CdTe/ZnTe QDs. This behavior is attributed to the better capture of carriers into QDs within the surrounding QW.

Electron and hole scattering dynamics in InN films investigated by infrared measurements

AbstractInN layers have electron accumulation structure around the surfaces and interfaces with the substrates. Infrared (IR) spectroscopy enables the analysis of the inside bulk region in spite of the high sheet electron density of the order of 1013 cm−2 in the accumulation layers using the dispersion of the penetration depth. The polarization spectroscopy shows the anisotropic electron and hole scattering rates. The higher scattering rates of electron and hole plasmons vibrating along the c axis are attributed to edge‐type dislocations, while the scattering by Mg or related complex dominates the damping processes of hole plasmons vibrating vertical to the c axis in highly Mg‐doped p‐InN. The smaller photoluminescence (PL) intensity of p‐InN is attributed to the smaller activation energy of carriers to be captured by deep levels than that from the captured carriers to the ground state.

Enhanced Electrical Properties of Reduced Graphene Oxide Multilayer Films by In-Situ Insertion of a TiO2 Layer

Wrinkle-free reduced graphene oxide (rGO)/TiO(2) hybrid multilayer films were directly fabricated using an rGO solution stabilized by a TiO(2) precursor sol applied over a large area by an air spraying method without the use of additional reduction processes. In-situ insertion of the TiO(2) layer between rGO sheets dramatically increased the conductivity and carrier mobility despite the insulating properties of amorphous TiO(2). The TiO(2) situated between rGO sheets also induced significant hole doping. Electrical hysteresis caused by adsorbed water molecules and residual oxidative moieties in the rGO nanosheets vanished due to TiO(2)-assisted screening of charged impurities. These effects decreased the thermal carrier activation energy and increased the density of states at the Fermi level. Ambipolar transport properties were converted into unipolar-like hole transport characteristics by extensive hole doping in the TiO(2) layer.

Temperature Dependence of Photoluminescence from Epitaxial InGaAs/GaAs Quantum Dots with High Lateral Aspect Ratio

Hereby, we present a study of a thermal quenching of emission from self-assembled epitaxial highly asymmetric quantum dots in InGaAs/GaAs material system for both ensemble and single dot regime. Pronounced interplay between the intensity of wetting layer and quantum dots originated emission was observed as the temperature was increased, evidencing a thermally activated energy transfer between the two parts of the system and an important role of the wetting layer in determining the optical properties of these anisotropic nanostructures. The carrier activation energies have been derived and possible carrier loss mechanisms have been analyzed. Single dot study revealed activation energies slightly varying from dot to dot due to size and shape distribution. The problem of the shape uniformity of individual quantum dot has also been addressed and possibility of additional carrier localization within the investigated structures has been found to be insignificant based on the recorded spectroscopic data.

Carrier localization and related photoluminescence in cubic AlGaN epilayers

The steady state and time-resolved photoluminescence (PL) spectra of cubic AlxGa1-xN have been measured for 0 &amp;lt; x &amp;lt; 1. The intensity of the room temperature PL increases by an order of magnitude when the AlN content increases from x = 0 to x = 0.95. Additionally, the PL decay slows down with the decrease of temperature and increase of x. These results show that strong localization of carriers on alloy composition fluctuations plays a large role in determining the intensity and temporal evolution of the PL. The activation energy for the localized carriers increases with the increase of x and reaches the value of 55 meV at x = 0.95.

Charge transfer in metallopolymer structure based on Cu(II) complexes

The process of ac electric conductivity in thin films of the poly[Cu(mSalpn-1,3)] complex compound has been studied for the first time. The experimental frequency dependence of the ac conductivity agrees with the model based on the hopping mechanism of charge transfer. The effect of temperature has been studied and the activation energies for charge carriers involved in the conductivity are determined. The role of the metal center (divalent copper) and the influence the electron structure of a ligand environment on the charge exchange in the metallopolymer structure are discussed.

Carrier Dynamics and Activation Energy of CdxZn1−xTe/ZnTe Quantum Dots on GaAs and Si Substrates

We have investigated the carrier dynamics and activation energy of CdxZn(1-x)Te/ZnTe quantum dots (QDs) on GaAs and Si substrates. The carrier dynamics of QDs on GaAs and Si substrates is studied using time-resolved photoluminescence (PL) measurements, revealing shorter exciton lifetimes of QDs on Si substrate. In particular, the activation energy of electrons confined in QDs on the GaAs substrate, as obtained from temperature-dependent PL spectra, is higher than that of electrons confined in QDs on the Si substrate. Both results confirm that defects and dislocations in QDs on the Si substrate provide nonradiative channels.

Progress on n‐type doping of AlGaN alloys on AlN single crystal substrates for UV optoelectronic applications

AbstractAs the building blocks of deep UV light emitting diode (LED) technology and high‐power electronic devices, AlGaN alloys have attracted considerable attention. In this study, AlGaN films with varying compositions doped with Si were deposited on homoepitaxial AlN layers grown on AlN single crystal substrates. The room temperature resistivity of AlGaN alloys of different compositions grown on AlN and sapphire substrates with a constant Si doping level of 6x1018 cm‐3 was compared. AlGaN films grown on AlN substrates consistently exhibited a lower n‐type resistivity than those grown on sapphire. An n‐type resistivity of 0.1 Ω cm was obtained for an AlGaN film with 80% Al content and a sheet resistance of 235 Ω/sq. for an AlGaN film with 70% Al content. The carrier activation energy as a function of Al content in AlGaN for these n‐type films was measured. For compositions below 80% Al, the activation energy was around 15 meV due to impurity potential screening. For higher Al compositions, the carrier concentration was limited by a high compensation ratio, except for AlN, which has activation energy of 250 meV. (© 2011 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Dielectric properties of perovskite ceramics of (1–x)BiFeO3 − x(KBi)1/2TiO3 (0.40 &lt; x &lt; 0.85) solid solutions from impedance spectroscopy data

The dielectric properties of the ceramics of (1 − x)BiFeO3 − x(KBi)1/2TiO3 (0.40 < x < 0.85) solid solutions with an orthorhombic structure have been studied using impedance spectroscopy in the frequency range 25–106 Hz at different temperatures. It has been shown that these solid solutions undergo a diffuse ferroelectric phase transition. The Curie temperature is found to be in the range 620–640 K. The activation energies of dielectric polarization relaxation (δEM) and dc charge carriers (ΔEdc) are determined. It has been established that, in the vicinity of 460 K, ΔEdc increases jumpwise as the temperature increases.

High Temperature Surface Conductivity of Hydrogenated Diamond Films Exposed to Humid Air

Nicolaus Copernicus University, Jagiellonska 13, 85-067 Bydgoszcz, Poland Surface conductivity of thin diamond films was measured as a function of temperature up to 450 ◦C. Hydrogenated diamond was synthesized by chemical vapor deposition in hydrogen/carbon plasma. Low values of charge carrier activation energy (≈ 10 meV) were observed, when hydrogenated diamond films were exposed to the ambient humid air. However, the activation energy increased by two orders of magnitude as film temperature exceeded 300 ◦C. We have attributed this behavior to the desorption of the H2O adlayer. The jump of the activation energy did not occur, when experiment was performed in vacuum. We have also shown that donor doping leads to the up-shift of the Fermi level much above the acceptor-like band gap levels induced by surface C–H bonds, which cannot be compensated by transfer of electrons from diamond to the double H–H2O layer.

Structural and electrical conductivity studies on nanocrystalline undoped and silver doped zinc sulphide

Zinc sulphide (ZnS) and silver doped zinc sulphide nanocrystallites (ZnS:Ag) of average size 4 and 8 nm, respectively, have been synthesized by chemical precipitation technique. The structural and morphological studies using X-ray and high resolution transmission electron microscopy (HRTEM) measurements have confirmed hexagonal structure for the samples. Using the impedance spectroscopy method, the effect of grain interior and electrode–sample interface effect on their conductivity have been studied at various temperatures. In high temperature region, the electrode–sample interface effect is found to be larger than that of the grain interior region. Further, the results of the activation energies of the charge carriers in both the regions are determined and analyzed. The conduction mechanism of silver doped zinc sulphide nanocrystallites has been studied at various temperatures and the results are reported.

Temperature dependent transient velocity and mobility studies in an organic field effect transistor

We have investigated the temperature-dependent behavior of a pentacene organic field effect transistor (OFET) by measuring dc current and voltage characteristics and the transient response of the OFET to a sharp voltage pulse applied at the source contact. Standard transistor equations were used to extract the dc field-effect mobility, μFE, and the turn on time of the OFET was used to extract a dynamic mobility, μdynamic. Temperature dependent measurements were used to extract both field-effect and dynamic activation energies, Ea,FE and Ea,dynamic, over a range of effective gate voltages in order to vary the charge carrier density in the channel. We found that at higher temperatures μdynamic&amp;gt;μFE, while at lower temperatures μdynamic&amp;lt;μFE. We attribute this varying relationship between dynamic and field effect mobilities to the fact that μFE is an average mobility of all the charge carriers in the channel, while μdynamic is a measure of the mobility of the fastest charge carriers in the channel. We also found Ea,dynamic to be greater than Ea,FE by approximately 7 meV at the same effective gate voltage. We attribute this to the fact that Ea,dynamic is extracted from transient measurements made during the process of channel formation, and therefore at lower charge carrier densities than the corresponding values of Ea,FE. We also note that Ea,dynamic is a measure of the activation energy of the most energetic charge carriers in the channel, while Ea,FE is a measure of the average activation energies of all charge carriers in the channel.

Charge Transport Mechanism and the Effects of Device Temperature on Electrical Parameters of Au/ZnPc/N-Si Structures

Gold/Zinc Phthalocyanine/n-Si metal semiconductor contact with organic interfacial layer have been developed and characterized by Current–Voltage-Temperature (I-V-T) measurements, to study its junction and charge transport properties. The junction parameters, of diode ideality factor (n), barrier height (b) and series resistance (R¬S), of the device are found to shift with device temperature. The barrier height and the diode ideality factor are found to increase and the series resistance is found to decrease with increasing device temperature. The activation energy of the charge carriers is found to be 44 meV and the peak of interface state energy distribution curves is found to shift in terms of Ess-Ev value from 0.582 eV to 0.776 eV with increasing device temperature. The data analysis implies that the Fermi level of the organic interfacial layer shifts as function of device temperature by 100 meV in the device temperature range of 283K to 343K. In terms of dominant conduction mechanism, the I-V-T data analysis confirms the fit of data to the relationship log (IV4)  V1/2 for higher device temperatures and the Poole-Frenkel type is found to be the dominant conduction mechanism for the hybrid device.