Trap Ionization Research Articles

Charge transport mechanism of high-resistive state in RRAM based on SiOx

Nonstoichiometric silicon oxide SiOx is a promising material for developing a new generation of high-speed, reliable flash memory based on the resistive effect. It is necessary to understand the electron transport mechanism of the high-resistive state in SiOx to develop a resistive memory element. At present, it is generally accepted that the charge transport of the high-resistive state in the Resistive Random Access Memory (RRAM) is described by the Frenkel effect. In our work, the charge transport of the high-resistive state in RRAM based on SiOx is analyzed with two contact-limited and five volume-limited charge transport models. It is established that the Schottky effect model, thermally assisted tunneling, the Frenkel model of Coulomb trap ionization, the Makram-Ebeid and Lannoo model of multiphonon isolated trap ionization, and the Nasyrov-Gritsenko model of phonon-assisted tunneling between traps, quantitatively, do not describe the charge transport of the high-resistive state in the RRAM based on SiOx. The Shklovskii-Efros percolation model gives a consistent explanation for the charge transport of the high-resistive state in the RRAM based on SiOx at temperatures above room temperature.

On the limit of defect doping in transition metal oxides

Transition metal oxides are being increasingly used in many applications like nonvolatile memory, contacts to transition metal dichalcogenide transistors and photovoltaics, and thin-film transistors, to name a few, because the conductivity can be tuned by defect doping. The mechanism of conduction through substoichiometric oxides is however not well understood. Earlier studies attributed the conduction in substoichiometric oxides to Poole–Frenkel emission. But the assumptions underlying the Poole–Frenkel model break down in thin dielectrics and when a broad range of temperature is considered. The authors model the conduction through substoichiometric nickel oxide (NiOx) using a kinetic Monte-Carlo framework based on trap-assisted tunneling (TAT), by studying devices made of metal/NiOx/Si stacks. Modeling the temperature dependence of I–V characteristics enables the extraction of the trap parameters, like trap ionization energy and trap relaxation energy. The authors study the effects of the UV/ozone treatment, which has been shown to reduce the resistivity of NiOx by orders of magnitude, as well as the choice of metal electrode on the trap properties. The high trap relaxation energy (∼1.6 eV) is identified as an important factor in limiting the effectiveness of defect doping in NiOx, because it hinders the carrier emission step of the TAT process. The relaxation energy is another design knob that can be used when screening oxide candidates for various applications.

Multiphonon trap ionization transport in nonstoichiometric SiNx

It is generally accepted that the charge transport in dielectrics is governed by coulombic trap ionization due to a barrier lowering in high electric fields (Frenkel effect). In this paper, the charge transport mechanism in Si3N4 and nonstoichiometric silicon rich SiNx is experimentally studied and quantitatively analyzed with five theoretical models: Frenkel model of Coulomb traps ionization, Hill-Adachi model of overlapping Coulomb traps, Shklovskii-Efros percolation model, Makram-Ebeid and Lannoo model of multiphonon isolated traps ionization and Nasyrov-Gritsenko model of phonon-assisted electron tunneling between nearby traps. It is shown that the charge transport in Si3N4 and SiNx is qualitatively described by Frenkel effect, but Frenkel effect predicts an enormously low attempt to escape factor value. The charge transport at traps energies Wt = 1.6 eV and Wopt = 3.2 eV in Si3N4 and SiNx can be described by an increase in traps concentration in the framework of Makram-Ebeid and Lannoo model and Nasyrov-Gritsenko model. The Makram-Ebeid and Lannoo model quantitatively describes the charge transport in Si3N4 and SiNx with low silicon enrichment. The charge transport in nonstoichiometric SiNx with high silicon enrichment is well explained by Nasyrov-Gritsenko model.

Leakage mechanisms of sol–gel derived multiferroic Bi5Ti3FeO15 thin films of layered perovskite

Polycrystalline Bi5Ti3FeO15 (BTFO) thin films of layered perovskite are prepared on (111)Pt/Ti/SiO2/Si via a sol–gel route. The BTFO thin films exhibit room-temperature multiferroic properties with the remanent polarization (2Pr) of ~ 56 µC/cm2 and saturated magnetization (Ms) of ~ 0.45 emu/cm3. Their leakage current characteristics are investigated at different temperatures from 53 to 293 K. Their leakage currents are found to be dominantly controlled by space charge limited current under low electric fields and Poole–Frenkel emission at high electric fields. Their zero-field trap ionization energy is determined to be 0.196 eV, suggesting the existence of shallow traps in the BTFO films.

Atomic and Electronic Structures of Intrinsic Defects in Ta2O5: Ab Initio Simulation

The atomic and electronic structure of intrinsic point defects in orthorhombic tantalum oxide has been studied by numerical simulation within the density functional theory. It has been shown that all defects responsible for metal enrichment of Ta2O5 serve as electron and hole traps. Under conditions of strong oxygen depletion and at a metal–insulator interface, which are characteristic of resistive memory elements, interstitial tantalum atoms compete with an oxygen vacancy in the formation of a conducting filament. Interstitial oxygen atoms are not involved in charge transport. Tantalum substituting oxygen can be considered as a combination of the oxygen vacancy and interstitial tantalum. The analysis of the calculated thermal and optical energies of trap ionization shows that the oxygen vacancy is a key defect for charge transport in Ta2O5.

Laser trap ionization for identification of human erythrocytes with variable hemoglobin quantitation.

An approach to an established technique that is potentially applicable for a more comprehensive understanding of the electrical properties of red blood cells (RBCs) is presented. Using a high-intensity gradient laser trap, RBCs can be singly trapped and consequentially ionized. The subsequent dynamics of the ionized cell allows one to calculate the charge developed and the ionization energy (IE) through a Newtonian-based analysis. RBCs with two different hemoglobin (Hb) types were ionized. The first sample was identified as carrying Hb HbAA (normal Hb) and the second one was identified as carrying HbAC (HbC trait). By analyzing the charge developed on each cell and several other related factors, we were able to discern a difference between the main Hb types contained within the individual RBC, independent of cell size. A relationship between the charge developed and the IE of the cell was also established based on the electrical properties of RBCs. Thus, we present this laser trapping technique as a study of the electrical properties of RBCs and as possible biomedical tool to be used for the differentiation of Hb types.

Oxygen Polyvacancies as Conductive Filament in Zirconia: First Principle Simulation

The atomic and electronic structure of oxygen vacancy and polyvacancy in the cubic, tetragonal and monoclinic zirconium oxide were investigated using quantum-chemical density functional theory simulation. It is shown that the neutral oxygen vacancy in crystalline zirconia can act as electron and hole trap. An electron added to ZrO2 structure with the oxygen monovacancy has a bonding charge density character. The defect levels position as well as thermal and optical trap ionization energies are consisted with the previously defined experimentally values. Each subsequent vacancy is formed near the already existing one, and no more than 2 removed oxygen atoms are related to Zr atom. The levels from oxygen polyvacancies are distributed in the bandgap preferentially localized close to the monovacancy level. The ability of oxygen vacancy chain in crystalline ZrO2 to act as a conductive filament is discussed.

Three-Dimensional Non-Linear Complex Model of Dynamic Memristor Switching

A thermodynamical model of filament growing when a current pulse via memristor flows is introduced. The model is the boundary value problem, which includes nonstationary heat conduction equation with non-linear Joule heat source, Poisson equation, and Shockley-Read-Hall equations taking into account strong electron-phonon interactions in trap ionization and charge transport processes. The charge current, which defines the heating in the model, depends on the rate of the oxygen vacancy generation. The latter depends on the local temperature. The solution of the introduced problem allows one to describe the kinetics of the switch process and the final filament morphology.

Non-linear memristor switching model

We introduce a thermodynamical model of filament growing when a current pulse via memristor flows. The model is the boundary value problem, which includes nonstationary heat conduction equation with non-linear Joule heat source, Poisson equation, and Shockley- Read-Hall equations taking into account strong electron-phonon interactions in trap ionization and charge transport processes. The charge current, which defines the heating in the model, depends on the rate of the oxygen vacancy generation. The latter depends on the local temperature. The solution of the introduced problem allows one to describe the kinetics of the switch process and the final filament morphology.

Three-Dimensional Non-Linear Complex Model of Dynamic Memristor Switching

In recent years significant efforts are being made for implementation of fourth electronic element – resistor with memory called memristor. This element is a passive device whose resistance can be changed by passing through a certain electric current pulse. The memristor has a simple metal-high-k-metal structure. Functionally the memristors can be divided into two-level (one-bit) and multilevel (multibit) ones. If the one-bit device may be used as a cell of non-volatile memory with a large storage time and high resistance to radiation, the multibit memristors on the one hand can increase the density of integration of the non-volatile memory, and on the other hand can be used to form the basis of adaptive neuromorphic (cognitive) computational systems. One of the most interesting and hitherto unsolved problems is the nature of the intermediate (discrete) multi-level states in a memristor. The hypothesis that the effect of memristive switch is directly connected with the formation of a filament, that occurs when certain current pulse pass over a dielectric, is distributed among specialists. However, the kinetics of filament formation during the transition from the high resistance state of the memristor to a low resistive state is still not clear. Another unsolved problem in the way of developing memristor arrays is a description of the forming process of memristor elements – the first switch from the initial high resistance state to a low resistance at high voltages, accompanied by intense Joule heat release. Nature of the forming of memristor matrix is still unclear, and the absence of any plausible physical model constrains the practical implementation of these elements. It is considered that charge transport in high-k is associated with the presence of defects. The most probable and the most widespread defects are oxygen vacancies. Properties of these vacancies are actively studied both experimentally and theoretically. However, many contradictory data can be found in literature, and the role and characteristics of oxygen vacancies in the charge transport through dielectric process are not established yet. It is obvious that rate of change in structure of dielectric (namely the generation rate of oxygen vacancies associated with conductivity) in strong electric field is mainly determined by non-stationary processes of heat and mass transfer. Thus, the kinetics of such processes determines final morphology and properties of memristor. In the presented work we introduce thermodynamical model of filament growing when a current pulse of variable length and value flows. The model is the boundary value problem, which includes nonstationary heat conduction equation with non-linear Joule heat source, Poisson equation, and Shockley-Read-Hall equations taking into account strong electron-phonon interactions in trap ionization and charge transport processes. The charge current, which defines the heating in the model, depends on the rate of the oxygen vacancy generation. The latter depends on the local temperature. Kinetic parameters of our model are obtained from the transport and optical experiments and ab initiosimulations [V.A.Gritsenko, T.V.Perevalov, D.R.Islamov, Physics Reports 613, 1 (2016)]. The solution of the introduced problem allows us to describe the kinetics of the switch process and the final filament morphology. The resulting filamentary structure in turn may explain the memristor switch. End-to-end solution of the task allows us to develop recommendations for optimizing the memristor technology and predict the behavior of memristor arrays, including neuromorphic electronics and non-volatile large memory arrays. The work is supported by Russian Science Foundation (grant #16-19-00002).

Leakage Currents Mechanism in Thin Films of Ferroelectric Hf0.5Zr0.5O2

Hafnia was considered as a paraelectric material until observation of ferroelectric effect in thin films of doped HfO2 after high-temperature annealing (~1000°C). [T.S. Böscke et al., Appl. Phys. Lett. 99, 102903 (2011); S. Mueller et al., Adv. Function. Mater. 22, 2412 (2012)]. Of particular interest is the fact that ferroelectricity was also demonstrated in thin of the solid solution Hf0.5Zr0.5O2 which requires annealing at significantly lower temperatures [J. Müller et al., Appl. Phys. Lett. 99, 112901 (2011); J. Müller et al., Nano Lett. 12, 4318 (2012); M.H. Park et al., Appl. Phys. Lett. 102, 112914 (2013); A. Chernikova et al., Microelectron. Eng. 147, 15 (2015)]. Ferroelectricity in these materials is associated with the ability to stabilize noncentrosymmetric orthorhombic phase Pbc2 1 [J. Müller et al., Nano Lett. 12, 4318 (2012)]. It should be noted that the hafnia-based materials have a number of advantages over conventional ferroelectric regarding compatibility with technological processes used in microelectronics, and has already demonstrated their ability to provide very high density of elements. Taking into account advantages of the ferroelectric random access memory (FeRAM) as non-volatile, high-speed performance, high number of switching cycles, the discovery of ferroelectric effect in these materials gave an impetus for development of universal memory concept, which may lead to a significant breakthrough in the development of memory devices [M.H. Park et al., Adv. Mater. 27, 1811 (2015)]. An unsolved problem in the way of development of FeRAM-based universal memory is the spontaneous depolarization of the active medium, which leads to short data storage time (retention) that is observed in Ref. [C.-H. Cheng, A. Chin, IEEE Electron Dev. Lett. 35, 138 (2014)]. One of the possible reason of spontaneous depolarization is leakage currents through the ferroelectric thin films. High-κ Hf0.5Zr0.5O2 thin films (κ>16 depending on structure phase) can be used as sub-gate dielectrics in MOSFET and FinFET transistors instead of SiO2. Thus, it is very important to know charge transport mechanisms in thin dielectrics films to control the leakage currents for development of high quality memory devices. Purpose of the present work is to study charge transport mechanism in ferroelectric Hf0.5Zr0.5O2. Transport measurements were performed for TiN/Hf0.5Zr0.5O2/Pt structures. Test structure were fabricated with atomic layer deposition (ALD) technique. 10-nm-thick TiN layer was deposited on oxidized Si (100) substrate. Then the 10-nm-thick Hf0.5Zr0.5O2 films we deposited at 240°C from TEMAHf and TEMAZr precursors using H2O as oxygen source. Laser ellipsometry and Rutherford backscattering spectroscopy confirmed the thickness and stoichiometry of as deposited Hf0.5Zr0.5O2 films. Some samples were annealed at 400°C in N2 environment during 30sec (rapid thermal annealing, RTA). The crystalline structures of as deposited and annealed films were examined by symmetrical X-Ray diffraction (XRD). Pt top electrodes (thickness of ~30nm) were deposited through shadow mask with round holes (area is 7.1×104μm2) by electron beam evaporation on as deposited Hf0.5Zr0.5O2films and after RTA. The electronic structure of Hf0.5Zr0.5O2 was calculated within the spin polarized density functional theory using the ab initio simulation code Quantum ESPRESSO [P. Giannozzi et al., J. Phys.: Condens. Matter 21, 395502 (2009)] with B3LYP hybrid exchange-correlation functional. The oxygen vacancy was generated by the removal of an O atom, followed by relaxation of remaining atoms in 96-atom supercell. The XRD spectra of Hf0.5Zr0.5O2 films show that as deposited films have amorphous structure (a-Hf0.5Zr0.5O2), while annealed films are polycrystalline with monoclinic (P2 1/c), tetragonal (P4 2/nmc) and noncentralsymmetric orthorhombic (Pbc2 1) phases. The presence of ferroelectric properties of f-Hf0.5Zr0.5O2 films after RTA is confirmed by observing characteristic hysteresis on the P-V plate for Pt/ Hf0.5Zr0.5O2/TiN structures. Comparison of experimentally measured leakage currents-voltage dependencies at different temperatures (I-V-T) with Frenkel model of charged trap ionization returns overestimated value of dynamic permittivity with respect to predicted by ab initio calculations and underestimated value of frequency factor ν<<W/h (W is trap energy; h is the Planck constant). Phonon-assisted tunneling between traps describes experimental I-V-T with very good quantitative agreement with thermal and optical trap energies W t=1.25eV and W opt=2.5eV, respectively. The charge transport mechanism of leakage currents does not depend on crystal structure of Hf0.5Zr0.5O2 films. The only difference is charge trap density, which is lower in f-Hf0.5Zr0.5O2 (3×1019cm-3 with respect to 1×1020cm-3 in a-Hf0.5Zr0.5O2). Despite that ab initio calculations predict amphoteric nature of traps, C-V measurements on trapped charge accumulation demonstrate that mostly holes are involving in transport processes. The work was supported by the Ministry of Education and Science of the Russian Federation (project #RFMEFI57614X0065). Figure 1

Nature of traps responsible for the memory effect in silicon nitride

Nature of traps responsible for the memory effect in Si3N4 still remains the subject matter of much discussion. Based on our quantum chemical simulation results, Si–Si bonds can be identified as traps for electrons and holes with localization energies falling within the ranges of Wte=1.2−1.7 eV and Wth=0.9−1.4 eV. Within the multiphonon trap ionization model, our experimental data on Si3N4 conductivity have allowed us to evaluate the thermal ionization energies of electron and hole traps in Si3N4 as Wte=Wth=1.4 eV. The same value of 1.4 eV was obtained as half the Stokes shift of the 2.4 eV green photoluminescence line observed in Si3N4 films under excitation with 5.2 eV. Thus, the data obtained in the present study strongly suggest that Si–Si bonds are responsible for localization of electrons and holes in Si3N4.

Improved dielectric properties of CaCu3Ti4O12 films with a CaTiO3 interlayer on Pt/TiO2/SiO2/Si substrates prepared by pulsed laser deposition

We report the greatly improved dielectric properties of CaCu3Ti4O12 (CCTO) films with a 60 nm-thick CaTiO3 (CTO) interlayer on Pt/TiO2/SiO2/Si substrates. Both CCTO films and CTO interlayers were prepared by pulsed laser deposition (PLD). With increasing the thickness of CCTO from 200 nm to 1.3 μm, the dielectric constants (e r ) at 10 kHz in both CCTO single-layered and CCTO/CTO double-layered films increased from ∼260 to ∼6000 and from ∼630 to ∼3700, respectively. Compared with CCTO single-layered films, CCTO/CTO double-layered films irrespective of CCTO film thickness exhibited a remarkable decrease in their dielectric losses (tanδ) (<0.1 at the frequency region of 1 - 100 kHz) and highly reduced leakage current density at room temperature. The reduced leakage currents in CCTO/CTO double-layered films are attributable to relatively higher trap ionization energies in the Poole-Frenkel conduction model.

(Invited) The Influence of Defects on the Electronic Properties of Hafnia

Currently, high-κ dielectrics, such as hafnium oxide (hafnia) HfO2, zirconia, alumina etc. are replacing SiO2 - traditional dielectric in silicon devices. Among high-κ dielectrics the hafnia causes the greatest interest because it combines a wide band gap of E g=5.6-5.8eV, high permittivity κ=16-40, high thermal stability (melting point ≈2780°С), high thermodynamic stability in contact with silicon, and large energy barriers for electrons (2.0eV) and holes (2.5eV) with respect to the silicon [Robertson J, Wallace R M, Mater. Sci. Eng.: R: Reports 88, 1 (2015)]. Now, HfO2 is under intensively studied mainly due to its prospective application as high-κ gate dielectric in metal-oxide-semiconductor (MOS) field-effect transistors [Lee S J et al., J. Appl. Phys. 92, 2807 (2002)].In 2007, Intel Corporation implemented high-κ HfO2 as the gate dielectric in silicon devices of Intel Core family instead of SiO2. This phenomenon was called the revolution in microelectronics. Currently, hafnia replaces SiO2 in flash memory devices. Hafnia (pure, doped, and oxygen-deficient) attracts additional interest as a perspective candidate for nonvolatile resistive random access memory (ReRAM) and ferroelectric random access memory (FeRAM). Hafnia is widely used in optical and protective coatings in the production of special types of glass for fiber optic products.Hafnia has defects. The most thermodynamically favorable defects are oxygen vacancies (VO). The defects act as electron and hole traps and play a dual role in silicon devices. If HfO2 is used as a gate dielectric layer and the blocking elements in a flash memory, then the electrons capture on the oxygen vacancies (traps) and conductivity via traps will play negative roles, devices will degrade, reliability will reduce. At the same time, using the hafnia as the storage medium in the flash memory cell requires localization of electrons (and holes) at the traps to store information. Hence, understanding the nature of traps responsible for the electrons (and holes) localization and the charge transport is required to control the properties of HfO2-based electronic devices.According to quantum-chemical simulations, there are energy levels in the band gap for neutral and charged oxygen vacancies in HfO2 as shown in Fig.1: (a) [Xiong K et al., Appl. Phys. Lett. 87, 18350 (2005)], (b) [Gavartin J L et al., Appl. Phys. Lett. 89, 36 (082908)], and (c) [Broqvist P, Pasquarello A, Appl. Phys. Lett. 89, 262904 (2006)]. Indeed, XPS experiments and ab initio simulations show electron states at 3.3eV above the valence band ceiling (Fig.2) [Perevalov T et al., Microelectron. Eng. 109, 21 (2013)]. Optical transitions on the VO accord to blue photoluminescence (PL) band at 2.7eV [Ito T et al., J. Appl. Phys. 97, 054104 (2005)], which is excited by photons with energy near 5.2eV (PLE) [Perevalov T V et al., Appl. Phys. Lett. 104, 071904 (2014)] (Fig.3). The configuration coordination energy diagrams of optical transition on a neutral oxygen vacancy in hafnia is shown in Fig.4.The current through HfO2 in hafnia-based structures grows exponentially with increasing of the gate voltage and temperature. So, Fowler-Nordheim emission does not limit the current in HfO2. Many studies of the charge transport in HfO2 described experiment results by Poole-Frenkel (PF) mechanism. However, the fitting parameters, obtained by experimental data analysis in terms of PF model, are far from realistic values. E.g., either the frequency factor in 5-7 order lower than expected, or trap density in 13-16 orders lower than values obtained from CV measurements. It was shown [Islamov D R et al., Appl. Phys. Lett. 105, 222901 (2014)] that the charge transport in HfO2 is described by phonon-assisted tunneling between traps (PATT) in the bulk of HfO2 [Nasyrov K A, Gritsenko V A, J. App. Phys. 109, 093705 (2011)]. Found thermal trap energy of 1.25eV and optical trap energy of 2.5eV, obtained from analysis of experiment data with PATT model, do not depend on technique of HfO2 synthesis. Fig.5 shows experiment I-V characteristics with results of PATT calculations. Fig.6 shows configuration coordination energy diagram of trap ionization process on negative charged oxygen vacancy in hafnia. Despite the fact that obtained trap density is ~1019-1020cm-3, CV measurements shows that trapped charge density is ~5×1018cm-3 [Islamov D R et al., Appl. Phys. Lett. 105, 222901 (2014); Lu W-T et al., Appl. Phys. Lett. 85, 3525 (2004)]. This phenomenon can be explained by the Coulomb repulsion of charge carriers, leading to the Wigner crystallization of trapped electrons (holes) to form a hexagonal glassy structure [Shaimeev S S, Gritsenko V A, Wong H, Appl. Phys. Lett. 96, 263510 (2010)].

Leakage current behavior of BiFeO3/BiMnO3 multilayer fabricated by pulsed laser deposition

The temperature dependence of the J–E characteristics of BiFeO3/BiMnO3 (BFO/BMO) multilayer thin film on LaNiO3/Si substrate was studied in the temperature range from 300K to 450K. In the light of different models the leakage behavior of BFO/BMO multilayer thin film was analyzed, which indicates the dominant leakage mechanism is Poole–Frenkel mechanism in the medium field region from 50 to 350kV/cm. With this Poole–Frenkel emission type conduction, the trap ionization energy range of ∼0.49 to 0.57eV was calculated. At higher applied electric fields the conduction is space charge limited where as Ohmic conduction is the dominant mechanism in the lower electric field region for all the temperatures in the given range. Such analysis of leakage current in multilayer thin film eases interface engineering of heterostructures for FeRAM applications.

Charge carrier transport mechanism in high-κ dielectrics and their based resistive memory cells

Current-voltage characteristics of thin dielectric films of HfO x in p-Si/HfO x /Ni structures are analyzed. Experimental results are compared with various theoretical models: the Poole-Frenkel trap ionization model, the multiphonon trap ionization model, and the Schottky effect at the Ni/HfO x interface. It is shown that in spite of the good qualitative description of the experimental results by all models, only the multiphonon trap ionization model provides a quantitative description of the data..

The effects of deep level traps on the electrical properties of semi-insulating CdZnTe

Deep level traps have considerable effects on the electrical properties and radiation detection performance of high resistivity CdZnTe. A deep-trap model for high resistivity CdZnTe was proposed in this paper. The high resistivity mechanism and the electrical properties were analyzed based on this model. High resistivity CdZnTe with high trap ionization energy Et can withstand high bias voltages. The leakage current is dependent on both the deep traps and the shallow impurities. The performance of a CdZnTe radiation detector will deteriorate at low temperatures, and the way in which sub-bandgap light excitation could improve the low temperature performance can be explained using the deep trap model.

Transport mechanisms of electrons and holes in dielectric films

Electron and hole transport mechanisms in amorphous silicon oxide, silicon nitride, and aluminum oxide, dielectric materials of high relevance to silicon device technology, are reviewed. It is established that the widely accepted Frenkel model provides a formal description of transport in trap-containing insulators, but nonphysical model parameters must be introduced in order to obtain quantitative agreement. It is shown that the multiphonon model of trap ionization consistently describes charge transport in insulators with traps.

Analysis of Charge-Pumping Data for Identification of Dielectric Defects

We introduce a data analysis methodology for multifrequency charge-pumping (CP) measurements, which allows extracting both spatial and energy profiles of the CP-active traps in the gate dielectrics along with the defect energy characteristics. The analysis is based on the charge trapping/detrapping model accounting for carriers tunneling between the substrate and the oxide traps and multiphonon-assisted structural trap relaxation associated with charge carrier localization in the trap. Comparison of the spatial and energy trap distribution profiles obtained from CP data collected on a set of high-k dielectric gate stacks of different thicknesses facilitate the calibration of the model parameters. Extraction of the bulk trap characteristics, including trap ionization and relaxation energies, extends the utility of the CP technique from quantifying defect density toward identifying the nature of defects in the dielectric.

Photo- and thermostimulated luminescence of ZnO nanowires

This is a study of the low-temperature photo- and thermostimulated luminescence of zinc oxide nanowires produced by gas-transport reactions. The parameters of the electron trapping centers are determined: trap ionization energy 0.53 ± 0.03 eV, electron capture cross section 4.7∙10–17 cm2, and frequency factor 1.1∙104 s–1. It is found that defects of the crystalline structure, such as interstitial zinc atoms, control the formation of the “green” emission band.