Multiphonon Ionization Research Articles

Carrier Recombination in Nitride-Based Light-Emitting Devices: Multiphonon Processes, Excited Defects, and Disordered Heterointerfaces.

We study recombination processes in nitride LEDs emitting from 270 to 540 nm with EQE ranging from 4% to 70%. We found a significant correlation between the LEDs' electro-optical properties and the degree of nanomaterial disorder (DND) in quantum wells (QWs) and heterointerfaces. DND depends on the nanoarrangement of domain structure, random alloy fluctuations, and the presence of local regions with disrupted alloy stoichiometry. The decrease in EQE values is attributed to increased DND and excited defect (ED) concentrations, which can exceed those of Shockley-Read-Hall defects. We identify two mechanisms of interaction between EDs and charge carriers that lead to a narrowing or broadening of electroluminescence spectra and increase or decrease EQE, respectively. Both mechanisms involve multiphonon carrier capture and ionization, impacting EQE reduction and efficiency droop. The losses caused by these mechanisms directly affect EQE dependencies on current density and the maximum EQE values for LEDs, regardless of the emission wavelength. Another manifestation of these mechanisms is the reversibility of LED degradation. Recombination processes vary depending on whether QWs are within or outside the space charge region of the p-n junction.

PHYSICAL MODEL OF TEMPORARY CURRENT INSTABILITY IN ION- SELECTIVE FIELD-EFFECT TRANSISTORS WITH SILICON OXIDE/NITRIDE DIELECTRIC LAYERS

The work is devoted to the study of the instability (drift) of the threshold voltage of p-channel ion selective field- effect transistors (ISFET) with an induced channel, caused by the long-term effect of a negative voltage applied to the channel section of the transistor through a double- layer dielectric SiO2/Si3N4. Based on the obtained experimental data, a physical model of the observed instability is proposed, according to which it is caused by the process of accumulation of an unbalanced positive charge in the near-surface layer of silicon nitride. The mechanisms of Pool–Frenkel superbarrier ionization and multiphonon ionization of deep centers are involved in the quantitative calculation of model parameters. Design and technological improvements are outlined that can improve the stability of ISFET sensors for long-term continuous measurements in solutions.

Моделирование поверхностно-объемного заряжения диэлектрика электронами с энергией от 6 до 30 keV

The physico-mathematical model applied to ground tests for geomagnetic plasma exposure based on the combined consideration of surface and bulk processes of transport and charge accumulation for calculating the kinetics of charging high-resistance dielectrics irradiated by medium-energy monoenergetic electrons (from 6 to 30 keV) is proposed. The model takes into account the contribution to the charging of the dielectric by the trains of longitudinal optical phonons generated by each thermalizing primary electron with energy below the band gap of the dielectric, which supplements the induced conduction current due to the generation of electron-hole pairs. As a result, the current induced by trains of longitudinal optical phonons of the tunnel conductivity through free electron traps is introdused, as well as the current induced in the conduction band due to multiphonon ionization the electron traps by trains of longutudinal optical phonons in the region of existence of electric field. Using the example of the α-Al2O3 (sapphire) dielectric, the results of computer simulation of the internal currents distributions, charges, and electric field in the dielectric with the open surface irradiated by monoenergetic electrons with energies from 6 to 30 keV are presented according with the achievement the quasi-equilibrium in the irradiated part of the dielectric and with switching of the energy of primary electrons during the irradiation process.

Multiphonon trap ionization mechanism in amorphous SiNx

The charge transport mechanism in amorphous silicon nitride (a-SiNx) is experimentally analyzed in a wide range of electric fields and temperatures. The Frenkel effect with thermally assisted tunneling (TAT) and the multiphonon mechanism were used to describe the trap ionization. It is shown that the widespread Frenkel effect with TAT formally describes the experiment, but the agreement with the experiment is obtained if a small frequency factor (109 s−1) and a large tunneling effective mass (m*=3m0) are used. Thus, the Frenkel effect does not describe the charge transport in a-SiNx. The charge transport in a-SiNx is satisfactorily described by the multiphonon trap ionization mechanism with the following parameters: m* = 0.6m0, thermal and optical energies - WT = 1.6 eV and WOPT = 3.2 eV, respectively.

Current Filamentation and Switching Effect in Chalcogenide Glassy Semiconductors: A Review

A review on current filamentation and switching effect in chalcogenide glassy semiconductors (CGSs), which are promising materials for the development of phase change memory devices, is presented. First, a history of the research on CGSs and their properties is considered. Next, formation of a current filament in CGSs is discussed and the scale of heat release in the material as well as the geometric shape of the filament is analyzed. Finally, various hypotheses developed for the explanation of the switching effect in CGSs are reviewed. It is shown that the most relevant model of the switching effect in CGS is the model of multi-phonon tunneling ionization of the so-called ‘negative-U centers’. This model is based on the assumption that an avalanche-like increase in current at a certain point in time is associated with mass tunneling of electrons located on atoms, occuring due to thermal vibrations of atoms.

The charge transport mechanism in amorphous boron nitride

The charge transport mechanism in thick film (~ 100 nm) amorphous boron nitride (a-BN) was studied experimentally and theoretically. Applying the experiments on the injection of minor carriers of n- and p-type silicon, the contribution of electrons and holes to the a-BN conductivity in the Si/BN/Al structure was determined. It was established that electrons and holes contribute to the a-BN conductivity, i.e. the a-BN conductivity is two-band. In a broad range of electric fields and temperatures, the charge transport in a-BN is satisfactorily described in the framework of the multiphonon trap ionization theory with thermal WT = 1.0 eV and optical Wopt = 2.0 eV trap ionization energies, respectively.

Optical properties and charge transport of textured Sc2O3 thin films obtained by atomic layer deposition

Scandium oxide films with thickness d = 20–100 nm were deposited by atomic layer deposition (ALD) using tris(methylcyclopentadienyl) scandium (III) Sc(MeCp)3 and water vapors as precursors at reactor temperature range of 200–400 °C. The ALD-window was detected in the range of 230–370 °C. Growth per cycle remained constant and was 0.080–0.084 nm/cycle in this range. O/Sc ratio was found to be 1.49 which is close to stoichiometric Sc2O3. The films were polycrystalline. The grains were more apparent for the films grown at higher temperatures. The grain size increased with thickness. Cubic Sc2O3 phase was determined by FTIR, Raman spectroscopy and X-rays diffraction.In general, different crystallographic directions are more preferential for different process conditions. Films were textured and their growth occurred mainly in the (400) direction. The refractive index dispersions of deposited films were well described by the Cauchy model. Optical properties depended weakly on process parameters (temperature or thickness). As it was detected for the films with close thickness the refractive index slightly increased with deposition temperature increase. The Nasyrov-Gritsenko (N-G) multiphonon trap ionization model well describes the charge transport. The trap parameters were determined to be: concentration N = 1.5 × 1019 cm−3, thermal energy Wt = 0.83 eV, and optical energy Wopt = 1.66 eV.

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.

Charge transport-accumulation in multilayer structures with Si3N4 and thick(5.5 nm) SiO2

Double-injection, transport, and accumulation of charge in metal-thick oxide-nitride-silicon and silicon-tunnel oxide-nitride-thick oxide-silicon structures have been theoretically studied. Calculation results were compared to experimental results. The charge transport in Si3N4 is quantitatively described assuming the multiphonon ionization theory of neutral traps with a capture cross-section less than 10−14 cm2. With traps amphoterism taken into account, the calculation predicts the existence of a layer with their excessive concentration near the SiO2/Si3N4 interface. The model satisfactorily describes the write/erase characteristics in silicon-oxide-nitride-oxide-silicon-structures from Bu and White (Solid-State Electron. 45, 113 (2001)).

Thermal ionization decay of E′ centers in germanium dioxide

The thermally induced decay of oxygen-deficient E′ centers in GeO2 glasses and ceramics has been studied experimentally and theoretically. The electron emission effect, which accompanies the thermally induced decay of these defects, has been interpreted based on the Perel’-Karpus model for the multiphonon ionization of centers in an electric field. It has been established that the decay of E′ centers in amorphous and crystalline modifications of GeO2 is reversible and occurs according to the thermal ionization mechanism.

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..

Physics of Switching and Memory Effects in Chalcogenides

A review of the main experimental features of switching and memory effects in chalcogenide glassy semiconductors (CGS), review and analyze of the models of these phenomena was done. An electronic-thermal model of the switching effect taking into account multiphonon tunnel ionization of negative-U centers and heating is presented. The model fits experimental current-voltage characteristics of a GeSbTe films both in ohmic and exponential regions. Also the model is in good agreement with experimental dependences of threshold voltage and threshold current on temperature and thickness. This indicates that multiphonon tunnel ionization of negative-U centers and heating is the most probable mechanism of the switching effect.

Interpretation of experimental dependencies of the switching effect in GeSbTe

AbstractAn electronic–thermal model of the switching effect in chalcogenide glassy semiconductors (CGSs) is investigated. The model fits the experimental current–voltage characteristics (CVC) of GeSbTe films in both the ohmic and exponential regions. Also, the model is in good agreement with the experimental dependences of threshold voltage and threshold current on temperature and thickness. The results indicate that multiphonon tunnel ionization (MTI) of negative‐U centers and heating is a possible mechanism for the CVC nonlinearity and the switching effect in chalcogenides.

Multiphonon ionization of traps formed in hafnium oxide by electrical stress

AbstractWe have investigated behavior of traps formed in hafnium oxide (HfO2) by electrical stress and their influence on the charge carrier transport through Si/SiO2/HfO2/poly‐Si nanostructures. The traps govern the transport process assuming a capture of charge carriers followed by their ionization via the multiphonon transition mechanism. The multiphonon transitions via the Poole–Frenkel effect or electron tunneling as well as the multiphonon tunneling ionization of neutral traps have been carefully considered for charged traps. We also provide a set of parameters including the trap concentration, ionization energy, the frequency factor, the effective mass of charge carriers, optical energy, and phonon energy in order to reproduce and reasonably fit available experimental data.

Mechanism of GeO2 resistive switching based on the multi-phonon assisted tunneling between traps

Model of evenly distributed traps in bulk dielectric is proposed for the resistive memory switching mechanism. Switching from high resistance to the low resistance state is explained by several-fold increase in trap concentration after the application of switching voltage. Both high and low resistance conductivities are governed by multi-phonon ionization and tunneling between neighboring traps. Thermal trap energy for oxygen vacancy and electron effective mass for crystal α-GeO2 were calculated using density functional theory and used for the fitting of our charge transport model of resistive memory. The model was verified on the TaN-GeO2-Ni structure with good semi-quantitative agreement with experiment.

Modeling the charge transport mechanism in amorphous Al 2O 3 with multiphonon trap ionization effect

The charge transport mechanism in amorphous alumina, Al 2O 3, is investigated both theoretically and experimentally. We found that the experimental current–field–temperature dependencies can hardly be understood based on the commonly used Frenkel effect or the thermally-assisted tunneling model. Instead, we suggest that the charge transport in Al 2O 3 is related to the ionization of the deep trap by multiphonon tunneling. Excellent agreements between the predicted, the measured data were obtained by using the proposed multiphoton model with the following values of trapping parameters: thermal ionization energy of 1.5 eV, optical ionization energy of 3.0 eV, phonon energy of 0.05 eV, electron effective mass of 0.4 m e . The density of electron trap and electron capture cross-section of neutral traps are 2 × 10 20 cm −3 and 5 × 10 −15 cm 2, respectively.

Nonlinearity of current-voltage characteristics of chalcogenide glassy semiconductors, caused by multiphonon tunnel ionization of negative-U-centers

The behavior of negative-U-centers in high electric fields was considered. It was shown that multiphonon tunnel ionization of negative-U-centers in chalcogenide glassy semiconductors results in a significant increase in the number of conduction electrons, hence, to highly nonlinear current-voltage characteristics. This nonlinearity mechanism well explains the experimentally observed current-voltage characteristic of chalcogenide glassy semiconductors currently used as memory cells.

Multiphonon mechanism of the ionization of traps in Al2O3: Experiment and numerical simulation

Charge transfer in Al2O3 has been investigated experimentally and theoretically. The experimental results are in qualitative agreement with the theory of the multiphonon ionization of deep centers. The thermal (WT = 1.5 eV) and optical (Wopt = 3.0 eV) energies of the deep centers have been determined. It has been found that the experimental data are unsatisfactorily described by the Pool-Frenkel mechanism, which provides a non-physically small frequency factor and anomalously large effective tunneling mass.

Charge transport mechanism in amorphous alumina

The charge transport mechanism in amorphous Al2O3 was examined both experimentally and theoretically. We have found that electrons are dominant charge carriers in Al2O3. A satisfactory agreement between the experimental and calculated data was obtained assuming the multiphonon ionization mechanism for deep traps in Al2O3. For the thermal and optical trap ionization energies in Al2O3, the values WT=1.5 eV and Wopt=3.0 eV were obtained.

The charge transport mechanism in silicon nitride: Multi-phonon trap ionization

The charge transport mechanism in amorphous silicon nitride, Si 3N 4, was experimentally examined to compare measured data with theoretical calculations made within the Frenkel model and the multi-phonon model of trap ionization. A good agreement between the experimental data and theoretical predictions could be achieved assuming the multi-phonon mechanism to be in effect. The widely accepted Frenkel model, although capable of explaining the measured data, fails to yield realistic values of the electron tunnel mass and attempt-to-escape factor.