Deep Trap Energy Research Articles

The coupling effect of interfacial traps and molecular motion on the electrical breakdown in polyethylene nanocomposites

Low-density polyethylene (LDPE) based nanocomposites are capable of suppressing the accumulation of space charges and enhancing the resistivity and electrical breakdown strength, which are beneficial for the performance and reliability of high voltage direct current power cables. Incorporating nanofillers into polymers can form interfacial regions inside and affect both the trap distribution and molecular motion characteristics, resulting in changes in the dielectric properties of polymer nanocomposites. To unravel the influencing mechanism of interfacial traps and molecular motion on the dc electrical breakdown strength, we investigate the dc electrical breakdown properties of LDPE/Al2O3 nanocomposites as a function of nanofiller loading, pressure, ramping rate of voltage, and sample thickness by experiments and simulations of the charge transport and molecular displacement modulated electrical breakdown. Experimental and simulation results are consistent and show that dc electrical breakdown strength increases firstly and then decreases with the increase of nanofiller loading, increases monotonically with increasing pressure and ramping rate of voltage, and decreases with the increase in sample thickness, obeying an inverse power law. It is indicated that the dc electrical breakdown of LDPE/Al2O3 nanocomposites is triggered by the local current and energy multiplication caused by charge carriers jumping over deep traps when they gain sufficient energy in the enlarged free volume via molecular displacement. It is concluded that both the increase in deep trap energy and the restraint of the motion dynamics of molecular chains with occupied deep traps can enhance the dc electrical breakdown strength of LDPE/Al2O3 nanocomposites.

Nanoscale-trap-modulated electrical degradation in polymer dielectric composites using antioxidants as voltage stabilizers

Electrical degradation is critical in polymer dielectric composites for increasing the upper voltage limit in today's harsh-environment electrical and electronic applications. Here, an attractive potential method for extending the electrical degradation durability by using antioxidants as voltage stabilizers is reported, which introduces efficient charge traps (or localization states) between the conduction and valence bands of polymer dielectric composites. The origin and mechanism of charge traps are identified in terms of the antioxidants' electronic structures via density functional theory calculations. When the trap sites are on the nanoscale (>1 nm) and have large deep trap energy levels, they can play an essential role in trapping charges in the free volume of the amorphous regions. According to the results of an electrical tree experiment, electrical degradation is substantially restrained by incorporating antioxidants into polymer dielectric composites. By investigating the charge migration in electron and hole trap sites, the polarity differences in electrical degradation are fully distinguished. The main characteristics of electrical degradation inhibition are identified, thereby offering a new approach for realizing high-performance polymer dielectric composites by improving electrical degradation resistance.

Surface Discharge Property of Polypropylene/BN Nanocomposite for HTS Apparatus Application

Surface discharge can lead to the failures of insulation materials in LN2, especially when the bubbles are generated during the quenching process. In this paper, the surface discharge properties of polypropylene (PP)/boron nitride (BN) nanocomposites were investigated in the normal and quench conditions. The results showed that the surface discharge voltage was improved in the normal condition as the BN filler content was increased from 5 wt% to 10 wt%. But it was reduced as the BN filler content was 15 wt%. As the filler content was less than 10 wt%, the free charges were captured by traps, which were with deeper trap energy level. In quench condition, the bubbles were decreased as the BN filler content increased, which were associated with the higher thermal conductivity of BN to rapidly release the joule heat. Therefore, the surface discharge voltage was increased with the BN filler content. The research has the potential to restrain the surface discharges and extent the lifetime of insulation materials in high-temperature superconducting devices.

Temperature‐dependent surface charge and discharge behaviour of converter transformer oil–paper insulation under DC voltage

Ambient temperature has significant influence on properties of oil–paper insulation, which makes surface discharge process complex. This paper aims at revealing the influence mechanism of ambient temperature on surface charge and discharge behaviours under DC voltage. The oil–paper with thickness of 0.08 mm was used and the ambient temperature varies from 20 to 80°C in this paper. The results of surface potential decay (SPD) experiments show that the initial surface potential declines and the process of SPD is accelerated with increasing temperature because of higher carrier mobility. Additionally, both shallow and deep trap energy level become deeper, the shallow trap density is enlarged while the deep trap density is shrunken at higher temperature. The surface discharge tests were performed and Weibull results indicate that it is prone to occurring surface discharge at higher ambient temperature. The possibility of surface discharge under negative voltage is larger than that under positive voltage because of polarity effect. It is concluded that more carriers escape from deep traps to participate in the procedure of surface discharge at higher temperature, which declines the surface discharge voltage.

New Method for Shallow and Deep Trap Distribution Analysis in Oil Impregnated Insulation Paper Based on the Space Charge Detrapping

Space charge has close relation with the trap distribution in the insulation material. The phenomenon of charges trapping and detrapping has attracted significant attention in recent years. Space charge and trap parameters are effective parameters for assessing the ageing condition of the insulation material qualitatively. In this paper, a new method for calculating trap distribution based on the double exponential fitting analysis of charge decay process and its application on characterizing the trap distribution of oil impregnated insulation paper was investigated. When compared with the common first order exponential fitting analysis method, the improved dual-level trap method could obtain the energy level range and density of both shallow traps and deep traps, simultaneously. Space charge decay process analysis of the insulation paper immersed with new oil and aged oil shows that the improved trap distribution calculation method can distinguish the physical defects and chemical defects. The trap density shows an increasing trend with the oil ageing, especially for the deep traps mainly related to chemical defects. The greater the energy could be filled by the traps, the larger amount of charges could be trapped, especially under higher electric field strength. The deep trap energy level and trap density could be used to characterize ageing. When one evaluates the ageing condition of oil-paper insulation using trap distribution parameters, the influence of oil performance should not be ignored.

Localizing and analyzing defects in AlGaN/GaN HEMT using photon emission spectral signatures

Abstract This paper presents a reliability study of an AlGaN/GaN high electron mobility transistor (HEMT) by the photon emission (PE) and the spectral photon emission (SPE) techniques. The backside PE analysis of the studied AlGaN/GaN HEMT identifies PE signatures at the gate foot edge on the drain side, and at two new positions: under the middle of the gate or at the gate foot edge on the source side. The SPE analysis of the localized signatures defines the deep level trap energy Ec—1.35 eV which seems to be related to an interstitial carbon defect that forms along dislocations, or an omnipresent defect such as C or possibly dislocations.

Identification of deep trap energies and influences of oxygen plasma ashing on semiconductor carrier lifetime

We have performed an analytical study of the effects of oxygen plasma ashing processes in semiconductor device fabrication and its impact on minority carrier lifetime in high voltage semiconductor devices. Our work includes a critical background study of life time killing mechanisms by deep traps imparted into the semiconductor by barrel plasma ashing. The Elymat technique provides the opportunity to measure lifetime and diffusion length of minority carriers and surface photo voltage (SPV) measurement was used to analyse influences of process parameters such as photoresist, time budget and positioning in the process chamber. It was shown that in microwave plasma processes the diffusion length changes severely with tempering at 200 °C, whereas RF-plasma processes show a significant process time-dependence. Batch tools in general suffer from a strong first wafer effect which could be correlated with the static electrical parameters of the semiconductor devices. The trap identities were detected by using deep level transient spectroscopy and the chemical species of the traps has been proven by inductive coupled plasma mass spectrometry. The deep-bandgap trap energies are reliable fingerprints of the chosen process parameters such as process time and of resist-influences. By microwave plasma processes intrinsic Fe and FeB-complex levels were identified and a good agreement with the SPV-measurement and electrical device characteristic was shown. RF-plasma processes impart levels attributed to Pt levels and an additional level, which could be identified as a trap level probably forming a complex of Pt and H.

Preparation of Sr2MgSi2O7:Eu2+, Dy3+ nanofiber by electrospinning assisted solid-state reaction

Novel one-dimensional polyvinylpyrrolidone (PVP)/[Sr(NO3)2 + Mg(NO3)2 + TEOS + Eu(NO3)2 + Dy(NO3)2] composite fibers were prepared via electrospinning, and then it was calcined at high temperature to fabricate the long-persistent luminescence Sr2MgSi2O7:Eu2+, Dy3+ nanofiber by solid-state reaction under a reducing atmosphere. X-ray diffraction, Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy and fluorescence spectrophotometer as well as afterglow brightness tester were used to characterize the resulting samples. The results revealed that diameter of the composite nanofibers decreased firstly and then increased with the increasing of the calcination temperature. FTIR analysis manifested that there was two new absorption peaks around 660 and 834 cm−1, which corresponded to Mg–O stretching and Sr–O stretching, when PVP/[Sr(NO3)2 + Mg(NO3)2 + TEOS + Eu(NO3)2 + Dy(NO3)2] composite nanofibers was calcined at the temperature of 1,100 °C, indicating that the crystalline Sr2MgSi2O7:Eu2+, Dy3+ had formed. Furthermore, its luminescence properties were tested. Upon excitation in the UV region, the emission spectra consisted of broad emission band, and the emission peak was located at the wavelength of 468 nm. Decay process contained both rapid-decaying and the slow-decaying processes, which due to the short survival time of the electro in Eu2+ and the deep trap energy center of Dy3+.

Suppression of reverse recovery surge voltage of silicon power diode by adjusting trap energy levels through local lifetime control

To suppress the reverse recovery surge voltage of silicon power diodes, the effects of adjusting trap energy levels through local lifetime control were investigated by device simulation and theoretical analysis of the Shockley–Read–Hall (SRH) model. In general, local lifetime control techniques localize carrier traps at the anode side of a diode and optimize the carrier lifetime profile to suppress surge voltage. However, the suppression effect of a certain localized trap density distribution on surge voltage varies with a change in trap energy level, even if the trap density distribution is the same. It became clear that deep trap energy levels suppress surge voltage more than shallow trap energy levels at 1000 A/cm2 or less. Thus, deep trap energy levels such as Et − Ei = 0.0–0.2 eV are favorable for suppressing surge voltage in almost all power devices.

Conduction of (Na,Ce) doped Bi5Ti3FeO15 ceramics after different annealing processes

Bi5−xNax/2Cex/2Ti3FeO15 (BNTF-100x, x = 0, 0·05, 0·10, 0·20, 0·30, 0·40 and 0·60) ceramics were prepared via solid state sintering process. With x increasing, the resistivity increases at first and then decreases. The lower the concentration of oxygen vacancies, caused by more (Na,Ce) dopant adding, the less the deep trap energies in the band gap for the activated electrons to be mobile. For the samples containing high concentration of oxygen vacancies, the conductivities are higher when they are annealed in the air and oxygen than that in the vacuum. On the contrary, for the samples containing low concentration of oxygen vacancies, the conductivities of the samples in different annealing conditions behave quite the same way. Most (Na,Ce) doped Bi5Ti3FeO15 ceramics exhibit intrinsic conduction at high temperatures with corresponding activation energies of 1·1–1·6 eV, while the extrinsic conduction has a close relationship with the concentration of oxygen vacancies and the activation ability of electrons.

Effects of Trap Levels on Reverse Recovery Surge of Silicon Power Diode

In this paper, we report on the effects of trap energy levels on the reverse recovery surge, for the first time. The different current and temperature dependences of the reverse recovery surge with shallow and deep trap energy levels were measured. Results of simulations of current and temperature dependences of the reverse recovery surge with different trap energy levels were similar to measurement results. Through numerical and theoretical analyses based on the Shockley–Read–Hall (SRH) model, it was confirmed that variations in recombination rate due to different trap energy levels affect the current and temperature dependences of the reverse recovery surge. We found that in order to achieve a soft recovery in the design of silicon power diodes, the trap energy levels play a crucial role along with the carrier lifetime profile.

Field Dependent Carrier Transport Mechanisms in Metal-Insulator–Metal Devices with Ba0.8Sr0.2TiO3/ ZrO2 Heterostructured Thin Films as the Dielectric

ABSTRACTBa0.8Sr0.2TiO3/ZrO2 heterostructured thin films with different individual layer ZrO2 thicknesses are deposited on Pt/Ti/SiO2/Si substrates by a sol-gel process. The current versus voltage (I-V) measurements of the above multilayered thin films in metal-insulator-metal (MIM) device structures are taken in the temperature range of 310 to 410K. The electrical conduction mechanisms contributing to the leakage current at different field regions have been studied in this work. Various models are used to know the different conduction mechanisms responsible for the leakage current in these devices. It is observed that Poole-Frenkel mechanism is the dominant conduction process in the high field region with deep electron trap energy levels (φt) whereas space charge limited current (SCLC) mechanism is contributing to the leakage current in the medium field region with shallow electron trap levels (Et). Also, it is seen that Ohmic conduction process is the dominant mechanism in the low field region having activation energy (Ea) for the electrons. The estimated trap level energy varies from 0.2 to 1.31 eV for deep level traps and from 0.08 to 0.18 eV for shallow level traps whereas the activation energy for electrons in ohmic conduction process varies from 0.05 to 0.17 eV with the increase of ZrO2 sub layer thickness. An energy band diagram is given to explain the dominance of the various leakage mechanisms in different field regions for these heterostructured thin films.

Investigating minority carrier trapping in n-type Cz silicon by transient photoconductance measurements

Minority carrier trapping was investigated in n-type Cz silicon by means of transient-photoconductance (PCD). A simplified Hornbeck and Haynes model was developed for fitting results from transient-PCD to calculate trap density, and it was found to be identical to the model developed for quasi-steady-state photoconductance technique. This indicates that the model can be applied to all photoconductance techniques for lifetime measurement. The results revealed that the trap density is dependent on the concentration of interstitial oxygen and thermal donors, indicating a good agreement with reported results and the results from annealing experiments in this work. Meanwhile, a deep trap energy level was revealed, probably implying that traps also act as recombination centers in n-type silicon. By studying detrapping processes, the concentration of the trapped holes was found to decrease exponentially with time, resulting in a detrapping constant of 167 s.

Luminescent Properties, Afterglow Behavior and Thermoluminescence Characteristics of (Eu, Dy) Doped Sr<sub>3</sub>Al<sub>2</sub>O<sub>6 </sub>Phosphors

(Eu, Dy) doped Sr3Al2O6 phosphors with high brightness and long afterglow were achieved by a high-temperature solid state reaction. Luminescence measurements indicate that the phosphor Sr3Al2O6:Eu prepared in normal atmosphere exhibits a sharp orange emission peaking at 591 nm excited by 221nm light, which is intrinsic f-f transition generated from Eu3+. Whereas, the phosphors Sr3Al2O6:Eu and Sr3Al2O6:Eu,Dy prepared in a weak reducing atmosphere show both a sharp orange emission peaking at 591nm excited by 221-nm light and a broad green emission peaking at 510nm excited by 328nm light, which resulted from Eu2+ transition between 4f65d1 and 4f7 electron configurations. The investigation results suggest that Eu3+ and Eu2+ co-exist in Sr3Al2O6 matrix synthesized in weak reducing atmosphere. In all samples, only Sr3Al2O6: Eu, Dy prepared in a weak reducing atmosphere has high intensity afterglow after excited by the UV source. The decay curve of Sr3Al2O6: Eu, Dy phosphor contains the rapid-decaying process and the slow-decaying process and can be fitted by a bi-exponential decay function. The measurement of thermal simulated luminescence demonstrates that only appropriate deep trap energy level and high trap concentration can generate optimum long-afterglow performance.

Investigation of Ti-doped Gd2O3 charge trapping layer with HfO2 blocking oxide for memory application

In this study, Ti-doped gadolinium oxide (Gd2TiO5) is investigated by X-ray diffraction, atomic force microscopy, and capacitance voltage curves (C–V) as the charge trapping layer in metal-oxide-high-k material-oxide-silicon structure memories. It was found that the Gd2TiO5 charge-trapping layer with an HfO2 blocking layer annealed at 900°C had a larger window of 4.8V in the C–V hysteresis loop, a faster program/erase speed and good retention without significant drift up to 104cycles. This excellent performance was attributed to the well-crystallized Gd2TiO5 structure and the higher probability of charges being trapped in the deep trap energy level of the Gd2TiO5. This Gd2TiO5 memory device with post-annealing shows considerable promise for use in future flash memory applications.

Electrical characteristics and TDDB breakdown mechanism of N 2-RTA-treated Hf-based high-κ gate dielectrics

This study investigates the effects of rapid thermal annealing (RTA) in nitrogen ambient on HfO 2 and HfSiO x gate dielectrics, including their electrical characteristics, film properties, TDDB reliability and breakdown mechanism. The optimal temperature for N 2 RTA treatment is also investigated. The positive oxide trap charges (oxygen vacancies) in HfO 2 and HfSiO x dielectric films can be reduced by the thermal annealing, but as the annealing temperature increased, many positive oxide trap charges (oxygen vacancies) with shallow or deep trap energy level will be formed in the grain boundaries, degrading the electrical characteristics, and changing the breakdown mechanism. We believe that variation in the number of positive oxide trap charges (oxygen vacancies) with shallow or deep trap energy levels is the main cause of the CV shift and difference in the breakdown behaviors between HfO 2 and HfSiO x dielectrics. With respect to CV characteristics and TDDB reliability, the optimal temperature for N 2 RTA treatment is in the range 500–600 °C and 800–900 °C, respectively.

A Robust Data Retention Characteristic of Sol–Gel-Derived Nanocrystal Memory by Hot-Hole Trapping

A new sol-gel-derived TixZrySizO nanocrystal (NC) memory with a high-performance data retention characteristic is demonstrated by the hot-hole-trapping method. Prior to rapid thermal annealing, the high-density NC layer is formed by depositing a well-mixed solution of titanium tetrachloride, silicon tetrachloride, and zirconium tetrachloride. The electrical properties of the sol-gel-derived NC memory are demonstrated in terms of memory window, charge retention, program speed, and endurance. The memory window of the NC memory from the novel hot-hole-trapping mechanism can be achieved up to 4.18 ± 0.21 V, and long retention times obtained from extrapolation up to 106 s are observed as 8%, 13%, and 21% window narrowing under respective temperatures of 25 °C, 85 °C, and 125 °C. The good electrical performance is attributed to the contribution of the high density of isolated NCs and hole-trapped into the deep-trap energy level, so no significant lateral and vertical charge leakage occurs.

Extraction of trap energy and location from random telegraph noise in gate leakage current (Ig RTN) of metal–oxide semiconductor field effect transistor (MOSFET)

Study of random telegraph noise in gate leakage current (Ig RTN) through thin gate oxide (2.6nm) as well as drain current random telegraph noise (Id RTN) has been conducted in MOSFET. RTN having two discrete current levels was observed in gate leakage current. Capture and emission time constants of Ig fluctuation were found to depend on drain voltage as well as gate voltage. Capture time showed an increase while emission time showed a decrease with respect to gate voltage. New equations for extracting trap locations and its energy level were derived. The oxide trap extracted from Ig fluctuation was observed to react with the gate and have a deep trap energy level from the conduction band edge of oxide.

Resonance energy transfer based on shallow and deep energy levels of biotin-polyethylene glycol/polyamine stabilized CdS quantum dots

Fluorescent resonance energy transfer between the poly(ethylene glycol)-b-poly(2-(N,N-dimethylamino)ethyl methacrylate) stabilized CdS quantum dots (QDs) and texas-red streptavidin was observed. We propose a four-state model to explain photoluminescence (PL) process of CdS QDs and suggest that there are two emission processes originated from shallow and deep trap energy levels corresponding to fast and slow components of PL decay, respectively. Energy transfer mechanism was discussed based on Dexter theory [J. Chem. Phys. 21, 863 (1953)] and the proposed four-state model. It is found that the energy transfer efficiency of deep energy level is higher than that of shallow energy level. The calculated distance between QD and texas red with the parameters of shallow energy level is the same with that of deep level, which indicates that the proposed model is reasonable for explaining the PL dynamics of CdS QDs.

Conduction mechanism in antiferrolectric PbZrO3 thin films—analysis of charge carrier trapping phenomenon

Antiferroelectric compositions, such as PbZrO3, are attractive candidates in charge storage devices and actuator/transducer applications in MEMs technology. Thin films of PbZrO3were deposited on Pt coated Si substrates by a pulsed excimer ablation process. The process of field induced ferroelectric phase switching involves the domain wall reorientation in the polycrystalline thin films. The presence of grain boundaries and various defects in the polycrystalline thin films acts as the pinning sources for the various domain walls. These defects capture the charge carriers in the presence of external applied field and hinders further switching of the dipoles in the domains, thereby increases the response times and threshold voltages for the devices operations. Understanding of the trapping phenomenon in these films is very essential. Using Lampert's theory of space charge limited conduction both shallow and deep trap energies were estimated approximately from charge transport analysis.