Influence of sub-bandgap illumination on electric field distribution at grain boundary in CdZnTe crystals

The space charge accumulation in CdZnTe crystals seriously affects the performance of high-flux pulse detectors. The influence of sub-bandgap illumination on the space charge distribution and device performance in CdZnTe crystals were studied theoretically by Silvaco TCAD software simulation. The sub-bandgap illumination with a wavelength of 890 nm and intensity of 8 × 10−8 W/cm2 were used in the simulation to explore the space charge distribution and internal electric field distribution in CdZnTe crystals. The simulation results show that the deep level occupation faction is manipulated by the sub-bandgap illumination, thus space charge concentration can be reduced under the bias voltage of 500 V. A flat electric field distribution is obtained, which significantly improves the charge collection efficiency of the CdZnTe detector. Meanwhile, premised on the high resistivity of CdZnTe crystal, the space charge concentration in the crystal can be further reduced with the wavelength of 850 nm and intensity of 1 × 10−7 W/cm2 illumination. The electric field distribution is flatter and the carrier collection efficiency of the device can be improved more effectively.

CdZnTe recently emerged as a leading semiconductor crystal for fabricating room-temperature x- and gamma-ray imaging detectors, due to its excellent energy resolution and sensitivity. However, its wide deployment is hampered by the low availability of high-quality CdZnTe crystals. As-grown CdZnTe crystals generally encounter the problems arising from the impurities and defects, especially deep level defects. The presence of impurities and defects leads to severe charge trapping, which significantly affects detector performance. Especially for high counting rate imaging detector used in medical imaging and tomography, the accumulation of space charge at deep levels significantly deforms the electric field distribution and subsequently reduces the charge collection efficiency. Therefore, a considerable interest is focused on the investigation of the space charge accumulation effect in CdZnTe crystal, which is the key factor to improve the performance of high counting rate imaging detector. Thus, the goal of this work is to investigate the effects of deep level defects on space charge distribution and internal electric field in CdZnTe detector. In order to reveal the major problem therein, Silvaco TCAD technique is used to simulate the space charge and electric field distribution profile in CdZnTe detector with considering the typical deep level defects <inline-formula><tex-math id="Z-20201111102325-1">\begin{document}$ \rm Te_{Cd}^{++} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="22-20200553_Z-20201111102325-1.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="22-20200553_Z-20201111102325-1.png"/></alternatives></inline-formula>in CdZnTe crystals with activation energy of <i>E</i><sub>v</sub> + 0.86 eV and concentration of 1 × 10<sup>12</sup> cm<sup>–3</sup> at room temperature. The simulation results demonstrate that the Au/ CdZnTe /Au energy band tilts intensively with the increase of applied bias, which makes the deep level ionization fraction increase. The space charge concentration also increases in the crystal. Meanwhile, the dead layer of electric field distribution decreases, which is of benefit to the carrier collection of CdZnTe detector. In addition, under the premiseof the high resistivity of CdZnTe crystal, the reduction of deep level defect concentration located at <i>E</i><sub>v</sub> + 0.86 eV can narrow the internal dead layer moderately. The deep level defect located at <i>E</i><sub>v</sub> + 0.8 eV can also reduce the space charge concentration near the cathode, which flattens the electric field distribution with narrower dead layer, thus significantly improving the carrier collection efficiency of CdZnTe detector. These simulation results will provide meaningful theoretical guidance for further optimizing the CdZnTe crystal growth, device design and fabrication.

Post-growth manipulation of the internal electric field in CdZnTe crystals using sub-bandgap illumination is measured as a function of temperature through infrared (IR) transmission measurements. Using near sub-bandgap IR illumination, both the optical de-trapping of charge carriers and the reduction in carrier recombination increased the mobility lifetime in the crystal. The increased carrier transport is a direct result of decreased hole and electron trapping in addition to other underlying mechanisms. Concentration of the electric field near the cathode is also observed. We measured the electric field distribution with sub-bandgap illumination as a function of temperature via the Pockels effect.

Summary form only given. Due to the effect of space charge, the electric field distributions cannot be calculated from knowledge of system geometries and material dielectric properties alone using Laplace's equation, as the system is then described by Poisson's equation. To optimize the electrical insulation design, it is necessary to on-line obtain the electric field distribution between the electrical electrodes. The Kerr electro-optic technique has the advantage that the devices create less disturbances in the field distribution itself. In the past, most Kerr electro-optic measurements have been limited to cases where the electric field direction and magnitude are constants along the light path for the electric field measurement results are the integration effects along the direction of light propagation. In many reality circumstances, the electrode structures which generate nonuniform electric field are common, so the direction of the electric field vector is no longer constant and may be variable along the light propagation direction. Some transformations which are being used in image reconstructions can be used in these cases to obtain the electric field distribution for a specific electrode structure. But, by using this method, many data should be obtained in the space between the electrodes, and this is usually realized through the movement of optical measurement system using some mechanical devices, and these mechanical devices may be the principle error sources for the rigid requirements of the optical measurement. Beside, after many data from different space points obtained, the electric field reconstruction can only be implemented in a PC off-line. The entire measuring processes are tiredness and complicated. In this paper, we use an electro-optical measurement matrix to measure the electric field distribution of the nonuniform electrode structure without any mechanical devices. The output of all PINs in the electro-optical measurement matrix are connected to a precise data acquisition board, together with the high speed embedded MCU to realize the transformation of the measuring results using ABEL transforms in real time, the electric field and space charge distribution are on-line obtained. The measuring results are given for needle-plane electrodes immersed in propylene carbonate.

To accurately evaluate the electric and magnetic field distribution characteristics around transmission lines under different tower structures and operating conditions, this study systematically investigates the spatial electric and magnetic fields of transmission line towers based on Grid Information Model (GIM) file parsing and finite element simulation. First, key information, including tower geometric configuration, conductor suspension point locations, and voltage level, is extracted by parsing the GIM file. A unified transformation method from geographic coordinates to three-dimensional Cartesian coordinates is established, and a three-dimensional electric and magnetic field calculation model is constructed in the ANSYS Maxwell platform, incorporating a catenary conductor model and an equivalent representation of bundled conductors. Furthermore, the accuracy of the proposed calculation method is validated based on field measurement data. Second, under single-circuit operating conditions, the spatial electric and magnetic field distributions of the Goblet-shaped suspension tower and the Drum-type transmission tower are analyzed under different phase sequence arrangements and different conductor-to-ground heights, and the shielding effect of the tower structure on the local electric field is investigated. On this basis, an electric field fitting method based on a proportional polynomial model is proposed, enabling the prediction of electric field distribution under tower-present conditions using simulation results obtained without tower structures. Subsequently, the influence of different phase sequence combinations on the spatial electric field distribution is systematically examined. The fitting method is further extended to double-circuit transmission lines, and its accuracy and effectiveness in rapid electric field assessment are verified. Finally, from an engineering practice perspective, the effects of the presence of jumper conductors and variations in conductor turning angles on the spatial electric field distribution of double-circuit towers are analyzed, and an optimized estimation approach for electric fields under different turning angle conditions is proposed. The results demonstrate that tower structural configuration and conductor arrangement significantly affect the electric field distribution, and the proposed fitting method effectively reduces modeling complexity while maintaining computational accuracy. The findings of this study provide a theoretical basis and technical reference for electric and magnetic environment assessment and engineering design of transmission lines.

Submarine cables are widely used in submarine power grid systems, and the operating environment is complex and harsh. Anchor damage is the most fatal factor affecting the safe and stable operation of submarine cable lines. In this paper, the finite element analysis is used to study both the electric and magnetic field distribution of submarine cables to evaluate the degree of anchor damage. Process principles of the two working conditions, anchor drop and anchor drag, are considered and described respectively. In the simulation environment, the 2D finite element model of 110 kV single-core AC submarine cable is built, simulating the anchor damage through longitudinal compression and overall deformation of the stressed section. After solving the electric and magnetic field distribution of the insulation layer, the correlation between the electric field distribution, magnetic field distribution and the deformation degree of anchor damage are finally established. Results show that the deformation of submarine cables caused by anchor damage lead to uneven distribution of both electric field strength and magnetic flux density in the insulation layer. The compression of the cable in the stress direction results in the thickness reduction of the material, thus weakening its magnetic shielding ability. With the simulation conclusion, the internal electric and magnetic field contribution of the submarine cable insulation layer can be inferred according to the insulation deformation degree, which contributes to the status evaluation of the submarine cable after the anchor damage and further ensures the safety and reliability of submarine cable operation.

Data obtained with BNL's National Synchrotron Light Source (NSLS) has helped to elucidate, in detail, the roles of non-uniformity and extended defects on the performance of CZT detectors, as well as the root cause of device polarization during exposure to a high flux of incident X-rays. Measurements of carrier traps will be reported, including their nature and relationships to different growth methods (conventional Bridgman, high-pressure Bridgman, traveling heater, and floating zone methods). Most findings will be correlated with the performance of spectrometer-grade CZT Xray and gamma detectors, and new directions to resolve the material deficiencies will be offered.

The performance of CdZnTe X/γ-ray detectors is strongly affected by the electric field distribution in terms of charge transport and charge collection. Factors which determine the electric field distribution are not only electric contact, but also intrinsic defects, especially grown-in twin boundaries. Here, the electric field distribution around twin boundaries is investigated in a CdZnTe bicrystal detector with a {111}–{111} twin plane using the Pockels electro-optic effect. The results of laser beam induced current pulses are also obtained by the transient current technique, and we discuss the influence of the twin boundary on the electric field evolution. These studies reveal a significant distortion of the electric field, which is attributed to the buildup of space charges at twin boundaries. Also, the position of these space charge regions depends on the polarity of the detector bias. An energy band model based on the formation of an n–n+–n junction across the twin boundary has been established to explain the observed results.

The over 9 million deaths in 2018, and 10 million in 2020, worldwide, due to cancer, indicates that the current standard of treatments is inadequate; there is an urgent and critical need for additional/alternate physical therapies. Towards this, electroporation-based chemotherapy, known as Electrochemotherapy is emerging. This involves application of high intensity, short duration pulses at the tumor site, which enhances the biopotential across the phospholipid bilayers of the cell plasma membrane and hence opens up pores for enhanced uptake. The electric field intensity and distribution is shaped by the electrode geometry, size, material and the tissue treated. In this research, we investigated the influence of different electrodes on the electric field intensity and distribution. For this purpose, platinum and surgical steel needle array hexagonal and pentagonal electrodes were used. ANSYS, the industry standard software that uses finite element method was used to study the electric field distribution, intensity and contour. Both, healthy tissue and tumor tissue were used to identify the electric field intensity and distribution using these various electrode configurations and materials, for unipolar and bipolar voltages were studied. The results indicate that the electric field distribution, both in magnitude and pattern is similar for both electrodes, for both configurations and materials, which is desired from the clinical aspect. The electric field intensities for the hexagonal and pentagonal needle electrodes were 1280V/cm and 1180V/cm respectively in the case of tumor tissue (correlating well with the desired level of 1200V/cm). They were 835V/cm and 843V/cm for these electrodes in the case of healthy tissues. The values were same in the case of bipotential and negative voltages too.

In this paper we describe the application of the finite element method (FEM) in modelling spatial distributions of electric and elastic fields in a ferroelectric crystals with three domains separated by a 90° domain walls. There are three various configurations computed. The domain boundary is idealized as a two-dimensional defect in an electro-elastic continuum. It represents the source of inhomogenity and internal distortion in both elastic and electric fields. The main results are distributions of electric field, strain along the domain boundary.

Distributions of electric and elastic fields at domain boundaries

Electrical field distribution along the insulator surface is considered one of the important parameters for the performance evaluation of outdoor insulators. In this paper numerical simulations were carried out to investigate the electric field and potential distribution along silicone rubber insulators under various polluted and dry band conditions. Simulations were performed using commercially available simulation package Comsol Multiphysics based on the finite element method. Various pollution severity levels were simulated by changing the conductivity of pollution layer. Dry bands of 2 cm width were inserted at the high voltage end, ground end, middle part, shed, sheath, and at the junction of shed and sheath to investigate the effect of dry band location and width on electric field and potential distribution. Partial pollution conditions were simulated by applying pollution layer on the top and bottom surface respectively. It was observed from the simulation results that electric field intensity was higher at the metal electrode ends and at the junction of dry bands. Simulation results showed that potential distribution is nonlinear in the case of clean and partially polluted insulator and linear for uniform pollution layer. Dry band formation effect both potential and electric field distribution. Power dissipated along the insulator surface and the resultant heat generation was also studied. The results of this study could be useful in the selection of polymeric insulators for contaminated environments.

The insulation system represents one of the most critical elements in any high voltage equipment, inclusive of any cabling and machineries. 60% of the faults and errors occurred in the insulation system are due to partial discharge occurrence which damage the high voltage machines and equipment, leading to an incurrence of huge expenses to replace them. The focus of this research is on the electric field distribution inside stator bar insulation system machine related to partial discharge phenomena. This research is manifested through the study of high voltage stator bar insulation’s electric field and potential distribution, coupled with follow up investigations into the ramifications of cavities of different distinctive shapes and the impact of the different positioning and sizes of cavities on the insulation system. The Finite element method (FEM) is the method that will be utilized in analyzing such simulation of the high voltage stator bar with the COMSOL software. A 2D modelling of stator bar insulation is conducted for this research to enhance an advanced understanding into the response of electric field distribution corresponding to distinctive shapes, positions and sizes of cavities within the insulation of high voltage stator bar. This outcome of this research will contribute majorly to the electrical power industry through acknowledging the presence of cavities and high electric field distribution relational to partial discharge activities while minimizing or preventing any faulty breakdown in stator bar machine that causes costly power failure in generation, distribution and transmission of electricity. The results from this research shows that the shapes, locations and sizes of cavities have a major influence on the electric field distribution inside the stator bar insulation whereby the presence of ellipsoidal shapes cavities give rise of electric field intensity twice the original (when no cavity is present), followed by the unknown shapes cavities which contributes 72.31% increment and spherical cavity which brings about 54% rise in the electric field strength. In terms of locations of cavities, the nearer the cavities located to the conductor region (at the inner insulation surface) as well as the edgy parts of the geometry, the higher the electric field is established inside the cavities. Apart from that, as the sizes of cavities increases from 0.22mm to 1.10mm, the electric field stresses inside spherical, ellipsoidal and unknown cavities sustain a drop of 19.08%, 12.09% and 28.57% respectively. This result deduces that highest inhomogeneous electric field stress is detected inside unknown shape cavity which increases the risk of electrical breakdown in this shape of cavity.

Effects of electric field intensity and distribution on flame propagation speed of CH4/O2/N2 flames

As motor capacity and rated voltage increase, the demand for motor insulation also increases. Additionally, the electric field distribution at the end of a large-scale hydro generator is extremely non-uniform, and corona discharge readily occurs. This destroys the main insulation, which significantly affects the service life of electrical machinery. Thus, the regulation of the electric field concentration at the end of a large-scale hydro generator needs to be addressed. There are many problems in resistance–capacitance chain model research. Particularly, these models cannot accurately reflect the insulation, corona structure, and electric field distribution in electrical machinery. Additionally, the corner electric field and loss distributions cannot be obtained, leading to a higher calculation error. The electric field distribution at the motor end and the loss distribution were analyzed using the finite-element method. First, by applying the basic principles of electric circuits and electromagnetic field theory, we calculated the electric field distribution at the stator bar end. Second, a 3D model of the stator bar was built using Creo Parametric, yielding a model that is more closely related to the prototype wirebar model. Then, the potential, electric field, and loss distributions around the stator bar were simulated by using COMSOL simulation software. The effects of the circular arc corner, nonlinearity coefficient, anti-corona coating length, and resistivity of the stator bar on the electric field distribution at the motor end were explored.