Thermally Stimulated Current Research Articles

MIS-TSC: A combination of the thermally stimulated current method and a metal-insulator-semiconductor device for unipolar trap spectroscopy

To determine the density of states distribution of traps within a semiconductor, the thermally stimulated current (TSC) method is often applied. However, the bipolar nature of the typical device structure does not allow for strict unipolar operation, and therefore the method does not allow for the separate evaluation of electron and hole traps. The recombination between electrons and holes makes the interpretation of the data difficult, which becomes an essential drawback of this method. To address these issues, we propose the use of a metal insulator semiconductor (MIS) device structure for TSC measurements, which can be operated strictly unipolar by the sign of the applied voltage during the charging process. Thus, the problem of recombination and bipolar contribution to the measurement signal is avoided. As an additional benefit, the MIS device structure typically results in very low leakage currents, and thus a low noise level for the measurement. This permits precise measurements even below 1 pA, and consequently increases the resolution of the method. This aspect is especially important for fractional TSC, as the measurement time is long and the current low when compared to the envelope measurement. Here, we demonstrate the basic principle of this TSC approach, which we name MIS-TSC, using the well-studied organic semiconductor P3HT as a benchmark.

Specific Features of Photoconductivity of Tl1-xIn1-xSnxSe2 Monocrystals at Low Temperatures

The photoconductivity spectra in the temperature range T≈36-200 K and the spectra of thermostimulated currents in the temperature range T≈70-300 K of Tl1-xIn1-xSnxSe2 single crystals obtained by directional crystallization of Bridgman-Stockbarger have been studied. The induced photoconductivity and long-term photoconductivity relaxation processes have been found. To interpret the found results, a model of two-center recombination has been suggested. It is illustrated that the role of the r-centers of slow recombination are formed by Tl vacancies. On the basis of the studies of the spectra of thermally stimulated currents, the thermal energy of electrons activation with t-levels of adhesion has been determined.

Deep level defects in β-Ga2O3 pulsed laser deposited thin films and Czochralski-grown bulk single crystals by thermally stimulated techniques

Thermally stimulated techniques—thermally stimulated current (TSC) spectroscopy and thermally stimulated depolarization current (TSDC) spectroscopy—were used to comparatively study the electrical properties and deep level defects in β-Ga2O3 pulsed laser deposited thin films and Czochralski-grown bulk crystals. It was found that the samples are highly resistive and each sample may have different dark current activation energy. Deep level defects revealed by the thermally stimulated techniques vary from sample to sample. In addition to the common traps E1 (∼0.56 eV), E2 (∼0.84 eV), and E3 (∼0.99 eV), reported in the literature and revealed by DLTS studies of Ga2O3 bulk crystals, that were also found in our samples by the thermally stimulated techniques, a trap at ∼110 meV and several other traps are revealed specifically by TSDC between 105 and 225 K.

Erratum: Influence of nano layer interface on space charge behavior and trap levels using polyimide sandwich structure

Measurements of space charge density and trap levels are informative ways to predict failure conditions of insulation materials. The charges are injected from electrodes and penetrate from surface towards deep inside of the insulation material. In order to resist the charge injection, trapping, migration and increase charge recombination, de-trapping and extraction rate, layer (nanocomposite-PI-nanocomposite) sandwich structure samples are used. Two techniques Pulse Electro Acoustic (PEA) and Thermal Stimulated Current (TSC) are combined to characterize space charge behavior and trap levels. Lab-view based program is used to detect the charges density distribution and total charge decay, different peaks of current using TSC technique are used to get activation energy and trap level density. The effects of structural interface (single, double, three layers) and types of nano (Al 2 O 3 , SiO 2 ) fillers are analyzed to influence charge accumulation polarity and trap levels. Trap levels are calculated using TSC data as well as total charge decay data. The trap values calculated from both data match each other. Al 2 O 3 -PI-Al 2 O 3 sandwich structure showed remarkable improvements to resist accumulation of space charge for longer time. Mostly charges are shallow traps with 1.126eV trap level and recombination rate is higher. In double layer structure in which interface is made up of SiO 2 and Al 2 O 3 , deep trap level of 1.26 eV and higher trap density is observed. The charges decay is faster in three layer structure than double and single layer structure. It is concluded that the interface formed with different type of nano and structure of insulation, both are an important parameters for manufacturing industry to suppress space charges accumulation and traps.

Defective States in Micro-Crystalline CsPbBr₃ and Their Role on Photoconductivity.

Intrinsic defects in CsPbBr3 microcrystalline films have been studied using thermally stimulated current (TSC) technique in a wide temperature range (100–400 K). Below room temperature, TSC emission is composed by a set of several energy levels, in the range 0.11–0.27 eV, suggesting a quasi-continuum distribution of states with almost constant density. Above room temperature, up to 400 K, the temperature range of interest for solar cells, both dark current and photocurrent, are mainly dominated by energy levels in the range 0.40–0.45 eV. Even if measured trap densities are high, in the range 1013–1016 cm−3, the very small capture cross-sections, about 10−26 m2, agree with the high defect tolerance characterizing this material.

Improvement to the Carrier Transport Properties of CdZnTe Detector Using Sub-Band-Gap Light Radiation.

The effects of sub-band-gap light radiation on the performance of CdZnTe photon-counting X-ray detectors were studied using infrared light with different wavelengths in the region of 980–1550 nm. The performance of the detectors for X-ray detection was improved by the radiation of infrared light with the wavelengths of 1200 nm and 1300 nm. This was because the increase of the electron indirect transition, and the weakening of the built-in electric field induced by the trapped holes, reduced the drift time of the carrier, and increased the charge collection efficiency. To further analyze the intrinsic behavior of the trapped charge, the deep-level defects of CdZnTe crystal were measured by thermally stimulated current spectroscopy (TSC). The deep-level defect indicated by the trap named T4 in TSC spectra with the ionization energy of 0.43 eV should be responsible for the performance deterioration of CdZnTe detectors.

Role of GeI2 and SnF2 additives for SnGe perovskite solar cells

The distribution of trap states within perovskite vicinity or hetero-interfaces is the prime attribution towards carrier dynamics inferiority and low photovoltaic performances. In this work, thermally stimulated current (TSC) is performed to unravel the impact of germanium (Ge) addition in passivating and reducing trap states; consequently, to improve its carrier dynamics. The addition of 5 mol% germanium into the FA0.75MA0.25Sn1-xGexI3 (FMSGI(5)) framework strikingly suppresses the trap density from 1015–1017 cm−3 (without Ge) to 108–1014 cm−3, thereby renders longer charge diffusion length (~1 µm) and lifetime; coupled with excellent charge mobility and efficiency of 7.9%. Interestingly, the FMSGI(5) perovskite exhibits indistinguishable trap densities profile from that of MAPbI3 perovskite and exhibits a long charge diffusion length of 1 µm. Another important information to be highlighted in this paper is the advantage of SnF2 to subside the vacancy of Sn2+. This study provides deep intuitive on trap landscape, which unlocks opportunities for the designation of high performance lead-free perovskite solar cells.

Electrical Properties, Deep Trap and Luminescence Spectra in Semi-Insulating, Czochralski β-Ga2O3 (Mg)

The temperature dependence of conductivity, thermally stimulated current (TSC), photoinduced current transient spectroscopy (PICTS) and microcathodoluminescence (MCL) were studied for Czochralski-grown β-Ga2O3 doped with Mg. The crystals had resistivity of 4.5 × 1011 Ω.cm at 450K. The activation energy of the conductivity in the dark was 1.3 eV. TSC spectra revealed deep traps with activation energy ∼ 1 eV. In PICTS, a minor peak with activation energy ∼0.8 eV, two major peaks with activation energy 1.05 eV and 1.35 eV, and a broad band corresponding to negative photoconductivity were observed. From the dependence of the peak amplitude on bias polarity, the 1.05 eV peak was attributed to a Mg-related hole trap at Ev+1.05 eV. The higher energy peak was assigned to electron emission from a deep electron trap at Ec-1.35 eV that pins the Fermi level. Photocurrent spectra showed deep traps with optical ionization thresholds at 2 eV and 2.3 eV. MCL spectra showed the presence of traps with peak emission energies at 3.1 eV, 2.81 eV, and 2.56 eV.

Thermal behaviour of two anti-inflammatory drugs (celecoxib and rofecoxib) and slow relaxation dynamics in their amorphous solid state. Comparison between the dynamic fragility obtained by dielectric spectroscopy and by thermostimulated currents

ABSTRACTThis study of the thermal behaviour of two glass formers showed that rofecoxib has a good ability to vitrify while celecoxib displays a moderate glass forming ability. On the other hand, celecoxib forms an instable glass while rofecoxib displays moderate glass stability. The α-relaxation of the two amorphous drugs was studied by differential scanning calorimetry (DSC) and thermally stimulated depolarization currents (TSDC). The values of the dynamic fragility obtained by the two techniques are in good mutual agreement and suggest that both drugs are moderately fragile glass formers. These values are however considerably lower than those obtained by dielectric relaxation spectroscopy (DRS) and published in the literature. In the present work we will compare the values of the dynamic fragility obtained by TSDC and DRS for a set of ~30 glass-forming liquids, in order to evaluate their relative suitability for the determination of the m-index. The observed differences are discussed and interpreted. Finally, secondary mobility modes were detected by TSDC in both celecoxib and rofecoxib. The kinetic parameters are identical in both cases and similar to those found by DRS for the slow-b relaxation of celecoxib. These secondary relaxations, that are precursors of the main relaxation on its lower temperature side, are believed to be Johari-Goldstein relaxations.

Influence of nano layer structure of polyimide film on space charge behavior and trap levels

Measurements of space charge density and trap levels are informative ways to predict failure conditions of insulation materials. The charges are injected from electrodes and penetrate from surface towards deep inside of the insulation material. In order to resist the charge injection, trapping, migration and increase charge recombination, detrapping and extraction rate, layer (nanocomposite-PI-nanocomposite) sandwich structure samples are used. Two techniques Pulse Electro Acoustic (PEA) and Thermal Stimulated Current (TSC) are combined to characterize space charge behavior and trap levels. Lab-view based program is used to detect the charge density distribution and total charge decay, different peaks of current using TSC technique are used to get activation energy and trap level density. The effects of structural interface (single, double, triple layers) and types of nano (Al 2 O 3 , SiO 2 ) fillers are analyzed to influence charge accumulation polarity and trap levels. Trap levels are calculated using TSC data as well as total charge decay data. The trap values calculated from both data match each other. Al 2 O 3 -PI-Al 2 O 3 sandwich structure showed remarkable improvements to resist accumulation of space charge for longer time. Mostly charges are shallow traps with 1.126 eV trap level and recombination rate is higher. In double layer structure in which interface is made up of SiO 2 and Al 2 O 3 , deep trap level of 1.26 eV and higher trap density is observed. The charges decay is faster in three-layer structure than double and single layer structure. It is concluded that the interface formed with different type of nano and structure of insulation, both are an important parameter for manufacturing industry to suppress space charges accumulation and traps.

The effects of γ-ray on charging behaviour using polyimide

Insulation material is a key component of electrical equipment in satellites; its electrical properties determine the reliability and lifetime of the whole satellite. High-energy radioactive rays in space affect the molecular structure of the polymeric insulating materials. Under the action of plasma, high energy particles, along with the magnetic fields experienced in orbits, electric charges get injected into and trapped by the insulating material creating distortions in the electric field and even electrostatic discharges. Polyimides have been widely used for insulation in spacecraft. Choosing Co-60 gamma ray with irradiation doses of 1 MGy and 5 MGy to simulate the radiation environment of space, we investigated the effect of radiation on charging behaviour. The thermal stimulated current (TSC) from a high electric field over a wide range of temperatures was measured from which the activation energy was calculated. These results for the two sources show that the percentage increase in total charge was 133.3% and 119.4%. The γ, β3, and α charge peaks of specimens after an irradiation dose of 1 MGy rose. In comparison, the β2 peak of the 5 MGy-dosed specimens was enhanced. Also, there is almost no change in the γ, β3, and α peaks. To understand the mechanism behind the TSC changes, the resulting physicochemical characteristics of an irradiated specimen were observed employing various analyses of chemical characteristics (x-ray photoelectron spectroscopy, differential scanning calorimetry and x-ray diffraction). Compared with the non-dosed specimen, the relative content of C–N and the glass transition temperature of the 1 MGy sample decreased, and the crystallinity increased, thus increasing the γ and α peak intensities. Compared with the 1 MGy sample, only the glass transition temperature had risen, thereby enhancing the β peak intensity. With the foregoing, a theoretical base for the selection and modification of insulation materials for spacecraft is provided.

Chain dynamics of human dermis by Thermostimulated currents: A tool for new markers of aging.

The purpose of this clinical study was to identify dielectric markers to complete a previous thermal and vibrational study on the molecular and organizational changes in human dermis during intrinsic and extrinsic aging. Sun-exposed and non-exposed skin biopsies were collected from 28 women devised in two groups (20-30 and ≥60years old). The dielectric relaxation modes associated with localized and delocalized dynamics in the fresh and dehydrated state were determined by the Thermostimulated currents technique (TSC). Intrinsic and extrinsic aging induced significant evolution of some of the dielectric parameters of localized and delocalized dynamics of human skin. With photo-aging, freezable water forms a segregated phase in dermis and its dynamics is close to free water, what evidences the major role of extrinsic aging on water organization in human skin. Moreover, TSC indicators highlight the restriction of localized mobility with intrinsic aging due to glycation, and the cumulative effect of chronological aging and photo-exposition on the molecular mobility of the main structural proteins of the dermis at the mesoscopic scale. TSC is a well-suited technique to scan the molecular mobility of human skin. It can be uses as a relevant complement of vibrational and thermal characterization to follow human skin modifications with intrinsic and extrinsic aging.

Study of point- and cluster-defects in radiation-damaged silicon

Non-ionising energy loss of radiation produces point defects and defect clusters in silicon, which result in a significant degradation of sensor performance. In this contribution results from TSC (Thermally Stimulated Current) defect spectroscopy for silicon pad diodes irradiated by electrons to fluences of a few 1014cm−2 and energies between 3.5 and 27 MeV for isochronal annealing between 80 and 280∘C, are presented. A method based on SRH (Shockley–Read–Hall) statistics is introduced, which assumes that the ionisation energy of the defects in a cluster depends on the fraction of occupied traps. The difference of ionisation energy of an isolated point defect and a fully occupied cluster, ΔEa, is extracted from the TSC data.For the VOi (vacancy-oxygen interstitial) defect ΔEa=0 is found, which confirms that it is a point defect, and validates the method for point defects. For clusters made of deep acceptors the ΔEavalues for different defects are determined after annealing at 80∘C as a function of electron energy, and for the irradiation with 15 MeV electrons as a function of annealing temperature. For the irradiation with 3.5 MeV electrons the value ΔEa=0 is found, whereas for the electron energies of 6–27 MeV ΔEa>0. This agrees with the expected threshold of about 5 MeV for cluster formation by electrons. The ΔEavalues determined as a function of annealing temperature show that the annealing rate is different for different defects. A naive diffusion model is used to estimate the temperature dependencies of the diffusion of the defects in the clusters.

Preparation and Dielectric Properties of SiC/LSR Nanocomposites for Insulation of High Voltage Direct Current Cable Accessories.

The conductivity mismatch in the composite insulation of high voltage direct current (HVDC) cable accessories causes electric field distribution distortion and even insulation breakdown. Therefore, a liquid silicone rubber (LSR) filled with SiC nanoparticles is prepared for the insulation of cable accessories. The micro-morphology of the SiC/LSR nanocomposites is observed by scanning electron microscopy, and their trap parameters are characterized using thermal stimulated current (TSC) tests. Moreover, the dielectric properties of SiC/LSR nanocomposites with different SiC concentrations are tested. The results show that the 3 wt % SiC/LSR sample has the best nonlinear conductivity, more than one order of magnitude higher than that of pure LSR with improved temperature and nonlinear conductivity coefficients. The relative permittivity increased 0.2 and dielectric loss factor increased 0.003, while its breakdown strength decreased 5 kV/mm compared to those of pure LSR. Moreover, the TSC results indicate the introduction of SiC nanoparticles reduced the trap level and trap density. Furthermore, the SiC nanoparticles filling significantly increased the sensitivity of LSR to electric field stress and temperature changes, enhancing the conductivity and electric field distribution within the HVDC cable accessories, thus improving the reliability of the HVDC cable accessories.

Space charge dynamic of irradiated cyanate ester/epoxy at cryogenic temperatures

Glass fibre reinforced polymers (GFRPs) have been widely used as one of the main electrical insulating structures for superconducting magnets. A new type of GFRP insulation material using cyanate ester/epoxy resin as a matrix was developed in this study, and the samples were irradiated by Co-60 for 1 MGy and 5 MGy dose. Space charge distributed within the sample were tested using the pulsed electroacoustic method, and charge concentration was found at the interfaces between glass fibre and epoxy resin. Thermally stimulated current (TSC) and dc conduction current were also tested to evaluate the irradiation effect. It was supposed that charge mobility and density were suppressed at the beginning due to the crosslinking reaction, and for a higher irradiation dose, molecular chain degradation dominated and led to more sever space charge accumulation at interfaces which enhance the internal electric field higher than the external field, and transition field for conduction current was also decreased by irradiation. Space charge dynamic at cryogenic temperature was revealed by conduction current and TSC, and space charge injection was observed for the irradiated samples at 225 K, which was more obvious for the irradiated samples.

Distinctive distribution of defects in CdZnTe:In ingots and their effects on the photoelectric properties**Project supported by the National Natural Science Foundations of China (Grant Nos. 51502244, 51702271, U1631116, and 51372205), the National Key Research and Development Program of China (Grant Nos. 2016YFF0101301 and 2016YFE0115200), the Fund of the State Key Laboratory of Solidification Processing in Northwestern Polytechnical University, China (Grant

Photoelectric properties of CdZnTe:In samples with distinctive defect distributions are investigated using various techniques. Samples cut from the head (T04) and tail (W02) regions of a crystal ingot show distinct differences in Te inclusion distribution. Obvious difference is not observed in Fourier transform infrared (FTIR) spectra, UV–Vis–NIR transmittance spectra, and I–V measurements. However, carrier mobility of the tip sample is higher than that of the tail according to the laser beam induced current (LBIC) measurements. Low temperature photoluminescence (PL) measurement presents sharp emission peaks of D0X and A0X, and relatively large peak of D0X (or A0X) / Dcomplex for T04, indicating a better crystalline quality. Thermally stimulated current (TSC) spectrum shows higher density of shallow point defects, i.e., Cd vacancies, , etc., in W02 sample, which could be responsible for the deterioration of electron mobility.

Large-size TlBr single crystal growth and defect study

Thallium bromide (TlBr) is an attractive semiconductor material for fabrication of radiation detectors due to its high photon stopping power originating from its high atomic number, wide band gap and high resistivity. In this paper the vertical Bridgman method was used for crystal growth and TlBr single crystals with diameter of 15 mm were grown. X-ray diffraction (XRD) was used to identify phase and orientation. Electron backscatter diffraction (EBSD) was used to investigate crystal microstructure and crystallographic orientation. The optical and electric performance of the crystal was characterized by infrared (IR) transmittance spectra and I-V measurement. The types of point defects in the crystals were investigated by thermally stimulated current (TSC) spectra and positron annihilation spectroscopy (PAS). Four types of defects, with ionization energy of each defect fitting as follows: 0.1308, 0.1540, 0.3822 and 0.538 eV, were confirmed from the TSC result. The PAS result showed that there were Tl vacancies in the crystal.

Thermally Stimulated Currents in Nanocrystalline Titania.

A thorough study on the distribution of defect-related active energy levels has been performed on nanocrystalline TiO2. Films have been deposited on thick-alumina printed circuit boards equipped with electrical contacts, heater and temperature sensors, to carry out a detailed thermally stimulated currents analysis on a wide temperature range (5–630 K), in view to evidence contributions from shallow to deep energy levels within the gap. Data have been processed by numerically modelling electrical transport. The model considers both free and hopping contribution to conduction, a density of states characterized by an exponential tail of localized states below the conduction band and the convolution of standard Thermally Stimulated Currents (TSC) emissions with gaussian distributions to take into account the variability in energy due to local perturbations in the highly disordered network. Results show that in the low temperature range, up to 200 K, hopping within the exponential band tail represents the main contribution to electrical conduction. Above room temperature, electrical conduction is dominated by free carriers contribution and by emissions from deep energy levels, with a defect density ranging within 1014–1018 cm−3, associated with physio- and chemi-sorbed water vapour, OH groups and to oxygen vacancies.

Role of Stoichiometry in the Growth of Large Pb2P2Se6 Crystals for Nuclear Radiation Detection

Pb2P2Se6 as a heavy element, chemically robust semiconductor, has been identified as a promising material for cost-effective room temperature X/γ-ray detection. Here, we report the properties of Pb2P2Se6 crystals grown by a vertical Bridgman method under off-stoichiometric Se-rich and Pb-rich conditions. Regardless of the conditions the resulting single crystals exhibited high bulk resistivity on the order of 1011 Ω·cm. However, the photoconductivity and charge transport properties varied based on growth condition indicating the different dominant defects associated with the type of stoichiometric deviation. The formation and nature of intrinsic defects in Pb2P2Se6 crystals were also studied by first-principles density functional theory (DFT) calculations as well as thermally stimulated current (TSC) spectroscopy. The TSC results indicated that four traps were common to both Se-rich and Pb-rich Pb2P2Se6, while a higher density of shallow defects were observed in Se-rich Pb2P2Se6. DFT calculations predict ...

Thermally stimulated capacitance in gamma irradiated epitaxial 4H-SiC Schottky barrier diodes

Deep level defects in 4H-SiC Schottky barrier diodes (SBDs) fabricated on n-type epitaxial 4H-SiC have been identified by thermally stimulated capacitance (TSCAP) spectroscopy prior to and after 60Co-gamma irradiation. The TSCAP measurements on the non-irradiated SBDs reveal two electron traps at Ec-0.63 eV (∼250 K) and Ec-1.13 eV (∼525 K), whereas only one trap at Ec-0.63 eV is identified by conventional thermally stimulated current (TSC) measurements. Hence, TSCAP spectroscopy is more effective in identifying deep level defects in epitaxial 4 H-SiC SBDs as compared to the TSC spectroscopy. Upon exposure to 60Co-gamma rays up to a dose of 100 Mrad, significant changes in the concentration of the traps at Ec-0.63 eV, Ec-1.13 eV, and one new trap at Ec-0.89 eV (∼420 K) are observed. The electrical characteristics of the SBDs are considerably changed after gamma irradiation. The dominant mechanisms responsible for the irradiation induced changes in the SBD electrical characteristics are analyzed by incorporating the trap signatures in the commercial Silvaco® TCAD device simulator. The extracted trap parameters of the irradiated SBDs may be helpful in predicting the survival of 4H-SiC SBD detectors at higher irradiation levels.