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With the rapid advances in the Internet of Things, it is possible to construct a self-charging power system integrating a triboelectric nanogenerator (TENG) and supercapacitor (SC), which represents an excellent tool for simultaneous conversion and storage of distributed environmental energy. In particular, the well-researched Ti3C2T x MXene materials for triboelectric nanogeneration lack high and stable power density, mainly due to the charge dissipation effect on their surface. Herein, the effectiveness of MXenes is enhanced by encrusting TiO2 on the inner and outer surfaces via a hydrothermal method. TiO2, which has inherent dielectric properties, could serve the dual function of electron trapping/blocking and surface polarization, mitigating the diffusion and drifting of surficial tribo-charges and thus increasing output TENG performance. An integrated TENG based on MXene/TiO2 composites with a TiO2 concentration of 3 mM has a higher output voltage than a pristine MXene-based TENG (110 V, a 1.83-fold increase) and achieves a maximum instantaneous power density of ∼1440 mW m−2. TiO2 is also conductive to pseudo-faradaic reactions, and the integrated MXene/TiO2 based symmetric SC exhibits an enhanced specific capacitance of 231.08 F g−1 at 1 A g−1, which is 4.52 times that of pristine MXene, with a maximum energy density of 12.74 W h kg−1 at a power density of 483.06 W kg−1. Finally, utilizing polyimide sheets as substrates, the flexible self-charging power system was integrated: the TENG charges the SC up to 0.8 V with a charging/discharging time of 37 s/40 s, showing great promise for the demands of flexible and self-powered electronics. [ABSTRACT FROM AUTHOR]

The characteristics of an AlGaN/GaN high-electron-mobility transistor buffer structure are studied and optimized by employing an AlN/GaN superlattice (SL) structure. Through vertical leakage analysis and back-gate measurement, combined with Silvaco-TCAD simulation, the influence of buffer trapson the carrier transport behaviors and electrical performance for SL buffer structures under a high electric field is analyzed. The AlN/GaN SL buffer structures are further optimized with various AlN/GaN thickness ratios and their total thickness through both simulation and experimental studies. As a result, a high breakdown voltage of up to 1.3 kV with a maximum breakdown electric field of 2.8 MV cm−1 has been achieved. Moreover, the buffer trapping effect is dramatically suppressed, leading to a minimum drop of channel current for the optimized sample, in which donor traps are found to play a positive role in the device dynamic characteristics. [ABSTRACT FROM AUTHOR]

Heavily Sn-doped films of α -Ga2O3 were grown by halide vapor phase epitaxy (HVPE) on basal plane c-sapphire and on (10-12) r-sapphire substrates with and without α -Cr2O3 thin buffers prepared by magnetron sputtering and annealing in air at 500 °C for 3 h. For both substrate orientations, the use of α -Cr2O3 buffers led to three major effects. The first was a substantial decrease of the half-width of the symmetric and asymmetric x-ray reflections. The second was an order of magnitude decrease of the net donor concentration produced by flowing the same amounts of Sn into the reactor. Third, there was a reduction in the concentration of the major electron trap in the films near E c âˆ' 1 eV by more than a factor of two. These results show the major influence of sapphire substrate orientation on the electrical and structural properties of α -Ga2O3 grown by HVPE. [ABSTRACT FROM AUTHOR]

Charge collection efficiency (CE) η 0 under small signal conditions, corresponding to a uniform field in the detector medium, has been widely used in evaluating the performance of photoconductive detectors. The present paper answers the question, ‘ What is the variance of the collected charge in an integrating detector as a function of photoinjection level and what are the errors if we continue to use the small signal equations? ’ The variance σ 0 2 in η 0 under small signals has been theoretically derived in the literature and has been a key factor in the detective quantum efficiency modeling of integrating detectors based on various semiconductors. σ 0 2 is a noise source and can degrade the detector performance under incomplete charge collection. The statistical variance σ 0 2 in the CE η 0, under small signals and the variance σ r 2 in the CE ηr under an arbitrary injection level r (injected charge divided by charge on the electrodes) have been studied using the Monte Carlo simulation model developed in this work to evaluate the difference between σ r 2 and σ 0 2 from small to large signals. Initial injection of electron and hole pairs and their subsequent transport and trapping in the presence of an electric field, which is calculated from the Poisson equation, is used to calculate the photocurrent. Each injected carrier is tracked as it moves in the semiconductor until it is either trapped or reaches the collection electrode. Trapped carriers do not contribute to the photocurrent but continue to contribute to the field through the Poisson equation. The instantaneous photocurrent i ph(t) is calculated from the drift of the free carriers through the Shockleyâ€"Ramo theorem. i ph(t) is integrated over the duration of the photocurrent to calculate the total collected charge and hence the CE ηr. The variance σ r 2 in ηr is found from multiple simulations of ηr. The ηr and σ r 2 have been generated over varying charge injection ratios r, the electron and hole ranges ÎĽĎ„, mean photoinjection depths δ and drift mobility ratios b. At full injection, the deviation Î" σ r 2 of the CE variance σ r 2 from the uniform field case σ 0 2 ( i. e. Î" σ r 2 = σ r 2 âˆ' σ 0 2) may be as much as 40% larger or 20% lower than the small signal model prediction. This study provides the extent of errors involved in the variance of the CE in non-uniform fields and quantifies the increase in errors that can occur in high injection cases. In practice, typical injection ratios are less than 0.2, which means that the magnitude of percentage error Î" σ r 2 / σ 0 2 is less than 5%. [ABSTRACT FROM AUTHOR]

Dilute bismides (%Bi ∼ 1%–3%) are excellent candidates for the fabrication of optoelectronic devices, thanks to the strong reduction in the bandgap with increasing bismuth content, the weak temperature dependence of the bandgap, and the small Auger recombination coefficient for high bismuth concentrations. Since Shockley–Read–Hall recombination may significant impact on the electrical and optical properties of the devices, describing the defects within the semiconductor material is of paramount importance for the optimization of device technology. To this aim, this paper investigates the deep levels within the bandgap in un-annealed n-type GaAsBi grown by molecular beam epitaxy at low temperature (390 °C) by means of deep level transient spectroscopy and filling time-dependent measurements. The original results described in the paper indicate (a) the presence of four majority and two minority carrier traps, and (b) that, from the analysis of the charge-capture kinetics, the dominant electron and hole traps originate, respectively, from a dislocation-related and a point defect with capture barrier of 0.48 eV. In addition, (c) we demonstrate that the incorporation of bismuth in GaAs generates only one additional electrically active defect with concentration higher than the sensitivity of the measurement setup, because most of the relevant traps found in GaAsBi layers have been identified in pure GaAs grown at low temperature. Finally, (d) the trap concentration is relatively constant along the growth direction, indicating a uniform defect density. [ABSTRACT FROM AUTHOR]

Extensive research has been carried out to improve the breakdown strength (BDS) of polymer materials used in high-voltage power equipment. However, almost all the modifications, including nanocomposites, polymer blends, and multilayer films have enhanced the BDS by introducing alien material, which inevitably resulted in an increase in the dielectric losses. Therefore, we propose a multilayer structured film simplex composed of polypropylene (PP) to simultaneously achieve high BDS and low losses. By including virgin and fluorinated bi-axially oriented PP (BOPP) films, three different interface structures were constructed. All the multilayer PP films showed DC BDSs that were improved by varying degrees, compared to the single-layer film. In particular, owing to the enhanced electron trap depth and density caused by fluorination, the DC BDSs of multilayer films with fluorinated BOPP reached 458.7 kV mm−1, which was 20% higher than that of a single-layer PP film of the same thickness, while their dielectric loss was even lower than that of the single-layer film. [ABSTRACT FROM AUTHOR]

Buffer related electron trapping and hot electron injection are responsible for Ron degradation in devices, but the effects of substrate termination are still uncertain. In this work, both positive and negative substrate bias are applied to investigate the different vertical trapping mechanisms in 650 V gallium nitride (GaN) power devices. Ron shows an instant and significant increase under vertical bias stress, and the magnitude of downward buffer electron trapping induced Ron increase is relatively larger than that induced by upward trapping. Additionally, the substrate floated and grounded GaN devices are also submitted to both off-state and semi-on-state stresses to investigate the effects of substrate termination on hot electron injection induced Ron increase. The intensity of the upward electron trapping increases faster with temperature resulting in a higher Ron increase than the downward situation. The hot electron effect is only obvious when the substrate is grounded, suggesting that the main injection destination is not in the buffer. The substrate floated device exhibits a lower Ron increase after both off-state and semi-on-state stresses at elevated temperatures. Substrate floated packages are suggested to ensure reliable dynamic performance of device, especially for high voltage application design. [ABSTRACT FROM AUTHOR]

Maintaining a stable spectrum in white organic light-emitting diodes (WOLEDs) with multi-emissive layers (EMLs) remains a challenge. Herein, four-chromatic (blue–green–red–orange) WOLED with stable spectrum based on ultrathin EMLs and mixed bipolar interlayers was fabricated. We discovered that the locations of various color EMLs in the bipolar interlayers are essential for achieving the stable spectrum. The direct carrier trapping effects which destabilize the spectrum can be suppressed by placing red and green EMLs with both hole and electron traps in the middle of the bipolar interlayer and placing blue and orange EMLs with single-carrier traps on the two sides of the bipolar interlayer respectively. The resulting device exhibited the negligible color coordinate shifts of (0.008, 0.010) during the wide brightness range from 1000 cd m−2 to 10 000 cd m−2. Moreover, a high color rendering index of approximately 90 was obtained simultaneously. Our work demonstrated a significant method to achieve stable spectra in multi-EML WOLEDs based on bipolar interlayer. [ABSTRACT FROM AUTHOR]

Si6−zAlzOzN8−z (β-SiAlON):Eu2+ is known as a high brightness green phosphor. When β-SiAlON:Eu2+ is excited with UV light (approximately 265 nm), a curved decay afterglow is observed as a result of the trap levels created by the defects in the host crystal. However, the defect signals are hardly detected by electron spin resonance (ESR) and thermoluminescence (TL), which are common defect detection methods. Non-doped (Eu = 0) β-SiAlON emits blue light from a nitrogen defect, and the defect can be detected by time-resolved fluorescence (TR-F) measurement at 15 K. Similarly, upon measuring TR-F at 15 K for Eu-doped β-SiAlON, a blue emission (460 nm) is detected in addition to the green emission of Eu2+ (530 nm). The green emission has an afterglow of several milliseconds that decays with the same decay curve as the blue emission of the defect, and its time constant is 5–6 ms. This blue emission is quenched by the Eu concentration and temperature. The Si dangling bond signal intensity, observed by ESR, and the glow intensity, observed by TL, also decrease with the increment of the Eu concentration. It is difficult to detect the defect as an electron trap owing to the interaction between Eu2+ and the nitrogen defect. However, the afterglow arising from the electrons trapped at the defect level does not decrease with the Eu concentration. The blue emission was quenched at room temperature but the afterglow was not reduced, which also affected the light emission above room temperature. Therefore, it is possible to detect nitrogen defects optically by TR-F at low temperature, as well as the Eu2+ afterglow of several milliseconds. [ABSTRACT FROM AUTHOR]

Si6−zAlzOzN8−z (β-SiAlON):Eu2+ is known as a high brightness green phosphor. When β-SiAlON:Eu2+ is excited with UV light (approximately 265 nm), a curved decay afterglow is observed as a result of the trap levels created by the defects in the host crystal. However, the defect signals are hardly detected by electron spin resonance (ESR) and thermoluminescence (TL), which are common defect detection methods. Non-doped (Eu = 0) β-SiAlON emits blue light from a nitrogen defect, and the defect can be detected by time-resolved fluorescence (TR-F) measurement at 15 K. Similarly, upon measuring TR-F at 15 K for Eu-doped β-SiAlON, a blue emission (460 nm) is detected in addition to the green emission of Eu2+ (530 nm). The green emission has an afterglow of several milliseconds that decays with the same decay curve as the blue emission of the defect, and its time constant is 5–6 ms. This blue emission is quenched by the Eu concentration and temperature. The Si dangling bond signal intensity, observed by ESR, and the glow intensity, observed by TL, also decrease with the increment of the Eu concentration. It is difficult to detect the defect as an electron trap owing to the interaction between Eu2+ and the nitrogen defect. However, the afterglow arising from the electrons trapped at the defect level does not decrease with the Eu concentration. The blue emission was quenched at room temperature but the afterglow was not reduced, which also affected the light emission above room temperature. Therefore, it is possible to detect nitrogen defects optically by TR-F at low temperature, as well as the Eu2+ afterglow of several milliseconds. [ABSTRACT FROM AUTHOR]

Achieving frequency- and temperature-independent colossal permittivity (CP) with low dielectric loss is a long-standing challenge for electronic materials, in which the basic issue is understanding the underlying relaxation mechanism. In this paper, taking CaCu3Ti4O12 ceramics as an example, CP was ascribed to electron-trapping behaviors at the edge of a double Schottky barrier (DSB). On the one hand, the widely reported origins of CP, i.e. Maxwell–Wagner relaxation and polaronic relaxation, were identified as two aspects of the same bulk conductivity. This caused the insights derived from the commonly employed impedance and admittance spectra to be revisited. On the other hand, hysteresis between CP and external voltages at low temperatures, which was caused by electron filling of interface states, was predicted and experimentally confirmed. This further supported the proposal that CP arose from electron trapping at the DSB. Moreover, multiple relaxations were foreseen when more than one kind of point defect existed in the depletion layers of a DSB. The establishment of intense 'effective' relaxation, which was related to shallow traps, was indispensable for achieving CP, while 'redundant' relaxation was induced by deep-level defects, resulting in relatively high dielectric loss. Therefore, proper manipulation of the DSB and its related defect structures was crucial for achieving stable CP with sufficiently low dielectric loss. [ABSTRACT FROM AUTHOR]

Degradation in low-temperature polycrystalline-silicon thin-film transistors after electrical stress was thoroughly investigated in this work. Main channel degradation, abnormal hump generation and hysteresis appearing in the hump region can be observed after positive bias stress. Furthermore, the difference in subthreshold swing (SS) values between forward/reverse sweep is observed. The electron trapping into the gate insulator (GI) dominates the main degradation and the hump generation. Additionally, the difference in SS values which appears in the hump region is attributed to the interface traps and the hysteresis is caused by electron trapping/detrapping into GI. [ABSTRACT FROM AUTHOR]

Measurements of deep trap spectra in bulk β-Ga2O3 crystals showed the parameters of the two dominant centers with levels near Ec-0.8 eV (E2) and Ec-1 eV(E3) are affected the electric field during deep level transient spectroscopy (DLTS). Both DLTS spectra measurements of the emission rates of the E2 and E3 traps and measurements of emission rates as a function of electric field from capacitance decay curves obtained at a fixed temperature (380 K) show that, for strong electric field with magnitude above ∼5 × 105 V.cm−1, the emission rates of these traps increase with increasing field. For the E2 traps, the increase is driven by phonon assisted tunneling. This points to the trap being an acceptor, which is consistent with reported attribution of the center to substitutional Fe acceptors. For the E3 trap, the field dependence indicates the dominant mechanism is the Poole–Frenkel effect, operable for Coulombic centers. It is concluded that this commonly observed trap is a deep donor. [ABSTRACT FROM AUTHOR]

The effects of pulsed neutron irradiation on Si doped n-type β-Ga2O3 films grown by halide vapor phase epitaxy (HVPE) on bulk Sn doped n+ β-Ga2O3 substrates are reported. This irradiation leads to an almost linear increase with neutron fluence of the density of deep electron traps E2* (Ec − 0.74 eV), E3 (Ec − 1.05 eV), and E4 (Ec − 1.2 eV), with an introduction rate close to 0.4–0.6 cm−1 while the density of the E2 traps (Ec − 0.8 eV) related to Fe was virtually unchanged. In addition, the increase in the density of deep traps with optical ionization threshold of 1.3 eV, 2.3 eV, and 3.1 eV with an introduction rate close to 0.8–2 cm−1 was observed. The carrier removal rate under our conditions was 28 cm−1. Neutron irradiation also led to a measurable decrease of the diffusion length of nonequilibrium charge carriers. The results are qualitatively similar to previous reports for proton and α-particle irradiation of HVPE β-Ga2O3. When comparing the findings with those described earlier for bulk neutron irradiated Ga2O3, we observe lower starting densities of electron and hole traps and lower introduction rates for these traps in the epitaxial structures. The carrier removal rates were comparable to those in bulk crystals. [ABSTRACT FROM AUTHOR]

The effects of pulsed neutron irradiation on Si doped n-type β-Ga2O3 films grown by halide vapor phase epitaxy (HVPE) on bulk Sn doped n+ β-Ga2O3 substrates are reported. This irradiation leads to an almost linear increase with neutron fluence of the density of deep electron traps E2* (Ec − 0.74 eV), E3 (Ec − 1.05 eV), and E4 (Ec − 1.2 eV), with an introduction rate close to 0.4–0.6 cm−1 while the density of the E2 traps (Ec − 0.8 eV) related to Fe was virtually unchanged. In addition, the increase in the density of deep traps with optical ionization threshold of 1.3 eV, 2.3 eV, and 3.1 eV with an introduction rate close to 0.8–2 cm−1 was observed. The carrier removal rate under our conditions was 28 cm−1. Neutron irradiation also led to a measurable decrease of the diffusion length of nonequilibrium charge carriers. The results are qualitatively similar to previous reports for proton and α-particle irradiation of HVPE β-Ga2O3. When comparing the findings with those described earlier for bulk neutron irradiated Ga2O3, we observe lower starting densities of electron and hole traps and lower introduction rates for these traps in the epitaxial structures. The carrier removal rates were comparable to those in bulk crystals. [ABSTRACT FROM AUTHOR]

We have investigated Ge nanowire (NW) metal–semiconductor–metal (MSM) photodetectors with high specific detectivity and low dark current, in which various sizes Ge NWs were fabricated by three-dimensional (3D) Ge condensation techniques. It has been demonstrated that the photocurrent gain increases significantly from 6.31  ×  104 to 4.47  ×  106 with the reduction of Ge NW width from 170 to 35 nm. A low dark current of 5.1 nA and an ultra-high specific detectivity of 1.26  ×  1014 cm·Hz1/2·W−1 at 560 nm under 0.51 V bias are achieved for the 35 nm wide Ge NW photodetector. It has been proposed that the interface states provided by SiGeOx formed during Ge condensation process serve as electron traps to generate photogating effect, resulting in high photocurrent gain and high specific detectivity in the MSM photodetector. The fully complementary metal-oxide-semiconductor (CMOS) compatible and scalable process suggests a great potential of the Ge NW for low cost, high performance near infrared photodetectors. [ABSTRACT FROM AUTHOR]

Carrier dynamics and photoconductivity in epitaxial-grown low-temperature GaAs on nominal and vicinal Si(1 0 0) substrates (‘LT-GaAs/Si’) were studied to predict their actual performance as THz photoconductive antenna (PCA) detectors. An optical-pump terahertz-probe technique was used to obtain the transmittance, carrier lifetime and photoconductivity of two LT-GaAs/Si samples, grown using different substrates and different growth protocols. The LT-GaAs grown on Si(1 0 0) substrate with a 4° tilt to 〈1 1 0〉 has better crystallinity, in agreement with other reports; while the LT-GaAs layer grown on nominal Si(1 0 0) substrate, though more structurally defective, has a much faster electron trapping time. Fabricated test PCAs with either dipole or bowtie geometries confirm the characterization results. The photoconductivity and carrier lifetime results manifest in the PCA performance, in responsivity, and in detection bandwidth. The prototypes’ sensitivities, bandwidths and dynamic ranges show that with some growth optimization, LT-GaAs/Si can be tailored to create economical, broadband THz detectors. [ABSTRACT FROM AUTHOR]

The impact of gamma irradiation on GaN quasi-vertical Schottky barrier diodes (SBDs) has been investigated for the first time. Compared with original GaN SBDs, the ideality factor decreases from 1.2 to 1.01–1.02 and the on/off ratio increases from 109 to 1012 for the irradiated GaN SBDs. The reduction of dynamic on-resistance from 0.67 mΩ · cm2 to 0.54 mΩ · cm2 was observed at the quiescent bias of  −100 V compared with the original SBDs. The temperature dependent current characteristics has revealed the existence of Schottky barrier inhomogeneities at the anode/GaN Schottky interface, and the level of barrier inhomogeneities can be effectively suppressed after gamma irradiation. Based on x-ray photoelectron spectroscopy, cathodoluminescence and x-ray diffraction results, the interface state density at the interface and the deep electron trap in the bulk GaN are reduced after gamma irradiation. The voltage dependent capacitance-frequency measurements further confirm that the interface trap states dominate the degraded characteristics of pre-irradiated devices and the trap time constant is estimated to be in the range of 5 μs to 50 μs. [ABSTRACT FROM AUTHOR]

Secondary electron emission (SEE) induced by interaction between positive ion and dielectric surface is essential physical process for maintaining sustained discharge and controlling the characteristics of atmospheric pressure dielectric barrier discharge (DBD). In this work, SEE is described based on Auger neutralization theory. Dielectric energy band structure and defect energy level, including hole and electron trap energy levels, are taken into account to build a hypothetical relationship γi  =  f (σ) between secondary electron emission coefficient γi and surface charge density σ. With the introduction of γi  =  f (σ) in DBD model, the characteristics of DBD are discussed in both first and steady discharges. It is found that, in steady discharge, γi has higher value during the beginning and development state of discharge pulse of DBD, and γi decreases in extinction stage. The negatively charged dielectric surface enhances SEE before discharge, which benefits the formation of diffuse discharge, compared with DBD of constant γi. Moreover, the increase of energy band gap of dielectric reduces γi, leading to the contractive discharge in DBD. The relationship between γi and σ can be further applied to study the influences of defect energy level parameters on SEE and DBD characteristics. [ABSTRACT FROM AUTHOR]

Multiscale simulation combining density functional theory of defect physics and charge transport calculation is carried out to understand the intrinsic mechanism of the lateral charge loss in silicon nitride (Si3N4)-based 3D NAND flash memory. In this work, the defects’ structures, trapping centers, and trap levels are investigated by ab initio calculations. Wherein, the focus is put on the nitrogen vacancy (VN), puckered nitrogen vacancy (VNP) and H-/O- incorporation. It shows that the VNP and O atom will introduce extremely shallow electron traps which can be eliminated by the H passivation. The stability of several kinds of defects is also studied. To shed new light on the impact of trap levels on the charge de-trapping and the lateral charge loss, numerical simulations are performed with the drift-diffusion model and Poole–Frenkel model. [ABSTRACT FROM AUTHOR]

Transient current density and luminance from an organic light-emitting diode (OLED) driven by voltage pulses were investigated. Waveforms with different repetition rate, duty cycle, off-period, and on-period were used to study the injection and transport characteristics of electron and holes in an OLED under pulse operation. It was found that trapped electrons inside the emitting layer (EML) and the electron transporting layer (ETL) material, tris(8-hydroxyquinolate)aluminum (Alq3) helped for attracting the holes into the EML/ETL and reducing the driving voltage, which was further confirmed from the analysis of capacitance–voltage and displacement current measurement. The relaxation time and trapped filling time of the trapped electrons in Alq3 layer were ~200 µs and ~600 µs with 6 V pulse operation, respectively. [ABSTRACT FROM AUTHOR]

Deep levels in lattice-matched undoped and Si-doped InAlN/GaN grown by plasma-assisted molecular beam epitaxy have been identified and characterized by capacitance and photocapacitance measurements. From x-ray diffraction, reflectance measurements, electron energy loss spectroscopy and high-resolution transmission electron microscopy it is evident that the material has two distinct phases with different compositions. These correspond to In compositions of 18.1% and 25.8%, with corresponding bandgaps of 4.6 eV and 4.1 eV, respectively. The lower bandgap material is present as columnar microstructures in the form of quantum wires. A dominant electron trap with an activation energy of 0.293  ±  0.01 eV, a small capture cross-section of (1.54  ±  0.25)  ×  10−18 cm2, and density increasing linearly with Si doping density is identified in all the samples. The characteristics of the electron trap and variation of diode capacitance are discussed in the context of carrier dynamics involving the dominant trap level and the quantum wires. [ABSTRACT FROM AUTHOR]

A theoretical model is established to describe the emergence of the Meyer–Neldel rule (MNR) based on trap-limited current (TLC) theory. The model produces both MNR and anti-MNR behavior, and is available to various trap distributions. Moreover, TLC-based MNR is connected to persistent photocurrent (PPC) phenomenon. The information from MNR and PPC as well as their connection can be used to probe the distribution of the traps in materials. [ABSTRACT FROM AUTHOR]

The temperature-dependent electrical transport properties of nonvolatile organic field-effect transistor (OFET) memories with Poly (methyl methacrylate) (PMMA) as a charge trapping layer were characterized at four typical temperatures (20 °C, 60 °C, 80 °C and  −78.5 °C). It was found that the OFET memories showed strong temperature dependence. The performance degradations, including the memory windows and the retention characteristics, could be observed at both high and low temperatures. The degradations of the OFET memories at 60 °C, 80 °C and  −78.5 °C were attributed to both the less electrons trapped by the PMMA film and the easier release of the trapped electrons from the PMMA film, which is caused by the lower crystallinity of pentacene film and the larger contact area between pentacene film and PMMA film, respectively. [ABSTRACT FROM AUTHOR]

Deep level transient spectroscopy (DLTS) has been applied to study electron and hole traps in InPBi alloys with 2.2 and 2.4% Bi grown by molecular beam epitaxy. One donor-like trap with the activation energy of 0.45–0.47 eV and one acceptor-like trap with activation energy of 0.08 eV have been identified in DLTS measurements. For the reference sample (InP grown at the same temperature), the deep donor trap has also been observed, while the acceptor trap was not detected. According to the literature, the deep donor level found in InP(Bi) at 0.45–0.47 eV below the conduction band has been attributed to the isolated PIn defect, while the second trap, which is observed only for Bi containing samples at 0.08 eV above the valence band can be attributed to Bi clusters in InPBi. This acceptor level was proposed to be responsible for the observed partial compensation of native free electron density in InPBi layers. It is also shown that the deep donor traps are active in photoluminescence (PL). A strong radiative recombination between donor traps and the valence band are observed in PL spectra at energy 0.6–0.8 eV, i.e. ~0.47 eV below the energy gap of InPBi, which is determined by contactless electroreflectance. [ABSTRACT FROM AUTHOR]

A reversible resistive switching effect is detected in films created from the suspension of partially fluorinated graphene (more specifically, small graphene or few-layer graphene quantum dots in a fluorographene matrix), which makes them promising for resistive memory applications. This paper is focused on the investigation and comparison of the traps and transport in such films in both the low- and high-resistance state. The appearing set of traps for holes and electrons in the band gap of fluorinated graphene is revealed in the films at the low-resistance state, and their parameters (activation energy and trap density) are defined using charge spectroscopy. The minimum relaxation time of nonequilibrium carriers from different traps is found to be about 700 ns, and the energy level position of corresponding traps from the conduction band of a silicon substrate equals 0.08 eV. It has also been demonstrated that the carrier transport in the low-resistance state is determined by the same traps, and they form conductive channels in the film. Transport and non-equilibrium recharging processes in the state of high resistance are found to occur above all by means of carrier tunneling through the potential barriers in the films. [ABSTRACT FROM AUTHOR]

The role of an interface as an electron-trapping layer in double-stacked indium gallium zinc oxide (IGZO) thin-film transistors (TFTs) was investigated and interface location-controlled (ILC) IGZO TFTs were introduced. In the ILC TFTs, the thickness of the top and bottom IGZO layers is controlled to change the location of the interface layer. The system exhibited improved electrical characteristics as the location of the interface layer moved further from the gate insulator: field-effect mobility increased from 0.36 to 2.17 cm2 V−1 s−1, and the on-current increased from 2.43  ×  10−5 to 1.33  ×  10−4 A. The enhanced electrical characteristics are attributed to the absence of an electron-trapping interface layer in the effective channel layer where electrons are accumulated under positive gate bias voltage. [ABSTRACT FROM AUTHOR]

Electronic structures of intrinsic vacancy defects in Sr2MgSi2O7 phosphorescent host material are investigated using first-principles calculations. Si vacancies are too high in energy to play any role in the persistent luminescence of Sr2MgSi2O7 phosphor. Mg vacancies form easier than Sr vacancies as a result of strain relief. Among all the vacancies, O1 vacancies stand out as a likely candidate because they are the most favorable in energy and introduce an empty triply degenerate state just below the CBM and a fully-occupied singlet state at ~1 eV above the VBM, constituting in this case effective hole trap level and electron trap levels, respectively. Mg vacancies are unlikely to explain the persistent luminescence because of its too shallow electron trap level but they may compensate the hole trap associated with O1 vacancies. We yield consistent evidence for the defect physics of these vacancy defects on the basis of the equilibrium properties of Sr2MgSi2O7, total-energy calculations, and electronic structures. The persistent luminescence mechanism of Sr2MgSi2O7:Eu2+, Dy3+ phosphor is also discussed based on our results for O1 vacancies trap center. Our results provide a guide to more refined experiments to control intrinsic traps, whereby probing synthetic strategies toward new improved phosphors. [ABSTRACT FROM AUTHOR]

The electronic properties of manganese in crystalline germanium have been investigated by means of deep level transient spectroscopy (DLTS). Mn was diffused in the material by a thermal treatment at 700 °C. Next to the deep levels of nickel and copper, which are known contaminants in Ge treated at high temperature, three not previously reported levels were observed. These two hole and one electron traps, with apparent energy level positions at EV +0.136 eV, EV +0.342 eV and EC − 0.363 eV, were assigned to substitutional Mn. The analysis of the carrier capture cross-sections, the absence of field-assisted emission and the observation of the Mn2− electron paramagnetic resonance spectrum in n-type Ge:Mn at low temperature are all compatible with Mn introducing two acceptor and one donor levels in the band gap of Ge. [ABSTRACT FROM AUTHOR]

Defect levels in semi-insulating Tl6I4S single crystals grown by the horizontal Bridgman technique have been characterized using photo-induced current transient spectroscopy (PICTS). These measurements revealed six electron traps located at (0.059  ±  0.007), (0.13  ±  0.012), (0.31  ±  0.074), (0.39  ±  0.019), (0.62  ±  0.110), and (0.597  ±  0.105). These defect levels are attributed to vacancies (VI, VS) and antisite defects (IS, TlS, TlI) upon comparison to calculations of native defect energy levels using density functional theory and defects recently reported from photoluminescence and photoconductivity measurements. [ABSTRACT FROM AUTHOR]

Electron tunnelling from an Ln2+-electron trap (Ln = Er, Nd, Ho, Dy) to a Ce4+-recombination centre is investigated experimentally and theoretically in YPO4 : Ce3+,Ln3+. Low temperature thermoluminescence, fading and isothermal decay measurements for samples with concentrations of Ce and Ln ranging from 0.05 to 5.0% are analysed. We observe a temperature activated tunnelling that depends on type of Ln and concentration. Results are simulated with simple quantum mechanical concepts. The average distance between traps and centres is altered by the Ce and Ln concentrations. The higher the concentration, the higher the electron tunnelling probability which can be attributed to a shorter average Ce4+–Ln2+ distance. As a result, changes in the thermoluminescence characteristics like the fading rates and the isothermal decay curves are observed. [ABSTRACT FROM AUTHOR]

Electron trapping phenomena have been investigated with respect to the energy levels of localized trap states and bias-induced device instability effects in pentacene field-effect transistors. The mechanism of the photoinduced threshold voltage shift (ΔVT) is presented by providing a ΔVT model governed by the electron trapping. The trap-and-release behaviour functionalized by photo-irradiation also shows that the trap state for electrons is associated with the energy levels in different positions in the forbidden gap of pentacene. Spectroscopic analysis identifies two kinds of electron trap states distributed above and below the energy of 2.5 eV in the band gap of the pentacene crystal. The study of photocurrent spectra shows the specific trap levels of electrons in energy space that play a substantial role in causing device instability. The shallow and deep trapping states are distributed at two centroidal energy levels of ∼1.8 and ∼2.67 eV in the pentacene band gap. Moreover, we present a systematic energy profile of electron trap states in the pentacene crystal for the first time. [ABSTRACT FROM AUTHOR]

We report variations in the currents of CdZnTe semiconductor crystals during exposure to a series of light emitting diodes of various wavelengths ranging from 470 to 950 nm. The changes in the steady-state current of one CdZnTe crystal with and without illumination along with the time dependence of the illumination effects are discussed. Analysis of the de-trapping and transient bulk currents during and after optical excitation yield insight into the behaviour of charge traps within the crystal. Similar behaviour is observed for illumination of a second CdZnTe crystal suggesting that the overall illumination effects are not crystal dependent. [ABSTRACT FROM AUTHOR]