Intrinsic Trapping Research Articles

High‐Gain and Tunable Linear Photodetection in 2D Tunneling Heterostructures Through Potential Engineering

Abstract2D materials are extensively employed in the fabrication of high‐performance photodetectors owing to their exceptional physical properties. However, most 2D material photodetectors fail to sustain high gain under intense illumination due to the limited intrinsic trap states. Here, an n‐n type Bi2O2Se/SnSe2 van der Waals tunneling heterojunction photodetector with a detection range from visible to near‐infrared (VIS‐NIR) is presented. Under reverse bias, the heterojunction induces a significant electron barrier and hole potential well, ensuring low leakage current and ample hole defect states. Therefore, the photodetector demonstrated a responsivity of 1636.3 AW−1 and a detectivity of 1.39 × 1014 Jones under 660 nm illumination, maintaining a tunable linear dynamic range (LDR) of ≈74.7 dB. This performance is attributed to the hole potential well‐suppressing the recombination of photogenerated carriers, thereby enhancing the device's gain. Furthermore, the tunneling of photogenerated electrons within the heterojunction's space charge region under bias enables rapid response (75.1 and 15.6 µs). In summary, the study introduces a novel strategy to overcome the limited detection capabilities of 2D devices under intense illumination, characterized by outstanding linearity for rapid detection and high‐resolution imaging.

Evidence and engineering of x-ray luminescence in lead free perovskite Cs2AgInCl6 with Bi substitutions

Cs2AgInCl6 belongs to the family of lead-free halide double perovskites. Lead-free halide double perovskite appears as a viable contender for scintillator applications due to its inexpensive production costs, low intrinsic trap density, and nanosecond quick reaction. Perovskite crystals have a substantially lower trap density than lead halide and traditional oxide scintillator materials, according to thermo-luminescence measurements. Cs2AgInCl6 structure and dimensionality were engineered by Bi doping. Bi substitution reduces the bandgap, making it suited for scintillation applications. Bi substitution allows for easy tuning of Cs2AgIn(1−x)BixCl6 (0 ≤ x ≤ 50) due to its wide versatility in scintillation properties. For Cs2AgIn(1−x)BixCl6 (0 ≤ x ≤ 50), x-ray power dependent luminescence increases with increasing power. Because of their nontoxicity, sensitivity, reaction time, and stability, Cs2AgIn(1−x)BixCl6 (0 ≤ x ≤ 50) double perovskite crystals are promising for x-ray scintillation.

Formation of a combined electron-hole emission state in the LiRbSO4 – Eu phosphor

In the irradiated phosphor 4 LiRbSO Eu , the mechanisms of formation of the induced or combined electron-emitting state at 3.1-2.94 eV were studied using optical and thermal activation spectroscopy methods. It has been shown experimentally that the combined electron-emitting state of the phosphor is formed from the electron states of impurity and intrinsic electron and hole trapping centers of 24Eu SO   and 34 4 SO SO . Electron and hole trapping centers are created by irradiating the phosphor with photons exceeding the width of the forbidden band of the matrix, where free electrons are created in the conduction band and a hole in the valence band. The trapping center is formed by the capture of free electrons by impurities and anionic complexes according to the reaction 3 2 Eu e Eu      ,2 34 4 SO e SO    . In one process with electron centers, holes in the form of 24SO are localized. Thus, impurity and intrinsic 2 4Eu SO   and 34 4 SO SO  electron-hole trapping centers are formed. Similarly, trapping centers are formed as a result of charge transfer from the excited anion of the 24SO complex to the 3Eu  impurities and to the neighboring 2 4 SO anions according to the reaction ( 2 3 O Eu   ) and ( 2 24O SO  ), and localized holes are also formed in one act along with it. Combined electron-emitting states consisting of impurity and intrinsic electron states are excited by photons with energies of ~4.0 eV and ~4.5 eV.

Passivated indium oxide thin-film transistors with high field-effect mobility (128.3 cm2 V−1 s−1) and low thermal budget (200 °C)

Here, we demonstrate a high-mobility indium oxide (In2O3) thin-film transistor (TFT) with a sputtered alumina (Al2O3) passivation layer (PVL) with a low thermal budget (200 °C). The sputtering process of the Al2O3 PVL plays a positive role in improving the field-effect mobility (µ FE) and current on/off ratio (I ON/I OFF) performance of the In2O3 TFTs. However, these enhancements are limited due to the high density of intrinsic trap defects in the In2O3 channels, as reflected in their large hysteresis and poor bias stability. Treating the In2O3 channel with oxygen (O2) plasma prior to sputtering the Al2O3 PVL results in notable improvements. Specifically, a high µ FE of 128.3 cm2V−1 s−1, a high I ON/I OFF over 106 at V DS of 0.1 V, a small hysteresis of 0.03 V, and a negligible threshold voltage shift under negative bias stress are achieved in the passivated In2O3 TFT (with O2 plasma pretreatment), representing a significant improvement compared to the passivated In2O3 TFT (without O2 plasma pretreatment) and the unpassivated In2O3 TFT. The remarkable reduction of intrinsic trap defects in the passivated In2O3 TFT compensated by O2 plasma is the primary mechanism underlying the improvement in µ FE and bias stability, as validated by x-ray photoelectron spectra, hysteresis analysis, and temperature-stress electrical characterizations. Plasma treatment effectively compensates for intrinsic trap defects in oxide semiconductor (OS) channels, when combined with sputter passivation, resulting in a significant enhancement of the overall performance of OS TFTs under low thermal budgets. This approach offers valuable insights into advancing OS TFTs with satisfactory driving capability and wide applicability.

Ultrafast hot electron transfer and trap-state mediated charge separation for boosted photothermal-assisted photocatalytic H2 evolution

Comprehensive interpretation of photo-generated carrier dynamics in photocatalytic systems will strengthen its position as a candidate for future utilization and development of solar energy resources. As exploratory models, aggregated carbon dots (A-CDs) and dispersed carbon dots (D-CDs) were coated on the surface of g-C3N4 nanovesicles (CNNVS) to form A-CDs/CNNVS and D-CDs/CNNVS composite systems. Among of them, A-CDs/CNNVS exhibits a superior photothermal-assisted photocatalytic H2 evolution of up to 24.8 mmol/g, which was about 2.03 and 1.23 times higher than that of CNNVS and D-CDs/CNNVS, respectively. Ultrafast transient absorption spectroscopy (TAS) demonstrates that the improved thermalization of photo-generated electrons and trapping behavior of cooled electrons via the introduction of A-CDs in A-CDs/CNNVS to complement the hot electrons of intrinsic excitation and electrons trapping of CNNVS at a higher extent in comparison of D-CDs/CNNVS. This work presents an in-depth insight to investigate CDs-based photothermal-assisted photocatalytic H2 evolution system for realizing solar energy conversion.

Hydrogen Impact: A Review on Diffusibility, Embrittlement Mechanisms, and Characterization.

Hydrogen embrittlement (HE) is a broadly recognized phenomenon in metallic materials. If not well understood and managed, HE may lead to catastrophic environmental failures in vessels containing hydrogen, such as pipelines and storage tanks. HE can affect the mechanical properties of materials such as ductility, toughness, and strength, mainly through the interaction between metal defects and hydrogen. Various phenomena such as hydrogen adsorption, hydrogen diffusion, and hydrogen interactions with intrinsic trapping sites like dislocations, voids, grain boundaries, and oxide/matrix interfaces are involved in this process. It is important to understand HE mechanisms to develop effective hydrogen resistant strategies. Tensile, double cantilever beam, bent beam, and fatigue tests are among the most common techniques employed to study HE. This article reviews hydrogen diffusion behavior, mechanisms, and characterization techniques.

Luminescence properties of a green-emitting mechanoluminescent phosphor CaSrGa4O8:xTb3+ without pre-excitation.

In this study, both mechanoluminescence (ML) and long persistent luminescence (LPL) characteristics were first observed in CaSrGa4O8 doped with Tb3+ ions, which confirmed that CaSrGa4O8 is a high-quality host for luminescent material research. Notably, the samples show stronger mechanoluminescent intensity with increasing Tb3+ doping. Additionally, the introduction of Tb3+ led to a shift of the thermoluminescence peak towards higher temperatures and a substantial increase in its intensity, suggesting that Tb3+ doping enhances the overall trap concentration and introduces deeper trap energy levels. Presumably, the free carriers in the system recombine upon mechanical stimulation, releasing energy that is transferred to Tb3+ ions. Investigations into the intrinsic structure, matrix effects, and trap evolution of the material confirmed that deep and shallow traps are responsible for the observed ML and LPL phenomena, respectively. The elucidation of the unique luminescent properties of the material provides us with some guidance for the development of new multi-functional luminescent materials.

Mechanisms of intrinsic and impurity electron-hole trapping centers in K_3 Y〖(SO_4)〗_3-Eu and LiY〖(SO_4)〗_2-Eu double cation phosphors

Mechanisms of intrinsic and impurity electron-hole trapping centers in K_3 Y〖(SO_4)〗_3-Eu and LiY〖(SO_4)〗_2-Eu double cation phosphors

Intrinsic Charge Trapping and Reversible Charge Induced Structural Modifications in a‐Si3N4

AbstractAmorphous silicon nitride (a‐Si3N4) is an essential material for a wide variety of electronic devices, ranging from its use in dielectric layers to its paramount importance for memory applications. In particular, the latter has triggered the interest in charge trapping, for which so‐called N‐ and K‐centers have been identified in experiments – with the atomistic configuration still subject of vigorous debate. Here, the range of hole and electron traps in stoichiometric a‐Si3N4 are revealed by combining atomistic calculations at different levels of theory. The variety of sites within the amorphous network are characterized by introducing a statistical sampling method to quantify the statistical completeness of structural models obtained from a melt‐quench procedure, in combination with a powerful local descriptor inspired by Tolman's angle. Hole trapping is dominated by two‐coordinate N‐centers, resulting in shallow hole traps. In contrast, electron trapping exhibits more nuanced behavior, encompassing both intrinsic polaronic trapping and the previously identified K‐center type trapping (silicon dangling bond *SiN3). Intrinsic polaronic trapping originates from distorted SiN4 tetrahedra. Structural relaxation of the intrinsic polaron sites results in significant elongation of a Si‐N bond and reversible generation of *SiN3 and N3Si‐SiNx ∈ {3, 4} defects.

In Situ Measurement of Effective Gate Bias Voltage in Ionic Liquid-Gated Organic Field-Effect Transistors: Exploring Intrinsic Performance and Trap Density of States.

Electric double layer (EDL)-mediated transistors with ionic liquid (IL) gating have garnered substantial interest due to their exceptional properties, such as high transconductance and low-voltage operation, positioning them as promising candidates for organic electronics. In this study, we present an in situ measurement of effective gate bias voltage (VGS,eff) in IL-gated organic field-effect transistors (IL-OFETs) using a modified current-voltage measurement configuration. The results reveal a significant deviation between VGS,eff and the applied gate bias (VGS,app), indicating that the EDL at the gate/IL interface screens the applied voltage. It is observed that the screening effect varies depending on the specific cation and anion present in the IL. The evaluation of VGS,eff plays a pivotal role in understanding the intrinsic behavior of IL-OFETs and addresses the challenges associated with accurate performance assessment. Inherently, IL-OFETs demonstrate high transconductance, achieving values of approximately 9 mS while operating at a low threshold voltage of around 0.55 V. Through the acquisition of VGS,eff, we have successfully addressed the limitations impeding the numerical estimation of the trap density of states (trap DOS) in IL-OFETs. Remarkably, our calculations reveal an exceptionally low density of deep traps, which serves as a crucial factor contributing to the near-ideal subthreshold swing (61-68 mV dec-1) observed in IL-OFETs. Further investigations unveil the neutral electrical nature of the IL bulk during OFET operation, confirming the hypothesis that the applied gate bias voltage in electrolyte-gated OFETs drops across the EDLs formed at the interfaces. The impedance spectroscopic (IS) analysis confirms the low contact resistance (≈1 Ω·m) of IL-OFETs calculated using the transition voltage method. The IS analysis also reveals the low-transmissive nature of the IL/organic semiconductor interface. The knowledge gained from this study holds significant implications for realizing high-performance electrolyte-gated OFETs in various applications including digital electronics, energy storage, and sensing. By unraveling the factors influencing the device performance, such as VGS,eff and trap DOS, this research contributes to the advancement of organic electronics and paves the way for future developments in the field.

Highly‐Doped Lanthanide‐Based Nanocrystals with Cooperative Core‐Shell Upconversion Emission for Multicomponent One‐Pot Chemical Transformations

AbstractIn order to apply near infrared (NIR) light‐activated upconversion nanocrystals (UCNCs) in photochemistry, extremely bright luminescence is needed to excite the ultraviolet (UV)‐visible light absorbing photocatalyst/substrate. In this study, a multilayered UCNC consisting of a β‐NaYF4:Yb0.2, Tm0.005 core, heavily Yb3+‐doped β‐NaYbF4:Y0.09, Tm0.01 intermediate shell, and inert β‐NaYF4 outer shell is prepared. By compartmentalizing the sensitizer (Yb3+)‐activator (Tm3+) pair in the core and intermediate shell with different concentration ratios, a cooperative luminescence effect is discovered. Apart from core emission, energy harvesting followed by sequential energy transfer from a high density of neighboring Yb3+ to Tm3+ in the intermediate shell induces a large population of excited emitter ions. Furthermore, after back energy transfer from the core to intermediate shell, the energy is not quenched by intrinsic trap sites but is instead transferred to Tm3+, further boosting emission in the UV, blue, and NIR regions. The exceptionally bright UCNC is then used to drive NIR‐light‐activated one‐pot multicomponent reactions involving the upconversion energy transfer from UCNC to UV‐visible light absorbing photocatalyst/substrate, Lewis acid catalytic activity of the lanthanide ions (Y3+) on the surface, and photothermal property of the UCNC. The reactions studied include the deacetalization‐Knoevenagel condensation reaction, photooxidation‐cyanation reaction, and hydrodehalogenation‐cyanosilylation reaction.

Tunable photoluminescence of intrinsic oxygen vacancies and Bi3+/Eu3+/Li+ tridoped BaZnOS for application in wLEDs

Quaternary wide-band-gap oxychalcogenides (MZnOS, M = Ca, Sr, and Ba) are underexplored inorganic semiconductors compared with pure chalcogenides or oxides, in which more dopants could be simultaneously coordinated by oxide and chalcogenide anions. In this kind of materials, color-tunable photoluminescence (PL) could well be obtained without destructing structure. Due to the need of complex conditions for synthesis compared with Ca(Sr)ZnOS, the unique structure of BaZnOS remains largely unexplored as host for application in lighting/display fields. Spectroscopic measuring combined with XPS and DFT computational studies on pristine BaZnOS reveal that the weak multi-colored self-PL were originated from the intrinsic trap states of oxygen vacancies (VO2+, VO+ and VO0). The crystallographic occupancies of dopants Bi3+/Eu3+ and Li + at Ba2+ and Zn2+ sites, respectively were proved based on the Rietveld refinements and crystal chemistry rules. Tunable and thermally stable PL in the regions of cyan, white and even yellow could be systematically obtained from the BaZnOS: Bi/Eu via changing concentrations of dopants with the help of energy transfer (ET) from the host to dopants as well as Bi to Eu. The effect of unlit Li+ is acting both as charge balancer and fluxing agent for reducing calcination temperature and improving PL efficiency. Finally, as a proof-of-concept experiment, the BaZnOS: Bi/Eu/Li phosphor converted white light emitting diode (pc-wLED) was fabricated and produced attractive performances including high CRI of 82.5, low CCT of 4024 K, CIE coordinates of (0.3462, 0.3531), and luminous efficiency (LE) of 16.5 lm/W. Altogether, the stable Bi/Eu/Li tridoped BaZnOS phosphor is a promising candidate to be applied in lighting/display fields.

Significantly enhanced flashover voltage of epoxy in vacuum by graded surface roughness modification

AbstractThe flashover strength of epoxy (EP) insulations in the High voltage direct current applications of future energy grids can be improved by tailoring their surface condition. This work aims to improve the DC surface flashover characteristics of EP after being treated with sandpaper of different gradings. Samples with virgin EP and homogenously modified EP considering varying surface roughness (Ra = 0.54, 3.16, 5.24, and 8.35 μm) are prepared. Different experimental characterisations, such as water contact angle, surface intrinsic conductivity, surface voltages, flashover strength, and trap distributions are conducted and evaluated to analyse the difference between virgin and treated EP. Moreover, based on the obtained experimental results of homogenously treated EP and theoretical analysis, the concept of surface functionally graded materials (SFGMs) is put forward. The flashover voltages of homogenously treated EP are augmented significantly compared to virgin EP regardless of the voltage polarity and enhanced by enhancing the surface roughness. The sample TModel‐C with SFGM design shows a 45.02% and 43.75% improvement in the negative and positive flashover voltages than that of the virgin EP. In the end, COMSOL simulations are conducted to justify the experimental findings and to analyse the difference between virgin and modified samples in terms of electric field distribution.

Characterizing and correcting electron and hole trapping in germanium cross-strip detectors

We present measurements of electron and hole trapping in three COSI germanium cross-strip detectors. By characterizing the relative charge collection efficiency (CCE) as a function of interaction depth, we show that intrinsic trapping of both electrons and holes have significant effects on the spectroscopic performance of the detectors. We find that both the electron and hole trapping vary from detector to detector, demonstrating the need for empirical trapping measurements and corrections. Using our measurements of charge trapping, we develop a continuous depth-dependent second-order energy correction procedure. We show that applying this empirical trapping correction produces significant improvements to spectral resolution and to the accuracy of the energy reconstruction.

Specific Features of Formation of Electron and Hole Trapping Centers in Irradiated CaSO4-Mn and BaSO4-Mn

Spectroscopic and thermoactivation methods were used to study the processes of accumulation of electron and hole trapping centers and energy transfer of electronic excitations to impurities in CaSO4-Mn and BaSO4-Mn. It is shown that electronic trapping centers are created during the excitation of an anionic complex as a result of charge transfer from O2−→SO42− to closely spaced anionic complexes SO42− in CaSO4 and BaSO4. In CaSO4 and BaSO4, energy transfer from the host to impurities occurs at the moment of charge transfer from the excited anionic complex to the combined radiative electronic state at 2.95–3.1 eV. This combined state is formed from electronic trapping centers Mn+-SO4− and SO43−-SO4−. It was found that the emerging combined radiative states at 2.95–3.1 eV of sulfates, which are formed as a result of charge transfer from the excited anionic complexes to the excited state of impurities, Tl+,Cu+,and Mn2+, occupy the same energy levels as the intrinsic electronic trapping center SO43− of the host at 2.95–3.17 eV. Experimental results show that during UV photon irradiation, anionic complexes are excited mainly near impurities in sulfates.

Defect-rich selenium doped graphitic carbon nitride for high-efficiency hydrogen evolution photocatalysis

Graphitic carbon nitride (g-C3N4) has been demonstrated as a promising non-metal material for photocatalytic hydrogen evolution (PHE), while its photocatalytic activity is greatly limited due to the narrow visible light response-ability and the intrinsic severe charge deep trapping and recombination effects. Herein, a co-functionalized g-C3N4 system by Se doping and nitrogen vacancies modification is developed through a Se vapor-assisted-chemical vapor deposition synthetic strategy. Advanced characterization results revealed that Se dopants promote the visible-light absorption ability of g-C3N4, while nitrogen defects-induced shallow trap states are constructive to improving charge separation/transportation efficiency by effectively retarding the detrimental charge deep trapping and recombination. As a result, the synergistic effect of the Se dopants and nitrogen defects leads to a highly efficient PHE performance of g-C3N4. The integrated engineering strategy and mechanism understanding provided in this work may offer new insights into developing other novel photocatalysts for various applications.

Electron-hole trapping centers in Na2SO4 with a transition metal impurity Mn

The Na 2 SO 4 samples were obtained by slow evaporation method. The mechanisms of the formation of electron and hole trapping centers are investigated by spectroscopic methods. Intrinsic recombination emission of 2.9–3.1 eV and impurity emission of 1.85 eV are excited at 4.0–4.5 eV. Intrinsic SO 3− 4 −SO − 4 and impurity Mn + − SO − 4 trapping centers were revealed. The local levels corresponding between the electron and hole trapping center are 4.0–4.5 eV. The decay of intrinsic and impurity trapping centers was recorded at temperatures of 130–150 K and 280–350 K.

Influence of Two- and Three-Dimensional Engineering on the Trap State Distribution and Photophysical Properties of Lead Halide Perovskite Polycrystals

Constructing a two- and three-dimensional (2D/3D) heterojunction structure on the surface of a 3D perovskite film, termed 2D/3D engineering, is effective in elevating the stability of perovskite polycrystal-based photovoltaic and photoelectronic devices; however, it remains controversial whether this protocol is favorable or detrimental to the device performance. Here, we prepare a series of 2D/3D perovskite films by post-treating the perovskite polycrystalline film with different concentrations of phenethylammonium iodide (PEAI). Systematic spectroscopy and electrochemical studies illustrate that PEAI can penetrate the 3D perovskite network and eliminate the intrinsic trap states of perovskite polycrystals, while the 2D perovskite nanosheets enriched on the top of the polycrystalline film may introduce additional trap states, which manipulate the photoluminescence performance and dynamics of the as-prepared perovskite films in an opposite manner. Based on this finding, the strategy of optimizing the photophysical properties of the host 3D perovskite through 2D/3D engineering is elaborated, paving the way for fabricating high-performance and high-stability perovskite polycrystalline films.

Cr dopant induced tailoring of intrinsic defects and trap distribution in MgAl2O4 nanocrystals: electron spin resonance and thermoluminescence

Thermoluminescence (TL) response of γ-irradiated Cr3+ doped MgAl2O4 nanocrystals is studied to investigate the impact of dopant ions on intrinsic defects and trap distribution. At low doping concentration, the broad TL glow curve has a dominant incomplete peak attributed to deep F+ centers around 673 K and contribution from shallow , , and trapping states in low temperature region. TL glow curve intensity and trap distribution is found to be influenced with increase in Cr doping concentration. Electron spin resonance spectra show the interaction of electron spins at paramagnetic F+/V− centers with isolated and paired Cr3+ ions with increase in Cr doping concentration. Cr3+ ions doped at octahedral sites are found to be perturbed by the presence of , , etc defect centers and may cause the formation of Cr associated defect clusters at higher doping concentration. A trapping mechanism is proposed as per the TL response obtained upon γ-irradiation to comprehend the intertrap charge transfer among various shallow and deep trapping states.

White Light Emission from Single-Component Cs7Cd3Br13:Pb2+,Mn2+ Crystals with High Quantum Efficiency and Enhanced Thermodynamic Stability

Single-component white light emitters are particularly attractive for fabricating economical solid-state devices for display and lighting. Herein, an efficient white light with photoluminescence quantum yields approaching 98% has been obtained in Mn2+ and Pb2+ co-doped Cs7Cd3Br13 crystals. The quantified bonding and nonbonding characters calculated by the crystal orbital Hamilton population analysis demonstrate that the Mn2+ and Pb2+ occupy preferentially in the [CdBr4]2– tetrahedrons rather than the [CdBr6]4– octahedrons in Cs7Cd3Br13. According to the PL spectral characteristic and the theoretical results, the broadband white light emission from Cs7Cd3Br13:Pb2+,Mn2+ crystals is ascribed to the multiple PL origins, i.e., the first self-trapped exciton (STE1) from the intrinsic trapping states of host lattice Cs7Cd3Br13, the d–d transition of Mn2+, and the second self-trapped exciton (STE2) induced by the introduction of Pb2+, respectively. The results calculated by density functional theory reveal that the incorporation of Mn2+ and Pb2+ has significantly improved the thermodynamic stability of the Cs7Cd3Br13 structure with lower defect formation energies, which is verified by the experimental observation in the temperature-dependent PL spectra of the emitting crystals. The findings here provide a new perspective for a single-component white light via creating multiple PL centers in a single matrix as well as help in the elucidation of the preferential site occupancy mechanism of the dopants in different symmetrical units.