Carrier Transport Mechanism Research Articles

Tensile strain-induced disorder and weak localization in SrRuO3 thin films on (100) KTaO3 substrates

Abstract SrRuO3 (SRO) thin (~12 nm) films have been grown on KTaO3 (001) substrates by RF magnetron sputtering. The as-prepared films are under enormous in-plane tensile strain, which corresponds to the elastic energy of ~1.5 MJ. Annealing in oxygen at 900 C for 6 hr relaxes strain, partially lowering the elastic energy. The surface topography shows a transition from granularity as the Ar+O2 pressure increases from 5 mTorr to 200 mTorr, with a simultaneous change in the average surface roughness from 4 nm to 0.8 nm. Annealing transforms the topography to island-type and enhances surface roughness. The films deposited at 5 mTorr are semiconducting, and annealing further enhances the resistivity. The -T of films grown at 200 mTorr shows a metallic behavior with an inflection in the -T at TC~150 K, FM transition. The low-temperature resistivity upturn shows the disordered nature of these films. The eq. ρ(T)=1/(σ_0+aT^(1/2)+a_1 T^(p/2) )+bT^α (p=2 & =2) describes the transport behavior from 2K to 300K of 5 mTorr deposited films. In the 200 mTorr deposited film, the above eq. is valid at T<95 K with p=2 and =1.5. At TC<T300 K, the -T follows eq. ρ(T)=ρ_0+ ρ_1 T^α with =1.3 and 1.5 for the as-grown and annealed films. The lower temperature -T upturn appears to have contributions from the disorder-enhanced renormalized e-e interaction (REEI) and weak localization (WL) effects. The magnetoresistance behavior supports a substantial WL effect in the films grown at 200 mTorr. Our results establish a strong correlation between the nature of strain, surface topography, and carrier transport mechanisms.

Toward Ultrathin: Advances in Solution-Processed Organic Semiconductor Transistors.

In recent years, organic semiconductor (OSC) ultrathin films and their solution-processed organic field-effect transistors (OFETs) have garnered attention for their high flexibility, light weight, solution processability, and tunable optoelectronic properties. These features make them promising candidates for next-generation optoelectronic applications. An ultrathin film typically refers to a film thickness of less than 10 nm, i.e., several molecular layers, which poses challenges for OSC materials and solution-processed methods. In this paper, first we introduce the carrier-transport regulation mechanism under ultrathin limits. Second, we summarize various solution-processed techniques for OSC ultrathin films and elucidate advances in their OFETs performance, such as enhanced or maintained mobilities, improved switching ratios, reduced threshold voltages, and minimized contact resistance. The relationship between the ultrathin-film thickness, microstructure of various OSCs (small molecules and polymers), and device performance is discussed. Third, we explore the recent application of OSC ultrathin-film-based OFETs, such as gas sensors, biosensors, photodetectors, and ferroelectric OFETs (Fe-OFETs). Finally, the conclusion is drawn, and the challenges and prospects of ultrathin OSC transistors are presented. Nowadays, research on ultrathin films is still in its early stages; further experience in precise film deposition control is crucial to advancing research and broadening the scope of applications for OSC ultrathin devices.

Carrier Generation and Recombination in AC-QLEDs with a Synergistic Capacitance Effect of ZnO/PVDF Heterofunction Layers.

The alternating current-driven electroluminescence (AC-EL) of Cd-based quantum dots is garnering increasing attention due to advantages such as high efficiency and an extended operating lifetime. However, the generation and transport mechanisms of charge carriers within devices still need to be more understood. Here, we construct a simple device and investigate its luminance mechanisms within a single cycle using time-resolved spectroscopy. We tested the luminance-voltage and luminance-frequency characteristics of the device as the thickness of the insulating layer varied, finding that they both exhibited a trend of initially increasing and then decreasing as the voltage or frequency increased. We subsequently investigated the transient electroluminescent characteristics of the device, which featured a P(VDF-TrFE-CFE) layer as the insulator. This layer prevents carrier injection from the Al electrode, while the ZnO layer acts as a charge-generating layer to provide additional carriers. We observed that with an increase in AC voltage, the strongest luminance peak is advanced in the cycle compared to when lower voltages were applied. The position of the strongest luminance peak is delayed with an increasing AC frequency. The C-V characteristics demonstrated that the synergistic P(VDF-TrFE-CFE)/ZnO exhibited a displacement current transforming to a conduct current, which activates the forward operation of the QLED and enables it to emit light. The mechanism we present may serve as a benchmark for improving the luminance and longevity of such devices.

Highly Diffusive Nonluminescent Carriers in Hybrid Phase Lead Triiodide Perovskite Nanowires

AbstractCrystal structural rearrangements unavoidably introduce defects into materials, where even these small changes in local lattice structure could arouse a prominent impact on the overall nature of crystals. Contrary to the traditional notion that defects obstruct carrier transport, herein, we report a promoted transport mechanism of nonluminescent carriers in single‐crystalline CH3NH3PbI3 nanowires (1345.2 cm2 V−1 s−1, about a 14‐fold improvement), enabled by the phase transition induced defects (PTIDs). Carriers captured by PTIDs evade both the radiative and non‐radiative recombinations during the incomplete tetragonal‐to‐orthorhombic phase transition at low temperatures, forming a specific nonluminescent state that exhibits an efficient long‐distance transport and thereby realize a prominent enhancement of photocurrent responsivity for photodetector applications. The findings provide broader insights into the carrier transport mechanism in perovskite semiconductors and have significant implications for their rational design for photoelectronic applications at varied operating temperatures.

Highly Diffusive Nonluminescent Carriers in Hybrid Phase Lead Triiodide Perovskite Nanowires.

Crystal structural rearrangements unavoidably introduce defects into materials, where even these small changes in local lattice structure could arouse a prominent impact on the overall nature of crystals. Contrary to the traditional notion that defects obstruct carrier transport, herein, we report a promoted transport mechanism of nonluminescent carriers in single-crystalline CH3NH3PbI3 nanowires (1345.2 cm2 V-1 s-1, about a 14-fold improvement), enabled by the phase transition induced defects (PTIDs). Carriers captured by PTIDs evade both the radiative and non-radiative recombinations during the incomplete tetragonal-to-orthorhombic phase transition at low temperatures, forming a specific nonluminescent state that exhibits an efficient long-distance transport and thereby realize a prominent enhancement of photocurrent responsivity for photodetector applications. The findings provide broader insights into the carrier transport mechanism in perovskite semiconductors and have significant implications for their rational design for photoelectronic applications at varied operating temperatures.

Large area, ultrafast, suppressed dark current and high-performance PtSe2/MoS2 van der Waals heterostructure based visible to NIR broadband photodetector

Group-10 transitional metal dichalcogenide, in particular Platinum selenide (PtSe2), have attracted substantial attention owing to its fascinating properties such as high carrier mobility, narrow bandgap, and high stability in contrast to other low bandgap 2D materials. However, in bare PtSe2, high dark current and lower sensitivity restrict to make high-performance broadband photodetector. Herein, a large area and stable PtSe2/MoS2 heterostructure based photodetector is fabricated which exhibits suppressed dark current and high-performance with broad 400-1200 nm detection, covering visible to near-infrared region (NIR). The PtSe2/MoS2 heterostructure device exhibits ∼103 order reduction in the dark current, high detectivity, and better stable response as compared to its bare PtSe2 device. Moreover, under NIR (900 nm) illumination, the PtSe2/MoS2 device demonstrates high responsivity of 17.9 AW−1 and high specific detectivity of 9.8 × 1012 Jones at amoderate bias of −5V. It exhibits ultra-fast response with rise/ fall time of 103 μs/117 μs corroborating its high performance. To understand the working of PtSe2/MoS2 photodetector, a detailed carrier transport mechanism is investigated based on the interface. This work provides a facile strategy to fabricate large area, fast response and high-performance broadband photodetector to build future optoelectronic devices.

Dual-Electrically Configurable MoTe2/In2S3 Phototransistor toward Multifunctional Applications.

Photodetectors, essential for a wide range of optoelectronic applications in both military and civilian sectors, face challenges in balancing responsivity, detectivity, and response time due to their inherent unidirectional carrier transport mechanism. Multifunctional photodetectors that address these trade-offs are highly sought after for their potential to reduce costs, simplify system design, and surpass Moore's Law limitations. Herein, we present a multimodal phototransistor based on a 2D MoTe2/In2S3 heterostructure. Through dual electrical modulation employing bias voltage and gate voltage, we engineer the energy band to achieve switchable photoresponse mechanisms between photoconductive and photovoltaic modes. In photoconductive mode, the device exhibits a responsivity of 320 A/W and a specific detectivity of 1.2 × 1013 Jones. Meanwhile, in photovoltaic mode, it exhibits a light on/off ratio of 2 × 105 and response speed of 0.68/0.60 ms. These capabilities enable multifunctional applications such as high-resolution imaging across various wavelengths, a conceptual optoelectronic logic gate, and dual-channel optical communication. This work makes an advancement in the development of future multifunctional optoelectronic devices.

Fröhlich Scattering Effects on Electron Mobility in β‐Ga2O3 Power Devices under High Temperature

The impact of Fröhlich scattering on β‐Ga2O3 Schottky barrier diodes (SBDs) electron mobility, particularly at high temperatures, is investigated. This scattering is crucial due to electron–polar optical phonon interactions. Temperature‐dependent I–V characteristics of a β‐Ga2O3 SBD from 300 to 473 K showed significant current reduction due to electron–polar optical phonon scattering, supported by correlation with mobility profiles. Additionally, in situ temperature‐dependent XPS analysis revealed a notable positive shift in core‐level binding energy, attributed to heightened electron–phonon interactions. This study provides crucial insights into carrier transport mechanisms, essential for power device design and operation.

Atom layer deposited TiO2 electron transport layer for silicon heterojunction solar cells to achieve high performance

Silicon/compound heterojunction (SCH) solar cells based on p-type and n-type c-Si wafers using atom layer deposition-TiO2 and low work function metal as the electron transport layer and rear electrode are fabricated. Efficiencies of 20.6 % and 21.6 % are achieved on p-type and n-type silicon solar cells, respectively. High Voc exceeding 700 mV have been realized on both kinds of Si wafers. Special attention has been paid to the SCH solar cells based on p-type c-Si wafers in which the TiO2 electron transport layer serves as the emitter. Carrier transport mechanisms and junction characteristics of the SCH solar cells are analyzed based on dark J-V measurement. The formation of a strong inversion layer at the Si surface region is determined, which implies the high Voc potential of the SCH solar cells based on p-type Si. An optical loss analysis is performed along with a possible solution to further improve the Jsc. The feasibility of TiO2 applied as an efficient electron transport layer (emitter) in p-type SCH solar cells with high performance has been showed.

Flexible Artificial Ag NPs:a-SiC0.11:H Synapse on Al Foil with High Uniformity and On/Off Ratio for Neuromorphic Computing.

A neuromorphic computing network based on SiCx memristor paves the way for a next-generation brain-like chip in the AI era. Up to date, the SiCx-based memristor devices are faced with the challenge of obtaining flexibility and uniformity, which can push forward the application of memristors in flexible electronics. For the first time, we report that a flexible artificial synaptic device based on a Ag NPs:a-SiC0.11:H memristor can be constructed by utilizing aluminum foil as the substrate. The device exhibits stable bipolar resistive switching characteristic even after bending 1000 times, displaying excellent flexibility and uniformity. Furthermore, an on/off ratio of approximately 107 can be obtained. It is found that the incorporation of silver nanoparticles significantly enhances the device's set and reset voltage uniformity by 76.2% and 69.7%, respectively, which is attributed to the contribution of the Ag nanoparticles. The local electric field of Ag nanoparticles can direct the formation and rupture of conductive filaments. The fitting results of I-V curves show that the carrier transport mechanism agrees with Poole-Frenkel (P-F) model in the high-resistance state, while the carrier transport follows Ohm's law in the low-resistance state. Based on the multilevel storage characteristics of the Al/Ag NPs:a-SiC0.11:H/Al foil resistive switching device, we successfully observed the biological synaptic characteristics, including the long-term potentiation (LTP), long-term depression (LTD), and spike-timing-dependent plasticity (STDP). The flexible artificial Ag NPs:a-SiC0.11:H/Al foil synapse possesses excellent conductance modulation capabilities and visual learning function, demonstrating the promise of application in flexible electronics technology for high-efficiency neuromorphic computing in the AI period.

A Review: Application of Doped Hydrogenated Nanocrystalline Silicon Oxide in High Efficiency Solar Cell Devices.

Due to the unique microstructure of hydrogenated nanocrystalline silicon oxide (nc-SiOx:H), the optoelectronic properties of this material can be tuned over a wide range, which makes it adaptable to different solar cell applications. In this work, the authors review the material properties of nc-SiOx:H and the versatility of its applications in different types of solar cells. The review starts by introducing the growth principle of doped nc-SiOx:H layers, the effect of oxygen content on the material properties, and the relationship between optoelectronic properties and its microstructure. A theoretical analysis of charge carrier transport mechanisms in silicon heterojunction (SHJ) solar cells with wide band gap layers is then presented. Afterwards, the authors focus on the recent developments in the implementation of nc-SiOx:H and hydrogenated amorphous silicon oxide (a-SiOx:H) films for SHJ, passivating contacts, and perovskite/silicon tandem devices.

Study of mechanical, optoelectronic, and thermoelectric characteristics of Be/Mg ions Based double perovskites A2FeH6 (A= Be, Mg) for hydrogen storage applications

This study addresses the hydrogen storage capabilities and mechanical, optoelectronic, and thermoelectric features of double perovskite hydrides A2FeH6 (A = Be, Mg). The structural aspects suggest the cubic symmetry of studied hydrides. The formation enthalpy value calculation has confirmed the structures' thermal stability. The gravimetric ratios of Be2FeH6 and Mg2FeH6 hydrides are 7.50 wt% and 5.43 wt%, respectively. The desorption temperatures are predicted to be 230.32 K and 208.67 K, respectively. The mechanical and thermophysical characteristics have been elaborated, which demonstrate mechanical stability, higher stiffness, ductile behavior, and higher temperature stability of both materials. The examined electronic properties have revealed band gap values of 2.89 and 3.08 eV, respectively. The optical properties have been assessed to predict the appropriateness of these hydrides for deployment in photovoltaic systems. The thermoelectric characteristics have been evaluated to examine the carrier transport mechanism and efficiency for converting heat into electricity. Finally, the investigated properties and hydrogen storage capacity of these compounds suggest that they are suitable for hydrogen storage and have the potential to play a key role in many energy generation applications.

Maximizing Potential Applications of MAX Phases: Sustainable Synthesis of Multielement Ti3AlC2.

This study employs the molten-salt-shielded method to dope the Ti3AlC2 MAX phase with Nb and Mo, aiming to expand the intrinsic potential of the material. X-ray diffraction confirms the preservation of the hexagonal lattice structure of Ti3AlC2, while Raman and X-ray photoelectron spectroscopic analyses reveal the successful incorporation of dopants with subtle yet significant alterations in the vibrational modes and chemical environment. Scanning electron microscopy with energy-dispersive X-ray spectroscopy characterizations illustrate the characteristic layered morphology and uniform dopant distribution. Density functional theory simulations provide insights into the modified electronic structure, displaying changes in carrier transport mechanisms and potential increases in metallic conductivity, particularly when doping occurs at both the M and A sites. The computational findings are corroborated by the experimental results, suggesting that the enhanced material may possess improved properties for electronic applications. This comprehensive approach not only expands the MAX phase family but also tailors its functionality, which could allow for the production of hybrid materials with novel functionalities not present in the pristine form.

First-principles study of phase-dependent carrier transport mechanism for MASnI3 Sn-based halide perovskite

Organic-inorganic hybrid perovskites have attracted tremendous attentions owing to their excellent properties as next-generation photovoltaic devices. With soft covalent framework, organic-inorganic hybrid perovskites exhibit different phases at different temperatures. The band-edge features of perovskites are mainly contributed by inorganic framework, which means the structural differences between these phases would lead to complex carrier transport. We investigated the carrier transport of Sn-based organic-inorganic hybrid perovskite CH3NH3SnI3 (MASnI3), considering acoustic deformation potential scattering, ionized impurity scattering, and polar optical phonon scattering. It is found that the electron mobility of each phase of MASnI3 is strongly correlated with the Sn–I–Sn bond angle and there is in-plane/out-of-plane anisotropy. The projected crystal orbital Hamilton population analysis suggested that the tilt and rotation of the [SnI6]4− octahedron influence the Sn(p)–I(p) orbital electron coupling and the electron transport, leading to different band-edge features in multiple phases. The carrier mobility with respect to temperature was further calculated for each phase of MASnI3 in respective temperature intervals, showing lower carrier mobility in high temperature. Comparing the contribution of different scattering mechanisms, it was found that the dominant scattering mechanism is polar optical phonon scattering, while multiple scattering mechanisms compete in individual cases.

An investigation on low operating voltage induced self-rectifying multilevel resistive switching in AgNbO3

This study presents a resistive random-access memory (RRAM) based on silver niobate (AgNbO3) perovskite films prepared via sputtering for the first time. The device exhibits a self-rectifying behavior at low operating and switching voltages, with a set voltage of about −0.4 V. Bipolar resistive switching was realized at a low operating voltage and with small set and reset voltage distributions. Compared to previously reported resistive switching perovskite materials, the device displays a superior resistive switching capability while maintaining a uniform memory window of up to 102, excellent endurance of over 104 cycles, and a long retention period of over 106 s. Moreover, the RRAM device exhibits four levels of resistive switching when the compliance current is varied, with each level of resistance state demonstrating uniformity and discrete read windows. The carrier-transport mechanism of the device was elucidated by considering various conduction mechanisms, including Schottky emission and space-charge-limited conduction. The resistive switching behavior was found to follow the conductive filamentary model, which is governed by the migration of oxygen vacancies when an electric field is applied. These outstanding properties of AgNbO3 make it a promising perovskite material option for future nonvolatile multilevel RRAM device applications.

Carrier transport mechanisms of titanium nitride and titanium oxynitride electron-selective contact in silicon heterojunction solar cells

It is widely accepted that an effective carrier-selective contact is indispensable for high performance crystalline silicon (c-Si) solar cells. However, the properties of these carrier-selective contact materials significantly differ from c-Si in terms of band gap, work function, lattice constant. Consequently, this gives rise to challenges such as band discontinuity and suspended bonds at the interface, which subsequently impact the specific carrier transport process and potentially lead to a reduction primarily in the fill factor at the device level. Titanium nitride (TiN) and titanium oxynitride (TiOxNy) have been employed as an electron-selective contact in both c-Si and perovskite solar cells, demonstrating their effectiveness in enhancing the performance of these devices. Based on the detailed characterizations of the band alignment, the carrier transport mechanisms are analyzed using multiple models, and the theoretical results are basically self-consistent through the verification of variable temperature experiments. These analytical methods can also provide solutions for analyzing the band structure and transport mechanism of diverse heterojunctions, ultimately contributing to the design and optimization of semiconductor heterojunction devices.

Giant photoelectric energy conversion via a 3C-SiC Nano-Thin film double heterojunction

Enhancing the energy conversion efficiency is utmost important in renewable energy and self-powered optoelectronic sensing applications. In this study, we propose the concept of a p-3C-SiC nano-thin film/p-Si/n-Si double junction (DJ) structure, which exhibits a massive photoelectric energy conversion efficiency and ultra-high sensitivity of optoelectronic sensors. The optoelectronic characteristics of this DJ heterostructure are compared to those of a p-3C-SiC/n-Si single-junction (SJ) heterostructure, which shares similarities in all technical and material parameters, except for the inclusion of the middle p-Si layer in the DJ structure. The experimental results reveal that the lateral photocurrent, sensitivity, theoretical power and maximum power of the DJ structure are more than 100 times (i.e. over 10,000%) greater than those of the SJ structure. We then demonstrated these excellent features of DJ heterostructure through developing of a self-powered position sensitive sensor, which showed an ultrahigh sensitivity. The enormous enhancement in the performance has been elucidated through the efficient photogeneration of charge carriers, electron-hole pair splitting, and the improved charge carrier transport mechanisms in the double heterojunction. This research represents a notable breakthrough in ultra-sensitive optoelectronic sensors and photoenergy conversion, since the proposed concept and theoretical model can be extended to multiple junctions of various semiconductor materials.

Carrier transport mechanisms and photovoltaic performance of Ag/MoOx/Ag/MoOx/n-Si/C60/Al heterojunction solar cell

Carrier transport mechanisms and photovoltaic performance of Ag/MoOx/Ag/MoOx/n-Si/C60/Al heterojunction solar cell

Insights into mechanism of UV-induced degradation in silicon heterojunction solar cells

The ultraviolet-induced degradation (UVID), with losses of up to 11 % after 2000 h-exposure (Sinha et al., 2023) [1], impairs long-term stability of silicon heterojunction (SHJ) solar cells at present. However, the mechanism of UVID has remained only roughly understood till now. Herein, we shed light on the electrical properties of defects in SHJ solar cells to elucidate the underlying mechanism. Defect generation in SHJ solar cells after ultraviolet (UV) irradiation can be observed from photoluminescence (PL) images. Furthermore, we extract the density of states near Fermi level in hydrogenated amorphous silicon (a-Si:H) through analyzing carrier transport mechanism, and find the increment of state density induced by the UV irradiation. In conjunction with Fourier-transform infrared (FTIR) spectra, we ascribe the UV-induced defects to the rupture of Si–H and Si–H2 bonds. Besides, the intersection point between Fermi levels of the c-Si and a-Si:H/c-Si interface can be found shift toward valence band from admittance spectrum analysis, which is the cause of the higher interface state density based on the theory of Fermi energy dependent hydrogen diffusion energy. As a result, a potential mechanism of generation of recombination centers responsible for UVID in SHJ solar cells is proposed, which could provide insights into the possible solutions for UVID and enhance the long-term stability of SHJ solar cells.

Atomically Resolved Defect-Engineering Scattering Potential in 2D Semiconductors.

Engineering atomic-scale defects has become an important strategy for the future application of transition metal dichalcogenide (TMD) materials in next-generation electronic technologies. Thus, providing an atomic understanding of the electron-defect interactions and supporting defect engineering development to improve carrier transport is crucial to future TMDs technologies. In this work, we utilize low-temperature scanning tunneling microscopy/spectroscopy (LT-STM/S) to elicit how distinct types of defects bring forth scattering potential engineering based on intervalley quantum quasiparticle interference (QPI) in TMDs. Furthermore, quantifying the energy-dependent phase variation of the QPI standing wave reveals the detailed electron-defect interaction between the substitution-induced scattering potential and the carrier transport mechanism. By exploring the intrinsic electronic behavior of atomic-level defects to further understand how defects affect carrier transport in low-dimensional semiconductors, we offer potential technological applications that may contribute to the future expansion of TMDs.