Semiconductor Layers Research Articles

Thermal-induced bandgap broadening phenomenon in copolymer organic semiconductors

This study elucidates the thermal-induced bandgap broadening (TBB) phenomenon in copolymer organic semiconductors (OSCs). From the perspective of device physics, the diketopyrrolopyrrole-based copolymer was employed as the semiconductor layer to fabricate a back-to-back Schottky junction structure. Characterization through the analysis of I–V curves enables the qualitative exploration of the correlation between bandgap and temperature in copolymer OSCs. Then, technology computer-aided design was utilized to explore the influence of thermal-induced bandgap broadening on the back-to-back Schottky I–V curves. Subsequently, the variable temperature UV-VIS-NIR absorption spectra of the copolymer OSCs were analyzed, providing quantitative evidence of the thermal-induced bandgap broadening phenomenon and confirming its recoverability. Through the research of the Schottky junction and absorption spectra, we verified the consistency of the TBB phenomenon in both the electrical and optical bandgaps. From the scanning electron microscope images of the copolymer OSC films, it is found that the thermal-induced bandgap broadening phenomenon is mainly caused by thermal expansion and increased disorder of copolymer molecules. This study highlights a physical phenomenon of copolymer OSCs that is different from most inorganic semiconductors, and such insight offers a theoretical perspective for the application and thermal stability investigation of copolymer devices under high temperature conditions.

Verifying the physical role of upper-active-layer on charge transport together with bias stability in bilayer-channel oxide thin-film transistors

In this work, we report the fabrication of solution-processed bilayer-structure oxide thin-film transistors (TFTs) exhibiting superior electrical characteristics and enhanced positive/negative bias stabilities. This was achieved by tuning the carrier concentration and bandgap of the top active layer in the bilayer semiconductor. The characteristics of the top layer were modulated through aluminum (Al) doping in indium oxide semiconductors. Bilayer-channel TFTs with an optimized indium-aluminum-oxide top layer (In:Al ratio of 8:2) demonstrated effective electron transport via percolation conduction and exhibited high mobility. Furthermore, the optimized bilayer TFTs displayed small threshold voltage shifts under positive and negative bias stress, attributed to the effective formation of a quasi-two-dimensional electron gas and the suppression of oxygen vacancies. An in-depth study on engineering the carrier concentration and bandgap of the bilayer structure provides insights into material design and fabrication strategies for high-performance and stable heterostructure transistors.

Rapid Electrohydrodynamic Jet Printing for Self-Aligned Organic Semiconducting Layers and Printed Organic Electronics

Rapid Electrohydrodynamic Jet Printing for Self-Aligned Organic Semiconducting Layers and Printed Organic Electronics

Design and calculation of photoelectric properties of resonance enhanced InAs/GaSb type-II superlattices photodetectors with diffraction rings structure

The resonance enhanced InAs/GaSb type-II Superlattices (T2SLs) infrared detectors with diffraction rings is designed, and the photoelectric characteristics are calculated and studied in this paper. The diffraction rings are designed on the top surface of T2SLs detector to control the incident light inside the device by forming the resonant cavity. We designed the structure of the conventional PIN InAs/GaSb T2SLs photodetector, calculated the energy band structure of the absorption layer, and analyzed the influence of the thickness of the absorption layer on the photoelectric performance. It is proved that blindly increasing the thickness of the absorption layer cannot effectively improve the device performance. We further studied the quantum efficiency (QE) and electric field distribution of the device after adding the diffraction ring structure. The results show that the structure with diffraction rings can significantly improve the QE of the photodetector without increasing the dark current. The interaction between the diffraction ring and the metal contact layer will enhance the localization of the electric field and further increase the light absorption between the semiconductor layers.

Structure-performance relationship of polypropylene/elastomer/carbon black composites as high voltage cable shielding layer

As polypropylene (PP) is a competitive insulating material for next generation high-voltage cable, the corresponding PP based cable semi-conductive shielding layer material needs to be developed. This paper developed an excellent material prescription and proposed an analytical method of structure-performance relationship for the application and the evaluation of PP-based cable shielding layer. First, PP/POE/CB and PP/SEBS/CB composites with different carbon black (CB) loading were prepared and their electrical and mechanical properties were compared. Through thermal analysis technique, crystalline property and thermal stability of the composites were studied in detail. And the synchrotron radiation X-ray scattering techniques were employed to analyze the distribution of carbon black in the blend semi-quantitatively. The analysis result turns out the enrichment of carbon black in POE phase and its instability at high temperature limits its application under cable operation conditions. In contrast, PP/SEBS/CB30phr is recommended for lower thermal deformation, lower PTC effect and better mechanical parameters.

Nonlinear vibration of five-layered functionally graded piezoelectric semiconductor nano-plate on Pasternak foundation

The vibration character of piezoelectric semiconductor nano-plate is important for understanding the multi-fields coupling and optimizing the serving behavior. In this article, the nonlinear vibration of five-layered functionally graded piezoelectric semiconductor nano-plate based on Pasternak foundation is studied, and the nonlocal theory is used to analyze the size-dependent dynamic response of nano-plate. Combining the Von karman’s nonlinear deformation theory and the constitutive of piezoelectric semiconductor layers, Hamilton’s principle is introduced to derive the nonlinear governing equations. To solve the nonlinear governing equations, the updated iteration method for this problem is proposed. Through numerical examples, it is found that the initial electron concentration in piezoelectric semiconductor layer, the nonlocal parameter, the functionally graded index in the plate, the elastic modulus of Pasternak foundation and the geometrical parameters can be designed to effectively tune the dynamic nonlinear frequency and damping of layered functionally graded piezoelectric semiconductor nanoplate. The interaction of these parameters is also analyzed in detail. Comparison with existing numerical results is also presented. A new way is provided to tune the nonlinear vibration of multi-layered piezoelectric semiconductor nano-plate.

P‐19: High Mobility and Reliability Oxide Stacked TFT for Application to Next Generation Display

The stacked structure thin film transistors (TFT) has caused the widespread attention to achieve high mobility and reliability simultaneously. To ensure the stacked structure TFT application to mass production, it is critical to reduce the number of mask‐count. In this paper, 8‐mask‐count stacked TFT‐array process using the first semiconductor layer overlapped with the source and drain layer directly, which is the first layer on the glass substrate, is studied. By adopting this novel process, the device mobility is 25.4 cm2/Vs, which is more than twice that of conventional top‐gate self‐aligned a‐IGZO device. Besides, the ΔVth under the positive bias stress of 30V and negative bias temperature illumination stress of ‐30V for 1 h is +0.41V and ‐0.13V, respectively, achieving the stability to the level of a‐IGZO TFTs.

Interfacial Charge Transport Enhancement of Liquid-Crystalline Polymer Transistors Enabled by Ionic Polyurethane Dielectric.

In organic field-effect transistors (OFETs) using disordered organic semiconductors, interface traps that hinder efficient charge transport, stability, anddevice performance are inevitable. Benchmark poly(9,9-dioctylfuorene-co-bithiophene) (F8T2) liquid-crystalline polymer semiconductor has been extensively investigated for organic electronic devices due to its promising combination of charge transport and light emission properties. This study demonstrates that high-capacitance single-layered ionic polyurethane (PU) dielectrics enable enhanced charge transport in F8T2 OFETs. The ionic PU dielectrics are composed of a mild blending of PU ionogel and PU solution, thereby forming a solid-state film with robust interfacial characteristics with semiconductor layer and gate electrode in OFETs and measuring high capacitance values above 10 µF cm-2 owing to the combined dipole polarization and electric double layer formation. The optimized fabricated ionic PU-gated OFETs exhibit a low-voltage operation at -3V with a remarkable hole mobility of over 5 cm2 V-1 s-1 (average = 2.50 ± 1.18 cm2 V-1 s-1), which is the highest mobility achieved so far for liquid-crystalline F8T2 OFETs. This device also provides excellent bias-stable characteristics in ambient air, exhibiting a negligible threshold voltage shift of -0.03V in the transfer curves after extended bias stress, with a reduced trap density.

Impedance and Interface States Depending on Frequency Analysis of Al/(ZnFe2O4-PVA)/p-Si Structures

This study investigates the properties of a film made of zinc ferrite (ZnFe2O4) doped polyvinyl alcohol (PVA). The film is sandwiched between an aluminum (Al) and p-Si semiconductor layers, and electrical measurements are conducted on the structure in a wide scope of frequency besides voltage. The study evaluates the impacts of the ZnFe2O4-PVA interlayer on surface-states (NSS), and complex-impedance (Z* = Z' - jZ''). A remarkable impact of the values of series resistance (RS) and the interlayer on the capacitance-voltage (C-V) and conductance-voltage (G/ω-V) data has been observed at moderate and high frequencies. Hence, the C and G/ω versus V qualities were modified at high frequency to eliminate the outcome of RS. The Hill-Coleman approach was utilized to estimate the values for NSS. Experimental results confirm that both the NSS , RS and the interlayer in the metal-polymer-semiconductor (MPS) structures are critical factors that significantly alter the electrical and dielectric properties. The analysis of the results obtained from the impedance study showed divergent behavior. It was observed that the impedance values increase in the low frequency, while they diminish in the higher frequencies, as a result of the mutual effect between the interface and the dipole polarization. The study suggests that due to its high dielectric value, the ZnFe2O4-PVA interlayer may be a better alternative to conventional insulators for charge/energy storage.

Theory of acoustic polarons in the two-dimensional SSH model applied to the layered superatomic semiconductor Re6Se8Cl2.

Layered superatomic semiconductors, whose building blocks are atomically precise molecular clusters, exhibit interesting electronic and vibrational properties. In recent work [Tulyagankhodjaev et al., Science 382, 438 (2023)], transient reflection microscopy revealed quasi-ballistic exciton dynamics in Re6Se8Cl2, which was attributed to the formation of polarons due to coupling with acoustic phonons. Here, we characterize the electronic, excitonic, and phononic properties with periodic density functional theory. We further parameterize a polaron Hamiltonian with nonlocal (Su-Schrieffer-Heeger) coupling to an acoustic phonon to study the polaron ground state binding energy and dispersion relation with variational wavefunctions. We calculate a polaron binding energy of about 10meV at room temperature, and the maximum group velocity of our polaron dispersion relation is 1.5 km/s, which is similar to the experimentally observed exciton transport velocity.

Step-edge-guided nucleation and growth mode transition of α-Ga2O3 heteroepitaxy on vicinal sapphire

Abstract Controlling the epitaxial growth mode of semiconductor layers is crucial for optimizing material properties and device performance. In this work, the growth mode of α-Ga2O3 heteroepitaxial layers was modulated by tuning miscut angles (θ) from 0° to 7° off the (10-10) direction of sapphire (0002) substrate. On flat sapphire surfaces, the growth undergoes a typical three-dimensional (3D) growth mode due to the random nucleation on wide substrate terraces, as evidenced by the hillock morphology and high dislocation densities. As the miscut angle increases to θ=5°, the terrace width of sapphire substrate is comparable to the distance between neighboring nuclei, and consequently, the nucleation is guided by terrace edges, which energetically facilitates the growth mode transition into the desirable two-dimensional coherent growth. Consequently, the mean surface roughness decreases to only 0.62 nm, accompanied by a significant reduction in screw and edge dislocations to 0.16×107 cm-2 and 3.58×109 cm-2, respectively. However, the further increment of miscut angles to θ=7° shrink the terrace width less than nucleation distance, and the step-bunching growth mode is dominant. In this circumstance, the misfit strain is released in the initial growth stage, resulting in surface morphology degradation and increased dislocation densities.

First principles calculation of interface interactions and photoelectric properties of ZnSe/SnSe heterostructure.

Heterostructure engineering is an effective technology to improve photo-electronic properties of two dimensional layered semiconductors. In this paper, based on first principles method, we studied the structure, stability, energy band, and optical properties of ZnSe/SnSe heterostructure change with film layer. Results show that all heterostructures are the type-II band arrangement, and the interlayer interaction is characterized by van der Waals. The electron concentration and charge density difference implies the electron (holes) transition from SnSe to monolayer ZnSe. By increasing the layer of SnSe films, the quantum effects are weakened leading to the band gap reduced, and eventually show metal properties. The optical properties also have obvious change, the excellent absorption ability of ZnSe/SnSe heterostructures mainly near the infrared spectroscopy. These works suggest that ZnSe/SnSe heterostructure has significant potential for future optoelectronic applications.

Catalytic Pyrolysis of Polypropylene for Cable Semiconductive Buffer Layers.

With the progress of the power grid system, the coverage area of cables is widening, and the problem of cable faults is gradually coming to affect people's daily lives. While the vast majority of cable faults are caused by the ablation of the cable buffer layer, polypropylene (PP), as a common cable buffer material, has pyrolysis properties that critically impact cable faults. Studying the semiconductive buffer layer of polypropylene (PP) and its pyrolysis properties allows us to obtain a clearer picture of the pyrolysis products formed during PP ablation. This understanding aids in the accurate diagnosis of cable faults and the identification of ablation events. In this study, the effects of temperature and catalyst (H-Zeolite Standard Oil Corporation Of New York (Socony) Mobil-Five (HZSM-5)) content on the PP thermolysis product distribution were studied by using an online tubular pyrolysis furnace-mass spectrometry (MS) experimental platform. The results showed that PP/40% HZSM-5 presented the highest thermolytic efficiency and relative yield of the main products at 400 °C.

Coexistence of Interacting Charge Density Waves in a Layered Semiconductor.

Coexisting orders are key features of strongly correlated materials and underlie many intriguing phenomena from unconventional superconductivity to topological orders. Here, we report the coexistence of two interacting charge-density-wave (CDW) orders in EuTe_{4}, a layered crystal that has drawn considerable attention owing to its anomalous thermal hysteresis and a semiconducting CDW state despite the absence of perfect Fermi surface nesting. By accessing unoccupied conduction bands with time- and angle-resolved photoemission measurements, we find that monolayers and bilayers of Te in the unit cell host different CDWs that are associated with distinct energy gaps. The two gaps display dichotomous evolutions following photoexcitation, where the larger bilayer CDW gap exhibits less renormalization and faster recovery. Surprisingly, the CDW in the Te monolayer displays an additional momentum-dependent gap renormalization that cannot be captured by density-functional theory calculations. This phenomenon is attributed to interlayer interactions between the two CDW orders, which account for the semiconducting nature of the equilibrium state. Our findings not only offer microscopic insights into the correlated ground state of EuTe_{4} but also provide a general nonequilibrium approach to understand coexisting, layer-dependent orders in a complex system.

Role of ultrathin Ti3C2Tx MXene layer for developing solution-processed high-performance low voltage metal oxide transistors

Metal oxide transistors have garnered substantial attention for their potential in low-power electronics, yet challenges remain in achieving both high performance and low operating voltages through solution-based fabrication methods. Optimizing interfacial engineering at the dielectric/semiconductor interface is of utmost importance in the fabrication of high-performance thin film transistors (TFTs). In the present article, a bilayer Ti3C2Tx-MXene/SnO2–semiconductor (Tx stands for surface termination) configuration is used to fabricate a high-performance n-type thin film transistor by using an ion-conducting Li-Al2O3 gate dielectric on a p+-Si substrate, where electrical charges are formed and modulated at the Li-Al2O3/SnO2 interface, and Ti3C2Tx-MXene nanosheets serve as the primary electrical charge channel due to their long lateral size and high mobility. A comparative characterization of two distinct TFTs is conducted, one featuring Ti3C2Tx MXene and SnO2 semiconductor layer and the other with SnO2 only. Notably, the TFT with the Ti3C2Tx MXene layer has shown a significant boost in the carrier mobility (10.6 cm2/V s), leading to remarkable improvements in the on/off ratio (1.3 × 105) and subthreshold swing (194 mV/decade), whereas the SnO2 TFT without the Ti3C2Tx MXene layer shows a mobility of 1.17 cm2/V s with 8.1 × 102 on/off ratio and 387 mV/decade subthreshold swing. This investigation provides a possible way toward the development of high-performance, low-voltage TFT fabrication with the MXene/semiconductor combination.

Patterned Liquid Crystal Polymer Thin Films Improved Energy Conversion Efficiency at High Incident Angles for Photovoltaic Cells.

In this report, micro-patterned silicon semiconductor photovoltaic cells have been proposed to improve the efficiency in various incident sunlight angles, using homeotropic liquid crystal polymers. The anisotropic liquid crystal precursor solution based on a reactive mesogen has good flowing characteristics. It can be evenly coated on the silicon solar cells' surface by a conventional spreading technique, such as spin coating. Once cured, the polymers exhibit asymmetric transmittance properties. The optical retardation characteristics of the coated polymer films can be eventually determined by the applicable coating and curing parameters during the processes. The birefringence of light then influences the optical path and the divergence of any encountered sunlight. This allows more photons to enter the active semiconductor layers for optical absorption, resulting in an increase in the photon-to-electron conversion, and thus improving the photovoltaic cell efficiency. This new design is straightforward and could allow various patterns to be created for scientific development. The experimental results have evidenced that the energy conversion efficiency could be improved by 2-3% for the silicon photovoltaic cells, under direct sunlight or at no inclination, when the liquid crystal polymer precursor solution is prepared at 5%. In addition, the efficiency could be much more significantly improved to 14-16% when the angle is inclined to 45°. The unique patterned liquid crystal polymer thin films provide enhanced energy conversion efficiency for silicon photovoltaic cells. The design could be further evaluated for other solar cell applications.

Electrical properties of MAH-g-PP modified PP/SEBS matrix semi-conductive composite materials

Polypropylene (PP) becomes a superior candidate material for new environmental-friendly cable insulation layer with its excellent heat resistance, electrical properties and degradability. At present, most of studies focus on the insulation layer of PP cable. However, there are few studies on semi-conductive shielding layer of PP cable which match its insulation layer. In this paper, polypropylene (PP)/styrene ethylene butylene styrene (SEBS) is adopted as matrix of PP cable semi-conductive layer to matching its insulation layer. Meanwhile, Maleic anhydride grafted polypropylene (MAH-g-PP) is used to cooperatively improve the compatibility between PP and SEBS. The physicochemical properties, space charge injection properties and compatibility of semi-conductive composites with different CB and MAH-g-PP contents is studied by combining experiment and simulation methods. The experimental results show that the surface roughness of the semi-conductive layer and the space charge inside the insulation layer decrease first and then increase with the increase of CB addition. Among them, the two parameters of 25 phr CB semi-conductive layer is the lowest, respectively 13.98 nm and 2.25 × 10−8C. These two parameters are significantly reduced after the addition of compatibilizer MAH-g-PP, which decreased by 29.47 % and 62.22 %, respectively. The simulation results show that the Flory-Huggins interaction parameters (χ) of MAH-g-PP with PP and SEBS are −73.3 and −45.2, respectively, which are 236.24 % and 107.34 % lower than those of PP/SEBS. The χ value of MAH-g-PP/CB is 8.20, which is 33.27 % and 9.59 % lower than CB/PP and CB/SEBS, respectively. It shows that MAH-g-PP can effectively improve the compatibility of matrix and filler. This work has important guiding significance for the research of semi-conductive layer formulation of PP cable.

Research progress on the application of two-dimensional layered semiconductors in optoelectronic devices

In recent years, traditional 2D layered materials such as graphene have been widely used in the photoelectric area. As the emerging research and development of 2D layered materials, there are more and more newly developed 2D layered semiconductors being applied to this field, such as MoS2, phosphorene, and other nanomaterials. 2D layered MoS2 can be utilized as sensitive elements to obtain high-performance photodetectors with high responsivity, high current response rate, and short recovery time. Moreover, because phosphorene has adjustable bandgap width and strong light absorption, it has more potential in aspects of other semiconductors, and application in photoelectric devices. This article introduced the structures of some common 2D layered semiconductors, discussed their applications in photoelectric fields, and pointed out their limitations. For example, transition metal dichalcogenide (TMDC) materials generally have low carrier mobility, and black phosphorus is prone to adsorb water molecules from the air, leading to changes in its physical and chemical properties. Finally, improvement methods of applications and prospects for future development were provided.

Comparison of p-n and p-i-n vertical diodes based on p-PMItz/n-Si, p-PMItz/n-4HSiC and p-PMItz/i-SiO2/n-Si heterojunctions

In this paper, we present a comprehensive comparison study between p-n and p-i-n vertical diodes employing diverse heterojunction configurations under dark conditions. The diodes are fabricated utilizing p-PMItz as the organic semiconductor layer interfacing with different inorganic substrates, including n-Si (n-type silicon), n-4HSiC (n-type 4H silicon carbide), and incorporating an intrinsic SiO2 (silicon dioxide) layer in the p-PMItz/i-SiO2/n++-Si configuration. The current–voltage and dielectric characteristics are analyzed to discern the performance discrepancies among these diode configurations. The influence of heterojunction interfaces and band alignments on device behavior is investigated, shedding light on the charge transport mechanisms within these structures. Our findings reveal distinct trends in device characteristics for p-n and p-i-n diodes, highlighting the significance of heterojunction design in optimizing device performance. This comparative analysis offers valuable insights for the development of efficient organic–inorganic hybrid diodes tailored for various optoelectronic applications.

Enhancing Sensitivity in Gas Detection: Porous Structures in Organic Field-Effect Transistor-Based Sensors.

Gas detection is crucial for detecting environmentally harmful gases. Organic field-effect transistor (OFET)-based gas sensors have attracted attention due to their promising performance and potential for integration into flexible and wearable devices. This review examines the operating mechanisms of OFET-based gas sensors and explores methods for improving sensitivity, with a focus on porous structures. Researchers have achieved significant enhancements in sensor performance by controlling the thickness and free volume of the organic semiconductor layer. Additionally, innovative fabrication techniques like self-assembly and etching have been used to create porous structures, facilitating the diffusion of target gas molecules, and improving sensor response and recovery. These advancements in porous structure fabrication suggest a promising future for OFET-based gas sensors, offering increased sensitivity and selectivity across various applications.