Effective Carrier Mobility Research Articles

Coupling effect in field Hall elements based on thin-film SOI MOS transistors

The influence of the coupling effect on the parameters of field Hall elements based on thin-film MOS transistors has been studied. Analysis of the development of today’s microelectronics shows the necessity of developing the element base for high performance sensors based on silicon technologies. One way to significantly improve the performance of sensing elements including magnetic field sensors is the use of thin-film transistors on the basis of silicon on insulator (SOI) structures. It has been shown that field Hall sensors (FHS) may become the basis of high-performance magnetic field sensors employing the coupling effect occurring in the double gate vertical topology of these sensing elements. Electrophysical studies of FHS have been conducted for different gate bias and power supply modes. The results show that the coupling effect between the gates occurs in FHS if the thickness of the working layer between the gates is 200 nm. This effect leads to an increase in the effective carrier mobility and hence an increase in the magnetic sensitivity of the material. Thus field Hall elements based on thin-film transistors fabricated using silicon technologies provide for a substantial increase in the magnetic sensitivity of the elements and allow their application in highly reliable magnetic field sensors.

Identifying the Molecular Origins of High-Performance in Organic Photodetectors Based on Highly Intermixed Bulk Heterojunction Blends

A bulk-heterojunction (BHJ) structure of organic semiconductor blend is widely used in photon-to-electron converting devices such as organic photodetectors (OPD) and photovoltaics (OPV). However, the impact of the molecular structure on the interfacial electronic states and optoelectronic properties of the constituent organic semiconductors is still unclear, limiting further development of these devices for commercialization. Herein, the critical role of donor molecular structure on OPD performance is identified in highly intermixed BHJ blends containing a small-molecule donor and C60 acceptor. Blending introduces a twisted structure in the donor molecule and a strong coupling between donor and acceptor molecules. This results in ultrafast exciton separation (<1 ps), producing bound (binding energy ∼135 meV), localized (∼0.9 nm), and highly emissive interfacial charge transfer (CT) states. These interfacial CT states undergo efficient dissociation under an applied electric field, leading to highly efficient OPDs in reverse bias but poor OPVs. Further structural twisting and molecular-scale aggregation of the donor molecules occur in blends upon thermal annealing just above the transition temperature of 150 °C at which donor molecules start to reorganize themselves without any apparent macroscopic phase-segregation. These subtle structural changes lead to significant improvements in charge transport and OPD performance, yielding ultralow dark currents (∼10-10 A cm-2), 2-fold faster charge extraction (in μs), and nearly an order of magnitude increase in effective carrier mobility. Our results provide molecular insights into high-performance OPDs by identifying the role of subtle molecular structural changes on device performance and highlight key differences in the design of BHJ blends for OPD and OPV devices.

Mechanical, electronic and optical properties of K2TeX6 (X=Cl, Br, I) perovskite derivatives using density functional theory

In this study, the elastic, electronic, and optical properties of cubic, tetragonal and monoclinic K2TeX6 (X = Cl, Br, I) perovskite derivatives are investigated using first-principles calculations. The results reveal that different space groups have a minor influence while the atomic number of X has a significant influence on the physical properties of these perovskite derivatives. In their crystal structures, X and K atoms form X–K ionic bond, while X and Te atoms form X–Te ionic bond with more covalent components. For K2TeBr6 perovskite derivatives within the three different space groups, the close Br–Te bond lengths slightly decrease as the symmetry decreases. However, for the monoclinic K2TeX6 (X = Cl, Br, I) perovskite derivatives, as the atomic radius of X increases, the X–Te bond lengths increase with the decrease in covalent bond components. All the K2TeX6 (X = Cl, Br, I) perovskite derivatives exhibit obvious elastic anisotropy. The monoclinic K2Te2I6 perovskite derivative is brittle, but K2TeX6 (X = Cl, Br) perovskite derivatives are ductile. In the electronic structures of the perovskite derivatives, the top valence bands are primarily contributed by X-p (Cl-3p, Br-4p, or I-5p) and Te-5s orbits, and the bottom conduction bands are dominated by Te-6p orbit. The effective masses and carrier mobilities exhibit distinct anisotropy due to the anisotropic crystal structures. As the atomic number of X increases, the effective masses of electrons and holes gradually decrease, while the carrier mobilities increase. Especially, the higher carrier mobilities of monoclinic K2Te2I6 perovskite derivative are caused by its smaller effective masses. The K2TeX6 (X = Cl, Br, I) perovskite derivatives exhibit excellent dielectric functions and absorption coefficients in the visible and ultraviolet regions.

Free Carrier Mobility, Series Resistance, and Threshold Voltage Extraction in Junction FETs

In this brief, extraction methods are proposed for determining the essential parameters of double gate junction field-effect transistors (FETs). First, a novel method for determining free carrier effective mobility, similar to a recently proposed method for MOSFETs, is developed. The same method is then extended to cover also the case when series resistance is present, while series resistance itself may be determined from the measurement from two FETs with different channel lengths. The key technological and design parameter is the threshold voltage, which may be unambiguously determined from the transconductance-to-current ratio with a constant-current method. The new methods are shown to be effective over a wide range of technical parameters, using technology computer-aided design simulations.

Dynamic Response of Alternating-Current-Driven Light-Emitting Diodes Based on Hybrid Halide Perovskites

In this work, we report the dynamic response of alternating-current-driven light-emitting diodes based on a range of hybrid halide perovskites. Electroluminescence (EL), which appears only in the positive section of a dc voltage, arises in both cycles under a sinusoidal ac voltage. Appearance of EL emission in negative cycles of the ac voltage is explained in terms of available residual charges injected in the previous positive cycle of the sinusoidal voltage; the relative intensity of EL emission in the negative cycle can be correlated to the ambipolarity of charge carriers in the ${\mathrm{CH}}_{3}{\mathrm{NH}}_{3}{\mathrm{Pb}\mathrm{Br}}_{x}{\mathrm{I}}_{3\text{\ensuremath{-}}x}$ series. At low frequencies of the ac voltage, the dynamic response of EL emission in any cycle is in phase with the applied ac voltage; interestingly, the EL emission starts to lag the sinusoidal voltage at higher frequencies. The phase lag also has a correlation to the ambipolarity of the active perovskite material. Finally, the frequency dependence of EL emission under an ac voltage provides the limiting frequency of device operation (\ensuremath{-}3 dB frequency) and thereby the effective carrier mobility in the active heterostructure.

Analysis of Temperature Effect in Quadruple Gate Nano-scale FinFET

Quadruple gate FinFET is a promising candidate among other multi-gate MOS devices due to it’s better scalability and higher short channel effect suppression capability in advanced technology node. In this work, we report the effect of temperature on various performance metrics of quadruple gate FinFET like electrostatic integrity, carrier mobility, switching ratio, analog/RF, and linearity parameters with the help of well-calibrated numerical device simulation-based study (TCAD). While increasing the temperature from 250 °K to 450 °K, due to the enhanced bulk phonon scattering, degradation in carrier effective mobility is observed. Sub-threshold swing and drain induced barrier lowering coefficient vary linearly with temperature. At high temperature, due to the reduced carrier mobility, degradation in the analog figure of merits is observed. RF performance parameters also degrade primarily due to the enhanced gate capacitance and reduced trans-conductance. However, some linearity parameter improves at high temperature due to the reduced magnitude of the higher-order derivative of trans-conductance. Another major contribution of this work is, we demonstrate the inflection point or temperature compensation point in some analog/RF performance metrics where the device characteristics almost invariant with temperature.

Two novel SiC phases: structure, mechanical, and transport properties

Two novel phases of SiC are put forward in this paper, in which the crystal structural, mechanical, and electronic properties, as well as effective mass and carrier mobility of SiC in the Pnnm phase (Pnnm-SiC) and Pm phase (Pm-SiC) are researched utilizing first principles calculations. Both of the novel SiC phases are certificated to have good mechanical and dynamic stability. Through analysis of the three-dimensional perspective of Young’s modulus, shear modulus and Poisson’s ratio, visible anisotropies of mechanical properties are found. The band structure calculations predict two wide bandgap semiconductors, that the Pnnm-SiC is an indirect with a bandgap value of 3.12 eV, While the Pm-SiC is a quasi-direct with a bandgap value of 2.64 eV, which indicates the Pm-SiC has a higher application potential in the optoelectronic device area. An extremely large electronic mobility (7200 cm2 V−1s−1) is found in the Pnnm-SiC. Based on the wide band gap, large carrier mobility, good mechanical and dynamic stability, the Pnnm-SiC is a promising material in the field of high performance electronic device in harsh environment.

Influence of flexible substrate in low temperature polycrystalline silicon thin-film transistors: temperature dependent characteristics and low frequency noise analysis

The carrier transport of p-type low temperature polycrystalline silicon (LTPS) thin-film transistors (TFTs) on flexible substrate has been intensively studied and compared to that on glass substrate in order to improve device performance. To investigate the origin of carrier transport on different substrates, temperature dependent characterizations are carried out for electrical device parameters such as threshold voltage (VTH), subthreshold swing (SS), on-current (Ion) and effective carrier mobility (μeff). The poly-Si grain size Lgrain and the barrier height EB between grain boundaries are well known to be the main parameters to determine transport in polycrystalline silicon and can be extracted based on the polycrystalline mobility model. However, our systemic studies show that it is not grain size but EB that has more influence on the degradation of LTPS TFT on flexible substrates. The EB of flexible substrate is roughly 18 times higher than glass substrate whereas grain size is similar for both devices on different substrates. Compared to the LTPS TFT on glass substrate, higher EB degrades approximately 24 % of Ion, 30 % of SS and 21 % of μeff on the flexible substrate at room temperature. From low frequency noise (LFN) analysis, it is observed that the total trap density (Nt) for flexible substrate is up to four times higher than that of glass substrate, which also supports the high value of EB in the device fabricated on the flexible substrate.

Application of two Cu(II)-azido based 1D coordination polymers in optoelectronic device: Structural characterization and experimental studies

Two new azido bridged 1D polymeric Cu(II) chains, [Cu(L1)(μ1,3-N3)]∞ (1) and [Cu2(L2)2(μ1,1-N3)(μ1,3-N3)]∞ (2) have been synthesized by using two different N2O donor tridentate reduced Schiff base ligands, HL1 = 2-[(2-dimethylamino-ethylamino)-methyl]-4-nitrophenol, HL2 = 2-[(2-diethylamino-ethylamino)-methyl]-4-nitrophenol and both are structurally characterized. Cu(II) ions in both complexes occupy distorted pentacoordinated square pyramidal geometry. Both structures form polymeric chains, in 1, via μ1,3-N3− while in 2via both μ1,1-N3− and μ1,3-N3− bridges. The band gaps of the complexes (2.91 eV for 1 and 2.89 eV for 2) suggest that both polymeric chains are semiconducting and thus possess the potential for uses in devices. A detail I–V analysis was performed to measure device related parameters i.e. effective carrier mobility, transit time, carrier concentration, diffusion length and ideality factor. The results show that both polymeric chains behave as Schottky barrier diodes (SBD) and could be used in opto-electronic device. Between the two complexes, 2 performs better than 1 in terms of applicability as indicated by the calculated parameters.

Solid‐State Electrolyte Dielectrics Based on Exceptional High‐k P(VDF‐TrFE‐CTFE) Terpolymer for High‐Performance Field‐Effect Transistors

AbstractHigh‐performance and low‐voltage organic and inorganic field‐effect transistors (FETs) with solid‐state electrolyte gate insulator that is composed of an exceptional high‐k fluorinated dielectric and an ion‐gel‐blend polymer matrix are reported. The structuring polymer is high‐k poly(vinylidenefluoride‐trifluoroethylene‐chlorotrifluoroethylene) (P(VDF‐TrFE‐CTFE)) terpolymer. The ion gel is made of poly(vinylidene fluoride‐co‐hexafluroropropylene) (P(VDF‐HFP)) and 1‐ethyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl) imide ([EMIM][TFSI]) ion liquid. The blend polymer matrix has high measured capacitance of ≈2 to 5.5 µF cm−2 at 100 Hz, which is attributed to formation of electrical double layers (EDLs) at the insulator/semiconductor interface. High effective carrier mobility (μeff) and low operating voltage ≤2 V with just 0.5 v% of P(VDF‐HFP)‐[EMIM][TFSI] solution in the bulk P(VDF‐TrFE‐CTFE) insulating layer are demonstrated, coupled with low gate‐leakage current levels. Excellent μeff = 1.30 ± 0.19 cm2 V−1 s−1 is achieved in P3HT FETs with SEGI, which is a remarkable boost from 0.48 ± 0.09 cm2 V−1 s−1 at 30 V when pure P(VDF‐TrFE‐CTFE) dielectric is used. Other semiconductors are also tested: IGZO has μeff = 11.09 ± 2.07 cm2 V−1 s−1, and PDFDT has μeff = 2.42 ± 0.46 cm2 V−1 s−1. These remarkable increases in mobility are attributed to the high concentration of induced carriers in the semiconducting channel.

First principle study on interfacial interaction of black phosphorus and CsBr vdW heterostructure

Two dimensional crystalline materials have attracted much attentions due to the establishment of heterostructure that can adjust their electrical and optical properties, and have potential applications in lasers, light-emitting diodes, solar cells and high mobility transistors. And the interface engineering is an effective route to tune structural and electrical properties in semiconductor heterostructures. In this study, the electronic structure, charge transport and optical properties of monolayer caesium bromide and black phosphorus (CsBr/BP) heterostructure are calculated by the first principle based on density functional theory (DFT). It was found that the characteristics of electronic band structures of the monolayer CsBr and BP remain in the heterostructure, and the effective mass and carrier mobility are highly anisotropic. When the heterostructure is uniaxially stretched, the mobility of electron is greater than that of the hole, while the biaxial stretching is just the opposite, the mobility of hole is greater than that of the electron. In addition, compared with the CsBr monolayer, the light absorption of the heterostructure is significantly enhanced, especially in the infrared, indicating that the CsBr/BP heterostructure can be well applied to photovoltaic devices in the future.

Interlayers for Improved Hole Injection in Organic Field‐Effect Transistors

AbstractEfficient charge‐carrier injection is a critical requirement for high‐performance organic electronic devices, such as light‐emitting diodes, solar cells, and field‐effect transistors. In this work, a significantly improved charge‐carrier injection from high work‐function metal‐oxide electrodes in organic field effect transistors (OFETs) is demonstrated for amorphous organic semiconductors (OSCs) by using organic interlayers with a high ionization energy (IE). Molybdenum oxide (MoO3) exhibits limited injection into amorphous 2,2′,7,7′‐tetrakis(N,N‐diphenylamino)‐9,9‐spirobifluorene (Spiro‐TAD) and tris(4‐carbazoyl‐9‐ylphenyl)amine (TCTA) active layers, resulting in high contact resistance and threshold voltage. By inserting an interlayer of a few nanometers thick with high IE between the MoO3 electrode and the amorphous OSC films, the Spiro‐TAD and TCTA OFETs show a substantial enhancement in hole current, subthreshold swing, and effective charge carrier mobility due to the decreased contact resistance. However, for discontinuous interlayers formed on distinct grain domains as in the case of polycrystalline 2,7‐dioctyl[1]benzothieno[3,2‐b][1]benzothiophene (C8‐BTBT) films, the effect of the interlayer reduces. These results demonstrate that the utilization of smooth interlayers with IE higher than the semiconductor is a general approach to elevate the hole injection into amorphous OSCs with high IE in OFETs.

Electronic and optical properties of layered Ruddlesden Popper hybrid X2(MA)n-1SnnI3n+1 perovskite insight by first principles

Hybrid organic–inorganic lead (Pb) halide perovskite is still hampered by the toxicity of Pb as well as its structural stability in the open air. Herein, based on the density-functional theory computation, we show that tin based layered quasi two-dimensional (2D) Ruddlesden-Popper hybrid organic-inorganic perovskite, X2(MA)n-1SnnI3n+1, possesses desirable electronic, excitonic and light absorption properties. Moreover, the electronic and optical properties could be adjustable via surface passivation and reduction of layers. By increasing its layer thickness, we could see that the band gap of the X2(MA)n-1SnnI3n+1 could be moved towards an optimal range (0.9–1.6 eV) of solar cells. In addition, theoretical assessment indicates that effective masses, carrier mobility and optical absorption of such perovskite are notably enhanced when compared to those in their 3D bulk homologous analogue. These features of such layered quasi Sn-based 2D hybrid perovskite could be applied in their photovoltaic and/or photoelectric correlated industries.

Comparison of Effective Carrier Mobility Between Wire on Well and Planar Superlattice Using Time-of-Flight Measurement

Wire on well (WoW) structure, which is formed on a vicinal substrate, has been under consideration for a bandgap adjustor of multijunction cells. The photocurrent of a single-junction cell containing WoW is higher than that of a cell containing planar superlattice (PSL). This work provides direct evidence for the superiority of WoW over PSL in terms of the transport of photogenerated carriers. The time of flight (ToF) of the carriers that were photoexcited near the top surface of a cell was measured with photoluminescence by embedding a probe well beneath the nanostructures (WoW or PSL). The effective mobility of carriers in the nanostructures was obtained from the relationship between the ToF and the electric field applied via external bias. It was revealed that the carrier mobility in WoW was higher than that of PSL. The merit of enhanced mobility for WoW is discussed with device simulation and the potential for higher conversion efficiency is evidenced.

Liquid phase exfoliated boron nanosheets for all-optical modulation and logic gates

Boron nanosheets possess unique photoelectric properties, including photosensitivity, photoresponse, and optical nonlinearity. In this article, we show the interaction between light and boron nanosheets in which concentric rings formed in the far field, which attributed to the strong Kerr nonlinearity of boron nanosheets. Furthermore, the distortion, regulation and relationship between the Kerr nonlinearity and effective mass or carrier mobility of the diffraction rings of boron nanosheets have been investigated. Our work shows that the spatial self-phase modulation effect of boron nanosheets is indeed caused by nonlocal electronic coherence. In addition, we have implemented all-light modulation and all-light logic gates based on the prepared boron nanosheets. We believe that our results will provide a powerful demonstration of nonlinear photonic devices based on boron nanosheets and a reference for photonic devices based on two-dimensional materials.

Surface inversion layer effective minority carrier mobility as one of the measures of surface quality of the p-aSi:H/i-aSi:H/cSi heterojunction solar cell

The lateral transport of minority carriers in the surface inversion layer of a crystalline silicon (cSi) surface for a p-aSi:H/i-aSi:H/cSi heterojunction (SHJ) solar cell was experimentally analyzed to study defects/traps at the aSi:H/cSi interface and/or on the cSi surface. To extract the lateral surface inversion layer current, a field-effect transistor type test element group device was designed and fabricated on a cSi wafer where SHJ cells were co-integrated. By analyzing the lateral surface inversion layer current, the effective surface minority carrier mobility was calculated. The extracted mobility was one order of magnitude smaller than that of a reference MoOx/i-aSi:H/cSi structure but it increased by low-temperature post-deposition annealing with respect to the reference. This method is highly sensitive to the quality of the aSi:H/cSi interface and/or the cSi surface. The density of trap sites was estimated to be of the order of 1011 cm−2 at the aSi:H/cSi interface and/or on the cSi surface.

Band structure, effective mass, and carrier mobility of few-layer h-AlN under layer and strain engineering

Wide bandgap two-dimensional semiconductors are of paramount importance for developing van der Waals heterostructure electronics. This work reports the use of layer and strain engineering to introduce the feasibility of two-dimensional hexagonal (h)-AlN to fill the scientific and application gap. We show that such one- to five-layer h-AlN has an indirect bandgap, tunable from 2.9 eV for a monolayer to ∼3.5 eV for multilayer structures, along with isotropic effective masses and carrier mobilities between zigzag and armchair directions. With an increase in the layer number to bulk AlN, the bandgap will experience a transition from an indirect gap to direct gap. Surprisingly, high room-temperature mobilities of electrons and holes (of the order of 1000 cm2 V−1 s−1) in a relaxed monolayer h-AlN system and widely adjustable effective masses and carrier mobilities in a different layer h-AlN are observed. In the presence of strain engineering, the bandgap decreases obviously with an increase in tensile strain; meanwhile, the isotropy and value of effective mass or carrier mobility in monolayer h-AlN can also be modulated effectively; the hole mobilities in the armchair direction, especially, will be enhanced dramatically. With a tunable bandgap, high carrier mobilities, and modifiable isotropy, our results indicate that few-layer h-AlN has potential applications in future mechano-electronic devices.

Profiling Mobility Components near the Heterointerfaces of Thin Silicon Films

A method for profiling the components of effective carrier mobility μeff determined by scattering at surface phonons and the roughness of thin film/dielectric interfaces is proposed. The method is based on controlled carrier localization relative to the tested heterointerface due to the interrelation of potentials on opposite film sides (the coupling effect). The method makes it possible to independently separate mobility components near different film heterointerfaces. Its use when studying the electron mobility in silicon-on-insulator films makes it possible to acquire information on the interface roughness and structural perfection of an ultrathin (1–3 nm) silicon layer near the buried film/dielectric interface.

Understanding molecular surface doping of large bandgap organic semiconductors and overcoming the contact/access resistance in organic field-effect transistors.

The contact resistance (Rc) and the effective carrier mobility (μeff) are considered as the important indicators of the performance of organic field-effect transistors (OFETs). Conventionally, the contact resistance is regarded as the interface effect between the metal electrodes and the organic semiconductors, while the carrier mobility is correlated to the crystallinity and π-π stacking of the organic molecules. In the staggered OFETs, Rc is actually closely correlated to μeff through the channel sheet resistance. Besides, the accuracy of the carrier mobility directly extracted from the non-ideal transfer curves with significant contact effect is always questionable. Herein, a diffusion-lead surface doping approach is employed to improve the contact resistance and mobility issues simultaneously. By suppressing the trap states in the sublimated 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) organic semiconductor with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ), we observed a 3-fold increase in the carrier mobility from 0.5 to 1.6 cm2 V-1 s-1, and the Rc also drops remarkably from 25.7 kΩ cm to 5.2 kΩ cm. Moreover, the threshold voltage (VTH), subthreshold swing (SS) and the bias stability of the OFETs are also significantly improved. Based on the detailed characterization of the C8-BTBT film upon surface doping, including X-ray diffraction (XRD) for the film crystallinity, Kelvin probe force microscopy (KPFM) for the surface potential, trap state investigation by density of states (DOS) measurement and electrical circuit modeling for partial doping analysis, we confirmed that the spontaneous charge transfer process due to the diffusion of the F4-TCNQ dopants in the C8-BTBT matrix can lead to an effective trap filling. This technique and findings can be potentially developed into a general approach for the improvement of different performance parameters of OFETs.

Профилирование компонент подвижности вблизи гетерограниц тонких пленок кремния

In this paper, we proposed the method for profiling of the components of the effective mobility of charge carriers μeff defined by their scattering by surface phonons and by roughness at the film/insulator interfaces. The method is based on the controlled localization of charge carriers relative to the interface under study due to the coupling effect. The proposed method allows us to independently determine mobility components near different interfaces of films. The use of the proposed method for studying the mobility has allowed us to obtain information on the roughness of the interface and on the structural quality of the ultrathin (1–3-nm) layer of Si near the Si/buried oxide interface.