Bipolar Semiconductor Research Articles

Bipolar magnetic semiconductors and half-metals in transition metals doped SnSe2 zigzag nanoribbons

The magnetic and electronic properties of transition metals (TM) (TM = Sc, Ti, V, Cr, Mn, Fe, Co, and Ni) doped SnSe2 zigzag nanoribbons (ZNRs) are investigated by employing density functional theory. When an Sn atom on edge of ZNR is substituted by Sc atom, the ZNR behaves as bipolar magnetic semiconductors with 100% spin polarization of valence band and conduction band carriers, where the spin-polarization direction can easily be switched by an external electric field. The Cr-doped ZNR is a spin-gapless semiconductor in which the valence band and conduction band in the spin-up channel touch each other at Fermi energy. The others either are usual magnetic semiconductors or nonmagnetic semiconductors. When two Sn atoms on the edge are substituted by Cr atoms, it is observed that the SnSe2 nanoribbon exhibits half-metallic behavior. Either one Cr dopant or two Cr dopants on edge, the nanoribbons have stable 100% spin polarization of conduction carriers at a wide energy range. These findings demonstrate that the Sc-, Cr-, and 2Cr-doped SnSe2 zigzag nanoribbons are excellent candidates for spintronics.

Non-linear in Space Temperature Distribution and Thermo-E.M.F. in a Bipolar Semiconductor

Non-linear in Space Temperature Distribution and Thermo-E.M.F. in a Bipolar Semiconductor

A 220-GHz Energy-Efficient High-Data-Rate Wireless ASK Transmitter Array

In this work, we present a wireless energy-efficient fully integrated amplitude shift keying (ASK) transmitter (TX) array at 220 GHz. Each TX cell consists of an oscillator, a modulation switch, an on-chip antenna, and baseband amplifiers. The oscillator uses a harmonic generation technique that is optimized for maximum output power and efficiency. The ASK scheme is used for data modulation and is implemented with a fast switch that does not consume any dc power. Three of these TX cells are coherently coupled together to increase the signal-to-noise ratio (SNR) and, hence, the data rate. This also enables the possibility of having a four-level spatial ASK modulation. Fabricated in a 55-nm SiGe bipolar complementary metal oxide semiconductor (BiCMOS) process, the array dissipates 165.2 mW of dc power and generates 4.2-dBm effective isotropic radiated power (EIRP). The chip demonstrates a 20-Gb/s data transmission rate with on-off keying (OOK) modulation at a 28-cm distance using low-cost Teflon lenses. The measured energy efficiency of the array is 8.26 pJ/bit. To the best of our knowledge, this work demonstrates the best energy efficiency among TX arrays at this frequency range.

Joule Heating and Nonlinear Charge Transport in Bipolar Semiconductors

Joule heating of a homogeneous bipolar semiconductor leads to the appearance of nonequilibrium spatially inhomogeneous current carriers. Both energetic and concentration nonequilibrium states arise. Temperature and concentration gradients at the boundaries always have opposite signs. The concentration will become lower in heated regions, while it will become higher in less heated ones. Moreover, the spatial distributions of concentrations have one minimum in thin samples and two minimums and one maximum in thick samples. As a result, the current–voltage characteristic can take superlinear and sublinear forms.

Two-Dimensional Quaternary Transition Metal Sulfide CrMoA2S6 (A = C, Si, or Ge): A Bipolar Antiferromagnetic Semiconductor with a High Néel Temperature.

Bipolar antiferromagnetic semiconductors (BAFSs) make up a class of spintronic materials, holding great promise for the manipulation of spin-polarized currents simply upon application of a voltage gate, but only a few two-dimensional (2D) BAFSs with a high Néel temperature (TN) have been reported. Here, we report a family of magnetic quaternary MM'A2S6 (M = V, Cr, Mn, or Fe; M' = Nb, Mo, Tc, or Ru; A = C, Si, Ge, or Sn) nanosheets by isovalent alloying layered transitional metal trisulfides (MAS3) based on first-principles calculations. Our results show that 2D CrMoA2S6 (A = C, Si, or Ge) nanosheets are BAFSs with band gaps ranging from 1.89 to 2.23 eV. Among them, 2D CrMoC2S6 has the highest TN of 556 K with robust magnetism against carrier doping and external in-plane strain due to a strong delocalization superexchange interaction between the Cr3+ and Mo3+ cations. This study establishes that CrMoC2S6 is an ideal prototype platform for realizing electric control of spin polarization in 2D materials.

Bipolar semiconductor in two-dimensional covalent organic frameworks

As a tunable spintronic device, the bipolar magnetic semiconductor (BMS) has been intensively studied in recent years, but the candidate materials are limited in the magnetic system. In this work, we report an alternative strategy to realize it in a nonmagnetic system called bipolar semiconductor (BS). Utilizing doping-induced ferromagnetism, the enantiomorphic flat bands in BS are used to switch the spin carriers, achieving the same function as the BMS. Based on the frontier orbital of the molecular building blocks, a universal approach is proposed to search the BS in two-dimensional (2D) covalent organic frameworks (COFs), which is confirmed by first-principles calculations in the experimentally synthesized fluoride-graphdiyne (F-GDY). Moreover, the spin-polarized channels and giant anomalous Hall effect can also be created in F-GDY through the light irradiation. Our results demonstrate a new spintronic application for 2D COFs without the intrinsic magnetism.

Prediction of spin-dependent electronic structures of 3d transition metals doped Hittorf's violet phosphorene towards spintronics

Modulation of spin-dependent properties in semiconductor is of importance in exploring the potential application in spintronics. Here, we theoretically investigated the structural deformation, electronic characters, and magnetic properties of the single-layered Hittorf's violet phosphorene nanosheet with 3 d transition metal atoms (ranging from Sc to Ni) doping and under external electric field. The electronic band structures and magnetic properties was found to be obviously modulated by the dopants: the existence of a large spin splitting of the dopant 3 d states tailors the semiconducting phosphorene into simple magnetic semiconductor or bipolar magnetic semiconductor, except for the case of Sc. The application of an appropriate electric field to V-doped system could induce a transition from bipolar magnetic semiconductor to half metal with the carriers fully spin-polarized in alternative spin channel. Moreover, Hittorf's violet phosphorene-based field-effect transistor was proposed with the aim of realizing gate-voltage control on the carriers' spin orientation. Our findings pointed out the possibilities for realizing spin-dependent field-effect transistor in doped Hittorf's violet phosphorene nanosheet and opened a window for the burgeoning field of multifunctional 2D nanoelectronics and spintronics devices. • Ranging from Ti to Ni dopants can behave (bipolar) magnetic semiconductors. • Sc-doped Hittorfene is a nonmagnetic semiconductor. • The application of the electric field to V-doped Hittorfene can induce half metal transition. • The reversed carriers' spin orientation would be potential for spintronic devices.

The structural, electronic, magnetic and optical properties of 4d transition metal adatoms (Tc, Ru, Rh and Cd) adsorbed on monolayer blue phosphorene

The structural, electronic, magnetic and optical properties of 4d transition metal adatoms (Tc, Ru, Rh and Cd) adsorbed on blue phosphorene (blue P) monolayer have been systematically investigated by using the first-principles projector augmented wave (PAW) potential within the generalized gradient approximation (GGA) as well as taking into account the on-site Coulomb repulsive interactions (GGA + U). The pristine blue P monolayer is a nonmagnetic semiconductor, but adatom-doping with these 4d transition metals is an effective way to modify its electronic, magnetic and optical properties and thus expands its applications in spintronics, magnetoelectronics and optoelectronics. Except for the close-filled Cd adatom is unadsorbed, the Tc and Ru adatom-adsorbed blue P monolayers change to bipolar magnetic semiconductor, while the Rh adatom-adsorbed blue P monolayer turns into magnetic spin-gapless semiconductor. The binding energy and optical absorption results confirm that, the Tc, Ru and Rh adatom-adsorbed blue P monolayers are not only fabricable experimentally but also have enhanced absorption for visible and infrared lights.

C3Al: A tunable bandgap semiconductor with high electron mobility and negative Poisson’s ratio

Two-dimensional materials with suitable band gaps and high carrier mobility are considered to be ideal for fabricating next-generation microelectronics devices. In this paper, the C 3 Al crystal structure, electronic and mechanical properties are systematically investigated based on a first-principles method. We find that C 3 Al is an auxetic semiconductor material with wide band gap and high carrier mobility. Electrons have good transport properties but holes are almost completely scattered in the zigzag direction. C 3 Al is one of the few materials with negative Poisson’s ratio effect. In addition, the electronic properties of C 3 Al can transform from semiconductor to metal by tuning straining and stacking. The bare-edge and H-terminated C 3 Al nanoribbons shows an enriched set of electronic properties of semiconductors, half-semiconductor, bipolar magnetic semiconductors , non-magnetic metals, magnetic metals, and half-metals. These results not only provide a theoretically novel and promising crystal configuration, but also further explore the potential of the material for applications in biosensing, strain sensors, transistors, and various nano-optical devices. • The C 3 Al has excellent performance in terms of structural and thermodynamic stability. • C 3 Al is an auxetic semiconductor material with wide band gap and high carrier mobility. • The electronic properties of C 3 Al can transform from semiconductor to metal by tuning strain and stacking. • The bare-edge and H-terminated C 3 Al nanoribbons show an enriched set of electronic properties.

Electronic phase transition, spin filtering effect, and spin Seebeck effect in 2D high-spin-polarized VSi2X4 (X = N, P, As)

Spin gapless semiconductors (SGSs) and bipolar magnetic semiconductors (BMSs) are highly desirable for advanced spintronic applications due to their unique electronic and magnetic properties. Being inspired by the recent synthesis of the 2D MA2X4 family with various electronic properties, including nontrivial topological properties, 2D ferromagnetism, Ising superconductivity, and robust valley polarization, we systematically studied the electron structure, magnetism, and spin transport properties for VSi2X4 (X = N, P, As) monolayers by the density functional theory combined with the nonequilibrium Green's function method. The results show that VSi2X4 monolayers are ferromagnetic type-II SGS and BMS with high Curie temperatures 230–250 K. The interesting electronic phase transitions of type-II-SGS-to-metal-to-type-I-SGS for VSi2P4 and BMS-to-type-I-SGS-to-type-II-SGS for VSi2As4 can be achieved by applying the biaxial strain. Furthermore, the VSi2P4 monolayer exhibits the bias-dependent spin filtering effect and the temperature-driven spin Seebeck effect. The high Curie temperature, the versatile strain-tuned electronic phase transitions, and the excellent spin transport characteristics make 2D VSi2X4 the promising candidate for spintronic applications and will stimulate intensive studies on this class of high-spin-polarized 2D systems.

Tuning the magnetic and electronic properties of MoI3 monolayer by 3d transition metal doping: A first-principles study

Two-dimensional (2D) materials with intrinsic magnetism have sparked a lot of attention due to their potential applications in spintronics. Recently, monolayer molybdenum triiodide (MoI3), which is a member of the transition metal trihalides (MX3) family, has been predicted to be a stable bipolar ferromagnetic semiconductor (BFMS) with intrinsic magnetism. By means of first-principle calculations based on the GGA + Ueff approach, we modified MoI3 through substitutional doping with 3d transition metal (TM) atoms to improve its spintronic properties. We focused on the study of structural, electronic and magnetic properties of the pristine and 3d TM (TM = Sc, Ti, V, Cr, and Mn) doped MoI3 systems. Our findings reveal that substitutional doping of MoI3 monolayers with Sc and Ti atoms changes their electronic character from a BFMS to a ferromagnetic semiconductor, while V- and Cr-doped MoI3 monolayers result in half semiconducting properties (HSC). More interestingly, the Mn-doped MoI3 monolayer reveals a half-metallic character with enhanced magnetism and sustains these properties even under spin–orbit coupling (SOC). In addition, robust ferromagnetism and high mean-field Curie temperatures were found in all doped systems, especially in the V-doped MoI3 monolayer. By exhibiting these unique electronic and magnetic properties, these TM-doped MoI3 systems could serve as potential candidates for spintronic applications.

Computational Study of Metal-Free Magnetism and Spin-Dependent Seebeck Effect in Silicene Nanoribbons with Zigzag and Klein Edges

Nanoribbons based on low-dimensional materials are potential candidates for nanoscale spintronics devices. Here, some ferromagnetic silicene nanoribbons with zigzag and Klein edges (N-ZKSiNRs) are constructed. It is demonstrated that the N-ZKSiNRs with various widths (N) are placed in various spin-resolved electronic situations. With the increase of the width parameter N from 4 to 19, the N-ZKSiNRs pass from the indirect-gap bipolar magnetic semiconducting state (BMS) to the bipolar spin-gapless semiconductor (BSGS) and eventually to half-metallicity (HM). Moreover, applying a temperature gradient through the nanoribbons leads to spin-dependent current with the opposite flowing and spin orientations, demonstrating the spin-dependent Seebeck effect (SDSE). Besides, it was found that the BSGS phase is superior to the BMS and HM for generating SDSE. These findings confirm that the ZKSiNRs are promising choices for spin caloritronics devices.

The Magnetic and Thermally-Induced Spin-Related Transport Features Using Germanene Nanoribbons With Zigzag and Klein Edges

The current work employs the first-principles computations and non-equilibrium Greens function to investigate the magnetic and thermally-induced spin-related transport features using germanene nanoribbons with zigzag and Klein edges (ZKGeNRs). It was demonstrated that the ZKGeNRs with various widths (N) are placed in various spin-resolved electronic states. By increasing the width parameter N from 4 to 9, the ZKGeNRs moves from an indirect-gap bipolar magnetic semiconducting state (BMS) to bipolar spin gapless semiconductor (BSGS), and finally to ferromagnetic metal (FM). Moreover, since the right and the left temperatures of the ZKGeNRs device are different, the spin-up and spin-down currents flow in reverse orientations, demonstrating the spin-dependent Seebeck effect (SDSE). Besides, the threshold temperature decreases as N increases and then disappears, while the spin currents increase as N increases. Simulation results indicated that the ZKGeNRs could be an appropriate choice for spin caloritronic devices and could be utilized in future low-power consumption applications.

Heat dissipation of underlying multilayered graphene layers grown on Cu–Ni alloys for high-performance interconnects

Electromigration with Joule heating under high current results in the failure of metal interconnect, which affects the performance and lifetime of electronic devices. Furthermore, advanced semiconductor technologies, such as three-dimensional integrated chips and power devices, which include insulated-gate bipolar transistors and compound semiconductors, require an electrical conducting line with high charge-carrying capacity for effective transmission of electrical signal. In this study, we investigate the effect of underlying graphene layers on the electrical properties of Cu interconnects. Multilayered graphene with a thickness of a few nanometers and a flat surface is synthesized using Cu–Ni alloys. The maximum current capacity of the Cu interconnect is improved by increasing the graphene width to 1.60 × 108 A/cm2, which is approximately seven times greater than that of only Cu. In addition, the wide graphene layer prevents the sudden current drop due to breakage of the Cu interconnect. The results of thermal imaging and simulation reveal the importance of effective heat dissipation for realizing high performance of the interconnect.

Novel bipolar magnetic semiconductor materials formed by adsorption of methyl or halomethyles on the graphene: A spin-polarized density functional theory study

Exploring magnetic materials with electrically controlled spin polarization and room temperature magnetic ordering is of particular importance for applications in spintronic devices. In this study, we present a detailed theoretical study on the structural, electronic, and magnetic features of pristine graphene on which methyl(CH3) or a halomethyl (CH2F, CH2Cl, CH2Br, or CH2I) radical has been adsorbed. The framework of our calculations is dispersion-corrected density functional theory with due account of the spin degree of freedom within the Quantum-ESPRESSO package. The investigation starts with a complete discussion of the geometrical characteristics, followed by a thorough study of the manner of charge transfer and redistribution, electronic band structures, and density of states. The calculated adsorption energies and distances demonstrate the adsorption process to be of the chemisorption type. The adsorption of each radical on graphene is accompanied by a net charge transfer, changing the work function of the resulting compounds and modulating the electronic and magnetization characteristics of pristine graphene. Considerations of the calculated spin-distinct electronic band structure and density of states support the latter conclusion. The presence of unequal band gaps in the up and down spin channels also corroborates the aforementioned compounds' bipolar magnetic semiconductor nature.

High-Throughput Computational Screening for Bipolar Magnetic Semiconductors.

Searching ferromagnetic semiconductor materials with electrically controllable spin polarization is a long-term challenge for spintronics. Bipolar magnetic semiconductors (BMS), with valence and conduction band edges fully spin polarized in different spin directions, show great promise in this aspect because the carrier spin polarization direction can be easily tuned by voltage gate. Here, we propose a standard high-throughput computational screening scheme for searching BMS materials. The application of this scheme to the Materials Project database gives 11 intrinsic BMS materials (1 experimental and 10 theoretical) from nearly ~40000 structures. Among them, a room-temperature BMS Li2V3TeO8 (mp-771246) is discovered with a Curie temperature of 478 K. Moreover, the BMS feature can be maintained well when cutting the bulk Li2V3TeO8 into (001) nanofilms for realistic applications. This work provides a feasible solution for discovering novel intrinsic BMS materials from various crystal structure databases, paving the way for realizing electric-field controlled spintronics devices.

Bipolar 1,8-naphthalimides showing high electron mobility and red AIE-active TADF for OLED applications.

Aiming to design bipolar organic semiconductors with high electron mobility and efficient red thermally activated delayed fluorescence (TADF), three donor-acceptor compounds were designed and synthesized selecting 1,8-naphthalimide as an acceptor and phenoxazine, 3,7-di-tert-butylphenothiazine or 2,7-di-tert-butyldimethyl-9,10-dihydroacridine as donor moieties. Aggregation induced emission enhancement was detected for the compounds causing efficient TADF in the solid-state. Photoluminescence quantum yields up to 77% were observed for the films of the compounds doped in a host. The compounds exhibited small singlet-triplet splitting (0.03-0.05 eV), and high reverse intersystem crossing rates of 2.08 × 105-1.13 × 106 s-1. The compounds were characterized by satisfactory hole and electron-injecting properties with ionization potentials of 5.72-5.83 eV and electron affinities of 2.79-2.91 eV. Bipolar charge transport was revealed by time of flight measurements. Electron transport with low dispersity and mobilities exceeding 2 × 10-3 cm2 V-1 s-1 was observed at an electric field of 4.6 × 105 V cm-1. The compounds were used as emitters in red electroluminescent devices, which showed maximum external quantum efficiencies up to 8.2%. Utilization of host-guest systems as light-emitting materials with hosts preferably transporting holes and TADF guests which preferably transport electrons allowed maximum efficiencies to be achieved at a practical brightness of 700-2200 cd m-2. DFT calculations of the geometry, electronic structure, absorption and photoluminescence spectra of all compounds were carried out to prove the conclusions drawn from the experiment. The results of the calculations clearly show that the first excited state for all compounds is the intramolecular charge transfer state. Quantitative analysis of the separation degree of electronic density during excitation allows the observed dependence of the blue shift value in the absorption and emission spectra on the increasing polarity of the solvent to be explained.

Two-dimensional heterotriangulene-based manganese organic frameworks: bipolar magnetic and half semiconductors with perpendicular magnetocrystalline anisotropy

Two-dimensional (2D) organic intrinsic magnetic semiconductors have potential applications in low-dimensional organic spintronic devices due to their remarkable physical properties. However, 2D metal-organic frameworks with magnetic and semiconducting properties are rare. In this work, the electronic and magnetic properties of 2D heterotriangulene-based manganese organic frameworks including triphenylamine (TPA) and triphenylborane (TPB) organic ligands with methylene (M), carbonyl (C) or oxygen (O) coordination groups were studied by first-principles calculations. XTPA-Mn (X = M and O) is a bipolar magnetic semiconductor with a large spin-flip band gap. CTPA-Mn and XTPB-Mn (X = M, C and O) are half semiconductors with perpendicular magnetocrystalline anisotropy. The electronic properties of materials ranging from half semiconductors to bipolar magnetic semiconductors appear in CTPA-Mn and XTPB-Mn (X = M and C) at biaxial strains. XTPA-Mn and XTPB-Mn with a frustrated antiferromagnetic configuration are semiconductors with good ductility and stability. These results enrich the diversity of 2D organic intrinsic magnetic semiconductors, which have potential applications in spintronic devices.

Magneto-electronic properties and manipulation effects of Fe-adsorbed Sb/WS<sub>2</sub> heterostructure

To study the induced magnetism mechanism and magneto-electronic properties of non-magnetic two-dimensional van der Waals heterostructure adsorbing magnetic atoms, we construct Sb/WS<sub>2</sub> heterostructure, and consider its adsorbed Fe atoms. The calculated adsorption energy shows that T<sub>W</sub>, V<sub>Sb</sub> adsorption are the most likely positions for Fe atom adsorbed below and above the heterostructure, respectively, and T<sub>S_M</sub> adsorption is the most likely position for Fe atom adsorbed between two monolayers. The induced magnetism is due to the electron-spin rearrangement caused by the expansion of valence electronic configuration (VEC) and charge transfer after Fe atoms have been adsorbed. The T<sub>W</sub> adsorption and the T<sub>S_M</sub> adsorption make the nonmagnetic semiconducting heterostructure become a half-semiconductor (HSC), while V<sub>Sb</sub> adsorption turns the heterostructure into a bipolar magnetic semiconductor (BMS). In particular, the calculated magnetized energy indicates that the interlayer T<sub>S_M</sub> adsorption leads the heterostructure to holding the highest magnetic stability, which is enough to resist the influence of thermal fluctuation at room temperature. Quantum manipulation can cause the heterostructure to produce abundant magnetism, especially the flexible change of magnetic phase. For example, the application of external electric field can give rise to the magnetic phase transition among HSC, HM (half-metal) and BMS for the heterostructure, and the vertical strain can make the heterostructure realize the magnetic phase transition among HSC, HM and MM (magnetic metal). This study shows that the heterostructure can increase the adsorption region of transition metal atoms (below, interlayer and above), so as to produce rich magnetism, especially for the interlayer adsorption of transition metals, its magnetic stability against temperature is significantly enhanced.

Finding out square root of an integer number using Single Electron Transistor

The single-electron transistor (SET) attracts the researchers, scientists or technologists to design and construct large scale circuits for the sake of the consumption of ultra-low power and its small size. All the incidences in a SET-based circuit happen when only a single electron tunnels through the transistors under the proper applied bias voltage and a small gate voltage or multiple gate voltages. The oscillatory conduction as the function of the variable-multiple /single gate voltage is exhibited by SET. This uncommon characteristic provides the ability of executing the functions of AND, OR, XOR, Inverter and some combinational circuits like multiplexer, subtractor etc. For implementing a square root circuit, SET would be a best candidate to fulfil the requirements. The processing speed of SET based devices will be nearly close to electronic speed. Noise during processing gets ultra-low when the circuits is built with SETs. The square root circuit is presented here for sixteen bit input numbers. The input bit numbers can be increased with the increasing of the depth of the pattern very easily. And this will provide us the greater accuracy about the squared root value. Power consumption in the single electron circuit is low irrespective of bipolar junction transistor (BJT) or Complementary Metal Oxide Semiconductor (CMOS) circuits. Reducing the numbers of nodes, the power consumption is reduced.