Nonmagnetic Semiconductor Research Articles

Engineering the band gap of armchair MoSe2 nanoribbon with edge passivation

Based on first-principles calculations, we have investigated the structural and electronic properties of AMoSe2NRs with different edge functionalization. We have considered two patterns of edge passivation for AMoSe2NRs: one is simplex edge passivation and the other is hybrid edge passivation. In addition, different functionalization groups are taken into consideration. The results show that all these passivated strategies can be used to stabilize the pristine system, especially the hybrid passivation ones, and the pristine and edge functionalized nanoribbons are nonmagnetic semiconductors with the tunable band gaps varying in a range 0–1.19 eV and along with a gradient of near 0.1 eV. The O-functionalized nanoribbon is a nonmagnetic metal, however, when pristine nanoribbon is passivated by hybrid oxygen and hydrogen atoms, it returns to the nonmagnetic semiconductor. It is exciting to find that the electronegativity of passivated atom plays an important role in engineering the band gap of pristine AMoSe2NRs.

Rectification effects of C3N nanoribbons-based Schottky junctions

Electronic and transport properties of semiconductor materials are very important to electronic and optoelectronic devices. Here, we present theoretical predication on the band structures and transport properties of zigzag C3N nanoribbons (ZC3NNRs) and related Schottky junctions. The results show that pristine ZC3NNRs are ferromagnetic metal, while the H-passivated ZC3NNRs are either nonmagnetic semiconductor or metal depending on their edge configurations. Interestingly, in the partitioned passivation-induced ZC3NNRs Schottky junction, the rectification ratio (∼105) is directly proportional to the channel length of H-passivated ZC3NNRs. For edge aligning-induced ZC3NNRs Schottky junction, the rectification ratio of aligning the CC_edge is about 25 times higher than that of aligning the CN_edge. These results may be useful to design two-dimensional (2D) materials-based Schottky junction electronic devices.

Magnetic Transitions in K-Doped Biphenyl and ${p}$ -Terphenyl

Recently, an interesting superconductivity of the transition temperatures range from 7.2 to 43 K and then to 123 K in K-doped ${p}$ -terphenyl was reported, which attracts much attention. In this paper, to identify the superconducting phase from chemical component, we have investigated the crystal structures and electronic and magnetic properties in the cases of K-doped biphenyl and ${p}$ -terphenyl based on the first-principles calculations. We found that the change of doping concentration results in a series of magnetic transitions. Pristine biphenyl and ${p}$ -terphenyl are both nonmagnetic (NM) semiconductors. Doping one K atom for each organic molecule, the system exhibits the antiferromagnetism. With increasing the doping concentration of K atoms, however, the spin ordering disappears and the compound behaviors as the NM metal. Thus, we suggest that the superconducting phases observed experimentally are corresponding to the highly doping levels, which will deepen the understanding of the superconductivity of aromatic hydrocarbons.

Density functional theory study of tunable electronic and magnetic properties of monolayer BeO with intrinsic vacancy and transition metal substitutional doping

The anomalous electronic and magnetic properties of monolayer BeO with intrinsic vacancy and transition metal (TM) substitutional doping are investigated by means of extensive density functional theory calculations. Our calculations reveal that the Be vacancy (VBe) can give rise to a stable ferromagnetism, while the O vacancy (VO) does not show spin dependent electronic properties. More significantly, the monolayer BeO with VBe becomes the magnetic semiconductor with a direct band gap (0.97 eV), whereas the band gap of the monolayer BeO with VO drops to 3.56 eV, in comparison with the band gap of the pristine BeO (5.64 eV). It is found that the TM substituting Be atom (TM-BeO) is favorable and the ionic bonds are formed between TM and its neighboring O atoms. The electronic properties of the monolayer BeO are also considerably changed due to the induced impurity states. Only the Zn-BeO system preserves the nonmagnetic semiconductor characteristic, similar to the monolayer BeO. The Sc-, V-, Mn-, and Ni-BeO systems show dilute magnetic semiconductor (DMS) characters. More interestingly, the Ti-, Cr-, Fe-, Co- and Cu-BeO systems display half-metal characters. According to the study of magnetic coupling between two same TM impurity atoms, there exists antiferromagnetic coupling (AFM) in all TM-BeO systems. Therefore, it is concluded that TM substitutional doped BeO could cause useful magnetic properties, which may stimulate an experimental exploration of BeO for application in electronic and spintronic devices.

Stable H-Terminated Edges, Variable Semiconducting Properties, and Solar Cell Applications of C3N Nanoribbons: A First-Principles Study.

Motivated by the recent synthesis of the graphene-like C3N nanosheet, the geometrical structures and electronic properties of its ribbon form, that is, C3N nanoribbons (C3NNRs), are investigated by first-principles calculations. It is found that there are five types of energetically favorable H-terminated edges in the C3NNRs. Different from graphene nanoribbons, the corresponding stable C3NNRs are all nonmagnetic semiconductors regardless of the edge shape and termination. However, their band feature and gap size can be modulated by the ribbon width and edge termination, which brings direct-, quasi-direct-, and indirect-band-gap semiconducting behaviors in the nanoribbons. Comparing to the C3N nanosheet, the work function is reduced in the C3NNRs with fully di- and monohydrogenated edges, which results in a type-II band alignment with SiC and silicane nanosheets. More interestingly, the combined hetero-nanostructures will be promising excitonic solar cell materials with high power conversion efficiencies up to 17–21%. Our study demonstrates that the C3NNRs have distinct edge stabilities and variable semiconducting behaviors, which endow fascinating potential applications in the fields of solar energy and nanodevices.

Structural, electronic and magnetic properties of the H- passivated armchair MoSe2 nanoribbons with the periodic vacancy

Under the generalized gradient approximation (GGA), we have performed the spin-polarized first-principles calculations to systematically investigate structural, electronic and magnetic properties of the hydrogen passivated armchair MoSe2 nanoribbon (H-11-AMoSe2NR) with the periodic vacancy near the center of the nanoribbon. The results show that the formation of the single Se-vacancy is easier than those of others. For the cases of Se-vacancy, Se2-and MoSe-divacancy, an indirect-direct gap transition takes place along with the tunable band gap but do not induce any magnetic moment. However, for the case of MoSe2-triple vacancy, the system still remains non-magnetic indirect gap semiconductor with a smaller band gap of 0.108 eV. The calculated band gaps are 0.412, 0.447, and 0.091 eV for the Se-vacancy, Se2-, and MoSe-divacancy, respectively, which show great feasibility in the optoelectronics. In addition, Mo-vacancy induces a remarkable spin polarization and magnetic moments concentrated on the atoms around the Mo-vacancy, which suggests such vacancy-defective H-AMoSe2NR can be used in spintronics and nanomagnets.

Study on the electronic structures and transport properties of the polyporphyrin nanoribbons with different edge configurations

Combining the density functional theory with the non-equilibrium Green's function, three kinds of polyporphyrin nanoribbons (PPNRs) with different edge configurations have been considered: 1) all carbocyclic eight-membered rings (C8-Rs) located in edge are broken (M1); 2) all C8-Rs located in edge are perfect (M2); 3) partial C8-Rs located in edge are broken, subject to two kinds of configurations, as illustrated by M3 and M4. Calculation results indicate that the completeness of the C8-Rs can influence the electronic structures and transport properties of the nanoribbons. M1 is a nonmagnetic indirect semiconductor, while M2 and M3 are magnetic metals, M4 behaves as the bipolar magnetic semiconductor. Moreover, the spin-dependent transport properties of the two-lead devices based on PPNRs show that the significant spin-filtering effect can be realized in the device with partially broken C8-Rs in edge. Our results indicate that the PPNRs based devices would be suitable for spintronics devices.

Geometrical and electronic properties of C-doped graphyne-like BN sheets

ABSTRACTIt has been previously indicated that graphyne-like BN (BNyne) sheets have distinct and interesting properties with graphyne and h-BN sheets. Herein, the geometric and electronic properties of C-doped graphyne-like BN (C-BNyne) sheets (including α-, β- and γ-) were systematically investigated by the first-principles calculations. The results reveal that C impurity is more likely to substitute the linear-B and corner-N sites due to the lower formation energy. The C atom incorporation could lead to a change in electron transfer and local bond lengths and a pronounced structural distortion was observed in α C-doped linear-B BNyne and in γ C-doped linear-B BNyne configurations. When a single C impurity atom was doped in linear-B site, it introduced donor levels near the bottom of the conduction band and thus the structures show n-type semiconductor character. As for C-doped corner-N site BNynes, electronic structure calculation showed p-type semiconductor character. Meanwhile, strong spin splitting phenomenon occurs in β C-doped linear-B BNyne and the spin splitting character originated from the impurity C atom and its first neighboring B atom. However, the other doped configurations are nonmagnetic semiconductor.

Tunable direct-indirect band gaps of ZrSe2 nanoribbons

The atomic and electronic structures of armchair and zigzag ZrSe2 nanoribbons have been investigated systematically. Both the armchair and zigzag ZrSe2 nanoribbons are nonmagnetic semiconductors, while their bandgaps show quite different behaviors depending on the ribbon width. We find that all the zigzag ribbons possess direct energy gaps, which smoothly decline with the increasing ribbon width. On the other hand, energy gaps for the armchair ribbons change from direct gaps to indirect ones as the ribbon width increases and exhibit a width-dependent oscillation behavior. Moreover, the semiconducting behaviors and the bandgap types are robust, and they remain unchanged in bilayer and multilayer thin films with inter-layer interactions. These findings indicate that ZrSe2 nanoribbons are promising candidate materials for applications in nanoelectronic devices.

Defects-driven magnetism in bulk [formula omitted]-Li3N

Ab initio calculations based on density functional theory with local spin density approximation are used to study defects-driven magnetism in bulk α-Li3N. Our calculations show that bulk Li3N is a non-magnetic semiconductor. Two types of Li vacancies (Li-I and Li-II) are considered, and Li-vacancies (either Li-I or Li-II type) can induce magnetism in Li3N with a total magnetic moment of 1.0 μB which arises mainly due to partially occupied N-p-orbitals around the Li vacancies. The defect formation energies dictate that Li-II vacancy, which is in the Li2N plane, is thermodynamically more stable as compared with Li-I vacancy. The electronic structures of Li-vacancies show half-metallic behavior. On the other hand N-vacancy does not induce magnetism and has a larger formation energy than Li-vacancies. N vacancy derived bands at the Fermi energy are mainly contributed by the Li atoms. Carbon is also doped at Li-I and Li-II sites, and it is expected that doping C at Li-I site is thermodynamically more stable as compared with Li-II site. Carbon can induce metallicity with zero magnetic moment when doped at Li-I site, whereas magnetism is observed when Li-II site is occupied by the C impurity atom and C-driven magnetism is spread over the N atoms as well. Carbon can also induce half-metallic magnetism when doped at N site in Li3N, and has a smaller defect formation energy as compared with Li-II site doping. The ferromagnetic (FM) and antiferromagnetic (AFM) coupling between the C atoms is also investigated, and we conclude that FM state is more stable than the AFM state.

Tunable magnetic and electronic properties in 3d transition-metal adsorbed β12 and χ3 borophene

Recently, the experimental advances for the fabrication of various borophene sheets introduced novel lattice structures with a wide prospect of practical applications. Borophene with various structural polymorphs are metallic and nonmagnetic, which greatly limits its application in nanoelectronic and spintronic devices. Here, we predict that the 3d transition-metal adsorption is an effective approach to tailor the electronic structure of borophene by density functional theory. The Cr- and Mn-absorbed borophenes show magnetism, while non-magnetic states appear in Sc-, Ti-, V-, Fe-, Co-, Ni-, Cu- and Zn-adsorbed systems. Especially, Fe-adsorbed χ3 borophene is a non-magnetic semiconductor, whose gap opening and magnetic moment can be tailored by strain. Our work provides a clue for exploring the method to tailor the magnetic and electronic properties of two dimensional monolayer borophene.

Electronic, magnetic and transport properties of silicene armchair nanoribbons substituted with monomer and dimer of Fe atom

This study employed density functional theory calculations to investigate the structural, electronic and magnetic properties of an armchair silicene nanoribbon (ASiNR) substituted with a monomer and a dimer of Fe atom. As a result, the direct band gap of pristine ASiNR turns into a smaller indirect band gap by substituting an Fe atom in the proper position. The magnetic moment of doped Fe reduces and the structure keeps its nonmagnetic property. The substitution of the Fe-dimer can change the pristine ASiNR from a nonmagnetic semiconductor to a magnetic half-metal, which is favorable for spintronic devices. Two external electric fields were applied to the structure substituted with the Fe-dimer and electronic properties were studied in this situation. It was shown that the Fe-dimer substituted ASiNR is such a versatile material that a band gap can be tuned by using an external transverse electric field. Furthermore, the transport properties of these two structures were studied with non-equilibrium Greens function formalism. It is intriguing that single-spin negative differential resistance was observed in the Fe-dimer doped ASiNR.

The electronic, magnetic and optical properties of Co doped marcasite FeS2

The electronic, magnetic and optical properties of Co doped marcasite FeS2 compounds have been investigated through the first-principles calculations. No imaginary frequency emerges in the phonon dispersion curves confirms the Fe7CoS16 and Fe6Co2S16 compounds are dynamical stable. Although the pure Fe8S16 compound is a nonmagnetic semiconductor with band gap of 1.17 eV, the Fe7CoS16 compound changes to a magnetic semiconductor with a very narrow band gap of 0.106 eV, the Fe6Co2S16 compound changes to a half-metal with half-metal band gap of 0.37 eV in spin-down channel. For all three considered configurations of the Fe6Co2S16 compound, the ferromagnetic state is preferred over antiferromagnetic state, especially for smaller separation distance of two doped Co atoms. The higher Curie temperatures than room temperature indicates the Fe6Co2S16 compound is a promising candidate for spintronics applications. In addition, the calculated optical properties shows that Fe7CoS16 and Fe6Co2S16 compounds have stronger absorption than Fe8S16 compound when the wavelength more than 500 nm, which suggests the compounds are potential candidates for solar cells.

High-temperature ferromagnetism in new n-type Fe-doped ferromagnetic semiconductor (In,Fe)Sb

Over the past two decades, intensive studies on various ferromagnetic semiconductor (FMS) materials have failed to realize reliable FMSs that have a high Curie temperature (TC > 300 K), good compatibility with semiconductor electronics, and characteristics superior to those of their nonmagnetic host semiconductors. Here, we demonstrate a new n-type Fe-doped narrow-gap III–V FMS, (In1−x,Fex)Sb. Its TC is unexpectedly high, reaching ∼335 K at a modest Fe concentration (x) of 16%. The anomalous Hall effect and magnetic circular dichroism (MCD) spectroscopy indicate that the high-temperature ferromagnetism in (In,Fe)Sb thin films is intrinsic and originates from the zinc-blende (In,Fe)Sb alloy semiconductor.

Room-temperature large photoinduced magnetoresistance in semi-insulating gallium arsenide-based device**Project supported by the National Natural Science Foundation of China (Grant Nos. 11574243 and 11174231).

It is still a great challenge for semiconductor based-devices to obtain a large magnetoresistance (MR) effect under a low magnetic field at room temperature. In this paper, the photoinduced MR effects under different intensities of illumination at room temperature are investigated in a semi-insulating gallium arsenide (SI-GaAs)-based Ag/SI–GaAs/Ag device. The device is subjected to the irradiation of light which is supplied by light-emitting diode (LED) lamp beads with a wavelength in a range of about 395 nm–405 nm and the working power of each LED lamp bead is about 33 mW. The photoinduced MR shows no saturation under magnetic fields (B) up to 1 T and the MR sensitivity S (S = MR/B) at low magnetic field (B = 0.001 T) can reach 15 T−1. It is found that the recombination of photoinduced electron and hole results in a positive photoinduced MR effect. This work implies that a high photoinduced S under a low magnetic field may be obtained in a non-magnetic semiconductor device with a very low intrinsic carrier concentration.

Large current modulation and tunneling magnetoresistance change by a side-gate electric field in a GaMnAs-based vertical spin metal-oxide-semiconductor field-effect transistor

A vertical spin metal-oxide-semiconductor field-effect transistor (spin MOSFET) is a promising low-power device for the post scaling era. Here, using a ferromagnetic-semiconductor GaMnAs-based vertical spin MOSFET with a GaAs channel layer, we demonstrate a large drain-source current IDS modulation by a gate-source voltage VGS with a modulation ratio up to 130%, which is the largest value that has ever been reported for vertical spin field-effect transistors thus far. We find that the electric field effect on indirect tunneling via defect states in the GaAs channel layer is responsible for the large IDS modulation. This device shows a tunneling magnetoresistance (TMR) ratio up to ~7%, which is larger than that of the planar-type spin MOSFETs, indicating that IDS can be controlled by the magnetization configuration. Furthermore, we find that the TMR ratio can be modulated by VGS. This result mainly originates from the electric field modulation of the magnetic anisotropy of the GaMnAs ferromagnetic electrodes as well as the potential modulation of the nonmagnetic semiconductor GaAs channel layer. Our findings provide important progress towards high-performance vertical spin MOSFETs.

Ultrafast magnetization modulation induced by the electric field component of a terahertz pulse in a ferromagnetic-semiconductor thin film

High-speed magnetization control of ferromagnetic films using light pulses is attracting considerable attention and is increasingly important for the development of spintronic devices. Irradiation with a nearly monocyclic terahertz pulse, which can induce strong electromagnetic fields in ferromagnetic films within an extremely short time of less than ~1 ps, is promising for damping-free high-speed coherent control of the magnetization. Here, we successfully observe a terahertz response in a ferromagnetic-semiconductor thin film. In addition, we find that a similar terahertz response is observed even in a non-magnetic semiconductor and reveal that the electric-field component of the terahertz pulse plays a crucial role in the magnetization response through the spin-carrier interactions in a ferromagnetic-semiconductor thin film. Our findings will provide new guidelines for designing materials suitable for ultrafast magnetization reversal.

Coaxial Quantum Well Wires in Magnetic/Nonmagnetic Heterostructures

We propose a coaxial cylindrical quantum well wire which is composed of layers of a dilute magnetic semiconductor (DMS) and a nonmagnetic semiconductor (NMS). Using effective mass approximation, we present a numerical calculation of the eigenenergies and eigenstates of electrons in the heterostructure. The variation of the spin‐dependent energy levels is influenced by the giant Zeeman splitting and potential energies due to a vector potential for sufficiently low and high magnetic fields, respectively. It is found that crossing and anticrossing behaviors of energy levels can be controlled by the thickness of a NMS layer. The ballistic transport of the structure is also investigated. The ranges of the Fermi energy for obtaining full spin polarization are suggested in this work.

Time-resolved lateral spin-caloric transport of optically generated spin packets in n-GaAs

We report on lateral spin-caloric transport (LSCT) of electron spin packets which are optically generated by ps laser pulses in the non-magnetic semiconductor n-GaAs at K. LSCT is driven by a local temperature gradient induced by an additional cw heating laser. The spatio-temporal evolution of the spin packets is probed using time-resolved Faraday rotation. We demonstrate that the local temperature-gradient induced spin diffusion is solely driven by a non-equilibrium hot spin distribution, i.e. without involvement of phonon drag effects. Additional electric field-driven spin drift experiments are used to verify directly the validity of the non-classical Einstein relation for moderately doped semiconductors at low temperatures for near band-gap excitation.

The structural, elastic, electronic and optical properties of orthorhombic FeX2 (X=S, Se, Te)

The structural, elastic, electronic and optical properties of FeX2 (X = S, Se, Te) with orthorhombic (space group Pnnm) structure have been investigated through the first-principles calculations. The calculated lattice constants, internal structure parameters and two kinds of Fe-X bond lengths agree reasonably with the experimental results. The corresponding single crystal elastic constants, polycrystalline elastic moduli, transverse, longitudinal, average elastic wave velocities, Debye temperature and minimum thermal conductivity decrease from FeS2 to FeTe2 while the elastic anisotropy index increases from FeS2 to FeTe2. All the three compounds show the brittle nature and covalent bonding. The orthorhombic FeX2 are non-magnetic semiconductors with indirect band gaps of 1.17eV, 0.64eV and 0.27eV, respectively. There have strong hybridizations between Fe-d orbitals and X-p orbitals. The real part and imaginary part of the dielectric function, refractive index and absorption coefficient are obtained and analyzed, the results show that the three compounds possess excellent absorption properties in ultraviolet and visible light regions. Both elastic properties and optical properties exhibit obvious anisotropy in the three compounds.