Electron Effective Mass Research Articles

Exploring the physical properties of novel ACu3S3 (A = Sc, Y) semiconductors via first-principles calculation

Some of the distinguishing features of direct band gap ternary-type semiconductors include their adjustable optoelectronic properties and high thermal stability. The state-of-the-art density functional theory is employed to investigate the complex interplay in novel ACu3S3 (A = Sc, Y) ternary chalcogenides' electronic, optical, thermodynamic, and thermoelectric features. Based on the results, direct energy gaps nature in both these materials were observed as a result of the S-p and the Sc/Y-d orbital hybridizations. The YCu3S3 possesses a greater energy gap at the (Γ) point, resulting in higher effective mass for holes and lower effective mass for electrons as compared to ScCu3S3. The prime distinctive peaks in the ε1(ω) are observed in the visible range which then drops to zero at 8.5 eV and 8.0 eV for ScCu3S3 and YCu3S3, respectively. Both ScCu3S3 and YCu3S3 exhibited strong absorption over the whole visible and ultraviolet regions. From the noticed peaks in the reflectivity spectra, these materials can be employed efficiently as ultra-violet reflectors. The drop in the Grüneisen parameter with rising temperature shows that some vibrational modes relaxed as the temperature rises. The ScCu3S3 and YCu3S3 show a p-type conduction nature due to the positive value of the Seebeck coefficient over the entire temperature range.

Tunable plasmon-induced transparency in anisotropic graphene-black phosphorus photonic device for high-performance sensors and switchers

A novel photonic device composed of graphene and black phosphorus (G-BP) has been proposed, which achieves high-performance plasmon-induced transparency (PIT) effect within the THz range and maintains substantial tunability and anisotropy. The anisotropy of the PIT effect arises from the near-field coupling between two bright modes characterized by distinct effective electron masses of BP, resulting transparency window at 33.35 THz for TE polarization and at 26.92 THz for TM polarization. Through the modulation of Fermi energy in graphene, doping levels of BP and geometric parameters separately, a tunable transparency window is achieved. Notably, the convergence or divergence of the anisotropic transparency windows can be well manipulated with different BP doping levels. Furthermore, the proposed G-BP photonic device exhibits a high sensitivity to changes in the surrounding refractive index and substrates, with a maximum sensitivity of 12.04 THz/RI, rendering it suitable for sensor applications. Overall, the proposed photonic device exhibits notable PIT effects characterized by high anisotropic performance, substantial tunability, great sensitivity, and stability, making it a promising candidate for applications in sensors, polarizers, and switchers.

The electronic structure, optical property and n-type conductivity for W-doped α-Ga2O3: hybrid functional study

Based on the hybrid functional method, the electronic structure, optical property and electron effective mass of α-Ga2O3, together with the properties for intrinsic and extrinsic defects incorporated into α-Ga2O3 are studied. Obtained results indicate the α-Ga2O3 possesses a wide band gap (5.31 eV), small electron effective mass (0.22 m0) and a high visible light transmittance. The nonstoichiometric α-Ga2O3 is not an excellent n-type semiconductor. To improve the n-type conductivity, the W-doped α-Ga2O3 is studied. We find that W Ga is a promising n-type defect due to its relatively small ionization energy ϵ(0/+) (0.30 eV). When the equilibrium fabrication method is selected, the WO2 is a promising dopant source. Using the equilibrium fabrication method, the defect complex (V O+ W Ga) would be formed, and the ionization energy ϵ(0/+) for defect complex (V O + W Ga) would decrease to 0.08 eV, which implies that a great number of free electrons could be induced in the samples. We expect that this work can promote the understanding of the n-type conductivity for α-Ga2O3 and provide significant insights for the development of a transparent n-type semiconductor.

Characterization of induced quasi-two-dimensional transport in n-type InxGa1−xAs1 − yBiy bulk layer

The temperature-dependent transport properties of n-type InGaAsBi epitaxial alloys with various doping densities are investigated by conducting magnetoresistance (MR) and Hall Effect (HE) measurements. The electronic band structure of the alloys and free electron distribution were calculated using Finite Element Method (FEM). Analysis of the oscillations in the transverse (Hall) resistivity shows that quasi-two-dimensional electron gas (Q-2D) in the bulk InGaAsBi epitaxial layer (three-dimensional, 3D) forms at the sample surface under magnetic field even though there is no formation of the spacial two-dimensional electron gas (2DEG) at the interface between InGaAs and InP:Fe interlayer. The formation of Q-2D in the 3D epitaxial layer was verified by temperature and magnetic field dependence of the resistivity and carrier concentration. Analysis of Shubnikov-de Haas (SdH) oscillations in longitudinal (sample) resistivity reveals that the electron effective mass in InGaAsBi alloys are not affect by Bi incorporation into host InGaAs alloys, which verifies the validity of the Valence Band Anti-Crossing (VBAC) model. The Hall mobility of the nondegenerate samples shows the conventional 3D characteristics while that of the samples is independence of temperature for degenerated samples. The scattering mechanism of the electrons at low temperature is in long-range interaction regime. In addition, the effects of electron density on the transport parameters such as the effective mass, and Fermi level are elucidated considering bandgap nonparabolicity and VBAC interaction in InGaAsBi alloys.

Effects of Impurities and Deformations on Electronic Effective Mass in Quantum Revival Time within the Infinite Square Well

Effects of Impurities and Deformations on Electronic Effective Mass in Quantum Revival Time within the Infinite Square Well

Unusual Dzyaloshinskii-Moriya Interaction in Graphene/Fe3GeTe2 Van der Waals Heterostructure.

Dzyaloshinskii-Moriya interaction (DMI) is shown to induce a topologically protected chiral spin texture in magnetic/nonmagnetic heterostructures. In the context of van der Waals spintronic devices, graphene emerges as an excellent candidate material. However, due to its negligible spin-orbit interaction, inducing DMI to stabilize topological spins when coupled to 3d-ferromagnets remains challenging. Here, it is demonstrated that, despite these challenges, a sizeable Rashba-type spin splitting followed by significant DMI is induced in graphene/Fe3GeTe2. This is made possible due to an interfacial electric field driven by charge asymmetry together with the broken inversion symmetry of the heterostructure. These findings reveal that the enhanced DMI energy parameter, resulting from a large effective electron mass in Fe3GeTe2, remarkably contributes to stabilizing non-collinear spins below the Curie temperature, overcoming the magnetic anisotropy energy. These results are supported by the topological Hall effect, which coexists with the non-trivial breakdown of Fermi liquid behavior, confirming the interplay between spins and non-trivial topology. This work paves the way toward the design and control of interface-driven skyrmion-based devices.

Carrier transport simulation methods for electronic devices with coexistence of quantum transport and diffusive transport

In this manuscript, carrier transport simulation methods are proposed for devices with the coexistence of quantum transport and diffusive transport by combining the nonequilibrium Green's function method with the drift-diffusion transport simulation method. Current continuity between quantum transport and drift-diffusion transport is ensured by setting quantum transport current as the connection boundary condition of drift-diffusion simulation or by introducing quantum transport-induced carrier generation rates to drift-diffusion simulation. A comprehensive study of our method and the method combining the Wentzel–Kramers–Brillouin (WKB) method with the drift-diffusion transport simulation method is performed for n-type tunnel oxide passivating contact solar cell to investigate their applicable conditions and balance the accuracy and computational cost. As the oxide barrier width, barrier height, and electron effective mass increase, or the doping concentration in the electron transport layer decreases to the extent that the blocking effect of the oxide barrier on light-generated electrons becomes significant, method I is more accurate since the transmission coefficient near the conduction band edge calculated by WKB is overestimated; otherwise, method II is more suitable due to its low computational cost without the loss of accuracy. In addition, the differences between current densities, carrier densities, and Shockley–Read–Hall recombination rates simulated under the two current continuity conditions for the solar cell with different carrier mobilities are also further explored and analyzed.

Structural Preferences of Metal Chalcogenide based Nanothreads (MX; M=Au, Ag; X=S, Se): A Computational Study

AbstractThis study investigates the structural stability and electronic properties of α‐MX nanothreads and β‐MX nanosheets (M=Au, Ag; X=S, Se) using density functional theory. Our findings confirm the thermal and dynamic stability of all nanostructures, with β‐MX phases being more stable than α‐MX, albeit with minimal energy differences between the two phases. Electron localization analysis reveals predominantly ionic bonding character between M (Ag and Au) and X (S and Se) atoms. All the phase exhibits metallophilic interactions (Argentophilic and Aurophilic), with α‐MX nanothreads demonstrating a higher level of interaction compared to β‐MX nanosheets, attributed to the curvature inherent in the nanothreads. Significantly, these interactions are effectively small and do not compromise the relative stability between the α‐MX and β‐MX phases. Additionally, both α‐MX and β‐MX structures exhibit characteristics of indirect bandgap semiconductor behaviour. The band gap values do not significantly differ between α‐MX and β‐MX phases. Fermi analysis reveals that α‐MX phases exhibit small effective electron masses and large hole mobility along the uniaxial direction. These findings suggest promising prospects for α‐MX nanothreads as 1D semiconductors in nano‐electronics and nano‐optoelectronics applications in the future.

The photocatalytic degradation performance of Dion-Jacobson-type layered perovskites AMCa2Ta3O10 (AM=Rb, Cs): A DFT study

The structural, electronic, redox potential, mechanical, photocatalytic, and optical properties of the Dion-Jacobson-type triple-layered perovskites AMCa2Ta3O10 (AM = Rb, Cs) are investigated via density functional theory (DFT) study. The electronic properties are calculated through HSE-06 functional technique which confirmed the semiconducting behavior with the energy band gap values of 1.67 eV and 1.71 eV for RbCa2Ta3O10 and CsCa2Ta3O10, respectively. The calculated results of redox potential indicate that both materials are favorable for water splitting and as an agent for pollutant degradation. Both studied compounds exhibit a reduced effective mass of electrons, which suggests the high capacity to transfer the charge to the surface, indicative of superior electrical conductivity. Poisson's and Pugh's ratios suggest that both the materials are brittle. Optical parameters are calculated within the energy range of 0–6 eV, which strongly correlates with the energy band gap's high absorption and low reflection in the visible region. Our findings indicate high photocatalytic efficiency in organic pollutant degradation, suggesting the potential for developing advanced photocatalytic devices for water splitting and environmental pollutant decomposition.

Dependence temperature on effective mass and susceptibility in quantum well-wires

In this study, we investigated the simulation impact of carrier density and temperature on properties such as susceptibility and effective mass of electrons in GaAs/Al x Ga1−x As quantum-well wires, involving the treatment of Coulomb interaction and the interaction between electrons and holes with longitudinal optical phonons (LO-phonon) on an equal basis. The susceptibility and effective mass were calculated and compared with the results when no phonon coupling was considered. Furthermore, the key findings were compared with results from the sum-rule version of the Singwi-Tosi-Land-Sj ö lander (STLS) theory, mean-spherical approximation (MSA) theory, and there is a high level of concordance between this formula and experimental values obtained by other researchers. Our results reveal that carrier concentration and temperature significantly affect susceptibility and effective mass of the quantum well-wires in both cases, with LO-phonon contributions. These results contribute to illuminating how Coulomb interactions and exchange-correlation energies influence the susceptibility and effective mass of GaAs/Al x Ga1−x As across a broad range of temperature and carrier density conditions.

Bi(III)‐based oxide semiconductors with ambipolar doping: (Na, K)BiO2

AbstractBi(III)‐based oxides are emerging as important semiconductors for future electronic applications. Through hybrid density functional theory calculations and defect analysis, we demonstrate that ABi(III)O2 (A = Na or K) is a promising wide‐band‐gap bipolar semiconductor. Our calculations predict ABiO2 to have a large band gap of 1.97 eV for NaBiO2 and 2.77 eV for KBiO2. Unlike widely‐used oxide semiconductors such as In2O3 and ZnO, the spatially extended cation states (Bi 6s) of ABiO2 significantly contribute to the valence band maximum, enhancing p‐type dopability. We indeed show that potential acceptors, such as SrBi, produce shallow levels. In addition, n‐type doping is found to be possible through the extrinsic doping of heterovalent elements such as Te and F. The band‐structure analysis reveals that ABiO2 has small effective masses for electrons and holes (< 1m0 where m0 is the electron rest mass), indicating favorable electron and hole transport properties.

High-Performance Sub-10 nm Two-Dimensional SbSeBr Transistors through Transport Orientation.

Exploring two-dimensional (2D) materials with a small carrier effective mass and suitable band gap is crucial for the design of metal oxide semiconductor field effect transistors (MOSFETs). Here, the quantum transport properties of stable 2D SbSeBr are simulated on the basis of first-principles calculations. Monolayer SbSeBr proves to be a competitive channel material, offering a suitable band gap of 1.18 eV and a small electron effective mass (me*) of 0.22m0. The 2D SbSeBr field effect transistor (FET) with 8 nm channel length exhibits a high on-state current of 1869 μA/μm, low power consumption of 0.080 fJ/μm, and small delay time of 0.062 ps, which can satisfy the requirements of the International Technology Roadmap for Semiconductors for high-performance devices. Moreover, despite the monolayer SbSeBr having an isotropic me*, the asymmetrical band trends enable SbSeBr FETs to display transport orientation, which emphasizes the importance of band trends and provides valuable insights for selecting channel materials.

Theoretical study on photoelectric properties of ferroelectric photovoltaic perovskite CsGeBr3 based on first-principle calculations

Ferroelectric photovoltaic materials have attracted great attention because of their unique photoelectric conversion mechanism, high photo-generated voltage, and adjustable polarization intensity. Traditional ferroelectric oxide perovskites such as BaTiO3, BiFeO3, and Pb(ZrTi)O3 have attracted much attention but they are not suitable as light absorbing layers in solar cells, due to the large optical bandgap, low light absorption rate, and small photogenerated current. Therefore, it is necessary to seek prominent materials with both ferroelectric and suitable band gaps. Recently, the evidence of ferroelectricity in the typical three-dimensional all-inorganic halide perovskites CsGeX3, with band gaps of 1.6 eV to 2.3 eV has been confirmed. However, the spontaneous polarization of ferroelectric perovskite CsGeX3 is ∼10 to 20 μc cm−2 which is weaker than that of ABO3 (∼26 to 75 μc cm−2). Strain engineering has a significant influence on the properties of semiconductor materials by controlling the lattice scaling and the internal atomic spacing. Hence, in this work, strain engineering is introduced to adjust the ferroelectric polarization and the photoelectric properties of ferroelectric perovskite CsGeBr3. The calculated results show that when the applied compressive strain increases from 0% to −4%, the spontaneous polarization of ferroelectric perovskite CsGeBr3 increases from 14.23 μc cm−2 to 51.61 μc cm−2, and the band gap reduces from 2.3631 eV to 1.5310 eV. The effective mass of electrons and holes gradually reduces, exciton binding energies decrease from 48 meV to 5 meV, and the optical absorption coefficient is strongly enhanced from 3 × 105 cm−1 to 5 × 105 cm−1 in the visible range. Besides, the power conversion efficiency(PCE) of CsGeBr3 is significantly increased from 16.95% to 26.77%. Therefore, the results indicate that the application of compressive strain can increase the ferroelectric polarization and enhance the original photovoltaic performance of ferroelectric perovskite CsGeBr3. Our theoretical calculations can provide useful insights and beneficial guidance into experimental studies of ferroelectric perovskites in photoelectric applications.

Study on the effects of VO and Hi on the absorption spectrum and conductivity of Ti doped β-Ga2O3

β-Ga2O3 has many excellent properties, but poor electrical conductivity limits its application in optoelectronic devices. At present, some progress has been made in the study of Ti doping on the photoelectric properties of β-Ga2O3. However, few studies on the effects of Ti doping and VO-Hi co-existence on photoelectric properties of β-Ga2O3. Defects (VO) and unintentional impurities (Hi) will inevitably exist during the preparation of β-Ga2O3. Given these problems, the effects of Ti doping and VO-Hi co-existence on photoelectric properties of β-Ga2O3 were studied using first-principles GGA+U method. The electronic structure, dielectric function, absorption spectrum, effective mass, mobility, and conductivity of the system were calculated and analyzed. The results indicate that with the increase of Ti doping concentration, the bandgap of the Ti doped β-Ga2O3 system gradually narrows. Ti doping causes a red shift in the peak of the absorption spectrum and effectively improves the conductivity of the system. The O vacancy reduces the conductivity of the system, while the interstitial H increases the conductivity of the system. Thus, Ti-doped β-Ga2O3 material is helpful for preparing new optoelectronic devices.

Energy structure of mixed halide CeF2Cl and CeFCl2 crystals

The band energy structures of CeF2Cl and CeFCl2 crystals have been calculated using the projector augmented-wave (PAW) method and the hybrid exchange-correlation functional PBE0. The valence band top consists of 2p states of F and 3p states of Cl. An energy gap is observed between the 5d states of Ce in the bottom part of the conduction band of both crystals, forming two subbands, 5d1 and 5d2, with very different effective electron masses (2.49 m0 and 0.19 m0 for CeF2Cl and 5.95 m0 and 0.84 m0 for CeFCl2, respectively). The 4f states of Ce are placed within the forbidden band. The obtained values for the band gap of CeF2Cl and CeFCl2 crystals are 6 eV and 4.6 eV, respectively.

Near-Field Radiative Heat Transfer between Layered β-GeSe Slabs: First-Principles Approach.

The group-IV monochalcogenide monolayers, GeSe, are interesting and novel two-dimensional (2D) semiconductor materials due to their highly anisotropic physical properties. Monolayers of the different GeSe polymorphs have already had their physical properties and potential applications extensively investigated. However, few-layer homostructures, which can also be approximated as 2D systems in many cases, have not received the same attention. For this reason, in this work, we investigate the optical properties of a free-standing few-layer β-GeSe system and use this information to investigate their performance in the near-field radiative heat transfer (NFRHT). The required optical conductivity of the few-layer 2D material is calculated by using density functional theory (DFT), including spin-orbit coupling. The band structure is investigated for up to five layers, and the effective electron masses are calculated correspondingly. Using this information, both the intraband transitions due to the presence of free electrons introduced by doping and the interband transitions are considered. The contribution of the ionic vibrations is also included in calculating the optical properties because of its relevance to NFRHT through the resulting active optical phonons. With all these contributions included, more realistic predictions of the NFRHT between the layered 2D β-GeSe materials can be obtained. It is found that the heat transfer attainable with the layered system is similar to that of a single layer of β-GeSe we have obtained previously.

Electronic and optical properties of MgTe quantum dots: size effect

The size-dependent electronic and optical properties of magnesium telluride quantum dots are investigated using a pseudopotential scheme. The emphasis is focused on the effect of the size of the quantum dots on the undertaken properties. The quantum dot radius is considered to be varying in between 1 and 10 nm. It is found that the direct- and indirect band gaps as well as the electron and hole effective masses decrease non-linearly as the quantum dot radius is increased. However, the refractive index, the static- and high frequency dielectric as well as the transverse effective charge increase as the quantum dot size is augmented. The quantum confinement is found to play a major role for the studied physical quantities as long as the quantum dot radius remains less than 5 nm. This permits to tailor the electronic and optical properties of our material according to the desired application.

Calculation of the effective mass of electrons and holes of TlGaTe2 compound

Based on the band structure of TlGaTe2 compound, the extrema of the valence and conduction bands were determined and the tensor of the components of the inverse effective mass of electrons and holes was calculated.

Performance analysis of un-doped and doped titania (TiO ) as an electron transport layer (ETL) for perovskite solar cells.

Density functional theory (DFT) calculations are carried out on pure and doped rutile TiO . The bandgap (E ) for pristine, S-doped, Fe-doped, and Fe/S co-doped materials is direct, with values of 2.98 eV, 2.18 eV, 1.58 eV, and 1.40 eV. The effective mass of charge carriers (m*) and ratio of effective masses of holes to effective masses of electrons (R) are also investigated, and it is discovered that Fe/S co-doped materials have the lowest charge carrier recombination rate. The Fe/S co-doped material has the highest . of doped materials shifted into the visible range. Due to the high dopant concentration in Fe and Fe/S-doped cases, the E is lowered to a relatively small value; hence, only pristine and S-doped materials are verified as electron transport layer (ETL). A solar cell device analysis employing pure and S-doped rutile TiO as ETL is completed using DFT-derived parameters in SCAPS-1D modeling software for the first time. For the optimized solar cells, current-voltage (IV) characteristics, quantum efficiency (QE), capacitance-voltage (CV) characteristics, and capacitance-frequency (Cf) characteristics are provided. The aim of the present study is to improve efficiency of perovskite solar cell by doping as well as to improve accuracy of simulation by applying DFT extracted parameters as input. From the analysis, improvement is found in efficiency of doped TiO compared to un-doped TiO . The efficiency of the PSC with S-doped ETL is 1.418% higher than the PSC with un-doped ETL. Quantumwise Automistic Tool Kit (ATK) is used to extract DFT parameters. Using these DFT parameters as input in SCAPS-1D (Solar Cell Capacitance Simulator), solar cells for doped and un-doped material are simulated. The density functional theory (DFT)-based orthogonalized linear combination of atomic orbital (OLCAO) technique is used. Structural optimization is done using the LBFGS (Limited-memory Broyden-Fletcher-Goldfarb-Shanno). PBESol-GGA (Perdew-Burke-Ernzerhof solid-generalized gradient approximation) is applied as exchange correlation for calculating structural parameters, while MGGA-TB09 (meta-generalized gradient approximation-Tran and Blaha) is applied as exchange correlation for calculating optical and electronic properties.

High-performance optoelectronic and thermoelectric properties of transparent conductors based on Tl2O3 under pressure

In this work, the full-potential linearized augmented plane wave method (FP- LAPW) and the modified Becke-Johnson (mBJ) functional with spin–orbit (SO) coupling are used the obtain the structural, optoelectronic and thermoelectric properties of Tl2O3 under pressure. The results show that Tl2O3, as transparent conducting oxide (TCO), is a direct bandgap semiconductor with a band gap of 1.23 eV. The band gap value and the effective mass of electrons increases by increasing pressure. Density of state spectra reveal that the nature of electrons in Tl-6s state in the bottom of conduction band, like free electrons in s state, is responsible for the conducting behavior of Tl2O3. A blue shift is observed in optical spectra such as electron energy loss and absorption spectra with an increase in pressure. Obtained dielectric constants under pressure are inversely proportional to the band gap value according to Penn model. The effects of pressure on thermometric properties are also explored. The hydrostatic pressure increases Seebeck coefficient, while it decreases thermal conductivity that is an effective way to the enhancement of the thermoelectric efficiency of TCOs. A figure of merit (ZT) of 0.98 in p-type Tl2O3 is achieved that is desirable for using in thermoelectric devices.