The energy band structure of Si and Ge nanolayers

First-principles calculation based on density functional theory (DFT) with the generalized gradient approximation (GGA) were carried out to investigate the energy band gap structure of Si and Ge nanofilms. Calculation results show that the band gaps of Si(111) and Ge(110) nanofilms are indirect structures and independent of film thickness, the band gaps of Si(110) and Ge(100) nanofilms could be transfered into the direct structure for nanofilm thickness of less than a certain value, and the band gaps of Si(100) and Ge(111) nanofilms are the direct structures in the present model thickness range (about 7 nm). Moreover, the changes of the band gaps on the Si and Ge nanofilms follow the quantum confinement effects. It will be a good way to obtain direct band gap emission in Si and Ge materials, and to develop Si and Ge laser on Si chip.

Download Full-text

Effect of Yb Concentration on the Structural, Magnetic and Optoelectronic Properties of Yb Doped ZnO: First Principles Calculation

10.21203/rs.3.rs-877060/v1 ◽

2021 ◽

Author(s):

Mohamed Achehboune ◽

Mohammed Khenfouch ◽

Issam Boukhoubza ◽

Issam Derkaoui ◽

Bakang Moses Mothudi ◽

...

Keyword(s):

Band Gap ◽

Conduction Band ◽

Density Functional ◽

Blue Shift ◽

First Principles Calculation ◽

Theoretical Research ◽

Generalized Gradient ◽

Functional Theory ◽

Doped Zno ◽

Good Agreement

Abstract Density functional theory-based investigation of the electronic, magnetic, and optical characteristics in pure and ytterbium (Yb) doped ZnO has been carried out by the plane-wave pseudopotential technique with generalized gradient approximation. The calculated lattice parameters and band gap of pure ZnO are in good agreement with the experimental results. The energy band-gap increases with the increase of Yb concentration. The Fermi level moves upward into the conduction band after doping with Yb, which shows the properties of an n-type se miconductor. New defects were created in the band-gap near the conduction band attributed to the Yb-4f states. The magnetic properties of ZnO were found to be affected by Yb doping; ferromagnetic property was observed for 4.17% Yb due to spin polarization of Yb-4f electrons. The calculated optical properties imply that Yb doped causes a blue shift of the absorption peaks, significantly enhances the absorption of the visible light, and the blue shift of the reflectivity spectrum was observed. Besides, a better transmittance of approximately 88% was observed for 4.17% Yb doped ZnO system. The refractive index and the extinction coefficient were observed to decrease as the Yb dopant concentration increased. As a result, we believe that our findings will be useful in understanding the doping impact in ZnO and will motivate further theoretical research.

Download Full-text

Electronic Properties of Calcium and Zirconium Co-Doped BaTiO3

Materials Science Forum ◽

10.4028/www.scientific.net/msf.1010.308 ◽

2020 ◽

Vol 1010 ◽

pp. 308-313

Author(s):

Akeem Adekunle Adewale ◽

Abdullah Chik ◽

Ruhiyuddin Mohd Zaki

Keyword(s):

Band Gap ◽

Electronic Properties ◽

Density Of States ◽

Energy Band ◽

Density Functional ◽

Partial Density ◽

Total Density ◽

Energy Band Gap ◽

Wide Energy ◽

Direct Band

Barium titanate (BaTiO3) is a perovskite based oxides with many potential application in electronic devices. From experimental report BaTiO3 has wide energy band gap of about 3.4 eV which by doped with Ca and Zr at A- and B- sites respectively can enhance their piezoelectric properties. Using first principles method within the density functional theory (DFT) as implement in Quantum Espresso (QE) with the plane wave pseudo potential function, the influence of the Ca and Zr doping in BaTiO3 are studied via electronic properties: band structure, total density of states (TDOS) and partial density of states (PDOS). The energy band gap calculated was underestimation which is similar to other DFT work. Two direct band gap where observed in Ba0.875Ca0.125Ti0.875Zr0.125O3 sample at Γ- Γ (2.31 eV) and X- X (2.35 eV) symmetry point.

Download Full-text

First-principles study on the band structure, magnetic and elastic properties of half-metallic Cr2MnAl

Modern Physics Letters B ◽

10.1142/s0217984915501390 ◽

2015 ◽

Vol 29 (24) ◽

pp. 1550139 ◽

Cited By ~ 6

Author(s):

Santao Qi ◽

Chuan-Hui Zhang ◽

Bao Chen ◽

Jiang Shen

Keyword(s):

Band Structure ◽

Band Gap ◽

Elastic Properties ◽

Density Functional ◽

Stable State ◽

Generalized Gradient ◽

Half Metallic ◽

Text Type ◽

Calculation Results ◽

Indirect Band Gap

In this study, we have investigated the structural, electronic, magnetic and elastic properties of the full-Heusler [Formula: see text] alloy in the framework of density functional theory with generalized gradient approximation (GGA). The calculated results showed that [Formula: see text] was stable in ferrimagnetic configuration and crystallized in the [Formula: see text]-type structure. From the band structure and density of states calculation results, we concluded that [Formula: see text] belongs to a kind of half-metallic compound with an indirect band gap of 0.37 eV. Immediately thereafter, we have analyzed the origin of half-metallic band gap. The total magnetic moment of [Formula: see text] at the stable state is [Formula: see text] per formula unit, obeying the Slater–Pauling rule [Formula: see text]. In addition, various mechanical properties have been obtained and discussed based on the three principle elastic tensor elements [Formula: see text] and [Formula: see text] for the first time in the present work. We expect that our calculated results may trigger the application of [Formula: see text] in future spintronics field.

Download Full-text

Theoretical Investigation on Electronic Properties of ZnO Crystals Using DFT-Based Calculation Method

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.1112.41 ◽

2015 ◽

Vol 1112 ◽

pp. 41-44 ◽

Cited By ~ 9

Author(s):

Yudi Darma ◽

Freddy Giovanni Setiawan ◽

Muhammad Aziz Majidi ◽

Andrivo Rusydi

Keyword(s):

Band Gap ◽

Valence Band ◽

Density Functional ◽

Electronic Band Structure ◽

Valence Band Maximum ◽

Band Gaps ◽

Generalized Gradient ◽

Strong Electron ◽

Electronic Band ◽

Rocksalt Structure

We study the electronic band structure and density of states (DOS) on ZnO material in various crystal structures : wurtzite (W), zincblende (ZB), and rocksalt (RS) phases. Calculations are based on Density Functional Theory (DFT) with Generalized Gradient Approximation (GGA) for exchange-correlation functional and Hubbard correction to consider the strong electron correlations in 3d orbitals. After structural optimization, GGA results show that wurtzite and zincblende structures have a direct band gap of 0.749 eV and 0.637 eV, respectively, whereas rocksalt structure has an indirect band gap of 0.817 eV. Symmetrical shape of total DOS for spin up and spin down electrons indicates a zero total magnetic moment. For all ZnO structures, the upper valence band is formed by hybridization among O 2p and Zn 3d orbitals, while lower valence and conduction band are primarily filled by O 2s and Zn 4s, respectively. The GGA+U approach is found to improve the calculated band gaps and correct the position of Zn 3d state below Valence Band Maximum (VBM). From GGA+U, the band gaps for W-ZnO, ZB-ZnO, and RS-ZnO are 1.12 eV, 1.00 eV, and 1.11 eV, respectively.

Download Full-text

Electronic structures and optical properties of IV A elements-doped 3C-SiC from density functional calculations

Modern Physics Letters B ◽

10.1142/s021798491850389x ◽

2018 ◽

Vol 32 (32) ◽

pp. 1850389 ◽

Cited By ~ 4

Author(s):

Xuefeng Lu ◽

Tingting Zhao ◽

Xin Guo ◽

Meng Chen ◽

Junqiang Ren ◽

...

Keyword(s):

Optical Properties ◽

Band Gap ◽

Electronic Structures ◽

Density Functional ◽

Visible Region ◽

First Principles Calculation ◽

Charge Difference Density ◽

Direct Band ◽

Density Analysis ◽

Indirect Band Gap

Electronic structures and optical properties of IV A elements (Ge, Sn and Pb)-doped 3C-SiC are investigated by means of the first-principles calculation. The results reveal that the structure of Ge-doped system is more stable with a lower formation energy of 1.249 eV compared with those of Sn- and Pb-doped 3C-SiC systems of 3.360 eV and 5.476 eV, respectively. Doping of the IV A elements can increase the band gap, and there is an obvious transition from an indirect band gap to a direct band gap. Furthermore, charge difference density analysis proves that the covalent order of bonding between the doping atoms and the C atoms is Ge–C [Formula: see text] Sn–C [Formula: see text] Pb–C, which is fully verified by population values. Due to the lower static dielectric constant, the service life of 3C-SiC dramatically improved in production practice. Moreover, the lower reflectivity and absorption peak in the visible region, implying its wide application foreground in photoelectric devices.

Download Full-text

STUDY ON BAND STRUCTURE OF NANOPOROUS SILICON THIN FILM

Surface Review and Letters ◽

10.1142/s0218625x18500452 ◽

2018 ◽

Vol 25 (01) ◽

pp. 1850045

Author(s):

XUEKE WU ◽

YANLIN TANG

Keyword(s):

Thin Film ◽

Band Structure ◽

Density Functional ◽

First Principles Calculation ◽

Generalized Gradient ◽

Silicon Thin Film ◽

Functional Theory ◽

Nanoporous Silicon ◽

Matrix Layer ◽

Calculation Results

We investigate the energy band structure of nanoporous silicon thin film using first principles calculation based on density functional theory (DFT) with the generalized gradient approximation (GGA). The calculation results show that the band gaps of nanoporous silicon increase with increasing porosity, increase with decreasing the thickness of matrix layer, and almost independent of the thickness of pore layer. Moreover, the band structure of nanoporous silicon can be transformed from indirect to direct gap on thin films of (111) and (110) faces. It will be the guidance and reference for the fabrication of porous silicon optoelectronic devices.

Download Full-text

Increased Malleability in Tetragonal Zrx Ti1−x O2 Ternary Alloys: First-Principles Approach

Zeitschrift für Naturforschung A ◽

10.1515/zna-2017-0036 ◽

2017 ◽

Vol 72 (6) ◽

pp. 567-572

Author(s):

F. Ayedun ◽

P.O. Adebambo ◽

B.I. Adetunji ◽

V.C. Ozebo ◽

J.A. Oguntuase ◽

...

Keyword(s):

Band Gap ◽

First Principles ◽

Density Functional ◽

Ternary Alloys ◽

Generalized Gradient ◽

Functional Theory ◽

Direct Band ◽

Indirect Band Gap ◽

Projector Augmented Wave ◽

Alloying Effects

AbstractTetragonal phase of ZrxTi1−xO2ternary alloys is studied using generalized gradient approximation (GGA) projector augmented wave-based density functional theory (DFT). The calculations are used to characterize alloying effects of Zr substituting Ti in tutile TiO2. Band gap calculations show a direct band gap atx=0, while at other concentrations, an indirect band gap is observed. Electronic structure analysis shows that Zr alloying is capable of lowering the band gap transition of ZrxTi1−xO2atx=1 by the presence of an impurity state of transition metal Zr 5S2on the upper edge of the valence band. The addition of Zr also results in the corresponding increment in lattice constant with the material becoming more ductile and malleable.

Download Full-text

Band Gap Widening and Quantum Confinement Effects of ZnO Nanowires by First-Principles Calculation

Materials Science Forum ◽

10.4028/www.scientific.net/msf.675-677.243 ◽

2011 ◽

Vol 675-677 ◽

pp. 243-246 ◽

Cited By ~ 1

Author(s):

Mei Li Guo ◽

Xiao Dong Zhang

Keyword(s):

Optical Properties ◽

Band Gap ◽

First Principles ◽

Quantum Confinement ◽

Density Functional ◽

High Energy ◽

Zno Nanowires ◽

First Principles Calculation ◽

Confinement Effects ◽

Quantum Confinement Effects

ZnO nanowires are promising for photonic devices, biosensor and cancer cell imaging. We have performed a first-principles study to evaluate the electronic and optical properties of ZnO nanowires. We have employed the Perdew–Burke–Ernzerhof form of generalized gradient approximation in the frame work of density functional theory. Calculations have been carried out at different configurations. With decreasing diameter, the band gap of ZnO nanowires is increased due to the increase of quantum confinement effects. The results of imaginary part of the dielectric function indicate that the optical transition between valence band and conduction band has shifted to the high energy range as the diameter decreases. The ZnO nanowires show size-tunable optical properties.

Download Full-text

Study of Electronic Structures and Transport Properties on Saturated GaN Nanowires

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.465.118 ◽

2012 ◽

Vol 465 ◽

pp. 118-124 ◽

Cited By ~ 1

Author(s):

En Ling Li ◽

Peng Fei Zhu ◽

Tao Zhao ◽

De Ming Ma ◽

Xue Wen Wang

Keyword(s):

Transport Properties ◽

Band Gap ◽

Density Functional ◽

Growth Direction ◽

Generalized Gradient ◽

Electronic Density ◽

Voltage Range ◽

Gan Nanowires ◽

Pulse Type ◽

Direct Band

Geometry structure, electronic structure and electronic transport properties of saturated hexagonal single crystalline GaN nanowires in the [001] growth direction have been investigated based on generalized gradient approximation (GGA) of density functional theory (DFT) and non-equilibrium green's function (NEGF) method. The results show, there is a contraction of the bond lengths of the saturated GaN nanowires after optimization; the nanowires have direct band gap, and band gap decreases with the increase of the cross section of nanowires; the electronic density of state and electronic transmission spectra of two-probe system have their own pulse-type sharp peaks with almost the same location of electron energy; the curves of I-V characteristics of the three saturated GaN nanowires are symmetric over the entire bias-voltage range, and they are semiconducting.

Download Full-text

AB INITIO STUDY OF STRUCTURAL, ELECTRONIC AND OPTICAL PROPERTIES OF MgxCd1-xX (X = S, Se, Te) ALLOYS

International Journal of Modern Physics B ◽

10.1142/s0217979212501688 ◽

2012 ◽

Vol 26 (30) ◽

pp. 1250168 ◽

Cited By ~ 19

Author(s):

N. A. NOOR ◽

A. SHAUKAT

Keyword(s):

Optical Properties ◽

Band Gap ◽

Density Functional ◽

Theoretical Calculations ◽

Ternary Alloys ◽

Full Potential ◽

Generalized Gradient ◽

Calculated Density ◽

Electronic And Optical Properties ◽

Direct Band

This study describes structural, electronic and optical properties of Mg x Cd 1-x X (X = S, Se, Te) alloys in the complete range 0≤x ≤1 of composition x in the zinc-blende (ZB) phase with the help of full-potential linearized augmented plane wave plus local orbitals (FP-LAPW+lo) method within density functional theory (DFT). In order to calculate total energy, generalized gradient approximation (Wu–Cohen GGA) has been applied, which is based on optimization energy. For electronic structure calculations, the corresponding potential is being optimized by Engel–Vosko GGA formalism. Our calculations reveal the nonlinear variation of lattice constant and bulk modulus with different concentration for the end binary and their ternary alloys, which slightly deviates from Vegard's law. The calculated band structures show a direct band gap for all three alloys with increasing order in the complete range of the compositional parameter x. In addition, we have discussed the disorder parameter (gap bowing) and concluded that the total band gap bowing is substantially influenced by the chemical (electronegativity) contribution. The calculated density of states (DOS) of these alloys is discussed in terms of contribution from various s-, p- and d-states of the constituent atoms and charge density distributions plots are analyzed. Optical properties have been presented in the form of the complex dielectric function ε(ω), refractive index n(ω) and extinction coefficient k(ω) as function of the incident photon energy, and the results have been compared with existing experimental data and other theoretical calculations.

Download Full-text