Comprehension of defect states induced by fluorine ions substituting for oxygen ions in Sr3MgSi2O8−δF2δ by first principles calculation

2021 ◽  
Vol 14 (06) ◽  
pp. 2151039
Author(s):  
Meng Zhang ◽  
Ting Song ◽  
Hancheng Zhu ◽  
Xinyang Zhang
Keyword(s):  
Band Gap ◽  
First Principles ◽  
Visible Region ◽  
First Principles Calculation ◽  
Defect State ◽  
Defect States ◽  
Light Emitting Devices ◽  
Oxygen Ions ◽  
Host Materials ◽  
Fluorine Ions

Study of the defect states in the luminescent host materials has always been a significant point in improving the light emitting devices performances. To afford candidate luminescence host materials, defect states in Sr3MgSi2O[Formula: see text]F[Formula: see text] induced by substitution of fluorine ions (F[Formula: see text] substituting for oxygen ions (O[Formula: see text] have been studied through first principles calculation and the related results are presented in this work. First, chemical formulas have been confirmed to be Sr3MgSi2O[Formula: see text]F[Formula: see text] through calculations of the possible crystal structures with increasing F[Formula: see text] substituting for O[Formula: see text] concentrations while band gap values decrease from 5.889 eV to 5.328 eV. When the fluorine ion substituting concentration [Formula: see text] reached 0.5, a new defect state near 3.002 eV in the band gap appeared and it can be concluded that the defect state originates from the two fluorine ions bonding to the same Si–O–F2 group. In addition, there arose a new absorption band in the visible region and it can also be attributed to the introduced color [Formula: see text] center in Sr3MgSi2O[Formula: see text]F. The aforementioned results show that tiny doping amounts of fluorine ions could make Sr3MgSi2O[Formula: see text]F[Formula: see text] suitable for luminescence host materials.

Amorphous Semiconductors Studied by First-principles Simulations: Structure and Electronic Properties

2009 ◽  
Vol 1153 ◽  
Author(s):  
Karol Jarolimek ◽  
Robert A. de Groot ◽  
Gilles A. de Wijs ◽  
Miro Zeman
Keyword(s):  
Band Gap ◽  
Electronic Properties ◽  
First Principles ◽  
Density Functional ◽  
Large Cell ◽  
Band Gap Energy ◽  
Amorphous Semiconductors ◽  
Structural Defects ◽  
Defect States ◽  
Wide Range

AbstractAtomistic models of amorphous solids enable us to study properties that are difficult to address with experimental methods. We present a study of two amorphous semiconductors with a great technological importance, namely a- Si:H and a-SiN:H. We use first-principles density functional theory (DFT), i.e. the interatomic forces are derived from basic quantum mechanics, as only that provides accurate interactions between the atoms for a wide range of chemical environments (e.g. brought about by composition changes). This type of precision is necessary for obtaining the correct short range order. Our amorphous samples are prepared by a cooling from liquid approach. As DFT calculations are very demanding, typically only short simulations can be carried out. Therefore most studies suffer from a substantial amount of defects, making them less useful for modeling purposes. We varied the cooling rate during the thermalization process and found it has a considerable impact on the quality of the resulting structure. A rate of 0.02 K/fs proves to be sufficient to prepare realistic samples with low defect concentrations. To our knowledge these are the first calculations that are entirely based on first-principles and at the same time are able to produce defect-free samples. Because of the high computational load also the size of the systems has to remain modest. The samples of a-Si:H and a-SiN:H contain 72 and 110 atoms, respectively. To examine the convergence with cells size, we utilize a large cell of a-Si:H with a total of 243 atoms. As we obtain essentially the same structure as with the smaller sample, we conclude that the use of smaller cells is justified. Although creating structures without any defects is important, on the other hand a small number of defects can give valuable information about the structure and electronic properties of defects in a-Si:H and a-SiN:H. In our samples we observe the presence of both the dangling bond (undercoordinated atom) and the floating bond (over-coordinated atom). We relate structural defects to electronic defect states within the band gap. In a-SiN:H the silicon-silicon bonds induce states at the valence and conduction band edges, thus decreasing the band gap energy. This finding is in agreement with measurements of the optical band gap, where increasing the nitrogen content increases the band gap.

First Principles Investigation on the Structural, Electronic and Optical Properties of Amorphous Silica Glass

2017 ◽  
Vol 268 ◽  
pp. 92-96
Author(s):  
R.M. Nor ◽  
S.N.M. Halim ◽  
Mohamad Fariz Mohamad Taib ◽  
M. Kamil Abd-Rahman
Keyword(s):  
Optical Properties ◽  
Band Gap ◽  
Electronic Properties ◽  
Amorphous Silica ◽  
First Principles ◽  
Glass Structure ◽  
Small Sample ◽  
First Principles Calculation ◽  
Electronic And Optical Properties ◽  
Amorphous Quartz

The structural, electronic, and optical properties of an amorphous SiO2 (a-SiO2) model is investigated by using first-principles calculation. Most research works used beta-cristobalite glass structure as a reference to amorphous silica structure. However, only the electronic properties were been presented without any link towards the optical properties. Here, we demonstrate simultaneous electronic and optical properties, which closely matched to a-SiO2 properties by generating small sample of amorphous quartz glass. Using the Rietveld refinement, amorphous silica structure was generated and optimized using density functional theory in CASTEP computer code. A thorough analysis of the amorphous quartz structure obtained from different thermal treatment was carried out. The structure of amorphous silica was validated with previous theoretical and experimental works. It is shown that small sample of amorphous silica have similar structural, electronic and optical properties with a larger sample. The calculated optical and electronic properties from the a-SiO2 glass match closely to previous theoretical and experimental data from others. The a-SiO2 band gap of 5.853 eV is found to be smaller than the experimental value of ~9 eV. This is due to the underestimation and assumption made in DFT. However, the band gap value is in good agreement with the other theoretical works. Apart from the absorption edge at around 6.5 eV, the refractive index is 1.5 at 0eV. Therefore, this atomic structure can served as a reference model for future research works on amorphous structures.

scholarly journals Electrical Defect State Distribution in Single Crystal ZnO Schottky Barrier Diodes

Coatings ◽  
2020 ◽  
Vol 10 (3) ◽  
pp. 206
Author(s):  
Jinhee Park ◽  
You Seung Rim ◽  
Pradeep Senanayake ◽  
Jiechen Wu ◽  
Dwight Streit
Keyword(s):  
Single Crystal ◽  
Band Gap ◽  
Schottky Barrier ◽  
Deep Level ◽  
Depletion Region ◽  
Intrinsic Defect ◽  
Defect State ◽  
Schottky Barrier Diodes ◽  
Defect States ◽  
State Distribution

The characterization of defect states in a hydrothermally grown single crystal of ZnO was performed using deep-level transient spectroscopy in the temperature range of 77–340 K. The native intrinsic defect energy level within the ZnO band gap occurred in the depletion region of ZnO Schottky barrier diodes. A major defect level was observed, with a thermal activation energy of 0.27 eV (E3) within the defect state distribution from 0.1 to 0.57 eV below the conduction band minimum. We confirmed the maximum defect concentration to be 3.66 × 1016 cm−3 at 0.27 eV (E3). As a result, we clearly confirmed the distribution of density of defect states in the ZnO band gap.

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

2018 ◽  
Vol 32 (32) ◽  
pp. 1850389 ◽  
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.

Electronic Structure and Ground State Properties of A4[Ag4O4] (A=Na, K and Rb): A First-Principles Study

2013 ◽  
Vol 665 ◽  
pp. 43-48
Author(s):  
Rajagopalan Umamaheswari ◽  
M. Yogeswari ◽  
G. Kalpana
Keyword(s):  
Electronic Structure ◽  
Band Gap ◽  
Ground State ◽  
First Principles ◽  
Density Functional ◽  
Electronic Band Structure ◽  
First Principles Calculation ◽  
Partial Density ◽  
Electronic Band ◽  
Ground State Properties

The first-principles calculation within density functional theory is used to study in detail the electronic structure and ground state properties of alkali-metal oxoargenates A4[Ag4O4] (A= Na, K and Rb). The total energies calculated within the atomic sphere approximation (ASA) were used to determine the ground state properties such as equilibrium lattice parameter, c/a ratio, bulk modulus and cohesive energy. The theoretically calculated equilibrium lattice constants values are in well agreement with the available experimental values. The electronic band structures, total and partial density of states are calculated. The result of electronic band structure shows that the KAgO and RbAgO are direct band gap semiconductors with their gap lying between the Γ-Γ points, whereas NaAgO is found to be an indirect band gap semiconductor with its gap lying between Z-Γ points.

scholarly journals Influence of Secondary Phases in Kesterite-Cu2ZnSnS4Absorber Material Based on the First Principles Calculation

2015 ◽  
Vol 2015 ◽  
pp. 1-6 ◽  
Author(s):  
Wujisiguleng Bao ◽  
Masaya Ichimura
Keyword(s):  
Band Structure ◽  
Band Gap ◽  
First Principles ◽  
Structure Calculation ◽  
First Principles Calculation ◽  
Band Structure Calculation ◽  
Type I ◽  
Secondary Phases ◽  
Recombination Site ◽  
Absorber Material

The influence of secondary phases of ZnS and Cu2SnS3(CTS) in Cu2ZnSnS4(CZTS) absorber material has been studied by calculating the band offsets at the CTS/CZTS/ZnS multilayer heterojunction interfaces on the basis of the first principles band structure calculation. The ZnS/CZTS heterointerface is of type I and since ZnS has a larger band gap than that of CZTS, the ZnS phase in CZTS is predicted to be resistive barriers for carriers. The CTS/CZTS heterointerface is of type I; that is, the band gap of CTS is located within the band gap of CZTS. Therefore, the CTS phase will act as a recombination site in CZTS.

scholarly journals Stable sandwich structures of two-dimensional iron borides FeBxalloy: a first-principles calculation

RSC Advances ◽  
2017 ◽  
Vol 7 (48) ◽  
pp. 30320-30326 ◽  
Author(s):  
Shao-Gang Xu ◽  
Yu-Jun Zhao ◽  
Xiao-Bao Yang ◽  
Hu Xu
Keyword(s):  
Optical Properties ◽  
Band Gap ◽  
First Principles ◽  
Sandwich Structures ◽  
Wide Band ◽  
First Principles Calculation ◽  
Two Dimensional ◽  
Wide Band Gap ◽  
Electronic And Optical Properties ◽  
Wide Band Gap Semiconductors

Multilayer iron borides FeBx(x= 4, 6, 8, 10) are wide-band-gap semiconductors; the electronic and optical properties of these semiconductors may be modulated by biaxial strains.

Electronic Properties of Hydrogenated Graphene-Like Materials Under Strains

2014 ◽  
Vol 1658 ◽  
Author(s):  
K. Mihara ◽  
K. Shintani
Keyword(s):  
Band Gap ◽  
First Principles ◽  
Tensile Strain ◽  
Band Gaps ◽  
First Principles Calculation ◽  
Honeycomb Lattice ◽  
Electronic Band ◽  
Hydrogenated Graphene ◽  
Zigzag Direction ◽  
Electronic Band Structures

ABSTRACTThe electronic band structures of the hydrogenated graphene-like materials, graphane, silicane, and germanane, under tensile strains are calculated using first-principles calculation. The imposed tensile strain is in either the armchair or zigzag direction in the honeycomb lattice. It is found that the band gap of graphane gradually increases with the increase of the strain, whereas the band gaps of silicane and germanane decrease with the increase of the strain. There is little effect of the direction of the imposed strain on such strain dependences.

The Structures and Electronic Properties of Composite Material (LaxAl1-X)2O3 from First-Principles Study

2012 ◽  
Vol 583 ◽  
pp. 158-161
Author(s):  
Hui Yu Yan ◽  
Yan Rui Guo ◽  
Qing Gong Song
Keyword(s):  
Dielectric Constant ◽  
Composite Material ◽  
Band Gap ◽  
Electronic Properties ◽  
First Principles ◽  
Calculation Method ◽  
High Dielectric Constant ◽  
First Principles Calculation ◽  
Al Content ◽  
High Dielectric

The structures and electronic properties of (LaxAl1-x)2O3 are studied by first-principles calculation method. The results show that the composite material (LaxAl1-x)2O3 tend to be in sixfold-coordinated structure when x0.7. (LaxAl1-x)2O3 is in disorder structure and get the minimum band gap when x equals about 0.7. It suggest that (LaxAl1-x)2O3 can be synthesized as high dielectric constant material by doping La2O3 with a lower Al dopant concentrations or by fabricating (LaxAl1-x)2O3 with rich Al content.

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