共查询到20条相似文献,搜索用时 15 毫秒
1.
In this paper, we calculate the band gap and the band discontinuities of a GaN
y
AsBi
x
structure lattice matched to GaAs substrate using the conduction and the valence band anticrossing models at the same time.
The results obtained show a good agreement with experiment. The nitrogen and the bismuth concentrations leading to a wavelength
emission of 1.55 μm have been determined (x = 3.5%, y = 2%). This structure shows a good electron confinement resulting in a high characteristic temperature. 相似文献
2.
The effective mass of strained graphene is investigated by tight-binding and density-functional theory calculations. For graphene strained in the zigzag direction, we find a strong anisotropy in the effective mass near the gap opening, with an abrupt increase of the effective mass at the critical strain in one direction and a smooth variation perpendicular to it. There is no band-gap opening for isotropic strain, but at an expansive strain of about 28%, the lower edge of the s-band reaches the Fermi level and makes the graphene metallic. 相似文献
3.
Based on the non-symmetric transmission-line method, the band gap structure of disordered chiral photonic crystals (CPC) has
been investigated. The influence of the chiral parameters, the disorder, the periods and the refractive index on the band
gap structure has been discussed. It is found that the photonic band gap (PBG) in CPC is more obvious than that in the conventional
photonic crystals, and the PBG can be increased by increasing the periods or the contrast of the refractive index of the two
media. It is also found that the existence of disorder will influence the band edge of the PBG, and such influence will increase
with the increment of periods or the contrast of the refractive index of the two media. 相似文献
4.
A detailed theoretical study of terahertz (THz) optical absorption and transmission in graphene bilayer is presented. Considering an air/graphene/dielectric-wafer system, it is found that there is an absorption window in the range 3-30 THz and the optical transmission is up to 96%. Such an absorption window is induced by different transition energies required for inter- and intra-band optical absorption in the presence of the Pauli blockade effect. As a result, the position and width of this THz absorption window depend sensitively on temperature and carrier density of the system. These results are pertinent to the applications of recently developed graphene systems as novel optoelectronic devices such as THz photodetectors. 相似文献
5.
对于V高掺杂ZnO,当摩尔分数为0.0417—0.0625时,随着掺杂量的增加,吸收光谱出现蓝移减弱和蓝移增强两种不同实验结果均有文献报道.采用密度泛函理论的第一性原理平面波超软赝势方法,构建未掺杂ZnO单胞模型、V高掺杂Zn1-xVxO(x=0.0417,0.0625)两种超胞模型,采用GGA+U方法计算掺杂前后体系的形成能、态密度、分波态密度、磁性和吸收光谱.结果表明,当V的掺杂量(原子含量)为2.083%—3.125%时,随着V掺杂量增加,掺杂体系磁矩增大,磁性增强,并且掺杂体系体积增加,总能量下降,形成能减小,掺杂体系更稳定,同时,掺杂ZnO体系的最小光学带隙增宽,吸收带边向低能级方向移动.上述计算结果与实验结果一致. 相似文献
6.
A valid method is used to extend the omnidirectional electronic gap (OEG) of Gaussian gapped graphene superlattices (GSLs) heterostructure. The heterostructure consists of two superlattices with different width ratios of potentials. Each superlattice comprises a periodic repetition of a unit cell consisting of 21 layers with the potential voltages varying according to a Gaussian function and another layer with a fixed potential voltage. The potential width ratios of constituent Gaussian gapped GSL are established utilizing the lower and upper energy edges of omnidirectional electronic gap depending on the width ratio of potentials. Moreover, it is shown that the width of OEG of the heterostructure is sensitive to lattice constant, which can be applicable to the development of graphene-based electronics. 相似文献
7.
琚伟伟 《原子与分子物理学报》2016,33(6)
采用基于密度泛函理论的第一性原理方法研究了单层及多层黑磷晶体的能隙随层数和外加应力的变化.计算结果表明,体系能隙随着层数的增加而减小,当层数增加到10时,二维黑磷的能隙非常接近于其体材料值.层间的相互作用导致的能带劈裂是能隙减小的直接原因.应力对10层黑磷电子结构的影响也被研究.计算表明,压缩应力可以使10层黑磷从半导体转变为金属,而拉伸应力仅对能隙大小产生影响. 相似文献
8.
The effects of magnetic atom on the band structure of zigzag-edged graphene nanoribbons are investigated by the density functional theory. The results show that for narrow zigzag-edged graphene nanoribbons, the band gap can be opened duo to the spin-up/spin-down charges being re-enriched on the edge sites. However, for the wide zigzag-edged graphene nanoribbons, a spin-up/spin-down half-metallic property can be observed. Moreover, it is found that the Seebeck coefficients in the narrow zigzag-edged graphene nanoribbons are reversed and enlarged, which provides a way to design novel thermoelectric device. 相似文献
9.
采用基于密度泛函理论的第一性原理方法研究了单层及多层黑磷晶体的能隙随层数和外加应力的变化.计算结果表明,体系能隙随着层数的增加而减小,当层数增加到10时,二维黑磷的能隙非常接近于其体材料值.层间的相互作用导致的能带劈裂是能隙减小的直接原因.应力对10层黑磷电子结构的影响也被研究.计算表明,压缩应力可以使10层黑磷从半导体转变为金属,而拉伸应力仅对能隙大小产生影响. 相似文献
10.
First-principles calculations have been employed to investigate the structural transformation and direct to indirect band gap transition of ZnO nanotubes under uniaxial strain. The results show that armchair and zigzag nanotubes can be transformed to each other via unusual fourfold-coordinated structures under the applied strain. Both the armchair and zigzag nanotubes exhibit direct band gap while the unusual fourfold-coordinated ones display indirect band gap. The origin of such a direct-to-indirect band gap transition is explained based on the analyses of atomic orbital contributions. 相似文献
11.
目前, 虽然In和2N共掺对ZnO最小光学带隙和吸收光谱影响的实验研究均有报道, 但是, In和2N共掺在ZnO中均是随机掺杂, 没有考虑利用ZnO的单极性结构进行择优取向共掺, 第一性原理的出现能够解决该问题. 本文采用密度泛函理论框架下的第一性原理平面波超软赝势(GGA+U)方法, 计算了纯的ZnO单胞、择优位向高共掺In–2N原子的Zn1-xInxO1-yNy(x= 0.0625–0.03125, y=0.0625–0.125)八种超胞模型的态密度分布和吸收光谱分布. 计算结果表明, 在相同掺杂方式、不同浓度共掺In-2N的条件下, 掺杂量越增加, 掺杂体系体积越增加、能量越增加, 稳定性越下降、形成能越增加、掺杂越难、掺杂体系最小光学带隙越变窄、吸收光谱红移越显著. 计算结果与实验结果相一致. 在不同掺杂方式、相同浓度共掺In–2N的条件下, In–N沿c轴取向成键共掺与垂直于c轴取向成键共掺体系相比较, 沿c轴取向成键共掺体系最小光学带隙越变窄、吸收光谱红移越显著. 这对设计和制备新型光催化剂功能材料有一定的理论指导作用. 相似文献
12.
A. N. Priest R. J. Nicholas S. P. Najda G. Duggan A. H. Kean 《Physica E: Low-dimensional Systems and Nanostructures》1998,2(1-4)
We report magneto-luminescence studies of dense electron–hole plasmas in compressively strained GaInP/AlGaInP quantum wells. At carrier densities of order 1013 cm−2 many-body effects are investigated. The band gap is reduced by up to 36 meV, much less than expected from conventional random phase approximation calculations. However, much better agreement is obtained on comparison with recent density functional calculations which include the Hartree energy. The reduced mass is found to increase by up to 40% over values from low-excitation measurements. Comparison with other work suggests that the mass renormalisation is substantial in materials with wide band gaps. 相似文献
13.
14.
Xiaohui DengYanqun Wu Jiayu Dai Dongdong KangDengyu Zhang 《Physics letters. A》2011,375(44):3890-3894
A pathway to open the band gap of graphene by p-n codoping is presented according to the first principles study. Two models are used: Lithium adsorbed on Boron-doped graphene (BG) and Boron-Nitrogen (B/N) codoping into graphene. The stability of Lithium adsorbed on BG is firstly analyzed, showing that the hollow site is the most stable configuration, and there is no energy barrier from some metastable configurations to a stable one. After the p-n codoping, the electronic structures of graphene are modulated to open a band gap with width from 0.0 eV to 0.49 eV, depending on the codoping configurations. The intrinsic physical mechanism responsible for the gap opening is the combination of the Boron atom acting as hole doping and Nitrogen (Lithium) as electron doping. 相似文献
15.
In this work, we performed first principles calculations based on self-consistent charge density functional tight-binding to investigate different mechanisms of band gap tuning of silicene. We optimized structures of silicene sheet, functionalized silicene with H, CH3 and F groups and nanoribbons with the edge of zigzag and armchair. Then we calculated electronic properties of silicene, functionalized silicene under uniaxial elastic strain, silicene nanoribbons and silicene under external electrical fields. It is found that the bond length and buckling value for relaxed silicene is agreeable with experimental and other theoretical values. Our results show that the band gap opens by functionalization of silicene. Also, we found that the direct band gap at K point for silicene changed to the direct band gap at the gamma point. Also, the functionalized silicene band gap decrease with increasing of the strain. For all sizes of the zigzag silicene nanoribbons, the band gap is near zero, while an oscillating decay occurs for the band gap of the armchair nanoribbons with increasing the nanoribbons width. At finally, it can be seen that the external electric field can open the band gap of silicene. We found that by increasing the electric field magnitude the band gap increases. 相似文献
16.
First-principles calculations of the band structure for Hg3Se2Cl2 crystal were performed by means of density functional theory (DFT). The exchange and correlation potential was described within a framework of the local density approximation based on exchange-correlation energy optimization to calculate the total energy. DOS/PDOS and valence charge distribution were studied in details. Absorption near the fundamental edge was found to be due to indirect and direct allowed transitions. For device applications based on Hg3Se2Cl2 crystal, understanding these fundamental issues is highly important and essential. It should be noted that optoelectronic applications of Hg3Se2Cl2 are caused by coexistence of the large polarized Hg cations and a huge contribution of an harmonic phonon subsystem caused by anions. 相似文献
17.
Nickel-doped tin oxide nanoparticles (sub-5 nm size) with intense fluorescence emission behavior have been synthesized by sol-gel route. The structural and compositional analysis has been carried out by using XRD, TEM, FESEM and EDAX. The optical absorbance spectra indicate a band gap narrowing effect and it was found to increase with the increase in nickel concentration. The band gap narrowing at low dopant concentration (<5%) can be assigned to SnO2−SnO2−x alloying effect and for higher doping it may be due to the formation of defect sub-bands below the conduction band. 相似文献
18.
(Al,Mo)-codoped ZnO powders with a constant molar ratio of Zn:Al (99:1) and various molar ratios of Mo:Al (0-0.02) were synthesized by a sol-gel process and characterized by X-ray diffraction, field emission scanning electron microscopy, and UV-vis and luminescent spectrophotometry. The experiments indicated that the powders had random orientation and a slightly larger average particle size that increased with increasing Mo proportion. The Mo doping resulted in the enhancement of transmittance in the UV-visible light range and the widening of the band gap. Optimal efficiency appeared at molar ratio of Mo:Al = 0.01, and Mo doping resulted in the formation of a new emission center and the enhancement of the emissions in range of visible light. 相似文献
19.
Using experimental measurements of the open-circuit voltage and the short-circuit current density at different temperatures, for a solar cell, we investigate numerically the band gap evolution with temperature for the semiconductor constituting the concerned device. The application of the approach in the case of silicon semiconductor gives satisfying results compared to previous works. 相似文献
20.
采用基于密度泛函理论框架下的第一性原理平面波超软赝势方法, 建立了纯的和四种不同Ga掺杂量的ZnO超胞模型, 分别对模型进行了几何结构优化、能带结构分布、态密度分布和吸收光谱的计算. 结果表明, 在本文限定的Ga掺杂量2.08 at%–6.25 at%的范围内, 随着Ga掺杂量的增加, 掺杂后的ZnO体系体积变化不是很大, 但是, 掺杂体系ZnO的能量增加, 掺杂体系变得越来越不稳定, 同时, 掺杂体系ZnO的Burstein-Moss 效应越显著, 最小光学带隙变得越宽, 吸收带边越向高能方向移动. 计算结果和实验结果相一致.
关键词:
Ga高掺杂ZnO
电子结构
吸收光谱
第一性原理 相似文献