- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
Characterization of Lattice Parameters Gradient of Cu(In1-xGax)Se2 Absorbing Layer in Thin-Film Solar Cell by Glancing Incidence X-Ray Diffraction Technique
摘要： In or Ga gradients in the Cu(In1-xGax)Se2 (CIGS) absorbing layer lead to change the lattice parameters of the absorbing layer, giving rise to the bandgap grading in the absorbing layer which is directly associated with the degree of absorbing ability of the CIGS solar cell. We tried to characterize the depth profile of the lattice parameters of the CIGS absorbing layer using a glancing incidence X-ray diffraction (GIXRD) technique, and then allows to determine the In or Ga gradients in the CIGS absorbing layer, and to investigate the bandgap grading of the CIGS absorbing layer. When the glancing incident angle increased from 0.50 to 5.00°, the a and c lattice parameters of the CIGS absorbing layer gradually decreased from 5.7776(3) to 5.6905(2) ?, and 11.3917(3) to 11.2114(2) ?, respectively. The depth profile of the lattice parameters as a function of the incident angle was consistent with vertical variation in the composition of In or Ga with depth in the absorbing layer. The variation of the lattice parameters was due to the difference between the ionic radius of In and Ga co-occupying at the same crystallographic site. According to the results of the depth profile of the refined parameters using GIXRD data, the bandgap of the CIGS absorber layer was graded over a range of 1.222 to 1.532 eV. This approach nondestructively guess the bandgap depth profile through the refinement of the lattice parameters using GIXRD data on the assumption that the changes of the lattice parameters or unit-cell volume follow a good approximation to Vegard’s law.
关键词： Vegard’s law,Cu(In1-xGax)Se2 absorbing layer,Depth profile,Bandgap grading,Glancing incidence X-ray diffraction technique
更新于2025-09-23 15:21:01
-
Structural properties of silicon–germanium and germanium–silicon core–shell nanowires
摘要： Core–shell nanowires made of Si and Ge can be grown experimentally with excellent control for different sizes of both core and shell. We have studied the structural properties of Si/Ge and Ge/Si core–shell nanowires aligned along the [1 1 0] direction, with diameters up to 10.2 nm and varying core to shell ratios, using linear scaling density functional theory. We show that Vegard’s law, which is often used to predict the axial lattice constant, can lead to an error of up to 1%, underlining the need for a detailed ab initio atomistic treatment of the nanowire structure. We analyse the character of the intrinsic strain distribution and show that, regardless of the composition or bond direction, the Si core or shell always expands. In contrast, the strain patterns in the Ge shell or core are highly sensitive to the location, composition and bond direction. The highest strains are found at heterojunction interfaces and the surfaces of the nanowires. This detailed understanding of the atomistic structure and strain paves the way for studies of the electronic properties of core–shell nanowires and investigations of doping and structure defects.
关键词： Vegard’s law,nanowire,linear scaling density functional theory,core–shell
更新于2025-09-23 15:21:01
-
Tailoring the Band Gap in the ZnS/ZnSe System: Solid Solutions by a Mechanically Induced Self-Sustaining Reaction
摘要： The complete ZnSxSe1?x solid solution was successfully obtained by the mechanochemical process denoted as a mechanically induced self-sustaining reaction. Excellent control of the chemical stoichiometry of the solid solution was possible by adjusting the atomic ratio of the starting Zn/S/Se elemental mixture subjected to milling. A mixture of both wurtzite-2H (hexagonal) and zinc blende (cubic) structures was always obtained, although for a similar milling time the proportion of the zinc blende structure increased with the Se content in the solid solution. However, wurtzite was the major phase for S-rich compositions when milling was stopped just after ignition. It was demonstrated that milling induces the wurtzite-to-zinc blende phase transition. The 8H hexagonal polytype was also observed in samples subjected to long milling times. Variation of the lattice parameters for both structures with the x value in the solid solution presented an excellent linearity, confirming the validity of Vegard’s law. However, variation of the band-gap energy (Eg) with x was not perfectly linear, and a small bowing parameter of 0.34 was obtained. It was possible to tune the Eg value between those of the end members of the solid solution in a continuous manner by adjusting the stoichiometry of the solid solution. The morphology and crystalline domain size can also be controlled by adjusting, in this case, the postignition milling time of the mechanochemical process.
关键词： band gap tuning,phase transformation,Vegard's law,ZnS/ZnSe solid solution,mechanically induced self-sustaining reaction,mechanochemical synthesis
更新于2025-09-19 17:15:36
-
A novel numerical approach for the calculation of refractive index of Wurtzite InxGa1?xN
摘要： Accurate values of refractive indices for InxGa1?xN alloy as a function of indium mole fraction play a vital role in the modeling of InxGa1?xN-based optoelectronics devices. This work extensively investigated, analyzed and derived a conclusive numerical approach to calculate the refractive index of InxGa1?xN over a wide wavelength as a function of indium mole fraction based on Vegard’s law. The model is based on the fact that there is a strong correlation between the mole fraction (x) and the refractive index of ternary alloys AxB1?xC. An excellent agreement is observed between the computed values and experimental data which proves the e?ectiveness of our numerical approach.
关键词： refractive index,optical properties,InxGa1?xN,Vegard’s law
更新于2025-09-10 09:29:36
-
(TiO <sub/>2</sub> ) <sub/>1?x</sub> (TaON) <sub/>x</sub> Solid Solution for Band Engineering of Anatase TiO <sub/>2</sub>
摘要： Band engineering of anatase TiO2 was achieved by means of an anatase (TiO2)1?x(TaON)x (TTON) solid solution. Epitaxial thin films of TTON (0.1 ≤ x ≤ 0.9) were synthesized by nitrogen plasma-assisted pulsed laser deposition on (LaAlO3)0.3(SrAl0.5Ta0.5O3)0.7 substrates. Epitaxial growth of anatase TTON was confirmed by X-ray diffraction. The lattice constants of the TTON thin films increased with TaON content in accordance with Vegard’s law, indicating formation of a complete solid solution. The bandgaps, band alignment, and refractive indices of the TTON thin films were investigated by combination of spectroscopic ellipsometry and X-ray photoelectron spectroscopy. The bandgap of the anatase TTON systematically decreased with increasing x, mainly because of an upward shift in the valence band maximum caused by broadening of the valence band as a result of hybridization of the shallow N 2p orbital. The position of the conduction band minimum was rather insensitive to chemical composition, which makes the band alignment of anatase TTON suitable for photocatalytic water splitting with visible light. The refractive index of anatase TTON monotonically increased with an increase in x.
关键词： Epitaxial thin films,Vegard’s law,X-ray photoelectron spectroscopy,TTON solid solution,Band engineering,Photocatalytic water splitting,Spectroscopic ellipsometry,Nitrogen plasma-assisted pulsed laser deposition,Anatase TiO2
更新于2025-09-10 09:29:36
-
[Advances in Imaging and Electron Physics] || AlN/GaN and InAlN/GaN DBRs
摘要： This chapter presents the high resolution monochromated STEM-EELS characterization of two distributed Bragg re?ector (DBR) multilayer heterostructures, composed of a periodic staking of III-nitride layers. These heterostructures were grown by the group of E. Calleja at the Instituto de Sistemas Optoelectrónicos y Microtecnología (ISOM), from Universidad Politéc- nica de Madrid. One of these DBR is composed of an alternate staking of AlN and GaN layers, and the other one, of InAlN lattice matched to GaN. EELS at sub-nanometric spatial resolution and < 200 meV energy resolution was used to assess the electronic properties of the structures. The EELS signal was treated using ZLP subtraction and deconvolution methods, and non-linear ?tting tools complemented with theoretical modeling of the electron scattering distribution. In this sense, the log-ratio formula was used to calculate the relative thickness, related to the electron inelastic mean free path. Moreover, ?tting of the bulk plasmon peak was performed using Lorentzian and Drude free-electron models. As we have seen, in group-III nitride alloys, the energy position of this peak can be related to the chemical composition variation through Vegard’s law. Also, within the context of the Drude plasmon model, information regarding the structural properties of the material can be obtained from the lifetime of the oscillation. This structural and chemical characterization of the layers was complemented with experimental and simulated high angle annular dark ?eld (HAADF) images. Finally, information related to the dielectric response of the mate- rials was extracted using Kramers–Kronig analysis. Our results signi?cantly improve the understanding of previous macroscopic characterizations of the electro-optical properties of these structures.
关键词： AlN/GaN,InAlN/GaN,Kramers–Kronig analysis,STEM-EELS,Vegard’s law,plasmon peak,DBRs
更新于2025-09-04 15:30:14