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The role of oxygen doping on elemental intermixing at the PVD-CdS/Cu (InGa)Se <sub/>2</sub> heterojunction
摘要： Elemental intermixing at the CdS/CuIn1?xGaxSe2 (CIGS) heterojunction in thin‐film photovoltaic devices plays a crucial role in carrier separation and thus device efficiency. Using scanning transmission electron microcopy in combination with energy dispersive X‐ray mapping, we find that by controlling the oxygen in the sputtering gas during physical vapor deposition (PVD) of the CdS, we can tailor the degree of elemental intermixing. More oxygen suppresses Cu migration from the CIGS into the CdS, while facilitating Zn doping in the CdS from the ZnO transparent contact. Very high oxygen levels induce nanocrystallinity in the CdS, while moderate or no oxygen content can promote complete CdS epitaxy on the CIGS grains. Regions of cubic Cu2S phase were observed in the Cu‐rich CdCuS when no oxygen is included in the CdS deposition process. In the process‐of‐record sample (moderate O2) that exhibits the highest solar conversion efficiency, we observe a ~26‐nm‐thick Cu‐deficient CIGS surface counter‐doped with the highest Cd concentration among all of the samples. Cd movement into the CIGS was found to be less than 10 nm deep for samples with either high or zero O2. The results are consistent with the expectation that Cd doping of the CIGS surface and lack of Zn diffusion into the buffer both enhance device performance.
关键词： scanning transmission electron microscopy,Cu diffusion,Cu (In,Ga)Se2 photovoltaics,CdS structure,STEM‐EDS mapping
更新于2025-09-04 15:30:14
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Reimagining STEM Education and Training with e-REAL. 3D and Holographic Visualization, Immersive and Interactive Learning for an Effective Flipped Classroom
摘要： While the 19th and the 20th centuries were, in education, mainly about standardization, the 21st century is about visualization, interaction, customization, gamification and flipped teaching. What today we know about learning from cognitive psychology is that people learn by practicing, with feedback to tell them what they're doing right and wrong and how to get better. For STEM education, that means they need to practice thinking like a scientist in the field. So e-REAL is a cornerstone: developed as workplace learning system in a number of fields (from medical simulation to soft skills development within the continuing education), it’s an ideal solution to root a practical – but not simplicistic - approach for STEM education.
关键词： Immersive and Interactive Learning,e-REAL,STEM Education and Training,Flipped Classroom
更新于2025-09-04 15:30:14
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[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