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Overcoming doping bottleneck by using surfactant and strain

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Frontiers of Materials Science 2011年第4期5卷 335-341页

作者： Junyi ZHU su-huai wei National Renewable Energy Laboratory Golden Colorado 80401 USA

Overcoming the doping bottleneck in semiconductors, especially in wide band gap semiconductors, has been a challenge in semiconductor physics for many years. In this paper, we review some recent progresses in enhancing doping by surfactant and strain. We show that surfactant and strain are two effective approaches to enhance dopant solubility in epitaxial growth. The surfactant can introduce an energy level deep inside the band gap, making the host compound less stable, thus lower the formation energy of the intentional dopant. The strain enhanced doping is based on the observation that dopant induces volume change in the host. If the external strain is in the same direction as the dopant induced volume change, the formation energy of the dopant is reduced. This effect can be used to tune doping sites, thus doping type, in a host. A hybrid method to both include strain and surfactant is proposed, which can be a promising general method to further enhance doping.

关键词： semiconductor surfactant strain doping band gap

First-principles study of defect control in thin-film solar cell materials

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Science China(Physics,Mechanics & Astronomy) 2021年第3期64卷 28-45页

作者： Hui-Xiong Deng RuYue Cao su-huai wei State Key Laboratory of superlattices and Microstructures Institute of SemiconductorsChinese Academy of SciencesBeijing 100083China Center of Materials Science and Optoelectronics Engineering University of Chinese Academy of SciencesBeijing 100049China Beijing Computational Science Research Center Beijing 100193China

A solar cell is a photovoltaic device that converts solar radiation energy to electrical energy, which plays a leading role in alleviating global energy shortages and decreasing air pollution levels typical of conventional fossil fuels. To render solar cells more efficient, high visible-light absorption rates and excellent carrier transport properties are required to generate high carrier levels and high output voltage. Hence, the core material, i.e., the absorption layer, should have an appropriate direct band gap and be effectively doped by both p-and n-types with minimal carrier traps and recombination centers. Consequently, defect properties of absorbers are critical in determining solar cell efficiency. In this work, we review recent first-principles studies of defect properties and engineering in four representative thin-film solar cells, namely CdTe, Cu(In,Ga)Se2, Cu2ZnSnS4, and halide perovskites. The focal points include basic electronic and defect properties, existing problems, and possible solutions in engineering defect properties of those materials to optimize solar cell efficiency.

关键词： first-principles study thin-film solar cells defect engineering energy conversion efficiency

Inhomogeneous strain-induced half-metallicity in bent zigzag graphene nanoribbons

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npj Computational Materials 2017年第1期3卷 189-193页

作者： Dong-Bo Zhang su-huai wei Beijing Computational Science Research Center Beijing 100193P.R.China

Realization of half-metallicity in low dimensional materials is a fundamental challenge for nano spintronics,which is a critical component for next-generation information *** the method of generalized Bloch theorem,we show that an in-plane bending can induce inhomogeneous strains,which in turn lead to spin-splitting in zigzag graphene nanoribbons and results in the highly desired half-metallic *** the previously proposed scheme that requires unrealistically strong external electric fields,the obtained half-metallicity with sizeable half-metallic gap and high energetic stability of magnetic order of edge states requires only relatively low-level strain in the in-plane *** the superior structural flexibility of graphene and the recent experimental advances in controllable synthesis of graphene nanoribbons,our design provides a hitherto most practical approach to the realization of half-metallicity in low dimensional *** work,thus paves a way towards the design of nanoscale spintronic devices through strain engineering.

关键词： metallic zigzag bending

Advances and challenges in DFT-based energy materials design

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Chinese Physics B 2022年第10期31卷 34-52页

作者： Jun Kang Xie Zhang su-huai wei Beijing Computational Science Research Center Beijing 100193China

The growing worldwide energy needs call for developing novel materials for energy *** initio density functional theory(DFT)calculations allow the understanding and prediction of material properties at the atomic scale,thus,play an important role in energy materials *** to the fast progress of computer power and development of calculation methodologies,DFT-based calculations have greatly improved their predictive power,and are now leading to a paradigm shift towards theory-driven materials *** aim of this perspective is to introduce the advances in DFT calculations which accelerate energy materials *** first present state-of-the-art DFT methods for accurate simulation of various key properties of energy *** we show examples of how these advances lead to the discovery of new energy materials for photovoltaic,photocatalytic,thermoelectric,and battery *** challenges and future research directions in computational design of energy materials are highlighted at the end.

关键词： density functional theory materials design energy applications

Investigation of Ag(Ga,In)Se_(2)as thin-film solar cell absorbers:A first-principles study

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Science China(Physics,Mechanics & Astronomy) 2022年第10期65卷 101-108页

作者： Rong Wang Baoying Dou Yifeng Zheng su-huai wei Institute of Advanced Semiconductors&Zhejiang Provincial Key Laboratory of Power Semiconductor Materials and Devices ZJU-Hangzhou Global Scientific and Technological Innovation CenterHangzhou 311200China Beijing Computational Science Research Center Beijing 100193China

Using first-principles calculations,the structural,electronic,and defect properties of AgInSe_(2)(AIS),AgGaSe_(2)(AGS),and their alloys(AIGS)are systematically studied and compared with their Cu counterparts as potential candidates for thin-film solar cell *** bandgap energies of AIS(1.24 eV)and AGS(1.84 eV)are larger than their Cu counterparts,despite their larger lattice *** to the Shockley-Queisser theory,AIS or AIGS could be more suitable for solar-cell-absorber materials than their Cu ***,after investigating the band structures and intrinsic defect properties of AIS and AGS,we find that,(i)AIS and AGS have large negative crystal field splitting,thus low density of states near the valence band maximum(VBM);(ii)similar to the Cu counterparts,Ag vacancy(V_(Ag))is the main hole-carrier provider,while In_(Ag)(or Ga_(Ag))serves as the hole-carrier killer in p-type AIS(or AGS).However,because the positions of theVBM and conduction band minimum of AIS(or AGS)are lower than those of Cu In Se_(2)(CIS)[or Cu Ga Se_(2)(CGS)],the compensation of the p-type doping in AIS(or AGS)is more ***,the p-type doping of AIS(or AIGS)is more difficult than that of CIS(or CIGS),which is consistent with the doping limit *** improve the p-type doping of the AIS(or AIGS)as the solar-cell absorber,thus,improve the power conversion efficiency(PCE),the Ag-rich/(In,Ga)-poor/Se-rich growth condition is *** engineering of AIS with AGS can enhance the PCE because it can tune the bandgap energy of the absorber and band alignment at the absorber/buffer *** importantly,we suggest that for AIS(or AIGS)solar cell,the traditional buffer material of Cd S is not suitable anymore due to the large conduction band offset between AIS and Cd S.A new buffer layer material with a lower conduction band edge is necessary for better electron transport in AIS(or AIGS)solar cell.

关键词： thin-film solar cells chalcopyrites point defects alloys first-principles calculations

Selection of dopants and doping sites in semiconductors:the case of AlN

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Journal of Semiconductors 2024年第11期45卷 46-50页

作者： Yi-Feng Zheng Xuefen Cai su-huai wei Wenzhou Institute University of Chinese Academy of SciencesWenzhou 325001China College of Physics and Optoelectronic Engineering Shenzhen UniversityShenzhen 518060China School of Physics Eastern Institute of TechnologyNingbo 315200Chin

The choices of proper dopants and doping sites significantly influence the doping *** this work,using doping in Al N as an example,we discuss how to choose dopants and doping sites in semiconductors to create shallow defect *** comparing the defect properties of C_(N),O_(N),Mg_(Al),and Si_(Al)in AlN and analyzing the pros and cons of different doping approaches from the aspects of size mismatch between dopant and host elements,electronegativity difference and perturbation to the band edge states after the substitution,we propose that Mg_(Al)and Si_(Al)should be the best dopants and doping sites for p-type and n-type doping,*** first-principles calculations verify our predictions as these defects present lower formation energies and shallower defect *** defect charge distributions also show that the band edge states,which mainly consist of N-s and p orbitals,are less perturbed when Al is substituted,therefore,the derived defect states turn out to be delocalized,opposite to the situation when N is *** approach of analyzing the band structure of the host material and choosing dopants and doping sites to minimize the perturbation on the host band structure is general and can provide reliable estimations for finding shallow defect levels in semiconductors.

关键词： defect control band structure analysis wide-bandgap semiconductor

Band structure engineering and defect control of oxides for energy applications

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Chinese Physics B 2018年第11期27卷 112-119页

作者： Hui-Xiong Deng Jun-wei Luo su-huai wei State Key Laboratory of superlattices and Microstructures Institute of Semiconductors Chinese Academy of Sciences Beijing 100083 China University of Chinese Academy of Sciences Beijing 100049 China Beijing Computational Science Research Center Beijing 100193 China

Metal oxides play an essential role in modern optoelectronic devices because they have many unique physical properties such as structure diversity, superb stability in solution, good catalytic activity, and simultaneous high electron conductivity and optical transmission. Therefore, they are widely used in energy-related optoelectronic applications such as photovoltaics and photoelectrochemical（PEC） fuel generation. In this review, we mainly discuss the structure engineering and defect control of oxides for energy applications, especially for transparent conducting oxides（TCOs） and oxide catalysts used for water splitting. We will review our current understanding with an emphasis on the contributions of our previous theoretical modeling, primarily based on density functional theory. In particular, we highlight our previous work：（i） the fundamental principles governing the crystal structures and the electrical and optical behaviors of TCOs;（ii） band structures and defect properties for n-type TCOs;（iii） why p-type TCOs are difficult to achieve;（iv） how to modify the band structure to achieve p-type TCOs or even bipolarly dopable TCOs;（v） the origin of the high-performance of amorphous TCOs; and（vi） band structure engineering of bulk and nano oxides for PEC water splitting. Based on the understanding above, we hope to clarify the key issues and the challenges facing the rational design of novel oxides and propose new and feasible strategies or models to improve the performance of existing oxides or design new oxides that are critical for the development of next-generation energy-related applications.

关键词： band-structure engineering defect control oxides density functional theory

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Editorial

Science China(Physics,Mechanics & Astronomy) 2023年第12期66卷 1-2页

作者： su-huai wei Jingbi You Xudong Yang Beijing Computational Science Research Center Bejing 100193China Institute of Semiconductors Chinese Academy of SciencesBeijing 100190China Shanghai Jiao Tong University Shanghai 200240China

Modern society is becoming more dependent on clean and sustainable energy resources because of growing energy demand caused by population and economic expansion,as well as limited traditional fossil fuels,which can cause significant damage to our *** cell technology,which uses the photovoltaic effect to convert sunlight directly into electricity,has emerged as the most promising renewable energy source because of the infinite abundance of sunlight,low transportation costs,and low *** most cases,the core structure of a solar cell consists of an absorption layer,which uses the photon energy of sunlight to produce electron-hole pairs in a semiconductor,and a p-n junction,which induces a built-in electric field to separate light-generated carriers and creates a flow of electricity when connected to an external circuit.

关键词： infinite connected convert

Universal Theory and Basic Rules of Strain-Dependent Doping Behaviors in Semiconductors

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Chinese Physics Letters 2021年第8期38卷 90-95页

作者： Xiaolan Yan Pei Li su-huai wei Bing Huang Beijing Computational Science Research Center Beijing 100193China Department of Physics Beijing Normal UniversityBeijing 100875China

Enhancing the dopability of semiconductors via strain engineering is critical to improving their functionalities,which is,however,largely hindered by the lack of basic *** this study,for the first time,we develop a universal theory to understand the total energy changes of point defects(or dopants)with different charge states under strains,which can exhibit either parabolic or superlinear behaviors,determined by the size of defect-induced local volume change(ΔV).In general,ΔV increases(decreases)when an electron is added(removed)to(from)the defect ***,in terms of this universal theory,three basic rules can be obtained to further understand or predict the diverse strain-dependent doping behaviors,i.e.,defect formation energies,charge-state transition levels,and Fermi pinning levels,in *** three basic rules could be generally applied to improve the doping performance or overcome the doping bottlenecks in various semiconductors.

关键词： doping defect semiconductors