Direct calculations on the band offsets of large-latticemismatched and heterovalent Si and III-V semiconductors

Band offset in semiconductors is a fundamental physical quantity that determines the performance of optoelectronic devices.However,the current method of calculating band offset is difficult to apply directly to the large-lattice-mismatched and heterovalent semiconductors because of the existing electric field and large strain at the interfaces.Here,we proposed a modified method to calculate band offsets for such systems,in which the core energy level shifts caused by heterovalent effects and lattice mismatch are estimated by interface reconstruction and the insertion of unidirectional strain structures as transitions,respectively.Taking the Si and III-V systems as examples,the results have the same accuracy as what is a widely used method for small-lattice-mismatched systems,and are much closer to the experimental values for the large-lattice-mismatched and heterovalent systems.Furthermore,by systematically studying the heterojunctions of Si and III-V semiconductors along different directions,it is found that the band offsets of Si/InAs and Si/InSb systems in[100],[110]and[111]directions belong to the type I,and could be beneficial for silicon-based luminescence performance.Our study offers a more reliable and direct method for calculating band offsets of large-lattice-mismatched and heterovalent semiconductors,and could provide theoretical support for the design of the high-performance silicon-based light sources.

Electronic origin of the unusual thermal properties of copper-based semiconductors:The s-d coupling-induced large phonon anharmonicity

Copper(Cu)-based materials(such as cuprates,Cu chalcogenides,and Cu halides)often exhibit unusual properties such as superconductivity,ultralow thermal conductivity,and superionicity.However,the electronic origin of these unusual behaviors remains elusive.In this study,we demonstrate that the high-lying occupied 3d orbital of Cu causes a strong s-d coupling with its unoccupied 4s state when local symmetry is reduced.This leads to strong phonon anharmonicity and is responsible for these intriguing properties.For example,during thermal transport,symmetry-controlled s-d coupling can substantially lower the lattice potential barrier,thereby enhancing the anharmonicity and scattering between phonons and ultimately significantly reducing lattice thermal conductivity.We confirmed this understanding with Raman spectra measurements,which demonstrated a remarkable red shift in the phonon vibrational frequency with an increase in the temperature of Cu-based semiconductors.Our study shows that the cause of phonon anharmonicity is related to the fundamental electronic structures,which can also explain other unusual physical properties of the Cu compounds.

Effectively tuning the stability and optoelectronic properties of halide perovskites by B-site alloying

Halide perovskites(ABX_(3)), as promising candidates for solar cell photovoltaic devices, have recently attracted increasing research interest [1-3], but many issues remain unsolved for their practical applications. One such issue is their poor stability, which largely reduces device lifetime and efficiency [4]. In recent decades, using inorganic ions or organic molecules for replacement or alloying the A-site atoms in halide perovskites has improved thermodynamic stability to some extent.

Integrated optimization design of smart morphing wing for accurate shape control

Smart morphing wing, which is equipped with smart materials and able to change structural geometry adaptively, can further improve aerodynamic efficiency of aircraft. This paper presents a new integrated layout and topology optimization design for morphing wing driven by shape memory alloys(SMAs). By simultaneously optimizing the layout of smart actuators and topology of wing substrate, the ultimately determined configuration can achieve smooth, continuous and accurate geometric shape changes. In addition, aerodynamic analysis is carried out to compare smart morphing wing with traditional hinged airfoil. Finally, the optimized smart wing structure is constructed and tested to demonstrate and verify the morphing functionality. Application setbacks are also pointed out for further investigation.

半导体光电材料中的缺陷和掺杂调控

半导体材料在集成电路、光伏发电、信息通讯、微电子器件、照明等领域发挥着重要作用,已成为半导体学科研究的重要方向.然而,半导体材料的掺杂和缺陷调控能力在很大程度上制约着半导体器件的性能.本文首先回顾了半导体掺杂和缺陷计算理论的发展,阐述了传统的凝胶电荷模型方法的弊端和局限性.为了克服这一弊端,我们提出了一个严格的、统一的理论,即转移真实态模型.该模型可以直接计算三维及低维半导体的带电缺陷性质.其次,讨论了宽禁带半导体发展所面临的困难.通过分析掺杂极限定律,针对氧化物宽禁带半导体,介绍了行之有效的缺陷设计准则和调控方法,并用来提高p型半导体的导电率.再次,讨论了非晶态宽禁带半导体中离子化合物与共价化合物导电性差异的物理机制,以及低维宽禁带半导体赝氢钝化和真实氢钝化的差异原理.从次,分析了高浓度掺杂形成的半导体合金.由于带边波函数的局域性,异价半导体合金不满足统计平均规律,揭示出大失配同价高浓度掺杂能带交叉的物理原理.最后,聚焦金属杂质在半导体中的扩散现象,阐明了银和铜原子在离子半导体和共价半导体中扩散差异性的根本原因.

Optimal thermoelectric figure of merit of Si/Ge core-shell nanowires

我们调查 Si 和 Ge nanowires 的热电的精力变换效率，并且特别地， Si/Ge 核心壳 nanowires 的。我们显示出 Si 核心 nanowire 上的薄 Ge 壳的存在怎么增加优点的全面数字。我们发现 Ge 壳的最佳的厚度为设备提供优点的最大的数字。我们也认为 Ge core/Si 是壳 nanowires，并且证明 Si 壳的最佳的厚度不存在，自从优点的数字是 nanowire 的半径的 monotonically 减少的功能。最后，我们验证联系电子精力差距到最大化设备的效率的最佳的工作温度的实验法律。

Reviewing and understanding the stability mechanism of halide perovskite solar cells

Finding sustainable and renewable energy to replace traditional fossil fuel is critical for reducing greenhouse gas emission and avoiding environment pollution.Solar cells that convert energy of sunlight into electricity offer a viable route for solving this issue.At present,halide perovskites are the most potential candidate materials for solar cell with considerable power conversion efficiency,whereas their stability remains a challenge.In this work,we summarize four different key factors that influence the stability of halide perovskites:(a)effect of environmental moisture on the degradation of halide perovskites.The performance of halide perovskite solar cells is reduced due to hydrated crystal hinders the diffusion of photo-generated carriers,which can be solved by materials encapsulation technique;(b)photoinduced instability.Through uncovering the underlying physical mechanism,we note that materials engineering or novel device structure can extend the working life of halide perovskites under continuous light exposure;(c)thermal stability.Halide perovskites are rapidly degraded into PbI2 and volatile substances as heating due to lower formation energy,whereas hybrid perovskite is little changed;(d)electric field effect in the degradation of halide perovskites.The electric field impacts significantly on the carrier separation,changes direction of photo-induced currents and generates switchable photovoltaic effect.For each key factor,we have shown in detail the underlying physical mechanisms and discussed the strategies to overcome this stability difficulty.We expect this review from both theoretical and experimental points of view can be beneficial for development of perovskite solar cell materials and promotes practical applications.