Materials World Network, SusChEM: Collaborative Electron-lattice Dynamics at an Atomically Controlled Buried Interface

一项国际合作研究计划汇集了来自德国（马尔堡大学）、日本（国家材料科学研究所）和美国（匹兹堡大学和佛罗里达大学）的科学家，将研究GaP/Si埋藏界面的结构和动力学特性之间的相关性，以实现对此类材料的基本理解和实际应用。GaP/Si界面是一种具有潜在应用的材料，对高效太阳能电池和硅光电子产品具有高可持续性影响。埋藏界面、激发态和光与非平衡电荷分布的相互作用是凝聚态物理实验和理论的前沿挑战。通过结合材料生长，结构表征，超快电子和声子光谱以及理论方面的专业知识，我们的团队将研究GaP/Si界面的结构和超快光电性能之间的关系。两种电子材料界面上的光学和电荷输运特性取决于它们之间的能带排列，以及界面的原子尺度结构以难以用实验和理论表征的微妙方式。我们将使用相干声子光谱来研究界面电子和晶格子系统对带隙激发的超快响应。我们预计界面载流子分布和内置电场将对耦合载流子晶格动力学产生实质性的影响。通过与组件材料（单晶Si和GaP）的动力学比较，我们将确定可归因于界面存在的超快响应组件。我们将研究在不同条件下生长的材料的界面响应，这些条件会影响材料的组成和晶体结构，从原子尺度到纳米尺度。通过光谱测量和理论模拟，我们将确定材料结构如何影响GaP/Si界面的光学和电子特性。材料生长和分析的紧密集成，以及超快光谱测量将使GaP/Si材料优化用于实际应用。实验方法将适用于研究技术上重要的电子材料的广泛界面现象。优化的电子材料能够有效地产生和利用能源，促进经济的持续发展。GaP/Si接口具有应用于高效太阳能电池的潜力，用于太阳能到电能的转换，以及在硅基电子设备中实现光信号处理。然而，这种复合材料的功能取决于它们之间的界面。尽管GaP和Si的晶格尺寸几乎相同，使得在Si上生长几乎没有缺陷的GaP覆盖层，但它们不同的离子和共价特征导致界面上的电子性质突然改变。因此，复合材料的光学和电子性能在很大程度上取决于界面的原子尺度结构和组成。研究界面的结构和电子性质之间的关系是非常困难的，因为它需要能够生长具有特定特性的材料，将原子结构与生长参数联系起来，表征结构和电子性质之间的关系，以及为界面建立一个理论模型，可以关闭结构和功能研究之间的反馈。我们已经组建了一个由来自德国（马尔堡大学）、日本（国家材料科学研究所）和美国（匹兹堡大学和佛罗里达大学）的科学家组成的合作团队，他们将基于特定材料生长、电子显微镜结构表征、界面特定电子结构和光学响应的研究以及理论来研究GaP/Si界面的结构-功能关系。通过提议的研究获得的方法和理解将适用于广泛的电子材料之间界面的类似研究。

Technical Abstract An international collaborative research program bringing together scientists from Germany (Marburg University), Japan (National Institute for Materials Science) and the USA (Universities of Pittsburgh and Florida) will investigate the correlation between the structural and dynamical properties of GaP/Si buried interfaces in order to enable the fundamental understanding and practical applications of such materials. The GaP/Si interface is a material with potential applications having a high sustainability impact for high efficiency solar cells and silicon optoelectronics. Buried interfaces, excited states, and interaction of light with nonequilibrium charge distributions represent challenges at the forefront of condensed matter physics experiment and theory. By combining expertise in materials growth, structure characterization, ultrafast electronic and phonon spectroscopy, and theory, our team will investigate the relationship between the structural and ultrafast optoelectronic properties of GaP/Si interfaces. The optical and charge transport properties at an interface between two electronic materials depend on the band alignment between them, and the atomic scale structure of the interface in subtle ways that are difficult to characterize by experiment an theory. We will employ coherent phonon spectroscopy to investigate the ultrafast response of the interfacial electronic and lattice subsystems to band gap excitation. We expect that the interfacial carrier distributions and the built-in electric fields will substantially influence the coupled carrier-lattice dynamics. By comparison with the dynamics of the component materials (single crystal Si and GaP, we will identify the components of the ultrafast response that can be attributed to the existence of the interface. The interface response will be investigated for materials grown under different conditions that influence the material composition and crystalline structure on the atomic to the nanometer scales. From the spectroscopic measurements and theoretical simulations we will identify how the material structure affects the optical and electronic properties of GaP/Si interface. The tight integration of material growth and analysis, with ultrafast spectroscopic measurements will enable GaP/Si material optimization for practical applications. The experimental methodology will be applicable to studies of a broad range of interfacial phenomena of technologically important electronic materials. Non-technical Abstract Optimized electronic materials enable efficient generation and utilization of energy for continued economic development. The GaP/Si interface has the potential for applications in high efficiency solar cells for solar-to-electrical energy conversion, as well as for enabling optical signal processing within Si based electronic devices. The function of such composite materials, however, depends on the interface between them. Even though the dimensions of the crystalline lattices of GaP and Si are nearly identical, enabling growth of nearly defect free GaP overlayers on Si, their disparate ionic and covalent characters cause the electronic properties at the interface to change abruptly. Therefore, the optical and electronic properties of the composite materials strongly depend on the atomic scale structure and composition of the interface. Studying the relationship between the structure and electronic properties of interfaces is extremely difficult because it requires the ability to grow materials with particular characteristics, to correlate the atomic structure with the growth parameters, to characterize the relationship between the structure and electronic properties, as well as to develop a theoretical model for the interface that can close the feedback between the structural and functional investigations. We have constituted a collaborative team involving scientists from Germany (Marburg University), Japan (National Institute for Materials Science) and the USA (Universities of Pittsburgh and Florida) that will study the structure-function relationship of the GaP/Si interface based on specific materials growth, structure characterization by electron microscopy, investigation of the interface-specific electronic structure and optical response, as well as theory. The methodology and understanding obtained through the proposed study will be applicable to similar studies of a broad range of interfaces between electronic materials.