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, the 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 and theory. The team will employ coherent phonon spectroscopy to investigate the ultrafast response of the interfacial electronic and lattice subsystems to band gap excitation. It is expected 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), the team 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 the team 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. Students will be trained in an area highly relevant to the technical workforce and will gain global experience through the exchange among the partner laboratories.
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. This is 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 study will be applicable to similar studies of a broad range of interfaces between electronic materials. Students will be trained in an area highly relevant to the technical workforce and will gain global experience through the exchange among the partner laboratories.
