Formation of heterovalent interfaces: A combined photoemission and ab initio DFT study of GaP/Si heterostructures

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Integration of III-V semiconductors on silicon is desirable for a new generation of microelectronic power devices, high-efficiency multi-junction solar cells and photolytic tandem absorbers for the renewable generation of hydrogen. GaP/Si(001) is the ideal candidate for a pseudomorphic virtual substrate, a generic element for high-efficiency optoelectronic device structures. The goal is to overcome the today limiting challenges, which are related to polar-on-nonpolar heteroepitaxy, prior further III-V integration in order to grow low-defect active material. The preparation of sharp GaP/Si(001) interfaces thereby is the critical technological step in metalorganic chemical vapor deposition (MOCVD), because it strongly impacts the quality of subsequently grown epitaxial films and the final device performance. Preliminary work showed that the additional group-V element arsenic plays a decisive role for tuning the interfacial structure. Today, interface formation mechanisms are not well understood at the atomic scale and the electronic structure of these buried interfaces has not yet been resolved. Recently, there has been much progress to reduce defect formation considerably at buried GaP/Si(001) heterointerfaces. Therefore, this interface is not only significant as generic element for optoelectronic application, but also as model structure, which is the key to enable comparative experimental and ab initio studies of the interface electronic structure. In this bilateral project, we will join our complementary expertise in industrially scalable, state-of-the-art epitaxial growth by MOCVD, in advanced interface analysis and in ab initio theory to provide all essential elements for a comprehensive heterointerface study. Thereby, we aim to resolve a historic open question in polar-on-nonpolar heteroepitaxy: How can interfaces form as sharp as possible, while compensating interface charges in order to get well-defined electronic properties across the interface? We will apply a unique methodology combining preparation, optical in situ spectroscopy, lab-based as well as synchrotron-based photoelectron spectroscopy techniques, depth profiling and ab initio density functional theory calculations in order to establish a conclusive atomic-scale understanding of the structural and electronic properties of GaP/Si(001) and GaP/Si(001):As heterointerfaces. The structure of the interface will be studied both with bottom-up, top-down and in situ approaches. We will introduce dedicated modifications of the atomic structure in order to understand how the electronic properties of the heterointerface can be tuned and how this can be controlled in situ. The objective of this project is to gain a fundamental understanding of III-V/IV heterointerface formation on the atomic scale with direct implications for high-performance device applications.