Density functional theory calculations of lithium niobate surfaces and interfaces with III-nitrides

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The combination of wide bandgap semiconductors and ferroelectric materials like lithium niobate (LiNbO3 or LN) by means of direct interfacing opens a wide range of new device concepts both optical and electronic. The successful realization of these concepts depends largely on the quality of the interface formed. The nearly complete lack of knowledge about the microscopic structure and the properties of LN surfaces and interfaces is one major obstacle in this respect. The project proposed here aims at the detailed understanding of the atomic structure and electronic properties of LN surfaces and LN interfaces with III-nitride semiconductors. The calculations suggested in the following will (i) explore uncharted territory in surface science and are (ii) expected to help devising and optimizing LN-based hybrid structures such as periodically poled materials. We combine microscopic electronic structure calculations based on density functional theory with macroscopic thermodynamics. Particular attention will be paid to the influence of intrinsic defects on the surface and interface characteristics as well as to the vibrational fingerprints of the ferroelectric domains. The calculated structural, vibrational and chemical properties of LN surfaces shall be used for the optimization of GaN growth on LN substrates and the interpretation of experimental surface analysis studies such as, e.g., μ-Raman spectroscopy.