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

宽带隙半导体与铁电材料如LiNbO_3(LiNbO_3或LN)通过直接接口相结合，开辟了一系列新的光学和电子器件概念。这些概念的成功实现在很大程度上取决于所形成的界面的质量。几乎完全缺乏关于液氮表面和界面的微观结构和性质的知识是这方面的一个主要障碍。该项目的目的是详细了解LN表面和LN与III-氮化物半导体的界面的原子结构和电子性质。下面提出的计算将(I)探索表面科学中的未知领域，(Ii)有望有助于设计和优化基于LN的混合结构，例如周期性极化材料。我们将基于密度泛函理论的微观电子结构计算与宏观热力学相结合。将特别注意本征缺陷对表面和界面特性的影响以及铁电畴的振动指纹。计算的LN表面的结构、振动和化学性质应用于优化在LN衬底上生长GaN以及解释实验表面分析研究，例如μ-拉曼光谱。

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.