Epitaxial lattice-matched TiN/(Al,Sc)N metal/semiconductor superlattices have attracted significant interest in recent years for their potential applications in thermionic emission-based thermoelectric devices, optical hyperbolic metamaterials, and hot-electron-based solar-energy converters, as well as for the fundamental studies on the electron, photon, and phonon propagation in heterostructure materials. In order to achieve high efficiency devices and for the quest to discover new physics and device functionalities, it is extremely important that the superlattices exhibit atomically sharp and abrupt interfaces with minimal interface mixing and surface roughness. Moreover, as the energy transport across the cross-plane direction of these superlattices depends on the interface-properties, it is important to characterize the interfacial electronic structure and the chemistry of bond formation. Employing a combination of soft x-ray scattering techniques such as x-ray diffraction and synchrotron-based x-ray reflectivity, in this article, we demonstrate sharp and abrupt TiN/(Al,Sc)N superlattice interfaces with an asymmetric interface roughness ranging from two-to-three unit cells. Synchrotron-based soft x-ray absorption analysis revealed similar peak positions, line shapes, and absorption edges of different atoms in the individual thin films and in the superlattices, which demonstrate that the oxidation state of the atoms remains unchanged and rules-out the secondary structure or phase formation at the interfaces. The x-ray scattering results were further verified by aberration-corrected high-resolution scanning transmission electron microscopy imaging and energy dispersive x-ray spectroscopy mapping analysis. These results will be important for understanding of the transport properties of metal/semiconductor superlattices and for designing superlattice-based energy conversion devices.

中文翻译：

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外延晶格匹配的TiN / Al0.72Sc0.28N金属/半导体超晶格的界面化学和电子结构，通过软X射线散射测定

近年来，外延晶格匹配的TiN /（Al，Sc）N金属/半导体超晶格因其在基于热离子发射的热电器件，光学双曲超材料和基于热电子的太阳能转换器中的潜在应用而引起了巨大兴趣，以及对电子，光子和声子在异质结构材料中传播的基础研究。为了获得高效率的器件并寻求发现新的物理学和器件功能，超晶格具有原子锐利且突然的界面，同时最小化界面混合和表面粗糙度，这一点极为重要。此外，由于这些超晶格的跨平面方向上的能量传输取决于界面属性，重要的是表征界面电子结构和键形成的化学性质。通过结合使用软X射线散射技术（如X射线衍射和基于同步加速器的X射线反射率），在本文中，我们演示了尖锐而陡峭的TiN /（Al，Sc）N超晶格界面，界面粗糙度范围不对称从2到3个单位单元。基于同步加速器的软X射线吸收分析显示了各个薄膜和超晶格中不同原子的相似峰位置，线形和吸收边缘，这表明原子的氧化态保持不变并且排除了次级原子界面处的结构或相形成。通过像差校正的高分辨率扫描透射电子显微镜成像和能量色散X射线光谱图分析进一步验证了X射线散射结果。这些结果对于理解金属/半导体超晶格的传输特性以及设计基于超晶格的能量转换装置将是重要的。