Structural Insights using Synchrotron X-ray diffraction into Heteroepitaxial Films for Nanoelectronics and Quantum Computing

Chao-Kai Cheng^1*, Yen-Hsun Glen Lin¹, Hsien-Wen Wan¹, Lawrence Boyu Young¹, Yi-Ting Cheng¹, Wan-Sin Chen¹, Chia-Hung Hsu², Jueinai Kwo³, Minghwei Hong¹

¹Graduate Institute of Applied Physics and Department of Physics, National Taiwan University, Taipei, Taiwan
²National Synchrotron Radiation Research Center, Hsinchu, Taiwan
³Department of Physics, National Tsing Hua University, Hsinchu, Taiwan

* Presenter:Chao-Kai Cheng, email:f02245005@ntu.edu.tw

With the continuous advancement of computing technology, researchers are increasingly focused on enhancing computational speed and efficiency. A very important area of research is dedicated to improving the quality of heterogeneous interfaces. This work explores the enhancement of heterointerface and heteroepitaxial thin-film quality for advanced applications across promising fields, including complementary metal-oxide-semiconductor (CMOS) transistors, and quantum computing. High crystallinity and smooth interfaces are essential for optimal device performance, and we used high-resolution synchrotron X-ray diffraction (XRD) to characterize the structural quality of thin films.
For metal-oxide-semiconductor field-effect-transistors (MOSFETs) applications, SiGe and Ge channels provide higher carrier mobility than Si, but GeO_x formation at the interfaces can degrade electrical performance. To tackle this issue, we deposited angstrom-scale silicon layers on Ge to suppress GeO_x formation. Due to the properties of Ge, Ge atoms tend to diffuse into the Si layer, segregating at the surface and forming GeO_x during oxide deposition. The thickness of epi-Si films and the amount of Ge diffusion were precisely characterized using XRD and the crystal truncation rod analysis technique. In GaAs-based metal oxide semiconductor capacitors (MOSCAPs), epitaxial nanometer-thick Y₂O₃ layers were deposited on GaAs via atomic layer deposition. XRD analysis confirmed the high-quality bixbyite structure of Y₂O₃ and established its orientation relationship with GaAs.
In quantum computing, X-ray reflectivity reveals that superconducting aluminum films protected with in-situ Al₂O₃ exhibit superior quality compared to those with native AlO_x. Additionally, we achieved single-domain aluminum films on GaAs(111)A, successfully addressing the twin domain issue commonly found in Al/sapphire(0001) heterostructures. This breakthrough paves the way for manufacturing high-quality, large-scale Al films for practical applications.
These studies demonstrate that synchrotron XRD is a powerful tool for investigating crystallographic qualities in heteroepitaxial films, from nanometer to angstrom scales, offering critical insights into material and interface quality for emerging electronic and quantum devices.

Keywords: Heterostructure, Complementary metal-oxide-semiconductor transistors, Quantum Computing