Single-crystal superconducting ultra-thin aluminum films grown on GaAs(111)A - low twin ratios, transport, and microwave properties
Hsien-Wen Wan1*, Yi-Ting Cheng2, Chao-Kai Cheng1, Jui-Min Chia2, Chien-Ting Wu3, Chia-Hung Hsu4, Ruey-Tai Wang5, Sheng-Shiuan Yeh5, Yen-Hsiang Lin2, Jueinai Kwo2, Minghwei Hong1
1Graduate Institute of Applied Physics and Department of Physics, National Taiwan University, Taipei, Taiwan
2Department of Physics, National Tsing Hua University, Hsinchu, Taiwan
3Taiwan Semiconductor Research Institute, Hsinchu, Taiwan
4National Synchrotron Radiation Research Center, Hsinchu, Taiwan
5International College of Semiconductor Technology, National Yang Ming Chiao Tung University, Hsinchu, Taiwan
* Presenter:Hsien-Wen Wan, email:f04222061@ntu.edu.tw
The disordered grain boundaries of polycrystalline thin films and interface inhomogeneity to adjacent layers are sources of energy relaxation channels that limit the performance of superconducting quantum devices. In this work, we have grown single-crystal aluminum (Al) thin films 1.5 to 20 nm in thickness on GaAs (111)A substrates with high crystallinity and low twin ratios. The Al films were protected with an in-situ deposited Al₂O₃, preventing the formation of native oxides upon air exposure. Synchrotron radiation X-ray diffraction scans of these Al films show that the films are single-crystal with clear Pendellösung fringes, indicative of high crystallinity. The full-width at half-maximum of θ-rocking curves and in-plane Al(111̅) peaks are low values of 0.018°-0.027° and 0.76°-1.88°, respectively. The surfaces and interfaces of the samples are smooth and atomically sharp as characterized by atomic force microscopy and scanning transmission electron microscopy, respectively. These nm-thick Al films exhibited high residual resistance ratios (RRR) from 1.11 to 4.46, indicating the high quality of the Al films with low twin ratios. Microstrip resonators were fabricated using these single-domain ultra-thin Al films to improve the internal quality factors for building superconducting quantum circuits.


Keywords: Superconducting ultra-thin films, single-crystal aluminum, high crystallinity, internal quality factor, superconducting quantum circuits