title: Nanoengineering of an Si/MnGe quantum dot superlattice for high Curie-temperature ferromagnetism.
abstract: The realization and application of spintronic devices would be dramatically advanced if room-temperature ferromagnetism could be integrated into semiconductor nanostructures, especially when compatible with mature silicon technology. Herein, we report the observation of such a system - an Si/MnGe superlattice with quantum dots well aligned in the vertical direction successfully grown by molecular beam epitaxy. Such a unique system could take full advantage of the type-II energy band structure of the Si/Ge heterostructure, which could trap the holes inside MnGe QDs, significantly enhancing the hole-mediated ferromagnetism. Magnetic measurements indeed found that the superlattice structure exhibited a Curie temperature of above 400 K. Furthermore, zero-field cooling and field cooling curves could confirm the absence of ferromagnetic compounds, such as Ge8Mn11(Tc∼ 270 K) and Ge3Mn5(Tc∼ 296 K) in our system. Magnetotransport measurement revealed a clear magnetoresistance transition from negative to positive and a pronounced anomalous Hall effect. Such a unique Si/MnGe superlattice sets a new stage for strengthening ferromagnetism due to the enhanced hole-mediation by quantum confinement, which can be exploited for realizing the room-temperature Ge-based spin field-effect transistors in the future.
authors.affiliation: Device Research Laboratory, Department of Electrical Engineering, University of California, Los Angeles, 90095, California, USA. wang@seas.ucla.edu nietianxiao@gmail.com.
authors.forename: Tianxiao
authors.identifier: http://orcid.org/0000-0001-9067-9931
authors.initials: T
authors.lastname: Nie
authors.affiliation: Device Research Laboratory, Department of Electrical Engineering, University of California, Los Angeles, 90095, California, USA. wang@seas.ucla.edu nietianxiao@gmail.com.
authors.forename: Xufeng
authors.initials: X
authors.lastname: Kou
authors.affiliation: IBM Thomas J. Watson Research Center, Yorktown Heights, New York 10598, USA.
authors.forename: Jianshi
authors.identifier: http://orcid.org/0000-0001-8369-0067
authors.initials: J
authors.lastname: Tang
authors.affiliation: Device Research Laboratory, Department of Electrical Engineering, University of California, Los Angeles, 90095, California, USA. wang@seas.ucla.edu nietianxiao@gmail.com.
authors.forename: Yabin
authors.initials: Y
authors.lastname: Fan
authors.affiliation: Institute of Materials Science and Engineering, National Central University, 300 Jung-Da Rd, Chung-Li 320, Taiwan.
authors.forename: Shengwei
authors.initials: S
authors.lastname: Lee
authors.affiliation: Device Research Laboratory, Department of Electrical Engineering, University of California, Los Angeles, 90095, California, USA. wang@seas.ucla.edu nietianxiao@gmail.com.
authors.forename: Qinglin
authors.initials: Q
authors.lastname: He
authors.affiliation: Device Research Laboratory, Department of Electrical Engineering, University of California, Los Angeles, 90095, California, USA. wang@seas.ucla.edu nietianxiao@gmail.com.
authors.forename: Li-Te
authors.initials: LT
authors.lastname: Chang
authors.affiliation: Device Research Laboratory, Department of Electrical Engineering, University of California, Los Angeles, 90095, California, USA. wang@seas.ucla.edu nietianxiao@gmail.com.
authors.forename: Koichi
authors.initials: K
authors.lastname: Murata
authors.affiliation: Device Research Laboratory, Department of Electrical Engineering, University of California, Los Angeles, 90095, California, USA. wang@seas.ucla.edu nietianxiao@gmail.com.
authors.forename: Yin
authors.initials: Y
authors.lastname: Gen
authors.affiliation: Device Research Laboratory, Department of Electrical Engineering, University of California, Los Angeles, 90095, California, USA. wang@seas.ucla.edu nietianxiao@gmail.com.
authors.forename: Kang L
authors.initials: KL
authors.lastname: Wang