High Curie Temperature Achieved in the Ferromagnetic MnxGe1−x/Si Quantum Dots Grown by Ion Beam Co-Sputtering

Abstract

Ferromagnetic semiconductors (FMSs) exhibit great potential in spintronic applications. It is believed that a revolution of microelectronic techniques can take off, once the challenges of FMSs in both the room-temperature stability of the ferromagnetic phase and the compatibility with Si-based technology are overcome. In this article, the MnxGe1−x/Si quantum dots (QDs) with the Curie temperature (TC) higher than the room temperature were grown by ion beam co-sputtering (IBCS). With the Mn doping level increasing, the ripening growth of MnGe QDs occurs due to self-assembly via the Stranski–Krastanov (SK) growth mode. The surface-enhanced Raman scattering effect of Mn sites observed in MnGe QDs are used to reveal the distribution behavior of Mn atoms in QDs and the Si buffer layer. The Curie temperature of MnxGe1−x QDs increases, then slightly decreases with increasing the Mn doping level, and reaches its maximum value of 321 K at the doping level of 0.068. After a low-temperature and short-time annealing, the TC value of Mn0.068Ge0.932 QDs increases from 321 K to 383 K. The higher Ge composition and residual strain in the IBCS grown MnxGe1−x QDs are proposed to be responsible for maintaining the ferromagnetic phase above room temperature.

Microstructure and Ferromagnetism of Mn0.05Ge0.95 Quantum Dots/Graphene Heterostructures for Spintronic Devices

“…The peaks at 31.15 and 32.78 eV correspond to Ge 2+ and Ge 4+ , respectively, due to surface oxidation. 19,20,22 The peaks for +4 or even a higher valence of Ge have been mentioned in several types of research studies about Mn x Ge 1−x materials, which can be attributed to the interaction between Ge atoms and Mn atoms during the sputtering process. 19,38,47 Thus, the appearance of the Ge−Ge bond and +4 valence of Ge demonstrate that the quantum dots deposited on the graphene substrate are mainly constructed by the Ge atoms and Mn atoms.…”

“…19,20,22 The peaks for +4 or even a higher valence of Ge have been mentioned in several types of research studies about Mn x Ge 1−x materials, which can be attributed to the interaction between Ge atoms and Mn atoms during the sputtering process. 19,38,47 Thus, the appearance of the Ge−Ge bond and +4 valence of Ge demonstrate that the quantum dots deposited on the graphene substrate are mainly constructed by the Ge atoms and Mn atoms. The combination of Ge 4+ and Mn 2+ facilitates the formation of a p-type semiconductor through low-valence state substitutional doping of a highvalence state.…”

“…18 temperature spintronic devices based on mainstream silicon technology. 19,20 Gao et al studied the effect of Co ion implantation on Ge 1−x Mn x films. 21 Wu et al prepared doublelayered Mn x Ge 1−x Te polycrystalline films by introducing a Si space layer, enhancing the magnetic properties of Mn x Ge 1−x Te.…”

“…Duan et al utilized ion beam sputtering deposition (IBSD) technology to fabricate uniformly aligned Mn x Ge 1– x QDs with a Curie temperature of 383 K. The introduction of Te doping resulted in a 4.3-fold increase in saturation magnetization and a 7.9-fold increase in residual magnetization, providing an effective strategy for enhancing and modulating ferromagnetism in Mn x Ge 1– x DMSs. This achievement established a robust foundation for realizing room temperature spintronic devices based on mainstream silicon technology. , Gao et al studied the effect of Co ion implantation on Ge 1– x Mn x films . Wu et al prepared double-layered Mn x Ge 1– x Te polycrystalline films by introducing a Si space layer, enhancing the magnetic properties of Mn x Ge 1– x Te .…”