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 GeMn (T ∼ 270 K) and GeMn (T ∼ 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.

High Curie Temperature Ferromagnetism and High Hole Mobility in Tensile Strained Mn‐Doped SiGe Thin Films

“…Since tensile strain can separate heavy holes and light holes on the valence band top and increase hole mobility in SiGe alloys [ 17 ] and enlarging lattice constant also benefits the ferromagnetic (FM) order in Mn‐doped group‐IV semiconductors, [ 18 ] we speculate that tensile‐strained Mn‐doped SiGe thin films on Ge substrates may be promising for high‐performance spintronic materials. However, although there were reports on the studies of Mn‐doped Si or Ge, [ 8,9,19–21 ] no investigation on the tensile‐strained Mn‐doped SiGe thin films has been reported.…”

Engineering Magnetoresistance in MnxGe1−x System for Magnetic Sensor Application

“…The former has been well recognized in Figure 3, whereas the latter could be occasionally observed by comprehensive TEM characterization. Such fact proves that the ZFC and FC measurement in SQUID is more sensitive to detect magnetic particles than TEM [44,54].…”

“…in Figure 4(b). The differences between them give an insight into the anisotropic barrier distribution, blocking temperature, and Curie temperature [54]. Two blocking temperatures could be well resolved with one at 25 K and the other at 250 K. As discussed above, the two blocking temperatures indicate the coexistence of Mn-rich Mn x Ge 1−x nanostructures and Mn 5 Ge 3 nanoparticles in the film.…”

“…Engineering Magnetoresistance in Mn x Ge 1−x System for Magnetic Sensor Application http://dx.doi.org/10.5772/intechopen.70206 distinguish two states (0 and 1); meanwhile, the material for MR sensor could be easily scaled down and integrated with other electric components. Compared to the metal component in current MR sensor, Mn x Ge 1−x could have high compatibility with the mature Si technology [54] and hence significantly reduces the manufacturing cost. By utilizing the well-designed giant MR in Mn x Ge 1−x system, it will be of much interest to develop Mn x Ge 1−x -based MR sensor for high-density magnetic record technology.…”

Atomic layer doping of Mn magnetic impurities from surface chains at a Ge/Si hetero-interface

“…Si and Ge, have great potential as dilute magnetic semiconductors (DMS) for spintronic applications with complementary metaloxide-semiconductor (CMOS) compatibility [1][2][3] . Structural engineering is being intensively explored as a method to enhance the Curie temperature (T c ) of group IV based DMSs 4,5 . However, compared to III-V and II-VI semiconductors, e.g.…”