Progress in Preparation of Diluted Ferromagnetic MnxGe1-x Quantum Dots by Molecular Beam Epitaxy
HUANG Xunji1,2, YANG Jie1,2, LI Guangyang1,2, WANG Chong1,2, YANG Yu2,3
1 School of Materials Science and Engineering, Yunnan University, Kunming 650091; 2 International JointResearch Center for National Optoelectronic Energy Materials, Yunnan University, Kunming 650091; 3 School of Energy, Yunnan University, Kunming 650091
Abstract: Diluted magnetic semiconductors (DMSs) integrate the dual properties of semiconductor materials and magnetic materials by simultaneously utilizing the charge and spin characteristics of electrons. The use of charge carriers and their spins makes it possible for spintronic devices to be used for information storage, transmission and processing. Consequently, Mn-doped Ge quantum dots(QDs) diluted ferromagnetic semiconductors, as an important part of the microelectronics industry, have aroused enormous interests because of its compatibility with current Si microelectronics and the possibility to possess higher Curie temperature (TC) than those of group Ⅲ-Ⅴ materials. The prepared MnxGe1-x QDs spintronic devices exhibit excellent performances including small size, low energy consumption, fast data processing, high integration and favorable stability, which will play a crucial role in the future development of spintronic devices. Although Mn doped group Ⅳ MnxGe1-x QDs DMSs materials are considered to be ideal candidates for room temperature controllable electronic spin devices and controllable ferromagnetic properties. However, the MnxGe1-x QDs DMSs materials with high performance and stability are still confronted with great challenges.Ⅰ. Although high TC of the system can be obtained by raising the concentration of magnetic dopant in the matrix, the solubility limit of Mn dopant in Ge is far lower than the dopant concentration which endows the system with high TC. Ⅱ. The high concentration of Mn dopant in Ge1-xMnx QDs is likely to cause the formation of intermetallic precipitates (Mn5Ge3 and Mn11Ge8). Ⅲ. Low growth temperature and low surface diffusivity are demanded for incorporating Mn into Ge under the state much higher than chemical equilibrium, while high growth temperature and high surface diffusivity are always required in self-assembly growth of QDs. Namely, achieving higher doping levels of metastable may become a breakthrough point for enhancing TC in DMSs. Ⅳ. The theoretical explanation of ferromagnetism, the origin of high TC and enhancement mechanism of TC are still unclear and worth further exploration. Therefore, great attempts have been made and fruitful results have been achieved by researchers in optimizing the preparation process of MnxGe1-x QDs films by selecting suitable growth parameters in recent years. Ⅰ. The TC of MnxGe1-x QDs is raised above 400 K. Ⅱ. It is defined that the TC of intermetallic precipitates (Mn5Ge3 and Mn11Ge8) are 296 K and 270 K, which tends to room temperature. Ⅲ. The electric-field-controlled ferromagnetism and the magnetotransport properties have been found. Electric-field manipulation of ferromagnetism temperature has been raised over 300 K for the first time, which was attributed to the quantum confinement effect. Ⅳ. Due to the existence of quantum effects in MnxGe1-x QDs, the modulated doping of boron (B) can increase the hole concentration in the MnxGe1-x QDs, which contributed to enhancing the TC of the MnxGe1-x QDs. This review offers a retrospection of the research efforts with respect to the MnxGe1-x diluted ferromagnetic semiconductor materials, and provides elaborated descriptions about the MnxGe1-x QDs prepared by molecular beam epitaxy (MBE). And the effects of growth parameters on the morphology and magnetic properties of QDs are also introduced. The difficulties that remain to be solved in the current research are briefly described, and the application prospects for the material in the field of microelectronics are proposed.
黄训吉,杨杰,李广洋,王茺,杨宇. 分子束外延制备稀铁磁性MnxGe1-x量子点研究进展[J]. 材料导报, 2018, 32(19): 3338-3347.
HUANG Xunji, YANG Jie, LI Guangyang, WANG Chong, YANG Yu. Progress in Preparation of Diluted Ferromagnetic MnxGe1-x Quantum Dots by Molecular Beam Epitaxy. Materials Reports, 2018, 32(19): 3338-3347.
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