Research Update: Strain and composition effects on ferromagnetism of Mn0.05Ge0.95 quantum dots

• Published in: APL materials 2016-04, Vol.4 (4), p.040701-040701-9
• Main Authors: Wang, Liming, Liu, Tao, Jia, Quanjie, Zhang, Zhi, Lin, Dongdong, Chen, Yulu, Fan, Yongliang, Zhong, Zhenyang, Yang, Xinju, Zou, Jin, Jiang, Zuimin
• Format: Article
• Language: English
• ISSN: 2166-532X; 2166-532X
• DOI: 10.1063/1.4945657

Mn0.05Ge0.95 quantum dots (QDs) samples were grown by molecular beam epitaxy on Si substrates and 15-nm-thick fully strained Si0.8Ge0.2 virtual substrates, respectively. The QDs samples grown on the Si0.8Ge0.2 virtual substrates show a significant ferromagnetism with a Curie temperature of 227 K, while the QDs samples grown on the Si substrates are non-ferromagnetic. Microstructures of the QDs samples were characterized by high resolution transmission electron microscopy and synchrotron radiation X-ray diffraction. Interdependence between microstructure and ferromagnetism of Mn-doped Ge QDs was investigated. For the QDs sample grown on the strained Si0.8Ge0.2 virtual substrate, although the ferromagnetic phase Mn5Ge3 clusters were found to be formed in small dome-shaped dots, the significant ferromagnetism observed in that sample is attributed to ferromagnetic phase Mn-doped large dome-shaped Ge QDs, rather than to the ferromagnetic phase Mn5Ge3 clusters. The fully strained Si0.8Ge0.2 virtual substrates would result in a residual strain into the QDs and an increase in Ge composition in the QDs. Both consequences favor the formations of ferromagnetic phase Mn-doped Ge QDs from points of view of quantum confinement effect as well as Mn doping at substitutional sites.