Magnetic Mn-Doped Ge Nanostructures

Abstract

With the seemly limit of scaling on CMOS microelectronics fast approaching, spintronics has received enormous attention as it promises next-generation nanometric magnetoelectronic devices; particularly, the electric field control of ferromagnetic transition in dilute magnetic semiconductor (DMS) systems offers the magnetoelectronic devices a potential for low power consumption and low variability. Special attention has been given to technologically important group IV semiconductor based DMSs, with a prominent position for Mn doped Ge. In this paper, we will first review the current theoretical understanding on the ferromagnetism in MnxGe1−x DMS, pointing out the possible physics models underlying the complicated ferromagnetic behavior of MnxGe1−x. Then we carry out detailed analysis of MnxGe1−x thin films and nanostructures grown by molecular beam epitaxy. We show that with zero and one dimension quantum structures, superior magnetic properties of MnxGe1−x compared with bulk films can be obtained. More importantly, with MnxGe1−x nanostructures, such as quantum dots, we demonstrate a field controlled ferromagnetism up to 100 K. Finally we provide a prospective of the future development of ferromagnetic field effect transistors and magnetic tunneling junctions/memories using dilute and metallic MnxGe1−x dots, respectively. We also point out the bottleneck problems in these fields and rendering possible solutions to realize practical spintronic devices.

Growth of room temperature ferromagnetic Ge1-xMnx quantum dots on hydrogen passivated Si (100) surfaces

“…The picture in figure 1(d) was further analyzed using clustering-based image thresholding, exploiting Otsu's method. This analysis, presented in figure 1(e), was carried out on a surface of 12×10 -8 cm 2 and confirmed that distribution of dots equivalent radii is broad indeed (2 nm < r < 22 nm). However, two peaks could be identified: one centered at r ∼ 4 nm and a second at r ∼ 15 nm.…”

“…The discovery of room-temperature ferromagnetism in germanium manganese (Ge 1-x Mn x ) quantum dots obtained via heteroepitaxy on silicon 2 had attracted much attention due to the possibility to realize electric field control of ferromagnetism, 3 and indicates Ge 1-x Mn x alloys as good candidates for applications in spintronics.…”

“…5 These crystallites could be easily detected by magnetic characterization because they display a well-defined Curie temperature, usually much higher than that of the diluted phase: T C ∼ 270 K for Ge 3 Mn 5 and T C ∼ 296 K for Ge 8 Mn 11 . 2,6 In this work GeMn Quantum Dots have been successfully produced by heteroepitaxy on hydrogen passivated silicon surfaces displaying room temperature ferromagnetic behavior.…”

Experimental insight into the magnetic and electrical properties of amorphous Ge1-xMnx

“…By plotting the value of dM/dT as a function of T ( Figure 5(b)) it is possible to identify two characteristic temperatures for the samples aGeMn2.2 (10%) and aGeMn2.3 (17%) that are at ∼ 12.5 K and ∼ 14.7 K respectively. By defining these two values as the Curie temperatures, we can fit the FC curves for T < T C by employing Equation (8). The two fits in Figure 5(d) display the good agreement between the experimental dependence and Equation (8), whereas this correspondence starts to vanish above T C .…”

“…in the case of Ge 1-x Mn x DMS, T C ∼ 270K (Ge 3 Mn 5 ) and T C ∼ 296K (Ge 8 Mn 11 ). [7,8] In recent decades diluted magnetic alloys, such as Fe or Mn dispersed in Cu, have been extensively studied. [9,10] In these metallic alloys, the low-density spins could be treated as a perturbation of the Fermi liquid, representing the host non-magnetic metal.…”