Our main research field is “Spin-Electronics” or “Spintronics“, in which we try to utilize the spin degrees of freedom in artificially synthesized materials. We are studying epitaxial growth, structural characterizations, electronic/optical/magnetic/spin-related properties (in particular, spin-dependent transport and mageto-optical properties), and device applications of various new structures.

The following are some of the structures and devices we are working on:

  • Ferromagnetic metal / semiconductor hybrid structures
  • III-V based magnetic semiconductors and their heterostructures
  • Group-IV based magnetic semiconductors
  • Ferromagnetic nanoparticles / semiconductor hybrid heterostructures
  • Delta doping of magnetic impurities in semiconductor heterostructures
  • Oxide based spintronics
  • New spin transitors (eg. spin-MOSFET) and reconfigurable logic devices

SOME RECENT RESEARCH TOPICS

◆ Fe Based Ferromagnetic Semiconductors and Devices Applications

Figure: Spontanous spin splitting observed for the first time in the conduction band of n-type FMS (In,Fe)As [5]

Ferromagnetic semiconductors (FMSs) with high Curie temperature (Tc) are highly desired for spintronic applications. So far, the mainstream study of FMSs is the Mn-doped III-V FMSs, which, however, have only p-type and Tc much lower than 300K. To search for new high-performance FMSs, there have been world-wide efforts that were mainly concentrated on wide-gap materials. However, reliable and systematic results have not yet been presented.
In this research, we present an alternative approach by using Fe instead of Mn as the magnetic dopants in narrow-gap III-V semiconductors; InAs, GaSb, and InSb. In these Fe-based FMSs, because the Fe atoms are in the isoelectronic Fe3+ state, the carrier type (electrons or holes) can be controlled independently by co-doping with non-magnetic dopants. These carriers would reside in the conduction band (CB) or the valence band (VB) of the host semiconductors and thus move faster with higher coherency. Using low-temperature molecular beam epitaxy, we have successfully grown single-phase crystal of both p-type FMS [(Ga,Fe)Sb [2]] and n-type FMSs [(In,Fe)As [3], (In,Fe)Sb [4]]. TC increases monotonically with the Fe content; and there is a tendency that TC is higher in narrower-gap host semiconductors. Intrinsic room-temperature ferromagnetism has been observed in (Ga1-x,Fex)Sb with x > 23% [2] and (In1-x,Fex)Sb with x > 16% [4]. In n-type FMS (In,Fe)As, large spontaneous spin splitting in the CB was observed, which is the first in all FMSs [5]. These results raise new issues in the magnetism of semiconductors and indicate that the Fe-doped III-V FMSs are promising for high-performance spintronic devices.
Ref: [1] N. T. Tu et al., APL 108, 192401 (2016). [2] P. N. Hai, APL 101, 182403 (2012). [3] N. T. Tu et al., arXiv:1706.00735 (2017). [4] L. D. Anh et al., PRB 92, 161201(R) (2015). [5] L. D. Anh et al., Nat. Commun. 7, 13810 (2016).

◆ Oxide-based spintronics

We are trying to explore new materials and physics for future oxide-based spintronics by developing various single-crystalline thin films, heterostructures, and magnetic nano structures.

More details on the ongoing projects can be found in the following homepage of prof. Ohya Research Group.