GP-Spin Seminar

June 12,2017
1:30pm-3:00pm"Epitaxial ferromagnetic Heusler
alloy/semiconductor hybrid structures
for spintronic application"

Dr. Jens Herfort

Senior Scientist
Core Research Area Coordinator
Paul-Drude-Institut
für Festkörperelektronik

Date and Venue

Time 1:30pm-3:00pm
Date June 12,2017
Venue Seminar room 407,

Education and Research Bldg(B01),
Material Science and Engineering,

Aobayama-Campus
Contact us

International Joint Graduate Programs Office GP-Spin team+81-22-795-5716/3657
spin.all[at]grp.tohoku.ac.jp

Epitaxial ferromagnetic Heusler alloy/semiconductor hybrid structures for spintronic
application
J. Herfort
Paul-Drude-Institut für Festkörperelektronik, Hausvogteiplatz 5-7, 10117 Berlin, Germany
herfort@pdi-berlin.de
Semiconductor spintronics offers the possibility to develop hybrid devices that can perform theprocessing, communication, and storage of information within one chip. Furthermore, taking advantage ofthe electron spin as an additional degree of freedom entails the potential to increase the functional density inintegrated circuits instead of scaling down the packing density by further reducing the size of single devices.
Important building blocks of spintronic devices involve the generation, transport, detection, andmanipulation of spin-polarized carriers in semiconductors. Particularly because of their potential for
non-volatile memory applications, hybrid structures consisting of ferromagnetic (FM) metals andsemiconductors (SC) are of major interest for semiconductor spintronics. Our investigations combine two
mutually dependent directions. The first aims at a comprehensive understanding of the heteroepitaxial
growth by molecular beam epitaxy (MBE) as well as the structural and magnetic properties of theferromagnet/semiconductor hybrid system as a whole. The second one aims at identifying and understanding
the mechanisms involved in spin transport which are relevant for spintronic device concepts.
The ability to inject, transport, manipulate, and detect spin-polarized carriers by purely electricalmeans is a prerequisite for most proposed spin-based semiconductor devices. Local spin valves are essentialbuilding blocks for such spintronic applications. We have demonstrated for the Co 2 FeSi/GaAs hybrid system
the all-electrical injection and detection of spins employing a lateral device structure by both spinvalve
measurements and experiments utilizing the Hanle effect. Furthermore, a new spintronic device concept

has been established for which a cascade of spin extraction instead injection events is utilized forthe functionality as a nonvolatile reconfigurable current divider.
The preparation of fully crystalline thin film stacks consisting of a semiconducting channel
sandwiched between two ferromagnetic layers constitutes a prerequisite for the engineering of a new device
type. For the underlying device concept, the heights and shapes of the potential barriers formed at theinterface between the ferromagnet and the semiconductor are crucial. However, the major obstacle for therealization of crystalline layer stacks of a semiconductor sandwiched between two ferromagnets is theconsiderable difficulty to overgrow metals with a fully crystalline semiconductor while preserving a goodinterface quality. Indeed, apart from the different crystal structures, ferromagnet and semiconducting
materials generally have incompatible crystallization energies (larger for semiconductings compared toferromagnets). As a consequence, chemical reactions are likely to occur during the growth of thesemiconducting layer. In order to overcome the challenges with the semiconducting on ferromagnet growth,
we have chosen solid-phase epitaxy as an approach where an amorphous film of Ge is deposited on Fe 3 Si
and then recrystallized slowly by thermal annealing.