Pulsed-laser processing of ferromagnetic semiconductors

Oscar D. Dubón, Jr.
Department of Materials Science and Engineering University of California Berkeley 
and 
Lawrence Berkeley National Laboratory Berkley, CA

Abstract

Because of their unique combination of magnetic and semiconducting properties and their potential as both injection sources and filters for spin-polarized carriers, ferromagnetic semiconductors have attracted much attention for spin-based electronics, or spintronics. These novel materials are formed by the substitution of a relatively small fraction of host atoms—a few atomic percent—with a magnetic species such as Mn. In the prototypical ferromagnetic semiconductor Ga1-xMnxAs, inter-Mn exchange is known to be mediated by holes in extended or weakly localized states; however, the fundamental nature of exchange across the Ga-Mn-pnictide series is less clear. Unfortunately, challenges in materials synthesis have obstructed both the further understanding of these materials and their application in practical devices. Even the relatively low alloying levels necessary for ferromagnetism require the application of non-equilibrium growth strategies, in particular low-temperature molecular beam epitaxy (LT-MBE). 

At Berkeley we have undertaken investigations on the synthesis of ferromagnetic semiconductors using a combination of Mn ion implantation and pulsed-laser melting (II-PLM). By this simple process we have produced epitaxial, single crystalline films of ferromagnetic GaxMn1-xAs. These epilayers display the essential magnetic and electrical properties observed in films grown by LT-MBE. We have used II-PLM to produce new Ga-Mn-pnictide alloys including ferromagnetic Ga1-xMnxP. This material represents an intriguing system in which strongly localized carriers in a detached impurity band stabilize ferromagnetism. The possibility of introducing more than one species by ion implantation into a semiconductor host opens further opportunities to study quaternary alloys and probe chemical trend in the ferromagnetic Curie temperature. I will present results from our studies of these novel ferromagnetic semiconductors as well as efforts to develop laser patterning techniques for the realization of planar spintronic structures.


Time and Location

Thursday, January 29, 2008, 1:00 pm
OHE 122

The Scientific Community is Cordially Invited.