SCIENCE
Physicist Ian Appelbaum Puts New Spin on Semiconductors

University of Delaware's Dr. Ian Appelbaum is looking to "spin" his research on the magnetic properties of electrons to get more electronic enhancements from semiconductors.

Appelbaum's research is now funded in part with a nearly half-million dollar grant from the U.S. Department of Defense Experimental Program to Stimulate Competitive Research (DEPSCoR). Since the Fall of 2004, he has headed a research team at the University of Delaware.

As an MIT graduate student, the spintronics physicist conceived, developed, and experimentally demonstrated a mechanism for hot electron injection luminescence in scanning probe microscopy on buried-heterostructure light-emitting devices. He applied this luminescence mechanism to hot-electron-mediated direct optical up-conversion. He also developed computational schemes to model hot electron transport in nanoscale semiconductor heterostructures via ballistic electron emission spectroscopy.

The purpose of it all: making better semiconductor devices. The developments could one day result in new hardware found in things like computer hard drives.

These early accomplishments led to further recognition for his efforts as semiconductor specialist working to gain benefits from spin characteristics of electrons, or spintronics. He earned his doctoral degree in physics at the Massachusetts Institute of Technology (MIT) in June 2003. After one year as a postdoctoral fellow at Harvard University, Appelbaum became an assistant professor of electrical engineering at the University of Delaware in the fall of 2004.

Appelbaum's research group developed innovative hot electron techniques for both injection and detection of spins in semiconductors. Also, his research group was the first to overcome significant electronic structure and materials challenges to demonstrate spin transport in silicon.

Starting with the spring semester of 2009, Appelbaum will move his research team to the University of Maryland, where he will be a tenured associate professor of physics.

Pursuing DEPSCoR

Universities and colleges in certain states apply annually for special funding consideration in research projects that may benefit U.S. national defense. Known as "The Department of Defense Experimental Program to Stimulate Competitive Research (DEPSCoR) Program," the application process involves a yearly peer review competition for funds.

Besides meeting Department of Defense (DoD) goals, the program supports EPSCoR member states' efforts for stimulating competitive research capabilities. In fiscal year 2007, the DoD awarded US$9 million to 14 academic institutions in nine states to perform research in science and engineering fields important to national defense.

"Historically, about half the 50 states get less money for research. Other than being an EPSCOR state, the awards are based on research merit," Appelbaum told TechNewsWorld in explaining his involvement with the grant award. "The grant pays for research expenses such as supplies and equipment, and for expenses associated with hiring graduate students."

The DEPSCoR program is sponsored by the Office of the Deputy Under Secretary of Defense for Laboratories and Basic Sciences. It is administered by the Army Research Office (ARO), the Office of Naval Research (ONR) and the Air Force Office of Scientific Research (AFOSR) in cooperation with the state EPSCoR offices.

Appelbaum's Lab

TechNewsWorld spoke with Appelbaum recently to discuss his research as he prepared to move his lab.

TechNewsWorld: In layman's terms, what is spintronics?

Appelbaum: "Spintronics" means spin transport electronics, where "spin" is the intrinsic angular momentum of electrons. This angular momentum is coupled to a magnetic moment, so each electron behaves like a quantum magnet where the north-south magnetic orientation can be "up" or "down." In non-magnetic semiconductors, there are just as many up- as down-oriented electron spins, so the effects of spin are averaged out. Creating an imbalance of one spin orientation over the other provides new ways to operate devices, or improved performance.[*See editor's note]

TNW: Obviously semiconductors have been a vital part of computer technology in particular and electronics in general for some time. What are you looking for?

Appelbaum: One key property of an electron charge is what is called its "magnetic moment." We've known about these properties for a very long time. We continue to look for breakthroughs in what is now called "spin technology."

TNW: How evident is this electron spin to researchers?

Appelbaum: Many phenomena show the effects of spin, especially optical effects such as changes in the polarization of light emitted by semiconductors in a magnetic field.

TNW: Is spin technology a relatively new field of study?

Appelbaum: My research grew out of work done in the 1980s and 1990s with semiconductor materials.

TNW: Since your grant award is connected to a DoD interest, you must be pursuing spintronics for more than the benefits of pure research. What are you trying to accomplish?

Appelbaum: Manipulation of electron spins in semiconductors could potentially lead to new ways of processing information encoded in the spin orientation -- up and down may replace 1 and 0. This paradigm may also have the potential to operate at lower power than present-day technology.

TNW: How is this related to your research?

Appelbaum: We are developing silicon-based transistors utilizing spin-polarized electron transport to control the output characteristics. Silicon has several intrinsic qualities that make it the ideal semiconductor for spintronics.

TNW: How might this advance the field of electronics?

Appelbaum: Spintronics has not yet been useful in information-processing circuits. To enable spin-based integrated circuits, long spin lifetimes are needed. Silicon has been broadly viewed as the ideal material for spintronics due to its properties.

TNW: Has your research produced any solutions?

Appelbaum: Over the last two years we have shown how to apply certain methods [of achieving coherent spin transport in silicon] that are not hinging on silicon's properties. These methods involve using unique spin-polarized hot-electron injection and detection techniques.

TNW: How soon before you will see applications for consumer products?

Appelbaum: In terms of those results, it is way off in the future. We are nowhere near consumer applications. Right now we are doing pure science, but we also want to keep an eye on doing something useful.

TNW: Is your research isolated from other study of spintronics, or are you working with other teams of researchers in sharing results?

Appelbaum: I see others getting involved in this research, especially theorists who can help us understand the subtle new concepts governing spins in semiconductors.