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Spring 2008 Seminar Series
Friday, April 11, at 3:30 p.m.
Room 264 MacQuigg Labs
Michael Scarpula
Postdoctoral Scholar
University of California, Santa Barbara
Epitaxial Films of Unconventional Dilute Semiconductor Alloys
Abstract
In contrast to conventional band engineering where alloying at 10's of percent levels is used to manipulate bandgaps, in some unconventional alloys dramatic electronic, optical, and magnetic effects emerge at 1-5 percent alloying. In this talk, I will discuss my research into the synthesis and properties of epitaxial films of such unconventional dilute alloys of compound semiconductors.
First, I will discuss studies of Ga1-xMnxAs and Ga1-xMnxP where ferromagnetism emerges for Mn concentrations of x=0.02. Some examples will also be given from dilute III-V-nitrides, where the addition of 1% N reduces the GaAs bandgap 20 times faster than it increases for alloying with Al, and from II-VI-oxides where the addition of ∼1% O causes a splitting of the conduction band into two distinct bands. Epitaxial films for all of these studies were synthesized using ion implantation and pulsed-laser melting, which allowed the synthesis of some alloys unobtainable by traditional crystal growth techniques.
Second, I will discuss the properties of films of Ga1-xErxAs and Al1-xErxAs grown using molecular beam epitaxy. In these films, semimetallic ErAs nanoparticles of 2 nm diameter spontaneously phase segregate during growth and introduce an extremely strong absorption feature near 1.5 μm. The energy of this absorption peak varies strongly with small changes in nanoparticle diameter, suggesting a quantum confinement-induced semimetal-semiconductor transition as the origin of the absorption.
Lastly, I will briefly outline my plans for future research into thin films of non- toxic sulphide semiconductors for terrestrial thin-film photovoltaics and the applications of rare earth nitride nanoparticles in nitride semiconductor devices.
Bio
Mike's research interests are in solid-state materials for thin film photovoltaics, semiconductor alloys, ferromagnetic semiconductors, and the integration of rare earth pnictides with III-V semiconductors. Mike received his bachelors in Materials Science & Engineering with honors from Brown University in 2000. He then worked for IBM's Almaden Research Center for 1 year. He received his PhD from UC Berkeley in Materials Science and Engineering in 2006 where his advisor was Prof. Oscar Dubon and he worked on pulsed-laser processing of semiconductors and ferromagnetic semiconductors. Since late 2006, Mike has been a postdoctoral scholar with Prof. Art Gossard where he has been working on integration of rare earth pnictides with III-V semiconductors using MBE growth.
Please join our speaker for light refreshments in 479 Watts Hall following the talk.
