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Title:Atom-by-Atom Substitution of Transition Metals in GaAs and Visualization of Hole-Mediated Interactions
Author(s):Kitchen, Dale Spencer
Director of Research:Yazdani, Ali
Doctoral Committee Chair(s):Cooper, S. Lance
Doctoral Committee Member(s):Martin, Richard M.; Junk, Thomas
Department / Program:Physics
Subject(s):atom-by-atom substitution
Mn doped GaAs
scanning tunnelling microscope (STM)
Abstract:The discovery of ferromagnetism in Mn doped InAs and GaAs has ignited interest in the development of semiconductor technologies based on the electron spin. A major hurdle remaining for realistic applications of ferromagnetic semiconductors, such as Ga(1-x)Mn(x)As, is their below room-temperature ferromagnetic transition temperature. Enhancing ferromagnetism in semiconductors requires understanding the mechanisms for interactions between magnetic dopants and identifying the circumstances that maximize ferromagnetic interactions. In this thesis, we present a novel atom-by-atom substitution technique with the scanning tunnelling microscope (STM) to controllably incorporate transition metal dopants into GaAs. We compare the electronic states of isolated single acceptors in an identical configuration - Ga sites in the top layer of a GaAs surface. The acceptor levels and anisotropic shape of the hole states for manganese, iron, cobalt; and zinc are determined with STM topography and spectroscopy. The manganese acceptor has a deeper acceptor level than the nonmagnetic zinc acceptor. The iron and cobalt acceptors have two acceptor levels that are complementary in their spatial distribution. We discuss the influence of the GaAs band structure and the p-d hybridization on the hole states. In addition, we probe the Mn acceptor in n-type and p-type GaAs to understand the role of tip-induced band bending in our experiments. We also present the first controlled atomic scale study of the interactions between isolated Mn impurities mediated by electronic states in GaAs. High-resolution STM measurements provide visualization of the GaAs electronic states that participate in Mn-Mn interactions. We quantify the interaction strengths between Mn pairs as a function of relative position and orientation. Our experimental findings, which can be explained using tight-binding model calculations, reveal a strong dependence of ferromagnetic interaction on crystallographic orientation. This anisotropic interaction can potentially be exploited by growing oriented Ga(1-x)Mn(x)As structures to enhance the ferromagnetic transition temperature beyond that achieved in randomly doped samples.
Issue Date:2006-11-28
Genre:Dissertation / Thesis
Rights Information:©2006 Kitchen
Date Available in IDEALS:2012-06-07
Identifier in Online Catalog:Q. 530.416 Tc6k
FILM 2006 K647

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