Growth, Characterization and Application of Aluminum-Gallium - Arsenide/gallium-Arsenide Modulation Doped Heterostructures
Drummond, Timothy J.
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https://hdl.handle.net/2142/69274
Description
Title
Growth, Characterization and Application of Aluminum-Gallium - Arsenide/gallium-Arsenide Modulation Doped Heterostructures
Author(s)
Drummond, Timothy J.
Issue Date
1983
Department of Study
Electrical Engineering
Discipline
Electrical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Electronics and Electrical
Abstract
Modulation doped heterostructures show great potential for being the basis of a new family of high speed electronic devices, including photodetectors, charge-coupled devices and field effect transistors. This has motivated an extensive study of the growth and physical properties of Al(,x)Ga(,1-x)As/GaAs heterostructures. Molecular beam epitaxy is the preferred crystal growth technology for this structure because of the ease with which high quality epitaxial layers and abrupt compositional and doping profiles may be obtained.
In a "selectively doped" or "modulation doped" heterostructure only the Al(,x)Ga(,1-x)As is doped with a donor impurity. Electrons diffuse into the GaAs and are confined in a plane at the heterojunction by the larger electron affinity of the GaAs and the space charge layer in the Al(,x)Ga(,1-x)As. The electrons in the GaAs behave dynamically as a two-dimensional electron gas. Both the electron mobility and velocity parallel to the heterojunction are enhanced with respect to GaAs uniformly doped to a comparable electron density. Mobility enhancement is most dramatic at low temperatures where phonon scattering is negligible.
The growth and characterization of both normal and inverted single interface heterostructures are described. Recognizing that there is an intrinsic difference between the two structures in terms of obtaining mobility enhancement, the normal structure, which reproducibly demonstrates good transport properties, was studied in greatest detail.
The application of modulation doped heterostructures to field effect transistors was investigated experimentally and theoretically. High current, high transconductance transistors were fabricated by maximizing the transferred electron density at the expense of high electron mobilities. Because performance in short channel devices is limited by the electron velocity, which is nearly independent of the electron density, the low mobilities do not seriously affect device performance.
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