Deep-Level Transient Spectroscopy Studies of Gallium Arsenide - Aluminum Gallium Arsenide Heterostructures and Superlattices
Martin, Paul Alan
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https://hdl.handle.net/2142/69339
Description
Title
Deep-Level Transient Spectroscopy Studies of Gallium Arsenide - Aluminum Gallium Arsenide Heterostructures and Superlattices
Author(s)
Martin, Paul Alan
Issue Date
1986
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
This thesis presents the results of two projects. First, the feasibility of using deep-level transient spectroscopy (DLTS) to measure conduction band-edge discontinuities in GaAs - AlGaAs quantum-well heterostructures is evaluated theoretically and experimentally. Second, defects in GaAs - AlGaAs superlattices are examined using DLTS.
Deep-level transient spectroscopy is reviewed, as are theoretical and experimental attempts to preduct and measure band offsets. A theory of electron capture into and emission out of quantum wells in response to pulsed bias is developed. DLTS studies of GaAs AlGaAs quantum-well structures are presented and compared with the results of previous studies of defects in MOCVD GaAs and AlGaAs. Emission of electrons out of the GaAs quantum well is observed, but at emission rates in excess of those predicted by thermionic emission or by phonon assisted tunneling. In the absence of a model for the emission process, meaningful data for band-edge discontinuities cannot be extracted from the measured emission rates. Further characterization of the emission process would be of great value in the development of devices based on heterojunction technology.
Data are also presented from a DLTS study of defect states in GaAs - AlGaAs superlattices. Doubling the layer thickness from 50 to 100 (ANGSTROM) resulted in a dramatic change in the defects observed. This is accounted for by the presence of a conducting miniband in one superlattice and its absence in the other. In the presence of a conducting miniband, activation energies are measured with respect to the miniband and not with respect to the conduction band edge of either the GaAs or the AlGaAs. In the absence of a conducting miniband, activation energeis are measured with respect to the AlGaAs conduction band edge.
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