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https://hdl.handle.net/2142/23287
Description
Title
Photo-Hall studies of compound semiconductors
Author(s)
Kim, Matthew Hidong
Issue Date
1989
Doctoral Committee Chair(s)
Stillman, Gregory E.
Department of Study
Physics
Discipline
Physics
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Physics, Condensed Matter
Language
eng
Abstract
The III-V compound semiconductor materials are used in a wide variety of electronic, optoelectronic and microwave device applications. Temperature dependent photo-Hall effect measurements have been made on the high purity compound semiconductors GaAs, InP and a ternary alloy In$\sb{0.53}$Ga$\sb{0.47}$As. The major emphasis of this work involves the phenomenon of persistent photoconductivity. This phenomenon has been used to facilitate the electrical characterization of homogeneous and inhomogeneous thin epitaxial semiconductor layers. This effect is associated with a reduction in the surface and substrate interface depletion that occurs upon illumination of the sample with above band gap light at cryogenic temperatures. After illumination, the effects of a photoinduced charge neutral region persists, until at higher temperatures, the sample relaxes back to its original state. For homogeneous layers, the mobility, which is a measure of the microscopic quality of the crystal, remains unchanged after illumination. The persistent photoeffect strictly results from the increase in the effective electrical thickness of the layer. By utilizing the persistent photoeffect, electrical measurements have been made on thin high purity GaAs, which was semi-insulating in the dark because of surface and interface depletion.
The effects of illumination of inhomogeneous materials has also been studied. Hall measurements on inhomogeneous GaAs and InP layers in the dark show no unusual features. When these layers are illuminated with above band gap light at low temperatures, anomalous values for the mobility and carrier concentration have been measured. In one metalorganic chemical vapor deposition (MOCVD) grown GaAs sample, the low temperature mobility was decreased by two orders of magnitude after illumination. These particular results have their origin in the occurrence of an accumulation of impurities at the epilayer-substrate interface. The presence of this doping spike is not detected when electrical measurements are made in the dark because of the interface depletion.
These results clearly show that the persistent photo-Hall (i.e., Hall data taken with momentary illumination of the sample with above band gap light at low temperatures) is a powerful method for looking at the electrical properties of thin high purity semiconductors.
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