Structure and dynamics of vacancies on GaAs(110) studied by scanning tunneling microscopy /
The properties of single-atom vacancies at As and Ga sites on the (II()) cleavage face of GaAs have been studied with the scanning tunneling microscope (STM). Ga vacancies are found on degenerate n-type (but not p-type) material, and are negatively charged, whereas As vacancies occur on degenerate...
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| Format: | Thesis Book |
| Language: | English |
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[Place of publication not identified] :
[publisher not identified] ;
1995.
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| Online Access: | http://proxy.library.tamu.edu/login?url=http://proquest.umi.com/pqdweb?did=742744861&sid=1&Fmt=2&clientId=2945&RQT=309&VName=PQD |
| Summary: | The properties of single-atom vacancies at As and Ga sites on the (II()) cleavage face of GaAs have been studied with the scanning tunneling microscope (STM). Ga vacancies are found on degenerate n-type (but not p-type) material, and are negatively charged, whereas As vacancies occur on degenerate p-type (but not n -type) samples, and are positively charged. Simple electron counting arguments are used to rationalize the correlation of both vacancy abundance and charge state with bulk doping. At As vacancies, nearest-neighbor Ga atoms in the same zigzag chain exhibit a small upward shift but no detectable lateral displacements. This phenomenon is interpreted as a local reversal of the native surface relaxation. Small lateral displacements of the neighboring As atoms are found at Ga vacancies, but vertical shifts, if any, are obbscured by electronic effects. Measurements of the current-voltage characteristics directly over an As vacancy establish that the surface Fermi level shifts into the bulk and gap, but remains close to the valence-band edge. Similar measurements over a Ga vacancy indicate the local Fermi-level shifts a larger amount into the band gap, but remains close to the conductionband edge Tip-induced migration of surface vacancies has also been observed. In the case of As vacancies, this motion is highly anisotropic, occurring much more frequently across the surface zigzag chains than along them, whereas the motion of Ga vacancies is more nearly isotropic. Because of the polar nature of the material, the surface bonding is asymmetric under mirror reflection in a (001) plane, and vacancy migration is sensitive to this fact: As vacancies may move in the [001], but not [001], direction, whereas the behavior of Ga vacancies is the opposite. This migration also depends strongly on the bias polarity of the STM tip: motion occurs only when minority carriers are injected into the surface in close proximity to the defect site. The mechanism responsible for vacancy migration on GaAs(I 10) is the surface analogue of a well-known bulk phenomenon, the recombination enhanced defect reaction (REDR). |
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| Item Description: | Vita. "Major Subject: Physics". In title, numerals are used. |
| Physical Description: | xii, 118 leaves : illustrations ; 28 cm. Issued also on microfiche from University Microfilms Inc. |
| Bibliography: | Includes bibliographical references. |