Spectroscopic characterization of the near-surface electronic structure of surface-modified III-V semiconductors
Dorsten, Jeffrey F.
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https://hdl.handle.net/2142/20298
Description
Title
Spectroscopic characterization of the near-surface electronic structure of surface-modified III-V semiconductors
Author(s)
Dorsten, Jeffrey F.
Issue Date
1996
Doctoral Committee Chair(s)
Bohn, Paul W.
Department of Study
Chemistry
Discipline
Chemistry
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Electronics and Electrical
Physics, Condensed Matter
Engineering, Materials Science
Language
eng
Abstract
Investigations of the near-surface electronic structure of n$\sp+$-GaAs and n$\sp+$-InAs are presented. Recent studies of the GaAs surface have been carried out which demonstrate that the surface states which arise from termination of the crystal lattice, which are known to cause pinning of the Fermi energy level and an increase in the Schottky barrier in the semiconductor, can be passivated using inorganic sulfides. Although treatment with the inorganic sulfides is effective in reducing the surface recombination velocity, the loss of the surface As atoms during the treatment causes an electronic reorganization in the semiconductor which actually pins the Fermi level closer to the valence band and subsequently increases the band-bending at the surface. In this research, passivation with a long-chain alkane thiol demonstrates the ability to passivate the surface while unpinning the Fermi level and reducing the surface band-bending. This change is measured quantitatively by applying Raman spectroscopy is a probe of the near-surface region. The distinct electronic regions of the semiconductor surface can be differentiated by monitoring the predominant crystal vibrations from each region which give rise to Raman scattering.
In a second system, Raman spectroscopy is again used to probe the surface electronic characteristics of a semiconductor. A semiconductor/superconductor interface is investigated to explore Cooper pair transport across the interface while the system is in a superconducting state. Previous investigations of a Nb/InGaAs system show an anomalous current at zero bias which arises when the system is superconducting. However, this phenomenon is not explained by current superconducting models. Typical contact probes which are often used to investigate small superconducting currents are difficult to employ in this system, so the Raman optical probe was used to carry out the research. An InAs/Nb structure was fabricated such that an Ohmic contact was made to provide a barrier-free interface for electron flow. The temperature of the system was lowered below the superconducting transition temperature and the resulting optical measurements were compared to those of the system taken in a normal state. These initial investigations show a change in the electronic character of the InAs supporting a case for Cooper pair transport in the system.
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