Planar tunneling spectroscopy of thin-film Nb, Nb/normal metal and Nb/semiconductor structures
Abeyta, Adam Christopher
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https://hdl.handle.net/2142/31248
Description
Title
Planar tunneling spectroscopy of thin-film Nb, Nb/normal metal and Nb/semiconductor structures
Author(s)
Abeyta, Adam Christopher
Issue Date
2000
Doctoral Committee Chair(s)
Greene, Laura H.
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
thin films
planar tunneling spectroscopy
niobium
semiconductors
Language
en
Abstract
The electrical characteristics of thin film niobium, and tunnel junctions formed between thin-film
niobium and both normal metals and semiconductors have been investigated. A thickness dependence
of the superconducting critical temperature Tc and the superconducting gap parameter Δ
have been observed for thin film superconductor/normal metal structures. Although many studies
exist, the underlying mechanism is not fully understood. The niobium-semiconductor system offers
new opportunity to investigate superconductor/normal metal interfaces and holds promise for
microelectronics applications. Studies of the electrical transport across the interface between the
two materials are presented.
The thickness dependence study was performed on high-quality, DC-magnetron sputter deposited
Nb on single-crystal sapphire. The DC resistivity was measured as a function of ternperature
to evaluate the film quality and determine Tc. The critical temperature was found to
monotonically decrease with decreasing thickness, consistent with existing theory. Additionally,
the superconducting gap 2Δ was measured as a function of film thickness for Nb/Al2O 3/Ag tunnel
junctions. This value was found to also decrease monotonically with decreasing thickness. Furthermore,
the first observation of an increase in the ratio of 2Δ(0)/kBTc with decreasing thickness is presented.
The superconductor-semiconductor study was performed on Nb-InGaAs bilayers. The Schottky
barrier formed at the interface between these two materials was utilized as a tunneling barrier. A
method was developed to fabricate small area junctions. The tunneling conductance as a function
of semiconductor properties and sample temperature have been found to be consistent with results
reported in the literature.
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