Studies of thermal emission rates and optical cross sections of carriers at gold centers in silicons using the impurity photovoltaic effect
Tasch, Aloysious Felix
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https://hdl.handle.net/2142/25788
Description
Title
Studies of thermal emission rates and optical cross sections of carriers at gold centers in silicons using the impurity photovoltaic effect
Author(s)
Tasch, Aloysious Felix
Issue Date
1969
Doctoral Committee Chair(s)
Sah, C.T.
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
thermal emission rates
optical cross sections
carriers at gold centers
silicon
impurity photovoltaic effect
recombination generation
optical behavior of impurities
Language
en
Abstract
A new method for studying the recombination-generation and
optical behavior of impurities in semiconductors is presented. This
method is known as the impurity photovoltaic effect. The basic idea
of the impurity photovoltaic effect is to study the photo-response
of a reverse biased PIN junction that, is doped with the impurity of
interest. The energy of the incident photons is less than, the
forbidden energy band·gap but greater tban the impurity ionization
energy. From the photocurrent it is possible to determine the
thermal emission (or generation) rates and photoionization cross
sections of carriers from the impurity centers! This information
may be obtained without knowledge of the impurity concentration.
The impurity photovoltaic effect is applied to study the
acceptor level of gold in silicon. The thermal ,emission rates of
electrons and holes from negatively ionized and neutral gold atoms,
respectively, are determined as a function of temperature in the
range 1950 -300oK. It is concluded that the gold is mostly in the
neutral charge state in the depletion region of a PN junction.
Capture rates and capture cross sections are also deduced ,from the
thermal emission rates. The results are not too definite since they
are sensitive to the exact location of the gold acceptor level and
the degeneracy factor associated with the acceptor level.
The electric field dependence of the thermal emission rates is
measured and can be explained qualitatively by the Poole-Frenkel effect.
The measured field dependences are compared with the field dependence·
calculated from the Poole-Frenkel model for Coulomb, square well,
and polarization potentials. Partial agreement with the square well
and polarization potentials is obtained, indicating that the
impurity potential as seen by an electron or hole is not of the long range
Coulomb type. Rather it appears to be short range in nature.
The photoionization cross sections of electrons and holes from
negatively charged and neutral gold atoms are also measured in the
spectral range .57-.8gev. The hole photoionization cross section
is compared with an expression derived by Lucovsky. Thea greement
is fairly good for reasonable choices of the effective field ratio and
the effective mass of the bcmnd hole. The electron photoionization
cross section is compared with a theoretical expression derived by
Eagles and Dumke. The agreement is poor and is probably.due to the
deviation of gold in silicon from the model and assumptions employed
by Eagles and Dumke. The photoionization cross sections are checked
for electric field dependence. There appears to be little or no field
dependence in the range 3-14xlO 4 volts/cm.
The location of the acceptor level is estimated from the spectral
dependence of the photoionization cross sections. The result of
.53-.55ev for the location of the acceptor level below the conduction
band is in good agreement with the other reported results,
The theory for the impurity photovoltaic effect is analyzed with
the donor level included. The results are compared with those that
follow from the single-level treatment. The comparison indicates
that the single7level treatment is a very good approximation for
photon energies less than .8ev,
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