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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
Doctoral Committee Chair(s):Sah, C.T.
Department / Program:Physics
Subject(s):thermal emission rates
optical cross sections
carriers at gold centers
impurity photovoltaic effect
recombination generation
optical behavior of impurities
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,
Issue Date:1969
Genre:Dissertation / Thesis
Rights Information:1969 Aloysious Felix Tasch, Jr.
Date Available in IDEALS:2011-07-13
Identifier in Online Catalog:6067277

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