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https://hdl.handle.net/2142/23696
Description
Title
Neutron irradiation effects in gallium arsenide
Author(s)
Patel, Jagdishbhai Umedbhai
Issue Date
1992
Doctoral Committee Chair(s)
Williams, J.G.
Department of Study
Engineering, Electronics and Electrical
Engineering, Nuclear
Discipline
Engineering, Electronics and Electrical
Engineering, Nuclear
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Electronics and Electrical
Engineering, Nuclear
Language
eng
Abstract
Changes in electrical properties of n-GaAs as a result of irradiations with fast neutrons have been studied, after epitaxial layers doped with Si at concentrations in the range 1.35 $\times$ 10$\sp{15}$ to 1.60 $\times$ 10$\sp{16}$ cm$\sp{-3}$ were irradiated with reactor neutron fluences up to 1.31 $\times$ 10$\sp{15}$ cm$\sp{-2}.$ When the changes in carrier concentration, Hall mobility and resistivity were more than 25% of their initial values, nonlinear dependence on neutron fluence was apparent. New theory is proposed which explains the changes in electrical properties in terms of rates of trapping and release of charges. A theoretical relationship is derived for the change in carrier concentration as a function of neutron fluence and doping level. A linear relationship between neutron fluence and Fermi level shift was found to be consistent with the observed changes in carrier concentration.
A correlation has been found between the changes in carrier concentration and mobility with neutron fluence using newly defined physically meaningful parameters in the case of two pairs of samples. The correlation has been explained in terms of the increased scattering of charge carriers from the defects created by neutrons that trap the free carriers.
Mobility changes were measured at temperatures from 15 K to 305 K in n-GaAs van-der Pauw samples irradiated by fast reactor neutrons. The inverse mobility values obtained versus temperature, from the variable temperature Hall measurements, in the case of irradiated and un-irradiated samples were fitted using the relation $\rm\mu\sp{-1}=A\ T\sp{-3/2}+B\ T\sp{3/2}.$ The inverse mobility increased as a result of neutron irradiations over the whole range of temperature, the increase being attributed to the increased scattering from neutron induced charged defects. The values of A found by least square fitting were used to estimate the increased scattering effect from neutron induced ionized defects after each step of irradiation. It is concluded that in order to explain the experimental results presented here, the creation of multiply charged defects must be considered.
Effects of different neutron fields are compared in terms of the damage coefficients for carrier concentration and mobility. The ratio of averaged damage coefficients reflects the hardness of each neutron-energy spectrum with respect to one reference neutron-energy spectrum.
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