The changes in electrical properties of n-GaAs as a result of irradiations with fast neutrons have been studied. Epitaxial layers doped with Si at concentrations in the range 1.35×1015 to 1.599×1016 cm−3 were irradiated with reactor neutron fluences up to 1.31×1015 cm−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.
Mobility changes were measured at temperatures from 15 to 305 K in n-GaAs van der Pauw samples irradiated by fast reactor neutrons. The inverse mobility values, obtained from the variable temperature Hall measurements were fitted using the relation μ−1=AT−3/2+BT3/2. The inverse mobility was found to increase as a result of neutron irradiations over the whole range of temperature; the increase is attributed to the increased scattering from neutron induced charged defects. The values of A found by the 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.
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