  We examine the radiation induced modification of the Hall effect in high
mobility GaAs/AlGaAs devices that exhibit vanishing resistance under microwave
excitation. The modification in the Hall effect upon irradiation is
characterized by (a) a small reduction in the slope of the Hall resistance
curve with respect to the dark value, (b) a periodic reduction in the magnitude
of the Hall resistance, $R_{xy}$, that correlates with an increase in the
diagonal resistance, $R_{xx}$, and (c) a Hall resistance correction that
disappears as the diagonal resistance vanishes.
