An exact solution of the equation describing the dynamics of the current generation in the avalanche region of the Read diode is presented. The avalanche current is composed of a transient component and a steady-state component. For ac diode excitation the latter one contains a large number of harmonics. A brief study, in which the space-charge effect is neglected, illustrates the usefulness of the presented solution. A threshold frequency is defined which characterizes the avalanche current transients and specifies the range of validity of the resuits obtained by commonly used simplified approaches.