Application restrictions for two-level models of the resonance interaction of electrons with an alternating electric field in two-barrier structures

We analyze the applicability of different variants of the two-level approximation in the problem of electron transitions in a two-barrier structure with current pumping in a resonant electric field of finite amplitude. We show that the solution obtained by a direct iteration of the perturbation method of the first order in the field amplitude can be essentially continued outside the convergency domain of the iteration procedure. On the other hand, the two-level approximation becomes invalid at field amplitudes much smaller than commonly assumed ones because of the influence of side satellites, the nonresonant components of the wave function.