Charging effects and bistability in resonant quantum wire structures

Abstract

Ballistic electron transport in resonant quantum-wire structures (double point contacts in series) is investigated taking into account charge build-up effects. It is shown that when the resonant condition holds (i.e. when the Fermi energy of incoming electrons coincides with the energy of the quasibound state), the charge stored in the structure may lead to a bistable behaviour of the system. In the linear-response approximation, when the current flowing through the structure is described by the two-terminal Landauer formula, a closed non-linear equation is derived relating the transmitted current to the energy of the resonant level and the width of the resonance Gamma . It is shown that the condition that must be satisfied for bistability to occur is e3V/ pi C Gamma 2>or approximately=1, where V is the applied bias and C is the capacitance of the structure. The dependence of the width of the resonant level and its position on the device geometry is investigated using the match-mode technique for calculations of the electron transmission coefficient. The width of the resonance is shown to increase with increasing length of the contacts, but the position of the resonant level (in units of the propagation threshold energy in the contact regions) is insensitive to the length of the contacts as well as to the lengths of the side arms. On the basis of the results obtained, the bistability in the I-Vg characteristic (current-gate voltage) is studied for structures of realistic dimensions.