Charge-ring model for the charge-induced confinement enhancement in stacked quantum-dot transistors

A model is proposed to explain the charge-induced confinement enhancement o bserved in a stacked quantum-dot transistor that has a floating dot on top of a channel quantum dot. The model assumes that the charge on the floating dot distributes on its rim, forming a ring and creating a confinement pote ntial that squeezes the electrons in the channel dot toward its center. The charge on the floating dot can be calculated from the device geometry and from the measured threshold voltage difference before and after the chargin g. Given the charge on the floating dot, the spatial confinement and the en ergy level spacing increase induced by the charging can be obtained. The ca lculation based on the model agrees with the observed increase of the energ y level spacing. (C) 1998 American Institute of Physics. [S0003-6951(98)048 49-9].