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

Abstract

A model is proposed to explain the charge-induced confinement enhancement observed 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 potential 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 charging. Given the charge on the floating dot, the spatial confinement and the energy level spacing increase induced by the charging can be obtained. The calculation based on the model agrees with the observed increase of the energy level spacing.