We propose here a model for the pair tunneling states observed by Ashoori et al. [Phys. Rev. Lett. 68, 3088 (1992)] in GaAs quantum dots. We show that, while GaAs is a weakly polar semiconductor, coupling to optical phonons is sufficiently strong to mediate a negative- U pairing state. The physical potential in which the two electrons are bound can be composed of a Si impurity and a parabolic well that originates from the potential created by the dopants in the backing layer of the dot. Such a pair state breaks up at moderate magnetic field strengths (2 T), as is seen experimentally, and is unstable when the confining radius of the dot is smaller than 400.
ASJC Scopus subject areas
- Physics and Astronomy(all)