Coulomb staircase in theI-Vcharacteristic of an ultrasmall double-barrier resonant-tunneling structure

An analytical study is presented for the Coulomb staircase in the I-V curve of an ultrasmall double-barrier resonant-tunneling system. Below a certain threshold voltage V₁, the charging effect of a single electron in the ultrasmall confinement makes the tunneling current I₀=0 at very low temperature. As the voltage V rises above V₁ but below V₂ at which the charging energy is overcome, the first step of current I₁ shows up. When V becomes even greater than V₂, both the charging energy and the Coulomb repulsion between two electrons of opposite spin are overcome and the current jumps onto the second step I₂. The ratio between the two current steps (I₂-I₁)/(I₁-I₀) depends upon the ratio of the tunneling rates of the two barriers. Our results agree well with a recent experiment by Su, Goldman, and Cunningham.