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

Abstract

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 ${\mathit{V}}_1$, the charging effect of a single electron in the ultrasmall confinement makes the tunneling current ${\mathit{I}}_0$=0 at very low temperature. As the voltage V rises above ${\mathit{V}}_1$ but below ${\mathit{V}}_2$ at which the charging energy is overcome, the first step of current ${\mathit{I}}_1$ shows up. When V becomes even greater than ${\mathit{V}}_2$, both the charging energy and the Coulomb repulsion between two electrons of opposite spin are overcome and the current jumps onto the second step ${\mathit{I}}_2$. The ratio between the two current steps (${\mathit{I}}_2$-${\mathit{I}}_1$)/(${\mathit{I}}_1$-${\mathit{I}}_0$) 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.