Recent advances and future prospects in single-electronics

Abstract

We will introduce new developments in single-electron logic technology and review a few clever applications made possible when single-electron transistors are combined with CMOS.

Detecting Single Photons Using Capacitive Coupling of Single Quantum Dots

“…As elucidated in Working Modes of the Proposed SQDSPD, the operation of the SQDSPD relies on the successful quantum confinement of a single electron or a single hole in the QD. Like in SETs, the strength of the quantum confinement is directly related to the barrier thickness and height, and can be measured by a phenomenological quantity “tunnel resistance” in the small bias limit . To achieve a good confinement for the single charges in the QD, it requires that the tunnel resistance R T satisfies the relationship R T ≫ h / e 2 ≈ 25.8 kΩ, where h is the Planck constant and e is the elementary charge.…”

“…Using the Wentzel–Kramers–Brillouin (WKB) approximation, the tunnel resistance is linked to the barrier thickness through the following equations: where ℏ is the reduced Planck constant, | T | 2 is the tunneling probability through the barrier, D i and D f are, respectively, the density of states on the initial side and on the final side of the tunnel barrier, d is the barrier thickness, m * is the electron or hole effective mass in the tunnel barrier, V ( y ) is the potential energy profile of the barrier for the electron or the hole, and E y is the carrier kinetic energy in the y direction. For the R T estimation, constant V ( y )′ s equal to the band offsets shown in Figure b–e were used.…”

“…Below we estimate the intrinsic timing jitter of Mode II at a sufficiently low temperature by calculating the tunnel rate Γ ed using the Fermi’s golden rule. The transition rate Γ i→f from an initial state i in the QD to a final state f in the metal contact was expressed as where | T if | 2 was the tunneling probability from the initial state to the final state, E i and E f were, respectively, the energies of the initial and final state, and Δ F was the free energy change of the system caused by the transition. The delta function ensured that the energy was conserved for the transition process.…”

“…It was assumed that only one energy level in the QD was involved in the transition. Due to its finite width, the DOS of the quantized energy level in the QD was approximated with a Lorentzian function: where Γ was the electron transition rate. It was essentially the tunnel rate Γ ed in Figure c since it was assumed that Γ ed ≫ Γ r .…”

“…Increase of the gate bias to V bg2 from V bg1 puts the device again into the Coulomb blockade state and leads to the trapping of an electron in the QD (Figure c). In practice, drain and gate biases used in Figure b and Figure c can be determined from the stability diagram of the device . Once a single photon with proper energy is absorbed by the QD, the trapped electron is promoted to the ES (Figure d).…”