Background charges and quantum effects in quantum dots transport spectroscopy

Abstract

We extend a simple model of a charge trap coupled to a single-electron box to energy ranges and parameters such that it gives new insights and predictions readily observable in many experimental systems. We show that a single background charge is enough to give lines of differential conductance in the stability diagram of the quantum dot, even within undistorted Coulomb diamonds. It also suppresses the current near degeneracy of the impurity charge, and yields negative differential lines far from this degeneracy. We compare this picture to two other accepted explanations for lines in diamonds, based respectively on the excitation spectrum of a quantum dot and on fluctuations of the density-of-states in the contacts. In order to discriminate between these models we emphasize the specific features related to environmental charge traps. Finally we show that our model accounts very well for all the anomalous features observed in silicon nanowire quantum dots.

Localization effects in the tunnel barriers of phosphorus-doped silicon quantum dots

“…1). Such feature could be found in single quantum dot where additional parallel channels via edge states are opened for tunneling or when trap-assisted tunneling is present 13 or in the case of spin dependent transport. 14 Here, the position of the NDC clearly follows the shape of the Coulomb diamonds, at a fixed distance from their edges.…”

Quantum dot spectroscopy using a single phosphorus donor

“…Since in the lower bias triangle the total observed SET current is proportional to the average fraction of the time the donor is unoccupied, the observed SET current is thus significantly reduced along the resonance lines. Reductions in the conductivity such as we see have also been explained using a model of a single charge trap [15]. However, for this to explain the features we see would require multiple accidental charge traps in the vicinity of the quantum dot, each with indistinguishable capacitive couplings to the gates, a possibility we find very unlikely.…”

Single-dopant resonance in a single-electron transistor

“…We observe between 1 and 5 of such anomalies in each device in different ranges of the top-gate voltage V g . In previous reports of anomalous behaviour of the SET 25,[27][28][29] , the coupling between the SET island and the single dopants has been predominantly capacitive. Here we observe dramatic increase of the current through the SET due to resonant tunneling through single dopants.…”

“…(A13) can be interpreted as a kinetic energy term, and thus, can be included into the kinetic-energy term of Eq. (27) as an additional energy level in the SET island. The second term represents the usual Coulomb energy of an island, with the difference that the donor appears as part of that island too (the total charge being n+N ).…”