Single-Electron Dynamics of an Atomic Silicon Quantum Dot on theH−Si(100)−(2×1)Surface

Abstract

Here we report the direct observation of single electron charging of a single atomic Dangling Bond (DB) on the H-Si(100) 2 × 1 surface. The tip of a scanning tunneling microscope is placed adjacent to the DB to serve as a single electron sensitive charge-detector. Three distinct charge states of the dangling bond, positive, neutral, and negative, are discerned. Charge state probabilities are extracted from the data, and analysis of current traces reveals the characteristic single electron charging dynamics. Filling rates are found to decay exponentially with increasing tip-DB separation, but are not a function of sample bias, while emptying rates show a very weak dependence on tip position, but a strong dependence on sample bias, consistent with the notion of an atomic quantum dot tunnel coupled to the tip on one side and the bulk silicon on the other.

Scanning tunneling spectroscopy reveals a silicon dangling bond charge state transition

“…If we further reduce the voltage to -1.4 V, -1.3 V and -1.2 V as seen in figures 5(i)-(k), respectively, the halo surrounding the dark DB becomes more and more extended. This can be explained by the effect of the TIBB, similarly to what was reported for empty-state imaging of DBs [22,23]. Indeed, the TIBB and the tunneling current from the silicon sample increase as the voltage is increased.…”

“…This was modeled in an earlier study by Livadaru et al [26] and was shown to arise from the nonequilibrium charging of the DB during STM imaging in unoccupied states. The dynamic aspect of it could be accessed experimentally using a low-temperature scanning tunneling microscope by studying the telegraph noise seen on the edge of the halo surrounding the DB [23].…”

“…Interestingly, other studies showed that a DB can be considered as a single-atom quantum dot [20][21][22][23] and thus can be used to build charge quantum bits (qubits) [21], artificial molecules [22,24], quantum-dot cellular automata (QCA) cells [20,25] and QCA-based circuits [20,24]. The important property allowing such consideration is the DB's quantized charge state levels lying in the silicon bandgap.…”

“…The important property allowing such consideration is the DB's quantized charge state levels lying in the silicon bandgap. In fact, a DB can be either empty, singly, or doubly occupied, which corresponds, respectively, to the DB being positive(DB + ), neutral (DB 0 ), or negative(DB -) [20,22,23,26]. This makes conduction through the DB predominantly governed by tunneling rates through its charge states [22,[26][27][28], hence, the quantum dot analogy.…”

The butterfly – a well-defined constant-current topography pattern on Si(001):H and Ge(001):H resulting from current-induced defect fluctuations

“…These charge related halos have been consistently reported for single DBs, 19,21 but are completely absent when imaging DBDs. For single DBs it is typically possible to generate long-lived charged states that cause bright/dark halos in the STM images around the defects depending on the charge state and imaging conditions.…”