Kok Wai Chan

Transport Spectroscopy of Single Phosphorus Donors in a Silicon Nanoscale Transistor

We have developed nanoscale double-gated field-effect-transistors for the study of electron states and transport properties of single deliberately implanted phosphorus donors. The devices provide a high-level of control of key parameters required for potential applications in nanoelectronics. For the donors, we resolve transitions corresponding to two charge states successively occupied by spin down and spin up electrons. The charging energies and the Lande g-factors are consistent with expectations for donors in gated nanostructures.

Observation of the single-electron regime in a highly tunable silicon quantum dot

We report on low-temperature electronic transport measurements of a silicon metal-oxidesemiconductor quantum dot, with independent gate control of electron densities in the leads and the quantum dot island. This architecture allows the dot energy levels to be probed without affecting the electron density in the leads and vice versa. Appropriate gate biasing enables the dot occupancy to be reduced to the single-electron level, as evidenced by magnetospectroscopy measurements of the ground state of the first two charge transitions. Independent gate control of the electron reservoirs also enables discrimination between excited states of the dot and density of states modulations in the leads.

Probe and control of the reservoir density of states in single-electron devices

We present a systematic study of quasi-one-dimensional density of states (DOS) in electron accumulation layers near a Si–SiO2 interface. In the experiments we have employed two conceptually different objects to probe DOS, namely, a phosphorus donor and a quantum dot, both operating in the single-electron tunneling regime. We demonstrate how the peaks in DOS can be moved in the transport window independently of the other device properties, and in agreement with the theoretical analysis. This method introduces a fast and convenient way of identifying excited states in these emerging nanostructures.

Electron counting in a silicon single-electron pump

We report electron counting experiments in a silicon metal-oxide-semiconductor quantum dot architecture which has been previously demonstrated to generate a quantized current in excess of 80 pA with uncertainty below 30 parts per million. Single-shot detection of electrons pumped into a reservoir dot is performed using a capacitively coupled single-electron transistor. We extract the full probability distribution of the transfer of n electrons per pumping cycle for We find that the probabilities extracted from the counting experiment are in agreement with direct current measurements in a broad range of dc electrochemical potentials of the pump. The electron counting technique is also used to confirm the improving robustness of the pumping mechanism with increasing electrostatic confinement of the quantum dot.

Three-waveform bidirectional pumping of single electrons with a silicon quantum dot

Semiconductor-based quantum dot single-electron pumps are currently the most promising candidates for the direct realization of the emerging quantum standard of the ampere in the International System of Units. Here, we discuss a silicon quantum dot single-electron pump with radio frequency control over the transparencies of entrance and exit barriers as well as the dot potential. We show that our driving protocol leads to robust bidirectional pumping: one can conveniently reverse the direction of the quantized current by changing only the phase shift of one driving waveform with respect to the others. We anticipate that this pumping technique may be used in the future to perform error counting experiments by pumping the electrons into and out of a reservoir island monitored by a charge sensor.

A silicon single-electron pump with tunable electrostatic confinement

Nanoscale single-electron pumps could serve as the realization of a new quantum standard of electrical current. Here, a silicon quantum dot with tunable tunnel barriers is used as a source of quantized current. By controlling the electrostatic confinement of the dot via purposely engineered gate electrodes, we show that the stability of the pumping mechanisms can be dramatically enhanced. Our pump can produce a current in excess of 80 pA with experimentally determined relative uncertainty lower than 50 parts per million (ppm).

Effects of electrostatic confinement in a silicon single-electron pump

Nanoscale single-electron pumps could serve as the realization of a new quantum standard of electrical current. Here, a silicon quantum dot with tunable tunnel barriers is used as a source of quantized current. By controlling the electrostatic confinement of the dot via purposely engineered gate electrodes, we show that the robustness of the pumping mechanism can be dramatically enhanced and the detrimental effects due to non-adiabatic transitions are largely reduced. Our pump can produce a current in excess of 80 pA with experimentally determined relative uncertainty lower than 50 parts per million.

Independent Control of Dot Occupancy and Reservoir Electron Density in a One‐electron Quantum Dot

We report on low‐temperature electronic transport measurements and Technology Computer Aided Design (TACD) modeling of a silicon metal‐oxide‐semiconductor (MOS) quantum dot, with independent gate control of electron densities in the leads and the quantum dot island. This architecture allows the dot energy levels to be probed without affecting the electron density in the leads and vice versa. Appropriate gate biasing enables the dot occupancy to be reduced to the single‐electron level. Independent gate control of the electron reservoirs also enables discrimination between excited states of the dot and density of states (DOS) modulations in the leads.