EDMR
The goal of this research project is to study the coherence of phosphorus electron spins in silicon using electrically detected magnetic resonance (EDMR) as readout method. To this end, we developed a silicon MOSFET device that can be cooled down to mK temperatures and subject to strong magnetic fields in a dilution refrigerator. In contrast to conventional cavity-based EPR experiments, here the oscillating magnetic field, required for magnetic resonance, is applied to the device by a terminated coplanar stripline (CPS) which allows broadband operation. The EDMR technique is much more sensitive to small number of spins as compared to standard EPR. Recently we implemented a radio frequency detection scheme for EDMR with a bandwidth of about 20 MHz. This technique would be the candidate for the study of spin coherence in pulsed microwave EDMR experiments.
In an external DC magnetic field the phosphorous electron spins precess with the Larmor frequency. An applied microwave field tuned into resonance with this precession frequency leads to rotations of the phosphorus spins, subsequently changing the spin-dependent scattering with the gate induced free electrons in the MOSFET channel. Either magnetic field modulation or microwave frequency modulation can be used for phase-sensitive detection of the resonant current change to be measured. This EDMR spectroscopy allows the observation of the hyperfine splitting for Si:P and the identification of other resonances, such as exchange-coupled spin pairs and conduction band electrons.
In an external DC magnetic field the phosphorous electron spins precess with the Larmor frequency. An applied microwave field tuned into resonance with this precession frequency leads to rotations of the phosphorus spins, subsequently changing the spin-dependent scattering with the gate induced free electrons in the MOSFET channel. Either magnetic field modulation or microwave frequency modulation can be used for phase-sensitive detection of the resonant current change to be measured. This EDMR spectroscopy allows the observation of the hyperfine splitting for Si:P and the identification of other resonances, such as exchange-coupled spin pairs and conduction band electrons.
Si QDs
The goal of this research project is to study the electrical transport properties of electrostatically-defined silicon (double) quantum dots (QDs) in silicon. We aim to push the occupancy of the dots to the single electron level in order to study the spin-properties in such systems.
The silicon quantum dots are fabricated by patterning two aluminum barrier gates using electron-beam lithography, followed by subsequent oxidation. An aluminum top gate is then fabricated and covers the ohmic regions on the wafer in order to accumulate an electron gas. The barrier gates are used to induce a potential well that defines the quantum dot. Bias spectroscopy is performed at cryogenic temperatures to study the energy level diagrams in this system. A Si QD can also be used in electrometry experiments, where the dot acts as a charge sensor.
The silicon quantum dots are fabricated by patterning two aluminum barrier gates using electron-beam lithography, followed by subsequent oxidation. An aluminum top gate is then fabricated and covers the ohmic regions on the wafer in order to accumulate an electron gas. The barrier gates are used to induce a potential well that defines the quantum dot. Bias spectroscopy is performed at cryogenic temperatures to study the energy level diagrams in this system. A Si QD can also be used in electrometry experiments, where the dot acts as a charge sensor.
Si NWs
The goal of this research project is to study the electrical transport properties of chemically synthesized Si nanowires. Furthermore, we will investigate the feasibility of implementing electron spin qubits in Si based (e.g. Si/SiGe) nanowire quantum dots (QDs).
The silicon nanowires are chemically synthesized by the vapour-liquid-solid (VLS) growth technique and subsequently processed in order to define source and drain contacts for electrical characterization. To define quantum dots in these electrically contacted nanowires, a set of narrow finger gates is fabricated by electron beam lithography to locally create tunable tunnel barriers. This device is then subject to electrical transport measurements, such as voltage bias and magnetic field spectroscopy. These give us detailed knowledge of the systems energy spectrum. Furthermore, a nearby aluminum SET can be incorporated in an rf-circuit for fast and sensitive sensing of the charge state of the QD. A pulse scheme can be implemented for single shot electron spin readout, from which we extract the electron spin lifetime.
The silicon nanowires are chemically synthesized by the vapour-liquid-solid (VLS) growth technique and subsequently processed in order to define source and drain contacts for electrical characterization. To define quantum dots in these electrically contacted nanowires, a set of narrow finger gates is fabricated by electron beam lithography to locally create tunable tunnel barriers. This device is then subject to electrical transport measurements, such as voltage bias and magnetic field spectroscopy. These give us detailed knowledge of the systems energy spectrum. Furthermore, a nearby aluminum SET can be incorporated in an rf-circuit for fast and sensitive sensing of the charge state of the QD. A pulse scheme can be implemented for single shot electron spin readout, from which we extract the electron spin lifetime.