A. Gunther

Spectroscopy of a silicon quantum dot

We have fabricated a silicon quantum dot embedded in a metal–oxide–semiconductor field-effect transistor structure. Two side gates deplete the quasi-two-dimensional electron gas created by a top inversion gate. We have tested devices ranging in size from 40 to 200 nm. By varying the density with the top gate, the conductance peaks reveal the details of the energy-level structure within the dot and their interactions with one another.

Silicon Quantum Dot in a Metal-Oxide-Semiconductor Field Effect Transistor (MOSFET) Structure

We have fabricated a 200 nm quantum dot in a silicon Metal-Oxide-Semiconductor Field Effect Transistor (MOSFET) structure. Confining gates situated on top of a 10 nm oxide deplete the electron gas created by an inversion gate 70 nm away from the Si-SiO2 interface. Measurements indicate that the size of the dot can be tuned by the gates. Furthermore, we observe conductance fluctuations in the gate characteristic which are indicative of single-electron behavior.

3D simulation of GaAs/AlGaAs quantum dot point contact structures

We present simulation results for the activation barrier O 0 and the number of electrons N in a quantum dot structure that are obtained from the self-consistent solution of the 3D Schrodinger-Poisson problem. We observe an approximately linear rise in the electrostatic barrier O 0 as a function of the gate bias once pinchoff occurs. There is an associated linear decrease in the number of the electrons in the dot region. Calculated values of O 0 and N are in an agreement with those utilized in the energy balance analysis for similar structure investigated experimentally in connection with negative conductance behaviour. The simulation results also suggest that, if the dot area is too small, all particles may be depleted from the dot before the input and output barrier forms, thus preventing the bistable operation.

Acoustic phonon scattering in silicon quantum dots

Intravalley acoustic phonon scattering of electrons in fully quantized systems based on n-type inversion layers on a (100) surface of p-type Si is studied theoretically. The confining potential normal to the Si/SiO2 interface is modelled by a triangular quantum well. For the confinement in the lateral directions we assume a parabolic potential. The calculations reveal that the anisotropic electron-acoustic-phonon interaction strongly affects the scattering rate and the average scattering angle. The calculated transition rate of electrons from the first excited state to the ground state shows a strong dependence on spatial confinement and lattice temperature, with the longitudinal phonon mode giving the main contribution to the total rate.

Single-electron charging effects in Si MOS devices

Abstract Single-electron charging of small quantum dot structures has been observed for many years. Only recently, however, have the effects been observed in Si device structures suitable for integration into other Si technologies. In this talk, the background of work in Si will be reviewed and its applications to unique device and circuit architectures will be discussed. Experimental results obtained using double-gated quantum dots embedded within a Si MOSFET will be discussed. While the present results are primarily at low temperature, they promise the application of single-electron technology to more integrated circuitry.

Single electron effects in silicon quantum dots in a MOSFET structure

We have fabricated silicon quantum dot devices based on a dual gate technique. Two lateral gates deplete the inversion layer which is induced by a top gate, thus forming a quantum dot located between the source and drain of a long channel MOSFET. Lithographic dimensions of the dots ranged from 40 nm to 200 nm. Measurements at low temperatures indicate that electrostatic confinement reduces the dot size to 15 nm. We observe evidence of quantum effects as we step the fermi energy by the top gate as well as magnetic field.

Compatibility of cobalt and chromium depletion gates with RPECVD upper gate oxide for silicon-based nanostructures

Three-dimensional confinement of electrons in silicon-based nanodevices may be achieved using a dual gate structure to confine carriers laterally in a 2D MOSFET inversion layer. We have investigated the temperature stability of cobalt and chromium for thin depletion gates, using remote plasma enhanced chemical vapour deposited (RPECVD) SiO 2 for the deposited dielectric. The thermal stability of the oxide/metal/oxide structure for various annealing regimes was studied by Auger electron spectroscopy sputter profiling and high-resolution cross-sectional transmission electron microscopy. Improvements to the RPECVD oxide for comparable annealing were characterized by electrical measurements on MOS capacitors made from deposited RPECVD oxide.

Transport in split gate MOS quantum dot structures

We have fabricated symmetric 200 nm and asymmetric 100 by 200 nm quantum dots by the split gate technique within a MOSFET structure. DC electrical and magnetotransport measurements were performed at 4.2 K in a liquid-Helium cryostat. It is found that varying the electrochemical potential by changing the bias on a top gate leads to oscillations in the DC conductance through the dot resembling Coulomb blockade peaks, but when the depletion gate biases are swept, these peaks become more complex in nature, exhibiting crossing or anti-crossing behavior.

Silicon quantum dots in a MOSFET structure: level structure

We have fabricated silicon quantum dot devices based on a dual gate technique in a silicon MOS technology. Two lateral gates deplete the inversion layer which is induced by a top gate, thus forming a quantum dot. Hence, the dot is located between the source and drain of a long channel MOSFET. Here, we report on the dependence of the charging of the dot with variation in the top gate, as well as a study of the magnetic field effect on the energy level structure.

Electron relaxation in silicon quantum dots by acoustic phonon scattering

Acoustic phonon scattering of electrons in fully quantized systems based on n-type inversion layers on a [100] surface of p-type Si is studied theoretically. The confining potential normal to the Si/SiO/sub 2/ interface is modeled by a triangular quantum well. For the confinement in the lateral directions we assume a parabolic potential. The calculations reveal that the anisotropic electron-phonon interaction strongly affects the scattering rate. The calculated transition rate of electrons from the first excited to the ground state shows a strong dependence on spatial confinement and lattice temperature.