Single-electron Tunneling Oscillations Research Articles

Study of single-electron tunneling oscillations using monte-carlo based modeling algorithms to a capacitive slanted two-dimensional array of tunnel junctions

<abstract> This work simulates and examines the circuit's operation for a single-electron nanostructure which is composed of slanted coupled two-dimensional arrays of tunnel junctions. The structure under study is modeled by combined computational simulation methods, both the Master Equation and the Monte-Carlo techniques. Throughout this process, the distribution of the time between successive random events could be computed at a reference junction. From these time distribution values, further calculations have been carried out to obtain the power spectral density trends, which reflect the corresponding properties on the frequency domain. For these homogeneous structures, the biasing conditions have been inspected for a combination of the two array's legs. It is found that, for some shorter lengths 3, 5, and up to 7 tunnel junctions could be triggered from any same or opposite side ends having different voltage polarities. For relatively longer structures of sizes 10, 15, 20, and 30 tunnel junctions, the circuit initial parameters are readjusted for obtaining remarkable results for their oscillations study. By increasing the value of the slanted coupling capacitance, the steady-state currents are in terms increased, and in this way, it is possible to realize the tunnel events correlations. It is shown that tuning the stray capacitances by slightly increasing their values will lead to a good clearer effect, especially for those longer array sets. </abstract>

Charge fluctuations in single-electron tunneling oscillations

It has been predicted that in the presence of a sufficiently high-dissipative environment transport in a small tunnel junction can become extremely regular, giving rise to the phenomenon of single-electron tunneling oscillations. Recent progress in detection of high-frequency current fluctuations and the interest in single-electron sources motivate further investigations on the expected accuracy of the charge oscillations as a function of the impedance of the environment. In this paper we study theoretically the charge-fluctuation spectrum at finite frequency for the system at hand, and investigate its evolution as a function of the external impedance. The evolution and the disappearance of the single-electron oscillations peak is described by analytical and numerical methods.

Charge noise analysis of an AlGaAs/GaAs quantum dot using transmission-type radio-frequency single-electron transistor technique

Radio-frequency (rf)-operated single-electron transistors (SETs) are high-sensitivity, fast-response electrometers, which are valuable for developing new insights into single-charge dynamics. We investigate high-frequency (up to 1 MHz) charge noise in an AlGaAs/GaAs quantum dot using a transmission-type rf SET technique. The electron capture and emission kinetics on a trap in the vicinity of the quantum dot are dominated by a Poisson process. The maximum bandwidth for measuring single trapping events is about 1 MHz, which is the same as that required for observing single-electron tunneling oscillations in a measurable current (∼0.1 pA).

Dynamics of phonon-assisted tunneling in a silicon degenerate pn junction

The charge distribution and junction voltage on an indirect-band-gap semiconductor tunnel junction (that is in parallel with a resistor and current source) were obtained by solution of the master equation. Expressions for the tunneling rate in a silicon degenerate pn junction are presented. Phonon-assisted tunneling permits relaxation of a requirement (that the external resistance be much larger than the resistance quantum) for the observation of single electron tunneling oscillations. Consequently, that process may enable observation of such oscillations in practical single junction circuits.

Bistable locking of single-electron tunneling elements for digital circuitry

Bistable phase locking of single-electron tunneling oscillations is proposed as the basis for digital logic circuitry. A simple model of single-electron tunneling is used to examine the locking of capacitively coupled junctions pumped at twice the tunneling frequency and activated by clocking the dc bias. The locking to sinusoidal input signals and the locking between coupled junctions is examined. It is shown that bistable locking exhibits an input amplitude threshold and phase noise margin and that junctions rapidly lock in antiphase due to a strong interaction between tunneling events. Conditions under which the operation is potentially useful for digital circuitry are identified.

Single-Electron Tunneling in One-Dimensional Arrays of Small Tunnel Junctions

Experimental results of one-dimensional arrays of small-area Al/Al x O y / Al tunnel junctions are presented. Single-electron tunneling oscillations (SETO's) were observed as peaks of differential resistance in the presence of external microwaves. SETO was very pronounced when the array was longer than the single-electron soliton, suggesting that the soliton picture of the electron motion is correct. SETO disappeared when superconductivity set in.

Single electron tunneling oscillations in one-dimensional arrays of ultrasmall tunnel junctions

Time correlation of Single Electron Tunneling events i.e. SET-oscillations has been observed in one dimensional arrays of Al/AlxOy/Al tunnel junctions with very small areas (0.006μm2). They are detected by phase locking to external microwaves with frequency fext between 0.7GHz and 5GHz. Peaks in the differential resistance occur at currents corresponding to l=efext. Good agreement is obtained with theoretical data.

Standard quantum limit and squeezing of mesoscopic tunneling current

This paper identifies the standard quantum limit of the mesoscopic tunneling current and proposes a new strategy to surpass this limit. A new methodology is used to solve the problem in a fully analytic manner. The degree of randomness of single-electron tunneling oscillations is defined as the ratio of the standard deviation of dwell times to their mean value. The minimum degree of randomness achievable under the ideal constant-current-bias condition is determined. This may be referred to as the standard quantum limit of the tunneling current by analogy with quantum optics. This quantum limit originates from the time-energy uncertainty relationship and but it can be surpassed by constructing an appropriate feedback loop between the injection current rate and the voltage across the junction.

Coulomb blockade in a superlattice of normal tunnel junctions.

The effects of Coulomb blockade are studied in many normal tunnel junctions connected in series. Such a structure is a natural way for creating the small capacitance necessary for Coulomb blockade. The amplitude of single-electron tunneling oscillations is exponentionally small at high temperature and is proportional to the number of junctions. The resistance of a voltage-biased superlattice at high temperature has an activated temperature dependence. The activation energy goes to zero at some threshold voltage proportional to the number of the junctions.