Single-electron transistor: Difference between revisions

Revision as of 11:48, 4 November 2019

Revision as of 17:03, 3 December 2019

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When the applied voltage is zero, the Fermi level at the metal electrodes will be inside the energy gap. When the voltage increases to the threshold value, tunnelling from left to right occurs, and when the reversed voltage increases above the threshold level, tunnelling from right to left occurs.

The existence of the Coulomb blockade is clearly visible in the [[current-voltagecurrent–voltage characteristic]] of a SET (a graph showing how the drain current depends on the gate voltage). At low gate voltages (in absolute value), the drain current will be zero, and when the voltage increases above the threshold, the transitions behave like an ohmic resistance (both transitions have the same permeability) and the current increases linearly. It should be noted here that the background charge in a dielectric can not only reduce, but completely block the Coulomb blockade. <math>q_0 = \pm (0.5 + m) e.</math>

In the case where the permeability of the tunnel barriers is very different <math>(R_{T1} \gg R_{T2} = R_T),</math> a stepwise I-V characteristic of the SET arises. An electron tunnels to the island through the first transition and is retained on it, due to the high tunnel resistance of the second transition. After a certain period of time, the electron tunnels through the second transition, however, this process causes a second electron to tunnel to the island through the first transition. Therefore, most of the time the island is charged in excess of one charge. For the case with the inverse dependence of permeability <math>(R_{T1} \ll R_{T2} = R_T),</math> the island will be unpopulated and its charge will decrease stepwise.<ref>{{cite journal|last1=Gupta|first1=M.|title=A Study of Single Electron Transistor (SET)|journal=International Journal of Science and Research|volume=5|issue=1|year=2016|pages=474–479|issn=2319-7064|doi=10.21275/v5i1.NOV152704}}</ref> Only now can we understand the principle of operation of a SET. Its equivalent circuit can be represented as two tunnel junctions connected in series via the QD, perpendicular to the tunnel junctions is another control electrode (gate) connected. The gate electrode is connected to the island through a control tank <math>C_{\rm G}.</math> The gate electrode can change the background charge in the dielectric, since the gate additionally polarizes the island so that the island charge becomes equal to