Comparison and Difference between SET and FET:
Comparison and Difference between SET and FET
Though, the structure of Single electron transistors [SETs] is almost same as that of MOSFETs (in terms of source, drain and gate) but still there are some differences between the SETs and MOSFETs. Let’s see the similarities, comparison and difference between SET and Mosfet :
- SETs have tunnel junction. In the case of MOSFETs, it is a p-n junction.
- SET has a small conducting island [quantum dot]. FET has a channel region.
- In SET, the tunnelling electrons are transferred one-by-one through the island from source to drain due to the effect of Coulomb blockade. Due to the Coulomb blockade effect, an electron approaching a small negative charged region experiences the electrostatic repulsion by the previous electron in that region. This regulates the number of electrons one-by-one in the channel and hence the drain current varies accordingly. Whereas, in Mosfet the number of electrons is transferred through the channel at a time. Thus many electrons simultaneously participate to the drain current.
- In case of SETs, the drain current (Id) does not depend on the number of electron transferring through the channel or on the Fermi velocity. The Id-Vg characteristic of SET is periodic which shows a finite drain current only for the specific gate voltages where the energies for N and N+ 1 electron in the channel are degenerated. In case of FETs, the drain current (Id) depends on the number of electrons passes through the channel. i.e. more electrons in the channel, larger the drain current.