Page 69 - Principles and Applications of NanoMEMS Physics

56 Chapter 2

2.2.3 Single-Electron Tunneling

Upon the island being populated by the injected charge, the charge
tunnels through C J and diffuses to the leads in a characteristic time τ given
by the uncertainty principle (38) [69].

E ≥ = , (38)
C τ

If the bias V G causes the injection of a charge q every τ seconds, then a
current of magnitude I = τ / q is set up, Figure 2- .
7

I I
C C
0 0
V V
Q= n
G G Q= n q q
+ +
- -
C C
J J

Figure 2-7. Single-electron tunneling schematic.

However, if this time is too short, then the current would appear to be
continuous, as opposed to pulse-like. In this case, no discrete, single-electron
tunneling event is observed. To observe single-electron tunneling, the
characteristic time must exceed the product of the capacitance times the lead
τ
resistance, > RC , a condition which leads to a minimum value for lead
resistance, Eq. (38).

R > 2= (38)
q 2

Notice that transport is occurring through a tunneling junction.

2.2.3.1 Quantum Dots

Quantum Dots (QDs) are structures in which electrons are confined in all
three dimensions [59]. These structures include both gated layered structures