NANOSCALE DEVICES: APPLICATIONS AND MODELING - Bio-Inspired and Nanoscale Integrated Computing - page 44

Figure 2.8. Schematic top view of a QD created in a 2DEG.

presented earlier. As can be seen, going from 100 to 1 nm changes the energy level
separations significantly.
Note that the thermal energy of electrons at room temperature is kT=25.9meV
(k is Boltzmann's constant and T is temperature on the absolute or Kelvin scale). If
the separation of levels is smaller than this value, the thermal energy of the electrons
will be enough to allow them to freely move between these levels; subsequently, the
quantization of levels becomes masked at room temperature. Table 2.1 shows that
one can hope to see room temperature operation only if the device size is on the
order of 10 nm or less. This is in fact the case, and most experiments on QD-type
devices are performed at very low temperatures (cryogenic temperatures such as
liquid helium temperature). A similar effect also exists with regards to the Coulomb
blockade energy e 2 /C. This energy will be large enough to have an effect at room
temperature only if the device dimensions, and therefore its capacitance, are small
enough. This typically happens at the nanoscale. An example of room temperature
operation can be seen in [20].

2.4.2. Less Traditional Nanodevices
By making the ''island'' of electrons smaller and smaller in the devices discussed in
the previous section, one goes from the world of microdevices to that of
nanodevices. This could be accomplished, for instance, by using lithography

TABLE 2 . 1 . The First Four Energy Levels in an Infinite Potential Well with Various Widths
N e N (meV)

for W=100 nm

e N (meV)
for W=10 nm

e N (meV)
for W=1 nm

1 0.038 3.8 380

2 0.151 15.1 1510

3 0.339 33.9 3390

4 0.603 60.3 6030