Major Areas of Opportunity - Implications of Emerging Micro-and Nanotechnologies - page 47

Double
Heterostructure

10,000

1,000

Quantum
Dot

100

Quantum
Well

10

10 A/cm − 2

1

1960 1970 1980 1990 2000 2010

Year

FIGURE 3-4 Diode laser thresholds. SOURCE: Adapted from Ledentsov, N.N., M.
Grundmann, F. Heinrichsdorff, D. Bimberg, V.M. Ustinov, A.E. Zhukov, M.V. Maximov,
Z.I. Alferov, and J.A. Lott. 2000. Quantum dot heterostructure lasers. IEEE Journal of
Selected Topics in Quantum Electronics 6(3): 439-451. © 2000 IEEE.

corresponds to three-dimensional confinement of the electrons in quantum dots
for which all three dimensions are on the nanometer scale. Quantum dots will be
discussed in more detail below; for the nonce it is sufficient to appreciate that
nanoscale confinement in three dimensions serves to further modify the elec-
tronic wavefunctions and density of states, now to an atomic-like discreteness,
and to increase the local electronic density of states.
As is clear from this brief overview, micro- and nanotechnologies are al-
ready having dramatic effects on optoelectronics. Modern telecommunications is
based on quantum-well lasers, optical fibers and waveguides, modulators, detec-
tors, wavelength- and time-division multiplexers, etc.—all of which are based on
structures that provide for careful control of electronic and optical wavefunctions,
and all of which are on the nanometer scale.

Electronic Confinement. Quantum wells have been investigated since the early
development of epitaxial growth capabilities. Nonetheless, new innovations con-