stacked QD structure and is useful for examining the possibility of all-
optical measurement of stacked QD layers. Optical absorption spectra of
self-assembled QDs has been little reported, and further investigation
in necessary to study hole-burning memory. 2.5 Summary This chapter
describes recent advances in quantum dot fabrication tech- nologies,
focusing on our self-formed quantum dot technologies including TSR
quantum dots and SK-mode self-assembled quantum dots. As is described in
this chapter, there are many possible device applications such as
quantum dot tunneling memory devices, quantum dot fioating-dot gate
FETs, quantum dot lasers, and quantum dot hole-burning memory devices.
The quantum dot laser applications seem to be the most practicable among
these applications. However, many problems remain to be solved before
even this application becomes practical. The most important issue is to
of self-assembled quantum dots more pre- control the size and position
cisely, with an accuracy on an atomic scale. The confinement must be
enough to keep the separation energy between quantized energy levels
high enough to get high-temperature characteristics. The lasing
oscillation frequency should be fixed at 1.3 f.lITl or 1.5 f.lITl for
optical communication. Phonon bottleneck problems should be solved by
the optimization of device structures. Fortunately, there is much
activity in the area of quantum dot lasers and, therefore, many
breakthroughs will be made, along with the exploration of other new
application areas.
