Quantum structures consisting of Si and Ge were successfully formed by
using gas source molecular beam epitaxy (GSMBE). The growth was stron
gly dependent on growth temperature and crystalline orientation. The S
iGe/Si quantum wells grown by the method clearly showed size quantizat
ion effects when the well width as well as Ge content were changed and
coupling of wells was well understood in terms of effective mass appr
oximation. The luminescence peak energy, however, was found not to pre
cisely follow the Ge content dependence, theoretically predicted above
40% of Ge. It was also followed by the deviation of Ge content depend
ence of activation energy of PL intensity. These properties were shown
to come from island formation on SiGe layers. In the case of pure Ge
wells, the critical thickness where the PL properties significantly ch
anged was found to be 3.7 MLs above which quantum islands were formed
on wet layers with 3 MLs thickness. When the Ge thickness was reduced
to sub-monolayer, the formation of quantum wires was found, which was
confirmed both in PL aspects as well as TEM observation. Band filling
effect characteristic of SiGe/Si quantum wells diminished probably due
to the change in the density of states and a new luminescence which w
as reasonably assigned to biexcitons was found to be formed in the wir
es. The formation of quantum structures in the Si/Ge system was promis
ing to realize optoelectronic devices and light emitting diodes operat
ing at room temperature was demonstrated.