ABSTRACT
A superlattice (SL) is amultilayered structure with a large number of alternating layers of two semiconductors or insulatorswith different
band-gap energies. The materials are deposited or grown with
sublayer thicknesses up to 10 nm. Usually, a multilayered structure
of alternate materials is called a multiquantum well (MQW) when sublayers are thicker than this. In practice, this thickness division
is somewhat arbitrary and a particular definition should be done
for each material system. In an ideal SL all the quantum wells
(QWs) are coupled and thus carriers are delocalized. Hence, in a
SL the individual levels of each QW turn into a miniband of the whole structure. In contrast, the width of the barriers in an MQW
is large enough to prevent carrier tunneling between wells. Esaki
and Tsu were the first to propose a semiconductor 1D SL [1]. In
addition to the compositional SLs they also envisioned doping SLs,
in which both sublayers are of the same material but have different
doping type. SLs can be fabricated from crystalline, amorphous,
or nanocrystalline materials. Amorphous and nanocrystalline ma-
terials provide great flexibility in composition and have relaxed
requirements of latticematching and interfacial strain. Nevertheless,
understanding transport in these materials is much more difficult
than in crystalline ones due to the presence of defects, gap states, disorder, and hopping transport.
