A superlattice (SL) is a multilayered structure with a large number of alternating layers of two semiconductors or insulators with 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