of al 1 x ga x as as shown in fig8 a the minimum of the conduction band remains located as the maximum of the valence band at the u03b3 point the edges of the brillouin zone are located at k m u03c0 4a and k m u03c0 4a the parts of the curve in fig5 which are located outside the brillouin zone are again folded inwards as a result of which the band structure shown in fig7 is obtained fig8 b shows a different method of obtaining the band structure shown in fig7 in which sublayers 6a of three unit cell layers of alas alternate with sublayers 6b of one unit cell layer of al 1 x ga x as the minimum of the conduction band remains located above the maximum of the valence band so that direct transitions with u03b4k 0 are possible the lattice constant a of the materials used here is 5 66 u00b7 10 1 nm with an overall thickness of about 5 nm the overall number of elementary cell layers in the superlattice is at most about 10 such sublayers have great advantages with respect to thicker layers on the one hand it is possible to make the number of subcells in the superlattice very large because for a band structure a very large number of enlarged unit cells is required when this number is too small the energy bands can be subdivided into discrete levels as is the case for example in the quantum well laser on the other hand local band structures are not defined in the subcells of the superlattice moreover in increasingly larger subcells in the superlattice the already large effective mass of electrons.