When two indirect only slightly different semiconductor materials having a suitable band gap, for example, AlAs and Al.sub.0.8 Ga.sub.0.2 As, are grown epitaxially one onto the other in layers of a few unit cell layers thick, the electronic band structures are folded so that the indirect minimum of the conduction band is displaced from the edge of the Brillouin zone to the center. The two indirect materials then constitute a superlattice with a band transition with a band gap of 2.2 eV.