ORDERED AND RANDOMLY DISORDERED ALAS GAAS SHORT-PERIOD SUPERLATTICES/

Unique optical signatures of different atomic arrangements of Al0.5Ga0 .5As, deposited by molecular-beam epitaxy and having nominally identic al average composition, have been observed in steady-state photolumine scence and photoluminescence excitation spectroscopies. Compared to th e observations from a random pseudobinary alloy and a (AlAs)2(GaAS)2 o rdered superlattice, intense photoluminescence emission is observed fr om disordered (AlAs)n(GaAS)4-n superlattices where n is randomly chose n from the sets 0 less-than-or-equal-to n less-than-or-equal-to 4 or 1 less-than-or-equal-to n less-than-or-equal-to 3. The photoluminescenc e peak energies of the randomly ordered superlattices are Ted-shifted by 100-400 meV from the emission energy of the pseudobinary alloy, sug gesting that a significant density of localized or band tail states ex ists at energies lower than the band gap, which are confirmed by photo luminescence excitation spectroscopy. We also measure greatly increase d photoluminescence intensity from the randomly ordered superlattices at high temperatures indicating that these materials may be suitable f or optoelectronic applications in previously unattainable energy regio ns.