Ordered and randomly disordered AlAs/GaAs short-period superlattices

Abstract

Unique optical signatures of different atomic arrangements of Al0.5Ga0.5As, deposited by molecular-beam epitaxy and having nominally identical average composition, have been observed in steady-state photoluminescence and photoluminescence excitation spectroscopies. Compared to the observations from a random pseudobinary alloy and a (AlAs)2(GaAs)2 ordered superlattice, intense photoluminescence emission is observed from disordered (AlAs)n(GaAs)4−n superlattices where n is randomly chosen from the sets 0≤n≤4 or 1≤n≤3. The photoluminescence peak energies of the randomly ordered superlattices are red-shifted by 100–400 meV from the emission energy of the pseudobinary alloy, suggesting that a significant density of localized or band tail states exists at energies lower than the band gap, which are confirmed by photoluminescence excitation spectroscopy. We also measure greatly increased photoluminescence intensity from the randomly ordered superlattices at high temperatures indicating that these materials may be suitable for optoelectronic applications in previously unattainable energy regions.