Localization and band-gap pinning in semiconductor superlattices with layer-thickness fluctuations
K. A. Mader, A. Zunger
Abstract
We consider (AlAs)n/(GaAs)n superlattices with random thickness fluctuations Delta-n around the nominal period n. Using three-dimensional pseudopotential plane-wave band theory, we show that (i) any amount Delta-n/n of thickness fluctuations leads to band-edge wavefunction localization, (ii) for small Delta-n/n the SL band gap is pinned at the gap level produced by a single layer with ``wrong'' thickness n + Delta-n, (iii) the bound states due to monolayer thickness fluctuations lead to significant band-gap reductions, (iv) <001> AlAs/GaAs SL's with monolayer thickness fluctuations have a direct band gap, while the ideal <001> SL's are indirect for n<4.
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