Abstract
The spontaneous formation of lateral composition modulation in AlAs/lnAs short period superlattices on InP (001) substrates has been investigated. Transmission electron microscopy and x-ray diffraction reciprocal space mapping show that the lateral modulation is very regular, with a periodicity along the [110] direction on the order of 180A. A surprising: result is that this material system also exhibits a lateral modulation along the [1–10] direction, with a periodicity of 330A. Reflection high energy electron diffraction performed during the deposition revealed that the reconstruction changed from (2 × 1) during the InAs deposition cycle to (1 × 2) during the AlAs cycle, which may be related to the presence of the modulation in both directions. High magnification transmission electron micrographs show that the surface is undulated and that these undulations correlate spatially with composition modulation. Detailed analysis of the images shows that the contrast observed is indeed due to composition modulation. Photoluminescence from the modulated layer is strongly polarized and red-shifted by 220 meV.
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