MORPHOLOGICAL AND COMPOSITIONAL VARIATIONS IN STRAIN-COMPENSATED INGAASP INGAP SUPERLATTICES/

We have investigated the properties of strain-compensated InGaAsP/InGa P superlattices, grown by metalorganic vapor phase epitaxy, with and w ithout InP interlayers inserted in the InGaP barrier. Using cross-sect ional scanning tunneling microscopy and spectroscopy, we observe later al variations in layer thickness and electronic properties. When the n umber of superlattice periods is increased from 8 to 16, the growth fr ont develops large undulations in the top two to four superlattice per iods. For structures with InP layers inserted in the InGaP barrier, on ly slight undulations of the top superlattice periods occur. We discus s the origins of the growth front undulations in terms of the elastic relaxation of strain arising from thickness and/or composition variati ons in the superlattice layers. Finally, we observe a fourfold periodi city of the [001] atomic spacing, presumably arising from atomic order ing in the alloys. (C) 1997 American Vacuum Society.