Modulated structures and atomic ordering in InP_ySb_1-y layers grown by organometallic vapor phase epitaxy

Modulated structure in organometallic vapour phase epitaxially grown InPSb(001) layers has been investigated using transmission electron microscopy (TEM) and transmission electron diffraction (TED). TEM results show that a fine scale modulated contrast (15-20nm) and a fine scale speckled contrast (∼5 nm) are simultaneously present. In addition, a fine needle-like contrast (∼1.5-2.1 nm) is present. TED patterns show that (1̄11) and (11̄1) CuPt-type ordered variants are present. Diffuse streaks along the [110] direction are also observed in the [1̄10] TED pattern and found to be associated with the needle-like contrast. A possible model involving segregation of atoms associated with rows of missing dimers in the surface reconstruction or the presence of antiphase boundaries (APBs) and domain boundaries in CuPt-type ordered regions present in the layers is suggested to explain the origin of the needle-like contrast.