Cross-sectional transmission electron microscopy and scanning tunnelling microscopy applied to investigation of phase segregation in III-V multilayers grown by molecular beam epitaxy

We report the results of a comparative investigation of cross-sectional transmission electron microscopy (XTEM) and cross-sectional scanning tunnelling microscopy (XSTM) applied to the study of InxGa1-xAsyP1-y layers grown by molecular-beam epitaxy (MBE). Contrast fluctuations perpendicular to the growth direction are observed using both techniques and the spatial wavelength of the contrast variation is the same in both types of image. The origin of the contrast is discussed; the XTEM contrast is due to strain-induced distortion of the lattice planes near the surface, while the XSTM contrast arises from differences in the local electronic structure within the InxGa1-xAsyP1-y layers. Both of these effects have the same root cause, namely phase segregation within the alloy layer during MBE growth.