Transmission electron microscopic evaluation of InGaAs/InAlAs in-plane superlattices grown on slightly misoriented (110) InP substrates by molecular beam epitaxy

InGaAs/InAlAs in-plane superlattices (IPSLs) consisting of InAs/GaAs and InAs/AlAs monolayer superlattices grown on slightly misoriented (110)InP substrates by molecular beam epitaxy have been structurally evaluated by transmission electron microscopy. We used (110)InP 3° tilted toward the [001] direction. The ISPLs were fabricated by an alternative growth of half monolayers of AlAs and GaAs and one monolayer of InAs while maintaining regular arrays of one monolayer steps on the growth surface. In electron diffraction patterns from the (110) cross-section, two types of superstructure spots double-positioned in the 〈001〉 direction are observed, consistent with the existence of the IPSLs. Dark-field imaging from the superstructure spots reveal a periodic diffraction contrast with an average lateral periodicity of about 4 nm, i.e., one terrace width. However, meandering of the vertical interface and partial disordering in the IPSLs are often observed. From high resolution (110) cross-sectional TEM images, the presence of IPSLs was also confirmed with an atomic scale resolution, although their vertical interface are meandering. In electron diffraction patterns from the (110) plan-view, extra-spots similar to those observed in the (110) cross-section were seen. Dark-field images from the superstructure spots indicated that the IPSLs were formed almost exactly along the 〈110〉 direction, suggesting that the steps on the growth surface are very straight along the 〈110〉 direction.