Structure analysis of composition modulation in epitaxially-grown III-V semiconductor alloys

It has been reported that composition modulation is naturally formed in some of the epitaxially-grown thin films. Structural characterization of these materials is necessary for controlling their nanostructures precisely. Here, we prepared epitaxially-grown III-V semiconductor alloys and characterized their atomistic structures by means of diffraction crystallography and electron microscopy techniques. As a consequence, we found that the following quantum well structures are spontaneously formed: (1) ultrashort period lateral composition modulation (LCM) with a modulation period of ∼1 nm; (2) complex vertical composition modulated (VCM) structures consisting of two modulated structures with a different period (∼4 and ∼25 nm). The former LCM structure is created via nanoscale phase separation at the growth surface, while the shorter-period modulation in the later VCM structure is induced by rotating a substrate through an inhomogeneous distribution of the anion flux within a chamber.