Electron Microscopy Study of Surface Islands in Epitaxial Ge 3 Sb 2 Te 6 Layer Grown on a Silicon Substrate

Islands in the form of truncated triangular pyramids on the surface of an epitaxial Ge 3 Sb 2 Te 6 layer grown on a Si(111) substrate are identified by scanning electron microscopy. It is established that sides of their bases are oriented along the Si〈110〉 directions, and sizes vary from several tens to several hundred nanometers. It is shown by high-resolution electron microscopy of cross-sectional specimens that the (111) planes of the cubic phase or (0001) planes of the hexagonal phase of Ge 3 Sb 2 Te 6 in the epitaxial layer are oriented parallel to Si(111) and, in surface domains, can make an angle of 70.5° with the layer–substrate interface. It is established, using an atomic structure analysis and energy-dispersive X-ray microanalysis, that the composition in islands changes from Ge 3 Sb 2 Te 6 to GeSb 2 Te 4 along the growth direction.