Epitaxial growth and structure of Ge–Sb–Te phase change materials on GaSb

The growth rate of nominal Ge2Sb2Te5 phase change material epitaxially grown from the elements by molecular beam epitaxy rapidly decreases above ≈180 °C substrate temperature. A theoretical estimate of this behavior reveals congruent sublimation of the layer, suggesting that it may possess characteristics of a molecular crystal consisting of rather stable subunits with weaker bonds between them. In situ synchrotron x-ray diffraction data of the layers show a peculiar anisotropic broadening of the reflections, consistent with a small rhombohedral distortion of the unit cell analogous to GeTe. The three-dimensional mosaicity due to the growth on a strictly cubic substrate can be avoided by growing on the (111) plane, orienting the distortion in the growth direction to establish an exact match of the in-plane symmetries at the interface.