Kinetic limitation of chemical ordering in Bi$_2$Te$_{3-x}$Se$_x$ layers   grown by molecular beam epitaxy
  We study the chemical ordering in Bi$_2$Te$_{3-x}$Se$_x$ grown by molecular beam epitaxy on Si substrates. We produce films in the full composition range from x = 0 to 3, and determine their material properties using energy dispersive X-ray spectroscopy, X-ray diffraction and Raman spectroscopy. By fitting the parameters of a kinetic growth model to these results, we obtain a consistent description of growth at a microscopic level. Our main finding is that despite the incorporation of Se in the central layer being much more probable than that of Te, the formation of a fully ordered Te-Bi-Se-Bi-Te layer is prevented by kinetic of the growth process. Indeed, the Se concentration in the central layer of Bi$_2$Te$_2$Se$_1$ reaches a maximum of only $\approx$ 75% even under ideal growth conditions. A second finding of our work is that the intensity ratio of the 0 0 12 and 0 0 6 X-ray reflections serves as an experimentally accessible quantitative measure of the degree of ordering in these films. 
S. Schreyeck, K. Brunner, A. Kirchner, U. Bass, S. Grauer, C.   Schumacher, C.Gould, G. Karczewski, J. Geurts, and L. W. Mol...
cond-mat.mtrl-sci