Crystallization Study of Ge-Rich (GeTe) m (Sb 2 Te 3 ) n Using Two-Step Annealing Process

A combination of X-ray diffraction and Raman scattering is employed to investigate (GeTe) m (Sb 2 Te 3 ) n alloys crystallized by thermal annealing from the amorphous (a-) phase. The films are deposited by molecular beam epitaxy on Si(111) substrates. First, a series of a-GeSbTe (GST) films of different composition is deposited and studied by Raman spectroscopy to identify the Ge-rich features of the alloys. Second, the crystallization properties of Ge 10 Sb 2 Te 13 are studied upon different annealing conditions. The aim of this work is to develop a procedure to avoid segregation of Ge and GeTe at the GST crystallization onset (T x ). This is here achieved by means of an incubation step at temperature lower than T x . The crystallization onset T x increased to 270 °C, which is about 160 °C higher compared to a reference GeTe sample, while the alloy always crystallizes in the stable Ge 1 Sb 2 Te 4 composition. The increase of T x is observed for all annealing conditions, regardless the amount of crystalline Ge segregated. For the optimized annealing treatment, the presence of Ge nanocrystals along with crystalline GeSbTe is unveiled by Raman measurements, paving the way for the control of the microstructure and electrical/thermal properties of Ge-rich alloys.