Growth of Sb2Te3 thin films on Ge(111) sample by thermal deposition: Morphological and electronic properties

Sb2Te3 is a well-known thermoelectric material and a topological insulator and its utilization is foreseen for many applications, such as quantum computing, mode-locking of laser systems, and cooling systems. Various methods have been used to grow thin Sb2Te3 films on different substrates, such as molecular beam epitaxy or electrodeposition. Often, such methods require performing laborious and rigid steps in order to optimize film growth and reduce the amount of defects. For this reason, we investigate a simplified growth method: thermal deposition starting from Sb2Te3 lumps followed by annealing. By means of various surface science techniques (LEED, STM, XPS), we show that it is possible to obtain a single crystalline Sb2Te3 film on a Ge(111) substrate. The film, which is amorphous after deposition, undergoes a phase transition and becomes crystalline after annealing at 573 K. This is clearly shown by a 1x1 surface termination typical of a (0001) surface with hexagonal lattices. The presence of several quintuple-layer steps was observed by scanning tunneling microscopy. Photoelectron spectroscopy characterization confirms that the grown chalcogenide film presents the expected stoichiometry (Te/Sb=1.5). The proposed method simplifies the growth phase and seem to reduce the number of defects induced by the growth technique, major advantages for many applications.