Mechanisms of spiral growth in Bi2Te3 thin films grown by the hot-wall-epitaxy technique

Abstract The hot-wall-epitaxy (HWE) technique was used to deposit Bi 2 Te 3 thin films on amorphous (kapton and SiO 2 ) substrates. It was found that the growth proceeds under low supersaturation (2.5%) in the direction perpendicular to the basal plane of the hexagonal unit cell of Bi 2 Te 3 . Elementary spirals having a regular shape of hexagonal symmetry, reflecting the crystalline structure of Bi 2 Te 3, were clearly assessed by using an atomic force microscope (AFM). The height of the steps constituting these spirals was estimated to be 1 nm, corresponding to one unit cell, with an inter-step separation ranging from 180 to 200 nm. The growth mechanism and the final morphology of the films were explained in the light of the Burton–Cabrera–Frank (BCF) and the periodic-bond-chains (PBC) models. The size of the critical radius of nucleation and the edge surface free energy were estimated to be R * =10.5 nm and γ =560 erg/cm 2 , respectively. In addition, the modulus of the Burger’s vector was calculated to be | b |≈1 nm. These values are in good agreement with the theoretical ones, which permits the explanation of the final morphology of the films.