Investigations of the crystallization mechanism of CrSb and CrSb2 multilayered films using in-situ X-ray diffraction and in-situ X-ray reflectometry

Abstract

Chromium and antimony multilayered films with variable elemental layer thickness were deposited on (100)-Si substrate cooled with liquid nitrogen. The stoichiometry of the films was adjusted to Cr:Sb=1:1 and 1:2. The thickness of Cr–Sb repeating units of these multifilms was varied between 11.4 and 102.5Å. Satellite maxima in the X-ray reflectivity curves observed for films in the as-deposited state demonstrate an alternating stacking of the evaporated elements. The reactivity of the superlattice reactants was investigated with temperature dependent in-situ X-ray diffractometry and X-ray reflectometry. The crystallization temperature of CrSb depends on the double-layer thickness and is about 90°C for a Cr:Sb ratio of 1:1 and double-layer thickness of 53.7Å where nucleation and crystal formation occurs at the element interfaces, while for a thin double-layer thickness (11.4Å) first interdiffusion of the elements occurs before crystallization starts, i.e., an amorphous intermediate is formed prior to crystallization of CrSb. A decomposition reaction into CrSb2 occurs at about 230°C, and up to about 575°C, CrSb, CrSb2 and amorphous Cr coexist. For the ratio Cr:Sb=1:2 and a thin double-layer thickness prior to crystallization of CrSb2 nano-sized crystallites with a composition near CrSb2 nucleate and grow. These crystallites are then successively transformed in long-range ordered crystals exhibiting a pronounced preferred orientation. For films with a thicker repeat unit first formation of CrSb is observed which then reacts with elemental Sb yielding crystalline CrSb2. An activation energy for interdiffusion of Cr and Sb of about 1.8eV is estimated for a film with Cr:Sb=1:1 exhibiting a double-layer thickness of about 53.7Å and an energy for crystal growth of about 1.1eV. For the film with the thinner double-layer thickness of 11.4Å a lower value of the activation energy for interdiffusion is obtained. For CrSb2 the energy for crystal growth is about 3.0eV being significantly larger than for CrSb. Specific resistivity and Hall coefficient measurements were performed for crystalline CrSb and CrSb2 films. The temperature-dependent resistivity measurement exhibits a metallic behavior for CrSb and semi-conducting properties for CrSb2.