Co thin film with metastable bcc structure formed on GaAs(111) substrate

¹ Faculty of Science and Engineering, Chuo University, 1-13-27 Kasuga, Bunkyo-ku, Tokyo 112-8551, Japan
² Faculty of Engineering, Yamagata University, 4-3-16 Jonan, Yonezawa, 992-8510 Yamagata, Japan

^a Corresponding author: s-minakawa@futamoto.elect.chuo-u.ac.jp

Published online: 3 July 2014

Abstract

Co thin films are prepared on GaAs(111) substrates at temperatures ranging from room temperature to 600 ºC by radio-frequency magnetron sputtering. The growth behavior and the detailed resulting film structure are investigated by in-situ reflection high-energy electron diffraction and X-ray diffraction. In early stages of film growth at temperatures lower than 200 ºC, Co crystals with metastable A2 (bcc) structure are formed, where the crystal structure is stabilized through hetero-epitaxial growth. With increasing the film thickness beyond 2 nm, the metastable structure starts to transform into more stable A1 (fcc) structure through atomic displacements parallel to the A2{110} close-packed planes. The crystallographic orientation relationship between the A2 and the transformed A1 crystals is A1{111}<1 1̅ 0> || A2{110}<001>. When the substrate temperature is higher than 400 ºC, Ga atoms of substrate diffuse into the Co films and a Co-Ga alloy with bcc-based ordered structure of B2 is formed.