Magnetic thin films on semiconductors have been scientifically interesting and recently opened to applications such as magnetic memory devices, spin ingestion devices. Needless to say, the well controlled fabrication of the interfaces introduced in the devices is the key technology.
As we previously reported, the RF sputter-deposited Ni film grows epitaxially on the GaAs(001) surface covered with the MgO buffer with the mode of Ni(001)[001]//MgO(001)[001]//GaAs(001)[001] [1,2], where the MgO buffer plays a key role to grow the epitaxial growth without any compound formation at the interfaces.
On the basis of the previous result of the Ni/MgO/GaAs system, the present work aims to fabricate the epitaxial grown system of Co/MgO/GaAs with the h.c.p.Co which has a uniaxial magnetic anisotropy. Thus a study is made of the epitaxial growth condition of Co film on the GaAs(001) surface covered with the epitaxial MgO buffer as a function of a substrate temperature between ambient temperature and 700 degrees Celsius. Both of the Co film and the MgO buffer were deposited by RF magnetron sputtering in pure Ar gas flowing at a rate of 2.5 sccm. The epitaxial MgO films 8nm thick as a buffer were prepared on the GaAs(001) surface and then the Co film 25nm thick was in-situ prepared on such the substrate at a temperature ranged from 100 degrees Celsius to 500 degrees Celsius. The X-ray
diffractometry and the cross-sectional transmission electron microscopy were used to investigate the structure of the films. It is found that the crystalline structure of the Co film drastically changes between the cubic type and the hexagonal type depending on the MgO/GaAs substrate temperature,Ts, that is, the epitaxial Co film grows in the hexagonal closed pack structure with the mode of Co(0001)//MgO(001)//GaAs(001) at Ts between 300 degrees Celsius and 400 degrees Celsius and in the face centered cubic structure at Ts lower than 300 degrees Celsius or at Ts higher than 400 degrees Celsius with the mode of Co(001)//MgO(001)//GaAs(001).
[1]K. Makihara, M. Hashimoto, J. Shi, S. Maruyama, Y. Zohta, Abstract Book
of ICCG-14, 139(2004)
[2]K. Makihara, A. Barna, M. Hashimoto, J. Shi, S. Maruyama, Thin Solid Films, 485, 235-240(2005). |