Growth Kinetics of an Amorphous Phase Between GaAs and Co
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GROWTH KINETICS OF AN AMORPHOUS PHASE BETWEEN GaAs AND Co F.Y. SHIAU* AND Y.A. CHANG Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, W153706, U.S.A. *Currently with TzeSemiconductor Chiang Foundation of Science and Technology, Research Center, Hsin-Chu, Taiwan, R.O.C. ABSTRACT Solid-state amorphization reaction between GaAs and Co thinfilms was investigated by transmission electron micorscopy and Auger electron spectroscopy. Upon annealing of GaAs/Co thin-film couples at 260-300 OC, an amorphous phase was observed to form. The amorphization was attributed to the openness of the GaAs structure relative to the size of the Co atoms. This allows rapid diffusion of Co into the GaAs lattice and promotes the occurrence of SSAR. Annealing at higher temperatures or for longer times led to the formation of a crystalline phase,designated as the g-phase which was determined to be a metastable supersaturated solid solution of CoAs exhibiting the B31 structure of the approximate composition of Co(Ga. 4 8 As. 5 2 ). The growth kinetics of both the amorphous phase and the g-phase are parabolic in nature. The parabolic rate constant is higher for the g-phase than for the amorphous phase. The activation energies are 1.47 and 1.35 eV, respectively. INTRODUCTION Solid-state amorphization reaction (SSAR) has been reported in numerous binary metal/metal systems, including Au/Lal, Au/Y 2 , 3 5 6 7 8 Ni/Zr - , Co/Zr , Ni/Hf ,Co/Sn and the metal/silicon systems, Rh/Si 9 , Ni/Si 1 0 , Ti/Si1 1 , 1 2 , Hf/Si 1 3 and Zr/Si 1 3 . More recently SSAR has also been reported to occur in the III-V compound semiconductor/metal systems, GaAs/Ni 1 4, InP/Ni 1 5 , InP/Pd 1 6, 17 1 8 18 19 GaAs/Co , and InP/Co , . However, none of the III-V/metal studies has yet provided kinetic data for the growth of amorphous phases nor offered rationalization for the formation of these phases. The objective of the present study is to provide experimental information on the formation and growth of the amorphous phase between GaAs and Co and to provide a rationalization for the formation of this type of phase. In next paper, the role of thermodynamics in the formation of the amorphous phase will be discussed further,based on the experimentally determined phase equilibria in the Ga-As-Co system. EXPERIMENTAL PROCEDURE Si-doped (2-4x,0 1 7 cm- 3 ) (001) GaAs substrates were degreased in acetone and trichoroethylene (TCE), etched in 5 % HCI for 2 min., rinsed in de-ionized H2 0, and then dried with N2 gas before being loaded into the evaporation chamber. Cobalt thin films 40100 nm in thickness were deposited onto the wafers by electron beam evaporation under a vacuum of 10-7 torr. The deposition rate Mat. Res. Soc. Symp. Proc. Vol. 230. 01992 Materials Research Society
Downloaded from https://www.cambridge.org/core. Rice University, on 16 May 2020 at 19:48:34, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1557/PROC-230-47
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was about 0.2 nm/sec. The samples
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