Anomalous strain behavior on EuTe self-assembled islands

COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPESFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPCONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQEuTe is a magnetic semiconductor with potential applications in prototype optoelectronic and spintronic devices. In this work, we investigated the structural properties of EuTe grown on BaF2(111) substrates by molecular beam epitaxy. X-ray diffraction measurements were performed on two series of samples with different growth times and temperatures. The growth occurs in the Volmer-Webber mode, with initial formation of islands that then coalesce to form thin films. The islands size, mosaic spread, and strain state are deduced as a function of growth conditions. Surprisingly, the EuTe islands exhibit in-plane tensile strain, while compressive strain is expected for structures grown over a substrate with smaller lattice parameter. The islands tensile strain relaxes with increasing deposition times and substrate temperature, and it tends to zero for thick EuTe films. We propose that the EuTe/BaF2 lattice mismatch is compensated by the formation of interfacial misfit dislocations. The growth conditions out of equilibrium favor the formation of a metastable state with a high concentration of dislocations that over-compensates the original misfit. This is in agreement with the observed reduction of tensile strain as the substrate temperature increases. (C) 2013 Elsevier B.V. All rights reserved,EuTe is a magnetic semiconductor with potential applications in prototype optoelectronic and spintronic devices. In this work, we investigated the structural properties of EuTe grown on BaF2(111) substrates by molecular beam epitaxy. X-ray diffraction measurements were performed on two series of samples with different growth times and temperatures. The growth occurs in the Volmer-Webber mode, with initial formation of islands that then coalesce to form thin films. The islands size, mosaic spread, and strain state are deduced as a function of growth conditions. Surprisingly, the EuTe islands exhibit in-plane tensile strain, while compressive strain is expected for structures grown over a substrate with smaller lattice parameter. The islands tensile strain relaxes with increasing deposition times and substrate temperature, and it tends to zero for thick EuTe films. We propose that the EuTe/BaF2 lattice mismatch is compensated by the formation of interfacial misfit dislocations. The growth conditions out of equilibrium favor the formation of a metastable state with a high concentration of dislocations that over-compensates the original misfit. This is in agreement with the observed reduction of tensile strain as the substrate temperature increases.386139145COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPESFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPCONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQCOORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPESFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPCONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQSem informaçãoSem informaçãoSem informaçãoWe are grateful to M. de Koning for helping us understand some theoretical aspects of the growth process. E. Heredia also thanks Enzo Granato for the insightful discussions. This work was partially funded by CAPES, FAPESP, CNPq and LNLS