Dislocations in SrTiO 3 thin films grown on LaAlO 3 substrates
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H. Hao and X.X. Xi Department of Physics, The Pennsylvania State University, University Park, Pennsylvania 16802 (Received 16 April 2002; accepted 6 September 2002)
The dislocation configurations in SrTiO3 thin films grown epitaxially on LaAlO3 (100) substrates were studied by conventional and high-resolution transmission electron microscopy. Misfit dislocations had, in most cases, a Burgers vector a〈100〉 and line directions of 〈010〉. These dislocations constitute orthogonal arrays of parallel dislocations at the interface, relieving the lattice mismatch between SrTiO3 and LaAlO3. Threading dislocations were found to be the major defects in the films. Two types of threading dislocations with the Burgers vectors a〈100〉 and a〈110〉 were identified. The relations of these threading dislocations with the misfit dislocations were investigated and are discussed in this paper.
I. INTRODUCTION
SrTiO3 (STO) is a very promising candidate material for applications in future electronics devices, such as thin-film capacitors, phase shifters, filters, and tunable oscillators.1,2 However, the properties of STO thin films generally deviate significantly from those of corresponding bulk materials.3,4 For example, most STO thin films show very low dielectric constant, low tunability, and large dielectric loss compared with single-crystal STO. To improve the various electrical properties of the STO films, it is important to understand the structural nature of the property differences between thin-film and single-crystalline STO. One of the most critical problems for the property degradation is believed to be the residual strain due to the lattice mismatch between the film and substrate.5 It is well known that if the lattice mismatch is relatively small, films can grow coherently on substrates until a critical film thickness is reached. Within this thickness range, the misfit is accommodated by elastic strain. If the film thickness exceeds the critical value, misfit dislocations occur to relieve the strain. The formation mechanism of these misfit dislocations has been discussed elsewhere in literature.6–8 Investigations of misfit dislocations were also reported for epitaxial perovskite oxide thin films, such as PbTiO3, BaTiO3, SrZrO3, and BaZrO3 films.9–12 The misfit dislocations in the perovskite films grown on perovskite substrates were found to have a Burgers vector of the type a〈010〉 (a is the lattice constant),9–11 whereas those in the perovskite a)
Address all correspondence to this author. e-mail: [email protected] J. Mater. Res., Vol. 17, No. 12, Dec 2002
films on a rocksalt structure, e.g., on MgO single crystals, show Burgers vectors of the a/2〈110〉 type.12 More recently, Suzuki et al.13 analyzed the structure of dislocations in BaTiO3 films grown on STO (100) substrates in detail. Misfit dislocations with Burgers vectors of the a〈100〉 type and the related threading dislocations were found to be the major defects in these films. In addition, dissociation of the a〈100〉 misfit dislocations and the a〈110〉 threading dislocat
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