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In the work, we systematically investigate the microstructural properties of (110) oriented heterostructures on GaAs substrates by means of different transmission electron microscopy techniques. Three heterosystems are investigated as case studies including (Al,Ga)As/GaAs, MnAs/GaAs and CoAl/GaAs. These selected material systems cover three major lattice symmetries, i.e. fcc, hcp and bcc, and they differ from each other not only in the lattice mismatches with respect to GaAs(110), but also in their crystalline phases, from semiconductor compound over half-metal to metallic alloy. In order to verify the epitaxial alignment for the different cases, detailed investigations of the interfaces are carried out, including the atomic arrangements, the defect properties and the resulting strain states. The effect of different interface configurations on the microstructural properties of the layer is also researched. Fcc-type (Al,Ga)As/AlAs/GaAs multilayer structure on GaAs (110) presents different mismatch strain accommodation mechanisms along the perpendicular in-plane directions. With the introduction of short period superlattices, pseudomorphical growth is realized far beyond the critical thickness. Defect-free structures are successfully acquired by an appropriate type of AlAs/GaAs short period superlattice. Finally, artificial defects are intentionally produced by nano-indentation to the defectfree sample to verify the effect of short period superlattices. Hcp-type MnAs on GaAs (110) system is characterized by anisotropic lattice mismatches of −7.5% and 0.7% along the [112̄0] and [0001] direction, respectively. A wetting layer is observed prior to the formation of islands, indicating a StranskiKrastanov growth mode of MnAs. The strain corresponding to the 0.7% lattice misfit is accommodated elastically, whereas the mismatch stress along perpendicular direction is relived by the formation of a periodic array of perfect misfit dislocations with a stand-off position in MnAs lattice. The long range strain field associated with the dislocation array is constrained at the interface within a thickness of about 3.4 nm. An interfacial atomic configuration is also proposed based on the comparison between HRTEM image and the simulations. In addition, subsequent growth of GaAs on MnAs is three-dimensional with a huge amount of planar defects present. B2-type intermetallic CoAl alloys are realized on (001) and (110) oriented GaAs substrates for comparison. They are both characterized by a coexistence of B2 phase and its disordered version bcc phase. The disordering is induced partially by the epitaxial strain and partially by the diffusion of point defects. Additionally, (110) oriented CoAl presents a large number of misoriented domains originated from the interface roughness. They further reduce the volume fraction of the ordered B2 phase. The three case studies have pointed out the specific relevance of interfaces for the realization of tailored heterosystems and their resultant microstructure. The interface determines the epitaxial orientation geometry between the substrate and the epilayer, and accordingly the lattice mismatches along different in-plane directions as well as the specific ways of mismatch strain relaxation. Interface structure in a heterosystem generally describes a low-energy atom configuration, which is driven by the minimization of strain energy.

Transmission electron microscopy study of heterostructures grown on GaAs (110)