Stability of misfit dislocations in axial-heteroepitaxial nanopillar structures

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Heteroepitaxial systems permit to combine different semiconductor materials into functional devices, which stand out due to versatile electronic, optic and thermoelectric properties. By scaling the material dimensions down to the nanoscale, the formation of misfit related lattice defects can be avoided or at least reduced in such systems, thus considerably enhancing the applicable materials palette as well as range of applications and lifetime of corresponding devices. However, especially in the case of heteroepitaxial layers on the axial face of nanorods it is not yet well understood when misfit dislocations in which configuration are thermodynamically stable. Therefore, the present project addresses the creation of GaAs pillar nanostructures on substrate crystals by means of nanosphere lithography, the growth of mismatched InAs layers on top of the pillars by using molecular beam epitaxy, followed by experimental as well as theoretical analysis of misfit dislocation stability. Most importantly, a model is to be established that reliably predicts the critical dimensions for the transition between the coherent and the semicoherent state by considering realistic specimen morphologies. Furthermore, the restricted-equilibrium dislocation configuration with emphasis on dislocation position and type, and the influence of the finite chemical width of the hetero-interface shall be determined.