Three-dimensional, epitaxial GaAs crystals are fabricated on micro-pillars patterned into Si(001) substrates by exploiting kinetically controlled growth conditions in Molecular Beam Epitaxy. The evolution of crystal morphology during growth is assessed by considering samples with increasing GaAs deposit thickness. Experimental results are interpreted by a kinetic growth model, which takes into account the fundamental aspects of the growth and mutual deposition flux shielding between neighboring crystals. Different substrate pattern geometries with dissimilar lateral sizes and periodicities of the Si micro-pillars are considered and self-similar crystal structures are recognized. It is demonstrated that the top faceting of the GaAs crystals is tunable, which can pave the way to locally engineer compound semiconductor quantum structures on Si(001) substrates.
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According to Fig. 2, a {10n} pyramidal shape should be expected after 4 μm GaAs growth. Here, the “hut” shape still persists, possibly due to fluctuations in the growth conditions. The introduction of Al, whose diffusivity is at least one order of magnitude lower than the one of Ga (see Ref. 22) might also play a role in delaying the shape transition.