Observation of Focused Ion Beam-Induced Artifacts in Transmission Electron Microscopy Samples Leading to the Epitaxial Growth of AlGaSb Quantum Dots on the GaSb Substrate

We report an unusual artifact induced by Ga+ or Xe+ focused ion beam (FIB) preparation in transmission electron microscopy (TEM) samples with epitaxial layers on a GaSb substrate. The Ga+ FIB-ed TEM samples with a quantum structure made of Al/AlSb/GaSb/InAs/Al0.33Ga0.67Sb multilayers on a GaSb substrate are found to undergo phase modifications under certain conditions related to the beam energy. Dependent on the voltage used during thinning, the Al islands initially on top of the multilayer stack are gradually replaced by Ga, leading to the epitaxial formation of AlxGa1-xSb (AlGaSb) quantum dots (QDs) whose shapes are conformed to the initial Al islands. A similar effect is observed when the top Al islands are capped by an amorphous As layer. The artifacts can be avoided by extensive thinning at 5 kV followed by 2 kV polishing. Further experiments using Xe+ plasma FIB (PFIB) also produce similar artifacts, and those effects are eliminated by Xe+ PFIB under cryogenic conditions regardless of the beam conditions. The mechanism for forming the epitaxial AlGaSb QDs is investigated, and potential use of this phenomenon for QD fabrication is discussed.