He-Ion Microscopy as a High-Resolution Probe for Complex Quantum Heterostructures in Core-Shell Nanowires

Area of Science:

• Materials Science
• Nanotechnology
• Semiconductor Physics

Background:

• Core-shell semiconductor nanowires (NWs) with quantum heterostructures are complex nanostructured materials.
• Assessing these materials requires ultrahigh-resolution imaging techniques with minimal sample damage.
• Existing high-resolution microscopy methods have limitations for these ultrasmall quantum nanostructures.

Purpose of the Study:

• To demonstrate Scanning Helium Ion Microscopy (SHeIM) as a method for imaging quantum heterostructures in semiconductor NWs.
• To analyze the structure and composition of GaAs-Al(Ga)As core-shell NWs and GaAs/AlAs superlattices.
• To investigate alloy composition fluctuations and critical dimensions for intermixing effects.

Main Methods:

• Utilized Scanning Helium Ion Microscopy (SHeIM) for high-resolution imaging of semiconductor NW cross sections.
• Probed GaAs-Al(Ga)As core-shell NWs with coaxial GaAs quantum wells and short-period GaAs/AlAs superlattices.
• Correlated SHeIM analysis with scanning transmission electron microscopy and atom probe tomography.

Main Results:

• SHeIM provided unique material contrast at ~1 nm resolution, accurately discriminating Al-rich and Ga-rich layers.
• Quantitative SHeIM revealed alloy composition fluctuations (Al-rich clusters, 1-10 nm) in ternary AlGaAs shells and GaAs/AlAs SLs.
• Alloy clustering in GaAs/AlAs SLs vanished with increasing superlattice period (>5 nm-GaAs/4 nm-AlAs).

Conclusions:

• SHeIM is a powerful and straightforward technique for mapping quantum heterostructures in complex III-V semiconductor NWs.
• SHeIM offers unique benefits for imaging nanoscale topography, structure, and composition in diverse semiconductor nanostructures.
• The study provides insights into critical size dimensions for atomic intermixing in short-period superlattices within NWs.