Analysis of Bi Distribution in Epitaxial GaAsBi by Aberration-Corrected HAADF-STEM

Area of Science:

• Materials Science
• Solid State Physics
• Semiconductor Research

Background:

• GaAsBi alloys are promising for optoelectronic applications.
• Controlling Bi distribution is crucial for device performance.
• Molecular beam epitaxy (MBE) is a key growth technique.

Purpose of the Study:

• To investigate Bismuth (Bi) content and distribution in GaAs/GaAsBi/GaAs heterostructures.
• To understand the impact of Bi flux on material morphology and phase segregation.
• To correlate structural observations with lattice relaxation.

Main Methods:

• Aberration-corrected high-angle annular dark-field (HAADF) scanning transmission electron microscopy (STEM).
• Energy-dispersive X-ray (EDX) analysis.
• Fast Fourier Transform (FFT) analysis.
• X-ray Diffraction (XRD) analysis.

Main Results:

• Non-homogeneous Bi distribution observed at interfaces and within GaAsBi layers.
• Bi segregation and distorted atomic arrangements noted at low Bi flux.
• Formation of equiaxial, Bi-rich particles at higher Bi flux, dispersed in the matrix.
• Evidence of two phases (rhombohedral Bi and zinc blende GaAsBi) within clusters.
• Clusters influence local lattice relaxation, leading to a partially relaxed system.

Conclusions:

• Bi distribution in MBE-grown GaAsBi/GaAs heterostructures is highly non-uniform.
• Bi-rich clusters and phase segregation impact the material's structural properties.
• The observed relaxation is consistent with the presence of Bi clusters and phase separation.