Photoluminescence polarization in strained GaN/AlGaN core/shell nanowires

Area of Science:

• Materials Science
• Nanotechnology
• Solid State Physics

Background:

• Gallium nitride (GaN) and aluminum gallium nitride (AlGaN) heterostructures are crucial for optoelectronic devices.
• Understanding optical polarization is key to optimizing device performance.
• Core/shell nanowire (NW) architectures offer unique properties for advanced applications.

Purpose of the Study:

• To investigate the optical polarization properties of GaN/AlGaN core/shell NW heterostructures.
• To correlate polarization behavior with strain induced by the AlGaN shell.
• To validate experimental findings with a theoretical model.

Main Methods:

• Fabrication of core/shell NWs using molecular beam epitaxy (MBE) for GaN cores and halide vapor phase epitaxy (HVPE) for AlGaN shells.
• Polarization-resolved micro-photoluminescence (μ-PL) spectroscopy to analyze optical emission.
• Application of a strain-dependent 6 × 6 k·p theoretical model for interpretation.

Main Results:

• Uncoated, strain-free GaN NW cores exhibit polarization perpendicular to the c-axis.
• Compressively strained GaN cores (due to AlGaN shell) show polarization parallel to the c-axis.
• AlGaN shells display weak polarization perpendicular to the c-axis, attributed to tensile axial strain.

Conclusions:

• The study demonstrates a clear link between strain and optical polarization in GaN/AlGaN core/shell NWs.
• Strain engineering via shell epitaxy can control the polarization characteristics of the core.
• These findings are vital for designing polarization-controlled GaN-based optoelectronic devices.