Polarization-insensitive GaN metalenses at visible wavelengths

Area of Science:

• Optics and Photonics
• Materials Science
• Semiconductor Manufacturing

Background:

• Gallium nitride (GaN) light-emitting diodes (LEDs) benefit from growth on patterned substrates to enhance light output.
• Conventional inspection methods for patterned substrates, like scanning electron microscopy (SEM) and optical microscopy (OM), are expensive and cumbersome.
• Ultra-thin metasurfaces are increasingly utilized for optical applications, particularly as converging lenses.

Purpose of the Study:

• To develop and demonstrate high-performance, polarization-insensitive metalenses for inspecting patterned substrates.
• To offer a cost-effective and lightweight alternative to traditional inspection techniques in semiconductor manufacturing.
• To evaluate the imaging capabilities of newly designed metalenses using a standard test chart and patterned sapphire substrates.

Main Methods:

• Design and fabrication of metalenses utilizing hexagon-resonated elements (HREs) with subwavelength periods.
• Characterization of metalenses at wavelengths of 405, 532, and 633 nm, measuring diffraction-limited focusing efficiencies.
• Evaluation of imaging performance using the 1951 United States Air Force (USAF) test chart and patterned sapphire substrates (PSS).

Main Results:

• Fabricated metalenses achieved high diffraction-limited focusing efficiencies (93% at 405 nm, 86% at 532 nm, 92% at 633 nm).
• Metalenses demonstrated exceptional imaging capability, resolving features as small as 870 nm.
• Images of patterned sapphire substrates obtained with the metalenses were comparable to those from a higher numerical aperture (NA) objective (0.3 vs. 0.4).

Conclusions:

• The developed polarization-insensitive metalenses provide a viable, high-resolution inspection tool for patterned substrates in semiconductor manufacturing.
• These ultra-thin, lightweight metalenses can potentially replace bulky and expensive SEMs or OM objectives.
• This technology offers a pathway to more efficient and accessible quality control in GaN LED production.