Stacking III-Nitride Ultraviolet-B Light Emitters with High Efficiency via a Lattice-Engineered Architecture

Area of Science:

• Materials Science
• Optoelectronics
• Semiconductor Physics

Background:

• AlGaN-based ultraviolet (UV) light emitters operating in the 280-320 nm (UVB) range are crucial for medical applications.
• A significant challenge, known as the "UVB gap," results in low efficiency due to lattice mismatch in AlGaN epitaxy.
• This mismatch induces compressive stress, leading to dislocations and surface roughness, which degrade device performance.

Purpose of the Study:

• To overcome the efficiency limitations of AlGaN-based UVB LEDs.
• To develop a lattice-engineering strategy to improve the quality of AlGaN epitaxy.
• To enhance the performance of UVB light emitters for medical applications.

Main Methods:

• Introduced nanocrystalline graphite masks via metal-organic decomposition for surface pretreatment.
• Utilized controlled epitaxial lateral overgrowth to manage stress in AlN layers.
• Modulated stress in AlN from compressive to tensile (2.51 GPa, 0.51% strain) to match freestanding AlGaN.

Main Results:

• Achieved high-quality AlGaN epitaxy with high aluminum content, particularly below 50% Al.
• Successfully modulated the stress in AlN to achieve a lattice constant matching freestanding Al0.79Ga0.21N.
• Demonstrated significant performance improvement in 310-nm UVB LEDs, reaching a maximum wall-plug efficiency of 4.88%.

Conclusions:

• The proposed lattice-engineered architecture effectively resolves the "UVB gap" issue in AlGaN-based emitters.
• This method enables high-quality epitaxy crucial for efficient UVB light emission.
• The breakthrough accelerates the development and application of AlGaN-based UVB LEDs in medical care.