Development of highly efficient ultraviolet LEDs on hybrid patterned sapphire substrates

Area of Science:

• Materials Science
• Optoelectronics
• Semiconductor Physics

Background:

• Gallium nitride (GaN)-based ultraviolet light-emitting diodes (UV LEDs) are crucial for various applications.
• Improving the efficiency and light output of UV LEDs requires advanced substrate materials.
• Conventional patterned sapphire substrates (CPSS) offer some benefits but have limitations in light extraction.

Purpose of the Study:

• To develop and evaluate a hybrid patterned sapphire substrate (HPSS) for high-quality Al(Ga)N epilayer growth.
• To investigate the impact of HPSS on the performance of GaN-based UV LEDs.
• To enhance light extraction efficiency and device performance in UV LEDs.

Main Methods:

• Preparation of a hybrid patterned sapphire substrate (HPSS) with a patterned silica array on sapphire.
• Growth of Al(Ga)N epilayers on both HPSS and conventional patterned sapphire substrates (CPSS).
• High-resolution X-ray diffraction (HRXRD) for structural quality assessment.
• Optical measurements to evaluate light transmittance and device performance (light output power, external quantum efficiency).

Main Results:

• Al(Ga)N epilayers grown on HPSS and CPSS exhibited similar structural quality.
• HPSS demonstrated improved UV band transmittance due to higher refractive index contrast.
• UV LEDs grown on HPSS showed a 14.5% increase in light output power compared to those on CPSS.
• Peak external quantum efficiency was over 22.9% higher for LEDs grown on HPSS.

Conclusions:

• The HPSS is an effective substrate for growing high-quality Al(Ga)N epilayers.
• The enhanced light extraction efficiency of HPSS significantly boosts UV LED performance.
• HPSS presents a promising pathway for realizing future high-efficiency and high-power UV LEDs.