Design of high-voltage deep ultraviolet LED sub-mesas toward improved optoelectronic performance

Area of Science:

• Optoelectronics
• Materials Science
• Semiconductor Devices

Background:

• Deep ultraviolet light-emitting diodes (DUV LEDs) are crucial for various applications.
• Efficiency droop and self-heating are significant challenges in DUV LED performance.
• Mesa and sub-mesa structures influence light extraction and thermal management.

Purpose of the Study:

• To systematically investigate the impact of mesa/sub-mesa sidewall engineering on single-junction (SJ) and high-voltage (HV) DUV LEDs.
• To optimize sidewall angles and Al reflector configurations for enhanced light extraction.
• To analyze the effect of sub-mesa count on self-heating and external quantum efficiency (EQE) droop.

Main Methods:

• Fabrication and characterization of DUV LEDs with varying mesa/sub-mesa designs.
• Systematic investigation of sidewall angles (∼46°) and Al reflector integration.
• Analysis of EQE droop and self-heating effects under different input power conditions.
• Comparison between SJ and HV DUV LEDs with varying numbers of sub-mesas.

Main Results:

• A ∼46° inclined mesa/sub-mesa sidewall angle and Al reflector optimally promote light extraction.
• HV DUV LEDs with an increasing number of sub-mesas show substantial improvements in self-heating and EQE droop.
• EQE droops for HV DUV LEDs with two and four sub-mesas were 27.6% and 34.6% (at 6.4 W), significantly lower than 51.6% for SJ DUV LEDs.
• Improved performance is attributed to superior heat dissipation and light extraction from the high perimeter-to-area ratio of sub-mesas.

Conclusions:

• Mesa design, particularly the use of sub-mesas and optimized sidewall angles, is critical for enhancing DUV LED performance.
• Sub-mesa engineering effectively mitigates efficiency droop and improves thermal management in HV DUV LEDs.
• This study provides insights into mesa design for advancing AlGaN-based DUV LED technology.