Etching-free pixel definition in InGaN green micro-LEDs.

Area of Science:

• Materials Science and Engineering
• Optoelectronics
• Semiconductor Device Physics

Background:

• Traditional plasma etching for micro-light-emitting diode (micro-LED) fabrication causes sidewall damage, leading to non-radiative recombination and current leakage, which degrades device performance.
• Existing methods often require subsequent dielectric passivation steps, adding complexity to the manufacturing process.

Purpose of the Study:

• To introduce and validate a novel selective thermal oxidation (STO) method for micro-LED pixel definition.
• To demonstrate STO's capability to mitigate plasma-induced damage and eliminate the need for dielectric passivation.
• To investigate the impact of annealing time and protective layer thickness on device performance.

Main Methods:

• Developed a selective thermal oxidation (STO) process involving thermal annealing in ambient air.
• Utilized a pre-deposited SiO₂ layer to selectively protect specific areas during oxidation.
• Fabricated and characterized InGaN green micro-LED arrays with varying pixel sizes (50, 30, and 10 µm) using the STO method.

Main Results:

• The STO method successfully defined micro-LED pixels without plasma damage, reshaping p-layers and InGaN/GaN quantum wells.
• Prolonged annealing enhanced oxide insulation, significantly reducing leakage current density to 1.2 × 10^-6 A/cm² at -10 V for 10-µm pixels.
• Optimized annealing (4h) and a 3.5-µm SiO₂ layer yielded a peak on-wafer external quantum efficiency of ~6.48% for 10-µm micro-LEDs.

Conclusions:

• The STO method is an effective approach for micro-LED manufacturing, mitigating plasma etching damage and improving device efficiency, especially for smaller pixel sizes.
• The planar pixel geometry achieved through STO facilitates monolithic integration of driving circuits.
• The STO technique is versatile and applicable to other III-nitride devices, including photodetectors, laser diodes, and transistors.