Red emission from strain-relaxed bulk InGaN active region

Area of Science:

• Materials Science
• Solid State Physics
• Optoelectronics

Background:

• Conventional red light-emitting diodes (LEDs) utilize Indium Gallium Nitride (InGaN) quantum wells (QWs) grown at low temperatures for effective Indium incorporation.
• Achieving efficient red light emission from InGaN materials typically requires specific growth conditions to manage Indium content and phase separation.

Purpose of the Study:

• To demonstrate red LEDs employing a bulk InGaN active region instead of traditional quantum wells.
• To investigate a new epitaxial strategy for fabricating red InGaN LEDs with improved characteristics.

Main Methods:

• Grew bulk InGaN active regions at approximately 800°C, significantly higher than typical red QW growth temperatures.
• Introduced high-density trench structures in underlying green multi-quantum wells (MQWs) to relax compressive strain in the bulk InGaN.
• Analyzed the resulting InGaN material structure and optical properties under electrical injection.

Main Results:

• Achieved approximately 96% strain relaxation in the bulk InGaN layer due to the trench structures.
• Observed phase separation into low-In (blue) and high-In (red) phases within the bulk InGaN, with the red phase acting as carrier localization centers.
• Demonstrated red LEDs with superior wavelength stability (minimal shift from 648.6 nm to 642.4 nm across a current range) and a peak external quantum efficiency of 0.32%.

Conclusions:

• The developed epitaxial strategy enables the fabrication of red InGaN LEDs using a bulk active region grown at elevated temperatures.
• Strain relaxation via trench structures effectively facilitates phase separation, leading to efficient red light emission.
• This approach presents a viable and novel alternative for producing stable and efficient red InGaN LEDs.