Buried p-type GaN activation under V-pitted n-type GaN for tunnel junction micro-LEDs

Area of Science:

• Materials Science
• Semiconductor Physics
• Optoelectronics

Background:

• GaN-based micro-light-emitting diodes (μ-LEDs) utilize tunnel junctions (TJs) as an alternative electrode architecture.
• Performance limitations arise from incomplete Mg acceptor activation in p-type GaN, increasing resistivity and degrading tunneling efficiency.

Purpose of the Study:

• To investigate the impact of a V-pitted n-type GaN structure on the activation of buried p-type GaN and TJs in μ-LEDs.
• To compare the performance of V-pitted μ-LEDs (VP μ-LEDs) with a conventional flat n-type GaN structure (Flat μ-LEDs).

Main Methods:

• Growth of V-pitted n-type GaN on a TJ.
• Fabrication and characterization of VP μ-LEDs and Flat μ-LEDs.
• Electrical and optical performance testing (EL intensity, output power, forward voltage, leakage current, series resistance).
• Structural analysis using SEM to identify V-pit formation and channels.

Main Results:

• VP μ-LEDs exhibit enhanced optical performance: 1.35x higher integrated EL intensity and 1.3x higher optical output power compared to Flat μ-LEDs.
• Significant improvements in electrical characteristics: reduced forward voltage (3.48V vs 5.46V at 200 μA) and lower reverse leakage current (10⁻¹²–10⁻¹⁰ A vs 10⁻¹⁰–10⁻⁷ A at -15V).
• V-pits form nanoscale channels that facilitate H₂ out-diffusion during annealing, promoting uniform Mg activation and reducing effective series resistance from 2.77 kΩ to 1.66 kΩ.

Conclusions:

• The V-pitted n-type GaN structure effectively enhances Mg activation in buried p-type GaN and TJs.
• This structural modification leads to reduced leakage, improved carrier transport, and superior optical and electrical performance in GaN μ-LEDs.
• V-pit-induced channels are crucial for efficient hydrogen out-diffusion, optimizing the annealing process for μ-LED fabrication.