Study on the effect of size on InGaN red micro-LEDs

Abstract

In this research, five sizes (100 × 100, 75 × 75, 50 × 50, 25 × 25, 10 × 10 µm2) of InGaN red micro-light emitting diode (LED) dies are produced using laser-based direct writing and maskless technology. It is observed that with increasing injection current, the smaller the size of the micro-LED, the more obvious the blue shift of the emission wavelength. When the injection current is increased from 0.1 to 1 mA, the emission wavelength of the 10 × 10 μm2 micro-LED is shifted from 617.15 to 576.87 nm. The obvious blue shift is attributed to the stress release and high current density injection. Moreover, the output power density is very similar for smaller chip micro-LEDs at the same injection current density. This behavior is different from AlGaInP micro-LEDs. The sidewall defect is more easily repaired by passivation, which is similar to the behavior of blue micro-LEDs. The results indicate that the red InGaN epilayer structure provides an opportunity to realize the full color LEDs fabricated by GaN-based LEDs.

Technology and Applications of Micro-LEDs: Their Characteristics, Fabrication, Advancement, and Challenges

“…The same group investigated the effect of size on the emission wavelength and injection current of μLEDs. With the decrease in size, the injection current increased and there was a blue shift in the emission wavelength . In 2021, Lau et al also reported AlGaInP-based red AM microdisplays with Au/In flip-chip bonding technology …”

“…In 2022, Horng's team fabricated and analyzed red InGaN μLEDs of different sizes. 46 The team used the laser direct writing exposure technology to perform a maskless patterning process for μLEDs in different sizes (100 × 100, 75 × 75, 50 × 50, 25 × 25, and 10 × 10 μm 2 ). The sidewall damage from dry etching was effectively fixed with a SiO 2 passivation layer implemented by plasma-accelerated chemical vapor deposition (PECVD).…”

“…Those strategies used in conventional red LEDs, including the surface light extraction microstructure, regulating the In content in InGaN, fabricating the passivation layer, and current spreading layers with precise thickness control, may have important implications for enhancing the performance of red μLEDs. 46,50,93,97 For green μLEDs, the lower EQE compared to conventional LEDs is mainly due to a poor direct interband tunneling probability because of the wide band gap. 72,110−112 Therefore, a TJ μLED with a lower device resistance has been proposed, and it exhibits a higher EL intensity and lower efficiency drop compared to conventional μLEDs.…”

“…A different In content can be manipulated to tune the emission wavelength in the full visible spectral range. In 2022, Horng’s team fabricated and analyzed red InGaN μLEDs of different sizes . The team used the laser direct writing exposure technology to perform a maskless patterning process for μLEDs in different sizes (100 × 100, 75 × 75, 50 × 50, 25 × 25, and 10 × 10 μm 2 ).…”

“…With the decrease in size, the injection current increased and there was a blue shift in the emission wavelength. 46 In 2021, Lau et al also reported AlGaInP-based red AM microdisplays with Au/In flip-chip bonding technology. 28 The electrical, optical, and thermal characteristics of μLEDs mainly depend on the epitaxial materials, device pixel geometry, and packaging.…”