Analysis of size dependence and the behavior under ultrahigh current density injection condition of GaN-based Micro-LEDs with pixel size down to 3 μm

Abstract

In this paper, the GaN-based green Micro-LEDs with various sizes (from 3 to 100 μm) were fabricated and electro-optically characterized. Atom layer deposition (ALD) passivation and potassium hydroxide (KOH) treatment were applied to eliminate the sidewall damage. The size dependence of Micro-LED was systematically analyzed with current-versus-voltage and current density-versus-voltage relationship. According to the favorable ideality factor results (<1.5), the optimized sidewall treatment was achieved when the device size shrank down to <10 μm. In addition, the EQE droop phenomenon, luminance and output power density characteristics were depicted up to the highest current density injection condition to date (120 kA/cm2), and 6 μm device exhibited an improved EQE performance with the peak EQE value of 16.59% at 20 A/cm2 and over 600k and 6M cd/cm2 at 1 and 10 A/cm2, indicating a greater brightness quality for over 3000 PPI multiple display application. Lastly, the blue shift of 6 μm device with elevating current density was observed in electroluminescence (EL) spectra and converted to CIE 1931 color space. The whole shifting track and color variation from 1 A/cm2 to 120 kA/cm2 were demonstrated by color coordinates.

Impact of Sidewall Conditions on Internal Quantum Efficiency and Light Extraction Efficiency of Micro‐LEDs

“…Similar results were recently reported by Liu et al. [ 45 ] Figure 5c,d shows HAADF‐STEM image. After ICP‐RIE, there is a blur toward the sidewall (yellow arrow), i.e., the lattice distortion.…”

“…It is noted that the rough sidewall is flattened by the TMAH treatment (Figure 5b). Similar results were recently reported by Liu et al [43]. Figures 5c and 5d show HAADF-STEM image.…”

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

“…Red μLEDs face several challenges, including a low light extraction efficiency, reduction of EQE caused by the size effect, and blue shift of the emission wavelength under a high driving current which also seriously reduces the color gamut in displays. 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. ,,, 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. ,− 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 . Although the blue μLEDs also have a size effect on the EQE and emission wavelength, the impact to display applications is relatively low because the efficiency is high enough and the blue shift of emission wavelength improves the color gamut in the display instead.…”

Dennard Scaling in Optoelectronics: Scientific Challenges and Countermeasures of Micro‐LEDs for Displays

“…[39] However, it should be acknowledged that the potential of typical QW LEDs for further improvement is limited, which can be seen from Figure 3e where results on QW LEDs reported in the technical literature are summarized. [40][41][42][43][44][45][46][47][48][49][50][51] Even for largesize SSL LEDs fabricated under state-of-the-art techniques where size-dependent effect can be neglected, the J PEAK (several A cm −2 ) is still far higher than the expected working current density for Micro-LEDs. This is partially because carriers tend to form Wannier excitons (rather than Frenkel excitons in GaN-based materials), where the carrier interaction is much looser than that in OLEDs so that a large n cannot be achieved naturally.…”