Investigation and direct observation of sidewall leakage current of InGaN-Based green micro-light-emitting diodes

Abstract

Electrical and optical characteristics of InGaN-based green micro-light-emitting diodes (µLEDs) with different active areas are investigated; results are as follows. Reverse and forward leakage currents of µLED increase as emission area is reduced owing to the non-radiative recombination process at the sidewall defects; this is more prominent in smaller µLED because of larger surface-to-volume ratio. Leakage currents of µLEDs deteriorate the carrier injection to light-emitting quantum wells, thereby degrading their external quantum efficiency. Reverse leakage current originate primarily from sidewall edges of the smallest device. Therefore, aggressive suppression of sidewall defects of µLEDs is essential for low-power and downscaled µLEDs.

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

“…Meanwhile, for standard LEDs (e.g., > 300 µm square) and even recently reported µLEDs, p-GaN contact metal layer (ITO or Ni/Au) is deposited after mesa etching. This indicates that the alignment causes the occurrence of the space between p-contact and mesa [11][12][13]. As presented in Figure 1, the difference in PPI between a sample with 300 µm-size ITO and mesa (~84 PPI) and a sample with 300 µm ITO and 306 µm mesa (i.e., 3 µm spacer) (~82.3 PPI) is not significant.…”

“…This indicates that the alignment causes the occurrence of the space between p‐contact and mesa. [ 11–13 ] As presented in Figure , the difference in PPI between a sample with 300 µm‐size ITO and mesa (≈84 PPI) and a sample with 300 µm ITO and 306 µm mesa (i.e., 3 µm spacer; ≈82.3 PPI) is not significant. This behavior changes when the LED size gets smaller.…”

“…This indicates that the alignment causes the occurrence of the space between p-contact and mesa. [11][12][13] As presented in Figure 1, the difference in PPI between a sample with 300 µm-size ITO and mesa (≈84 PPI) and a sample with 300 µm ITO and 306 µm mesa (i.e., 3 µm spacer; ≈82.3 PPI) isThe sidewall condition is a key factor determining the performance of microlight emitting diodes (µLEDs). In this study, equilateral triangular III-nitride blue µLEDs are prepared with exclusively m-plane sidewall surfaces to confirm the impact of sidewall conditions.…”

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“…Nevertheless, there is a constant driving force to utilize µLEDs for high-resolution display due to their inherent advantages arising from inorganic materials. Various methods have been introduced to alleviate and overcome the size-dependent external quantum efficiency (EQE) reduction issue, such as chemical etching and aluminum oxide passivation by atomic layer deposition (ALD), wet reaction hydrogen, and sulfur-based passivation (2,3). Recently, the passivation approach with sol-gel method exhibited most effective passivation of sidewall defects so far than ALD-based process.…”