Improved performance of AlGaInP red micro-light-emitting diodes with sidewall treatments

Abstract

The electrical and optical improvements of AlGaInP micro-light-emitting diodes (µLEDs) using atomic-layer deposition (ALD) sidewall passivation were demonstrated. Due to the high surface recombination velocity and minority carrier diffusion length of the AlGaInP material system, devices without sidewall passivation suffered from high leakage and severe drop in external quantum efficiency (EQE). By employing ALD sidewall treatments, the 20×20 µm2 µLEDs resulted in greater light output power, size-independent leakage current density, and lower ideality factor. The forward current-voltage characteristic was enhanced by using surface pretreatment. Furthermore, ALD sidewall treatments recovered the EQE of the 20×20 µm2 devices more than 150%. This indicated that AlGaInP µLEDs with ALD sidewall treatments can be used as the red emitter for full-color µLED display applications.

Investigation of InGaN-based red/green micro-light-emitting diodes

“…This method can easily integrate RGB colors into matrices on the same substrate [7], yet the colorconversion efficiency of hybrid devices must be improved [8]. Another approach chooses to fabricate red and green µLEDs using different materials, AlInGaP for red µLEDs [9] and InGaN for green µLEDs [10]. This material difference causes a mismatched angular distribution between the red and green µLEDs [11], leading to a noticeable color shift at different observed angles.…”

High‐resolution and high‐brightness full‐colour “Silicon Display” for augmented and mixed reality

“…It was also shown that the surface recombination through Shockley‐Read‐Hall (SRH) recombination via defect levels is dominant in the smaller red LEDs. So the decrease in EQE is much more significant for red micro‐LEDs smaller than 10 μm, 16 although some improvement can be expected by surface treatment and sidewall passivation 25 …”

Micro‐Light Emitting Diode: From Chips to Applications

“…[ 10,13–29 ] For instance, Figure a–c exhibits the EQEs of different size red, green, and blue LEDs as a function of current density. [ 17,19,22 ] The maximum EQE decreases with decreasing LED size and the maximum EQE is obtained at higher current densities as chip size decreases. This behavior has been ascribed to leakage current and/or Shockley–Read–Hall (SRH) nonradiative recombination caused by sidewall defects in smaller chip geometries.…”

“…[ 13,17,25 ] The ideality factors were assessed using the current–voltage curves. Measurements of red AlGaInP‐based, and green and blue InGaN‐based LEDs showed that smaller devices had higher ideality factors, [ 17,19,22 ] indicating they suffered from carrier loss due to SRH nonradiative recombination at sidewall defects. [ 18,19,25 ] Further, the green and blue LEDs typically exhibit the maximum EQE at lower current than the red LEDs.…”