Sustained high external quantum efficiency in ultrasmall blue III–nitride micro-LEDs

Abstract

Ultrasmall blue InGaN micro-light-emitting diodes (µLEDs) with areas from 10−4 to 0.01 mm2 were fabricated to study their optical and electrical properties. The peak external quantum efficiencies (EQEs) of the smallest and largest µLEDs were 40.2 and 48.6%, respectively. The difference in EQE was from nonradiative recombination originating from etching damage. This decrease is less severe than that in red AlInGaP LEDs. The efficiency droop at 900 A/cm2 of the smallest µLED was 45.7%, compared with 56.0% for the largest, and was lower because of improved current spreading. These results show that ultrasmall µLEDs may be fabricated without a significant loss in optical or electrical performance.

Near‐Complete Elimination of Size‐Dependent Efficiency Decrease in GaN Micro‐Light‐Emitting Diodes

“…Summary of current density as peak EQE as a function of chip size of GaN micro‐LEDs reported in the literature and those fabricated in this work. Open squares, solid circles, and open triangles represent data taken from the studies by Olivier et al, Tian et al, Hwang et al, respectively. Solid triangles and solid stars are data obtained in this work.…”

52‐3: Invited Paper: Combining Engineered EPI Growth Substrate Materials with Novel Test and Mass‐Transfer Equipment to Enable MicroLED Mass‐Production

“…Figure 3 shows a six-inch GaAs on sapphire engineering growth substrate (QMAT). High peak MicroLED efficiency has been shown to be achievable down to 10µm x 10µm device size, however the peak values occur at current density values in the tens of A/cm 2 , substantially higher than the expected display operating points [1]. At a current density range of 1-1000 mA/cm 2 , traditional growth substrates can have low efficiency due to a higher value of its non-radiative recombination parameter A. Low-dislocation GaN material has been shown to improve device performance and limit nonradiative recombination under low injection conditions [2].…”

32‐1: Invited Paper: Review of Micro‐light‐emitting‐diode Technology for Micro‐display Applications

“…This can be assured by the fact that the external quantum efficiency (EQE), the ratio of the number of photons emitted from LED to the number of electrons injected into the device, drops down to below 50 % when the device size is shrunk from 500 μm to 10 μm. This phenomenon is mainly associated with the increased non-radiative surface recombination, which induces leakage currents, at the sidewall of the device [19,20]. The damage of the sidewall is primarily introduced by a dry etching process, and several approaches have been proposed to enhance the efficiency by minimizing the sidewall damage.…”