High efficiency of III-nitride micro-light-emitting diodes by sidewall passivation using atomic layer deposition

Abstract

Optoelectronic effects of sidewall passivation on micro-sized light-emitting diodes (µLEDs) using atomic-layer deposition (ALD) were investigated. Moreover, significant enhancements of the optical and electrical effects by using ALD were compared with conventional sidewall passivation method, namely plasma-enhanced chemical vapor deposition (PECVD). ALD yielded uniform light emission and the lowest amount of leakage current for all µLED sizes. The importance of sidewall passivation was also demonstrated by comparing leakage current and external quantum efficiency (EQE). The peak EQEs of 20 × 20 µm µLEDs with ALD sidewall passivation and without sidewall passivation were 33% and 24%, respectively. The results from ALD sidewall passivation revealed that the size-dependent influences on peak EQE can be minimized by proper sidewall treatment.

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

“…One possibility is the plasma damage induced during the deposition of the SiO 2 electrical isolation layer by PECVD. Indeed, Wong et al reported that SiO 2 passivation layer deposited on the sidewall surface of GaN micro‐LEDs by PECVD could reduce and that deposited by atomic layer deposition (ALD) could increase the light output power of GaN micro‐LEDs with respect to devices without a passivation layer . Therefore, optimization of the deposition process of the SiO 2 passivation and electrical isolation layer seems to be a possible way of suppressing the generation of the nonradiative defects responsible for the aging effect.…”

“…There is much current interest in developing micro‐light‐emitting diode (micro‐LED) display, which is expected as a low‐power consumption, high‐brightness, and high‐resolution display for next‐generation wearable information devices . One of the most serious technical obstacles toward the realization of high‐performance micro‐LED displays is the strong decrease in internal quantum efficiency (IQE) with the decrease in chip size to below a few tens of micrometers, especially at the current density region lower than 20 A cm −2 . In the fabrication of conventional GaN‐based micro‐LEDs, inductively coupled plasma (ICP) etching was typically used to define the LED mesa, during which high‐density crystalline defects acting as nonradiative recombination centers will be inevitably generated on the sidewall surface of the LED mesa over a depth of a few tens of nanometers due to ion bombardment and high‐energy and high‐density (≈50 mW cm −2 ) UV photon irradiation from the plasma .…”

Prospects and challenges of mini‐LED and micro‐LED displays

“…Besides ITO, multilayer metal electrode can also be used for LEDs to achieve good ohmic contact. A typical structure for forming multilayer metal contact contains three parts: (1) a thin layer physically attached to the semiconductor to form good ohmic contact, eg, a thin ITO; (2) intermediate layers serving as a diffusing barrier (eg, noble metals Pt, Pd, and Re as well as refractory metals Ti, W, Ta, and Mo); and (3) highly conductive metal (eg, Au) for bonding. The optical property of mini/micro‐LED electrode depends on the exact electrode structure employed.…”

Micro-LEDs, a Manufacturability Perspective

“…Chen et al have reported that in pyramidal micro-LEDs, a SiO 2 leakage current confinement layer can decrease the reverse leakage current by two orders of magnitude, and the light output of the micro-LEDs can be improved by 115% averagely [32]. Wong et al have demonstrated that using atomic-layer deposition (ALD) of SiO 2 for sidewall passivation, size-dependent factors on peak EQE of micro-LEDs can be minimized [33]. Enhancement in light extraction and reduction in leakage current caused by surface recombination and sidewall damage led to an EQE of 33% for 20 µm × 20 µm micro-LEDs with ALD passivation, compared to 24% without sidewall passivation.…”