# Impact of Surface Passivation on the Efficiency and High-Speed Modulation of III–V GaAs/AlGaAs Nanopillar Array LEDs

## TL;DR

This paper shows how surface passivation improves the efficiency and speed of tiny III–V nanopillar LEDs, making them viable for advanced optical technologies.

## Contribution

The study demonstrates electrically driven nanoLEDs with record carrier lifetimes and high modulation speeds through surface passivation techniques.

## Key findings

- Surface passivation achieved differential carrier lifetimes of ∼0.61 ns in nanoarray LEDs.
- Devices showed low surface velocity (S ∼ 0.7–2.7 × 10⁴ cm/s) and high internal quantum efficiency (∼0.45).
- NanoLEDs with subnanosecond modulation response are suitable for optical data communications and AR/VR displays.

## Abstract

III–V semiconductor
nanolight sources with deep-subwavelength
dimensions (≪1 μm) are essential for miniaturized photonic
devices such as nanoLEDs and nanolasers. However, these nanoscale
emitters typically suffer from substantial nonradiative recombination
at room temperature, resulting in low efficiency and ultrashort lifetimes
(<100 ps). Previous works have predominantly studied surface passivation
of nanoLEDs under optical pumping conditions, while practical applications
require electrically driven nanoLEDs. Here, we investigate the influence
of surface passivation on the efficiency and high-speed modulation
response of electrically pumped III–V GaAs/AlGaAs nanopillar
array LEDs. Surface passivation was performed using ammonium sulfide
chemical treatment followed by encapsulation with a 100 nm silicon
nitride layer deposited via low-frequency plasma-enhanced chemical
vapor deposition. Time-resolved electroluminescence (TREL) measurements
reveal differential carrier lifetimes (τ) of ∼0.61 ns
for nanoarray LEDs with pillar diameters of ∼440 nm, a record-long
lifetime for electrically driven GaAs-based nanopillar arrays. Under
low injection conditions, the devices exhibited carrier lifetimes
of ∼0.41 ns, only 4-fold shorter than those of larger microLEDs
(τ ∼ 1.67 ns for 10 μm pillar diameter), indicating
successful suppression of nonradiative effects and a low surface velocity,
ranging from S ∼ 0.7 × 104 to 2.7 × 104 cm/s. This reveals a potential high internal quantum efficiency
(IQE) ∼ 0.45 for our nanoLEDs operating under very high injection
conditions, limited only by Auger recombination and self-heating effects
at high current density. These miniaturized nanoLEDs with high radiative
recombination efficiency and subnanosecond modulation response pave
the way for optical data communications, energy-efficient optical
interconnects, AR/VR displays, and neuromorphic computing applications.