# Bandgap Engineering On Demand in GaAsN Nanowires by Post‐Growth Hydrogen Implantation

## TL;DR

This paper shows how hydrogen implantation can adjust the bandgap of GaAsN nanowires after they are grown, enabling precise and reversible control over their optical properties.

## Contribution

The novel contribution is achieving reversible and tunable bandgap engineering in GaAsN nanowires via post-growth hydrogen implantation and thermal annealing.

## Key findings

- Hydrogen implantation increases the bandgap of GaAsN nanowires by up to 460 meV in a reversible and non-destructive way.
- Thermal annealing allows partial dissolution of N–H complexes, tuning the bandgap over a 240 meV range.
- Laser annealing enables localized bandgap tuning, opening new possibilities for quantum structures in nanowires.

## Abstract

Bandgap engineering in semiconductors is required for the development of photonic and optoelectronic devices with optimized absorption and emission energies. This is usually achieved by changing the chemical or structural composition during growth or by dynamically applying strain. Here, the bandgap in GaAsN nanowires grown on Si is increased post‐growth by up to 460 meV in a reversible, tunable, and non‐destructive manner through H implantation. Such a bandgap tunability is unattained in epilayers and enabled by relaxed strain requirements in nanowire heterostructures, which enables N concentrations of up to 4.2% in core–shell GaAs/GaAsN/GaAs nanowires resulting in a GaAsN bandgap as low as 0.97 eV. Using μ‐photoluminescence measurements on individual nanowires, it is shown that the high bandgap energy of GaAs at 1.42 eV is restored by hydrogenation through the formation of N–H complexes. By carefully optimizing the hydrogenation conditions, the photoluminescence efficiency increases by an order of magnitude. Moreover, by controlled thermal annealing, the large shift of the bandgap is not only made reversible but also continuously tuned by breaking up N–H complexes in the hydrogenated GaAsN. Finally, local bandgap tuning by laser annealing is demonstrated, opening up new possibilities for developing novel, locally and energy‐controlled quantum structures in GaAsN nanowires.

The GaAsN bandgap in the GaAs/GaAsN core–shell nanowire shifts to lower energy for increasing N concentrations. By post‐growth H implantation the GaAsN bandgap is moved to a higher GaAs‐like energy through the formation of N–H complexes. By thermal annealing, these complexes can be partially dissolved, allowing to tune the GaAsN bandgap over a range of 240 meV.