Zinc doping makes GaAs nanowire lasers shine

Article By : Julien Happich

Gallium arsenide is used in smartphones and other electronic devices, but GaAs nanowires require surface passivation to minimise surface defects.

Scientists at the Australian National University (ANU) have improved the performance of unpassivated GaAs nanowire (NW) lasers more than a hundred folds, by adding zinc as a dopant, changing the crystal structure and increasing the device's radiative efficiency.

Gallium arsenide is extensively used in smartphones and other electronic devices, but typically GaAs nanowires require surface passivation to minimise surface defects and to minimise the rate of non-radiative recombinations. Such passivation adds to the complexity of device fabrication and may be incompatible with other processing steps, explain the researchers in their Nature Communications paper, "Doping-enhanced radiative efficiency enables lasing in unpassivated GaAs nanowires."

Unpassivated GaAs NWs, on the other hand, are usually characterised by a very low radiative efficiency and are not considered suitable for optical applications. Here the GaAs NWs were grown by metal-organic vapour phase epitaxy at 575°C, with a low V/III ratio of 1.4. The addition of zinc during the growth process turned the pure wurtzite crystal structure (SEM image d) to a zincblende twining superlattice (TSL) structure (SEM image f).

This doping and crystal structure change increased radiative efficiency without the need for further fabrication steps, combining excellent radiative efficiency with an ultrashort lifetime in the picosecond range.

The unpassivated but zinc-doped GaAs NWs exhibited a radiative efficiency several hundred times better than that of undoped GaAs NWs, while being more than two orders of magnitude brighter, considering that the doped NW is also spectrally broader than its un-doped counterpart.

__Figure 1:__ *(d) SEM image of an undoped GaAs NW. Scale bar, 500nm. (e) Photoluminescence spectra collected from single undoped and doped GaAs NWs under identical excitation and collection conditions. Emission from the doped NW is seen to be orders of magnitude brighter. (f) SEM image of a doped GaAs NW. Scale bar, 500nm.*

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