July 11, 2016

Gallium Arsenide nanowire lasers boosted by one hundred times with zinc dopants

Scientists at ANU have improved the performance of tiny lasers by adding impurities, in a discovery which will be central to the development of low-cost biomedical sensors, quantum computing, and a faster internet.

Researcher Tim Burgess added atoms of zinc to lasers one hundredth the diameter of a human hair and made of gallium arsenide - a material used extensively in smartphones and other electronic devices.

The impurities led to a 100 times improvement in the amount of light from the lasers.

"Normally you wouldn't even bother looking for light from nanocrystals of gallium arsenide - we were initially adding zinc simply to improve the electrical conductivity," said Mr Burgess, a PhD student in the ANU Research School of Physics and Engineering.

"It was only when I happened to check for light emission that I realised we were onto something."

Structure, morphology and photoluminescence (PL) of undoped and doped GaAs NWs.

Nature Communications - Doping-enhanced radiative efficiency enables lasing in unpassivated GaAs nanowires

Gallium arsenide is a common material used in photovoltaic cells, lasers and light-emitting diodes (LEDs), but is challenging to work with at the nanoscale as the material requires a surface coating before it will produce light.

Previous ANU studies have shown how to fabricate suitable coatings.

The new result complements these successes by increasing the amount of light generated inside the nanostructure, said research group leader Professor Chennupati Jagadish, from the ANU Research School of Physics Sciences.

"It is an exciting discovery and opens up opportunities to study other nanostructures with enhanced light emission efficiency so that we can shrink the size of the lasers further," he said.

Mr Burgess said that the addition of the impurity to gallium arsenide, a process called doping, did not only improve the light emission.

"The doped gallium arsenide has a very short carrier lifetime of only a few picoseconds, which meant it would be well suited to use in high speed electronics components," he said.

"The doping has really has given these nanolasers a performance edge."


Nanolasers hold promise for applications including integrated photonics, on-chip optical interconnects and optical sensing. Key to the realization of current cavity designs is the use of nanomaterials combining high gain with high radiative efficiency. Until now, efforts to enhance the performance of semiconductor nanomaterials have focused on reducing the rate of non-radiative recombination through improvements to material quality and complex passivation schemes. Here we employ controlled impurity doping to increase the rate of radiative recombination. This unique approach enables us to improve the radiative efficiency of unpassivated GaAs nanowires by a factor of several hundred times while also increasing differential gain and reducing the transparency carrier density. In this way, we demonstrate lasing from a nanomaterial that combines high radiative efficiency with a picosecond carrier lifetime ready for high speed applications.

SOURCES - Nature Communications, Australian National University

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