Lighting the future: The rising stock of Gallium nitrade

20 October 2014 (Last Updated October 20th, 2014 18:30)

Heralded as the most important semiconductor since silicon, gallium nitride holds potential for many important applications, such as LEDs, and could be the key material for the next generation of high-frequency, high-power transistors. Ross Davies asks what all the fuss is about?

Lighting the future: The rising stock of Gallium nitrade

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Unpopular a measure as it has been, the phasing out of the traditional 60-watt incandescent light bulb in several parts of the world, such as Europe and the US, has thrown up some lively debate.

Those inclined to romanticism and nostalgia have lamented the death of the "painterly glow" (as described by Slate contributor Ron Rosenbaum) emitted from tungsten filaments, and the idea of losing an illuminating link between this century and the last.

Others, however, have long clamoured for more efficient bulb technologies, capable of having a more positive impact on greenhouse gas emissions and curbing fossil fuel use. After all, as proponents of such progression may well argue, the energy burnt up by the average tungsten filament light bulb over its lifetime amounts to the same contained in three tonnes of coal.

There are, of course, alternatives to the incandescent bulb - which, as of 1 January 2014, was banned in the US - in the way we keep our homes and public spaces lit. One of the most popular options is the use of light emitting diodes (LEDs), due to their low energy consumption and longevity.

New light: The potential of gallium nitrade in creating more powerful LEDs

Nonetheless, the market-standard LED requires a DC power supply so as to resist current fluctuations. It is this need for high-frequency, high-speed transistors that make LEDs expensive when it comes to their use in large-scale commercial applications.

Gallium nitrade (GaN), a relatively new semiconductor - although already used in white LEDs - could provide a potential solution to this quandary. As well as operating at higher temperatures, voltages and currents, the switching capability of GaN transistors is ten times faster than that of their silicon equivalents.

While GaN's physical properties have been identified as very hard, with high-heat capacity and thermal conductivity - it is commonly used in cellular applications and military radar - it remains something of an unknown quantity in the general field of power technology.

However, as evidenced by an ongoing spike in research, GaN's stock is surely rising. Some claim that if the semiconductor is fostered to the right level, the upshot could be LED lamps that are cheaper, smaller and last for longer.

Bright sparks: Current GaN research taking place at the University of Cambridge

The University of Cambridge has a designated facility - the Cambridge Centre for Gallium Nitrade, based in its Department of Material Sciences and Metallurgy - which hopes to gain a greater understanding of GaN's physical properties and potential application in commercial energy products.



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"Gallium nitride is probably the most important semiconductor material since silicon," says professor Sir Colin Humphreys, who heads up the centre. "It can be used to emit brilliant light in the form of light emitting diodes and laser diodes, as well as being the key material for next-generation high-frequency, high-power transistors, capable of operating at high temperatures."

As well as nitrade for LED lighting, other research projects currently taking place at the department pertain to GaN growth on silicon and ultraviolet LED application. Drawing on the university's unparalleled research resources, Humphreys and his team are able to avail themselves of state-of-the-art equipment to examine the physical properties of GaN.

This includes a Thomas Swan (now Aixtron) MOCVD growth reactor, used for GaN and InGaN (indium gallium nitrade) growth and doping, while characterisation takes place through an electron microscopy and X-ray diffraction facilities. Researchers also perform computational modelling of III-nitride materials.

"The research team is thriving as we move into exciting new GaN based research areas," says Humphreys.

"We are one of a small number of places in the world to have, in close proximity and on the same site, gallium nitride growth equipment, extensive advanced electron microscopy characterisation facilities, advanced X-ray diffraction characterisation facilities, atomic force microscopy, photoluminescence [PL] for measuring optical properties, Hall effect equipment for measuring electrical properties and basic theory for understanding in detail physical properties."

Future challenges: Questions over efficiency and cost

"Prices remain high for GaN devices, such as those already used in military, radar and military applications."

The primary task for researchers will revolve around tackling questions related to LED efficiency. GaN LEDs are based on thin layers of material grown on other materials such as silicon or sapphire. Electric current is then passed into the active region of the LED, from which the light is emitted.

However, these GaN crystals are not perfect, and defects in their structure can lead to the disruption of the light emission process, resulting in the production of heat rather than light - meaning a reduction in LED efficiency.

There are also questions around cost. Prices remain high for GaN devices, such as those already used in military, radar and military applications. But, while those markets are typified by customers that are often willing to pay a premium with ROI firmly in mind, the same cannot be said for the average energy consumer.

"It is true that the main drawback of GaN is the cost," admits Humphreys. "But, by growing GaN devices on large area silicon substrates, substantial cost reductions are possible. I believe that GaN power electronic devices will be widely used in the future."

Humphreys does not provide a timeframe, but one senses that market penetration of GaN is well within the realms of near-future possibility. With its potential for adoption in numerous devices, unique physical attributes, and ability to drive down costs and save on energy, gallium nitrade is a buzzword that we should expect to hear more and more of in the coming years.

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