Thursday, 18 September 2014
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Researchers look to silicon semiconductor alternative

Researchers in the US believe they’ve overcome a major hurdle in developing a functional alternative to the silicon semiconductor.

Silicon semiconductors are ubiquitous in modern electronics but these devices have limitations, including a failure to operate properly at very high temperatures.

One promising alternative is a semiconductor made from aluminium and nitrogen to form aluminium nitride (AlN), which is stronger and more stable than its silicon counterpart, can function at high temperatures, is piezoelectric, and is transparent to, and can emit, visible light.

Conventional processes for producing AIN layers run at temperatures as high as 1150 degrees Celsius, and offer limited control over the thickness of the layers. Now a new technique is claimed to offer a way to produce high-quality aluminium nitride (AlN) layers with atomic-scale thickness and at half the temperature of other methods.

Neeraj Nepal and colleagues of the US Naval Research Laboratory in Washington, DC, formed AIN layers using atomic layer epitaxy (ALE), in which materials are ‘grown’ layer-by-layer by sequentially employing two self-limiting chemical reactions onto a surface.

‘For instance to grow aluminium nitride, you would inject a pulse of an aluminium precursor into the growth zone where it would coat all surfaces,’ Nepal said in a statement.

‘After purging any excess aluminium precursor away, you would then ‘build’ the crystal by injecting a pulse of the nitrogen precursors into the growth zone, where it reacts with the aluminium precursor at the surface to form a layer of AlN. Then you’d purge any excess nitrogen and reaction products away and repeat the process.’

With this process, the researchers produced a material with qualities similar to those synthesised at much higher temperatures, but under conditions that allow it to be integrated in new ways for the fabrication of devices for technologies such as transistors and switches.

Nepal said the work expands the potential for new advanced specialty materials that could be used in applications including next-generation high-frequency radio frequency electronics, such as those used for high-speed data transfer and cell phone services.

The work is described in Applied Physics Letters in an article entitled, Epitaxial Growth of AlN Films via Plasma-assisted Atomic Layer Epitaxy.


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