Instabilities found on common semiconductor material

Compound semiconductors are an integral part of electronic devices, from smartphones and GPS to satellites and laptops. But it turns out that the surface of a commonly used compound semiconductor material — gallium arsenide (GaAs) — is not as stable as previously thought.

Researchers at Cardiff University have identified small pockets of instability in the atomic structure of GaAs that have a tendency to appear and then disappear. Published in the journal Physical Review Letters, their discovery is said to mark the first time that this phenomenon, dubbed ‘metastability’, has been observed on GaAs surfaces.

Key to this discovery was the availability of equipment with capabilities that are not believed to exist anywhere else in the world. The labs at Cardiff’s School of Physics and Astronomy and Institute for Compound Semiconductors have a low-energy electron microscope combined with a molecular beam epitaxy machine which allows researchers to observe dynamic changes on the structure of materials while compound semiconductors are being fabricated.

Molecular beam epitaxy is the technique used to fabricate or ‘grow’ compound semiconductor devices and works by firing precise beams of extremely hot atoms or molecules at a substrate. The molecules land on the surface of the substrate, condense and build up very slowly and systematically in ultrathin layers, eventually forming a complex, single crystal.

“Even though GaAs has been well studied, the use of low-energy electron microscopy in the growing process allows us to observe dynamic events that have never been seen before,” said Dr Juan Pereiro Viterbo, a co-author on the study.

“At the moment we do not know whether this phenomenon is affecting the growth of semiconductor device structures — this is what we need to study next.

“If this phenomenon were to occur during the growth of semiconductor devices then this could have profound consequences.

“Ultimately, these findings are helping us to better understand what is happening at the molecular scale, which will enable us to develop new materials and structures, reduce defects in existing compound semiconductor devices and therefore develop better electronics for our communication systems, computers, phones, cars and more.”

Image credit: ©Edelweiss/Dollar Photo Club

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