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4 November 2019

Cardiff uses LEEM-MBE to observe metastability on GaAs surfaces

Researchers at Cardiff University’s School of Physics and Astronomy and the Institute for Compound Semiconductors say that they have, for the first time, spotted previously unseen ‘instabilities’ on the surface of gallium arsenide (GaAs) that have a tendency to appear and then disappear (K. Hannikainen et al, ‘Surface Phase Metastability during Langmuir Evaporation’, Phys. Rev. Lett. vol123, 186102).

Specifically, the team has directly imaged the spontaneous formation of metastable surface phase domains in the atomic structure of GaAs(001) during Langmuir evaporation. It is the first time that this phenomenon of metastability has been observed on GaAs surfaces.

These metastable phases transform to the thermodynamically stable parent phase, producing a dynamic phase coexistence with a temperature-dependent, time-averaged coverage. The measured temperature dependence of the time-averaged coverage has been explain using Monte Carlo simulations to identify the key kinetic processes and investigate the interplay between phase metastability and evolving surface morphology.

“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,” says co-author Dr Juan Pereiro Viterbo of the School of Physics and Astronomy. “If this phenomenon were to occur during the growth of semiconductor devices then this could have profound consequences,” he adds.

“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.”

Key to the discovery was the availability of equipment with capabilities that do not exist anywhere else in the world, it is claimed. The labs at the School of Physics and Astronomy and the Institute for Compound Semiconductors have a low-energy electron microscope (LEEM) combined with a molecular beam epitaxy (MBE) system, which allows researchers to observe dynamic changes on the structure of materials while compound semiconductors are being fabricated.

“Even though GaAs has been well studied, the use of low-energy electron microscopy in the growth process allows us to observe dynamic events that have never been seen before,” says Viterbo.

Tags: GaAs

Visit: https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.123.186102

Visit: https://leemlab.cf.ac.uk

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