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A New Way To Understand Band Gap Energies?

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Latest findings have implications for all semiconductors where alloying is the standard approach to band gap tuning, say researchers

An international team of scientists has published a paper in Physical Review B that gives a new way of thinking about semiconductor band gaps. They believe their findings have significant implications for optoelectronic devices in particular, but all semiconductors in general.

It has been known for a while that disorder can have a significant impact on the band gap of ZnSnN2 and closely related materials. But the researchers Robert Makin, Krystal York, Steven Durbin and Roger Reeves suggest there may be more to the story than we currently appreciate.

Starting with the earth-abundant element ternary compound ZnSnN2, a material of interest for potential application in photovoltaics, the team focused their energy on quantifying the amount of disorder (in terms of antisite defects) that characterises the Zn, Sn cation sublattice. They were able to show that the band gap energy is continuously tuneable not only between two previously established values, but can actually be made to 'go negative" - corresponding to inversion of the conduction and valence bands - passing through zero along the way.

They then turned their attention to binary compounds including GaN. Here they demonstrated experimentally that it is possible to achieve the same effect in those materials, as well, by exploiting what they refer to as 'structural motifs' and their relationship to disorder and stoichiometry.

Not content to stop there, they extended the model to show that it has predictive ability for the hybrid perovskite methylammonium lead iodide (MAPbI3), nanoporous graphene, and even silicon samples reported as porous or amorphous.

They believe their discovery has significant implications for all semiconductors where alloying is often the standard approach to band gap tuning to match the requirements of a specific device application.

'Revisiting semiconductor band gaps through structural motifs: An Ising model perspective' by Robert A. Makin et al; Phys. Rev. B 102, 115202, 8th September 2020


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