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New theory could lead to better optoelectronics

Researchers in Belfast and Zurich create framework for designing with 2D semiconductors

Researchers at Queen's University Belfast and ETH Zurich, Switzerland, have created a new theoretical framework which they think could help physicists and device engineers design better optoelectronics, leading to less heat generation and power consumption in devices which source, detect, and control light.

The model considers an interface formed between a layer of 2D material and a bulk semiconductor (e.g. traditional silicon microchip).

A key part of the research involved formulating an index or parameter that quantified the transparency of a monolayer 2D material to an electric displacement field. It showed that the transparency is determined by the combined effect of 2D material quantum capacitance and the classical semiconductor capacitance. By calculating the quantum capacitance for a variety of 2D materials, they predicted the ranking for a variety of 2D compounds according to their transparency to an electric displacement field as follows: graphene > silicene > germanene > WS2 > WTe2 > WSe2 > MoS2 > MoSe2 > MoTe2, when the majority carrier is electron.

Speaking about the research, Elton Santos from the Atomistic Simulation Research Centre at Queen's, said: "Imagine we can change the transparency of a material just using an electric bias, e.g. get darker or brighter at will. What kind of implications would this have, for instance, in mobile phone technologies? This was the first question we asked ourselves. We realised that this would allow the microscopic control over the distribution of charged carriers in a bulk semiconductor in a nonlinear manner.

"This will help physicists and device engineers to design better quantum capacitors, an array of subatomic power storage components capable to keep high energy densities, for instance, in batteries, and vertical transistors, leading to next-generation optoelectronics with lower power consumption and dissipation of heat (cold devices), and better performance. In other words, smarter smart phones."

Explaining how the theory could have important implications for future work in the area, Dr Santos added: "In principle, our approach can be readily extended to a stack of multiple 2D materials, or namely, van der Waals heterostructures recently fabricated. This will allow us to design and predict the behaviour of these cutting-edge devices in prior to actual fabrication, which will significantly facilitate developments for a variety of applications. We will have an in silico search for the right combination of different 2D crystals while reducing the need for expensive lab work and test trials."

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