3D metamaterials from semiconductors
Scientists at Princeton University, USA, claim to have produced the first 3D metamaterial constructed entirely from semiconductors. They believe the new design could offer a cost effective way of creating negative refractive lenses for high-speed communications, medical diagnostics and detecting terrorist threats.
‘For most applications, in order for the metamaterial to significantly affect incident light, the material must be optically thick (3D),’ explains lead researcher Anthony Hoffman. ‘The thicker the material, the longer it is governed by these unique material parameters.’
The team used molecular beam epitaxy (MBE) to ‘grow’ indium gallium arsenide (InGaAs) and aluminium indium arsenide layers on an indium phosphate substrate. ‘The InGaAs layers were doped with silicon to introduce free electrons [that] create plasma resonance, which is essential for the material to exhibit negative refraction,’ says Hoffman.
He explains that by creating a 3D design from semiconductors produced using MBE, a technology employed in telecommunications to make lasers and detectors, the researchers have found a simple, more reliable and cost effective technique to scale up the production of metamaterials.
He says, ‘Previous metamaterials achieve negative refraction by using sub-wavelength structures that have two resonances – one electric and the other magnetic. These are amazing feats of science and engineering [but] to produce them, one must have a firm understanding of the governing physics to devise an appropriate design, and the skill and capability to realise that design.’
Furthermore, the invention at Princeton is capable of negative refraction of light in the mid-infrared region, which is used in a range of sensing and communications applications.
The team claims there is also less light lost from its single-resonance invention, compared to double-resonance metamaterials that experience high optical absorption.
Commenting on the research, John Pendry, Professor of Physics at Imperial College London, UK, who has conducted extensive research into metamaterials, told Materials World, ‘This is an interesting experimental advance. The [researchers] deploy a new set of ingredients to make up a metamaterial functioning near to optical frequencies’.
He adds, ‘The anisotropic material concerned is not a negative index material, but what is known as an indeterminate material – a negative response to electric fields acting along one axis and a positive response along the other axis. Such materials have been studied in the past. The significance of the present work is the high quality of materials employed, which enables a better quality of product to be obtained.’