“The ability to improve electrical and optical access to a material is an important step towards higher efficiency optoelectronic devices,” said Professor DanielWasserman, from the University of Illinois.
According to Prof Wasserman, some light is always reflected at the interface between two materials, such as a semiconductor and air, limiting efficiency. If light is emitted in a semiconductor, some fraction of this light will never escape, he said. Similarly, for a sensor or solar cell, some fraction of light will never make it to the detector and be turned into an electrical signal.
“It has long been known that structuring the surface of a material can increase light transmission,” said Professor Viktor Podolskiy, from UMass. “Among such structures, one of the more interesting is similar to structures found in nature, and is referred to as a ‘moth eye’ pattern: tiny nanopillars which can ‘beat’ the Fresnel equations at certain wavelengths and angles.”
The researchers used MacEtch – a metal assisted chemical etching process developed at Illinois – to engrave a patterned metal film into a semiconductor to create an array of tiny nanopillars rising above the metal film. The combination of these nanopillars and the metal film created a partially coated material that outperformed the untreated semiconductor.
According to the team, its technique can transmit about 90% of light to or from the surface. In comparison, an unpatterned surface with no metal could only transmit 70% of the light, with no electrical contact.
“We are looking to integrate these nanostructured films with optoelectronic devices to demonstrate that we can simultaneously improve both the optical and electronic properties of devices operating at wavelengths from the visible all the way to the far infrared,” Wasserman concluded.
