Nanostructured metal coatings let the light through for electrical devices
Liz Ahlberg, U of I News Bureau
- A new anti-reflection coating developed at ECE ILLINOIS lets light through without hampering the flow of electricity, a step that could increase efficiency in devices like LEDs, solar cells, and sensors.
- The coating is a specially engraved, nanostructured thin film that allows more light through than a flat surface, yet also provides electrical access to the underlying material.
- The Illinois and Massachusetts team used a patented method of metal-assisted chemical etching called MacEtch that Li developed at Illinois.
Light and electricity dance a complicated tango in devices like LEDs, solar cells and sensors. A new anti-reflection coating developed in research led by Professor Daniel M Wasserman, in collaboration with researchers at the University of Massachusetts at Lowell, lets light through without hampering the flow of electricity, a step that could increase efficiency in such devices.
“The ability to improve both electrical and optical access to a material is an important step towards higher-efficiency optoelectronic devices,” said Wasserman, a member of the Micro and Nano Technology Laboratory at Illinois.
At the interface between two materials, such as a semiconductor and air, some light is always reflected, Wasserman said. This limits the efficiency of optoelectronic devices. If light is emitted in a semiconductor, some fraction of this light will never escape the semiconductor material.
“It has been long known that structuring the surface of a material can increase light transmission,” said study co-author Viktor Podolskiy, a professor at the University of Massachusetts at Lowell. “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.”
Although such pattered surfaces aid in light transmission, they hinder electrical transmission, creating a barrier to the underlying electrical material.
“In most cases, the addition of a conducting material to the surface results in absorption and reflection, both of which will degrade device performance,” Wasserman said.
“The nanopillars enhance the optical transmission while the metal film offers electrical contact. Remarkably, we can improve our optical transmission and electrical access simultaneously,” said Ryan Liu, an ECE ILLINOIS graduate student and researcher at Illinois. He is a co-lead author of the work, along with ECE ILLINOIS student and researcher Xiang Zhao and Massachusetts graduate researcher Christopher Roberts.
The researchers demonstrated that their technique, which results in metal covering roughly half of the surface, can transmit about 90 percent of light to or from the surface. For comparison, the bare, unpatterned surface with no metal can only transmit 70 percent of the light and has no electrical contact.
The researchers also demonstrated their ability to tune the material’s optical properties by adjusting the metal film’s dimensions and how deeply it etches into the semiconductor.
“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 said.
The National Science Foundation and Lam Research supported this work.