The technique involves growing metallic nanoparticles on and below the surface of semiconductors. These nanoparticles increase the efficiency of LEDs in several ways: by acting as ‘antennas’ that turn more of the electricity running through the semiconductor into light; and by helping to reflect light out of the device.
“This is a seamless addition to the manufacturing process and that’s what makes it so exciting,” said Michigan Professor Rachel Goldman. “The ability to make 3D structures with these nanoparticles throughout is going to open a lot of possibilities.”
While the idea of adding nanoparticles to increase LED efficiency is not new, previous efforts have used expensive metals. A further complication was the need for precise particle size and spacing.
Prof Goldman’s team used molecular beam epitaxy to spray multiple layers of metallic elements onto a wafer. An ion beam was then applied to push metal out of the wafer and onto the surface, forming nanoscale particles whose size and placement can be controlled precisely by varying the angle and intensity of the ion beam.
The team is now working to adapt the ion beam process to the specific materials used in LEDs and estimate that higher-efficiency lighting devices could be ready for market within the next five years.
However, because the approach is said to allow precise control over nanoparticle distribution, the researchers say it could induce a phenomenon known as ‘reverse refraction’, which potentially bends light waves in a way that doesn’t occur in nature. By carefully sizing and spacing an array of nanoparticles, reverse refraction might be induced and controlled in specific wavelengths of light.
