06 Jun 2008
Etching a photonic crystal structure onto the surface of an LED boosts light emission intensity by a factor of three.
Scientists from the University of Hong Kong used a nanopatterned mask to etch the surface on an LED. According to the researchers, the mask is composed of air holes between hexagonal-close-packed microspheres and could be a low-cost alternative to e-beam writers.
"It takes just 5 ml of a 1% silica microsphere suspension, which costs only tens of dollars, to coat a 2 inch wafer," Anthony H W Choi of the university's department of electrical and electronic engineering told nanotechweb.org. "Compared with the huge investment of an e-beam writer, high maintenance costs and expensive electron resists, microsphere lithography is a cheap and practical nanotechnology."
As the researchers explain, the introduction of a photonic crystal structure on the surface of an LED can improve light extraction by diffracting waveguided modes out of the semiconductor. The team observed that LEDs made without the array displayed interference effects caused by light bouncing to and fro within the device.
To pattern the LED wafer, the researchers begin by spin-coating a GaN substrate with a dispersion of silica microspheres (mean diameter of 500 nm) in deionized water. The particles spontaneously self-assemble into a single layered hexagonal-close-packed array, which doubles as an effective etching mask.
Choi and his colleagues use a dry etching process to transfer the pattern of air holes onto the LED wafer. The silica particles are subsequently removed from the substrate by sonification to reveal an array of triangular-shaped voids spaced at intervals of 290 nm along the semiconductor surface.
The researchers presented their work in Nanotechnology.