Liftoff Enables GaN on Silicon

Researchers at the University of California, Berkeley, and Oriol Inc. in Santa Clara, Calif., are using an excimer laser to separate LED heterostructures from their sapphire growth substrate so that they subsequently may bond them to silicon. Using silicon as a substrate for GaN-based LEDs would improve the performance and manufacture of the devices as well as ease their integration with electronics.

The scientists first attach the top of the LED structure to a silicon wafer using Krazy glue. They then melt the bottom of the stack through the sapphire with a 248-nm pulse from the KrF laser. The structure is bonded to another silicon wafer with a palladium-indium alloy at 200 °C, and the temporary adhesive is removed with acetone.

Current-voltage data and electroluminescence spectra of the LEDs confirmed that threshold voltages and output in the devices that were remounted on silicon had improved. The researchers reported their findings in the October issue of IEEE Photonics Technology Letters.