Silicon Glows With Iron 'Islands'

John Walko

GUILDFORD, UK -- Integrated optical devices are the ultimate application for a 1.54-µm light-emitting diode (LED) structure built in a conventional silicon diode junction.
While compound semiconductor LEDs based on gallium arsenide abound, an efficient silicon-based emitter would allow engineers to build monolithic integrated optic and electronic devices.
Scientists at the University of Surrey have built a silicon-based LED by burying islands of iron di-silicide (FeSi₂) in the recombination region of an otherwise conventional silicon PN junction.
Karen Reeson, who heads the research team with Kevin Homewood, said samples have operated for several hundred hours under a variety of conditions without any deterioration in output.
"The potential applications for industry are huge," Reeson said. "Anything which currently contains a silicon chip could operate 10 times faster. In fact, part of the chip will quite literally be operating at the speed of light."
Of course, this scenario is far from reality. Electroluminescence occurs under 0.6- to 0.8-V forward bias, and is strongest at low temperatures but still observable at room temperature.
The initial devices operate with quantum efficiencies of about 0.1 percent, compared with 3 to 5 percent for standard commercial LEDs. Reeson said that by optimizing material quality and device design, the team can improve the efficiency.
Another concern is recombination lifetime, which governs how long it takes for the light emission to begin after a voltage is applied, and then switch off when voltage is removed. Reeson said early indications are that the devices would be suitable for electronics applications.