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Silicon LEDs emit in the infrared

18 Mar 2005

Japanese researchers reveal an efficient emitter of near infrared light.

Scientists in Japan have fabricated a silicon-based LED that emits infrared light and boasts an external quantum efficiency of up to 0.3% (Applied Physics Letters 86 103509).

The device, consisting of strained GaSb quantum dots embedded in silicon, was made by molecular beam epitaxy by Susumu Fukatsu and his colleagues from the University of Tokyo in Japan.

It generated strong luminescence at a wavelength of around 1.2 microns (1000 meV) at a temperature of 11 K when driven by 3.7 mA at a bias voltage of 4 V. What’s more experiments with a pulsed drive voltage show that the LEDs can be modulated to transmit data.

The development of efficient, high-speed silicon LEDs is of interest to the electronics industry because it could ultimately enable the creation of high-speed optical interconnects between microchips. The big problem is that silicon does not naturally emit light and so it has to be doped with another material to get around the problem.

Previously, STMicroelectronics has doped silicon with light-emitting erbium ions while in this case the Japanese have used III-V quantum dots to change the behaviour of the electrons in the silicon.

“An efficiency of 0.3% and more than 10 microW output power per chip is not bad, but the problem is the temperature,” Fukatsu told Optics.org. “We are convinced that we are going to have to achieve comparable figures at room temperature if we wish our LEDs to be competitive.”

Although the Tokyo team has succeeded in driving their LEDs at room temperature the efficiency of the light generation drops by two orders of magnitude.

Fukatsu says that the group will now concentrate on improving the efficiency by incorporating several layers of the Qdot material and increasing the operation bandwidth.

Oliver Graydon is editor of Optics.org and Opto & Laser Europe magazine.

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