08 May 2003
Scientists in the US fabricate the first gallium arsenide LED emitting at 1.5 microns.
Researchers in the US claim to have fabricated the first gallium arsenide (GaAs) LED that emits at the crucial telecommunications wavelength of 1.5 microns. As the emitter can be pulsed at terahertz rates, the team from Yale University says its device is ideal for use in high-speed networks. (Nature Materials 4 May 10.1038/nmat887).
"Our result is important because it combines two very desirable properties: compatibility with fiber-optics at 1.5 microns for long-distance communications and the inexpensive, reliable GaAs integrated circuit technology," Yale researcher Janet Pan told Optics.org
GaAs is now an established material for making optoelectronic devices, but traditionally emits light at 850 nm. To engineer the 1.55-micron emission, Pan and colleagues introduced a substitution defect called an arsenic antisite into the GaAs lattice. Here, arsenic atoms sit on lattice sites normally occupied by gallium atoms.
Pan says these defects create "deep-level energy bands" within the GaAs that sit between the conduction and valence bands. This essentially introduces new energy states into the bandgap and allows the material to emit at longer wavelengths.
According to Pan, the key to producing these artificial energy bands is to carefully control the low-temperature MBE process used to grow the material.
The resulting LED emits between 1.4 and 1.7 microns, with a peak at 1.55 microns, and has an internal optical power of 24 mW. "The efficiency which is reported in this paper is 0.6%," she said. "The next steps are to increase the efficiency and reduce the operating currents. Practical applications are possible within 3 to 5 years."
Jacqueline Hewett is news reporter on Optics.org and Opto & Laser Europe magazine.