Emission observed at 1.55 microns from GaAs
The devices operate at 1.55 microns due to the creation of artificial deep-level energy bands in GaAs grown by MBE at low temperatures (see Nature Materials 4 May 2003, 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 with reliable GaAs IC technology," Yale researcher Janet Pan told Optics.org, a sister website of compoundsemiconductor.net.
The bandgap energy of GaAs corresponds to a wavelength of 850 nm. To engineer emission at 1.55 microns, Pan and colleagues introduced arsenic antisites (AsGa) into the GaAs lattice. These are substitutional defects, in which an arsenic atom sits on a lattice site normally occupied by a gallium atom.
The defects create deep-level energy bands that sit between the conduction and valence bands, allowing 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 low-temperature-grown GaAs layer was deposited at a temperature of only 225 degrees C.
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%," said Pan. "The next steps are to increase the efficiency and reduce the operating currents. Practical applications are possible within 3 to 5 years."
