Antimony LEDs promise smaller environmental sensors

17 Jun 2002

A consortium of researchers from European industry and academia has made antimony-based infrared LEDs and laser diodes by a commercially viable process.

The EU-funded ADMIRAL project made the devices by MOVPE, a well-established commercial technique for making LEDs and laser diodes that emit in the visible region. Precursors were trimethylindium, triethylgallium and triethylantimony.

ADMIRAL's devices currently emit at 135K but the team is optimistic that room temperature emission will be achieved once the fabrication process has been improved. "Considering that six months ago we didn't have any lasing at all, lasing at 135K is not bad," said Simon Rushworth, of the UK's Epichem, one of the partners in the project.

The team is now in the third year of a three-year project and aims to have achieved room temperature operation by the end of the project. Room temperature lasing of antimony-based devices made by molecular beam epitaxy (MBE) has already been demostrated in research laboratories, but MBE technique is not suitable for large-scale production.

The group's devices emit between 3.3 and 4.5 micrometres, which is attractive for sensing toxic and hazardous substances in the atmosphere or in human blood or tissue. It is difficult to get compact, high-energy devices that emit at these wavelengths. Antimony-based lasers provide attractive interband transitions so the bandgap can be tuned more effectively. This allows the devices to be miniaturized.

Rushworth believes that the cost of antimony-based devices will be low because they only require thin layers. The production costs will also be small because the can be mass-produced with existing MOVPE machines.

In addition to Epichem, the ADMIRAL consortium includes Aixtron and RWTH Aachen, of Germany, Montpellier University II, of France and IP-Czech Academy of Science.

The consortium is currently negotiating with a number of manufacturers of gas sensors, who would be able to incorporate the devices into existing equipment. "If we can [make these devices] on a reliable basis at room temperature, I think people will take it on board as quickly as they've adopted blue LEDs," predicted Rushworth.

SH