OPTOELECTRONIC DEVICES: Gallium nitride LED has the blues

A multiple-quantum-well indium gallium nitride (InGaN) light-emitting diode (LED) fabricated by Steve DenBaars and collaborators at the DARPA-sponsored GaN university consortion at the University of California, Santa Barbara (UCSB), generates bright blue direct-gap luminescence. With a turn-on voltage of 3.2 V, the bare chip emitted 572 µW at 20 mA dc. In contrast to early impurity-doped gallium nitride LEDs, device power output did not saturate; by increasing the current to 140 mA, the group obtained output powers of 1.6 mW.

Gallium nitride-based LEDs emitting in all colors have been fabricated; the race is now on to produce a blue-output diode laser from the material. The fabrication process is complicated by the volatility of indium at normal nitride growth temperatures (in excess of 1000°C) for metal-organic chemical-vapor deposition. An optically pumped InGaN laser has already been demonstrated; researchers are now working to produce a current-driven device. The UCSB group is part of an 11-member consortium to develop a gallium nitride vertical-cavity surface-emitting laser over the next three years.