Summary of EMC 1997 talks by CREE and Nichia

Kathy Doverspike, Cree

kathy_doverspike@cree.com

Cree presented results of room temperature pulsed operation lasing from an InGaN/GaN MQW separate confinement heterostructure grown on SiC. This is the first report of lasing in this material system on a SiC substrate. The thermal conductivity of SiC is approximately 10 times higher than that of sapphire and is probably playing a very important role in dissipating the heat. The active layer of the laser consisted of an 8-well InGaN/GaN MQW region with Al_0.06Ga_0.94N waveguide regions and Al_0.13Ga_0.87N cladding layers. The devices were fabricated into index-guided structures. High quality bars were fabricated by facet cleaving with a cavity length of 500µm. Below threshold a broad spontaneous emission peak was observed. As the current was increased, this peak shifted to shorter wavelengths and at threshold, narrow lasing modes abruptly appeared. Laser operation was confirmed by the observation of a sharp increase in light output vs current. Above threshold, the TE/TM polarization ratio was greater than 135.

Nakamura gave an invited talk on the status of GaN based lasers on sapphire. His threshold current has steadily improved and was reported as 20-30mA. The operating voltage was also quite low being under 5V at 100mA. At 100mA, the output power of the CW laser was 30mW. He also reported many results using gain spectroscopy and was trying to draw correlations between the differences in the gain spectra to fluctuations in the In% in the active layer (InGaN QWs). The lifetime that was reported was about 40 hours but this was last years result. The new lifetime will be reported this fall at the workshop in Japan.

Since the EMC meeting there has been two additional achievements in this area. In July, Fujitsu announced that it had succeeded in obtaining pulsed laser operation from a GaN based laser also on SiC. Also in July, Cree announced that it had succeeded in lowering the threshold current enough to demonstrate CW laser operation with a lifetime of approximately 15 seconds.