industry news ♦ Lasers
of 7.3 V and 130 mA, and a slope efficiency of 0.3 W/A.
The 60 mW, CW output of this device compares favourably with the 50 mW output of Osram’s 524 nm laser, which the German outfit reported this summer.
Soraa says that its success stems from only 15 months of effort, which indicates the great promise of green lasers built on non c-plane GaN. Turning to this orientation increases quantum well electron- hole overlap, reduces effective hole mass and boosts design freedom.
Soraa’s engineers, which include the University of California, Santa Barbara, academics James Speck, Steven DenBaars and Shuji Nakamura, and former director of Philips Lumileds’ Advanced Laboratories, Mike Krames, have detailed the results of these blue and green lasers in the latest edition of Applied Physics Express.
Semi-Polar GaN LDs Greener in More Ways Than One
Scientists at SEI have shown that green laser diodes grown on the semi-polar GaN plane have half the threshold current of green LDs grown on the commercially used GaN c-plane. Researchers from Sumitomo Electric Industries have discovered that green laser diodes (LD) grown on the semi-polar gallium nitride (GaN) plane are more efficient than those grown on the conventional c plane.
green region, which are based on second harmonic generation (SHG)technologies, suffer from size and stabiility problems. It’s therefore more viable to use III-nitride based LDs (which have preferable lifetimes to II-VI based green LDs).
The work published in Applied Physics Express describes results obtained for LD structures grown by metal organic chemical vapor deposition (MOCVD) on semi-polar GaN substrates grown by hydride vapor phase epitaxy (HVPE).
Far-field patterns (FFPs) indicate that the symmetry and optical confinement of a green LD with InGaN wells and InAlGaN cladding layers are comparable to traditional c-plane InGaN LDs.
The characteristic temperature for the semi-polar LD lasing at 525nm is 175K, much higher than the 145K at 518nm and 120K for 515nm previously demonstrated for c-plane LDs.
Furthermore, between 520 and 530nm, green LDs on the plane exhibit threshold current densities of almost half of those on the c-plane. Above 530nm, threshold current densities increase sharply for the c-plane but increase only slightly for the semi-polar plane LDs.
The reason for this improvement in efficiency, the scientists say, is most likely to be due to the superior compositional homogeneity of the InGaN quantum wells grown on the plane which has previously been experimentally shown using time- resolved photoluminescence.
In the future, the researchers plan to further optimize the device for high-power operation, and say a report is due in the ‘near future’.
Further details of this work are published in ‘Applied Physics Express 3 (2010) 121001’ and available via the following link:
http://apex.jsap.jp/ link?APEX/3/121001/
Currently, commercially available lasers in the November/December 2010
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