Quickly the Violet cometh!
I recently attended two meetings where Dr. Shuji Nakamura of Nichia
Chemicals gave invited talks on the subject of green and blue LED's and
blue laser diodes. At the Eighth International Conference on Solid Films
and Surfaces (ICSFS-8) in Osaka Japan (1-5 July 1996) he reported 24
hour lifetime, for low duty cycle pulsed operation, with Ith of 150-350
mA (about 5kA/cm2), Vth = 20-30 Volts, and wavelengths of 390-440
nm. They have made cleaved devices on A face sapphire. Lots of
threading dislocations (density of dislocations 1010 per cm2) are present
in XTEM pictures. He also demonstrated full color spectrum by shining a
violet laser on three different phosphorescent sheets (recall that Nichia
made its money in phosphors for CRT's). The laser is violet in color, about
420 nm. Two weeks later at the First Optoelectronics and Communications
Conference (OECC) in Chiba, Japan (16-19 July 1996) he reported 50% duty
cycle operation (no lifetime mentioned) and said they expected CW
operation "soon." He also reported 90 mA Ith and 10 Volt Vth! The
longitudinal mode spacing was 0.04 nm with length = 600 um, Jth = 3-10
kA/cm2, and it is TE mode polarized when lasing. Thus the progress at
Nichia is fast and furious in CW blue-violet laser diodes (And for those of
you who are curious he mentioned that the price of the blue led's is 1-2$
in quantities > 10,000.)
Also, at OECC there were many papers discussing the new multimedia
world and the soon to be available Digital versatile disk, or DVD, for which
people are already planning to use 420 nm laser diodes in a few years!
signing off from Tokyo
Dr. Robert Feuerstein, Visiting Scientist
Asian Office of Aerospace R&D, Air Force Office of Scientific Research
Research Professor, University of Colorado
robertf@colorado.edu
