41-42 Research Review v2 10/9/09 13:33 Page 41
research review
rhombus4
Sumitomo snatches the
green laser crown
Japanese substrate manufacturer Sumitomo has won the race for the first truly green nitride
laser with a 531 nm semi-polar device that it announced on 17 July, 2009.
A
lthough this device’s
performance
characteristics are not good enough
for commercialization, if they were
improved this laser could then
provide the green laser source for
laser TV and tiny color projectors.
These displays currently use
cumbersome, expensive green lasers
that combine an infra-red source with
crystals that convert 1064 nm
emission to 532 nm.
Sumitomo’s engineers grew their
laser structures on the {202
−
1} plane
of free-standing GaN substrates that
were fabricated in-house.
Credit: Sumitomo
The researchers say that the
selection of this plane is the key to 17.7 V, and produced a maximum Printing LED displays Sumitomo’s
their success – it enables the output power of 28 mW. Researchers at the University of semi-polar
fabrication of indium-rich InGaN Illinois at Urbana Champaign substrates were
quantum wells with a high degree of More recently, Sumitomo’s engineers (UIUC) have led the development of a key factor in
compositional uniformity. have improved the 520 nm laser a series of novel processes that can the fabrication
performance by adding a lattice- produce small and medium-sized of the first
A series of gain-guided lasers matched InAlGaN cladding layer, displays featuring an array of LED nitride-based
with 10 µm stripes were fabricated and switching to a ridge-stripe pixels. green laser
by conventional deposition and geometry. These refinements
lift-off techniques. The 531 nm created a device that delivers Conventional processes are unable
variant was driven in pulsed mode 2.5 mW in continuous-wave mode, to make LED displays of this size,
with a 0.5 percent duty cycle, and and has a threshold voltage and because they cannot produce
had a threshold current density of current density of 9.4 V and chips that are small enough.
15.4 kA cm
-2
. 7.9 kA cm
-2
, respectively. And even if this issue were
Y. Enya et. al. Appl. Phys. Express 2 overcome, this approach would not
Devices emitting at 520 nm had a 082101 (2009) be attractive due to the large
lower threshold current density of Y. Yoshizumi et. al. Appl. Phys. quantities of wiring needed to
8.2 kA cm
-2
, a threshold voltage of Express 2 092101 (09) interconnect pixels.
September 2009
www.compoundsemiconductor.net 41
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