Graphene-on-SiC - ISOM

NEWS REVIEW
Nitride semiconductors set a new
benchmark for UV LED output power
NITRIDE SEMICONDUCTORS has
released a portfolio of ultra-high power,
ultra-violet LEDs delivering output
powers that can be in excess of 3W.
One of these LEDs, the NS380L-6SVR,
produces 3200mW at 380 nm. According
to Nitride Semiconductors, the output
of this LED at this wavelength exceeds
all other commercial devices based on
a single chip. Nitride Semiconductors
has also launched a range of longer
wavelength cousins, such as the
NS400L-6SVR, which delivers an
output of 3200mW at 400nm. The new
range of chips combines an operating
voltage of 4V with very high efficiencies.
For example, driven at 800 mA, the
NS380L-5SVR produces 700 mW at 380
nm, equating to an external quantum
efficiency of 35 percent. Meanwhile, the
400 nm-emitting equivalent, the NS400L-
5SVR, delivers an external quantum
efficiency of 38.7 percent when driven at
1000mA, and emitting 1200mW. Typically,
ultraviolet LED chips have dimensions
of around 1 mm by 1mm. For example,
those made by SemiLEDs are 1.2 mm
square, while those produced by Nichia
are 1mm square. In contrast, Nitride
Semiconductors’ ultraviolet LEDs are 2.2
mm square - they are claimed to be the
biggest on the market.
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Scaling the size of the chip while
maintaining its performance is not trivial.
Although increases in the chip’s size boost
output, efficiency is often compromised,
due to heating issues and inferior current
spreading within the device.
To address these issues, the engineers
at Nitride Semiconductors produce
their UV LEDs in a different way. They
have developed a new layer structure
to release the heat efficiently and
introduced an electrode designed to
flow current uniformly. This has been
accomplished by minimising crystal
defects through optimisation of epitaxial
growth, and developing a vertical chip
design with an optimal electrode pattern.
The large size of these devices enables
the company to produce a single-chip
ultraviolet LED with an output of several
Watts; competing designs tend to be
based on multiple chips. According to
the company, the benefits of a single chip
design include simplification of optics
and a low driving voltage - when multiple
chips are used, they are connected in
series.
Meister Abrasives AG, Switzerland · www.meister-abrasives.com
Ultra-violet LEDs are packaged in a
surface mounted device format, and
available in three sizes, ranging from 4.2
mm square to 5.6 mm square. They are
designed for good heat transmission,
and because the thickness of package
is only 1.3mm, they can be mounted
in high density by reflow soldering.
The range of LEDs, which have been
produced at a manufacturing cost that
is just one tenth of that of the previous
generation of devices, will be available
for sampling from April 2013. Reliability is
quoted at 10,000 hours, and guaranteed
for 1000 hours.
10 www.compoundsemiconductor.net April/May 2013