Release Process Could Broaden Uses of GaN SCs
TOKYO, April 18, 2012 — Nitride semiconductors grow only on certain
surfaces, and their utility is limited by the substrate on which
they are fabricated. But a new release process not only makes the
method cheaper and easier, but also expands the potential uses of
Yasuyuki Kobayashi and colleagues at Nippon Telegraph and Telephone
Corp. (NTT) demonstrated the process using a technique called
mechanical transfer using a release layer (MeTRe). They grew a very
thin hexagonal layer of boron nitride (h-BN) between a sapphire
substrate and a gallium nitride (GaN)-based semiconductor.
Sandwiched in the middle, the h-BN works as a release layer,
allowing the investigators to easily detach the semiconductor and
transfer it to other substrates without using expensive laser beam
machining or chemical treatment.
Comparison between the traditional methods of fabricating GaN
semiconductors compared with that of Yasuyuki Kobayashi and
colleagues.(Images: NTT Science and Core Technology Laboratory
GaN-based semiconductors have a wide range of applications in
high-power electronic devices and light sources, but their utility
is hampered by the thickness of the substrates on which they are
grown. The substrates are hard to separate from the GaN and can be
100 times the size of the film. They also must be stable at high
temperatures because the GaN-based film's growth temperature is
1000 °C. Using the MeTRe fabrication process, GaN-based thin-film
devices can be separated easily from their substrate and
transferred onto other devices. They can be grown on nearly any
single crystal substrate, both of which greatly increase their
Prototype of a thin LED produced using nitride semiconductors.
Boron nitride also is difficult to grow on a single-crystal
sapphire substrate because of a very different crystal structure.
However, the researchers optimized its growth using metallorganic
chemical vapor deposition (MOCVD), which uses the constituent gases
to encourage single-crystal, thin-film growth on the substrate's
surface. They also found that the GaN layers could be grown on top
of the BN film if they used a buffer layer of Al1-xGaxN, an
aluminum/gallium nitride alloy.
A prospective use for flexible nitride semiconductors is in
window-based solar panels.
The MeTRe method of semiconductor fabrication is cheaper, faster
and easier than conventional methods, and there has been a
worldwide movement to develop such an efficient technique. The
process also allows thin, flexible semiconductors with a large
surface area (up to 2 cm) to be made. One key application of such a
semiconductor is in the development of flexible solar panels that
are sensitive to UV wavelengths only and can be put in windows to
filter out the harmful rays while also collecting and storing solar
energy. This can be accomplished easily by attaching GaN-based
solar cells to pre-existing Si-based ones.
Other potential applications include thin LEDs, highly functional
hybrid CMOS and flexible devices.
The research appeared in the April 12 issue of Nature.
For more information, visit: www.ntt.co.jp
Man höre und staune flexible nitride semiconductors
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