Page 423 - Academic Press Encyclopedia of Physical Science and Technology 3rd Chemical Engineering

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Encyclopedia of Physical Science and Technology EN009J-427 July 6, 2001 20:25

508 Metalorganic Chemical Vapor Deposition

to the production of LEDs, and the invention of new chip LEDs emitting white light have been developed using ni-
geometries and mounting techniques, has advanced the tride devices and UV phosphors. These devices have the
performance of these devices toward the realization of potential to provide very high efficiency lighting and il-
“the ultimate lamp.” lumination. In addition, using specially grown structures,
continuous-waveoperationofInGaN/GaNinjectionlasers
at 300 K for over 10,000 hr has been demonstrated by
5. GaAsP/GaP
Nakamura et al. (Nichia Chemical Co., Japan). These
Alloys in the GaAs x P 1−x system have been grown by devices will find application as the light source in high-
MOCVD using TMGa and AsH 3 and PH 3 . Both GaAs density and high-capacity digital versatile disk (H-DVD)
and GaP substrates have been used. While high-quality players in the near future.
materials have been produced by MOCVD, the commer-
cial production of these materials is still dominated by
8. Materials in the InGaAsN System
theestablished(andlow-cost)Ga–HCl–AsH 3 vapor-phase
epitaxy process. As mentioned previously, adding significant quantities
(>2%) of N to GaAs or InGaAs produces a dramatic
reduction in the bandgap energy of the semiconductor.
6. Sb-Containing III–Vs
Because of extreme bandgap “bowing” in these alloy sys-
One of the III–Vs that has recently received increased tems, the addition of a few percent of N to the GaAs or to
attention is the growth of Sb-containing compounds by InGaAs alloys results in a significantly smaller bandgap
MOCVD, e.g., the materials in the InAlGaAsSb system. energy than is found for the N-free compounds. It is found
Typically, TMIn, TMSb, TESb, TMAl, TMGa, and AsH 3 that the practical limit to the incorporation of N is, how-
are used as sources. The Sb-containing materials are gen- ever, only about 4%. High-quality thin films of these ma-
erally of interest for photodetectors operating in the 2– terials can be grown on GaAs substrates if the lattice mis-
5 µm spectral region and for InAs–GaSb transistors. One match created by the addition of N (or In + N) is not too
problem in the growth of these materials is that they melt great. This provides the potential for the realization of
at relatively low temperatures. In addition, there are se- the growth on GaAs substrates of an injection laser emit-
vere miscibility gaps in the Sb-based III–V systems. A ting at ∼1.33−1.55 µm. Recently, the MOCVD growth
relatively new application for Sb-containing materials is of such lasers operating continuously at 300 K has been
the growth of strained layers of specific InGaAsSb alloys demonstrated. This research result is not yet fully de-
on GaAs substrates for use in “long-wavelength” injection veloped for commercial applications, but it could make
lasers operating at λ ∼ 1.33 µm. a significant impact in optical communications systems
because it is relatively low cost compared to alternate ap-
proaches and the use of GaAs substrates makes the inte-
7. Materials in the InAlGaN System
gration of long-wavelength lasers with GaAs-based elec-
Recently, great success has been achieved in the growth of tronic circuits much more feasible.
III–V nitride films in the In y (Al x Ga 1−x ) 1−y N quaternary Another application of this alloy system is for an
system by MOCVD. The sources typically employed are ∼1 eV bandgap p-n junction for use in high-efficiency
TMGa, TMAl, TMIn, and NH 3 , although TEGa, TEAl, multiple-junction solar cells. Lattice matching to GaAs
and TBN have also been used. Since bulk GaN substrates substrates can be achieved by the incorporation of appro-
are not yet available commercially, (0001)-oriented sap- priate concentrations of both In and N in the InGaAsN
phire (or 6H-SiC) substrates are usually employed. The quaternary alloy films. MOCVD-grown solar cells with
use of a thin (t ∼ 20 nm) low-temperature GaN or AlN an ∼1 eV bandgap energy have been demonstrated using
◦
“buffer layer” (T g ∼ 450–500 C) is generally required to this material.
obtain high-quality heteroepitaxial growth. Growth tem-
peratures in the range T g ∼ 1050 C are used for the device-
◦
quality AlGaN and GaN layers, while T g ∼ 750–800 Cis
◦
IV. SOME REPRESENTATIVE OTHER
used for InGaN alloys. Recently, heteroepitaxial films of
MATERIALS GROWN BY MOCVD
InAlGaN films have been grown by MOCVD at temper-
atures T g ∼ 800 C in the range MOCVD is currently the
◦
A. IV–VI Semiconductor Compounds
only materials growth technology with the demonstrated
ability to produce high-performance AlGaN–InGaN green The compounds in the Pb 1−x Sn x Te ternary alloy sys-
and blue LEDs and also injection lasers operating in the tem are candidates for photodetectors in the midinfrared
390 <λ< 420 nm at 300 K. Recently, high-efficiency portion of the spectrum. Manasevit et al. were the first