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DTIC ADA099344: Evaluation of Gallium Nitride for Active Microwave ...
by Defense Technical Information Center
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The predicted figure of merit for GaN as a transit-time
limited microwave power amplifier material is
significantly greater than that of Si or GaAs because of
the small electron mass, the large optical phonon
energies and the large bandgap of GaN. To confirm these
predictions by measuring the saturated drift velocity and
the pair-production thresholds, it was necessary to
prepare uncompensated n-type single crystals with carrier
densities below about 10 to the 17th power/cc. Because
the melting point of GaN is extremely high, 2,000C, with
a corresponding equilibrium N2 pressure of 40,000 atm, it
was necessary to use a chemical vapor deposition method
(wherein GaCl was allowed to react with NH3, a more
active source of N than N2 and kinetically stable with
respect to N2 at temperatures below 1100C) to grow single
crystal GaN epitaxially on sapphire substrates. However,
their surface morphology was non-planar, and they
displayed Ga occlusions, microcracks and voids, the
latter two appearing only in the thicker layers. Very
slow growth eliminated all these problems except the non-
planarity. Epitaxial growth of planar,
crystallographically sound crystals was finally achieved
on basal plane substrates. All the crystals grown were n-
type with carrier densities of 10 to the 18th to the 20th
power/cc. These observed densities were more or less
independent of all crystal growth parameters, including
replacing the Ga halide reactant source with a Ga
organometal source.
Date Published: 2017-12-14 14:46:36
Identifier: DTIC_ADA099344
Item Size: 38869276
Language: english
Media Type: texts
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