Band structure of nitride semiconductors
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Band offsets at nitride semiconductors
The band discontinuities in valence and conduction bands are
the key
parameters governing the behavior of heterojunctions; these junctions
are
essential for the device properties of optoelectronic devices. The
large
lattice mismatch between the nitride semiconductors (AlN, GaN, InN)
complicates
determination of these offsets, which are strongly affected by strain.
We have performed a comprehensive investigation of the band offsets.
Our
resulting value for AlN/GaN is in line with experimental observations.
The value for GaN/InN, however, is rather smaller than expected.
For more information:
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"Small valence-band offsets at GaN/InGaN heterojunctions", Chris G. Van
de Walle and J. Neugebauer, Appl. Phys. Lett. 70, 2577
(1997).
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Zinc-blende/wurtzite band offsets
The nitride semiconductors crystallize in the wurtzite
structure –
but the zinc-blende structure is only slightly higher in energy. These
two structures differ from each other in the stacking sequence along
the
[0001} (or [111]) direction. Stacking faults can form relatively
easily;
we have investigated structure and energetics of various basal-plane
stacking
faults. Some stacking-fault structures can be thought of as a thin
layer
of zinc-blende material sandwiched between the wider-band-gap wurtzite
material. Because of the smaller band gap of zinc-blende, excitons may
be bound to such a defect. Knowing the band offsets between the
zinc-blende
and wurtzite phases therefore enables one to study the electronic
structure
of such defects. Our results are illustrated on the right.
For more information:
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"Energetics and electronic structure of stacking faults in AlN, GaN,
and
InN", C. Stampfl and Chris G. Van de Walle, Phys. Rev. B. 57,
R15052
(1998).
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Stability
and electronic properties of GaAsN alloys
The ability to form alloys between GaN and GaAs opens up
tremendous
potential for band-structure engineering. The large lattice mismatch
between
these semiconductors gives rise to unusual behavior, however. We find
that
GaAsN alloys are thermodynamically unstable over most of the range of
alloy
compositions, due to the large lattice mismatch between GaAs and GaN.
At
most a few percent of N can be incorporated in GaAs, and vice versa.
The
effect on the band gap of forming GaAsN is large and unexpected: adding
N to GaAs causes a decrease in the band gap, due to the extremely large
bowing of the conduction band.
For more information:
-
"Electronic structure and phase stability of GaAsN alloys", J.
Neugebauer
and C. G. Van de Walle, Phys. Rev. B 51, 10 568 (1995).
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