We predict the decomposition peculiarities of the heavy isoelectronic impurities doped Al
x
Ga1
-
x
N
y
As1
-
y
alloys. The AlN and GaAs precipitates in the high GaAs and AlN content Al
x
Ga1
-
x
N
y
As1
-
y
epitaxial layers,
respectively, should be formed. The free energy of the alloys is expressed as a sum of the free energies of the
constituent compounds, strain and elastic energies, and configurational entropy term. The regular solution model
is used for describing the free energies of the compounds and strain energy. The interaction parameters between
the compounds are estimated by the valence force field model. The stiffness coefficients of the wurtzite AlAs and
GaAs as well as the interaction parameter between AlN and AlAs are calculated.
We have described a spinodal decomposition range of the low N-content Al x Ga 1Ϫx N y As 1Ϫy alloys grown on GaAs͑001͒. In our analysis we take into account transformations of the bonds and strain, coherency strain, and elastic energies. The alloys are considered in the simple solution approximation. The strain energy is presented by the interaction parameters between the compounds estimated in the valence-force field model. The spinodal decomposition range of Al x Ga 1Ϫx N y As 1Ϫy alloys with compositions 0рxр0.4, yϭ0.01, 0.02, 0.03, 0.04, and 0.05 are demonstrated up to 1000°C. It is shown that Al and N increase dramatically the temperature of the phase separation.
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