  III-nitride alloys are wide band gap semiconductors with a broad range of
applications in optoelectronic devices such as light emitting diodes and laser
diodes. Indium gallium nitride light emitting diodes have been successfully
produced over the past decade. But the progress of green emission light
emitting devices has been limited by the incorporation of indium in the alloy,
mainly due to phase separation. This difficulty could be addressed by studying
the growth and thermodynamics of these alloys. Knowledge of thermodynamic phase
stabilities and of pressure - temperature - composition phase diagrams is
important for an understanding of the boundary conditions of a variety of
growth techniques. In this dissertation a study of the phase separation of
indium gallium nitride is conducted using a regular solution model of the
ternary alloy system. Graphs of Gibbs free energy of mixing were produced for a
range of temperatures. Binodal and spinodal decomposition curves show the
stable and unstable regions of the alloy in equilibrium.
