  Results solving the long standing puzzle regarding the phase diagram and the
pressure evolution of the melting temperature Tm(P) of gallium nitride (GaN),
the most promising semiconducting material for innovative modern electronic
applications, are presented. The analysis is based on (i) studies of the
decomposition curve in P-T plane up to challenging P equal 9 GPa, (ii) novel
method enabling Tm(P) determination despite the earlier decomposition, and
(iii) the pressure invariant parameterization of Tm(P) curve, showing the
reversal melting for P greater-than 22 GPa. This is linked to a possible
fluid-fluid crossover under extreme pressures and temperatures. The importance
of results for the development of GaN based technologies is indicated.

Materials Science