Experimental investigation of the enthalpy, entropy, and free energy of formation of GaN

The equilibrium pressures of N2 over Ga/GaN were measured from 1055 to 1350 K. We find that GaN is stable up to 1210±30 K at 1 bar N2. We obtain values of −165±16 kJ/mol, −136±14 J/mol K, and 19±14 kJ/mol K for the standard enthalpy of formation, the standard entropy change of formation, and the absolute entropy, respectively. The minimum partial pressure of NH3 in H2 for the stable growth of GaN was measured as a function of temperature and gas flow rate through the reactor. These data were used to define an upper bound on the standard Gibbs free energy. This upper bound is consistent with the results from the equilibrium N2 pressure measurements.