Activation Energy for the Sublimation of Gallium Nitride

Abstract

Gallium nitride was found to sublime congruently from a torsion—effusion cell when the ratio of orifice area to sample area was about 1/30 and incongruently to yield nitrogen gas and liquid gallium when this ratio was about 1/100 or less. A mass-spectrometer investigation revealed no measurable concentrations of gallium nitride vapor molecules. The heat of activation for the reaction 2GaN(s)=2Ga(1)+N2(g) was calculated to be 39 kcal at 1300°K from the temperature dependence of the effusion data. The rate of the reaction 2GaN(s)=2Ga(g)+N2(g) was measured by a torsion—Langmuir method. From the temperature dependence of sublimation the heat of activation for this reaction was calculated to be ΔH1300‡=218.6 kcal compared to 173 kcal for the equilibrium reaction, and the entropy of activation was calculated to be 74.3 cal/deg.