The authors have investigated the adsorption and subsequent desorption of Ga on AlN (0001) with line-of-sight quadrupole mass spectrometry (QMS). The authors present desorption data consistent with a continuous Ga-flux dependent accumulation of a laterally contracted Ga bilayer on AlN (0001) from 0 to 2.7 +/- 0.3 ML GaN equivalent coverage, and further Ga accumulation in macroscopic Ga droplets. The temperature dependence of Ga-adsorbate QMS desorption transients was investigated and the authors determined that the desorption activation energies for individual monolayers of the Ga adsorbate on AlN (0001) were similar to Ga desorption from GaN (0001). For the (first) pseudomorphic Ga-adsorbate monolayer on AlN, the authors measured a maximum Ga coverage of 1.0 +/- 0.1 ML and desorption activation energy of 6.2 +/-0.3 eV. For the (second) laterally contracted Ga monolayer (1.7 +/- 0.3 ML) the desorption activation energy was 3.8 +/- 0.1 eV. (c) 2006 American Vacuum Society.