Spectroscopic ellipsometry installed on a GEN-II plasma assisted molecular beam epitaxy machine has been shown to be an effective in situ real time tool for monitoring the kinetics of gallium adlayer adsorption/desorption on the GaN surface. In this work, the authors present data on the study of Ga adsorption/desorption on polar c -plane GaN (0001) and nonpolar m -plane GaN (1-100) surfaces for Ga beam equivalent pressures in the range of 8.96× 10-8 -1.86× 10-7 Torr, Ga pulses in the range of 5-360 s, and for substrate temperatures between 650 and 750 °C. © 2007 American Vacuum Society.