The adsorption, desorption and interaction behavior of gallium and nitrogen with 6H-SiC(0001), LiGaO 2 (001) and GaN surfaces has been studied by comparing the deposition of gallium from a metal evaporator source with gallium decomposed from (CH 3 ) 3 Ga over hot tungsten filaments. Nitrogen was generated by a microwave discharge in NH 3 . We have employed synchrotron radiation photoelectron spectroscopy to measure valence- and core-level spectra of substrate and overlayer components. The growth of metallic gallium on all three substrates is apparent from the spectral features in Ga3d. Subsequent nitrogen exposure results in a strong reaction with gallium metal to form GaN x species. Different NH x and gallium components can be identified and a stable GaN species exists after cycles of annealing and nitrogen exposure. The nitridation of gallium is more efficient on LiGaO 2 and GaN surfaces than on SiC under similar exposure conditions. This is probably due to the reduced interaction of gallium and nitrogen with the oxide and nitride substrates. Exposure of decomposed (CH 3 ) 3 Ga shows that cracking products adsorb on the surfaces prior to the nucleation of metallic gallium. The metallic species is easily desorbed from a strongly bound interlayer. Results relevant to the GaN growth process are discussed.