A SYNCHROTRON-RADIATION PHOTOEMISSION-STUDY OF GALLIUM AND NITROGEN ADSORPTION ON 6H-SIC, LIGAO2 AND GAN SUBSTRATES - INITIAL-STAGES OF GANFORMATION

The adsorption, desorption and interaction behavior of gallium and nit rogen with 6H-SiC(0001), LiGaO2(001) and GaN surfaces has been studied by comparing the deposition of gallium from a metal evaporator source with gallium decomposed from (CH3)(3)Ga over hot tungsten filaments. Nitrogen was generated by a microwave discharge in NH3. We have employ ed synchrotron radiation photoelectron spectroscopy to measure valence - and core-level spectra of substrate and overlayer components. The gr owth of metallic gallium on all three substrates is apparent from the spectral features in Ga 3d. Subsequent nitrogen exposure results in a strong reaction with gallium metal to form GaNx species. Different NHx and gallium components can be identified and a stable GaN species exi sts after cycles of annealing and nitrogen exposure. The nitridation o f gallium is more efficient on LiGaO2 and GaN surfaces than on SiC und er similar exposure conditions. This is probably due to the reduced in teraction of gallium and nitrogen with the oxide and nitride substrate s. Exposure of decomposed (CH3)(3)Ga shows that cracking products adso rb on the surfaces prior to the nucleation of metallic gallium. The me tallic species is easily desorbed from a strongly bound interlayer. Re sults relevant to the GaN growth process are discussed. (C) 1998 Elsev ier Science B.V. All rights reserved.