TEMPERATURE-PROGRAMMED DESORPTION INVESTIGATIONS OF HYDROGEN AND AMMONIA REACTIONS ON GAN

We report data for chemisorption and reaction of deuterium and isotopi cally labeled ammonia on single-crystalline GaN films grown on sapphir e substrates. Temperature programmed desorption (TPD) and Auger electr on spectroscopy (AES) studies, following exposure of the clean GaN fil m at room temperature to the probe reactant species, were conducted un der UHV conditions. Deuterium desorption took place over a wide temper ature range, 525-800 K, with molecular deuterium as the only product. At low exposures, two distinct deuterium desorption peaks at similar t o 660 and 770 K were observed. The deuterium desorption peak at 660 K shifted to lower temperatures with increasing D adatom coverages. TPD experiments after ammonia adsorption on GaN revealed small amounts of hydrogen desorbed at similar to 600 K and over a range 660-770 K, sugg esting partial decomposition of ammonia. Molecular ammonia desorption was observed at similar to 560 and 600 K, with the low temperature des orption state growing with increasing ammonia exposures. Further studi es on deuterium-precovered GaN films indicated that ammonia production resulted from recombination of NHx species and hydrogen adatoms on th e surface. (C) 1997 Elsevier Science B.V.