In situ monitoring of adsorption and desorption of atomic nitrogen on GaAs (001) and (111)A surfaces

Nitridation of GaAs (001) and (111)A surfaces grown by molecular beam epitaxy (MBE) is investigated by in situ Fourier transform infrared spectroscopy. Nitridation is carried out by exposing the GaAs surface to atomic nitrogen in the same MBE chamber used for growth using a tungsten filament resistively heated to 2100 degrees C. After nitridation for 90 minutes, the infrared reflectance spectra indicate that nitridation of the As-rich (2 x 4) surface at 450 degrees C results in two IR reflectance peaks at 1200 and 1000 cm(-1). On the other hand, nitridation of the Ga-rich (4 x 2) surface at 530 degrees C and the (111)A surface at 490 degrees C results in a single peak at 1200 cm(-1). These results indicate that the peak at 1200 cm(-1) is attributed to the Ga-N bond, and that at 1000 cm(-1) to the As-N bonds. Nitrogen desorption from the nitrided surface is found to occur at 450 degrees C and is induced by atomic hydrogen.