SURFACE OXIDATION OF GAAS(100) BY ADSORPTION OF NO2

The adsorption and reaction of NO2 on n-type Ga-rich GaAs(100) was stu died using AES, TPD, HREELS, and MQS. At 78 K all the adsorbed NO2 up to 4 L exposure reacts to oxidize the surface and desorb NO. At higher exposures NO2 accumulates on the surface as the N2O4 dimer. Saturatio n of the oxidation reaction, corresponding to monolayer oxide formatio n, occurs at a NO2 exposure of about 30 L. A small amount of NO3 is al so formed, which can be increased by repeated cycles of dosing and hea ting to 150 K to desorb unreacted NO2. Annealing the sample to 800 K d evelops a HREELS oxide band centered at 84 meV, which is assigned as a gallium oxide structure. All of the oxide is desorbed at Ga2O in a na rrow peak at about 800 K. Exposure of the clean surface to NO2 at 300 K is found to oxidize the surface as efficiently as at 78 K.