REACTION PATHWAYS AND INTERMEDIATES IN THE DECOMPOSITION OF DIMETHYLZINC ON GAAS(100)

The adsorption and reaction of dimethylzinc (DMZ) on the Ga-rich GaAs(100)-4 x 1 surface was studied using TPD, XPS, and HREELS. DMZ adsorbs readily on the GaAs(100)-4 x 1 surface at 110 K. Physisorbed molecular species desorb at 140 K, while more strongly bound species decompose at temperatures below 275 K to form adsorbed Zn metal and methyl species. The resulting methyl groups form stable surface gallium-ethyl complexes. The adsorbed zinc atoms interact weakly with the surface and desorb as zinc metal between 400 and 600 K. At low coverages, the adsorbed methyl groups desorb as methyl radicals at 625 K. At intermediate coverages a small fraction of the surface methyl groups undergo hydride transfer reactions at 575 K, producing gaseous methane and depositing a small amount of carbon into the surface. The deposited carbon diffuses into the bulk at temperatures above 700 K. Higher coverages result in the evolution of gaseous Ga-methyl species at 325, 410 and 525 K. This behavior is consistent with the formation of an adsorbed Ga(CH3)x layer. The 525 K Ga-methyl peak results from reaction between two adsorbed Ga(CH3) species, while the 325 and 410 K peaks result from the desorption of surface Ga(CH3)2.