Study of pathway of hydrogen migration and desorption on SiGe(100) surface using ab initio calculations

Ab initio calculations have been carried out to investigate the pathways of H-atom migration and H(2) desorption on a mixed SiGe(100)-2 x 1 surface using the cluster model. The H(2) recombinative desorption is the rate-detemining step in hydrogen migration and desorption on SiGe(100) surfaces, since the energy barrier to H-atom migration is generally lower than that of H(2) desorption. The energy barriers for H, desorption from the interdimer, the Si-Ge pair, (52.8 kcal/mol), and the Ge-Ge pair, (45.1 kcal/mol), are lower than that for the Si-Si pair by 7.5 and 15.2 kcal/mol, respectively. Thus, the SiGe(100)-2 x 1 surface in chemical vapor deposition provides more dangling bonds than the Si(100)-2 x 1 surface because of Ge inclusion. In contrast, the chemisorbed H tends to stay on the Si-site, since the barrier for H-migration from the Ge-site to the Si-site is lower that in the opposite direction by 5.6 kcal/mol. Hence, a considerably higher percentage of Ge sites are dangling bonds, compared with Si sites on the SiGe(100) surface. Related transition state structures in the migration and desorption steps are also discussed.