Study of Pathway of Hydrogen Migration and Desorption on SiGe(100) Surface Using Ab Initio Calculations

Abstract

Ab initio calculations have been carried out to investigate the pathways of H-atom migration and H2 desorption on a mixed SiGe(100)-2×1 surface using the cluster model. The H2 recombinative desorption is the rate-determining step in hydrogen migration and desorption on SiGe(100) surfaces, since the energy barrier to H-atom migration is generally lower than that of H2 desorption. The energy barriers for H2 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)-2×1 surface in chemical vapor deposition provides more dangling bonds than the Si(100)-2×1 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.

Ab Initio Study of H2 Associative Desorption on Ad-Dimer Reconstructed Si(001) and Ge(001)-(2×1) Surfaces

“…The kinetics of hydrogen on semiconductors surfaces is closely related to the surface reconstruction . There have been numerous experimental and theoretical studies on H 2 adsorption, dissociation, and further desorption from the dimerized Si(001)-(2×1) surface. ,− Also, to a lesser extent, the effect of Ge on H 2 desorption from Si(001) has motivated a number of experimental and theoretical studies on both Ge-covered Si(001)-(2×1) and SiGe alloy surfaces. ,− For H 2 desorption from the Si(001)-(2×1) surface, the mechanisms proposed in the literature involve the detachment of two H atoms from the same Si dimer (intradimer or “prepairing” mechanism) or from two different dimers (interdimer mechanism). , From a theoretical point of view, this latter mechanism involves different possibilities, depending on whether both dimers are fully passivated or not, i.e., with 2 or 4 H atoms (H2 or H4 reaction path mechanisms, respectively). , Experimental studies seem to support the interdimer mechanism, i.e., the recombinative desorption from two Si–H bonds on two adjacent dimers along a dimer row . For SiGe alloy surfaces, Ge neighboring atoms (either in the bulk or on neighboring dimers) have a minimal effect on the intradimer H 2 desorption .…”

Fabrication of high quality strained SiGe on Si substrate by RPCVD

“…Since the steady state concentration of free Ge sites is much higher than that of free Si sites during deposition of SiGe by RPCVD, equilibrium is achieved by transferring the H adatoms from Si to Ge. As the energy barrier for H 2 desorption from the Ge surface is lower than that for H 2 desorption from the Si surface, the growth rate enhancement with increasing GeH 4 flow can be explained by the lowering of energy barriers for hydrogen desorption [ [17][18][19][20]. According to the literature [13,21] Compared with the reported result [21], our revised relationship implies that a higher Ge content could be obtained if SiGe films were deposited with the same parameters.…”