Theoretical study of isolated dangling bonds, dangling bond wires and dangling bond clusters on H:Si(100)-(2$ imes$1) surface

摘要

We theoretically study the electronic band structure of isolated unpaired andpaired dangling bonds (DB), DB wires and DB clusters on H:Si(100)-(2$\times$1)surface using Extended H\"uckel Theory (EHT) and report their effect on the Siband gap. An isolated unpaired DB introduces a near-midgap state, whereas apaired DB leads to $\pi$ and $\pi^*$ states, similar to those introduced by anunpassivated asymmetric dimer (AD) Si(100)-(2$\times$1) surface. Such inducedstates have very small dispersion due to their isolation from the other states,which reside in conduction and valence band. On the other hand, the surfacestate induced due to an unpaired DB wire in the direction along the dimer row(referred to as $[\bar{1}10]$), has large dispersion due to the strong couplingbetween the adjacent DBs, being 3.84$\AA$ apart. However, in the directionperpendicular to the dimer row (referred to as [110]), due to the reducedcoupling between the DBs being 7.68$\AA$ apart, the dispersion in the surfacestate is similar to that of an isolated unpaired DB. Apart from this, a pairedDB wire in $[\bar{1}10]$ direction introduces $\pi$ and $\pi^*$ states similarto those of an AD surface and a paired DB wire in [110] direction exhibitssurface states similar to those of an isolated paired DB, as expected. Besidesthis, we report the electronic structure of different DB clusters, whichexhibit states inside the band gap that can be interpreted as superpositions ofstates due to unpaired and paired DBs.