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

TL;DR

This study uses Extended Hückel Theory to analyze the electronic band structure of various dangling bonds and clusters on H:Si(100)-(2×1) surfaces, revealing their effects on the silicon band gap and surface states.

Contribution

It provides a detailed theoretical analysis of isolated and clustered dangling bonds on H:Si(100)-(2×1) surfaces, highlighting their electronic states and dispersion characteristics.

Findings

Unpaired DBs create near-midgap states.

DB wires show dispersion depending on direction and coupling.

DB clusters exhibit combined states within the band gap.

Abstract

We theoretically study the electronic band structure of isolated unpaired and paired 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 Si band gap. An isolated unpaired DB introduces a near-midgap state, whereas a paired DB leads to $\pi$ and $\pi^*$ states, similar to those introduced by an unpassivated asymmetric dimer (AD) Si(100)-(2$\times$1) surface. Such induced states have very small dispersion due to their isolation from the other states, which reside in conduction and valence band. On the other hand, the surface state 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 coupling between the adjacent DBs, being 3.84$\AA$ apart. However, in the direction perpendicular to the dimer row (referred to as [110]), due to the reduced coupling between the DBs being 7.68$\AA$ apart, the dispersion in the surface state is similar to that of an isolated unpaired DB. Apart from this, a paired DB wire in $[\bar{1}10]$ direction introduces $\pi$ and $\pi^*$ states similar to those of an AD surface and a paired DB wire in [110] direction exhibits surface states similar to those of an isolated paired DB, as expected. Besides this, we report the electronic structure of different DB clusters, which exhibit states inside the band gap that can be interpreted as superpositions of states due to unpaired and paired DBs.