From Half-Metal to Semiconductor: Electron-Correlation Effects in Zigzag SiC Nanoribbons From First Principles

Abstract

We performed electronic structure calculations based on the first-principles manybody theory approach in order to study quasiparticle band gaps, and optical absorption spectra of hydrogen-passivated zigzag SiC nanoribbons. Self-energy corrections are included using the GW approximation, and excitonic effects are included using the Bethe-Salpeter equation. We have systematically studied nanoribbons that have widths between 0.6 nm and 2.2 nm. Quasiparticle corrections widened the Kohn-Sham band gaps because of enhanced interaction effects, caused by reduced dimensionality. Zigzag SiC nanoribbons with widths larger than 1 nm, exhibit halfmetallicity at the mean-field level. The self-energy corrections increased band gaps substantially, thereby transforming the half-metallic zigzag SiC nanoribbons, to narrow gap spin-polarized semiconductors. Optical absorption spectra of these nanoribbons get dramatically modified upon inclusion of electron-hole interactions, and the narrowest ribbon exhibits strongly bound excitons, with binding energy of 2.1 eV.Thus, the narrowest zigzag SiC nanoribbon has the potential to be used in optoelectronic devices operating in the IR region of the spectrum, while the broader ones, exhibiting spin polarization, can be utilized in spintronic applications.arXiv:1701.05971v2 [cond-mat.mes-hall]

Quasiparticle energies, exciton level structures and optical absorption spectra of ultra-narrow ZSiCNRs

“…1(b) in the red open circles, the GW band gap of 2-ZSiCNR is 2.911 eV, which is more than three times larger than the LDA band gap (0.927 eV) and is also larger than a recent GW band gap (2.4 eV). 37 As shown in Fig. 2(b) in the red open circles, the GW band gap of 3-ZSiCNR is 0.804 eV, which is more than 9 times larger than the LDA band gap (0.093 eV) and is also almost more than two times larger than the recent GW band gap (0.45 eV).…”

“…It is excitingly found that the GW band gap of 3-ZSiCNR is 0.804 eV, which is almost more than two times larger than the Alaal et al 37 GW band gap (0.45 eV). The GW band gap of 2-ZSiCNR is 2.911 eV, which is also larger than the Alaal et al 37 GW band gap (2.4 eV).…”

“…It is excitingly found that the GW band gap of 3-ZSiCNR is 0.804 eV, which is almost more than two times larger than the Alaal et al 37 GW band gap (0.45 eV). The GW band gap of 2-ZSiCNR is 2.911 eV, which is also larger than the Alaal et al 37 GW band gap (2.4 eV). Moreover, it is found that the optical absorption spectra of the 2-ZSiCNRs are dominated by edge-state-derived excitons with large binding energy, composed of a characteristic series of exciton states, instead of only one exciton state.…”

“…However, Alaal et al show that 2-ZSiCNR has only one strongly bound exciton, originating from optical transition between the rst valence band and the rst conduction band around the Brillouin zone (BZ) Z-point. 37 What is even more surprising is that unlike 2-ZSiCNR, 3-ZSiCNR does not have any strongly bound excitons. 37 Why?…”

“…37 What is even more surprising is that unlike 2-ZSiCNR, 3-ZSiCNR does not have any strongly bound excitons. 37 Why? Is that really so?…”