Excitonic effects in the optical properties of a SiC sheet and nanotubes

Abstract

The quasiparticle band structure and optical properties of single-walled zigzag and armchair SiC nanotubes (SiC-NTs) as well as single SiC sheet are investigated by ab initio many-body calculations using the GW and the GW plus Bethe-Salpeter equation (GW+BSE) approaches, respectively. Significant GW quasiparticle corrections of more than 1.0 eV to the Kohn-Sham band gaps from the local density approximation (LDA) calculations are found. The GW self-energy corrections transform the SiC sheet from a indirect LDA band gap to a direct band gap material. Furthermore, the quasiparticle band gaps of SiC-NTs with different chiralities behave very differently as a function of tube diameter, and this can be attributed to the difference in the curvature-induced orbital rehybridization between the different chiral nanotubes. The calculated optical absorption spectra are dominated by discrete exciton peaks due to exciton states with large binding energy up to 2.0 eV in the SiC sheet and SiC-NTs. The formation of strongly bound excitons is attributed to the enhanced electron-hole interaction in these low dimensional systems. Remarkably, the excited electron amplitude of the exciton wavefunction is found to peak on the Si atoms near the hole position (which is on the C site) in the zigzag SiC-NTs, indicating a charge transfer from an anion (hole) to its neighboring cations by photoexcitation. In contrast, this pronounced peak structure disappear in the exciton wavefunction in the armchair SiC-NTs. Furthermore, in the armchair SiC-NTs, the bound exciton wavefunctions are more localized and also strongly cylindrically asymmetric. The large excitation energy of ∼ 3.0 eV of the first bright exciton with no dark exciton below it, suggests that the small-radius armchair SiC-NTs be useful for optical devices working in the UV regime. On the other hand, the zigzag SiC-NTs have many dark excitons below the first bright exciton and hence may have potential applications in tunable optoelectric devices ranging from infrared to UV frequencies by external perturbations.

Quasiparticle GW calculations for solids, molecules, and two-dimensional materials

“…These observations are consistent with recent G 0 W 0 calculations for a SiC sheet, where the same trends were found. 71 First, we summarize the most important features of the band structure calculations for the freestanding h-BN as shown in Fig. 7.…”

Linear Scaling of the Exciton Binding Energy versus the Band Gap of Two-Dimensional Materials

“…In systems of reduced dimensionalities, the electronic screening is less effective, potentially resulting in more strongly bound excitons. Indeed, the exciton binding energies of several 1D and 2D materials [5][6][7] are at least an order of magnitude larger than those of bulk semiconductors, making excitonic effects more pronounced. In retrospect, each time a new and significant low-D material was discovered, its corresponding excitonic behavior would be routinely exploited on a timely manner, using state-of-the-art computational and experimental approaches.…”

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

“…Bulk SiC is a wide band gap semiconductor, and has been used in high-temperature, high-pressure and high-frequency device applications 18,19 . The 3 graphene-like 2D SiC monolayer has not been experimentally fabricated yet, but has been extensively studied using theoretical methods [20][21][22][23][24][25][26][27][28][29] . Unlike graphene, it is a direct band gap semiconductor with a band gap of 2.5 eV.…”