Reliable prediction of the band gap properties of graphene buffer layer on SiC using meta-GGA approximation

While different Density Functional Theory (DFT) methods have been performed to determine the electronic band structure of graphene buffer layer (GBL) over the Si-terminated SiC (0001) surface, still a correct band gap (E_gap) close to the experimental one has never been demonstrated. The novelty of this study is that for the first time the outcomes have reproduced the experimental E_gap (greater than 0.5 eV) of GBL@SiC (0001) system with an indirect/direct E_gap of 0.65/0.80 eV using improved Meta Generalized Gradient Approximation (MGGA) methodology with medium basis set (MGGA-Medium). The results revealed that GBL has lower E_gap with other basis sets of MGGA-High with 0.32 eV (indirect) and 0.33 eV (direct), whereas MGGA-Ultra estimated a zero E_gap. Absorption spectrum indicated that the presence of two peaks at 61,801 cm^-1 and 64,833 cm^-1 at 265 THz and 290 THz for GBL/SiC along the xx- and yy- (in-plane) directions, respectively. The Im(ω) reveal that the optical E_gap is around 181 THz. Furthermore, Re(ω) of GBL monolayer after the interface on SiC (0001) has predicted to be 2.34, 2.32 and 1.07 along with the xx-, yy- in-plane and zz- out-of-plane polarizations, respectively. More information about the optical properties of this interface show that maximum static value of $n$ along the xx- in-plane direction calculated to be 1.58, while initial non-zero value of $\kappa$ is about 12.08 THz.