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 (Egap) 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 Egap (greater than 0.5 eV) of GBL@SiC (0001) system with an indirect/direct Egap 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 Egap with other basis sets of MGGA-High with 0.32 eV (indirect) and 0.33 eV (direct), whereas MGGA-Ultra estimated a zero Egap. 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 Egap 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 k is about 12.08 THz.