Thickness dependent band gap and effective mass of BN/graphene/BN and graphene/BN/graphene heterostructures

摘要

Using the full potential based WIEN 2K method, we have explored thickness dependent energy band gaps and effective masses of BN layer sandwiched by graphene (G/BN/G) and graphene sandwiched by BN (BN/ G/BN) systems. Here, capping and substrate layer coverages are changed from 1 monolayer (ML) to 2 ML and 1 to 4 ML, respectively. In G/BN/G systems, we find rather small energy gaps and the energy dispersions become quadratic near the K-point. Unlike in G/BN/G, a trilayer BN/G/BN shows large gap of 117 meV and it decreases as the number of BN layer increases, but we still find a gap about 90 meV in BN (2 ML)/G/BN (4 ML) system. The thickness dependent suppression of band gap in BN/G/BN can be nicely interpreted in terms of interlayer distance from BN substrate to graphene. Furthermore, very interestingly, the energy dispersion is nearly linear near the K-point and this linearity is still preserved even in all BN/G/BN systems. Surprisingly, the effective mass decreases as the number of BN layer increases. For instance, the smallest effective mass of 0.00235 m_e is estimated in conduction band along K — Γ direction. Overall, our calculations may suggest that the BN/G/BN system has potential application for fast radio frequency (RF) device or on-off switching transistor because the linearity and small effective mass is kept without any external factors such as electric field, strain, and doping.