Thermoelectric properties of bilayer graphene structures with bandgap opening

Abstract

Bilayer graphene is very attractive for both the fundamental and technological standpoint due to the possible modulation of its physical properties by opening a bandgap. In this work, we show that the thermoelectric properties of bilayer graphene single and double barrier structures can be modulated by the bandgap opening. The effect of the bandgap on the thermoelectric properties was investigated by describing the charge carriers in bilayer graphene as massive Dirac electrons in combination with the hybrid matrix method and the Landauer–Büttiker formalism. Thermoelectric properties such as the Seebeck coefficient, power factor, figure of merit, output power and efficiency are analyzed. In the case of single barriers, we find that at low temperatures the thermoelectric properties enhance at a critical bandgap, while at T=200 K they reduce systematically as the bandgap increases. In particular, the figure of merit increases up to 0.65 for a bandgap of 30 meV and decreases up to 0.8 for a bandgap of 40 meV, representing an enhancement and a reduction of about 30% and 56% with respect to the gapless case. In the case of double barriers, the thermoelectric properties have a contrasting dynamic with the bandgap opening with respect to single barriers. At T=200 K the thermoelectric properties enhance at a critical bandgap, and at low temperatures they collapse in effective terms with the bandgap opening. Here, the figure of merit increases up to 5.2 for a bandgap of 20 meV and decreases up to 1.3 for a bandgap of 40 meV, constituting an enhancement and reduction of 11% and 73%, respectively. We also find that the charge neutrality point and Breit–Wigner resonances shape the thermoelectric response at low temperatures, while at T=200 K the Fano resonances determine the thermoelectric properties. In addition, we corroborate that the redistribution–accumulation of electronic states caused by the bandgap opening is behind the enhancement–reduction of the thermoelectric properties. Our results indicate that bandgap opening could be a versatile mechanism to modulate the thermoelectric performance of bilayer graphene barrier structures.