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Abstract
Research in graphene-based electronics is recently focusing on devices based on vertical heterostructures of two-dimensional materials. Here we use density functional theory and multiscale simulations to investigate the tunneling properties of single- and double-barrier structures with graphene and few-layer hexagonal boron nitride (h-BN) or hexagonal boron carbon nitride (h-BC2N). We find that tunneling through a single barrier exhibit a weak dependence on energy. We also show that in double barriers separated by a graphene layer we do not observe resonant tunneling, but a significant increase of the tunneling probability with respect to a single barrier of thickness equal to the sum of the two barriers. This is due to the fact that the graphene layer acts as an effective phase randomizer, suppressing resonant tunneling and effectively letting a double-barrier structure behave as two single-barriers in series. Finally, we use multiscale simulations to reproduce a current-voltage characteristics resembling that of a resonant tunneling diode, that has been experimentally observed in single barrier structure. The peak current is obtained when there is perfect matching between the densities of states of the cathode and anode graphene regions.
Highlights
Vertical heterostructures of two-dimensional materials are the subject of intense investigation for the possibility they offer to engineer and taylor specific electrical and optical characteristics[1]
In graphene-based electronics, transistors based on vertical heterostructures are studied because they can achieve large current modulation, if large bandgap layers are included that can effectively block current in the off state
We report some peculiar properties of vertical transport through single- and double-barrier heterostructures of graphene and Hexagonal boron nitride (h-BN) or h-BC2N layers, that we have studied by means of density functional theory
Summary
In this paper we have provided an accurate investigation of the tunneling properties of vertical h-BN/ graphene and h-BC2N/graphene heterostructures by means of ab-initio and multiscale simulations. We have shown that a set of remarkable behaviors emerge, not observed in the better known heterostructures based on III-V and II-VI materials systems. Such behaviors are due to the very different Hamiltonians and energy-dispersion relations between adjacent layers, and to the fact the the total system Hamiltonian cannot be decoupled in a longitudinal and a transversal component. We only observe an increase of average trasmission with respect to the corresponding single barrier systems obtained by removing graphene Both effects are explained by the non-separability of the Hamiltonian of the complete structure, that we have interpreted in terms of an “effective phase randomization” due to the intermediate graphene layer. Further study is required to better understand vertical transport in cases in which heterostructures are not lattice-matched, or misalignment and dissipation mechanisms are present
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