A Study of Vertical Transport through Graphene toward Control of Quantum Tunneling

Abstract

Vertical integration of van der Waals (vdW) materials with atomic precision is an intriguing possibility brought forward by these two-dimensional (2D) materials. Essential to the design and analysis of these structures is a fundamental understanding of the vertical transport of charge carriers into and across vdW materials, yet little has been done in this area. In this report, we explore the important roles of single layer graphene in the vertical tunneling process as a tunneling barrier. Although a semimetal in the lateral lattice plane, graphene together with the vdW gap act as a tunneling barrier that is nearly transparent to the vertically tunneling electrons due to its atomic thickness and the transverse momenta mismatch between the injected electrons and the graphene band structure. This is accentuated using electron tunneling spectroscopy (ETS) showing a lack of features corresponding to the Dirac cone band structure. Meanwhile, the graphene acts as a lateral conductor through which the potential and charge distribution across the tunneling barrier can be tuned. These unique properties make graphene an excellent 2D atomic grid, transparent to charge carriers, and yet can control the carrier flux via the electrical potential. A new model on the quantum capacitance's effect on vertical tunneling is developed to further elucidate the role of graphene in modulating the tunneling process. This work may serve as a general guideline for the design and analysis of vdW vertical tunneling devices and heterostructures, as well as the study of electron/spin injection through and into vdW materials.

A low Schottky barrier height and transport mechanism in gold–graphene–silicon (001) heterojunctions

“…When heavily doped Si is used, the G layer acts as an almost transparent tunnel barrier which makes it a promising candidate for spin ltering for example. [13][14][15] For lower doped Si, a reduced interface resistance or SBH has been observed for M/G/Si compared to M/Si. 5,11,16 On the other hand, other groups report no inuence of the G layer at all but with a large variation between the measured SBHs 7,17 for similar stacks.…”

Interfacial States and Fano–Feshbach Resonance in Graphene–Silicon Vertical Junction

“…Besides, as stated in a previous report, 14 majority of vertically tunneling electrons would not go into graphene lateral band through phonon-assisted process. Hence, according to our model, they would enter into the interfacial trap states and then release to graphene.…”

Deep-ultraviolet integrated photonic and optoelectronic devices: A prospect of the hybridization of group III–nitrides, III–oxides, and two-dimensional materials

“…Hence, we anticipate that future efficient DUV optoelectronic devices will take advantage of the unparalleled features unleashed by combining nanostructured devices and Ga 2 O 3 substrates. 2D materials and hybrid systems, such as phosphorene [743,744] , phosphorene-like structures [745,746] , 2D TMD heterojunctions [747][748][749][750][751][752] , and graphene/h-BN heterostructures [753,754] , have also been used to improve the use of contact interfacial layers as tunnel layers [755][756][757][758] , and are occasionally utilized for light coupling in visible and IR regimes because of their narrow bandgaps and high absorption of the signal [759] . We summarized key performance characteristics of state-of-the-art group III-nitride-based and hybrid UV and DUV PDs, as demonstrated in Table 3.…”