Thermal hot-carrier breakdown in metasurface structures based on coplanar arrays of graphene microribbons connected with wide-gap bridges

TL;DR

The paper addresses threshold switching in graphene microribbon metasurfaces where coplanar GMR arrays are connected by wide-gap nanobridges. It develops a thermionic transport model with trapezoidal barriers and an energy-balance equation that couples carrier heating to inter-GMR currents, including optical-phonon and supercollision relaxation. The main finding is that strong positive feedback between thermionic currents and hot-carrier temperature yields sharp threshold and multivalued (S-shaped) $T$–$V_G$ and $J$–$V_G$ characteristics, with hysteresis that persists under plausible lattice-heating scenarios; switching times are on the order of tens of picoseconds, suggesting potential fast voltage-controlled current switches and incandescent THz/IR sources. These insights provide design principles for graphene-based metasurfaces on h-BN to enable fast, thermally driven optoelectronic devices.

Abstract

We analyze the thermal and electrical characteristics of the metasurface consisting of the coplanar interdigital array of the graphene microribbons (GMRs) connected by nanobridges (NBs). These nanobridges could be implemented using graphene nanoribbons (GNRs), single-wall semiconducting carbon nanotubes (CNTs), or black-arsenic-phosphorus (b-AsP) nanostructures. The bias voltage applied between neighboring GMRs indices electron and hole two-dimensional systems in the GMRs and induces thermionic currents flowing through connecting NBs. The resulting self-heating increases thermionic currents providing an effective positive feadback between the carrier effective temperature and the injected currents. This mechanism may lead to thermal breakdown enabling threshold behavior of current-voltage characteristics and resulting in the S-shape of these characteristics. The devices based on the GMR/GNR, GMR/CNT, and GMR/AsP metasurface structures can be used as fast voltage-controlled current switches, sensors, thermal terahertz and infrared sources, and other devices.

Figures (11)

• Figure 1: Schematic view of (a) GMR/GNR, (b) GMR/CNT, and GMR/AsP metasurface structures with GL contacting pads.
• Figure 2: Band diagram of the structures under consideration with the trapezoid energy barriers in the bridges (one period).
• Figure 3: Carrier effective temperature $T$ vs. bias voltage $V_G$ for GMR/GNR structures with $\Delta=250$ meV (upper panel) and $\Delta= 300$ meV (lower panel) at $T_0 = 25$ meV for different values of relaxation ratio $c$.
• Figure 4: The $V_G - T - \Delta$ relations for GMR/GNR structures with $c= 1$ (upper panel) and $c = 8$ (lower panel) at $T_0 = 25$ meV.
• Figure 5: Terminal current (per one GMR pair) vs. bias voltage $V_G$ corresponding to Fig. 3 for GMR/GNR structures with $\Delta=250$ meV (upper panel) and $\Delta= 300$ meV (lower panel) for different values of relaxation ratio $c$ ($T_0 = 25$ meV).