High Performance Multiwall Carbon Nanotube–Insulator–Metal Tunnel Diode Arrays for Optical Rectification

Abstract

The operating regime of MIM diodes is governed by its cutoff frequency. High frequency operation requires ultralow diode capacitance, C D , and low diode resistance, R D . Capacitance can be lowered by fabricating structures with minimal diode area or using a thick dielectric. However, increasing the dielectric thickness will exponentially increase diode resistance by hindering electron tunneling probability through a wider energy barrier. [13] In addition to the barrier width, the height of the tunneling barrier also affects device resistance. Whereas the width is controlled by the insulator thickness, the barrier height is primarily governed by the metal work functions as well as the insulator electron affinity. [14] Diode rectification performance is also dictated by current-voltage asymmetry, nonlinearity, and responsivity. Generally, these figures of merit are controlled by the metal work functions (specifically the work function difference) along with the insulator thickness and dielectric properties. [15][16][17][18][19] A large difference in metal work functions creates a highly asymmetric tunneling barrier that influences the forward and reverse currents, yielding high current asymmetry and nonlinearity. [20] Alternatively, asymmetric diode response can be realized by utilizing multiple insulating layers that have dissimilar electron affinities and dielectric constants. Double-barrier metal-insulator-insulator-metal (MIIM) diodes have shown enhanced asymmetry, nonlinearity, and responsivity versus their single-barrier MIM counterparts. [15,[21][22][23] There are two primary mechanisms that govern tunneling phenomenon in MIIM structures: resonant tunneling and step tunneling. Resonant tunneling occurs when a triangular quantum well is created between the two barriers (Figure 1a). When bias is applied such that the Fermi level of one of the metals coincides with a bound energy state within the quantum well, then electron tunneling is abruptly enhanced, leading to sharp turn on voltage and high asymmetry. The quantum well formed between insulators must be sufficiently deep and wide enough to form bound quantum states. [23,24] The turn on voltage at which bound states form, and thus resonant tunneling begins, can be adjusted by changing the thickness of the first insulator, although the thicker insulator will reduce tunneling current. This work reports important fundamental advancements in multiwall carbon nanotube (MWCNT) rectenna devices by creating and optimizing new diode structures to allow optical rectification with air-stable devices.The incorporation of double-insulator layer tunnel diodes, fabricated for the first time on MWCNT arrays, enables the use of air-stable top metals (Al and Ag) with excellent asymmetry for rectification applications. Asymmetry is increased by as much as 10 times, demonstrating the effectiveness of incorporating multiple dielectric layers to control electron tunneling in MWCNT diode structures. MWCNT tip opening also reduces device resistance up to 75% due to an increase in...

High‐Frequency Light Rectification by Nanoscale Plasmonic Conical Antenna in Point‐Contact‐Insulator‐Metal Architecture

“…Among the fundamental parameters determining the actual photocurrent generated by the nanorectenna device, we shall recognize the barrier height, barrier thickness, and tunneling area. In this regard, as demonstrated in previous theoretical and experimental studies, [17,[22][23][24]55] studies, when a tunnel junction is illuminated with radiation of energy ℏω ph , an AC voltage of the form V opt • cos(ω ph • t) develops across the junction which leads to a net DC current component. This DC component, following Tien-Gordon and Tucker formulation, is described by the time-averaged Photon-Assisted Tunneling (PAT) theory: [56][57][58]…”

“…In this respect, the tables in Figure 6c,d show three different efficiencies obtained for both λ = 1064 nm and λ = 780 nm, respectively. In particular, the full cone-geometrical efficiency aims at a straight comparison to the works of Sharma et al and Anderson et al, [22][23][24] which report the best to date efficiencies of ≈10 -6 % (for λ = 532, 638, and 1064 nm). Our configuration provides an improved efficiency 2.3 × 10 -4 % at λ = 1064 nm and FF = 0.25 (as resulting from the triangle shape of Figure 3a).…”

“…Apart from these futuristic and fascinating scenarios, the rectenna concept has been demonstrated in the infrared range [13][14][15][16][17][18][19][20] also by employing 2D materials, [20,21] while in the visible range an interesting solution relying on carbon nanotubes (CNTs) was introduced, reaching conversion efficiency up to ≈10 -6 %. [22][23][24] The limited efficiency values obtained at high-frequencies are attributed to non-optimal geometry of CNTs and fabrication challenges inherent to the bottom-up fabrication process.…”

From classical optics to nanophotonics

“…These components, combining an antenna and a diode, are called rectenna for "rectifying antenna" (see schematic on figure 3a). It is possible to use Metal -Insulator -Metal (MIM) diodes [13] or even molecular diodes which rectifiying properties are obtained by the asymmetry of the molecule for example with ferrocenyl alkane thiol, which ferrocenyl group is placed either on one side or the other of the molecule [14][15][16]. Figure 3b presents nanopyramids periodically positioned in order to be a set of resonant antennae.…”

A microcantilever mechanical antenna

“…Optical rectennas, combining nanoantennas with ultrafast rectifiers, were proposed 4 as an extrapolation of the radio frequency rectennas to enhance conversion efficiency of solar photovoltaic technologies over 80%. 5,6 However, only a few experimental realizations have been reported until now, 7,8 due to the lack of efficiency of actual electron devices in rectifying currents oscillating at hundreds of terahertz. On the other hand, the dimensions of a rectenna are mainly limited by the antenna component, which in a classical radioelectric configuration will always be a fraction of the radiation wavelength (k) and will be related to the radiation frequency (f) through k ¼ c/f (with c being the speed of light).…”